Heat Shock Proteins in Thermotolerance and Other Cellular Processes1

Home , Heat shock protein, Hugh Pelham

[CANCER RESEARCH 47, 5249-5255, October 15, 1987) Perspectivesin CancerResearch Heat Shock Proteins in Thermotolerance and Other Cellular Processes1

Stephen W. Carper,2 John J. Duffy, and Eugene W. Gerner

Department of Radiation Oncology and Cancer Center, The University of Arizona Health Sciences Center, Tucson, Arizona S5724

Heat shock proteins are a unique set of highly conserved erentially synthesized (for recent reviews, see Refs. 7-13). The proteins induced by heat and other stresses. Their role in expression of hsps and the amino acid sequence of several hsps cellular responses to stress is currently unclear, due in part to are highly conserved throughout evolution, implying that they a variety of experimental findings that are apparently contra may have some universally important function(s). It is com dictory. The purpose of this review is to evaluate the evidence monly accepted that the function of the hsps is either to protect regarding the role of lisps-' in cellular responses to stress and to cells against subsequent heat stress or to enhance the ability of speculate on other possible physiological functions of these cells to recover from the toxic effects of heat or other stresses. unique proteins. This Perspectives article evaluates current evidence regarding Over the past 10 years, hyperthermia has gained increasing this possible role of hsps and considers alternate effects of hsps acceptance as a mode of cancer treatment, especially when used on cellular physiological responses. in combination with radiotherapy (1). In 1985, the United States Food and Drug Administration formally recognized hy perthermia therapy, generally meaning the elevation of tumor Operational Definitions of hsps and Thermotolerance temperatures to 40-45Â°C, as an effective form of treatment for certain types of cancer. A variety of preclinical laboratory Heat stress causes a variety of alterations in cellular physi studies have documented a wide range of biological effects in ology, including increases in the synthesis of certain proteins both normal and tumor cells and tissues (2-5) and have con and enzymes (2-13). Increased synthesis of proteins can occur tributed to the development of this therapy. One such effect is as a result of changes ranging from elevated transcription rates the development of thermotolerance (6). to enhanced translation of existing message. Further, activities Thermotolerance is the term generally used to refer to the of enzymes can be increased due to posttranslational modifi transient, nonheritable state of resistance to the cytotoxic ef cations which might be induced by heat shock. In order to more fects of subsequent hyperthermic treatments, which can be precisely define a heat shock protein, we will adopt the defini induced by a short exposure to a nonlethal heat treatment. The tion used by Schlesinger (12), which restricts the designation degree of resistance can be large. For example, mammalian heat shock protein to those proteins with encoding genes that cells expressing thermotolerance can exhibit survival levels contain one or more heat shock consensus sequences and the several hundred times those of control cells when both are synthesis of which is strongly stimulated by an environmental stress. The HSE sequence for eukaryotes is (CT-GAAâ€”TTC- subjected to the same lethal hyperthermic temperature. If this phenomenon could be manipulated, such that normal tissues AG), and it is sometimes referred to as the Pelham box after expressed thermotolerance while tumor cells did not, a tumor- Hugh Pelham (14) who was one of the first to describe this selective cytotoxicity might be exploited for therapeutic gain. conserved unit. It is located on the coding strand of DNA This possibility has provided the impetus for the study of upstream from the TATA box and is essential for the heat mechanism(s) responsible for the development of thermotoler shock inducibility of transcription from these genes. This defi nition has several advantages at a time when many new so- ance in normal and neoplastic cells. Although many models called "hsps" are being discovered. Proteins with mRNA that have been proposed, no single mechanism for the development of thermotolerance has been shown to apply generally. Several is increased due to enhanced transcription but with encoding DNA that does not contain a HSE, such as the recently reported agents are known that can increase or decrease cellular ability chicken "hsp" 108 (15), would be differentiated from hsps. This to develop thermotolerance, but the molecular mechanisms responsible for these changes are not known (7). Until the distinction (the presence of a HSE) may be desirable in eukar detailed mechanism for the development of