Separation and characterization of the subunits of the laminin of EHS sarcoma

Effects of peroxynitrite on sarcoplasmic reticulum Ca2+ pump in pig coronary artery smooth muscle

Peroxynitrite generated in arteries from superoxide and NO may damage Ca(2+) pumps. Here, we report the effects of peroxynitrite on ATP-dependent azide-insensitive uptake of Ca(2+) into pig coronary artery vesicular membrane fractions F2 [enriched in plasma membrane (PM)] and F3 [enriched in sarcoplasmic reticulum (SR)]. Membranes were pretreated with peroxynitrite and then with DTT to quench this agent. This pretreatment inhibited Ca(2+) uptake in a peroxynitrite concentration-dependent manner, but the effect was more severe in F3 than in F2. The inhibition was thus not overcome by excess DTT used to quench peroxynitrite and was not affected if catalase, SOD, or mannitol was added along with peroxynitrite. Such damage to the pump protein would be difficult to repair if produced during ischemia-reperfusion. The acylphosphates formed with ATP in F3 corresponded mainly to the SR Ca(2+) pump (110 kDa), but in F2 both PM (140 kDa) and 110-kDa bands were observed. Peroxynitrite treatment of F2 inhibited only the 110-kDa band. Inhibition of Ca(2+) uptake and acylphosphate formation from ATP correlated well in peroxynitrite-treated F3 samples. However, inhibition of acylphosphates from orthophosphate (reverse reaction of the pump) was slightly poorer. Peroxynitrite treatment also covalently cross-linked the pump protein, yielding no dimers but only larger oligomers. In contrast, cross-linking of the SR Ca(2+) pump in skeletal and cardiac muscles gives dimers as the first oligomers. Therefore, we speculate that SERCA2 has a different quaternary structure in the coronary artery smooth muscle.

Oligosaccharide sequence of human breast cancer cell heparan sulfate with high affinity for laminin

Laminin-1 is a basement membrane glycoprotein implicated in tumor-host adhesion, which involves the cell-binding domain(s) of laminin-1 and tumor cell surface heparan sulfate (HS). The specific tumor cell surface HS oligosaccharide sequences that are necessary for binding to laminin-1 have not been characterized. To identify this laminin-binding oligosaccharide sequence, GlcNSO4-rich oligosaccharides terminating with [3H]2,5-anhydromannitol (AManR) residues were isolated from human breast cancer cell (MCF-7)-derived HS through hydrazinolysis/high pH (4.0) nitrous acid treatment/[3H]NaBH4 reduction. These oligosaccharides were chromatographed on a laminin-1 affinity column. A high affinity dodecasaccharide was isolated and characterized. Disaccharide analysis yielded IdoA(2-SO4) --> AManR(6-SO4) as the only disaccharide upon treatment of this dodecasaccharide with nitrous acid at low pH (1.5). The sequence of laminin-binding high affinity oligosaccharide is therefore [IdoA(2-SO4) --> GlcNSO4(6-SO4)]5[IdoA(2-SO4) --> AManR(6-SO4)]. Low affinity dodecasaccharides composed of [IdoA(2-SO4) --> GlcNSO4(6-SO4)]5, [IdoA(2-SO4) --> GlcNSO4] were also isolated by laminin-1 affinity chromatography. Molecular modeling studies indicate that a heparin-binding peptide sequence corresponding to amino acid residues 3010-3031 (KQNCLSSRASFRGCVRNLRLSR) in the G domain of laminin-1, modeled as a right-handed alpha-helix, carries an array of basic residues well placed to bind to clusters of sulfate groups on the high affinity dodecasaccharide.

Identification of the B1 and B2 subunits of human placental laminin and rat parietal-yolk-sac laminin using antisera specific for murine laminin-beta-galactosidase fusion proteins

Antisera raised against fusion proteins consisting of murine laminin B1 and B2 subunit sequences fused to the C-terminus of Escherichia coli beta-galactosidase were tested for their subunit specificity on Western blots of deglycosylated murine Engelbreth-Holm-Swarm (EHS) laminin. The antisera raised against B2 subunit sequences (anti-XLB2.1 and anti-XLB2.2) bound only to the EHS laminin B2 subunit. One of the antisera raised against B1 subunit sequences (anti-XLB1.2) was specific for the B1 subunit, whereas two others (anti-XLB1.1 and anti-XLB1.3) cross-reacted with the EHS laminin B2 subunit. Gold-labelled heparin-albumin was shown to bind specifically to the A subunit of deglycosylated EHS laminin on Western blots. These reagents were used to identify the homologous subunits in rat parietal-yolk-sac laminin and human placental laminin. The anti-(fusion protein) antisera identified the B1 and B2 subunits of the rat laminin, and these were similar in size to the murine EHS B subunits. Human placental laminin gave bands of 400, 340, 230, 190 and 180 kDa on reducing SDS/PAGE. The anti-(fusion protein) antisera identified the 230 and 190 kDa bands as the B1 and B2 subunits respectively. Gold-labelled heparin-albumin bound to the 400, 340 and 190 kDa bands of human placental laminin and so did not unambiguously identify a single A subunit. The human placental laminin may contain a mixture of isoforms, with alternative subunits substituting for the A subunit.

Identification and characterization of a 43-kilodalton laminin fragment from the "A" chain (long arm) with high-affinity heparin binding and mammary epithelial cell adhesion-spreading activities

A recently described procedure of reduction and carboxymethylation followed by heparin-Sepharose chromatography [Arumugham et al. (1988) Connect. Tissue Res. 18, 135-147] was used to characterize high-affinity heparin binding fragments of the laminin "A" chain. Two laminin fragments of Mr 53K and 43K selectively bound to the heparin-Sepharose column from the chymotrypsin digest of laminin, indicating that these fragments originate from the "A" chain. Without reduction and carboxymethylation but in the presence of 2.0 M urea, the heparin-Sepharose-bound material from the chymotrypsin laminin digest contains all the attachment-promoting activity for normal mouse mammary epithelial cells. The reduced 200-kDa intact three short arm fragment, fragments of Mr 70K-160K obtained either from laminin or from the reduced 200-kDa three short arm fragment, and the 53-kDa heparin binding fragment were all inactive in promoting the adhesion of mouse mammary epithelial cells. The mammary epithelial cell adhesion and spreading properties of laminin are associated with the high-affinity heparin binding 43-kDa fragment. The mammary epithelial cells attach to the 43-kDa fragment substrate and synthesize laminin, collagen type IV, and desmoplankins I and II as are the cells attached to laminin substrate and to the cells grown on tissue culture dishes. The biologically active 43-kDa fragment is generated from laminin, but not from the three short arm fragment. These results suggest that normal mouse mammary epithelial cells interact with laminin through a single site which is present in the 43-kDa heparin binding fragment located on the long arm of the "A" chain.