Direct Interaction of Jak1 and v-Abl Is Required for v-Abl-Induced Activation of STATs and Proliferation

ABSTRACT

In Abelson murine leukemia virus (A-MuLV)-transformed cells, members of the Janus kinase (Jak) family of non-receptor tyrosine kinases and the signal transducers and activators of transcription (STAT) family of signaling proteins are constitutively activated. In these cells, the v-Abl oncoprotein and the Jak proteins physically associate. To define the molecular mechanism of constitutive Jak-STAT signaling in these cells, the functional significance of the v-Abl–Jak association was examined. Mapping the Jak1 interaction domain in v-Abl demonstrates that amino acids 858 to 1080 within the carboxyl-terminal region of v-Abl bind Jak1 through a direct interaction. A mutant of v-Abl lacking this region exhibits a significant defect in Jak1 binding in vivo, fails to activate Jak1 and STAT proteins, and does not support either the proliferation or the survival of BAF/3 cells in the absence of cytokine. Cells expressing this v-Abl mutant show extended latency and decreased frequency in generating tumors in nude mice. In addition, inducible expression of a kinase-inactive mutant of Jak1 protein inhibits the ability of v-Abl to activate STATs and to induce cytokine-independent proliferation, indicating that an active Jak1 is required for these v-Abl-induced signaling pathways in vivo. We propose that Jak1 is a mediator of v-Abl-induced STAT activation and v-Abl induced proliferation in BAF/3 cells, and may be important for efficient transformation of immature B cells by the v-abloncogene.

ACKNOWLEDGMENTS

We thank Robert Schreiber for purified his-Jak1, Kathryn Calame for v-Abl expression vector and anti-murine c-Myc antibody, Frank McCormick for the GST Raf RBD construct, and Jacalyn Pierce for v-HRas-transformed pre-B cells. We are grateful to Binfeng Lu for assistance with nude-mouse injections and Pang-Dian Fan for Abi-1 activation assays. We thank Konstantina Alexandropoulos, Marion Dorsch, and members of the Rothman laboratory for critical reading of the manuscript.

This work was supported by Cancer Research Institute/Partridge Foundation Clinical Investigator Award (to P.B.R.) and NIH grants 2T32DK07328-17 (to N.N.D.) and CA43054 (to J.Y.J.W.).