thermotolerance is yotic systems in that it classifies protein products (e.g., hsps, understood, the design of treatment protocols for tumor-selec steroid-regulated proteins, glucose-regulated proteins, etc.) into tive cytotoxicity will be severely hindered. groups based on common features in the encoding DNAs. In parallel with the preclinical studies referred to above, Various stresses such as heat shock and oxidative stress (16) investigators interested in developmental aspects of specific and heat shock and DNA-damaging agents (17) can induce the gene regulation discovered that hyperthermia, or heat shock, synthesis of common proteins in both prokaryotic and eukar caused certain genes to be activated. Like thermotolerance yotic organisms. However, not all proteins induced by one stress expression, this unique gene activation is apparently a universal are necessarily induced by the other stress, such that cellular response of all cells. When either prokaryotic, archaebacterial, responses to the various agents can be quite different and or eukaryotic cells are subjected to an increase in their normal complex (16, 17). This will most certainly also be the case in growth temperature, a specific set of proteins (hsps) are pref- mammalian cells. Table 1 lists a number of heat-inducible proteins, indicates Received 5/20/87; revised 7/22/87; accepted 7/23/87. whether the genes coding for these proteins contain an HSE, 1Supported by grants from the IS I'I IS National Cancer Institute (CA-17343, CA-30052, and CA-09213) and by an award from the Arizona Disease Research and also enumerates some of the known functions of these Commission. proteins in various species. These proteins, only some being 2To whom requests for reprints should be addressed. 3The abbreviations used are: hsps, heat shock proteins; hsp XX, a specific hsps by our definition, are involved in a variety of normal heat shock protein with a molecular mass of XX in kilodaltons; CHM, cyclohex- cellular functions, ranging from DNA and protein synthesis to imide; HSE, heat shock consensus element. glycolysis and changes in macromolecular structure. The most 5249

Table 1 Functions of some heat-inducible proteins Protein Source Reported function Ref. HSEDnak /. Proteins with genes that contain a PCgrÃ²or grÃ² coliE. synthesisNecessaryfor X-phage replication and RNA and DNA ESLysyl-tRNAEL, grÃ² coliE. weakATPasefor morphogenesis of X-phage; grÃ²EL displays activityCharging IIProtease synthetase Form coliE. tRNAATPof Lahsp coliYeastDrosophila proteaseInvolveddependent 70 (YG100)hsp temperaturesAssociateswith growth at high 32hsp28, 26, 23, cellsDrosophilaDrosophilaDrosophilaChickenKc cytoskeletonRecoverywith the 70hsp shocks.S. of nucleolar morphology after heat protein?1Involvednucleic acid-binding 68hsp 83Ubiquitinhsp fibroblastsChickenHeLaNecessaryembryodegradation791313131318192021222223,242526//.in targeting proteins for 70hsp 70E. HSEEnolase Proteins with genes that may contain a 1hsp inglycolysisCollagen-binding 47hsp fibroblastsDrosophila,embryo proteinAutodegradationmembrane 70hsp hamsterovary,Chinese endActin-binding via a serine-type protease in the COOH L-929ChineseMouse 90hsp ovaryMousehamster regulatedActin-bindingprotein calmodulin 90, hsp100hsp lineRatHeLaInvolvedlymphoma cell proteinFatty 71hsp proteinPolyadenylate-bindingacid-binding 73YeastChicken protein27282930313233///. HSEhsp Proteins with genes that probably do not contain a 70hps71hsp brainRatChickenATPase pitsFatty for clathrin-coated proteinBindsacid-binding 108Bovine to steroid receptor343215 abundant hsp in most species, hsp 70, has been shown to contain continuous heating protocols (6). Each method of heating re an ATPase activity in a highly conserved ammo-terminal region sults in a change in the shape of the single cell survival response (8, 12). hsp 70 has been reported to have autoproteolytic curve. The question of whether these different regimens of activity, which is of interest because two other hsps, the Ion A inducing thermotolerance actually represent different types of gene product (protease La) in Escherichia colt and ubiquitin in thermotolerance or a similar phenomenon remains unanswered. chickens, are known to either possess protease activity (protease Immediately after a heat shock there is a drastic reduction in La) or participate in specific protein degradation processes the rate of protein synthesis which can be measured by incor (ubiquitin). poration of radioactively labeled amino acids (usually [35S]- The definition of hsps used here is not meant to deemphasize methionine or (3H]leucine) into proteins. There is a decrease in the potential importance of those proteins the synthesis of general protein synthesis, although some proteins are unaf which may be markedly altered either during or after heat stress. fected (e.g., actin), while the rate of hsp