A Novel Human AlkB Homologue, ALKBH8, Contributes to Human Bladder Cancer Progression

Abstract

We recently identified a novel human AlkB homologue, ALKBH8, which is expressed in various types of human cancers including human urothelial carcinomas. In examining the role and function of ALKBH8 in human bladder cancer development in vitro, we found that silencing of ALKBH8 through small interfering RNA transfection reduced reactive oxygen species (ROS) production via down-regulation of NAD(P)H oxidase-1 (NOX-1) and induced apoptosis through subsequent activation of c-jun NH₂-terminal kinase (JNK) and p38. However, we also found that JNK and p38 activation resulted in phosphorylation of H2AX (γH2AX), a variant of mammalian histone H2A, which contributes to the apoptosis induced by silencing ALKBH8 and NOX-1. Silencing of ALKBH8 significantly suppressed invasion, angiogenesis, and growth of bladder cancers in vivo as assessed both in the chorioallantoic membrane assay and in an orthotopic mouse model using green fluorescent protein–labeled KU7 human urothelial carcinoma cells. Immunohistochemical examination showed high expression of ALKBH8 and NOX-1 proteins in high-grade, superficially and deeply invasive carcinomas (pT₁ and >pT₂) as well as in carcinoma in situ, but not in low-grade and noninvasive phenotypes (pT_a). These findings indicate an essential role for ALKBH8 in urothelial carcinoma cell survival mediated by NOX-1–dependent ROS signals, further suggesting new therapeutic strategies in human bladder cancer by inducing JNK/p38/γH2AX–mediated cell death by silencing of ALKBH8. [Cancer Res 2009;69(7):3157–64]