Oncogene (2001) 20, 1601 ± 1606 ã 2001 Nature Publishing Group All rights reserved 0950 ± 9232/01 $15.00 www.nature.com/onc G protein coupled receptor signaling through the Src and Stat3 pathway: role in proliferation and transformation

Prahlad T Ram*,1 and Ravi Iyengar1

1Department of Pharmacology, Mount Sinai School of Medicine, New York, NY 10029, USA

Extracellular signals when routed through signaling transducin; the Gai family which includes Gai, Gao pathways that use heterotrimeric G proteins can and Gaz; the Gaq/Ga11 family; and the Ga12/13 engage multiple signaling pathways leading to diverse family. As these new Ga subunits were identi®ed the biological consequences. One locus at which signal e€ectors pathways for these subunits were sought out, sorting occurs is at the level of G proteins. G protein and over the years a number of e€ector pathways such a-subunits appear to be capable of interacting with as the PLC, Rho/Cdc42 pathways, and the Ca2+ di€erent e€ectors leading to engagement of distinct channels have been identi®ed (Buhl et al., 1995; signaling pathways. Regulation of di€erent pathways Diverse-Pierluissi, 1995; €rench-Mullen et al., 1994; in turn leads to di€erent biological outcomes. The Taylor et al., 1990). In addition to activation of process of neoplastic transformation is controlled to a second messenger molecules, Ga subunits can also large extent through the activation and inhibition of modulate the activity of transcription factors, thereby signaling pathways. Signaling pathways such as the regulating gene expression (Corre et al., 1999; Fan et Ras-MAPK, v-Src-Stat3 pathways are activated in the al., 2000; Montminy, 1997; Ram et al., 2000). So process of transformation. Expression of activated Ga signaling by G protein coupled receptors is not just subunits have been shown to cause transformation of limited to second messenger molecules but also cells. While activation of the MAPK 1,2 pathway by includes transcription factors and molecules that a€ect various Ga subunits has been reported for several the cytoskeleton. Discovering the full array of down- years, recent studies show the activation and involve- stream e€ectors for G proteins is an ongoing process ment of Src and Stat3 pathways in Gao and Gai that will continue to yield new and exciting informa- mediated transformation of cells. Recent studies also tion. suggest that both Gai and Gas may be able to Recently the activation of Stat3 by members of interact with and activate Src. The activation of Src the Gai family, particularly Gao and Gai2 has and Stat3 by G proteins has also been demonstrated been identi®ed (Corre et al., 1999; Ram et al., by ligand-induced activation of G protein receptors. 2000). Additionally others have also reported the So increasingly it is becoming clear that the Src and ligand-induced activation of Stat's via activation of Stat3 pathways are potential e€ectors for G proteins G protein coupled receptors (Liang et al., 1999; and that they may play a role in G protein function. Marrero et al., 1995). The activation of the Stat Oncogene (2001) 20, 1601 ± 1606. pathway by Ga subunits appears to be mediated via Src. The modulation of a transcriptional Keywords: G protein alpha subunit; Src; Stat3; cofactor by Gaz has also been reported (Fan et transformation al., 2000). Taken together with the classical Gas?cAMP?PKA?CREB pathway it appears that in addition to regulation of cytoplasmic and Introduction membrane functions Ga subunits also regulate gene expression. Signal transduction pathways activated by G proteins The role of G protein a subunits in the neoplastic have been studied for a number of years. The classical transformation of cells has been studied for a number G protein signaling pathway that was identi®ed very of years. Expression of activated Gao, ai2, aq, a12, and early on was the activation of the adenylyl cyclase- a13, has been shown to cause transformation of cells cAMP pathway by Gas (Gilman, 1987). Subsequently (Jiang et al., 1993; Kalinec et al., 1992; Kroll et al., the inhibition of adenylyl cyclase by the Gai subunit 1992; Pace et al., 1991; Vara Prasad et al., 1994). was determined. Since these early discoveries several Additionally expression of constitutively activated G other Ga subunits as well as several isoforms of Gb protein receptors have also been shown to cause and Gg subunits have been characterized. The Ga transformation of cells (Allen et al., 1991; Arvanitakis subunits can be broadly classi®ed into four families: et al., 1997; Cesarman et al., 1996) Therefore, under- the Gas family including Gas, Gaolf, and a standing the signaling mechanism leading to the transformation of cells by G protein a subunits and G protein coupled receptor pathways will be very *Correspondence: PT Ram important. G protein regulation of Src and Stat's in transformation PT Ram and R Iyengar 1602 E€ectors for Gao and Gai2 and Stat3 in the transformation of cells (Corre et al., 1999) these data suggest that Gai2 as well Gaocan Among the Ga subunits, the Gao subunit has been play a role in the proliferation of cells. Their role in more dicult to study in terms of e€ector regulation. cell proliferation may be quite important in tumors of Gao belongs to the Gai family of G protein a subunits neuroendocrine origin such as in melanomas, where and shares about an 82% homology with Gai and is both Gai2 and Stat3 have