synthesis is dramatically These could include a group of proteins which are rapidly increased. Some hsps in the molecular mass range of 20-30 synthesized on preexisting mRNAs and which associate with kilodaltons do not contain methionine, so that labeling proto the cytoskeleton after hyperthermic exposures (35). Transla- cols using [35S]methionine will not measure the synthesis of tional regulation of these and other proteins has been shown to these proteins (7). During the initial recovery from heat shock, occur in the absence of new RNA transcription. It is worth hsps are preferentially synthesized, but when recovery is com noting that the effects of heat shock on general protein and hsp plete (the recovery period is a function of the heat dose given), synthesis can be quite different in various species. For example, a normal (pre-heat shock) pattern of protein synthesis returns. general protein synthesis is severely depressed and hsps are It appears that the reduction in general protein synthesis that selectively synthesized in Drosophila during and after heat usually accompanies a heat shock is not responsible for the shock. In contrast, the selectivity of hsp synthesis is much development of thermotolerance, since when minimally toxic reduced in mammalian cells. Thus, translational regulatory methods (e.g., 6% et Hanoi or 4 IT) of stressing cells are used, mechanisms operational in heat-stressed cells may be quite general protein synthesis is not depressed but thermotolerance species specific. still develops (36). Thermotolerance is a term which has been applied to a variety of cellular responses to stress. Two of the most common assays used to evaluate heat shock responses are colony-forming abil Heat Shock Proteins and Cell Survival Responses to Stress ity, which measures the ability of a single cell to proliferate and The most convincing evidence for a cause and effect relation form a colony of greater than 50 cells over the course of 1-2 ship between hsp synthesis and thermotolerance comes from weeks, and the incorporation of radiolabeled amino acids into studies on E. coli. A mutant (Tsn-K 165) that fails to synthesize proteins as a measure of protein synthesis. Thermotolerance is hsps shows a decrease in survival at 42Â°Ccompared to wild often specifically defined as a decrease in the rate of cell killing, type cells (37). It is also reported that thermotolerance expres based on colony formation assays, when cultures are subjected sion requires protein synthesis, since chloramphenicol com to transient increases in their environmental temperatures. pletely inhibits the development of thermotolerance. Therefore, Cellular expression of thermotolerance can be observed using a in prokaryotes hsps appear to be responsible for the develop variety of heating regimens. These include two or more heatings ment of thermotolerance. separated in time (split doses), continuous heating at some In lower eukaryotes there are many contradictory results hyperthermic temperature or a mixture of both split dose and involving hsps in thermotolerance. Studies correlating hsp syn- 5250

Downloaded from cancerres.aacrjournals.org on October 2, 2021. © 1987 American Association for Cancer Research. HEAT SHOCK PROTEINS AND THERMOTOLERANCE thesis and enhanced survival implicate lisps in the expression and biological systems (e.g., cell type/line specific responses) of thermotolerance in yeast (38-40) and Dictyostelium (41). used in the spÃ©culeexperiments. However, two general conclu Inhibition of protein synthesis by CHM suppresses thermotol sions emerge from the existing data, (a) Since thermotolerance erance expression in yeast (21, 22). However, other studies fail can be expressed under conditions where hsp synthesis is either to show a correlation between either specific hsps or general inhibited or substantially suppressed, it follows that enhanced protein synthesis and thermotolerance in yeast (42-46). There hsp synthesis is not necessary for thermotolerance expression. are no easy explanations for these confusing results; however, This enhanced synthesis is the parameter that several early no direct relationship between hsps and thermotolerance has studies correlated with thermotolerance expression (13,36). (h) been demonstrated. Since hsps can be overexpressed (both increased synthesis rate In higher eukaryotes only correlative, but not cause and effect, and molecule number) without subsequent expression of ther relationships between hsps and thermotolerance have been re motolerance, it follows that enhanced hsp expression is not ported. Parallel changes in hsp synthesis and degradation and sufficient for thermotolerance expression. Thus, we conclude resistance to heat shock cytotoxicity have been documented for that hsps do not act to protect cells against subsequent heat cell culture models including