SYP (SH-PTP2) IS A POSITIVE MEDIATOR OF GROWTH FACTOR-STIMULATED MITOGENIC SIGNAL-TRANSDUCTION

Syp (SH-PTP2) was recently identified as a phosphotyrosine phosphatase containing two SH2 domains within its primary structure. In response to appropriate growth factor stimulation, Syp becomes phosphorylated o n tyrosine residues and associates with insulin receptor substrate 1 ( IRS-1) and/or the corresponding growth factor receptor via its SH2 dom ains, leading to increased Syp activity. To assess the importance of S yp in mitogenic signaling, we microinjected mammalian fibroblasts with several reagents designed to interfere with Syp SH2/phosphotyrosine i nteraction in vivo. Insulin-, insulin-like growth factor-1-, and epide rmal growth factor-stimulated DNA synthesis, indicated by bromodeoxyur idine (BrdUrd) incorporation, was dramatically decreased following mic roinjection of a Syp antibody (Ab) (65-85%) or a Syp GST-SH2 fusion pr otein (similar to 90%) in comparison with cells microinjected with con trol IgG or glutathione S-transferase (GST), respectively. In addition , microinjection of an IRS-1-derived phosphonopeptide, which inhibits in vitro binding of Syp-SH2 to IRS-1 with an ED(50) value of similar t o 23 mu M, also decreased BrdUrd incorporation in vivo by approximatel y 50-75%. Microinjection of the Syp Ab, Syp GST-SH2 fusion protein, or the phosphonopeptide had no effect on serum-stimulated BrdUrd incorpo ration. In conclusion, disruption of Syp function in living cells inhi bited cell cycle progression in response to growth factor stimulation, indicating that Syp is a critical positive regulator of mitogenic sig nal transduction.