Matrix metalloproteinase-19 is expressed in myeloid cells in an adhesion-dependent manner and associates with the cell surface.

We have previously reported the isolation of the human matrix metalloproteinase (MMP)-19 (also referred to as RASI) from a synovium of a patient suffering from rheumatoid arthritis and its expression at the cell surface of activated PBMC. In this study, we have analyzed the regulation and cell surface expression of human MMP-19 in several human cell lines and blood-derived cells. Among the cell lines analyzed, MMP-19 is largely expressed by lung fibroblasts as well as by myeloid cell lines THP-1 and HL-60. After fractionating PBMC into CD14- and CD14+ populations we found that only the latter one expresses MMP-19. Although the myeloid cell lines as well as CD14+ cells express MMP-19 without stimulation, its production can be up-regulated by phorbol esters (PMA) or by adhesion. The adhesion-dependent expression was down-regulated or even abrogated by blockade of adhesion or interfering with adhesion-controlling signaling using alpha-tocopherol. We have shown that MMP-19 associates with the cell surface of myeloid cells. This cell surface association was not affected by phospholipase C. However, acidic treatment of the THP-1-derived cell membranes abolished the immunoprecipitation of MMP-19 thereof. Moreover, a high salt treatment of THP-1 cells diminished the MMP-19 detection on the cell surface. This implicates a noncovalent attachment of MMP-19 to the cell surface. Because a truncated form of the MMP-19, in which the hemopexin-like domain was deleted (Delta(hp)MMP-19), does not associate with the surface, the hemopexin-like domain appears to be critical for the cell surface attachment of human MMP-19.