Drosophila (47), hamster (36,48), stresses, as has been proposed (70) and which has been reiter and rat cells (49, 50), as well as in developmental models, ated in recent reviews (9, 11, 12). It is possible that hsps may including Xenopus (51), sea urchin (52), and Drosophila (53). function in some type of repair or recovery process affecting Evidence that heat-resistant variants of hamster cells overpro cell viability after heat shock, as has been suggested (58), but duce hsps is consistent with the hypothesis that hsps are in no evidence has as yet been presented to support this possibility. volved in the expression of thermotolerance (30, 54). Agents other than heat (e.g., sodium arsenite, alcohols) that induce the synthesis of stress proteins can also induce thermotolerance in Heat Shock Proteins and Other Cellular Responses to Stress hamster cells (36, 55). The correlation between hsp synthesis and resistance to sub While hsps do not appear to function in the development of sequent cytotoxic effects of heat shock is not, however, a general thermotolerance (in terms of colony formation assays), their finding in higher eukaryotes. Some studies failed to find a synthesis does appear to be involved in some cell structure correlation between hsp or general protein synthesis and ther changes following heat shock. Nucleoli are transiently damaged motolerance in either Drosophila (56) or Chinese hamster ovary by heat shock (20). Their morphology changes and assembly cells (57). Work from our laboratory shows that nearly complete and export of rRNA are blocked for several hours, hsp 70 has inhibition of general and hsp synthesis after an inducing heat been directly linked to molecular recovery after heat stress (20). stress fails to affect the expression of thermotolerance in rat Drosophila hsp 70, under EIA promoter control for constitutive cells (58). Similar results have also been reported showing little expression in COS cells, is found to replace endogenous hsp or no suppression of thermotolerance expression by CHM in function in this specific recovery process. Actin microfilament other mammalian cell lines (59, 60). Additional work confirms bundles dissociate during heating but will eventually reform that inhibition of protein synthesis by either CHM or puro- after a heat shock (71). The recovery of actin microfilament mycin does not increase cell killing by hyperthermia but can bundle morphology after heat shock occurs more slowly in cells increase cell survival by 10,000-fold under certain conditions in which protein synthesis is inhibited by an agent such as CHM than in non-CHM-treated cells, implying that hsps may be (61). Various studies using mammalian cell lines question the involved in the recovery (71, 72). causative role of hsps in the expression of thermotolerance. We have transfected CHO cells with a plasmid containing Addition of sodium arsenite to Morris hepatoma cells induces the hsp 70 gene from Drosophila. After a heat shock these stress proteins (identical to hsps) but not thermotolerance (60). transfected cells appear to reassemble their actin microfilament Glucocorticoids and 2,4-dinitrophenoI induce thermotolerance bundles differently (both sooner and with the formation of but not hsps (62, 63). SV40-transformed mouse embryo cells thicker bundles) than do cells transfected with the same vector without the hsp 70 gene.4 These findings, together with our constitutively produce more hsps but fail to develop thermotol erance to the same degree as nontransformed cells (64). No unpublished results and the data of Pelham (20), indicate that major differences are reported in the amounts of hsps observed the hsp 70 gene product from Drosophila can function in at in parental or heat-resistant B16 melanoma cells or RIF tumor least two separate processes in mammalian cells, nucleolar cells (65). Two human melanoma cell lines that develop ther morphology recovery and actin microfilament bundle reassem motolerance to different degrees produce similar amounts of bly. These molecular responses have not been correlated with hsp 70 (66, 67). Cells that are slowly heated from 37 to 42Â°C cell viability changes, at least as assayed by colony formation. display higher levels of general protein synthesis, lower levels Heat shock protein synthesis is not required for all cellular responses to this stress. Our laboratory has shown that both of hsp 70 synthesis, and a higher degree of thermotolerance hsp and general protein synthesis is enhanced after a 45Â°Cheat than cells that are rapidly heated (56, 68). Our laboratory has shock if cultures received a prior 45 "C stress several hours been able to dissociate the synthesis of a major hsp, hsp 68, the major heat-inducible protein in the M, = 70,000 range which earlier (58). This enhanced protein synthesis after heat stress is similar to other