マトリセルラー タンパクシツ Matricellular proteins ノ キノウ : トロンボスポンジン オ チュウシン トシテ

Matricellular proteins, components of the extracellular matrix (ECM) with no directly structural roles in the ECM, are expressed primarily during development and response to injury, but not abundant in the normal adults, except in tissues with continued turnover, such as bone. Members of this class including osteonectin, thrombospondin 1 (TSP1), thrombospondin 2 (TSP2), osteopontin, and tenascin-C serve as biological mediators of cell function by interacting directly with cells or by modulating the activity of growth factors, cytokines, proteases, and other extracellular macromolecules. In addition, matricellular proteins mediate cellular de-adhesion, which refers to a reversal of the adhesive process involving the transition from a strongly adherent state with focal adhesions and stress fibers to an intermediate state of adherence. The proteins stimulate reorganization of actin stress fibers and disassembly of focal adhesion complexes but maintain a spread cell shape, while employing each unique array of signaling. The adhesive state undergoes modulation in tissue remodeling during morphogenesis and wound healing, cellular metaplasia and proliferation, and tumor metastasis. Although matricellular protein-null mice are apparently normal possibly due to redundancy of these proteins, on more careful scrutiny they display some abnormalities in collagen fibril assembly, vascular morphology or density, and connective tissue organization that are often magnified under pathological conditions. In this review, TSP1 and TSP2 showing differential spatiotemporal expression in the developing skeleton will be mainly discussed in the context of mineralizing cell biology. TSP1 accumulates in both predentin and osteoid between mineralized and unmineralized tissues, whereas TSP2 acts an autocrine inhibitor of marrow stromal cell proliferation. In particular, it is clear that high levels of TSP1 inhibit pathophysiological mineralization and contribute to calcified tissue homeostasis in response to aging and remodeling as an interface molecule

Putrescine-dependent Tumor Invasion

Our previous study showed that treatment of highly invasive rat ascites hepatoma (LC-AH) cells with α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, decreased both their intracellular level of putrescine and their in vitro invasion of a monolayer of calf pulmonary arterial endothelial (CPAE) cells, and that both these decreases were completely reversed by exogenous putrescine, but not spermidine or spermine. Here we show that all adhering control (DFMO-untreated) cells migrated beneath CPAE monolayer with morphological change from round to cauliflower-shaped cells (migratory cells). DFMO treatment increased the number of cells that remained round without migration (nonmigratory cells). Exogenous putrescine, but not spermidine or spermine, induced transformation of all nonmigratory cells to migratory cells with a concomitant increase in their intracellular Ca2+ level, [Ca2+]i. The putrescine-induced increase in their [Ca2+]i preceded their transformation and these effects of putrescine were not affected by antagonists of the voltage-gated Ca2+ channel, but were completely suppressed by ryanodine, which also suppressed the invasiveness of the control cells. The DFMO-induced decreases in both [Ca2+]i and the invasiveness of the cells were restored by thapsigargin, which elevated [Ca2+]i by inhibiting endoplasmic Ca2+-ATPase, indicating that thapsigargin mimics the effects of putrescine. These results support the idea that putrescine is a cofactor for Ca2+ release through the Ca2+ channel in the endoplasmic reticulum that is inhibited by ryanodine, this release being initiated by cell adhesion and being a prerequisite for tumor cell invasion

Soluble matrix from osteoblastic cells induces mineralization by dental pulp cells

Dental pulp cells have a capacity to differentiate into mineralization-inducing cells. To clarify the molecular mechanism, we established an in vitro mineralization-inducing system by rat clonal dental pulp cell line, RPC-C2A, and tried to purify a mineralizationinducing factor in conditioned medium (CM) from preosteoblastic MC3T3-E1 cells. The active factor was impermeable to an ultrafiltrating membrane, and sedimented by ultracentrifugation. The sedimented factor was found as a needle-like structure about 1.3 μm in average length as observed by transmission electron microscopy. The factor contained type I collagen, suggesting not a matrix vesicle, but a soluble matrix. The mineralizationinducing activity was also detected in CM from primary culture of rat calvaria (RC) cells. These results suggested that the soluble matrices from osteoblastic cells serve, at least in part, as differentiation-inducing agents

Stimulation of transcript elongation requires both the zinc finger and RNA polymerase II binding domains of human TFIIS

The eukaryotic transcriptional factor TFIIS enhances transcript elongation by RNA polymerase II. Here we describe two functional domains in the 280 amino acid human TFIIS protein: residues within positions 100-230 are required for binding to polymerase, and residues 230-280, which form a zinc finger, are required in conjunction with the polymerase binding region for transcriptional stimulation. Interestingly, a mutant TFIIS with only the polymerase binding domain actually inhibits transcription, whereas a mutant in which the polymerase binding and zinc finger domains are separated by an octapeptide is only weakly active. The zinc finger itself has no effect on transcription, but in contrast to the wild-type protein, it binds to oligonucleotides. These findings suggest that TFIIS may interact with RNA polymerase II such that the normally masked zinc finger can specifically contact nucleotides in the transcription elongation zone at a position juxtaposed to the polymerization site