Morphine inhibits indolactam V-induced U937 cell adhesion and gelatinase secretion

We demonstrate that indolactam V, a non-phorbol protein kinase C activator, promotes U937 cell attachment to fibronectin, type IV collagen and laminin . in the absence of indolactam V, 2-4% of U937 cells attach to all test sub strates, however, in the presence of 100 nM indolactam V, 25, 16 and 11% of U937 cells attach to fibronectin, type IV collagen and laminin, respective ly. When added concomitantly, 90 muM H-7, a protein kinase C inhibitor, red uces indolactam V-induced U937 cell adhesion to fibronectin by 91%. Monoclo nal antibodies directed against both the beta1 and alpha5 integrin subunits inhibit indolactam V-induced U937 cell adhesion to fibronectin by 62 and 5 2%, respectively. Indolactam V also promotes homotypic aggregation in U937 cells, which is blocked with either anti-ICAM or anti-LFA-1 antibodies. In addition, indolactam V promotes U937 cell secretion of a 92 kDa gelatinase as demonstrated by zymography. In the presence of low levels of morphine (1 0 nM-1.0 muM), the U937 cell attachment to matrix proteins was not signific antly affected. However, in the presence of 10 muM morphine, the indolactam V treated cells exhibit a 71-74% reduction in cell adhesion to the matrix proteins. Further, 10 muM morphine also blocks indolactam V-induced homotyp ic aggregation and gelatinase secretion. The inhibitory effect of morphine on cell-matrix adhesion and gelatinase secretion was not inhibited by the o piate receptor antagonist naloxone (1 muM). While 10 muM naloxone did parti ally counteract the effect of 10 muM morphine on U937 cell attachment, this effect was likely non-specific since 10 muM naloxone alone increased cell adhesion. Supporting this conclusion, PCR analysis revealed that U937 cells do not express the mu high affinity morphine receptor. Also, indolactam V did not induce mu receptor expression, suggesting that morphine acts on U93 7 cells in a non-specific fashion. (C) 2001 Wiley-Liss, Inc.