Biosynthesis and Deposition of a Noncovalent Laminin-Heparan Sulfate Proteoglycan Complex and Other Basal Lamina Components by a Human Malignant Cell Line

125

107

Type IV collagen in Caenorhabditis elegans is produced by two essential genes, emb-9 and let-2, which encode α1- and α2-like chains, respectively. The distribution of EMB-9 and LET-2 chains has been characterized using chain-specific antisera. The chains colocalize, suggesting that they may function in a single heterotrimeric collagen molecule. Type IV collagen is detected in all basement membranes except those on the pseudocoelomic face of body wall muscle and on the regions of the hypodermis between body wall muscle quadrants, indicating that there are major structural differences between some basement membranes in C. elegans. Using lacZ/green fluorescent protein (GFP) reporter constructs, both type IV collagen genes were shown to be expressed in the same cells, primarily body wall muscles, and some somatic cells of the gonad. Although the pharynx and intestine are covered with basement membranes that contain type IV collagen, these tissues do not express either type IV collagen gene. Using an epitope-tagged emb-9 construct, we show that type IV collagen made in body wall muscle cells can assemble into the pharyngeal, intestinal, and gonadal basement membranes. Additionally, we show that expression of functional type IV collagen only in body wall muscle cells is sufficient for C. elegans to complete development and be partially fertile. Since type IV collagen secreted from muscle cells only assembles into some of the basement membranes that it has access to, there must be a mechanism regulating its assembly. We propose that interaction with a cell surface–associated molecule(s) is required to facilitate type IV collagen assembly.

Section: Discussionmentioning

confidence: 99%

Type IV Collagen Is Detectable in Most, but Not All, Basement Membranes of Caenorhabditis elegans and Assembles on Tissues That Do Not Express It

Graham

Johnson

Wang

et al. 1997

125

107

“…7 and 9) . Immunoprecipitates of [3sS]cysteine-labeled HSPG also contain the A chain (400 kD) and B1,B2 chains (-200 kD) of laminin which is coprecipitated as a result of non-covalent complexing of the HSPG core protein and laminin at an early posttranslational stage (15) .…”

Section: Basement Membrane Hspg Is Secreted Constitutively By Llc-pki Cellsmentioning

confidence: 99%

A heterotrimeric G protein, G alpha i-3, on Golgi membranes regulates the secretion of a heparan sulfate proteoglycan in LLC-PK1 epithelial cells.

Stow

Almeida

Narula

et al. 1991

295

147

Abstract. A heterotrimeric Gai subunit, «i-3, is localized on Golgi membranes in LLC-PKI and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence . The M-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The a;_3 subunit is found on isolated rat liver Golgi membranes by Western blotting and Gai-3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLC-PKI cells were stably transfected with GO ;-3 on an MT1, inducible promoter in order to overexpress ai-3 on Golgi membranes. The intracellular processing and

“…In keeping with the diversity of their structures, these complex glycoproteins have been found to be capable of interacting with a variety of different types of molecules. Interactions with proteoglycans have been reported for most, if not all, extracellular matrix molecules, including collagens (Ruoslahti and Engvall, 1980;Scott, 1988;Smith et al, 1985), laminin (Martin and Timpl, 1987;Frenette et al, 1989;Lander et al, 1985), fibronectin (Oldberg and Ruoslahti, 1982;Saunders and Bernfield, 1987;Ruoslahti 1988b), vitronectin (Suzuki et all., 1984(Suzuki et all., , 1985, and thrombospondin (Dixit et al, 1984;Sun et al, 1989). Cell surface molecules such as the neural cell adhesion molecule can also have binding sites for proteoglycans (Cole and Burg, 1989).…”

mentioning

confidence: 99%

Interaction of the NG2 chondroitin sulfate proteoglycan with type VI collagen.

Stallcup

Dahlin

Healy

1990

167

117

Abstract. The NG2 chondroitin sulfate proteoglycan is a membrane-associated molecule of ,o500 kD with a core glycoprotein of 300 kD. Both the complete proteoglycan and a smaller quantity of the 300-kD core are immunoprecipitable with polyclonal and monoclonal antibodies against purified NG2. From some cell lines, the antibodies coprecipitate NG2 and type VI collagen, the latter appearing on SDS-PAGE as components of 140 and 250 kD under reducing conditions. The immunoprecipitation of type VI collagen does not seem to be due to recognition of the collagen by the antibodies, but rather to binding of the collagen to NG2. Studies on the NG2-type VI collagen complex suggest that binding between the two molecules is mediated by protein-protein interactions rather than by ionic interactions involving the glycosaminoglycans.Immunofluorescence double labeling in frozen sections of embryonic rat shows that NG2 and type VI collagen are colocalized in structures such as the intervertebral discs and arteries of the spinal column. In vitro the two molecules are highly colocalized on the surface of several cell lines. Treatment of these cells resulting in a change in the distribution of NG2 on the cell surface also causes a parallel change in type VI collagen distribution. Our results suggest that cell surface NG2 may mediate cellular interactions with the extraceUular matrix by binding to type VI collagen.