Induction of matrix metalloproteinase MMP-9 (92-kDa gelatinase) by retinoic acid in human neuroblastoma SKNBE cells: Relevance to neuronal differentiation

Retinoic acid (RA) has been shown to induce human neuroblastoma SKNBE cell differentiation into a neuronal phenotype, Whether this neuronal differenti ation is associated with modulation of matrix gelatinase [matrix metallopro teinase (MMP)-2 and MMP-9] expression was investigated in SKNBE cell cultur es exposed to RA for 14 days. Their differentiation into a neuronal phenoty pe was typified by neural cell adhesion molecule and growth-associated prot ein-43 expression. Gelatinase expression was assessed by gel zymography, qu antitative RT-PCR, and immunocytochemistry. Neuronal markers were located i n neurites and ganglion-like clusters of neuronal cells induced upon RA exp osure. MMP-2 expression was constitutive and remained unchanged at both the mRNA and protein levels in response to RA, tumor necrosis factor-alpha (TN F alpha), or phorbol 12-myristate 13-acetate (PMA) treatment. In contrast, MMP-9 was inducible by RA, TNF alpha, or PMA. MMP-9 was progressively enhan ced by RA as a function of time exposure until day 14. The addition of TNF alpha or PMA potentiated RA-induced MMP-9 expression with a synergic maxima l effect at day 14 of RA exposure. Immunoreactive MMP-9 was located early i n outgrowing neurites, but only at day 14 of RA exposure in extensive neuri tic networks. Taken together, the correlation between the MMP-9 expression by SKNBE cells and the time scale of their differentiation into a neuronal phenotype allowed us to propose that MMP-9 could participate in the neurite growth process and cell migration and organization into ganglion-like clus ters.