Growth hormone induces the tyrosine phosphorylation and nuclear accumulation of components of the ISGF3 transcription factor complex.

Growth hormone induced the accumulation of the stat91 and p84 subunits of the transcription factor complex ISGF3 in nuclear fractions of 3T3-F442A cells. Nuclear levels of p84 and stat91 peaked 30-60 min after addition of growth hormone. Growth hormone also induced the tyrosine phosphorylation of two proteins, with similar sizes to stat91 and p84, in both nuclear and cytosolic fractions. The time course of growth hormone-induced tyrosine phosphorylation of these proteins paralleled the nuclear accumulation of stat91 and p84. Immunoprecipitation with stat91-specific antibodies confirmed that growth hormone induced the tyrosine phosphorylation of stat91 and an associated protein of M(r) = 120 kDa. These findings suggest a mechanism for the modulation of specific gene transcription by growth hormone.