p38MAPK Acts in the BMP7-dependent Stimulatory Pathway during Epithelial Cell Morphogenesis and Is Regulated by Smad1

Abstract

inhibitor, blocked the stimulatory effect of BMP7 on mIMCD-3 cell morphogenesis but had no effect on BMP7-dependent inhibition in a three-dimensional culture model. To identify mechanisms by which BMP7-dependent inhibitory signaling suppresses p38 MAPK activity, we measured p38 MAPK activity in ligand independent mIMCD-3 models of enhanced and suppressed Smad signaling. Basal activity of p38 MAPK was decreased in mIMCD-3 cells and in embryonic kidney tissue expressing a constitutively active activin-like kinase receptor, but was increased in mIMCD-3 cells stably expressing a dominant negative form of Smad1. We conclude that BMP7 stimulates renal epithelial cell morphogenesis via p38 MAPK and that p38 MAPK activity is negatively regulated by Smad1.Renal branching morphogenesis, defined as growth and branching of epithelial tubules during embryogenesis, is dependent on reciprocal inductive tissue interactions between the mesenchymal metanephric blastema and the epithelial ureteric bud and its daughter collecting ducts. These interactions are mediated, in part, by secreted growth factors and their cognate signaling effectors. Bone morphogenetic protein (BMP) 1 -7, a member of the transforming growth factor (TGF)-␤ superfamily, modulates renal branching morphogenesis, consistent with its spatial expression pattern during branching morphogenesis (1) and the arrested branching phenotype observed in Bmp7 null mice (2, 3). The response of ureteric bud and collecting duct cells to BMP7 is complex and distinct from that of other members of the TGF-␤ superfamily. BMP7 exerts dose-dependent and opposite effects on ureteric bud morphogenesis in embryonic kidney explants treated with BMP7-agarose beads and in the murine inner medullary collecting duct (mIMCD-3) cell culture model (4, 5). In contrast, BMP2, a related TGF-␤ superfamily member expressed during renal embryogenesis, only inhibits ureteric bud and collecting duct morphogenesis in a monophasic dose-dependent manner (4). These findings suggest that BMP7 acts via distinct intracellular signaling pathways to exert stimulatory and inhibitory effects.BMPs initiate intracellular signaling after binding to cell surface type I (activin-like kinase (ALK)) and type II serine/ threonine kinases. Upon ligand binding, the type II receptor, BMPRII, transphosphorylates and activates the ALK receptor. ALK receptors signal via Smad proteins and mitogen-activated protein kinases (MAPK). Activation of the ALK receptor leads to association and phosphorylation of a receptor-activated Smad protein. Phosphorylation induces the receptor-activated Smad to dissociate from the receptor, stimulates the assembly of a heteromeric complex between the phosphorylated receptoractivated Smad and the co-Smad, Smad 4, and induces nuclear accumulation of this complex (6). We have demonstrated that BMPs inhibit renal epithelial cell morphogenesis after binding ALK receptors and activating receptor-dependent Smads (7,8). In the case of BMP7, high doses activate Smad1 and induce formation of Smad1-Smad4 mo...

Podocyte-Derived BMP7 Is Critical for Nephron Development

“…30 Immunohistochemistry demonstrated wide distribution of phosphorylated p38 MAPK (phospho-p38 MAPK)-positive cells throughout the control kidneys ( Figure 9A); however, in BMP7 CKO kidneys, we observed decreased staining specifically in proximal tubules ( Figure 9, B and D). Western blot analysis of tissue from isolated cortex demonstrated marked decrease of phospho-p38 MAPK in BMP7 CKO kidneys ( Figure 9E), consistent with the immunohistochemistry ( Figure 9, B and D, compare with C and E).…”

Trps1 Functions Downstream of Bmp7 in Kidney Development

“…[12][13][14] During the process of kidney development, Bmp7 prevents metanephric mesenchymal cells from undergoing apoptosis, 12,15 promotes metanephric differentiation, 16 and controls the proliferation and apoptosis of epithelial cells in the collecting tubules. 17 In a previous study, we demonstrated that Trps1 is regulated by growth and differentiation factor 5 (Gdf5), another BMP that shares the same receptor with Bmp7, in ATDC5 chondrogenic cells. 18 This finding immediately raised the possibility that Trps1 may also act downstream of Bmp7 on metanephric mesenchymal cells during early kidney development.…”

BMP7 dose-dependently stimulates proliferation and cadherin-11 expression via ERK and p38 in a murine metanephric mesenchymal cell line

“…1997, 2001; Hu et al. 2004). In the ureteric bud, which differentiates into the collecting duct, a concentration gradient of BMP7 is considered to exist with higher concentration at the tip and lower level in the trunk.…”

“…1997; Hu et al. 2004). In murine inner medullary collecting duct (mIMCD) cells, BMP7 stimulated p38 but not ERK or JNK.…”

“…In contrast to metanephric mesenchymal cells, p38 was stimulated and inhibited by low dose (0.25 nmol/L) and high dose (10 nmol/L) of BMP7, respectively, in mIMCD cells (Hu et al. 2004). Furthermore, the time course of cell signaling was different.…”