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Isozymes in Cancer

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Isozymes in Cancer (CANCER RESEARCH 31, 1166-1167 August 1971) Isozymes in Cancer A conference on "Isozymes and Enzyme Regulation in Isozyme I was present in all tissues, including fetal liver, Cancer" was held in San Diego, Calif., March 15-17, 1971, whereas isozyme III was present only in brain and isozyme II sponsored by the U.S.-Japan Cooperative Program in Science. only in neonatal or adult liver. Six Yoshida ascites hepatomas Twenty-two scientists attended the 3-day meeting. A recurrent had only isozymes I and/or III, whereas several Morris theme of this conference, resulting largely from data obtained hepatomas had mixed patterns, such as I, I and II and I, II and with hepatoma lines derived by Harold P. Morris, Howard III. University, and Tumizo Yoshida, Sasaki Institute, Tokyo, was Calling attention to work from his laboratory on pyruvate that tumors display aberrant gene expression. Many kinase isozymes, as well as other earlier studies, Potter transplantable hepatomas have high activities of isozymes that reiterated his proposal that, in liver tumorigenesis, normal are normally low or absent in the fully differentiated adult hepatocytes may revert to a "more primitive phenotype by a reactivation of latent genes" and has termed "oncogeny hepatocyte, whereas other isozymes, usually those which are as blocked ontogeny." responsive to regulatory metabolites or hormones, are low or absent. A striking feature is the apparent activation in some Maria Under of MIT reported work from her laboratory hepatomas of isozymes characteristic of fetal or neonatal liver showing also that a ferritin present in various Morris or of other organs (or even other species). Such alterations are hepatomas is different from the one in normal rat liver. H. P. most marked in rapidly growing, poorly differentiated tumors. Morris of Howard University summarized his extensive work In one of the most striking examples of aberrant gene on the induction of 49 hepatomas, varying 20-fold in growth expression, N. Katunuma of Tokushima University reported rate, and pointed out that in work carried out with T. Otani there was a higher ratio of "anionic" to "cationic" that, whereas the liver of the ureotelic rat incorporated little, if any, serine-14 C into uric acid and allantoin, this occurs glutamate-oxaloacetate aminotransferase isozymes in the readily in the liver of the uricotelic chicken. Rat hepatomas, hepatomas than in normal rat liver. Isozyme patterns of however, incorporated considerable serine-14C radioactivity glutamate-pyruvate aminotransferase, malate dehydrogenase, into uric acid and allantoin but produced very little urea in and láclate dehydrogenase also differed from those of normal comparison to adult rat liver. Ornithine transcarbamylase, a liver, with greatest divergence in the fastest-growing tumors. urea cycle enzyme, was absent from adult chicken liver but Murray, University of Toronto, using starch gel was present in embryonic chicken liver. Katunuma cited these electrophoresis, observed no consistent differences in isozyme findings to suggest that some genes, acquired at early stages of pattern between rat liver and hepatomas in sorbitol evolution, may appear during ontogeny, are repressed after dehydrogenase or in activity levels of alcohol dehydrogenase birth, and can be reactivated and expressed in neoplasia. and 2 enzymes of heteroglycan synthesis found in the Golgi Another example of gene derepression reported by Katunuma apparatus: namely, CMP-sialic acid:glycoprotein is glutaminase, for which kidney and brain isozymes are absent sialyltransferase, and UDP-jV-acetylglucosamine:glycoprotein from adult liver but are present in fetal liver and in some jV-acetylglucosamine transferase. Esterase isozyme patterns hepatomas. were also studied but were too complex for definition. The replacement of liver-type isozymes by nonhepatic types Ohashi and Ono, National Cancer Institute (Tokyo), found 3 in rapidly growing liver neoplasms was also shown by Tsuiki of NADP-dependent glucose-6-P dehydrogenase isozymes in Tohoku University, using immunological and kinetic normal adult liver, one of which increases greatly by induction techniques, for fructose diphosphatase, glycogen synthetase, with glucose. The Morris 7288C hepatoma, maintained for and glucosamine-6-P synthetase. many years in cell culture, has the isozyme pattern of the Weinhouse of Fels Research Institute described work from induced liver and is incapable of modulation. This is his laboratory demonstrating the loss of such hepatic considered to be an example of permanent enzyme "marker" isozymes as glucokinase, aldolase B, pyruvate kinase derepression. II, and adenylate kinase III, and their replacement by isozymes Pedersen of Johns