ABSTRACT
High-risk human papillomavirus (HPV) types 16 and 18 are involved in the multistep process of cervical cancer. Transfection of normal keratinocytes with high-risk HPV-DNA generally gives rise to immortal cultures. This may be explained by the loss of senescence genes as a consequence of HPV-induced genetic instability. On the basis of the dominance of cellular senescence over immortality, fusion of normal keratinocytes with HPV-immortalized cells results in complementation of these putative gene defects. In a previous study, we showed that underrepresentation of chromosome 10 is a characteristic phenomenon during the early phase of immortalization. Here we show that introduction of a normal copy of chromosome 10 into HPV16-immortalized cells (HPKII) by Microcell-mediated chromosome transfer resulted in senescence of a significant number of hybrids. By using several derivatives of chromosome 10 for further fusion experiments, the chromosomal region responsible for senescence could be assigned to 10p14-p15. The potential significance of loss of gene function in this region is underlined by the high frequency (38.7%) of loss of heterozygosity in cervical cancers including early stage tumors.
Subject(s)
Cellular Senescence/genetics , Chromosomes, Human, Pair 10/genetics , Carcinoma, Squamous Cell/genetics , Carcinoma, Squamous Cell/pathology , Carcinoma, Squamous Cell/virology , Cell Line, Transformed , Cell Transformation, Viral , Chromosome Mapping , DNA, Viral/genetics , Female , Gene Deletion , Gene Transfer Techniques , Humans , Keratinocytes/cytology , Keratinocytes/physiology , Keratinocytes/virology , Loss of Heterozygosity , Papillomaviridae/genetics , Uterine Cervical Neoplasms/genetics , Uterine Cervical Neoplasms/pathology , Uterine Cervical Neoplasms/virology , Uterine Cervical Dysplasia/genetics , Uterine Cervical Dysplasia/pathology , Uterine Cervical Dysplasia/virologyABSTRACT
In this study we investigate the mechanism of intracellular pH change and its role in malignant transformation using the E7 oncogene of human papillomavirus type 16 (HPV16). Infecting NIH3T3 cells with recombinant retroviruses expressing the HPV16 E7 or a transformation deficient mutant we show that alkalinization is transformation specific. In NIH3T3 cells in which transformation can be turned on and followed by induction of the HPV16 E7 oncogene expression, we demonstrate that cytoplasmic alkalinization is an early event and was driven by stimulation of Na+/H+ exchanger activity via an increase in the affinity of the intracellular NHE-1 proton regulatory site. Annulment of the E7-induced cytoplasmic alkalinization by specific inhibition of the NHE-1, acidification of culture medium, or clamping the pHi to nontransformed levels prevented the development of later transformed phenotypes such as increased growth rate, serum-independent growth, anchorage-independent growth, and glycolytic metabolism. These findings were verified in human keratinocytes (HPKIA), the natural host of HPV. Results from both NIH3T3 and HPKIA cells show that alkalinization acts on pathways that are independent of the E2F-mediated transcriptional activation of cell cycle regulator genes. Moreover, we show that the transformation-dependent increase in proliferation is independent of the concomitant stimulation of glycolysis. Finally, treatment of nude mice with the specific inhibitor of NHE-1, DMA, delayed the development of HPV16-keratinocyte tumors. Our data confirm that activation of the NHE-1 and resulting cellular alkalinization is a key mechanism in oncogenic transformation and is necessary for the development and maintenance of the transformed phenotype.
