Abstract 1490: p38 MAPK mediates epithelial-mesenchymal transition by regulating p38IP and snail in head and neck squamous cell carcinoma (HNSCC).

Objectives: Understanding the molecular mechanisms that mediate HNSCC metastasis may enable identification of novel therapeutic targets. We have reported the role of the E-cadherin transcriptional repressor, Snail, in the inflammation-induced promotion of EMT in HNSCC. Herein we demonstrate that inflammatory mediators also upregulate p38 and p38 interacting protein (p38IP), thus further defining the cycle by which inflammation promotes tumor progression. Methods: A molecular biology study. Real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot analysis, and 3-D spheroid culture were used to determine how inflammation affects p38, p38IP and EMT. Results: p38 kinase inhibitor treated, and p38 shRNA HNSCC cell lines demonstrated a significant upregulation in E-cadherin mRNA and a decrease in the mRNA expression of the transcriptional repressor Snail. p38 shRNA HNSCC cell lines show a less invasive phenotype in a spheroid model, and demonstrate decreased tumor growth in a SCID mouse model. An inverse relationship between p-p38 and E-cadherin was demonstrated in situ by immunohistochemical staining of human HNSCC tissue sections. Activation of p38 is required for the robust IL-1β induced E-cadherin downregulation and Snail upregulation. IL-1β increases p-p38 and has a more rapid and robust effect on p38. Snail overexpression also enhanced p-p38 in vitro. Inhibition of p38 blocked HNSCC tumor growth in vivo. p38 activates p38IP, a p38 downstream component in STAGA transcriptional activator complex, in HNSCC cell lines. p38 bound to and stabilized p38IP, a subunit of histone acetyltransferase STAGA, resulting in enhanced transcription of Snail. Inhibition of p38IP blocked HNSCC migration and invasion both in vitro and in vivo. In HNSCC patient samples, p38IP expression was increased compared to adjacent normal tissue. Conclusions: In gastrulation, a Snail-independent P38/P38IP pathway is required in the primitive streak to downregulate E-cadherin expression at the posttranscriptional level. Herein we provide the first report that in HNSCC a snail-dependent p38/p38IP pathway is essential for E-cadherin down-regulation and cell invasion. Our work herein demonstrates for the first time that a snail-p38/p38IP feedback loop jointly down regulates E-cadherin and drives a potent EMT in HNSCC. This newly defined pathway has important implications for targeted chemoprevention and therapy. Citation Format: Yuan Lin, Guangyu Wang, Jie Luo, Chi Lai, Elliot Abemayor, David Elashoff, Steve Dubinett, Maie A. St. John. p38 MAPK mediates epithelial-mesenchymal transition by regulating p38IP and snail in head and neck squamous cell carcinoma (HNSCC). [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 1490. doi:10.1158/1538-7445.AM2013-1490