Intracellular localization of matrix metalloproteinases and their inhibitors in cultured tumor cell lines: flow cytometric analysis.

Coordinate cell-surface expression of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) on cancer cells, tumor-infiltrating lymphocytes (TIL) and cancer-associated myofibroblasts has been shown to play an important role in tumor invasion and metastasis in organ tissues. However, precise localization of tumor cell lines in vitro has remained obscure. The aim of this study was to investigate the spatial localization of these proteolytic enzymes in 21 tumor cell lines consisting of 8 gastric, 4 pancreatic, 2 gallbladder, 1 extrahepatic bile duct cancer and 6 T- or B-cell tumors. The cell-surface and/or intracellular localization of MMP-2, -7, and -9, membrane type-1 (MT1)-MMP and TIMP-2 and -4 was quantitatively determined by flow cytometry in living (non-permeabilized) and permeabilized tumor cell lines. As a result, all of the tumor cell lines showed a high level of intracellular expression, but a low or undetectable level of cell-surface expression of MMPs and TIMPs. The findings revealed that intracellular MMPs and TIMPs in tumor cell lines were preserved as latent pro-enzymes.