Uichi Ikeda

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

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.

Nitric Oxide Synthase Gene Transfer Inhibits Protein Synthesis of Rat Cardiac Mycocytes

We investigated whether nitric oxide (NO) synthase gene transfer could attenuate α-adrenergic agonist-induced growth of cardiac myocytes. First, we investigated the effects of exogenous NO and a cGMP analogue on protein synthesis of cultured neonatal rat cardiac myocytes. The NO donor, morpholinosydnonimine (SIN-1), and 8-bromo-cGMP caused concentration-dependent decreases in phenylephrine (Phe)-induced 3H-leucine incorporation into myocytes. We then transferred endothelial NO synthase (eNOS) gene into cardiac myocytes using adeno-associated virus (AAV) vectors. eNOS gene transfer into cardiac myocytes induced 140 kDa eNOS protein expression and significantly increased cGMP contents of myocytes compared with control cells. eNOS gene transfer also inhibited 3H-leucine incorporation into cardiac myocytes in response to Phe, which was significantly recovered in the presence of the NOS inhibitor NG-monometyl-L-arginine acetate. These results indicate that authentic NO attenuates the effects of the α-adrenergic agonist-induced cardiac hypertrophy at least partially via cGMP production, suggesting that eNOS gene transfer using AAV vectors is promising for the gene therapy of cardiac hypertrophy.