been shown to regulate pertussis toxin sensitive (Neer et al., 1984; Sternweis proliferation and transformation (Hermouet et al., and Robishaw, 1984; Van Meurs et al., 1987). The 1996; Niu et al., 1999). tissue distribution of Gao is quite interesting in that Gao is abundantly expressed in neuronal tissue (Gierschik et al., 1986). Intracellularly, Gao is found Role of Src and Stat3 in oncogenesis localized in the growth cones of neuronal tissue, suggesting a role for Gao in neuronal function (Nusse c-Src is a member of a family of cytoplasmic tyrosine and Neer, 1996). The constitutively activated Gaoin kinases that are involved in many biological processes which Gln 205 is changed to Leu (Q205L), thereby (Thomas and Brugge, 1997). Activities of the src family resulting in a mutant Gao subunit which lacks of kinases have been implicated in proliferation, guanosine triphosphatase (GTPase) activity, has migration and di€erentiation. The src family members greatly aided in the analysis of Gao function. are 52 ± 62 kDa proteins that have several domains Expression of activated GaoinXenopus oocytes including a catalytic domain, a regulatory domain, and triggers the oocyte to re-enter the cell cycle through SH2 and SH3 binding domains (Thomas and Brugge, the protein kinase C, c-mos dependent pathway (Kroll 1997). c-Src in its inactive form is phosphorylated at et al., 1991). Expression of activated Gao results in the Tyr-527 and interacts with its own SH2 domain, thus transformation of NIH3T3 cells (Kroll et al., 1992), masking its catalytic domain (Brown and Cooper, and it has also been demonstrated that expression of 1996). Upon activation c-Src is dephosphorylated at Gao in PC-12 cells results in increased neurite Tyr-527 and no longer interacts with its own SH2 outgrowth (Strittmatter et al., 1994). Gao has also domain, resulting in a conformational change which been shown to play a role in vesicle release in then activates its catalytic domain (Brown and Cooper, chroman cells (Ohara-Imaizumi et al., 1992; Sontag 1996). Activated c-Src is then capable of interacting et al., 1991) and modulation of Ca2+ channels in chick with and activating several substrates. Data from dorsal root ganglion (DRG) neurons (Diverse-Pierluissi several labs have shown that both v-Src and c-Src et al., 1997). While these physiological readouts have are capable of activating Stat3 in ®broblasts (Bromberg been observed for several years the downstream et al., 1998; Turkson et al., 1999; Yu et al., 1995). signaling mechanisms by which Gao regulates these The signal transducers and activators of transcrip- functions were not well understood. tion (Stat) family of proteins are implicated in the Over the years a few downstream e€ectors of Gao functions of a wide range of cells (Akira, 2000; have been discovered. The PLC/PKC pathway has Bromberg and Darnell, 2000). Stat proteins are been found to be activated during Xenopus germinal activated in response to several cytokines and growth vesicle breakdown (Kroll et al., 1991), and the Src factors. The classical example of Stat activation is via tyrosine kinase pathways in the activation of Ca2+ the interluekin/gp130 receptor, which is activated by Il- channels in chick DRG neurons (Diverse-Pierluissi et 6. Il-6 binding activates the receptor leading to al., 1997). The signaling pathways involved in the Gao recruitment of Janus kinases (Jak's). Jak activation induced transformation of NIH3T3 have been shown then results in binding, phosphorylation and activation to be by the Src and the Stat3 pathways (Ram et al., of Stats. When phosphorylated Stat3 is activated, it 2000). Direct binding partners of Gao include Rap1- dimerizes, and translocates to the nucleus where it GAP and GRIN (Chen et al., 1999; Jordan et al., binds DNA and modulates gene expression (Schindler 1999) and Darnell, 1995). Receptor tyrosine kinases (RTK) The role of the Gai subunit in transformation has such as PDGF-R and EGF-R also activate Stat3 been observed for several years. Gai2 has been (Zhong et al., 1994). Stat3 has been implicated in the implicated in ovarian and pituitary tumors (Lyons et neoplastic transformation of several cell types, and al., 1990). The mutant form of Gai2, which is thought transformation of NIH3T3 and mammary epithelial to be oncogenic, was termed gip2 and was found to be cells by the oncogene v-src is dependent on Stat3 over expressed in a small subset of ovarian tumors activation (Bowman et al., 2000; Bromberg et al., 1998; (Lyons et al., 1990), however this does not appear to Smith and Crompton, 1998), and further, expression of be widespread as other populations of ovarian tumors constitutively activated Stat3 itself results in transfor- have failed to show expression of gip2 (Shen et al., mation (Bromberg et al., 1999). MAPKinase 1,2 can 1996). Expression of Gai2 in Rat-1 cells results in phosphorylate Ser727 on Stat3 and phosphorylation of increased proliferation and transformation of cells this residue is thought to modulate the transcriptional (Pace et al., 1991). Additionally expression of domi- activity of Stat3 (Chung et al., 1997). Additionally, nant negative Gai2 has been shown to inhibit activation of p38 and JNK/SAPK is thought to be melanoma cell proliferation (Hermouet et al., 1996). required for v-Src activation of Stat3 (Turkson et al., Recent data shows that Gai2 like Gao activates c-Src 1999).