heat-inducible hsp 70s in mammalian cells, does not depend on hsp synthesis, inasmuch as similar patterns from resistance to heat shock-induced cytotoxicity in rat cells of protein synthesis after the second heat shock were obtained independent of the level of protein synthesis which occurred acclimated to different environmental temperatures (69). between the two heat doses in rat fibroblasts. Protein synthesis hsps appear to be causatively involved in thermotolerance between the heat doses was inhibited by treating cells with a expression in prokaryotes but not in eukaryotes. In mammalian range of CHM concentrations (58). Similar results have been cells, the evidence for hsps being involved in thermotolerance reported for Tetrahymena (73). appears conflicting. These conflicts are most probably due to Why is it that prokaryotes seem to require hsps for thermo- differences in both the physical parameters (e.g., temperature, rate of heating, time of hyperthermic temperature exposure) ' }. J. Duffy et al., submitted for publication. 5251

Downloaded from cancerres.aacrjournals.org on October 2, 2021. © 1987 American Association for Cancer Research. HEAT SHOCK PROTEINS AND THERMOTOLERANCE tolerance and eukaryotes do not? Prokaryotes have at least four naturally quiescent. The levels of hsp 70 mRNA are elevated in major rÃ©gulons,each activated by positive effectors of gene circulating peripheral blood mononuclear cells and decreased expression, which are induced by a variety of stressful agents. when cells are stimulated to proliferate by incubation with These include the SOS response (74), the adaptive response to serum, phytohemagglutinin, or culture medium (89). Synchro alkylating agents (75), the oxy R network (76), and the heat nous HeLa cells show a 10- to 15-fold increase in hsp 70 shock response (77). Each of these responses induces the syn mRNA upon entry into S phase which declines by late S or G2 thesis of a specific set of proteins the functions of which are to (90). The subcellular localization of the hsp 70 protein is repair the damaged cells. There is some overlap in the proteins diffusely distributed in the nucleus and cytoplasm in (Â¡,,local produced, such that the grÃ²EL and dna K heat shock proteins ized in the nucleus of S phase, and again diffusely distributed of /:'. coli are induced by UV irradiation or naladixic acid, in G2 cells. Other groups have also reported a cell cycle- treatments which induce the SOS response (77). regulated expression of hsps in HeLa cells. mRNA levels of Mammalian cells also have inducible repair systems, but the hsp 70 increased 20-fold, reaching a peak level in the post-S expression of these systems appears to be more complex than phase, after release from a thymidine-aphidicolin block (91). in prokaryotes (77, 78). Recently, genes in Saccharomyces Other experimental evidence supports the possibility of hsp cerevisiae and Drosophila have been reported to be transcrip- involvement in differentiation. The protozoan parasite in hu tionally regulated by DNA damage or by heat shock (79, 80). mans causing leishmaniasis (Leishmania tropica) synthesizes Further, enhanced cell survival does not appear to result from hsps as it is transferred from the sand fly vector (whose normal induction of new gene products following DNA damage when growth temperature is 22-28Â°C) to host (humans). There is a the mammalian cell (as opposed to an exogenous probe such as morphological change in the parasite shortly after the transfer a virus) is the target for damage (78). The mechanism of which can be induced outside of the host by raising the temper mammalian cell killing by heat shock is unknown. However, ature. It has been suggested that the expression of the heat direct DNA damage does not appear to result from this form shock genes may participate in differentiation processes of this of stress, at least for temperatures up to 43Â°C(81). parasite leading to successful infection of the host (92, 93). The hsps are highly conserved among species, but their hsp 70 from eukaryotes is part of a multigene family. In functions may be quite species specific. The highest degree of humans, chromosome 6 contains at least one gene for hsp 70 homology of hsp 70 is found in the NH2-terminus of the protein. (94). In HeLa cells there are at least 5 separate genes for hsp This region has been shown to contain an ATPase activity while 70 (95) with each gene having the possibility of unique expres the COOH-terminus is thought to control substrate recognition sion (i.e., one gene product could be heat inducible, while (82). Likewise, the low molecular weight hsps contain a ho another could be regulated by the cell cycle). Recently it has mologous amino acid sequence in the COOH-terminal portion been shown that one of the hsp 70 genes from HeLa cells not of these proteins, which is similar