Coordination of Proliferation and Apoptosis

DESCRIPTION (provided by applicant): In 1987, we published the first large scale screen of gene expression in normal and neoplastic colonic tissue, encompassing quantitative analysis of each of 4,000 cloned sequences. This led to the discovery that a coordinated decrease of the expression of the mitochondrial genome characterized the colonic mucosa at risk as well as colon tumors, with a return to normal levels of expression upon induction of cell maturation with a physiological regulator of cell maturation in the colon, the short-chain fatty acid butyrate (NaB). Subsequent papers dissected the role of mitochondrial function in colonic cell maturation, including apoptosis, and in 1998 we suggested that "the mitochondria may be the final integration site of multiple signals, which ultimately coordinate proliferation and apoptosis pathways". This application is to determine if TR3 (Nurr77), an orphan steroid receptor, plays a central role in this coordination achieved by the short-chain fatty acid butyrate. It has recently been demonstrated that TR3 resides in the nucleus and functions as a transcription factor during cell growth, but that apoptotic stimuli cause its translocation to the mitochondrial membrane, where it mediates release of cytochrome c and hence initiation of an apoptotic cascade. We will determine: 1) the effects of butyrate on expression and sub-cellular localization of TR3 in colonic cell lines that differ in their p53 and c-myc status; 2) how modulation of mitochondrial function and/or collapse of the membrane potential affects nuclear - mitochondrial translocation; 3) utilizing isogenic cell lines, how the presence of an activated k-ras allele, which is necessary for the butyrate stimulation of apoptosis, is linked to the expression and translocation of TR3; 4) how genetic manipulation in vivo alters expression and sub-cellular distribution of TR3 in relation to cell position along the crypt-lumen axis. These last experiments will make use of banked tissue from mouse experiments which have already reported the effect of targeted inactivation of Apc and p21 WAFl/cipl and a homozygous deletion for scad (short-chain acyl dehydrogenase), on mucosal apoptosis and proliferation in the duodenum, proximal and distal colon. Understanding the mechanism by which mitochondrial function coordinates cell maturation pathways in the intestinal mucosa has profound implications for understanding tumorigenesis and for effecting chemoprevention.