LMW-PTP IS A NEGATIVE REGULATOR OF INSULIN-MEDIATED MITOTIC AND METABOLIC SIGNALING

To understand the physiological role of low Mr weight phosphotyrosine protein phosphatase (LMW-PTP) in insulin mediated signaling, we establ ished clonal cell Lines overexpressing the dominant negative (C12S mut ant) LMW-PTP (dnLMW-PTP) hom NIH3T3 murine fibroblasts expressing insu lin receptor. Upon insulin stimulation we observe an association betwe en the dnLMW-PTP and the beta-subunit of the insulin receptor. This as sociation is dependent on the tyrosine phosphorylation of the insulin receptor since it is not observed in unstimulated cells. Furthermore, in vitro binding experiments between dnLMW-PTP and the insulin recepto r reveal that the interaction is mediated by the LMW-PTP catalytic sit e, as indicated by competition with orthovanadate. DnLMW-PTP overexpre ssion influences both the mitogenic and the metabolic bioeffects of in sulin. In particular, in cells overexpressing dnLMW-PTP we observe an increase in the glycogenosynthesis rate and in mitosis as indicated by glucose incorporation into glycogen and thymidine incorporation into DNA, respectively. Moreover, we studied the insulin mediated signal tr ansduction pathways starting from insulin receptor, such as the Src ki nase, the p21Ras/ERK and the PI3K routes. Our findings are consistent with a specific regulation of mitogenesis by LMW-PTP through a pathway involving c-Src kinase but independent by both PI3K and ERK. These da ta strongly suggest that LMW-PTP acts as a negative regulator of both mitogenetic and metabolic insulin signalling. (C) 1997 Academic Press.