to a sequence in a-crystallin only contains the heat shock consensus element but also con (8). Therefore, although both prokaryotes and eukaryotes make tains a serum-responsive element upstream from the start of hsps with some similarities (e.g., molecular weight, specific translation (95). Therefore one gene can be expressed by a amino acid sequence homologies), the hsps may have different variety of stimuli (i.e., heat or growth factors). This multiple functions in different species due to substrate specificity or induction of hsp 70 is not surprising if hsp 70 is essential for other differences as a result of the nonconserved regions of cell growth. these proteins. hsps and the Sharing of Certain Unique Features with Other hsp Expression Relationship to Proliferation and Differentiation Proteins Involved in Growth hsps probably function in growth and differentiation. Al hsps share several unique and interesting properties with though not all the hsp functions listed in Table 1 and Refs. 11 other proteins/enzymes, such as ornithine decarboxylase (96), and 12 would seem to support this idea, the following examples the adenovirus early proteins (97, 98), and certain retroviral do. It is known that expression of specific hsps is under devel oncogene protein products (99), which are known to be involved opmental control in sea urchins (52), Drosophila (53, 83, 84), in cellular growth and differentiation processes. These similar and mouse (85, 86). Hormones can affect the expression of ities are summarized in Table 2. All of these proteins are hsps. For example, insulin suppresses both basal and heat inducible by a variety of chemicals and hormones. The mRNAs shocked-induced hsp synthesis and glucocorticoids antagonize coding for these proteins have long 5' untranslated leader this insulin effect (87). hsp 70 synthesis in HeLa cells is stim sequences. Only 6% of 211 eukaryotic mRNAs surveyed have ulated by serum or by adenovirus infection indicating that its untranslated regions longer than 160 nucleotides (100) and it expression is regulated during cell growth (88). These findings is these regions of mRNA which are thought to regulate trans suggest that hsps may function in cellular growth and differ lation (101). This group of proteins possesses another unique entiation processes. feature, in that each member has one or more common amino In yeast the expression of the hsp 70 gene family is essential acid sequences, rich in proline, glutamic acid, serine, and thre- for growth. The yeast hsp 70 family is composed of eight onine residues, termed PEST sequences, which may be related separate genes (YG 100 through 107) only three of which to the very rapid rates of degradation of these proteins (102). increase expression after a heat shock (11). A disruption mu It is also interesting to note that many of these proteins are tation in the non-heat-inducible YG 104 is lethal but other either nuclear proteins or proteins which can be found in the single gene mutations are not. This result is not surprising since nucleus under certain conditions. Recently it has been reported several of the genes are greater than 90% homologous. How that hsp 70 (both cognate and heat-inducible forms) stabilized ever, double or triple gene mutations can affect germination p53, a unique protein expressed in transformed cells (103). In and optimum growth temperatures (39). general, the proteins listed in Table 2 have several unique Recently the expression of hsp 70 was shown to be cell cycle characteristics. These characteristics (a short half-life, a PEST dependent. Human peripheral blood mononuclear cells are sequence, long 5' untranslated leader sequences in the mRNAs, 5252

Table 2 Comparison ofhsp 70 to other growth related proteins

of PEST of 5' untrans Proteintop life-(h)1-2 sequenceYes locationNucleolus latedmRNA'2 TOOrnithine serum large T-an- growth and differen (after a heat 12 nucleotides tigen EIA proteins tiation shock) decarboxylasec-mycHalf- 0.50.5PresenceYesYesInductionHeat,Hormones,serumUnder Production of polyamines which CytoplasmicNuclearLength >190nucleotides408 are involved in growth and differentiation cell cycle con-FunctionProbablyCellular oncogeneCellular and 570 nucleotides trol EIA 0.5 Yes Virus infection Immortalization of cells helps in Nuclear 61 nucleotides the transformation of cells p53 0.5 Yes Carcinogens and onco- Participates in neoplastic trans- Nuclear Estimated 250 nucleo genes formation tides c-fos 0.5 Yes Stimulated by growth Required for normal cell prolif- Nuclear 155 nucleotides factors, under cell eration cycle control â€¢SeeRef.102. ' Lengths determined from data in Gene Bank. Only 6% of 211 eukaryotic mRNAs surveyed had untranslated regions longer than 160 nucleotides ( 100). and inducibility by hormones or growth factors) define a small tional Symposium on Cancer Therapy by Hyperthermia and Radiation. Philadelphia: ACR Press, 1976. group of proteins all of which are involved in growth and 3. Streffer, C. l >..vanBeuningen, (.. Dietzel, F., Rottinger, E., Robinson, J. differentiation. Since hsp 70 falls into this distinct group, E., Seherer, E., Seeber, S., and Trott, K.