Natural HPV58 E6 and E7 Variants Detected in Thai Breast Cancer Patients Cooperate to Induce Loss of p53 and Increase Cell Growth

Abstract

Background: Detection of human papillomavirus (HPV) in breast cancer patients has suggested a possible contributing role of the virus in cancer progression in this population. Objective: To investigate the presence of HPVs in Thai breast cancer patients and examine the potential activities of HPVs identified in both breast and cervical cancer cells. Materials and Methods: Fifty-five breast cancer tissues from Thai patients were subjected to HPV detection using PCR-EIA DNA sequencing. Detection of HPV E6 proteins in sample tissues was examined by fluorescence immunohistochemistry. Cervical and two types of breast cancer cell lines expressing HPV oncogenes were established. The separate and combination of HPV oncoproteins activity for p53 degradation and specific gene regulation were investigated using western blot analysis and qPCR. Cell proliferation was assessed by MTT assay. Results: Twenty-two percent (10/45) of invasive breast cancers were found infected with various high-risk HPV types, with HPV58 E6D4G/ E7T20IG63S being the most common variant. The percentage of HPV58 alone was approximately 50% (5/10) of all HPV positive samples. Similar potential oncogenic activity for this variant was observed in breast and cervical cancer cells. A separate analysis of single or combination of 58E6 (prototype or E6D4G) with 58E7 (prototype or E7T20IG63S) demonstrated that co-expression of 58E7T20IG63S with 58E6 (either prototype or E6D4G) significantly promoted cell proliferation compared to prototype 58E6/E7. Enhanced proliferation was mediated through elevated p53 degradation and reduced p21 expression. While p53 degradation activity was greatly diminished from E6 with D4G mutation, co-expression with E7T20IG63S cooperated to enhance degradation of p53 and promoted cell growth. Conclusion: HPV58 E6D4G/E7T20IG63S was the most HPV oncogene variant detected in Thai breast cancer patients. This variant exhibited in promoting cell proliferation and p53 degradation. A cooperative effect was observed in combination of HPV oncoproteins.