Expression signatures of HOX cluster genes in cervical cancer pathogenesis: Impact of human papillomavirus type 16 oncoprotein E7

The Homeobox (HOX) genes encode important transcription factors showing deregulated expression in several cancers. However, their role in cervical cancer pathogenesis, remains largely unexplored. Herein, we studied their association with Human Papillomavirus type 16 (HPV16) mediated cervical cancers. Our previously published gene expression microarray data revealed a significant alteration of 12 out of 39 HOX cluster members among cervical cancer cases, in comparison to the histopathologically normal controls. Of these, we validated seven (HOXA10, HOXA13, HOXB13, HOXC8, HOXC9, HOXC11 and HOXD10) by quantitative real-time PCR. We identified decreased HOXA10 expression as opposed to the increased expression of the rest. Such decrease was independent of the integration status of HPV16 genome, but correlated negatively with E7 expression in clinical samples, that was confirmed in vitro. HOXA10 and HOXB13 revealed association with Epithelial-Mesenchymal Transition (EMT). While HOXA10 expression correlated positively with E-Cadherin and negatively with Vimentin expression, HOXB13 showed the reverse trend. Chromatin immunoprecipitation study in vitro revealed the ability of E7 to increase HOX gene expression by epigenetic regulation, affecting the H3K4me3 and H3K27me3 status of their promoters, resulting from a loss of PRC2-LSD1 complex activity. Thus, besides identifying the deregulated expression of HOX cluster members in HPV16 positive cervical cancer and their association with EMT, our study highlighted the mechanism of HPV16 E7-mediated epigenetic regulation of HOX genes in such cancers, potentially serving as bedrock for functional studies in the future.