Bridging the gap: heparan sulfate and Scube2 assemble Sonic hedgehog release complexes at the surface of producing cells.

Decision making in cellular ensembles requires the dynamic release of signaling molecules from the producing cells into the extracellular compartment. One important example of molecules that require regulated release in order to signal over several cell diameters is the Hedgehog (Hh) family, because all Hhs are synthesized as dual-lipidated proteins that firmly tether to the outer membrane leaflet of the cell that produces them. Factors for the release of the vertebrate Hh family member Sonic Hedgehog (Shh) include cell-surface sheddases that remove the lipidated terminal peptides, as well as the soluble glycoprotein Scube2 that cell-nonautonomously enhances this process. This raises the question of how soluble Scube2 is recruited to cell-bound Shh substrates to regulate their turnover. We hypothesized that heparan sulfate (HS) proteoglycans (HSPGs) on the producing cell surface may play this role. In this work, we confirm that HSPGs enrich Scube2 at the surface of Shh-producing cells and that Scube2-regulated proteolytic Shh processing and release depends on specific HS. This finding indicates that HSPGs act as cell-surface assembly and storage platforms for Shh substrates and for protein factors required for their release, making HSPGs critical decision makers for Scube2-dependent Shh signaling from the surface of producing cells.

Effect of decorin on overcoming the extracellular matrix barrier for oncolytic virotherapy.

The pressing challenge for contemporary gene therapy is to deliver enough therapeutic genes to enough cancer cells in vivo. With the aim of improving viral distribution and tumor penetration, we explored the use of decorin to enhance viral spreading and tumor tissue penetration. We generated decorin-expressing replication-incompetent (dl-LacZ-DCNG, dl-LacZ-DCNQ and dl-LacZ-DCNK) and replication-competent (Ad-DeltaE1B-DCNG, Ad-DeltaE1B-DCNQ and Ad-DeltaE1B-DCNK) adenoviruses (Ads). Point mutants of decorin gene (DCNG), DCNK and DCNQ, have a negative and moderate binding affinity to type-I collagen fibril, respectively. In both tumor spheroids and established solid tumors in vivo, tissue penetration potency of dl-LacZ-DCNG was greatly enhanced than those of dl-LacZ, dl-LacZ-DCNQ and dl-LacZ-DCNK, and this enhanced tissue penetration effect derived from decorin-expressing Ad was dependent on the binding affinity of decorin to collagen fibril. Expression of DCNG enhanced viral spread of replicating Ad, leading to improved tumor reduction and survival benefit. Moreover, the tumoricidal effects of Ad-DeltaE1B-DCNQ and Ad-DeltaE1B-DCNK were lessened, as the binding affinity to collagen was decreased, showing that the increased cancer cell cytotoxicity was driven by the action of decorin on extracellular matrix (ECM). Furthermore, Ad-DeltaE1B-DCNG substantially decreased ECM components within the tumor tissue. Finally, intratumoral injection of Ad-DeltaE1B-DCNG in primary tumor site greatly reduced the formation of B16BL6 melanoma cell pulmonary metastases in mice. Taken together, these data show the utility of decorin as a dispersion agent and highlight its utility and potential in improving the efficacy of replicating Ad-mediated cancer gene therapy.

Different usage of the glycosaminoglycan attachment sites of biglycan.

Biglycan is a member of the small leucine-rich proteoglycan family. Its core protein comprises two chondroitin/dermatan sulfate attachment sites on serine 42 and serine 47, respectively, which are the fifth and tenth amino acid residues, respectively, after removal of the prepro peptide. Because the regulation of glycosaminoglycan chain assembly is not fully understood and because of the in vivo existence of monoglycanated biglycan, mutant core proteins were stably expressed in human 293 and Chinese hamster ovary cells in which i) either one or both serine residues were converted into alanine or threonine residues, ii) the number of acidic amino acids N-terminal of the respective serine residues was altered, and iii) a hexapeptide was inserted between the mutated site 1 and the unaltered site 2. Labeling experiments with [(35)S]sulfate and [(35)S]methionine indicated that serine 42 was almost fully used as the glycosaminoglycan attachment site regardless of whether site 2 was available or not for chain assembly. In contrast, substitution of site 2 was greatly influenced by the presence or absence of serine 42, although additional mutations demonstrated a direct influence of the amino acid sequence between the two sites. When site 2 was not substituted with a glycosaminoglycan chain, there was also no assembly of the linkage region. These results indicate that xylosyltransferase is the rate-limiting enzyme in glycosaminoglycan chain assembly and implicate a cooperative effect on the xylosyl transfer to site 2 by xylosylation of site 1, which probably becomes manifest before the removal of the propeptide. It is shown additionally that biglycan expressed in 293 cells may still contain the propeptide sequence and may carry heparan sulfate chains as well as sulfated N-linked oligosaccharides.

Expression of fibroblast growth factors 1 and 2 in a human retinal pigment epithelium cell line (K1034).

The primary source of fibroblast growth factors (FGFs) is the retinal pigment epithelium (RPE). Investigations on FGF secretion in RPE primary cultures are hampered by the rapid run-down of cell vitality after a few passages. Therefore, long-term experiments require an alternative to primary cultures. We detected FGF-1 and FGF-2 in the established human K1034 cell line by immunohistochemistry. In addition, mRNA for both FGFs was found by RT-PCR. By immunohistochemistry, the signal was more pronounced with FGF-2 than with FGF-1. K1034 is capable of expressing both FGF-1 and FGF-2. With respect to these features, this cell line can be used as an alternative to primary cultured human RPE cells.