We have demonstrated that an established Drosophila cell line (Kc cells) is a viable experimental model in which to define sterol independent regulation of HMG-CoA reductase (HMGR) activity. Kc cells modulated HMGR activity in response to mevalonate availability. Furthermore, current evidence suggests that a regulatory signal molecule, for HMGR suppression, was distal to isopentenyll-pyrophosphate (IPP). We observed no simple correlation between HMGR suppression and total IPP flux, total neutral isoprenoid lipid synthesis, or water soluble isoprenoid phosphate ester profile. Kc cells appeared to divert minimally 50% of their mevalonate carbon to n-fatty acids and TCA insoluble end products. Since we do not knot how Kc cells metabolize C10/C15 prenols nor the potential role intermediates from this pathway might play in the regulation of mevalonate synthesis, two related aims were developed for this proposal: (1) to determine if C10/C15 prenol catabolism was linked to mevalonate mediated modulation of HMG-CoA reductase activity and (2) to outline Kc cell C10/C15 prenol catabolism and define selected enzymes of this pathway. In order to demonstrate directly causal linkages between changes in HMG-CoA reductase's functional capacity and the putative post IPP regulatory signal molecule, an additional specific aim was formulated: (3) to utilize a functional, electroporated Kc cell model to identify, directly evaluate putative post IPP regulatory signal molecules, and investigate their mode of action(s). Realization of our Specific Aims, with the Kc model, should provide a clearer understanding of sterol-independent regulation of mevalonate metabolism by eukaryotic cells. Such information will also provide a framework in which to analyze mevalonate mediated regulation of isoprenoid synthesis in the more complex vertebrate cell.
