Down‐regulation of α3(VI) chain expression by γ‐interferon decreases synthesis and deposition of collagen type VI

Abstract

Treatment of cultured human skin fibroblasts with increasing doses of y-interferon produces a distinct reduction of steady-state levels of the a3 chain of collagen VI mRNA by about 60% but not of the a1 and a2 chain mRNAs. A similar decrease was also observed for collagen I and 111 mRNA while fibronectin mRNA remained at the same level. The decrease in a3(VI) mRNA is accompanied by a reduced synthesis of collagen VI and by a reduced deposition of both collagen VI and fibronectin in urea-insoluble form in the cell matrix. No other y-interferon effects were observed for fibronectin biosynthesis. Immunoprecipitation of metabolically labeled collagen VI demonstrated a strongly reduced synthesis (by 65 -80Y0) of intracellular a3(VI) chains with no decrease found for al(V1) and a2(VI) chains. All three chains were, however, found to be reduced in the culture medium. Pepsin treatment of immunoprecipitated collagen V1 showed similar chain ratios for material in the culture medium obtained in the absence or presence of y-interferon. It indicates that correctly assembled heterotrimers of the composition [al(VI) a2(VI) a3(VI)] are formed and secreted also in the absence of an equivalent a3(VI) chain synthesis but at a reduced rate. The data support previous predictions from sequence analyses J . Biol. Chem. 263, 18601-186061 that collagen VI molecules composed of all three constituent chains are more stable than other assembly alternatives.Several minor collagen types which are deposited in the extracellular matrix besides the major fiber-forming collagens 1, I1 and I11 and fibronectin have been recently identified [I]. They include collagen VI which is a structurally unique component found in the connective tissue of almost every organ [2]. Its molecular structure is distinguished from other collagens by a particularly short triple helix with large globular domains on both ends. These molecules have the potential to assemble into dimers and tetramers which form large microfibrillar aggregates stabilized by disulfide bonds [3]. Immunoelectron microscopy has shown that such fibrils represent a major part of the microfibrillar network within the extracellular matrix the composition of collagen VI is controlled at the transcriptional level. These three mRNAs have been recently cloned [14] and were shown to be distinctly different in their sequences which encode the triple-helical domain of the protein [16]. The distribution of cysteines and Gly-Xaa-Yaa triplet imperfections led also to the prediction that only a heterotrimer assembly of the chains would yield collagen VI molecules with the potential to form fully stable oligomers. This was of some interest since non-coordinated regulation of the gene expression either of a3(VI) or of al(V1) plus a2(VI) chains was observed for skin fibroblasts when grown in a collagen gel [15] and for cornea fibroblasts and some tumor cells [14]. The pattern of regulation could reflect the different localization of human collagen VI genes to either chromosome 2 (a3) or chromosome 21 (al, a2) ...

Recombinant expression and properties of the Kunitz‐type protease‐inhibitor module from human type VI collagen α3(VI) chain

“…Control precipitation with normal serum revealed a 250-kDa band in the medium and, to a lower extent, in the cell extract. This band was previously shown to correspond to fibronectin (Heckmann et al, 1989). Precipitation of medium with antisera against domain N9-N2 or domain C5 revealed after reduction an additional strong band at 140 kDa, which corresponds to the migration position of reduced al(V1) and a2(VI) chains.…”

“…Precipitation of medium with antisera against domain N9-N2 or domain C5 revealed after reduction an additional strong band at 140 kDa, which corresponds to the migration position of reduced al(V1) and a2(VI) chains. Furthermore, the band at approximately 250 kDa became stronger and much broader, indicating the precipitation of the a3(VI) chain (Heckmann et al, 1989). Neither of these bands could be detected if the precipitates were analyzed in non-reduced form, indicating their connection by disulfide bonds (data not shown).…”

Increased expression of type VI collagen genes in drug‐induced gingival enlargement

“…Type VI collagen which is composed of three different c~ chains, denoted as cO(VI), ~2(VI) and c~3(VI), is a ubiquitous component in many tissues of the body including normal gingiva [5,6]. Recently, non-co-ordinated regulation of gene expression of the three type VI collagen chains has been observed for some tumor cells [7] and in human skin fibroblasts grown in collagen gels [8] or treated with ),-interferon *Corresponding author. Fax: (81) (492) 876 657.…”

Recombinant expression and structural and binding properties of α1(VI) and α2(VI) chains of human collagen type VI

“…It was also predicted that a heterotrimeric chain assembly is required for the formation of stable and functionally active collagen VI molecules (Chu et al, 1988;Heckmann et al, 1989). Heterotypic binding has so far been shown for small proteoglycans (Bidanset et al, 1992;Stallcup et al, 1990), heparin and hyaluronan (Kielty et al, 1992;Specks et al, 1992), von Willebrand factor (Rand et al, 1991), collagen XIV (Brown et al, 1993) and to cellular receptors (Aumailley et al, 1989a;Pfaff et al, 1993).…”