pRb-expressing adenovirus Ad5-Rb attenuates the p53-induced apoptosis in cervical cancer cell lines

Abstract

The retinoblastoma protein (pRb), the gene product of the first reported tumour suppressor gene, is functionally inactivated by the E7 protein of high-risk human papillomavirus (HPV) found in most human cervical cancers. We have, in this study, constructed an adenoviral vector expressing wild-type pRb (Ad5-Rb) and used the constructed Ad5-Rb to transfect the osteosarcoma cell line Saos-2, and three cervical cancer cell lines HeLa, SiHa and C-33A. Our results showed that pRb caused G1 arrest in Saos-2 cells after transfection with Ad5-Rb. The number of colonies formed by the Ad5-Rb-transfected Saos-2 cells in soft agar was also found to be significantly lower (P<0.05) than those transfected with the adenoviral control expressing Escherichia coli beta-galactosidase (Ad5-LacZ). The transfection of Ad5-Rb caused an increase in the population of SiHa and C-33A cells in the G1 phase from 53.0 and 52.9% to 72.4 and 64.3%, respectively, but not in the HeLa cells. However, Ad5-Rb did not show any inhibitory effect on the growth of SiHa, HeLa and C-33A cells, and inhibition of colony formation in soft agar was not observed either. In contrast, flow cytometric analysis showed that Ad5-p53, a p53-expressing adenovirus, induced apoptosis, i.e. the appearance of sub-G1 peak, in all three tested cervical cancer cell lines. Nevertheless, the Ad5-p53-induced apoptosis was partially inhibited when Ad5-Rb was added simultaneously. These findings suggested that pRb may not be a good candidate for cervical cancer gene therapy. Our data also showed that the use of full-length pRb in combination with TP53 might not be a suitable strategy for cancer gene therapy.