Oncogene G protein regulation of Src and Stat's in transformation PT Ram and R Iyengar 1603 G protein coupled receptor mediated activation of Stat's (Ram et al., 2000). Expression of Q205L Gao increases endogenous c-Src activity, and expression of CSK G protein coupled receptors (GPCRs) are cell surface inhibits Gao mediated cell proliferation. Gao also receptors that are activated by hormones and neuro- increased Tyr705 phosphorylation of Stat3 as well transmitters. Activation of the angiotensin II (AT1) increased Stat3 transcriptional activity. Expression of receptor has also been shown to phosphorylate Stats 1, dominant negative Y705F Stat3 inhibited Gao 2 and 3 (Liang et al., 1999; Marrero et al., 1995). mediated Stat3 activity. Further both CSK and Additionally melanocyte stimulating hormone (MSH) Y705F Stat3 were able to inhibit Gao mediated binding and activating the melanocortin receptors has transformation of NIH3T3 cells. The signaling mech- also been shown to activate Stats in B-lymphocytes anism of Gai2 mediated transformation is also (Buggy, 1998). In addition to ligand induced activation regulated through the Src and Sta3 pathway (Corre of GPCR's several groups have identi®ed mutant et al., 1999). Hermout and colleagues have shown that GPCRs that are constitutively activated (Arvanitakis expression of dominant negative mutant of Gai2 et al., 1997; Cesarman et al., 1996). When these mutant inhibits v-fms mediated transformation of ®broblasts. receptors are expressed in NIH3T3 cells they result in Further dominant negative Gai2 inhibited both Src and increased proliferation and in the transformation of the Stat3 activities. cells. Mutant active melanocortin receptor has been In addition to the regulation of Stat3 mediated identi®ed (Robbins et al., 1993) and it is quite possible transcription activity another member of the Gai that mutant active GPCR's that are expressed in vivo family Gaz is also able to regulate transcriptional may activate Src and Stat3 leading to changes in the activity. Both GazandGai modulates transcription normal physiology of the cell. Therefore activation of activity by directly binding to the Eya2 transcription Stat's by G protein coupled receptor pathways may be co-factor, sequestering it in the cytoplasm thereby physiologically relevant for both proliferation and decreasing the transcriptional activity of the Six/Eye2 di€erentiation. transcription factor (Fan et al., 2000). These data show that Gao/i/z subunits are able to regulate transcrip- tional activities in addition to second messenger Gene expression by Gao and Gai through Src and Stat3 signaling pathways.

