Increasing experimental and clinical data has identified an association between increased levels of matrix metalloproteinase (MMP)-9 and shortened patient survival, cancer progression and metastasis. MMP-9 has a significant role in tumor cell invasion and metastasis, as it digests the basement membrane and components of the extracellular matrix. MMP‑9 is secreted in either a monomeric or dimeric form. Although limited evidence exists concerning MMP‑9 dimers, certain studies have demonstrated that the dimer is associated with aggressive tumor progression. This is believed to be due to the fact that cellular migration depends upon the MMP‑9 dimer, and not the monomer. Our previous study revealed that cancer cell MMP‑9 dimer secretion patterns could be divided into different categories, and that high MMP‑9 and MMP‑9 dimer secretion levels were correlated with the most aggressive cancer cell lines. It has been established that signal transduction pathways and cytokines, including those activated by phorbol 12‑myristate 13‑acetate (PMA), regulate the expression of MMPs. The aim of the present study was to analyze the expression patterns of MMP‑2, MMP‑9 and MMP‑9 dimer in normal human cells from a number of tissues treated with PMA. Muscle, epithelial and connective tissues were selected for use in the present study, since adenosarcomas, carcinomas and sarcomas are derived from these tissue types, respectively. The cell lines were first cultured in 24‑well tissue culture plates containing recommended media that was supplemented with 10% fetal bovine serum and antibiotics. When at confluency, the cells were washed and fresh medium was added. In addition, a parallel set of cultures was treated with PMA. Subsequent to a 24‑h incubation period, the media were collected and analyzed using gelatinase zymography for the expression of MMP‑2 and MMP‑9 monomer and dimer forms. The results revealed that the cellular expression of MMP‑2 and MMP‑9 was dependent upon the primary tissue subtype. All cell lines, regardless of tissue origin, expressed MMP‑2. PMA induced the expression of MMP‑9 in muscle tissue, glandular epithelia and supportive connective tissue cell lines. By contrast, cell lines of endothelial origin and proper connective tissue were insensitive to treatment with PMA. MMP‑9 dimer secretion was not observed in any of the cell lines, which indicated that cellular migration is not supported by these cells.

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