1. Papillomavirus infection and viral gene expressionHuman papillomavirus type 16 (HPV16) or 18 (HPV18) infection, acquired primarily via sexual transmission, is widely recognized as a leading cause of cervical and anal cancer and thus, are classified as being oncogenic. Infection with oncogenic HPV in other tissues could also lead to development of cancer. For example, we recently demonstrated that colorectal HPV infection, particularly with oncogenic HPVs, is common in patients (51%) with colorectal cancer. High prevalence and incidence of cervical HPV infection has been observed among HIV-positive and immunodeficient women. Oncogenic HPV16 DNA was also found in the peripheral blood mononuclear cells of transfusion-acquired pediatric HIV patients, but also from some healthy blood donors. Cervical cancer has been the most common malignancy among women with AIDS in both Europe and the United States. Two viral oncoproteins in particular, E6 and E7, of HPV16 and HPV18 are involved in cervical carcinogenesis and are known to inactivate cellular tumor suppressor proteins p53 and pRb, respectively. HPV16 and HPV18 E6 and E7 are transcribed as a single bicistronic RNA bearing 3 exons and 2 introns, with the intron 1 in the E6 coding region. Various studies, including those from our laboratory, have demonstrated that splicing of intron 1 in the HPV16 E6E7 pre-mRNA is highly efficient with the majority of the transcripts in cancer tissues and cervical cancer cell lines encoding E6*I, a spliced product without intron 1. It is our hypothesis that the E6 is expressed from a small portion of the bicistronic RNAs, without splicing of the intron 1, which has raised several important questions: 1. Why is efficient splicing of intron 1 in HPV16 or HPV18 E6E7 pre-mRNA needed for viral gene expression since splicing harms E6 expression? 2. How does a small portion of the total pool of E6E7 pre-mRNAs escape splicing of intron 1 and what regulates this escape? 3. How could an RNA molecule containing an intron be exported to the cytoplasm to translate E6 protein? The answers to these important questions will come from continuing our studies aimed at describing the mechanisms involved in this RNA splicing regulation. We have successfully demonstrated that intron 1 splicing subjects the RNA molecule to exon definition (size) by a cap structure on the RNA 5' end. Strong evidence, from multiple approaches in transient transfection and in cervical cancer-derived HPV16+ and HPV18+ cell lines, indicate that the ability of the RNA molecule to escape splicing of intron 1 results in production of unspliced E6 mRNA to subsequently encode viral oncoprotein E6, whereas splicing of the intron promotes E7 oncoprotein expression. We also identified several E6 and E7-specific siRNAs for selective post-transcriptional silencing of the two viral oncogenes. We further demonstrated that, although those siRNAs have therapeutic potentials for acute treatment, long-term delivery of the E6 or E7-specific siRNAs might induce cellular resistance to siRNA function. Recently, we have also demonstrated that some high-risk HPV proteins, such as HPV16 E2 and E6, are RNA binding proteins in vitro and that they interact with the cellular splicing factors responsible for regulating the splicing of HPV16 E6E7 pre-mRNAs. 2. KSHV Gene expression and post-transcriptional regulationKSHV is a lymphotropic DNA tumor virus that induces Kaposi's sarcoma (KS), body cavity-based B-cell lymphoma, and multicentric Castleman's disease. Among those malignancies, KS occurs frequently in patients infected with HIV. Latent KSHV infection in KS lesions and PEL-derived B cells features the highly restricted expression of only five viral genes. The lytic KSHV infection can be induced by chemicals in PEL-derived B cells with latent KSHV infection. In this lytic switch, a KSHV transactivator, ORF50, is absolutely required.
Showing the most recent 10 out of 16 publications
