Abstract 4044: MUC4 knockdown induces cellular senescence in head and neck cancer cells.
Authors: Macha Muzafar A. , Rachagani Satyanarayana , Pai Priya , Jain Maneesh , Lydiatt Williams M. , Smith Russell B. , Johansson Sonny L. , Lele Subodh M. , Kakar Sham S. , Ibrahim Farghaly H. , Lee John H. 
Published: August 2014

Abstract
The limited effectiveness of therapy for patients with advanced stage Head and Neck Squamous Cell Carcinoma (HNSCC) or recurrent disease is a reflection of an incomplete understanding of the molecular basis of HNSCC pathogenesis. Cellular senescence is an extremely stable form of cell cycle arrest that limits the proliferation of damaged cells and may act as a natural barrier to cancer progression. MUC4, a high molecular weight glycoprotein, is overexpressed in many cancers and is implicated in cell proliferation, adhesion, anti-apoptosis, cell cycle regulation, migration and invasion of various carcinomas, but nothing is known about its clinical relevance and the mechanism through which it regulates cancer progression in HNSCC. Therefore, the present study was aimed to investigate clinical relevance and a potential role of MUC4 in cellular senescence in HNSCCs.
Using immunohistochemical analysis, we observed a significant up regulation of MUC4 in 79% (68/86) of HNSCC tissue samples compared to only 10% (1/10) of benign tissues. Further, we observed high expression of MUC4 in a majority of HNSCC cell lines tested. Knockdown (KD) of MUC4 with specific shRNA in HNSCC cells markedly decreased cell proliferation. The doubling time increased from 26 h to 36 h and 34 h to 42 h in MUC4 silenced UMSCC-1 and SCC-10B cells, respectively as compared to their control counterparts. MUC4 KD in UMSCC-1 and UMSCC-10B cells resulted in accumulation of cells at the G0/G1 phase with concomitant decrease in the expression of cell cycle regulating proteins like Cyclin-E and Cyclin-D1, and decrease in BrDU incorporation. More importantly, MUC4 KD resulted in the induction of cellular senescence in both cell lines as indicated by an increase in the number of flat, enlarged and senescence-associated β-galactosidase (SA-β-Gal) positive cells. Further,
MUC4 KD resulted in the inhibition of FAK signaling, and decreased motility and invasive behavior in both UMSCC-1 and UMSCC-10B cells. Mechanistic dissection of senescent response to MUC4 silencing indicated decreased acetylated histone enrichment at Cyclin-E/Cyclin-D1 promoters, leading to their downregulation. Further, both cell lines UMSCC-1 and UMSCC-10B underwent a P16 and P21 dependent cellular senescence in response to MUC4 KD that requires inactivation of Akt and ERK signaling. In conclusions, these findings suggest a novel role of MUC4 in regulating cellular senescence and provide evidence of the functional role of MUC4 in the proliferation, motility and invasion of HNSCC cells. Therefore, downregulation of MUC4 may be a promising therapeutic approach for Head and Neck cancer treatment.
Citation Format: Muzafar A. Macha, Satyanarayana Rachagani, Priya Pai, Maneesh Jain, Williams M. Lydiatt, Russell B. Smith, Sonny L. Johansson, Subodh M. Lele, Sham S. Kakar, Farghaly H. Ibrahim, John H. Lee. MUC4 knockdown induces cellular senescence in head and neck cancer cells. [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 4044. doi:10.1158/1538-7445.AM2013-4044