Saturday, March 24, 2012: 8 a.m. - 9:30 a.m.
Presentation Type: Oral Session
The p38-MAPK pathway has a critical role in the production of pro-inflammatory cytokines that promote angiogenesis, thereby facilitating tumor progression in squamous cell carcinoma of the head and neck (SCCHN). Activated p38 triggers a phosphorylation cascade that regulates RNA binding proteins, such as tristetraprolin (TTP), in macrophages. Unphosphorylated TTP binds to and directs decay of cytokine mRNA transcripts, thereby reducing cytokine secretion. However, in inflammatory conditions, TTP is phosphorylated, which abrogates its ability to degrade cytokine mRNA. Previously, we showed that downregulation of TTP in SCCHN leads to increased IL-6 secretion, which is correlated with poor disease-specific survival. The role of the p38-MAPK pathway in TTP-regulated cytokine secretion has not been investigated in any cancer. Objective: The goal of this project was to investigate whether p38 phosphorylates TTP, thereby increasing cytokine secretion and angiogenesis in SCCHN. Methods: Cell lysates were generated from control or IL-1β induced cells. Phospho-p38, total p38, and total TTP were detected by immunoblot analysis. Phospho-TTP was determined by immunoprecipitation of TTP followed by immunoblot analysis with anti-phosphoserine. Knockdown of p38 and TTP was performed via siRNA transfection. Cytokines were quantified by ELISA. Angiogenesis assays were performed with human microvascular endothelial cells (HMEC-1) seeded on matrigel and exposed to SCCHN conditioned media. Results: Phospho-p38 activity is increased in SCCHN compared to normal keratinocytes. Phospho-TTP levels are variable in HNSCC cell lines. IL-1β induces p38 activation and knockdown of p38 decreases TTP phosphorylation and secretion of IL-6, VEGF, and PGE2. p38 knockdown also decreases length and number of endothelial cell sprouts, whereas TTP knockdown has the reverse effect. Conclusions: These findings suggest that targeting upstream regulators of cytokine secretion, such as p38 and TTP, may improve responsiveness of SCCHN to treatment via inhibiton of angiogenesis.This abstract is based on research that was funded entirely or partially by an outside source: AADR Student Research Fellowship, University of Michigan School of Dentistry Student Research Fellowship, NIDCR: DE018512-01, DE017977-01, DE0219513-01, DE007057-32, 1R01-DE021423, 5F32-DE21305-02
Keywords: Carcinogenesis, Cytokine, Inflammation, Inflammatory mediators and Pathology