Abstract 5243: The novel calcium-dependent direct binding of S100B to p90 ribosomal S6 kinase (RSK) decreases MAP kinase-mediated RSK activation in malignant melanoma.

Abstract

Abstract S100B is an effective and extensively used prognostic marker for melanoma, with increasing serum S100B being predictive of disease stage, increased recurrence, and low overall patient survival. Establishing the mechanism by which S100B alters cell signaling provides insight into how it may facilitate the progression of melanoma and aid in developing new pharmacological drugs to inhibit cancer advancement. To evaluate specific roles for S100B in malignant melanoma, our S100B knock-down and over-expression studies established a correlation between S100B expression and cell viability. ERK phosphorylation was also found to correlate with S100B levels. We have discovered RSK, a downstream ERK target, as a novel binding partner of S100B. RSK is known to regulate MAPK signaling in melanoma but the mechanism is unclear. We observed an inverse relationship between activated and phosphorylated RSK and S100B levels. We used a Ca2+-binding mutant of S100B (E31A + E72A) to demonstrate that the S100B-RSK interaction was calcium-dependent. Pull-down experiments revealed the C-terminal domain of RSK to be necessary for S100B binding. In vitro, S100B was found to reduce ERK-dependent phosphorylation of RSK at Thr573. Our cellular fractionation and immuno-fluorescence studies showed that S100B protein prevented nuclear localization of phosphorylated RSK. These data are consistent with a mechanism in which elevated S100B binds directly to RSK in a calcium-dependent manner, preventing ERK-mediated phosphorylation of RSK and inhibiting RSK localization to the nucleus. We have identified the S100B-RSK interaction as a novel drug target in melanoma cells. We are currently screening compounds for inhibitors of the S100B-RSK interaction. Citation Format: Adam D. Pierce, Kira G. Hartman, David Weber. The novel calcium-dependent direct binding of S100B to p90 ribosomal S6 kinase (RSK) decreases MAP kinase-mediated RSK activation in malignant melanoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5243. doi:10.1158/1538-7445.AM2013-5243