HPV Type 16 Infection Switches Keratinocytes from Apoptotic to Proliferative Fate under TWEAK/Fn14 Interaction

Previously, tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) had been known to be an inducer of apoptosis of keratinocytes by engaging the Fn14 receptor. However, the high-risk human papillomavirus (HPV) infection confers a proliferation advantage on keratinocytes that may consequently harbor tumorigenicity. This study was designed to investigate the cross-talk in keratinocytes between TWEAK/Fn14 signaling and HPV type 16 infection, which may cooperate in regulating cell-cycle progression. TWEAK and Fn14 expression was determined in anogenital warts and normal skin. Both primary keratinocytes and HaCaT cells were transfected with HPV16 E6/E7 genes. The results showed that Fn14 is highly expressed upon HPV16 transfection and accompanied by an increase in Ras GTPase activity and TNF-receptor-associated factor 2 (TRAF2) expression. Moreover, the E6/E7-transfected keratinocytes exhibit a shift of TNF receptor profile from type 1 to type 2 and weakened apoptotic response to TNF-α stimuli, when compared with the normal control. Surprisingly, significant increase in proliferation but not apoptosis was seen in E6/E7-positive keratinocytes, as TWEAK was additionally supplemented. In conclusion, the HPV16 infection in keratinocytes causes a switch of apoptotic to proliferative fate under TWEAK/Fn14 interaction, possibly by favoring Ras and TRAF2 activation and modulating TNF receptor expression.