Transcriptional regulation of the human alpha2(I) collagen (COL1A2) gene by tumor necrosis factor-alpha and interferon-gamma
The inflammatory response to acute cutaneous injury is a multi-step, coordinated process involving resident cells of the integument as well as cellular mediators of immunity recruited from the circulation. Once in place, these cells are able to orchestrate the tissue repair and remodeling process by elaborating a host of polypeptide cytokines, that have potent stimulatory and inhibitory effects on various extracellular matrix (ECM) genes. The production and degradation of type I collagen is a critical aspect of this ECM remodeling in human skin during both wound repair and normal physiologic states. Type I collagen synthesis is strongly affected by inflammatory cytokines such as transforming growth factor-$\beta$ (TGF-$\beta$), interferon-$\gamma$ (IFN$\gamma$), and tumor necrosis factor-$\alpha$ (TNF-$\alpha$). Specifically, TGF-$\beta$ is a potent inducer of type I collagen synthesis while both IFN-$\gamma$ and TNF-$\alpha$ are strong supressors of type I collagen gene transcription and subsequent protein production.^ Earlier studies documented that TNF-$\alpha$ inhibits type I collagen gene transcription in normal human dermal fibroblasts (NHF), and we have previously shown that the region of the human $\alpha$2(I) collagen promoter between $-$271 and $-$235, contains an essential TGF-$\beta$ response element which allows antagonistic activity by TNF-$\alpha$. The inhibitory response to TNF-$\alpha$ in vitro has now been localized to a specific region that contains non-canonical AP-1 and NF-$\kappa$B binding sites. TNF-$\alpha$-mediated inhibition of CAT activity was eliminated by mutation of the NF-$\kappa$B binding element. Gel mobility shift assays of human fibroblast nuclear extracts demonstrated enhanced binding of a specific factor that gel-supershift assays identified as the NF-$\kappa$B(p50/p65) heterodimer. These data suggest that in fibroblasts TNF-$\alpha$ activates the transcription factor NF-$\kappa$B (p50/p65) which binds the COL1A2 promoter and is responsible for the observed inhibition of $\alpha$2(I) collagen gene transcription.^ In a similar approach, we also examined the effect that IFN-$\gamma$ had on the activity of the COL1A2 promoter in vitro. Using transient transfection analyses of proximal promoter/CAT plasmids, we identified a previously uncharacterized region between $-$161 and $-$125 of the proximal promoter that mediated transcriptional repression by IFN-$\gamma$. Furthermore, we identified an unknown, multisubunit complex that specifically bound this element which was affected by the same mutations responsible for abrogating the IFN-$\gamma$ response in vitro.^ The activation of the TNF-$\alpha$ receptor complex initiates an expansive signaling cascade responsible for NF-$\kappa$B activation, activation of mitogen activated protein kinase (MAPK) cascades, and the induction of apoptosis. To date, two main TNF receptor 1 (TNFR1) dependent pathways have been well described: TNF-a receptor-associated molecules and ceramide signaling. The TNF receptor associated death domain (TRADD) and associated factors (TRAFs) are responsible for induction of apoptosis and NF-$\kappa$B activation. Herein, we have demonstrated that acidic sphingomyelinase, TRADD and TRAF2 inhibit the COL1A2 promoter and the TRADD/TRAF2-mediated inhibition of COL1A2 transcription is independent of NF-$\kappa$B. These results contribute to the general understanding of transcriptional control of COL1A2 by TNF-$\alpha$ and IFN-$\alpha$ and the signaling mechanisms utilized by TNF-$\alpha$ in repressing COL1A2 gene expression. ^
Biology, Molecular|Biology, Cell|Chemistry, Biochemistry
David Jonathan Kouba,
"Transcriptional regulation of the human alpha2(I) collagen (COL1A2) gene by tumor necrosis factor-alpha and interferon-gamma"
(January 1, 1999).
ETD Collection for Thomas Jefferson University.