MMP-2 and MMP-9 secretion is elevated in several types of human cancers and their elevated expression has been associated with poor prognosis. Expression of MMPs is highly regulated by cytokines and signal transducation pathways, including those activated by phorbol 12-myristate 13-acetate (PMA). The aim of this study was to examine the effect of PMA on MMP-2 and MMP-9 secretion in 42 different human cancer cell lines, selected on the basis of their organ malignancies. They were cultured in the recommended media supplemented with 10% FBS and antibiotics in 24-well tissue culture plates. At near confluence, the cells were washed with PBS, 0.5 ml of medium was added, and the cultures were incubated. Parallel sets of cultures were also treated with PMA for induction of enzymes. After 24 h the media were collected and MMP-2 and MMP-9 levels were assayed by gelatinase zymography. Based on MMP-2 and MMP-9 secretion without and with PMA treatment, the various human cancer cell lines fell into one of two major groups. The first group characterized by low basal MMP-9 secretion fell into three different categories of susceptibility to PMA induction of MMP-9 expression: resistant, moderately susceptible and highly susceptible. High basal MMP-9 levels responsive to PMA induction characterized the second group. Most cancer cell lines examined exhibited basal levels of MMP-2, MMP-9 or both. MMP-2 secretion was not induced by PMA in any of the cancer cells examined.

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