Expression of syndecan-1 changes during the differentiation of visceral and parietal endoderm from murine F9 teratocarcinoma cells

Syndecan-1 - A new piece in B-cell puzzle

Syndecans are transmembrane proteoglycans, with core proteins mainly decorated with heparan sulfate chains. Syndecan-1 is expressed in a tissue-, cell-and differentiation-specific manner. Its extra-cellular domain can bind via HS chains to matrix elements, to growth factors (especially "heparin-binding" proteins) and to certain biological agents. The ectodomain released by proteolysis can also be functionally active. The cytoplasmic domain can take part in signaling processes as well as in modifying cell shape. In hematopoietic cells syndecan-1 is expressed in normal pre-B-cells and plasma cells, as well as in plasmocytoid and lymphoplasmocytoid malignancies. According to our study syndecan-1 is expressed in B-CLL cells both in tissue environment and in circulation.

Specific glycosaminoglycans modulate neural specification of mouse embryonic stem cells

Mouse embryonic stem (mES) cells express a low sulfated form of heparan sulfate (HS). HS chains displayed by ES cells and their progeny become more complex and more sulfated during progression from pluripotency to neuroectodermal precursors. Sulfated epitopes are important for recognition and binding of a variety of ligands including members of the fibroblast growth factor (FGF) family. We demonstrated previously that mES cells lacking HS cannot undergo neural specification but this activity can be recovered by adding soluble heparin, a highly sulfated glycosaminoglycan (GAG). Therefore, we hypothesized that soluble GAGs might be used to support neural differentiation of HS competent cells and that the mechanisms underlying this activity might provide useful information about the signaling pathways critical for loss of pluripotency and early lineage commitment. In this study, we demonstrate that specific HS/heparin polysaccharides support formation of Sox1(+) neural progenitor cells from wild-type ES cells. This effect is dependent on sulfation pattern, concentration, and length of saccharide. Using a selective inhibitor of FGF signal transduction, we show that heparin modulates signaling events regulating exit from pluripotency and commitment to primitive ectoderm and subsequently neuroectoderm. Interestingly, we were also able to demonstrate that multiple receptor tyrosine kinases were influenced by HS in this system. This suggests roles for additional factors, possibly in cell proliferation or protection from apoptosis, during the process of neural specification. Therefore, we conclude that soluble GAGs or synthetic mimics could be considered as suitable low-cost factors for addition to ES cell differentiation regimes.

Shift of syndecan-1 expression from epithelial to stromal cells during progression of solid tumours

Syndecan-1 (SDC-1), a protein found on cells and in the extracellular matrix, participates in cell proliferation, cell migration and cell-matrix interactions. SDC-1 expression correlates with the maintenance of epithelial morphology and inhibition of invasiveness. In the present study, a second SDC-1 mRNA isoform was identified and the expression of both transcripts was investigated in various normal and malignant tissues. Both transcripts were coexpressed at equal levels in all tissues and organs analysed. Cancer-profiling array (CPA) analysis of 241 non-enriched tumour and normal cDNAs revealed stronger upregulation of SDC-1 in tumour tissues as compared with oligonucleotide array-based expression analysis of SDC-1 in microdissected breast, prostate, lung, and colon carcinoma cells. With in situ hybridisation and immunohistochemistry it was demonstrated that this difference in SDC-1 expression originates from stromal cells present in tumour connective tissue. But only the cells in connective tissue surrounding breast, lung, colon and bladder carcinoma showed upregulation of SDC-1. These stromal cells were characterised as spindle cells with myofibroblastic differentiation and they may contribute to the dedifferentiation of tumour cells and the development of metastasis.

A role for lipoprotein lipase during synaptic remodeling in the adult mouse brain

Lipoprotein lipase (LPL) is a member of a lipase family known to hydrolyze triglyceride molecules found in lipoprotein particles. This particular lipase also has a role in the binding of lipoprotein particles to different cell-surface receptors. LPL has been identified in the brain but has no specific function yet. This study aimed at elucidating the role of LPL in the brain in response to injury. Mice were subjected to hippocampal deafferentation using the entorhinal cortex lesion and mRNA and protein expression were assessed over a time-course of degeneration/reinnervation. Hippocampal LPL levels peaked at 2 days post-lesion (DPL) both at the mRNA and protein levels. No change was observed for receptors of the LDL-receptor family or RAP at DPL 2 in the hippocampus but the glia-specific syndecan-4 was found to be significantly upregulated at DPL 2. These results suggest that LPL is involved in the recycling of cholesterol and lipids released from degenerating terminals after a lesion through a syndecan-4-dependent pathway.

Volume of liquid below the epithelium of an F9 cell as a signal for differentiation into visceral endoderm

When retinoic acid-primed F9 cells are allowed to aggregate, they form embryoid bodies with an outer layer of (α)-fetoprotein-producing visceral endoderm cells and an internal cavity. I show that maturation of the visceral endoderm is dependent on the size of F9 aggregates. Size fractionation of aggregates of retinoic acid-primed F9 cells on Percoll density gradients revealed that only aggregates with diameters larger than 180 microm developed into embryoid bodies with an endoderm layer secreting (α)-fetoprotein. Size dependent alpha-fetoprotein-secretion was also observed when retinoic acid-primed F9 cells were cultured on porous microcarrier beads larger than 185 microm. Retinoic acid-primed F9 cells on flat microporous membranes did not differentiate and secrete alpha-fetoprotein unless exposed to a limited volume of medium at their basolateral surface. This suggested that maturation of the visceral endoderm is signaled by the volume of liquid phase below the epithelium. I postulate that the epithelial layer of an F9 aggregate encloses liquid and forms a barrier to diffusion of some critical factor(s). The concentration of such a factor may reach a threshold due to enlargement of the liquid phase during growth of the F9 aggregate and thereby signal maturation of the outer layer of cells into visceral endoderm.

Proteoglycan synthesis in haematopoietic cells: isolation and characterization of heparan sulphate proteoglycans expressed by the bone-marrow stromal cell line MS-5

Proteoglycans of bone-marrow stromal cells and their extracellular matrix are important components of the haematopoietic microenvironment. Recently, several studies have indicated that they are involved in the interaction of haematopoietic stem and stromal cells. However, a detailed characterization of the heparan sulphate proteoglycans synthesized by bone-marrow stromal cells is still lacking. Here we report on the isolation and characterization of proteoglycans from the haematopoietic stromal cell line MS-5, that efficiently supports the growth and differentiation of human and murine haematopoietic progenitor cells. Biochemical characterization of purified proteoglycans revealed that the haematopoietic stromal cell line MS-5 synthesizes, in addition to chondroitin sulphate proteoglycans, several different heparan sulphate proteoglycans. Immunochemical analysis, using specific antibodies against the different members of the syndecan family, glypican, betaglycan and perlecan, showed that MS-5 cells synthesize all these different heparan sulphate proteoglycans. These data were further supported by reverse-transcriptase PCR and confirmed by sequence and Northern blot analysis. The relative abundance of the different heparan sulphate proteoglycans was estimated on the protein and mRNA levels.