Bmi-1, a member of the polycomb group (PcG) transcription repressors, is implicated in human cancers and is closely associated with cellular transformation of oral epithelial cells.Previously, we showed that Bmi-1 alone failed to immortalize NHOKs but can efficiently immortalize NHOKs in cooperative manner with human papillomavirus type 16 (HPV-16) E6, but not E7. We also found that this immortalization capacity of E6 resides in the second zinc finger domain (amino acids 118-122) because E6Δ118-122 cannot immortalize Bmi-1-overexpressing human oral keratinocytes (HOK/Bmi-1). The current study was undertaken to further investigate the underlying mechanisms of immortalization of NHOKs by Bmi-1 and HPV-16 E6. We performed microarray analysis to identify the cellular genes that are differentially expressed in NHOKs that overexpress Bmi-1 alone (LXSN/Bmi-1) and that express both Bmi-1 and E6 (E6/Bmi-1). We screened more than 47,000 transcripts and found 32 upregulated genes (e.g., DnaJ homolog (DNAJC12), tumor necrosis factor superfamily (TNFSF11), UDP glucuronosyltranferase 1 family (UGT1A6), chemokine ligand 5 (CCL5), mesoderm-specific transcript homolog (MEST), and podocalyxin-like(PODXL)); and 5 downregulated genes (e.g., activating transcription factor 3 (ATF3), c-fos, Notch1, and death-associated protein kinase 1 (DAPK1)). Differential expression of these genes was confirmed by reverse transcription (RT)-PCR. Among the upregulated genes was C1orf59, a novel gene that was induced by 26-fold in Bmi-1/HOK cells expressing E6. Interestingly, this gene was not induced in E6Δ118-122/Bmi-1 cells, as confirmed by microarray and RT-PCR analysis. Furthermore, no expression of C1orf59 was observed in four different strains of NHOKs, whereas its overexpression was detected in the majority of cancer cell lines including 1483, SiHa, HeLa, SCC4, SCC15, Hep2, KB, and FaDu. These results suggest that C1orf59 may be a target gene of E6 that plays a role in Bmi-1/E6-mediated immortalization of NHOKs. This study was supported by NIDCR/NIH (DE15316, DE14147, and DE07296) and Oral and Maxillofacial Surgery Foundation.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA