The role of protein phosphatase 2a subunit ppp2r2b in atm nuclear localyzation in head and neck squamous cells carcinoma

Abstract

Protein phosphatase 2A (PP2A) has been implicated in radiation-induced activation of cellular responses. Recently, PP2A was found to prevent ataxia telangiectasia mutated (ATM) autophosphorylation and the inhibition of PP2A with okadaic acid (OA), a specific inhibitor to OA, predominantly localyzed ATM within cytoplasm. We found that HNSCC cell lines that had lower PPP2R2B mRNA expression exhibited low basal levels of ATMS1981p and -H2AX, an ATM downstream histone phosphorylation target. Interestingly, expression of PPP2R2B was found to be down-regulated in head and neck squamous cell carcinoma (HNSCC). Therefore, PPP2R2B may be important in ATM nuclear localyzation. To support our hypothesis, siRNA against PPP2R2B mRNA was employed. Interestingly, ATM of HNSCC cells containing a PPP2R2B siRNA was mainly localyzed within cytoplasm. In addition, siRNAPPP2R2B cells survived less after radiation. Our findings indicate the role of PPP2R2B in ATM nuclear localyzation.