is HPV16 E7 Oncoprotein Labile if it is Unliganded?

Objective: Human papillomavirus (HPV) infection is a major global health concern due to its association with several types of cancer, particularly cervical cancer. Among the various viral proteins produced by HPV, E6 and E7 oncoproteins have been identified as key players in the oncogenic transformation of infected cells. HPV E7 oncoprotein primarily targets the retinoblastoma protein (pRb) and related family members, retinoblastoma-like protein 2 (p130) and retinoblastoma-like protein 1 (p107) and disrupts their association with E2F transcription factors, releasing the E2F for transcriptional activation of genes required for cell cycle progression. E7 is an unstable protein with a half-life of less than 2 hours. We aimed to investigate whether the stability of the E7 protein would change when it has a binding partner such as pRb, p130 and p107. Methods: We transfected HEK293T cells with either Green Fluorescent Protein tagged E7 (GFP-E7) construct alone or together with one of the pRb (RB1), p130 (RBL2) or p107 (RBL1) constructs and observed the expression of GFP-E7 under a fluorescent microscope. We have also analysed the expression levels of E7, pRb, p130 and p107 by western blotting using specific antibodies. Results: We showed that E7 expression was more prominent in human embryonic kidney 293T (HEK293T) cells where one of the cellular target proteins was co-expressed. Conclusion: HPV E7 oncoprotein is an indispensable component for the pathogenesis of cervical cancer, and understanding the molecular mechanisms of how E7 maintains its stability in the cell may enable the development of targeted treatment approaches.