Hopkins University reported that that are normally low or absent in normal liver. This switching mitochondria of 2 well-differentiated Morris hepatomas, on and off of specific isozymes was most noticeable as the 9618A and 7800, resembled liver mitochondria in their degree of differentiation decreased, and Weinhouse suggested respiratory properties and in their content of monoamine that these changes probably influence the metabolic patterns oxidase, adenylate kinase, cytochrome oxidase, and malate and growth rates of hepatomas. The pronounced resemblance dehydrogenase. However, mitochondria from the poorly of the isozyme patterns of the poorly differentiated tumors to differentiated, rapidly growing 3924A hepatoma mitochondria those of fetal liver accord with the presence of fetal antigens in had generally lower enzyme activities and also deviated in hepatomas and other tumors and support previous some ultrastructural and respiratory properties from normal observations by Schapira and Sugimura that genes for fetal liver mitochondria. proteins tend to be derepressed in hepatic neoplasms. Another According to Pilot, University of Wisconsin, serine illustration of gene derepression was cited by Ichihara and dehydratase of rat liver occurs in 2 closely related forms which Ogawa of Tokushima University who found 3 branch ed-chain have identical catalytic activity but which can be distinguished amino acid aminotransferase isozymes in animal tissues. by electrophoresis and which apparently differ slightly in lysine and proline content. Pilot also found that tyrosine Received June 7, 1971; accepted June 7, 1971. aminotransferase is present in 4 molecular forms, separable on 1166 CANCER RESEARCH VOL. 31 Downloaded from cancerres.aacrjournals.org on September 26, 2021. © 1971 American Association for Cancer Research. Isozymes in Cancer hydroxylapatite. The least tightly bound form is present in all Thioredoxin and its reducíase,which are obligatory cofaclors tissues and is not affected by diet or hormones; the most for ribonucleolide reduction, were noi limiling in Ihe tightly bound form appears to be regulated by insulin, whereas formalion of deoxyribonucleolides in eilher liver or lumors. the 2 intermediary forms are probably regulated by steroids Thymidine kinase aclivily also paralleled hepaloma growth and cyclic nucleotides. rate, but ihere was lillle correlation with Ihymidylale A comprehensive study by Tanaka, Osaka University Medical synlhelase. Dala on Ihymidine kinase were also presented by School, showed that 2 pyruvate kinases, L and M,are present Fujii, Tokushima Universily. Allhough normal lissues, such as in rat liver. The M (muscle)-type pyruvate kinase can be aduli, regeneraling and felal liver, and bone marrow cells have separated electrophoretically into 2 immunologically a single molecular form, all lumors sludied, including some of indistinguishable forms; MI, present in muscle, heart, and Ihe Yoshida and Morris lypes, had 2 molecular forms, brain; and M2, present in all other tissues, including cancer separable by dielhylaminoelhyl cellulose chromalography. tissues. In its kinetic properties, M2 is intermediate between Several of Ihe reporled sludies dealt wilh some sinking M! and L (liver) types. Tanaka also described 4 preneoplaslic allerations. Endo, Kyushu Universily, reported thai after feeding rals 0.06% 3'-methyl-4-dimethylaminoazo- phosphofructokinase isozymes in rat tissues. Type I is present in muscle, heart, and brain; types II and III are widely present benzene for 1 lo 2 monlhs Ihere was, in ral liver prior to in many tissues; and type IV is found only in liver and neoplasia, a 2- lo 10-fold increase of muscle-lype pyruvale erythrocytes. Types II, III, and IV are also found in cancer kinase. This elevaled aclivily was mainlained long after tissues. cessalion of carcinogen Irealmenl and even survived partial Summarizing their extensive work on isozymes in cancer, hepaleclomy. Poller also reporled lhal 3'-melhyl-4-dimelhylaminoazobenzene feeding caused a Sugimura and associates pointed out that hepatic tumorigenesis is characterized by replacement of aldolase B by gradual loss of Ihe liver-lype pyruvale kinase and glucokinase aldolase A (and in some instances also, by aldolase C which is from rat livers. The period of preneoplasia was also normally present in brain) and by disappearance of hexokinase characterized by enhanced DNA synlhesis, considered to be isozyme IV (glucokinase). Although fast-growing hepatomas due partly to repair replication. had only isozymes I and II, slow-growing sublines thereof also Several other effecls of lumors on hosl tissues were also had isozyme III. Thus by slowing of growth, a tumor may reported. Following up earlier efforts to idenlify revert; or as Sugimura suggests it may undergo "reversal" or
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