Adeno-Associated Virus Type 2 Increases Proteosome-Dependent Degradation of p21 WAF1 in a Human Papillomavirus Type 31b-Positive Cervical Carcinoma Line

Abstract

ABSTRACT Adeno-associated virus type 2 (AAV2) seropositivity is negatively correlated with the development of human papillomavirus (HPV)-associated cervical cancer. We have begun analysis of the molecular mechanisms underlying AAV2-mediated oncosuppression through cell cycle regulation in HPV-infected keratinocytes isolated from a low-grade cervical lesion. AAV2 superinfection of HPV type 31b (HPV31b)-positive cells at early times postinfection resulted in degradation of the cyclin-dependent kinase (CDK) inhibitor p21 WAF1 protein in a proteosome-dependent manner. Downstream consequences of lowering p21 WAF1 levels included a proportional loss of cyclin E/CDK2 complexes bound to p21 WAF1 . The loss of stable p21 WAF1 /cyclin E/CDK2 complexes coincided with an increase in CDK2-associated kinase activity and cyclin E levels. Both events have the potential to enhance the G 1 /S transition point mediated by active cyclin E/CDK2 complexes. Concurrently, cyclin A and E2F levels were decreased, conditions reminiscent of delayed entrance into the S phase of the cell cycle. On the other hand, infection of primary human foreskin keratinocytes with AAV2 resulted in upregulation of p21 WAF1 protein levels, reminiscent of a block in G 1 phase progression. We propose that by downregulating p21 WAF1 , AAV2 initiates cell cycle activities leading to enhanced G 1 /S phase-like conditions which may be favorable for AAV2-specific functions and may lead to downstream interference with HPV-associated cervical cancer progression.