SOCS-1/JAB/SSI-1 Can Bind to and Suppress Tec Protein-tyrosine Kinase

Abstract

Tec is the prototype of a recently emerging subfamily among nonreceptor type protein-tyrosine kinases and is known to become tyrosine-phosphorylated and activated by a wide range of cytokine stimulations in hematopoietic cells. Although Tec was recently shown to be involved in the cytokine-driven activation mechanism of c-fos transcription, it is yet obscure how Tec relays the signals from cell surface receptors to the nucleus. To identify signaling molecules acting downstream of Tec, we have looked for Tec-interacting proteins (TIPs) by using the yeast two-hybrid system. Here we report the identification and characterization of a novel protein, TIP3, which has been simultaneously identified by other groups as SOCS-1, JAB, or SSI-1. TIP3 carries one Src homology 2 domain with a sequence similarity to that of CIS. In 293 cells, TIP3 associates with Tec and suppresses its kinase activity. Interestingly, TIP3 can also down-regulate the activity of Jak2 but not that of Lyn. We propose that SOCS-1/JAB/SSI-1/TIP3 is a novel type of negative regulator to a subset of protein-tyrosine kinases.Tec is the prototype of a recently emerging subfamily among cytoplasmic protein-tyrosine kinases (PTKs), 1 the Tec family comprised of Tec (1), Btk (2, 3), Itk/Tsk/Emt (4 -6), Txk (7), and Bmx (8). Many members of this family are abundantly expressed in hematopoietic tissues, and Tec has been shown to be involved in the intracellular signaling systems of a wide range of cytokines including interleukin (IL)-3, IL-6, stem cell factor, granulocyte colony-stimulating factor, erythropoietin, and thrombopoietin (9 -14). In addition to cytokine receptors, recent studies have indicated that other cell surface receptors on lymphocytes, such as CD28 (15) We have recently revealed that transient introduction of Tec into an IL-3-dependent cell line, BA/F3 (17), resulted in marked elevation of the promoter activity of the c-fos protooncogene and that introduction of kinase-dead Tec suppressed the IL-3-driven activation of the c-fos promoter, suggesting that Tec is directly involved in the cytokine-driven activation mechanism of c-fos proto-oncogene.2 To investigate how Tec regulates c-fos transcription, we have searched for Tec-interacting proteins (TIPs) by using yeast two-hybrid screening and have identified seven TIPs. Here we report the molecular cloning and characterization of a novel protein, TIP3. The predicted TIP3 protein contains one Src homology (SH) 2 domain with the highest similarity to that of mouse CIS (18). In the reconstitution system in 293 cells, TIP3 was shown to bind to Tec and suppress its activity. We could further reveal that TIP3 is a negative regulator of Jak2. EXPERIMENTAL PROCEDURESIsolation of TIP3 cDNA-By using the MATCHMAKER two-hybrid system (CLONTECH, Palo Alto, CA), we conducted a yeast two-hybrid screen in which human Tec kinase domain (amino acids 357-630) fused to the DNA-binding domain of GAL4 was used as a "bait" to identify cDNA clones from a variety of cDNA libraries. From more than three million transf...

The Role of SOCS-3 in Leptin Signaling and Leptin Resistance

“…Some data suggest that SOCS-2 may interact directly with the insulin-like growth factor-1 receptor and possibly regulate its function (45). Furthermore, SOCS-1 has been shown to inhibit Tec tyrosine kinases (46). These results suggest that the inhibitory function of SOCS proteins may extend beyond that of JAKs and cytokine receptors.…”

The tumor suppressor activity of SOCS-1

“…We have previously shown that the N-terminal sequences contain classical diproline motifs involved in the binding of SH3-containing molecules including ITK, p85 and GRB2 (De Sepulveda et al, 1999). The central SH2 domain is responsible for binding to both tyrosine phosphorylated proteins such as JAKs, KIT, and TEC and to the non-phosphorylated N-terminus of VAV Endo et al, 1997;Ohya et al, 1997). Lastly, the conserved C-terminal SOCS-Box binds to Elongin C (Kamura et al, 1998;Zhang et al, 1999).…”

Differential regulation of SOCS genes in normal and transformed erythroid cells

“…It can also associate with, and reduce the activity of, tyrosine kinases Tyk2 (Naka et al, 1997) and Tec, but not Lyn (Ohya et al, 1997). Interestingly, SOCS-1 has been shown to suppress stem cell factor (SCF)-induced proliferation, while favoring viability promoted by this cytokine (De Sepulveda et al, 1999).…”