Fig. 1. MEK/ERK signaling is required for MMP-9 expression in MK cells. Wild-type MK^+/+ cells were grown on laminin-5-rich extracellular matrix (LN-5 ECM) in serum-free medium for 36 hours in the presence or absence of the MEK inhibitor U0126 (10 µM), as indicated. MMP-9 levels in the culture medium were assayed by gelatin zymography (top panel). Position of the 105 kDa murine pro-MMP-9 (mMMP-9) is indicated on the left. S lane, positions of human MMP-9 (hMMP-9) and MMP-2 (hMMP-2) purified standards are indicated. ERK activation was assayed by immunoblot of the corresponding cell lysates for phospho-ERK (pERK panel). Blots were stripped and reprobed for total ERK (ERK panel).