DR. KEITH BONHAM
Project 1: Regulation of c-Src gene expression by Histone Deacetylase (HDAC) inhibitors.
HDAC inhibitor have generated much interest of late because of their potential chemotherapeutic and cancer chemopreventative properties. For example, butyrate is a highly abundant colonic component generated by the bacterial fermentation of dietary fiber and is thought to exert a protective effect against colon cancer. Very recent work by Calley Kostyniuk, Scott Dehm and Danielle Batten has shown that Butyrate and Trichostatin A (a highly specific HDAC inhibitor) are efficient inhibitors of c-Src gene expression.
This appears to be a direct effect on the SRC promoters. We are now very actively pursuing the mechanism behind this inhibition and expanding our observations to other genes which are either induced or repressed by these interesting agents.
Project 2: Regulation of the SRC1A promoter (SPy identified!)
Work performed by Shawn Ritchie in the lab has concentrated on an interesting factor called SPy. This factor binds to certain double stranded Pu:Py tracts present in the SRC1A promoter with high sequence specificity. However, the same factor binds to single stranded Py sequences with a higher affinity but relaxed sequence specificity. Deletion or point mutations in these tracts which abolish SPy's ability to bind had dramatic effects on SRC1A promoter activity. Shawn purified SPy and used Mass Spec. analysis to identify it. SPy was found to be identical to heterogeneous Ribonucleoprotein (hnRNP) K. Protein K is a fascinating protein implicated in many cellular processes and binds a variety of biomolecules including DNA, RNA and various proteins (including c-Src itself!). Danielle Batten is now carrying on some of this work as Shawn successfully defended his Ph.D. thesis in May 2002.
In a related project we are studying the induction of c-Src gene expression during monocyte differentiation in the U937 model system. Phorbol ester mediated differentiation of this cell line leads to massive c-Src induction exclusively from the SRC1A promoter.
Project 3: Regulation of the SRC1alpha promoter
Activity of the SRC1alpha promoter is absolutely dependent on the HNF-1 site. However work carried out by Scott Dehm has shown that SRC1alpha promoter activity is actually very weak compared to SRC1A, an observation inconsistent with the high in vivo activity of this promoter in certain cell lines. This has led to our conclusion that undiscovered additional elements, such as enhancers, exist in the SRC gene. We are using a variety of techniques to search for these sites.