S100B inhibits transcription activity of p-STAT3.

qRT-PCR was performed on STAT3 target genes CEBPD (A), SOCS3 (B), and SOCS1 (C) in shSCR and shS100B WM115 cells in the absence or presence of a STAT3 inhibitor S31-201 for 48 hours of treatment (100 μM). The knockdown of S100B results in increased transcription of all three p-STAT3 regulated genes. The introduction of the STAT3 inhibitor negated that effect for CEBPD and SOCS3 but was not statistically significant for SOCS1 (P = 0.07). (n = 3; mean + SD; *, P < 0.05; **, P < 0.005). (D) Immunoblot analysis of p-STAT3 (Tyr705) and S100B in shSCR and shS100B WM115 cells following 48 hours of S31-201 treatments (100 μM) confirmed the loss of p-STAT3 (Tyr705). (n = 3; mean + SD; *, P = 0.05; **, P < 0.005). Relative p-STAT3 protein levels were quantified using Image J software.