Gao and Gai2 mediated transformation of ®broblasts both signal via the Src and Stat3 pathway and this Role of small G proteins in Src and Stat3 signaling discovery was simultaneously made by Hermout and colleagues as well as in our laboratory (Figure 1) A step in the pathway of activation of Src and Stat3 (Corre et al., 1999; Ram et al., 2000). Expression of appears to involve small GTPases such as Ras, Rac-1, Q205L Gao in NIH3T3 cells results in increased Rap-1 and Ral-1 (Ceresa et al., 1997; Goi et al., 2000; proliferation and the transformation of the cells Simon et al., 2000). The di€erent small G proteins may

Figure 1 Pathways involved in mediating Gao activation of Stat3. Activation of Stat3 by Gao and Gai2 subunits in ®broblasts is mediated by Src activation. The mechanism of Src activation by Gao is currently not known. Downstream from Src, activation of Stat3 may be dependent on activation of JNK and/or the p38 kinases

Oncogene G protein regulation of Src and Stat's in transformation PT Ram and R Iyengar 1604 be either upstream or downstream of Src (Goi et al., with Stat3 leading to phosphorylation and activation 2000; Xing et al., 2000). The role of Ras signaling in of Stat3 (Simon et al., 2000). In addition to Ras and Stat3 activation has been demonstrated for a number Rac involvement in Src and Stat3 signaling another of years, whereby Ras activation of MAPK 1, 2 and small G protein, Ral-1, has been implicated in the the subsequent MAPK 1, 2 phosphorylation of Stat3 EGF-R mediated activation of Src and Stat3 (Goi et may be required for Stat3 activity (Herrmann et al., al., 2000). Additionally c-Src activation induced by Sin 1996). Another small G protein, Rac-1, has also been and Cas (SH3 domain containing multiadapter pro- demonstrated to be involved both in the IL-6 teins) is mediated by Rap-1 (Xing et al., 2000). Thus it activation of Stat3 (Schuringa et al., 2000) as well as appears likely that small G proteins may play an in v-Src mediated activation of Stat3 (Turkson et al., important role in signaling networks by acting as signal 1999). Recent data suggests the Rac-1 directly interacts integrators by connecting di€erent pathways.

Figure 2 Model of a possible signaling complex mediating Ga activation of Stat3. Direct interactions between Ga and Src, Src and Stat3, and Rac and Stat3 has been reported (see text). p38 is also be necessary for Stat3 activation by Src. While a sca€old for Rac and p38 has not yet been identi®ed, it is possible that one exists, since sca€olds for two other members of the MAPK family (MAPK 1, 2 and JNK) have been identi®ed

Figure 3 Alternate mechanism of Gao activation of Src. Gao subunits may utilize the small G proteins Rap1 and Ral1 to activate Src. Rap1-GAP has been identi®ed as a direct interacting protein for Gao. Rap1 in turn has been reported to activate Ral1, via Ral1-GEF in some cell lines. Ral1 in turn has been shown to mediate Src and subsequently Stat3 activation

