PURPOSE. Stromelysin-1 (MMP-3) degrades extracellular matrix and increases aqueous outflow. In the trabecular meshwork (TM), interleukin (IL)-1α is a potent inducer of MMP-3 expression. In different cells, IL-1α activates different signaling pathways, such as nuclear factor (NF)-κB-mediated protein expression, the phospholipase A2 (PLA2)-activated arachidonate cascade, and activator protein (AP)-1-associated transcription. In the present study, pharmacological tools were used to delineate the signaling mechanism involved in the effect of IL-1α on MMP-3 production in human TM cells compared with other ocular cells. METHODS. Human TM and three other ocular cells (ciliary muscle, corneoscleral fibroblast, and lamina cribrosa) were cultured in 24-well plates in the presence or absence of IL-1α, with or without specific inhibitors of selected signaling pathways. Secreted proMMP-3 was quantified by ELISA, and MMP-3 activity was assayed by casein zymography. RESULTS. IL-1α (5 ng/mL) increased proMMP-3 levels in human TM cells to 10- to 38-fold of control (P < 0.001). The effect of IL-1α was blocked by Gö6976, a protein kinase Cμ (PKCμ) inhibitor; PD98059, a mitogen-activated protein kinase kinase (MEK) inhibitor; SB202190, a p38 inhibitor; and SR11302, an AP-1 inhibitor; but not by inhibitors of casein kinase II, NFκB, PLA2, phospholipase D (PLD), cyclooxygenases, lipoxygenase, or sphingomyelinase. SR11302 did not inhibit the effect of IL-1α on MMP-3 production in the other ocular cells tested. CONCLUSIONS. Based on the pharmacological effects of the inhibitors, the data indicate that activation of PKCμ, MEK, and p38 leading to the activation of AP-1 is critical to the IL-1α-stimulated upregulation of MMP-3 in human TM cells. Therefore, it is likely that compounds that activate the AP-1 pathway would upregulate the production of MMP-3 and improve aqueous outflow.