-R. (eds.). Cancer Therapy by perhaps its regulation or general function may be related to the Hyperthermia and Radiation. Munich: Urban and Schwarzenberg, 1978. 4. Dethlefren, L. A., and Dewey, W. C. (eds.). Third International Symposium: other proteins listed in Table 2. Cancer Therapy by Hyperthermia, Drugs and Radiation. Nati. Cancer Inst. Monogr., 61: 3-547, 1982. 5. Overgaard, J. (ed.). Hyperthermic Oncology, Vols. 1 and 2, London: Taylor Summary and Francis, 1984. 6. Gerner, E. W. Thermotolerance. In: F. K. Storm (ed.), Hyperthermia in Heat shock proteins appear to be causatively involved in the Cancer Therapy, pp. 141-162. Boston: G. K. Hall Medical Publishers. acquisition of thermotolerance in prokaryotes but not in eukar- 1983. 7. Subjeck, J. R., and Shyy, T. T. Stress protein systems of mammalian cells. yotes. Further, the enhanced synthesis of hsps may be necessary Am. J. Physiol., 250: cl-cl7, 1986. for some cellular responses to stress but not others. In prokar- 8. Craig, E. A. The heat shock response. CRC Crit. Rev. Biochem., IS: 329- 380, 1985. yotic cells the development of thermotolerance, as measured by 9. Burdon, R. H. Heat shock and the heat shock proteins. Biochem. J., 240: cell survival, is dependent upon protein synthesis. However, in 313-324, 1986. eukaryotes, enhanced hsp synthesis following an inducing stress 10. Landry, J. Heat shock proteins and cell thermotolerance. In: L. J. Anghileri, and J. Roberts (eds.), Hyperthermia in Cancer Treatment, Vol 12., pp. 37- and prior to a subsequent heat shock is neither necessary nor 58. Boca Raton, FL: CRC Press, Inc., 1986. sufficient for the development of thermotolerance as measured 11. Lindquist, S. The heat shock response. Annu. Rev. Biochem.. 55: 1151- by colony-forming assays. The enhanced expression of hsps 1159, 1986. 12. Schlesinger, M. J. Heat shock proteins: the search for functions, i. Cell may be required for some mammalian cellular stress responses, Biol., 103: 321-325, 1986. such as the ability to reform both actin microfilament bundles 13. Neidhardt. F. C., VanBogelen, R. A., and Vaughn, V. The genetics and regulation of heat-shock proteins. Annu. Rev. Genet., IH:295-329, 1984. and nucleolar morphology. These latter two thermotolerant 14. Pelham. H. R. B. A regulatory upstream promoter element in the Drosophila responses have not been correlated with colony-forming ability. HSP 70 heat-shock gene. Cell, JO:517-528, 1982. 15. Sargan, D. R., Tsai, M. J., and O'Malley, B. W. hsp 108, a novel heat shock Future work should address the relationships between these inducible protein of chicken. Biochemistry, 25:6252-6258, 1986. various physiological responses to stress and determine if hsps 16. Morgan, R. N., Christman, M. F., Jacobson, F. S., Stevz, G., and Ames, B. function in some repair mode with regard to colony formation N. Hydrogen peroxide-inducible proteins in Salmonella typhimurium over responses. Evidence is accumulating that hsps or their cognates lap with heat shock and other stress proteins. Proc. Nati. Acad. Sci. USA, 83:8059-8063, 1986. may function in growth and differentiation in some manner as 17. McClanahan, T., and McEntee, K. DNA damage and heat shock dually yet to be fully explained. Recent studies indicate that genes regulate genes in Saccharomycescerevisiae. Mol. Cell. Biol., 6:90-96,1986. controlling cell division in E. coli may be linked to those of 18. Craig, E. A., and Jacobsen. K. Mutations of the heat inducible 70 Kd genes of yeast confer temperature sensitive growth. Cell, 38: 841-849, 1984. several stress rÃ©gulons(104), and it would not be surprising to 19. Leicht, B. G., Biessmann, H.. Palter, K. B., and Bonner, J. J. Small heat find a similar relationship in eukaryotes. At this time, it is shock proteins of Drosophila associate with the cytoskeleton. Proc. Nati. important that studies investigating the role of hsps in stress Acad. Sci. USA, S3:90-94, 1986. 20. Pelham. H. R. B. Hsp 70 accelerates the recovery of nucleolar morphology and other cellular responses such as growth and differentiation after heat shock. EMBO J., 3: 3095-3100, 1984. define the specific gene (including its regulatory sequences) that 21. Lindquist, S. Heat shockâ€”acomparison of Drosophila and yeast. J. 1 en bryol. Exp. Morphol., 83: 147-161, 1984. encodes the protein being investigated, in order to avoid appar 22. Holmgren, R. 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Stephen W. Carper, John J. Duffy and Eugene W. Gerner

Cancer Res 1987;47:5249-5255.

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