Saleem A. Khan, PhD
545 Bridgeside Point II
450 Technology Dr.
Pittsburgh, PA 15219
We are involved in three main areas of research. The first one deals with the role of microRNAs in human papillomavirus-associated cervical and oral cancers as well as role of miRNAs in aging. We are collaborating with several investigators in these studies, including Robert Ferris, Robert Edwards, Laura Niedernhofer and Patricia Opresko. The second area deals with the cellular functions and mechanism of action of the PcrA helicase which is specifically found in Gram-positive bacteria. In these studies, we are collaborating with Drs. Syam Anand and Sanford Leuba. The third area of our interest deals with a molecular analysis of the role of the RepX protein in the replication and segregation of the anthrax toxin-encoding pXO1 plasmid in Bacillus anthracis. We have identified several cellular miRNAs that appear to be targeted by the HPV E6 oncogene. For example, we showed that the HPV-16 E6 oncogene downregulates miR-218, which in turn is involved in the regulation of the cellular LAMB3 gene. We also found that E6 upregulates miR-363 in HPV-positive oral cancer cell lines. Our ongoing studies deal with the identification of the domain(s) and mechanism by which E6 affects miR-218 expression, including whether or not this effect is mediated through p53. We are also investigating the role of HPVs in oral cancers. Our studies have shown that the presence of HPV-16 in SCCHN cell lines alters the miRNA profiles. In particular, miR-363 was found to be upregulated in HPV-positive SCCHN cell lines and tissues. Furthermore, the E6 oncogene of HPV-16 was required for the increased expression of miR-363. Our studies suggest that in addition to their known effects on tumor suppressor proteins such as p53 and Rb, the HPV oncogenes may also regulate cellular pathways by alteration of specific cellular miRNAs. We are using the XPF mouse and the human Werner Syndrome progeroid models to study the potential role of miRNAs in aging. Our initial studies have identified several miRNAs that are affected in XPF and WS cell lines as compared to normal controls. We are now investigating the role of such miRNAs in cellular senescence.
We are involved in the identification of functional domains of the PcrA helicase, using genetic, biochemical and single-molecule approaches. We have studied the substrate specificity of PcrA and have developed a model to explain how PcrA blocks recombination by displacing the RecA protein bound to the DNA. Using various PcrA mutants, we are studying its domains that are essential for cell survival.
We have shown that the pXO1-encoded RepX is a novel protein that may be involved in both the replication and segregation of this plasmid. We have shown that RepX belongs to the tubulin/ FtsZ family of GTPases and forms polymers both in vitro and in vivo. We have identified proteins that interact with RepX and are currently studying the role of such interactions in pXO1 replication, stability and segregation.