Introduction: The E3 ubiquitin ligase TRIM8 has been initially identified as a Ring finger protein expressed in glioblastomas capable of binding SOCS-1, a member of the Suppressor of Cytokine Signaling family of molecules. It has been reported by us that TRIM8 appears to be a negative regulator of SOCS-1 stability by binding to its SH-2/SOCS box domains. Moreover, recent reports have documented that nucleocytoplasmic trafficking of TRIM8 is involved in positive regulation of TNF-ainduced NF-kB activation. Methods: Cell culture- For transfection experiments early cell passages from the established human Jurkat T cell line (ATCC) were used in all experiments. Generation of Recombinant TRIM8/ GERP Expression Vectors—Plasmid p612 was obtained by inserting a BamHI-BglII 612-bp fragment from the original pGAD-NOT containing the RING domain of TRIM8/GERP into the BamHI site of the pcDNA3.1 [(HisC)-Xpress-tagged vector (Invitrogen)]. Immunoprecipitation and Immunoblots—For Western blotting, cells were washed three times with cold phosphate-buffered saline and lysed using 0.5 ml of lysis buffer. Protein extracts were quantified using the Bio-Rad microassay, and 40 mg of total protein was run on a denaturing protein gel and electrotransferred onto membrane. Results: Here, we show that in Jurkat cell line, a human T cell lymphoma, PIM serine/threonine kinases, also bind and phosphorylate TRIM8, resulting in increased stabilization of the ubiquitin ligase activity. Since SOCS-1 is functionally phosphorylated and also stabilized by PIMs, co-expression of a heterotrimeric TRIM8/ SOCS-1/PIM complex promotes partial destabilization of the complexes and pursues degradation of the SOCS-1 protein. Additionally, co-expression of SOCS-1/TRIM8/PIM kinase complexes mitigates the repression of an interferon-γ-mediated signaling in responsive T cells in vivo. Conclusions: These data add new partners to the complex network of protein-protein interactions that regulate SOCS-1 function and modulate the proliferation of T cell lymphoma with particular regards to the activity of mitogen derived serine/threonine kinases.
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