BAFILOMYCIN A(1) INHIBITS IL-1-STIMULATED PROTEOGLYCAN DEGRADATION BYCHONDROCYTES WITHOUT AFFECTING STROMELYSIN SYNTHESIS

Interleukin-1 alpha (IL-1) stimulated the release of degraded proteogl ycan from primary cultures of chondrocyte monolayers in a time- and do se-dependent fashion. Bafilomycin A(1), a specific inhibitor of the va cuolar H+-ATPase, efficiently blocked acidification of the chondrocyte vacuolar system, Under these conditions, IL-1-stimulated proteoglycan degradation was inhibited by bafilomycin A(1) with an IC50 of <10 nM in both chondrocyte monolayers and articular cartilage explants, This concentration was at least 100-fold less than that required to partial ly inhibit total protein synthesis, In chondrocyte monolayers, bafilom ycin A(1) could be added several hours after IL-1 and complete inhibit ion was still observed, Tumor necrosis factor-alpha and retinoic acid also stimulated proteoglycan degradation in chondrocyte monolayers, an d in both cases the response was inhibited by bafilomycin A(1), These results suggest that maintenance of vacuolar acidity is required for c ytokine stimulated proteoglycan degradation and that this requirement is at a point distal to receptor binding and early signal transduction events. IL-1 also stimulated the synthesis and secretion of prostrome lysin by chondrocyte monolayers, however, under conditions in which IL -1 stimulated proteoglycan release was totally blocked by bafilomycin A(1), there was no effect on IL-1-stimulated stromelysin secretion or stromelysin enzyme activity, These results, in which stromelysin synth esis and proteoglycan degradation were dissociated, suggest that an ad ditional enzyme is responsible for proteoglycan degradation in this ch ondrocyte monolayer system. (C) 1995 Academic Press, Inc.