Oncogene G protein regulation of Src and Stat's in transformation PT Ram and R Iyengar 1605 Mechanism of Gao and Gai signaling to Src and Stat3 transformation, is evidence that understanding the signaling mechanism leading to neoplastic transforma- The mechanism of activation of Src by Ga subunits tion by the Ga subunits is important. Elucidating the may be direct. A recent report by Huang and exact signaling mechanism leading from Ga subunits to colleagues suggests that Gai and Gas are both able the activation of downstream signaling e€ectors such to directly bind Src, leading to its activation (Ma et al., as Src and Stat3 is ongoing. Several studies have shown 2000). However using co-immunoprecipitation experi- the direct binding of many if the signaling components ments we have been unable to see interactions between in a pair-wise manner, leading to the activation of Gao and endogenous c-Src in NIH3T3 cells (unpub- Stat3. Whether all these components can come together lished observation). How Gao activates c-Src is not yet in a large complex is not known. Also not clear is the known. Downstream from Src, data suggests that Stat3 role of the small G proteins and where along the and Src may also directly bind, leading to Stat3 signaling pathway they function since small G protein phosphorylation and activation (Cao et al., 1996). In signaling can occur both upstream and downstream of addition to direct Src and Stat3 binding recent work by Src. The role of the di€erent MAPkinases in Stat3 Guan and colleagues show that Rac-1 and Stat3 are signaling is also not clearly known. From the published also direct binding partners (Simon et al., 2000). Taken reports thus far it appears that both small G proteins together with the data that the downstream signaling and MAPkinases do play a role in Stat3 activation and molecules of Rac-1 such as p38 and JNK are necessary some reports even suggest an essential role for these for activation of Stat3 (Schuringa et al., 2000; Turkson signaling molecules leading to Stat3 activity. Clearly et al., 1999; Uddin et al., 2000), it is possible that all from all reports Stat3 plays an important role in these signaling molecules may come together in a large proliferation and transformation of cells. In cells where complex ultimately leading to Stat3 activation this endogenous GaoorGai are expressed, activation of speculative model is shown in Figure 2. GPCR's that couple to them could lead to activation An alternate mechanism of activation of Src and of Stat3 and changes in gene expression. This may be Stat3 by GaoandGai2 may exist through the Rap-1 an important pathway in neurons where Gao activa- and Ral pathways (Figure 3). In this paradigm the tion can lead to neurite outgrowth and neuronal direct binding partner for Gao, Rap-1-Gap, modulates plasticity. the activity of Rap-1 (Jordan et al., 1999) which in turn As we discover new signaling pathways that are can modulate the activity of Ral-1 (Herrmann et al., modulated by G proteins it is becoming apparent that 1996; Bos, 1998), Ral-1 in turn has been shown to GPCR mediated signaling utilizes several di€erent activate Src and subsequently Stat3 (Goi et al., 2000). signaling pathways. Understanding the mechanism of A third possible mechanism of activation of Src by signal sorting and integration between these di€erent Gao may occur through an indirect mechanism of signaling pathways and networks, and their role in activating metalloproteinases thereby leading to clea- physiological processes, is fast becoming an important vage of proHB-EGF and ligand induced activation of facet of modern biological research. Using the data EGF-R (Prenzel et al., 1999) and the subsequent from single signaling pathways and building up activation of Src and Stat3. This pathway may be complex signaling networks we can gain a systems speci®c for EGF and may not occur in all cell types. It understanding of the behavior and the physiological remains to be determined if any of these mechanisms outcome given speci®c stimuli. Gaining a systems are used for Gao activation of c-Src. understanding will be of great use for the design of strategies and molecules by which speci®c points in the signaling network can be modulated, thereby leading to Conclusion speci®c changes in the physiological endpoint.

G protein coupled receptors are capable of activating multiple signaling pathways and modulating several Acknowledgments physiological processes. The role of Ga subunits in the PT Ram was supported by an NIH post-doctoral fellow- transformation of cells has been investigated for several ship F32 CA79134. Parts of the work described here are years. The discovery of mutant GPCR's that couple to supported by NIH grants GM54508 and CA81050 to R Ga subunits, that have been shown to cause Iyengar.

References

Akira S. (2000). Oncogene, 19, 2607 ± 2611. Bromberg J and Darnell Jr JE. (2000). Oncogene, 19, 2468 ± Allen LF, Lefkowitz RJ, Caron MG and Cotecchia S. (1991). 2473. Proc. Natl. Acad. Sci. USA, 88, 11354 ± 11358. Bromberg JF, Horvath CM, Besser D, Lathem WW and Arvanitakis L, Geras-Raaka E, Varma A, Gershengorn MC Darnell Jr JE. (1998). Mol. Cell Biol., 18, 2553 ± 2558. and Cesarman E. (1997). Nature, 385, 347 ± 350. Bromberg JF, Wrzeszczynska MH, Devgan G, Zhao Y, Bos JL. (1998). EMBO J., 17, 6776 ± 6782. Pestell RG, Albanese C and Darnell Jr JE. (1999). Cell, 98, Bowman T, Garcia R, Turkson J and Jove R. (2000). 295 ± 303. Oncogene, 19, 2474 ± 2488.

