Analysis of surface interaction of CD44 with MMP-9 in different PC3 cell lines. Equal amount of proteins were immunoprecipitated with a vCD44 antibody or a non-immune serum as indicated in panels A and B. Immune complexes were subsequently pull-down with streptavidin agarose. A. One half of the immunoprecipitates were analyzed for MMP-9 activity associated with CD44 by zymogram analysis as described in the Methods section. Activity of a recombinant MMP-9 protein was used as an identification marker (lane 1). Arrows indicate pro- and active MMP-9 proteins. B and C. The second half of the immunoprecipitate was blotted with streptavidin HRP to detect surface levels of CD44 (B) and then immunoblotted with anti-MMP-9 (C) after stripping. The results represent one of the three separate experiments performed.