Ax1 receptor tyrosine kinase is implicated in several malignancies and is the receptor for the vitamin K-dependent growth factor Gas6. From a yeast two-hybrid screen of protein-protein interactions with the Ax1 cytoplasmic domain, we detected a previously uncharacterised SH2 domain-containing protein. We cloned two novel splice variants of this protein that give rise to 1409- and 1419-amino acid proteins, differing only in their N-terminal residues and yielding a 150-kDa protein product by in vitro translation. The Ax1-interacting C-terminus contains a tandem SH2 and PTB domain combination homologous to the focal adhesion protein tensin. We detected interaction of Ax1 with both domains in mammalian cells by co-immunoprecipitation and two-hybrid analyses. In addition, the protein possesses an N-terminal putative phorbol ester-binding C1 domain as well as a central tyrosine phosphatase motif. Thus, we have named the protein C1 domain-containing phosphatase and TENsin homologue (C1-TEN). Northern blot analysis of C1-TEN in human tissues revealed highest expression in heart, kidney, and liver. In summary, we have identified a novel multi-domain intracellular protein that interacts with Ax1 and which may furthermore be involved in other signal transduction pathways. (C) 2002 Elsevier Science (USA). All rights reserved.