PROTEIN-TYROSINE-PHOSPHATASE 1B ANTAGONIZES SIGNALING BY ONCOPROTEIN TYROSINE KINASE P210 BCR-ABL IN-VIVO

The p210 bcr-abl protein tyrosine kinase (PTK) appears to be directly responsible for the initial manifestations of chronic myelogenous leuk emia (CML). In contrast to the extensive characterization of the PTK a nd its effects on cell function, relatively little is known about the nature of the protein tyrosine phosphatases (PTPs) that may modulate p 210 bcr-abl-induced signalling. In this study, we have demonstrated th at expression of PTP1B is enhanced specifically in various cells expre ssing p210 bcr-abl, including a cell line derived from a patient with CML. This effect on expression of PTP1B required the kinase activity o f p210 bcr-abl and occurred rapidly, concomitant with maximal activati on of a temperature-sensitive mutant of the PTK, The effect is apparen tly specific for PTP1B since, among several PTPs tested, we detected n o change in the levels of TCPTP, the closest relative of PTP1B. We hav e developed a strategy for identification of physiological substrates of individual PTPs which utilizes substrate-trapping mutant forms of t he enzymes that retain the ability to bind to substrate but fail to ca talyze efficient dephosphorylation, We have observed association betwe en a substrate-trapping mutant of PTP1B (PTP1B-D181A) and p210 bcr-abl , but not v-Abl, in a cellular context. Consistent with the trapping d ata, we observed dephosphorylation of p210 bcr-abl, but not v-Abl, by PTP1B in vivo. We have demonstrated that PTP1B inhibited binding of th e adapter protein Grb2 to p210 bcr-abl and suppressed p210 bcr-abl-ind uced transcriptional activation that is dependent on Ras, These result s illustrate selectivity in the effects of PTPs in a cellular context and suggest that PTP1B may function as a specific, negative regulator of p210 bcr-abl signalling in vivo.