PKB-mediated negative feedback tightly regulates mitogenic signalling via Gab2.
Heregulin (HRG)-induced tyrosine phosphorylation of the Gab2 docking protein was enhanced by pretreatment with wortmannin, indicating negative regulation via a PI3-kinase-dependent pathway. This represents phosphorylation by the serine/threonine kinase protein kinase B (PKB), since PKB constitutively associates with Gab2, phosphorylates Gab2 on a consensus phosphorylation site, Ser159, in vitro and inhibits Gab2 tyrosine phosphorylation. However, expression of Gab2 mutated at this site (S159A Gab2) not only enhanced HRG-induced Gab2 tyrosine phosphorylation and association with Shc and ErbB2, but also markedly increased tyrosine phosphorylation of ErbB2 and other cellular proteins and amplified activation of the ERK and PKB pathways. The impact of this negative regulation was further emphasized by a potent transforming activity for S159A Gab2, but not wild-type Gab2, in fibroblasts. These studies establish Gab2 as a proto-oncogene, and a model in which receptor recruitment of Gab2 is tightly regulated via an intimate association with PKB. Release of this negative constraint enhances growth factor receptor signalling, possibly since Gab2 binding limits dephosphorylation and disassembly of receptor-associated signalling complexes.
Lynch
Danielle K
DK
Cancer Research Program, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Australia.
Daly
Roger J
RJ
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D005246:Feedback; D006801:Humans; D051379:Mice; D008938:Mitosis; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D020890:Neuregulin-1 / Q000378:metabolism; D018739:Oncogene Proteins v-erbB / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D014162:Transfection; D000077191:Wortmannin
D048868:Adaptor Proteins, Signal Transducing; D000730:Androstadienes; C490895:GAB2 protein, human; C490894:Gab2 protein, mouse; C000715470:MAS1 protein, human; D020890:Neuregulin-1; D018739:Oncogene Proteins v-erbB; D010750:Phosphoproteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D000077191:Wortmannin