Analyses of variant human papillomavirus type-16 E5 proteins for their ability to induce mitogenesis of murine fibroblasts

BACKGROUND: Human papillomavirus type 16 (HPV-16) E5 protein co-operates with epidermal growth factor to stimulate mitogenesis of murine fibroblasts. Currently, little is known about which viral amino acids are involved in this process. Using sequence variants of HPV-16 E5 we have investigated their effects upon E5 transcription, cell-cycling and cell-growth of murine fibroblasts. RESULTS: We demonstrate that: (i) introduction of Thr(64 )into the reference E5 sequence of HPV-16 abrogates mitogenic activity: both were poorly transcribed in NIH-3T3 cells; (ii) substitution of Leu(44)Val(65 )or, Thr(37)Leu(44)Val(65 )into the HPV-16 E5 reference backbone resulted in high transcription in NIH-3T3 cells, enhanced cell-cycle progression and high cell-growth; and, (iii) inclusion of Tyr(8 )into the Leu(44)Val(65 )backbone inhibited E5 induced cell-growth and repression of p21 expression, despite high transcription levels. CONCLUSION: The effects of HPV-16 E5 variants upon mitosis help to explain why Leu(44)Val(65 )HPV-16 E5 variants are most prevalent in 'wild' pathogenic viral populations in the UK.