MT1‐MMP, but not secreted MMPs, influences the migration of human microvascular endothelial cells in 3‐dimensional collagen gels

Matrix metalloproteinases (MMPs) and their specific inhibitors the TIMPs play significant roles in angiogenesis. We investigated how the expression of specific MMPs and TIMPs by human microvascular endothelial cells (hmECs) was modulated by culture of the cells in 3‐dimensional (3D) type I collagen gels versus 2‐dimensional (2D) collagen‐coated surfaces. By reverse‐transcription polymerase chain reaction (RT‐PCR), levels of mRNA for MMPs‐1, ‐2, and ‐13, MT1‐MMP, and TIMPs‐1 and ‐2 were similar in 2D versus 3D cultures. By Western blot assay, TIMP‐1 and proMMP‐1 were present and were expressed similarly in media from 2D versus 3D cultures, whereas active MMPs‐1, ‐9, and ‐13 were not detected. Active MMP‐13 was present in cell lysates (CL) and was increased in lysates from 3D cultures relative to 2D cultures. Relative to 2D cultures, CL and media from 3D cultures exhibited a decrease in expression of TIMP‐2 and an increased conversion of proMMP‐2 and proMT1‐MMP to active or processed forms. The MMP inhibitor GM6001 interfered with the migration of hmECs in 3D cultures, but not in 2D cultures. Addition of active MMP‐1 or blocking antibodies to TIMP‐1 did not affect the migration of hmECs in 3D collagen. Migration in 3D collagen was decreased by TIMP‐2 (an inhibitor of MT1‐MMP), but not by TIMP‐1 (a poor inhibitor of MT1‐MMP, but an efficient inhibitor of MMP‐2). Collectively, our data indicate that MT1‐MMP contributes significantly to the movement of hmECs through 3D collagen, in contrast to secretory‐type MMPs‐1, ‐2, ‐9, and ‐13, which are not critical for this movement. J. Cell. Biochem. 86: 748–758, 2002. © 2002 Wiley‐Liss, Inc.