Abstract
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 substrates, however, in the presence of 100 nM indolactam V, 25, 16 and 11% of U937 cells attach to fibronectin, type IV collagen and laminin, respectively. When added concomitantly, 90 μM H‐7, a protein kinase C inhibitor, reduces indolactam V‐induced U937 cell adhesion to fibronectin by 91%. Monoclonal antibodies directed against both the β1 and α5 integrin subunits inhibit indolactam V‐induced U937 cell adhesion to fibronectin by 62 and 52%, 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 (10 nM–1.0 μM), the U937 cell attachment to matrix proteins was not significantly affected. However, in the presence of 10 μM morphine, the indolactam V treated cells exhibit a 71–74% reduction in cell adhesion to the matrix proteins. Further, 10 μM morphine also blocks indolactam V‐induced homotypic aggregation and gelatinase secretion. The inhibitory effect of morphine on cell‐matrix adhesion and gelatinase secretion was not inhibited by the opiate receptor antagonist naloxone (1 μM). While 10 μM naloxone did partially counteract the effect of 10 μM morphine on U937 cell attachment, this effect was likely non‐specific since 10 μM naloxone alone increased cell adhesion. Supporting this conclusion, PCR analysis revealed that U937 cells do not express the μ high affinity morphine receptor. Also, indolactam V did not induce μ receptor expression, suggesting that morphine acts on U937 cells in a non‐specific fashion. © 2001 Wiley‐Liss, Inc.