Oncogene G protein regulation of Src and Stat's in transformation PT Ram and R Iyengar 1606 Brown MT and Cooper JA. (1996). Biochim. Biophys. Acta, Montminy M. (1997). Annu.Rev.Biochem.,66, 807 ± 822. 1287, 121 ± 149. Neer EJ, Lok JM and Wolf LG. (1984). J. Biol. Chem., 259, Buggy JJ. (1998). Biochem. J., 331, 211 ± 216. 14222 ± 14229. Buhl AM, Johnson NL, Dhanasekaran N and Johnson GL. Niu G, Heller R, Catlett-Falcone R, Coppola D, Jaroszeski (1995). J. Biol. Chem., 270, 24631 ± 24634. M, Dalton W, Jove R and Yu H. (1999). Cancer Res., 59, Cao X, Tay A, Guy GR and Tan YH. (1996). Mol. Cell Biol., 5059 ± 5063. 16, 1595 ± 1603. Nusse O and Neer EJ. (1996). J. Cell Sci., 109, 221 ± 228. Ceresa BP, Horvath CM and Pessin JE. (1997). Endocrinol- Ohara-Imaizumi M, Kameyama K, Kawae N, Takeda K, ogy, 138, 4131 ± 4137. Muramatsu S and Kumakura K. (1992). J. Neurochem., Cesarman E, Nador RG, Bai F, Bohenzky RA, Russo JJ, 58, 2275 ± 2284. Moore PS, Chang Y and Knowles DM. (1996). J. Virol., Pace AM, Wong YH and Bourne HR. (1991). Proc. Natl. 70, 8218 ± 8223. Acad.Sci.USA,88, 7031 ± 7035. Chen LT, Gilman AG and Kozasa T. (1999). J. Biol. Chem., Prenzel N, Zwick E, Daub H, Leserer M, Abraham R, 274, 26931 ± 26938. Wallasch C and Ullrich A. (1999). Nature, 402, 884 ± 888. Chung J, Uchida E, Grammer TC and Blenis J. (1997). Mol. Ram PT, Horvath CM and Iyengar R. (2000). Science, 287, Cell Biol., 17, 6508 ± 6516. 142 ± 144. Corre I, Baumann H and Hermouet S. (1999). Oncogene, 18, Robbins LS, Nadeau JH, Johnson KR, Kelly MA, Roselli- 6335 ± 6342. Rehfuss L, Baack E, Mountjoy KG and Cone RD. (1993). Diverse-Pierluissi M, Goldsmith PK and Dunlap K. (1995). Cell, 72, 827 ± 834. Neuron, 10, 753 ± 760. Schindler C and Darnell Jr JE. (1995). Annu. Rev. Biochem., Diverse-Pierluissi M, Remmers AE, Neubig RR and Dunlap 64, 621 ± 651. K. (1997). Proc. Natl. Acad. Sci. USA, 94, 5417 ± 5421. Schuringa JJ, Jonk LJ, Dokter WH, Vellenga E and Kruijer Fan X, Brass LF, Poncz M, Spitz F, Maire P and Manning W. (2000). Biochem. J., 347, 89 ± 96. DR. (2000). J. Biol. Chem., 275, 32129 ± 32134. Shen Y, Mamers P, Jobling T, Burger HG and Fuller PJ. €rench-Mullen JM, Plata-Salaman CR, Buckley NJ and (1996). J. Clin. Endocrinol. Metab., 81, 4159 ± 4161. Danks P. (1994). J. Physiol. (Lond.), 474, 21 ± 26. Simon AR, Vikis HG, Stewart S, Fanburg BL, Cochran BH Gierschik P, Milligan G, Pines M, Goldsmith P, Codina J, and Guan KL. (2000). Science, 290, 144 ± 147. Klee W and Spiegel A. (1986). Proc. Natl. Acad. Sci. USA, Smith PD and Crompton MR. (1998). Biochem. J., 331, 83, 2258 ± 2262. 