Expression of epidermal growth factor receptor and human papillomavirus E6/E7 proteins in cervical carcinoma cells

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Abstract
Background: Epidermal growth factor receptor (EGF-R) proteins are highly expressed in many tumors, including those of the cervix. We have observed previously that the introduction of a transcription unit containing an antisense sequence for the E6/E7 genes of human papillomavirus (HPV) 18, along with a transcription unit containing a sense complementary DNA sequence for the wild-type retinoblastoma (Rb) gene, decreased the growth of human cervical carcinoma HeLa cells (HPV 18 positive) both in vitro and in vivo . To clarify the regulatory mechanisms by which this reduction in cell proliferation occurred, we studied the expression of EGF-R proteins in these cells. Methods: Western blot and northern blot techniques were used to measure EGF-R expression, and a pulse-chase immunoprecipitation assay was used to measure the stability of EGF-R protein in HeLa cells and HeLa cells that had been transfected with the antisense E6/E7 or sense Rb sequences. Cell proliferation was measured by use of a tetrazolium-based colorimetric assay for numbers of viable cells. Results: The introduction of sense Rb or antisense E6/E7 transcription units or a combination of these two transcription units into HeLa cells dramatically decreased the level of EGF-R proteins in these cells; EGF-R levels were not affected at the transcriptional level but at the post-transcriptional level. Addition of the anti-EGF-R-specific monoclonal antibody 225mAb to HeLa cells caused 53% (95% confidence interval = 44%-62%) growth inhibition. Conclusions: These results suggest that HeLa cervical carcinoma cells are dependent on EGF-R for proliferation and that changes in functional levels of the E6/E7 HPV proteins and endogenous Rb proteins may alter the growth rate of cervical cancer cell lines by reducing the stability of EGF-R at the post-transcriptional level.

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