Expression of proteases in IEC-6 cell populations transduced with activated MEK isoforms. (A) Expression of MMP-13 was analyzed by immunoblotting. Induction of MMP activity was analyzed by zymography on acrylamide gels co-polymerized with casein (MMP-3/10) or gelatin (MMP2 and MMP9) substrates. Photographs of the gels are shown. (B) Quantitative PCR analysis of urokinase receptor mRNA levels. Expression levels are expressed as fold-increase relative to vector-infected cells.