Structure-activity relationship of hydroxamate-based inhibitors on membrane-bound Fas ligand and TNF-alpha processing

Both Fas ligand (FasL) and tumor necrosis factor-alpha (TNF-alpha) are type II integral membrane proteins. Recently, we have reported that FasL is processed to a soluble form by an unknown metalloproteinase at the cell surface and some hydroxamate matrix metalloproteinase (MMP) inhibitors inhibit the processing similar to the case observed with TNF-1alpha. We studied the inhibitory effects of various hydroxamate MMP inhibitors on FasL and TNF-alpha processing in order to characterize the processing enzymes using human FasL cDNA transfectants and LPS-stimulated THP-1 cells. It turned out that (1) the P1' group of hydroxamates was very important for the selective inhibitory activity toward TNF-alpha and FasL processing, (2) P1' 3-phenylpropyl group was favorable for the inhibition of FasL processing, and (3) P1' isobutyl and isopropyl groups were favorable for that of TNF-alpha processing. These differences in sensitivity to inhibitors imply that (1) membrane-bound FasL and TNF-alpha might be processed by distinct metalloproteinases, (2) the S1' site of FasL processing enzyme differs from that of MMP-1 and MMP-9, but appears to be similar to that of MMP-3, and (3) the S1' site of TNF-alpha processing enzyme is smaller than that of FasL processing enzyme. These results would be helpful in designing a more selective inhibitor.