Our Science – Zheng Website
Zhi-Ming Zheng, M.D., Ph.D.
Viral RNA Splicing and Oncogenesis
The Zheng laboratory studies protein-RNA interactions and their subsequent consequences in oncogenic DNA tumor virus infection. More specifically, the laboratory focuses on how protein-RNA interactions regulate gene expression of high-risk human papillomaviruses and Kaposi sarcoma-associated herpesvirus. In particular, this study aims to understand how RNA splicing and small regulatory RNAs regulates viral and cellular gene expression during oncogenic virus infection. Our long-term goal is to develope a series of RNA-based therapeutic approaches to control viral or cellular gene expression and to identify some biomarkers for clinical diagnosis and prognosis.
1. Papillomavirus infection and viral gene expression.
Human 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. Infection with oncogenic HPV in other tissues could also lead to development of cancer. For example, we recently demonstrated that colorectal oncogenic HPV infection 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. Cervical cancer has been the most common malignancy among women with AIDS in both Europe and the United States. Two viral oncoproteins, E6 and E7, of HPV16 and HPV18 are involved in cervical carcinogenesis and are known to destabilize cellular tumor suppressor proteins p53 and pRb, respectively. In 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. Splicing of the intron 1 in the E6E7 bicistronic pre-mRNAs is highly efficient and the majority of the spliced transcripts in cancer tissues and cervical cancer cell lines are E6*I, a spliced product without intron 1. We have demonstrated that the E6*1 is the authentic mRNA for E7 translation, while a small portion of the bicistronic RNAs with retention of the intron 1 encode E6 oncoprotein. This conclusion was based on our specific siRNA approaches that selectively silence the expression of each viral oncogene. During virus life cycle which is tightly regulated by keratinocyte differentiation, we found that a cellular RNA splicing factor, SRp20, which is also differentiately expressed, controls virus early-to-late switch. Overexpression SRp20 in cervical cancer promotes viral E6 and E7 expression, whereas a decreased SRp20 level promotes viral L1 expression and a productive HPV infection. Surprisingly, we characterized SRp20 as an oncoprotein which is required for cancer cell growth and tumor induction. Recently, we showed that high-risk HPV infection also deregulates the expression of tumor-suppressive miR-34a and p18Ink4c through viral oncoprotein E6. Aberrant expression of oncogenic and tumor-suppressive microRNAs in cervical cancer is required for cancer cell growth and viral oncoproteins are partially responsible for this deregulation.
While focusing on HPV and cellular microRNA interactions, we are also investigating HPV18 biology and gene expression. More recently, we finished the construction of a full transcription map of HPV18 in productive viral infection. HPV18 is the second most common HPV type found in cervical cancer, but a genome-wide full transcription map had been missing from the HPV field. We took the high risk and succeeded to construct a full transcription map of HPV18 in productive HPV infection. This was surprising to everyone in HPV field because elucidatiaon of a full transcription map of HPV16 took so many years by several labs in the world. The entire transcription map of HPV18 is now collected into HPV database (http://pave.niaid.nih.gov/#home) and is fully accessible world-wide. It is no doubt that this carefully mapped landscape of HPV18 transcripts will provide a solid foundation for future understanding of HPV18 molecular biology, pathogenesis, and prevention.
2. KSHV Gene expression and post-transcriptional regulation.
KSHV is a lymphotropic DNA tumor virus that induces Kaposi sarcoma (KS), primary effusion lymphoma (PEL) or body cavity-based B-cell lymphoma, and multicentric Castleman disease (MCD). Among those malignancies, KS occurs frequently in patients infected with HIV. PEL and MCD feature an increased levels of cytokines (IL6 and IL10). Latent KSHV infection in KS lesions and PEL-derived B cells can be reactivated as lytic KSHV infection by various stress conditions or inflammation. In this lytic switch, a KSHV transactivator, ORF50, is absolutely required to initiate expression of various viral lytic genes. One of these genes is ORF57, a caspase-7 sensitive viral protein, to ensures a subset of viral transcripts (ORF50, K8, K8.1, ORF56, ORF59, etc.) essential for virus production being appropriately processed, stabilized and translatable efficiently. We recently demonstrated that ORF57 promotes ORF59 expression by interaction with cellular RNA export cofactors RBM15 and OTT3. In our genome-wide search for ORF57 RNA targets, we identified that ORF57 regulates the expression of more than 16 KSHV genes at the posttranscriptional level. Strikingly, we found that, through interacting with the RNA target and microRNA pathway, ORF57 promotes IL6 expression by interrupting microRNA-mediated translational repression of IL6, which is necessary for cancer cell growth.
Our lab has extensive collaborations on various projects with many investigators. These include Elliot Androphy, University of Massachusetts; Joel Palefsky; University of California San Francisco; Shou-Jiang Gao, University of Texas; Adrian Krainer of Cold Spring Harbor Laboratory; Craig Meyers, Pennsylvania State University; Janet Rader, Washington University in St. Louis; Tom Broker and Louise Chow, University of Alabama at Birmingham, and Robert Yarchoan, Michael Kruhlak, J. Philip McCoy, Jr., Chuxia Deng, Jun Zhu, Curtis Harris, Kenneth Kraemer, Barbara Felber, George Pavlakis, Lauren Wood, and Harvey Alter at NIH.
This page was last updated on 6/7/2013.