J. Biol. Chem., Vol. 266, Issue 36, 24241-24244, 12, 1991

Insulin-like growth factor-1 induces tyrosyl phosphorylation of nuclear proteins

BS Oemar, NM Law and SA Rosenzweig
Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06510.

Stimulation of mesangial cells with insulin-like growth factor-1 (IGF- 1) resulted in the rapid tyrosyl phosphorylation of nuclear proteins as indicated by fluorescence microscopy of cells stained with anti- phosphotyrosine antibodies. Immunoprecipitation of nuclear extracts with anti-phosphotyrosine antibodies revealed that IGF-1 induced a transient increase in immunoreactive phosphotyrosine in nuclear proteins of 43, 95, and 160 kDa. Using a double immunoprecipitation protocol, the transcription factor c-Jun was also found to increase in immunoreactive phosphotyrosine in response to IGF-1. A similar pattern of tyrosyl phosphorylation of nuclear proteins was observed in the epidermoid carcinoma cell line CaSki. These data suggest that tyrosyl phosphorylation of nuclear proteins may be a step in the transduction of mitogenic signals.
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