Cell intrinsic & extrinsic factors in cervical carcinogenesis

Abstract

Human papillomavirus (HPV) infection is a common sexually transmitted infection which a majority of infected women are able to clear by mounting an effective immune response. Individuals with a suboptimal immune response may be at increased risk of persistent HPV infection leading to sequelae of various grades of dysplasias and / or associated malignancy. Both cell intrinsic and extrinsic phenomena work in concert to bring about oncogenesis. Cell intrinsic factors for cervical carcinogenesis are: integration of the viral genome into the genome of the host's cell which correlates with the progression of low grade lesions into high grade ones, inactivation of tumor suppressor genes like p53 and pRB by HPV oncoproteins particularly E6 and E7, deregulation of cell cycle regulators, host DNA synthesis and apoptosis. Cell extrinsic elements include factors contributing towards immune tolerance; some incriminated in the multistep carcinogenesis of HPV induced cervical cancer are: immunoregulatory enzyme indoleamine 2,3-dioxygenase expressing antigen presenting cells, low numbers of invariant Natural Killer T cells, anergic cytotoxic T lymphocytes, regulatory T cells (Tregs), an immunoregulatory microenvironment comprising of increased IL10, TGF and reduced IL2; reduced intralesional ratios of effectors (CD4 and CD8) vs. Tregs; and different types of Tregs in the lesions of invasive squamous cell carcinoma. Notch signaling plays a crucial role in regulating T cell differentiation and activation including induction of Tregs. Increased expression of Notch receptor-Jagged 1 and number of Tregs were seen in invasive disease when compared to precancer in cervical cancer. Tregs impart their function either through cytokines or by cell to cell contact. Investigation of the consequences of interference of Notch signaling in terms of the dynamics of intratumoral Tregs in cervical cancer would be interesting.