Spreading of embryologically distinct urothelial cells is inhibited by SPARC

Abstract

The AON epitope of secreted protein acidic and rich in cysteine (SPARC) is a conserved motif expressed by human SPARC in a variety of human cell types. Through the use of a monoclonal antibody that recognizes this epitope, transitional epithelium was found to restrict expression of SPARC to the suprabasal and intermediate layer. Such intracellular expression was defined by immunoreactive signals that localized to the apical plasma membranes of suprabasal and intermediate cells. Polarization of SPARC to apical plasma membranes of suprabasal cells was retained in vitro by a subpopulation of cells that exhibited characteristics of suprabasal cells--cell-cycle quiescence, large cell volumes, and multiple nuclei. In contrast, the basal layer of transitional epithelium in vivo and cycling cells in vitro did not exhibit this apical staining pattern, but instead sequestered the SPARC polypeptide within urothelial cytoplasm and/or nuclei, as revealed by immunohistochemical analysis. Elution of soluble proteins and DNA from urothelial cells revealed the presence of SPARC within the nuclear matrix--and that SPARC colocalized with the nuclear matrix Ki-67 antigen. rSPARC activity was demonstrated and quantified with a rounding assay whereby the spreading of freshly plated cells was inhibited by recombinant SPARC in a concentration- and time-dependent manner. Inhibition of spreading was observed in urothelial cells derived from endoderm (bladder) and mesoderm (ureter) germ layers. Statistically significant differences were seen between urothelial cells from these two layers. Mesodermal cells recovered more slowly from the inhibitory effects of rSPARC, such that at hour 6 endodermal cells underwent significantly more spreading, as shown by a rounding index (RI). These experiments provide new insights about the matricellular trafficking of SPARC and suggest that intra- and extra-cellular localization patterns influence the development, homeostasis, and differentiation of transitional epithelium.

The C‐terminal Ca2+‐binding domain of SPARC confers anti‐spreading activity to human urothelial cells

“…How urothelial cells spread is central to understanding a number of bladder diseases. The extracellular matrix-associated secreted protein acidic and rich in cysteine (SPARC), also known as BM-40 and osteonectin (Termine et al, 1981;Romberg et al, 1985), has been shown to inhibit the spreading of human urothelial cells derived from embryologically distinct origins in concentration-and time-dependent processes (Hudson et al, 2005). Such inhibitory activity provides a mechanism in which SPARC can modulate the interactions between basal urothelial cells and the urothelial basement membrane.…”

Loss of SPARC in bladder cancer enhances carcinogenesis and progression

“…SPARC is expressed in normal murine and human urothelia and suburothelial stroma (20) and in primary cultures of human urothelial cells (21)(22)(23). SPARC has been shown to exert an antiadhesive and antiproliferative effect on human and murine urothelial cells (21)(22)(23).…”

Sparc localizes to the blebs of hobit cells and human primary osteoblasts

“…A previous report [Gooden et al, 1999] has highlighted that SPARC localized to the nucleus during specific cell cycle phases. Moreover, Yan et al [2005] described a translocation of SPARC to the nucleus of lens epithelial cells and SPARC nuclear localization has also been observed in urothelial cells [Hudson et al, 2005]. In addition, it has been very recently demonstrated that recombinant SPARC can be internalized in the cell and be translocated to cell nucleus where it inhibits DNA synthesis [Kosman et al, 2007].…”

“…Cell Compartments of HOBIT Cells SPARC subcellular distribution is still debated, as some recent reports highlighted a nuclear staining for SPARC in human urothelial [Hudson et al, 2005] and immortalized murine lens epithelial cells [Yan et al, 2005], even though other studies demonstrated only a cytoplasmic localization. In several cell lines, intracellular SPARC has been co-localized to endoplasmic reticulum and Golgi complex, presumably destined for secretion [Lane and Sage, 1994], while Gooden et al [1999] presented evidence that the distribution of endogenous, intracellular SPARC can vary according to specific phases of the cell cycle.…”

“…This inhibition of cell adhesion gives rise to modifications in cell shape that are correlated with the induction of apoptosis, even though these changes may be temporarily necessary for cells undergoing migration and proliferation. In particular, the addition of recombinant SPARC to cultured cells causes either focal adhesion disassembly, or prevention of cell spreading and inhibition of proliferation [Funk and Sage, 1991;MurphyUllrich et al, 1995;Motamed and Sage, 1998;Hudson et al, 2005]. …”