A role for MT1-MMP as a cell death sensor/effector through the regulation of endoplasmic reticulum stress in U87 glioblastoma cells.

Recent findings in cell death signalling show that membrane type 1 matrix metalloproteinase (MT1-MMP), an MMP known for its involvement in cancer cell invasion and metastasis, can act as a "bioswitch" in the invasion versus cell death decision in brain tumour cells. Given that the endoplasmic reticulum (ER) is a subcellular compartment involved in metabolic control and cell death signalling and that cytoskeleton disruption, as encountered during cancer cell invasion, can lead to ER stress, we questioned whether MT1-MMP contributes to ER stress. We found that MT1-MMP gene silencing or pharmacological inhibition of vesicular trafficking with Brefeldin-A abrogated MT1-MMP cell surface-mediated proMMP-2 activation by the lectin Concanavalin-A (ConA) in U87 glioblastoma cells. ConA, also known to trigger the expression of pro-inflammatory cyclooxygenase (COX)-2 through MT1-MMP signalling from the plasma membrane, failed to do so when MT1-MMP was prevented from reaching the cell surface by Brefeldin-A. Gene silencing of MT1-MMP antagonized the expression of ConA-induced COX-2 and of the ER stress marker glucose-related protein 78 (GRP78), further suggesting that plasma membrane localization of MT1-MMP contributes to signalling ER stress. MT1-MMP maturation, which partially occurs during its trafficking from the ER to the plasma membrane, showed correlation of the 60 kDa MT1-MMP with GRP78 expression. Finally, Brefeldin-A treatment of glioblastoma cells led to Akt dephosphorylation; this effect was reversed when MT1-MMP was silenced. Collectively, our results provide a molecular rationale for a new role for MT1-MMP in the regulation of cancer cell death processes through ER stress signalling.