Autocrine regulation of macrophage differentiation and 92-kDa gelatinase production by tumor necrosis factor-a via α₅β₁ integrin in HL-60 cells

Tumor necrosis factor-α (TNF-α) gene is one of the early response genes induced by phorbol 12-myristate 13-acetate (PMA) in human HL-60 myeloid leukemia cells. In the present study, we examined the role of the TNF-α autocrine loop in PMA-induced macrophage differentiation and gene expression of 92- and 72-kDa gelatinases (MMP-9 and MMP-2). In HL-60 cells, PMA inhibited cell proliferation and induced cell adhesion and spreading, expression of surface maturation marker OKM1 and phagocytic activity, as well as the expression of both gelatinases, which all characterize the macrophage phenotype. In contrast, TNF-α alone was only effective in inhibiting cell proliferation. Blocking the endogenous TNF-α activity with neutralizing anti-TNF-α antibodies abolished all these PMA. induced events with the exception of MMP-2 gene expression. Since fibronectin (FN)-mediated cell adhesion and spreading are prerequisite for both macrophage differentiation and MMP-9 gene expression in HL-60 cells, we hypothesized that TNF-α might be involved in modulating the expression of either the FN or its integrin receptor genes. Whereas PMA substantially enhanced the steady state mRNA and protein levels of both FN and α₅β₁ integrins, TNF-α alone had little effect on the expression of these genes. However, anti-TNF-α antibodies blocked PMA-induced augmentation of both α₅ and β₁ integrin gene expression without affecting the expression of the FN gene. Our results suggest that TNF-α may regulate macrophage differentiation and critical matrix-degrading activities of myeloid progenitor cells in an autocrine manner by augmenting surface levels of the α₅β₁ integrin, thus promoting interactions with the extracellular matrix, a key event for maturation and migration of these cells during inflammation.