Chondroitin sulfate: inhibition of synthesis by puromycin

Altered patterns of proteoglycan deposition during maturation of the fetal mouse lung

Previous studies have shown that beta-xyloside inhibits maturation of the fetal mouse lung (Smith et al., Dev. Biol. 138, 42-52, 1990). Insofar as this drug inhibits proteoglycan deposition, the present studies were undertaken to examine the chemical composition and tissue distribution of proteoglycans in order to determine, more precisely, their role during lung morphogenesis. Autoradiography of labeled 16- and 19-day embryonic lungs demonstrated greater incorporation over the mesenchyme. Treatment with beta-xyloside did not alter the autoradiographic appearance; however, beta-xyloside treatment followed by nitrous acid digestion, eliminated most silver grains. Isolation of proteoglycans from extracellular, membrane and intracellular pools over the 16- to 19-day interval demonstrated redistribution of heparan sulfate proteoglycan from an intracellular to a membrane location, while chondroitin sulfate proteoglycan redistributed from intracellular to extracellular. Only the synthesis of chondroitin sulfate proteoglycan was inhibited by beta-xyloside. On the basis of these results we suggest that a chondroitin sulfate proteoglycan is required for lung maturation and that inhibition of its synthesis results in inhibition of septa formation and subsequent failure of morphogenesis and differentiation.

In vitro effects of insulin on macromolecular events in newt limb regeneration blastemata

This work provides data demonstrating a stimulatory effect of insulin on macromolecular events occurring in cultured regeneration blastemata and demonstrates a synergistic interdependence between nerves and insulin in newt limb regeneration. The current experiments provide evidence for the following: (1) Insulin is paramount for expression of the mitogenic effect of nerves on cultures blastemata. (2) Insulin stimulates the incorporation of (3H)uridine into the acid-insoluble fraction of blastemal homogenates, but it does not alter the turnover rate of incorporated labeled uridine. (3) Insulin also stimulates the incorporation of 35SO4 and (3H)leucine into both chondroitinase-sensitive and chondroitinase-resistant blastemal proteoglycans. (4) Insulin increases the uptake of radiolabeled precursors by the blastemata, namely, (3H)leucine, (3H)uridine, 35SO4, (3H)alpha-aminoisobutyrate, and (3H)2-deoxy-D-glucose. The importance of insulin in the regulation of newt limb regeneration is discussed.

Purification and characterization of 3'-phosphoadenylylsulfate: N-desulfoheparan sulfate sulfotransferase from arterial tissue

A 3'-phosphoadenylsulfate: N-desulfoheparan sulfate sulfotransferase (EC 2.8.2.12) was purified 450-fold from the microsomal fraction of calf arterial tissue and separated from 3'-phosphoadenylylsulfate:chondroitin sulfotransferase (EC 2.8.2.5) activity. The enzyme has optimal activity at neutral pH, requires divalent cations (Mn2+, Mg2+, Ca2+) for maximal activity and exhibits specificity towards N-desulfoheparan sulfate, N,O-desulfoheparan sulfate and oligosaccharides derived therefrom. N,O-desulfoheparan sulfate tetrasaccharides serve as acceptor substrates only if the nonreducing terminus is occupied by glucuronic acid (not iduronic acid). The N,O-desulfoheparan sulfate sulfotransferase transfers [35S]sulfate from 3'-phosphoadenylyl[35S]sulfate to the 2-amino groups and to the 6-hydroxy groups of glucosamine units of the acceptor substrates. The ratio of N/O-sulfation ranged between 3:1 and 2:1. O-[35S]Sulfated unsaturated disaccharides were obtained from enzymatically labelled [35S]N-desulfoheparan sulfate by heparitinase degradation and subsequent deamination. Evidence for the O-sulfation at C-6 of the glucosamine units was provided by isolation of anhydromannose [35S]monosulfate, which was formed from uronosylanhydromannose [35S]monosulfate by beta-glucuronidase treatment. An N-desulfo-N-[1-14C]lacetylheparan sulfate deacetylase activity was copurified with the N-desulfoheparan sulfate sulfotransferase.

Cell shape and cartilage differentiation of early chick limb bud cells in culture

The onset of chondrogenesis in te embryonic chick is preceded by a prechondrogenic condensation of the prospective cartilage cells. Similarly, in culture, the chondrogenic phenotype is only expressed by limb mesoderm cells plated at densities above confluence. This has led to the proposal that chondrogenic differentiation requires immediate histogenic interactions prior to overt chondrogenesis (Solursh et al., 1978, In Vitro 14, 51-61; and, 1980, Dev. Biol. 78, 141-150). It is noticeable that in both the in vitro situations cells secreting a cartilaginous matrix are rounded in shape. Recently, Glowacki, Trepman and Folkman (personal communication) have shown a dependence of phenotypic expression by mature chondrocytes on cell shape. Cells maintained in a rounded configuration by culturing on a semi-adhesive substratum (poly(HEMA)) synthesised more sulphur-containing extracellular matrix than cells allowed to flatten on normal tissue culture plastic. We have investigated whether there is a similar shape-dependent relationship in the differentiation of chick embryonic mesoblasts into actively secreting chondroblasts. Our results show that a rounded cell shape is conductive to the synthesis of a sulphated matrix.

