Differential effects of various growth factors and cytokines on the syntheses of DNA, type I collagen, laminin, fibronectin, osteonectin/secreted protein, acidic and rich in cysteine (SPARC), and alkaline phosphatase by human pulp cells in culture

Abstract

The purpose of this study is to differentiate roles of several growth factors and cytokines in proliferation and differentiation of pulp cells during development and repair. In human pulp cell cultures, laminin and type I collagen levels per cell remained almost constant during the whole culture period (22 days). On the other hand, secreted protein, acidic and rich in cysteine (SPARC/osteonectin) and alkaline phosphatase (ALPase) levels markedly increased after the cultures reached confluence. Laminin and type I collagen, as well as fibronectin, stimulated the spreading of pulp cells within 1 h. Adding transforming growth factor-beta (TGF-beta) decreased laminin and ALPase levels, whereas it increased SPARC and fibronectin levels 3- to 10-fold. Western and Northern blots showed that TGF-beta enhanced SPARC synthesis at the protein and mRNA levels. Basic fibroblast growth factor (bFGF) decreased type I collagen, laminin, SPARC, and ALPase levels without changing the fibronectin level. Platelet-derived growth factor (PDGF) selectively decreased laminin, SPARC, and ALPase levels. Epidermal growth factor (EGF) also decreased SPARC and ALPase levels. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) decreased type I collagen and laminin levels, and abolished SPARC and ALPase syntheses. Of these peptides, bFGF and PDGF showed the greatest stimulation of [3H]thymidine incorporation into DNA. TGF-beta, EGF, and TNF-alpha had less effect on DNA synthesis, whereas IL-1beta inhibited DNA synthesis. These findings demonstrated that TGF-beta, bFGF, EGF, PDGF, TNF-alpha, and IL-1beta have characteristically different patterns of actions on DNA, laminin, type I collagen, fibronectin, ALPase, and SPARC syntheses by pulp cells.

SPARC Inhibits Epithelial Cell Proliferation in Part through Stimulation of the Transforming Growth Factor-β–Signaling System

“…SPARC and TGF-␤ can engage one another in a reciprocal relationship, with SPARC inducing TGF-␤ expression and TGF-␤ inducing that of SPARC (Wrana et al, 1991;Ford et al, 1993;Reed et al, 1994;Shiba et al, 1998;Francki et al, 1999;Shanker et al, 1999;Bassuk et al, 2000). In light of the bidirectional relationship between SPARC and TGF-␤ and our finding that TGF-␤ stimulated Mv1Lu cells to express SPARC, we suspected that SPARC treatment of Mv1Lu cells would similarly stimulate their expression of TGF-␤.…”

“…SPARC has also been shown to both positively and negatively regulate cell proliferation (Funk and Sage, 1991;Sage, 1992;Funk and Sage, 1993;Sage et al, 1995;Kupprion et al, 1998;Motamed and Sage, 1998;Motamed et al, 2002). The biology of SPARC is further complicated by the fact that SPARC and TGF-␤ can mediate overlapping activities, as well as induce one another's expression (Wrana et al, 1991;Ford et al, 1993;Reed et al, 1994;Shiba et al, 1998;Francki et al, 1999;Shanker et al, 1999;Bassuk et al, 2000). The biology of SPARC is further complicated by the fact that SPARC and TGF-␤ can mediate overlapping activities, as well as induce one another's expression (Wrana et al, 1991;Ford et al, 1993;Reed et al, 1994;Shiba et al, 1998;Francki et al, 1999;Shanker et al, 1999;Bassuk et al, 2000).…”

“…TGF-␤ induces SPARC expression in fibroblasts, keratinocytes, smooth muscle, and endothelial cells (Wrana et al, 1991;Ford et al, 1993;Reed et al, 1994;Shiba et al, 1998;Shanker et al, 1999); however, its ability to stimulate SPARC expression in epithelial cells remains to be established. Because SPARC is expressed in epithelial cells, and because TGF-␤ regulates epithelial cell function, we speculated that TGF-␤ might induce SPARC expression in epithelial cells.…”

“…Similarly, the proliferation of epithelial, endothelial, and hematopoietic cells is inhibited by the potent tumor suppressor TGF-␤ (Massague, 1998;Blobe et al, 2000). For instance, SPARC induces TGF-␤ expression in mesangial cells Bassuk et al, 2000), and, conversely, TGF-␤ stimulates SPARC expression in a number of cell types, including fibroblasts, keratinocytes, smooth muscle cells, and endothelial cells (Wrana et al, 1991;Ford et al, 1993;Reed et al, 1994;Shiba et al, 1998;Shanker et al, 1999). For instance, SPARC induces TGF-␤ expression in mesangial cells Bassuk et al, 2000), and, conversely, TGF-␤ stimulates SPARC expression in a number of cell types, including fibroblasts, keratinocytes, smooth muscle cells, and endothelial cells (Wrana et al, 1991;Ford et al, 1993;Reed et al, 1994;Shiba et al, 1998;Shanker et al, 1999).…”

Anti-cancer role of SPARC, an inhibitor of adipogenesis

“…SPARC and TGF-β acts as inhibitors of cell cycle progression and proliferation in several types of cells 31, 32, 76, 77. SPARC stimulates TGF-β expression in mesangial cells and, on the other hand, TGF-β stimulates SPARC expression in a number of cell types, including endothelial cells, fibroblasts, keratinocytes, and smooth muscle cells 20, 78-81. SPARC inhibits epithelial cell proliferation by commandeering the TGF-β signaling system, via coupling of C-terminal extracellular calcium (EC)-domain (i.e., SPARC-EC) to a TGF-β receptor/Smad2/3-dependent pathway 82.…”