DIVERGENT REGULATION OF 92-KDA GELATINASE AND TIMP-1 BY HBECS IN RESPONSE TO IL-1-BETA AND TNF-ALPHA

In this study, we addressed the question of whether human bronchial ep ithelial cells (HBECs) contribute to the regulation of 92-kDa gelatina se activity by secreting tissue inhibitor of metalloproteinase (TIMP)- 1. We investigated expression of 92-kDa gelatinase and TIMP-1 in respo nse to lipopolysaccharide (LPS) and to the proinflammatory cytokines i nterleukin (IL)-1 beta and tumor necrosis factor (TNF)-alpha. Confluen t HBECs from explants were cultured in plastic dishes coated with type I and III collagen. We demonstrated that TIMP-1 was expressed at both the protein and mRNA levels by primary cultures of HBECs. Gelatin zym ography of HBEC-conditioned media showed that exposure of HBECs to LPS , IL-1 beta, or TNF-alpha induced a twofold increase in the latent for m of 92-kDa gelatinase production, as well as its activation. Also, qu antitative reverse transcriptase (RT)-polymerase chain reaction (PCR) demonstrated a twofold increase in the 92-kDa mRNA level in response t o both cytokines. In contrast, TIMP-1 production evaluated by immunobl otting was unchanged in the presence of LPS and IL-1 beta and was clea rly decreased in the presence of TNF-alpha. Quantitative RT-PCR demons trated that TIMP-1 mRNA levels remained unchanged in response to LPS o r IL-1 beta but decreased by 70% in the presence of TNF-alpha. All of these results strongly suggest that the control mechanisms regulating the expression of 92-kDa gelatinase and TIMP-1 by HBECs in response to inflammatory stimuli are divergent and result in an imbalance between 92-kDa gelatinase and TIMP-1 in favor of the metalloproteinase. Such an imbalance may contribute significantly to acute airway inflammation .