Ser727-dependent transcriptional activation by association of p300 with STAT3 upon IL-6 stimulation

Activation of the signal transducer and activator of transcription 3 (STAT3 ) in response to interleukin-6 (IL-6) type cytokines involves both phosphor ylation of Tyr705, which enables dimerization, nuclear translocation and DN A binding, as well as ser727 phosphorylation, Here, we describe that the 65 C-terminal amino acids of STAT3 can function as an independent transcripti on activation domain (TAD), particularly when a negative charge is introduc ed at position 727 by mutation of the serine residue into aspartate, The st rong transcriptional activity of the C-terminal STAT3 Ser727Asp TAD is coup led to a constitutive association with the co-activator p300, In HepG2 cell s, p300 associates with STAT3 upon IL-6 stimulation, and overexpression of p300 enhances the transcriptional activity of STAT3 alpha, but not of STAT3 beta or STAT3 Ser727Ala. We conclude that Ser727 phosphorylation in the C- terminal region of STAT3 is required for transactivation by association wit h p300, (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B,V. All rights reserved.