Abstract 2933: Inhibition of MAPK signaling prevents Fra-1-mediated CD44 expression in human brain tumor cells

Abstract

Abstract Glioblastoma multiforme (GBM) is a grade IV brain tumor that exhibits a high growth rate and the capacity to invade surrounding tissue. The invasive capacity displayed by GBM cells is a major reason patients diagnosed with GBMs have poor prognosis. Currently, there are few effective treatment options for GBM. The invasive capacity of GBM cells has been associated with CD44, a transmsmbrane glycoprotein. CD44 is a cell surface receptor for hyaluronic acid (HA) which is a major component of the extracellular matrix that comprises the brain. Recent studies demonstrate that CD44 expression has been associated with fos related antigen 1 (Fra-1) an AP-1 transcription factor in GBM. Specifically, our lab has shown that reducing Fra-1 protein levels with siRNA results in decreased amounts of CD44 protein. To better understand Fra-1 regulation of CD44 we examined the signaling mechanisms that mediate Fra-1-regulated CD44 expression. Several human GBM cell lines (U-251 MG, U-1242 MG, and A-172) were treated with epidermal growth factor (EGF 20ng/ml) at various time points to determine the role of EGF stimulation on Fra-1 and CD44 protein expression. In addition to EGF cells were treated with inhibitors to four known signaling pathways: PI3 kinase (LY 294002, 20µM); mTOR (rapamycin, 25nM); Jun kinase (SB203580, 20 µM); and MAP kinase (U-0126, 20µM) to determine whether these pathways mediate Fra-1-regulated CD44 expression. Western blot analysis was used to determine the level of protein expression of Fra-1 and CD44 following inhibitor treatment. Inhibition of the MAPK pathway demonstrated a significant decrease in Fra-1 and CD44 protein levels while inhibition of the AKT and mTOR signaling pathways respectively, exhibit less regulation of Fra-1 and CD44 levels. In addition to determining the regulation of Fra-1 and CD44 protein expression we also assayed the mRNA levels of Fra-1 and CD44 following inhibitor treatment. Fra-1 and CD44 mRNA levels decreased following U-0126 treatment, correlating the decrease of mRNA levels with the decrease of protein expression described previously. Taken together these data suggest that the MAP kinase pathway is responsible for regulating Fra-1-mediated CD44 mRNA and protein expression in malignant brain tumor cell lines. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2933. doi:10.1158/1538-7445.AM2011-2933