Cell biology of Smad2/3 linker region phosphorylation in vascular smooth muscle

Abstract

The transforming growth factor (TGF)-β superfamily of ligands regulates a diverse set of cellular functions. Transforming growth factor-β induces its biological effects through Type I and Type II transmembrane receptors that have serine/threonine kinase activities and weak tyrosine kinase activity. In vascular smooth muscle, TGF-β binds to the TGF-β Type II receptor (TβRII) at the cell surface, recruiting the Type I receptor (TβRI) to form a heterocomplex. Consequently, after phosphorylation and activation of TβRI, the transcription factors receptor activated (R-) Smad2 and Smad3 are recruited and activated through phosphorylation of C terminal residues. Overall, Smad2/3 and co-Smad4 have similar structures consisting of three regions an N-terminal MH1 domain, a C-terminal MH2 domain and a central linker region. Phosphorylation of the Smad linker region appears to have an important role in the regulation of Smad activity and function. The mitogen-activated protein kinase (MAPK) family, CDK2, CDK4 and calcium-calmodulin dependent kinase are the main kinases that phosphorylate sites in the linker region. The role of the linker region includes enabling the formation of Smad homo-oligomers and provision of phosphorylation sites for MAPK and other kinases. In some instances, linker region phosphorylation regulates the inhibition of the nuclear translocation of Smads. In the present review, we describe TGF-β signalling through Smad2/3 and the importance of the linker region in the regulation and expression of genes induced by TGF-β superfamily ligands in the context of vascular smooth muscle.

Endothelial Dysfunction Exacerbates Renal Interstitial Fibrosis through Enhancing Fibroblast Smad3 Linker Phosphorylation in the Mouse Obstructed Kidney

“…The function of Smad3 depends on extensive interactions (cross-talk) with other signalling pathways [59]. While the TGF-β-receptor I directly phosphorylates the SSXS motif in the Smad3 C-terminal domain, a range of other kinases such as mitogen-activated protein kinases (JNK, ERK, p38), protein kinase B (Akt) and cyclin-dependent kinases are involved in the phosphorylation of sites in the Smad3 linker region.…”

Transforming growth factor β-mediated site-specific Smad linker region phosphorylation in vascular endothelial cells

“…Smad2/3 and Smad4 are approximately 60 kDa proteins consisting of three distinct regions: a conserved N‐terminus domain or Mad‐homology (MH) 1 domain, a conserved C‐terminus (MH2 domain) and a non‐conserved proline‐rich linker region that joins these two domains [2,10]. In addition to carboxy‐terminal phosphorylation (exclusively by TβRI/Alk‐5), Smads can also be phosphorylated in the linker region [4,11].…”

“…In addition to carboxy‐terminal phosphorylation (exclusively by TβRI/Alk‐5), Smads can also be phosphorylated in the linker region [4,11]. TGF‐β stimulates signalling cascades, which activate intracellular serine/threonine kinases including mitogen‐activated protein kinases (MAPKs), cyclin‐dependent kinases (CDK), phosphoinositide 3 kinase (PI3K)/Akt and other kinases [10,12,13]. The linker region has been shown to play an important role in TGF‐β‐mediated biological activity, as Smad3 linker region mutants do not mediate TGF‐β transcriptional activation despite its being phosphorylated at the C‐terminus.…”

MiR-1 suppresses tumor cell proliferation in colorectal cancer by inhibition of Smad3-mediated tumor glycolysis

“…4, 5, 6, 7 In addition, phosphorylation of Smad3 linker regions, including Ser213, Ser204, Ser208 and Thr179, is an early event in colitis-associated colorectal cancer, and indirectly inhibits its COOH-terminal phosphorylation and subsequently suppresses tumor-suppressive pSmad3C signaling, generating resistance to the growth-inhibitory effect of TGF- β . 6, 8, 9, 10, 11, 12 A recent report by Yadav et al illustrated that conditional Smad3 knockout induced white fat to brown fat phenotypic transition and promoted mitochondrial biogenesis and function in white adipose tissue by regulating the PGC-1 α promoter and PRDM16 target genes. 13 This suggests an important role of Smad3 in regulating glucose and energy homeostasis, which is consistent with the finding by Sun et.al .…”