381 ± 385. Gilman AG. (1987). Annu. Rev. Biochem., 56, 615 ± 649. Sontag JM, Thierse D, Rouot B, Aunis D and Bader MF. Goi T, Shipitsin M, Lu Z, Foster DA, Klinz SG and Feig LA. (1991). Biochem. J., 274, 339 ± 347. (2000). EMBO J., 19, 623 ± 630. Sternweis PC and Robishaw JD. (1984). J. Biol. Chem., 259, Hermouet S, Aznavoorian S and Spiegel AM. (1996). Cell 13806 ± 13813. Signal., 8, 159 ± 166. Strittmatter SM, Fishman MC and Zhu XP. (1994). J. Herrmann C, Horn G, Spaargaren M and Wittinghofer A. Neurosci., 14, 2327 ± 2338. (1996). J. Biol. Chem., 271, 6794 ± 6800. Taylor SJ, Smith JA and Exton JH. (1990). J. Biol. Chem., Jiang H, Wu D and Simon MI. (1993). FEBS Lett., 330, 265, 17150 ± 17156. 319 ± 322. Thomas SM and Brugge JS. (1997). Annu.Rev.CellDev. Jordan JD, Carey KD, Stork PJ and Iyengar R. (1999). J. Biol., 13, 513 ± 609. Biol. Chem., 274, 21507 ± 21510. Turkson J, Bowman T, Adnane J, Zhang Y, Djeu JY, Kalinec G, Nazarali AJ, Hermouet S, Xu N and Gutkind JS. Sekharam M, Frank DA, Holzman LB, Wu J, Sebti S and (1992). Mol. Cell Biol., 12, 4687 ± 4693. Jove R. (1999). Mol. Cell Biol., 19, 7519 ± 7528. Kroll SD, Chen J, De Vivo M, Carty DJ, Buku A, Premont Uddin S, Lekmine F, Sharma N, Majchrzak B, Mayer I, RT and Iyengar R. (1992). J. Biol. Chem., 267, 23183 ± Young PR, Bokoch GM, Fish EN and Platanias LC. 23188. (2000). J. Biol. Chem., 275, 27634 ± 27640. Kroll SD, Omri G, Landau EM and Iyengar R. (1991). Proc. Van Meurs KP, Angus CW, Lavu S, Kung HF, Czarnecki Natl. Acad. Sci. USA, 88, 5182 ± 5186. SK, Moss J and Vaughan M. (1987). Proc. Natl. Acad. Sci. Liang H, Venema VJ, Wang X, Ju H, Venema RC and USA, 84, 3107 ± 3111. Marrero MB. (1999). J. Biol. Chem., 274, 19846 ± 19851. Vara Prasad MV, Shore SK and Dhanasekaran N. (1994). LyonsJ,LandisCA,HarshG,VallarL,GrunewaldK, Oncogene, 9, 2425 ± 2429. Feichtinger H, Duh QY, Clark OH, Kawasaki E and Xing L, Ge C, Zeltser R, Maskevitch G, Mayer BJ and Bourne HR. (1990). Science, 249, 655 ± 659. Alexandropoulos K. (2000). Mol. Cell Biol., 20, 7363 ± Ma YC, Huang J, Ali S, Lowry W and Huang XY. (2000). 7377. Cell, 102, 635 ± 646. YuCL,MeyerDJ,CampbellGS,LarnerAC,Carter-SuC, MarreroMB,Schie€erB,PaxtonWG,HeerdtL,BerkBC, Schwartz J and Jove R. (1995). Science, 269, 81 ± 83. Delafontaine P and Bernstein KE. (1995). Nature, 375, Zhong Z, Wen Z and Darnell Jr JE. (1994). Science, 264, 95 ± 247 ± 250. 98.

Oncogene