Viral integration sites in human papilloma virus-33-immortalized cervical keratinocyte cell lines

The viral organization of HPV-33 was determined by Southern blotting in 2 HPV-33-immortalized cervical cell lines (CK11 and CK12) and compared to our previous results obtained on 10 other already characterized HPV-33-immortalized cell lines (CK1 to CK10). As observed in CK1 to CK10, the viral DNA was found integrated in the cellular genome of CK11 and CK12. However, in CK11 and CK12, the integrated viral genome was deleted and mostly limited to the URR and the E6-E7 ORFs, stressing the importance of those sequences in the immortalization process. Furthermore, CK11 and CK12 showed a unique and identical integration site, as observed in CK1 to CK10, which also harbored HPV-33 integrated at a unique and identical site (which was however different from the one evidenced in CK11 and CK12). Indeed, in situ hybridizations on chromosomes allowed the precise localization of the viral DNA on chromosome 13q33-34 in CK1 to CK10 whereas it was mapped to chromosome 9p13 in CK11 and CK12. We discuss the possibility that integration of HPV-33 at those two particular sites has conferred some growth advantages to the cells and could have thus played a crucial role in the immortalization.