In vitro conditions affecting the synthesis of sulfated proteoglycans by normal and rheumatoid synovial cells in culture

In vitro conditions affecting synthesis of sulfated proteoglycans by cell suspensions derived from monolayer cell cultures of normal and rheumatoid synovial tissue were examined. The capacity of cells to synthesize proteoglycans was estimated by the incorporation of 35S--sulfate into cetylpyridinium chloride--precipitable material. Synthesis of sulfated proteoglycans was maximal during log phase, and after 2--3 hours of recovery from disaggregation. Normal synovial cells appeared to be more sensitive to changes in serum concentration than were rheumatoid synovial cells, but rheumatoid synovial cells were more sensitive to changes in cell density. The proportion of newly synthesized extracellular proteoglycans increased with the duration of incubation in 35S--sulfate.

Somite chondrogenesis. A structural analysis

Light and electron microscopy are used in this study to compare chondrogenesis in cultured somites with vertebral chondrogenesis These studies have also characterized some of the effects of inducer tissues (notochord and spinal cord), and different nutrient media, on chondrogenesis in cultured somites Somites from stage 17 (54-60 h) chick embryos were cultured, with or without inducer tissues, and were fed nutrient medium containing either horse serum (HS) and embryo extract (EE), or fetal calf serum (FCS) and F12X Amino acid analyses were also utilized to determine the collagen content of vertebral body cartilage in which the fibrils are homogeneously thin (ca. 150 A) and unbanded. These analyses provide strong evidence that the thin unbanded fibrils in embryonic cartilage matrix are collagen. These thin unbanded collagen fibrils, and prominent 200-800 A protein polysaccharide granules, constitute the structured matrix components of both developing vertebral cartilage and the cartilage formed in cultured somites Similar matrix components accumulate around the inducer tissues notochord and spinal cord. These matrix components are structurally distinct from those in embryonic fibrous tissue The synthesis of matrix by the inducer tissues is associated with the inductive interaction of these tissues with somitic mesenchyme. Due to the deleterious effects of tissue isolation and culture procedures many cells die in somitic mesenchyme during the first 24 h in culture. In spite of this cell death, chondrogenic areas are recognized after 12 h in induced cultures, and through the first 2 days in all cultures there are larger accumulations of structured matrix than are present in equivalently aged somitic mesenchyme in vivo. Surviving chondrogenic areas develop into nodules of hyaline cartilage in all induced cultures, and in most non-induced cultures fed medium containing FCS and F12X There is more cell death, less matrix accumulation, and less cartilage formed in cultures fed medium containing HS and EE. The inducer tissues, as well as nutrient medium containing FCS and F12X, facilitate cell survival, the synthesis and accumulation of cartilage matrix, and the formation of cartilage nodules in cultured somites.

Isolation of human synovial-fluid hyaluronate by density-gradient ultracentrifugation and evaluation of its protein content

1. A compound of hyaluronate and protein, called hyaluronate-protein was isolated from pooled human synovial fluids by caesium chloride density-gradient ultracentrifugation. 2. The isolated hyaluronate-protein was labelled with [(125)I]iodide and the following studies were done. (a) Ultracentrifugation in caesium chloride showed that the protein moiety ((125)I counts) and hyaluronate (hexuronate) sedimented together in the middle of the gradient. (b) The labelled hyaluronate-protein was treated with trypsin, and ultracentrifugation showed that peptide fragments ((125)I counts) were dispersed throughout the gradient, indicating proteolytic digestion. Hyaluronate sedimented in the middle of the gradient. (c) The labelled hyaluronate-protein was digested with streptococcal hyaluronidase, and ultracentrifugation showed that hyaluronate fragments were dispersed throughout the gradient, indicating digestion of the polysaccharide. The protein moiety, without attached hyaluronate, now sedimented at the top of the gradient. (d) Ultracentrifugation of labelled hyaluronate-protein in 4m-guanidinium chloride showed that protein and hyaluronate sedimented together. 3. These studies confirm that hyaluronate is combined with a small quantity of protein in normal human synovial fluid. A mild method for the rapid isolation of hyaluronate-protein in good yield is described.

Biosynthesis of intestinal mucins. Effect of puromycin on mucoprotein biosynthesis by sheep colonic mucosal tissue

1. Surviving sheep colonic mucosal tissue incorporated l-[U-(14)C]threonine when incubated in Krebs medium III at 37 degrees in an atmosphere of oxygen, into a well-characterized mucoprotein fraction, isolated by papain digestion of the incubated scrapings. 2. Acidic hydrolysis and chromatography of the labelled mucoprotein showed that threonine was the only constituent to become labelled. In the presence of puromycin the incorporation of l-[U-(14)C]threonine was considerably diminished (6.7 and 18.5% of control in duplicate experiments). Furthermore, puromycin also decreased incorporation of radioactivity from d-[U-(14)C]-glucose (48.0 and 31.6% of control) and (35)SO(4) (2-) (21.2 and 23.6% of control) into the mucoprotein fraction. 3. In a puromycin-inhibited system, with d-[U-(14)C]-glucose, where the overall specific radioactivity of the mucoprotein was 48% of control, the labelling of the individual monosaccharide constituents (as% of control) was: N-acetylneuraminic acid, 44%; N-glycollylneuraminic acid, 61%; hexosamines, 46%; fucose, 68%; galactose, 34%.

Simultaneous synthesis of DNA and specialized cellular products by differentiating cartilage cells in vitro

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