Inhibition Of Aggregate Formation Research Articles

Assembly of newly synthesized proteoglycan and link protein into aggregates in cultures of chondrosarcoma chondrocytes.

The synthesis and subsequent assembly of proteoglycan monomer and link protein into aggregates were examined using cultured chondrocytes from the Swarm rat chondrosarcoma. Proteoglycans purified directly from culture medium after a 6-h label with [14C]serine contained up to 80% of the radioactivity in aggregates, 8% of which was in link protein. The addition of hyaluronic acid oligosaccharides (averaging 50 monosaccharides) to the culture medium during labeling inhibited aggregate formation by 94%. More than 90% of the labeled link molecules (about 7% of the total radioactivity in the proteoglycan fraction) was associated in ternary complexes with monomeric proteoglycan and HA approximately 50. The stoichiometry of labeled link protein to labeled proteoglycan core protein aggregated with either macromolecular hyaluronic acid or hyaluronic acid oligosaccharides was calculated to be 1:1. The effect of exogenous proteoglycan on aggregate formation was examined by incubating cultures for 4 h with up to 5 mg of exogenous monomer. Over this time, about 85 micrograms of newly synthesized proteoglycan accumulated in the culture medium. With increasing amounts of exogenous monomer, up to 80 micrograms of 35S-labeled exogenous monomer was incorporated into link-stabilized aggregate, while the aggregation of endogenous proteoglycan decreased from 73 to 44%. The total endogenous plus exogenous monomer in link-stabilized aggregate increased to about 130 micrograms, approximately 1 1/2 times the total amount of endogenous monomer in the culture medium, indicating that at least 1 1/2 times more link molecules than endogenous proteoglycan molecules were present. Further, the molar ratio of labeled link to labeled monomer molecules associated with the nonaggregated proteoglycan fraction remained constant at approximately 1:1, indicating that the exogenous proteoglycans were ineffective in displacing link molecules from endogenous monomer.link complexes. The data suggest that the formation of proteoglycan aggregates may be a sequential process in which a link.monomer complex forms and this complex subsequently binds to hyaluronic acid.

Keratinization and the effect of vitamin A in aggregates of a squamous carcinoma cell line NBT II.

The terminal differentiation, keratinization, of a rat bladder tumor cell line, NBT II, occurred in multicellular aggregates. After aggregation, these cells did not undergo a round of mitosis before keratinization. 5-Bromodeoxyuridine added to the monolayer cell culture 2 days before aggregation completely prevented this differentiation; it was ineffective when added at the time of cell aggregation. Vitamin A prevented the keratinization of NBT II cells in aggregates but did not inhibit aggregate formation; it enhanced the number of cells engaged in DNA synthesis. This model appears to be very useful for analyzing the mechanisms of terminal differentiation and its modulation by vitamin A in tumor cells.

Specific factors influencing histotypic aggregation of chick embryo hepatocytes.

Conditions are described for the reproducible assay of substances affecting the in vitro rate of aggregation of isolated chick embryo hepatocytes. Two low molecular weight (less than 1000) fractions--one that promotes hepatocyte aggregation (HAP) and the other that inhibits this stimulation (HAI)--have been isolated and partially purified from adult chicken liver. One major active component of HAP was identified as taurine (2-aminoethanesulfonate). The presence of HAP during the entire time of assay was required for largest aggregate formation. HAP had no effect on aggregation of chick embryo neural retina, kidney, or heart cells. Our results and the fact that puromycin completely inhibits aggregate formation suggest that HAP and HAI influence the specific synthesis and interaction of membrane macromolecules involved in the aggregation process.

Dilute solution characterization of polyfluoroalkoxyphosphazenes

AbstractResults from the dilute solution characterization of polyfluoroalkoxyphosphazenes in Freon ether (E2) solutions are reported. Anomalous viscosity data suggest that polymer aggregation sometimes occurs in E2 and may be caused by the presence of relatively few anomalous polar groups on the polymer backbone. Since small amounts of acetone added to the E2 solutions inhibit aggregate formation, samples are also characterized in an E2‐acetone mixed solvent. Light scattering and osmometry indicate that E2 and E2‐acetone (9.09% by volume) are theta solvents for the polymers. High molecular weights (M̄w < 3 × 106) and unusually broad molecular weight distributions (M̄w/M̄n < 16) are found. One polymer is fractionated by extracting solutions in 1,1,2‐trichloro‐1,2,2‐trifluoroethane with acetone. Although the samples are highly polydisperse, intrinsic viscosities correlate with number‐average molecular weights satisfying the Mark‐Houwink relation with the exponent a ≈ 1/2. The z‐average mean‐square radius of gyration increases linearly with molecular weight so that 〈S2〉g/M̄w ≈ 0.098. Because of the large polydispersity and unknown form of the distribution function, a quantitative interpretation of characterization results relating dilute solution parameters to polymer skeletal structure is not possible. The tentative conclusion is that the fluoroalkoxy‐substituted phosphazene polymers are relatively linear and therefore that the broad distribution of molecular weights must be due to some polymerization mechanism other than branching.