TIMAP, the versatile protein phosphatase 1 regulator in endothelial cells

Abstract

Transforming growth factor (TGF)-β inhibited membrane associated protein, TIMAP, is the member of the myosin phosphatase targeting protein (MYPT) family of protein phosphatase 1 (PP1) regulatory subunits. The N-terminal part of TIMAP has a typical MYPT family structure with a sequence element called MyPhone (myosin phosphatase N-terminal element), a putative bipartite nuclear localization signal, a PP1 catalytic subunit binding motif, and five ankyrin repeats. The C-terminal half of TIMAP is intrinsically disordered, but ends with a functional CAAX box for lipid modification which allows localization of TIMAP at the plasma membrane. TIMAP is prenylated by farnesyl transferase with the contribution of the anchoring protein, RACK1 in the cytoplasm. The controlling effect of TIMAP on PP1 is moderated by PKA/GSK3β and PKC mediated phosphorylation of TIMAP, the sites are located in the disordered region of the protein. TIMAP is abundant in endothelial cells. A growing body of evidence attained through characterization of newly identified protein partners calls attention to its critical role in normal and pathological activities of the endothelium via regulation of PP1. TIMAP binds the non-integrin laminin receptor 1 and the endothelin converting enzyme 1, which may connect TIMAP to angiogenesis, tumor invasion and metastasis. Barrier protecting role of TIMAP was shown for pulmonary artery endothelial cells. ERM (ezrin-radixin-moesin) proteins, as potential in vivo PP1-TIMAP substrates, are critical targets in the barrier maintenance. TIMAP affects phosphorylation level and subcellular localization of merlin and eukaryotic elongation factor-1A1. Merlin is a key component of signaling pathways regulating cell proliferation, membrane domain formation and cell-cell junction organization. Noncanonical functions of the elongation factor include a role in organization of cytoskeleton dynamics and in apoptosis. The interacting/binding partners identified so far demonstrate a rather complex role of TIMAP in key functions of the endothelium offering TIMAP as a plausible target in pathological issues. © 2017 IUBMB Life, 69(12):918-928, 2017.

TIMAP inhibits endothelial myosin light chain phosphatase by competing with MYPT1 for the catalytic protein phosphatase 1 subunit PP1cβ

“…Although our experiments indicate that TIMAP/PP1cβ inhibits myosin phosphatase activity in ECs, it is still possible that TIMAP/PP1cβ targets other substrates; for instance, the ERM proteins moesin and merlin (17, 34, 56). In this regard, a previous study found that TIMAP WT overexpression did not alter baseline ERM phosphorylation (17), similar to findings in this study (Fig.…”

“…We investigated whether TIMAP/PP1cβ acts as a functional myosin phosphatase in living ECs because TIMAP is an EC-predominant MYPT1 family member (22) that supports myosin-dependent EC processes like angiogenesis (30) and maintenance of pulmonary EC barrier integrity (34). We found that, although TIMAP partially colocalizes and directly interacts with MLC2, it inhibits MLC2 dephosphorylation in ECs by competing for PP1cβ with MYPT1, leading to MYPT1 degradation (Fig.…”

Genome-wide association analysis of diverticular disease points towards neuromuscular, connective tissue and epithelial pathomechanisms

“…In the interaction between muscular layer and the vessel, vascular biology and contractility may play an additional role. CALCB , which plays a role in mesenteric vascular smooth muscle function50 and protein phosphatase 1 regulatory subunit 16B ( PPP1R16B ), which regulates endothelial cell function51 may provide a potential mechanistic basis for altered vascular biology at these entry points.…”

Application of Multiplex Bisulfite PCR–Ligase Detection Reaction–Real-Time Quantitative PCR Assay in Interrogating Bioinformatically Identified, Blood-Based Methylation Markers for Colorectal Cancer

“…70 Also reported to be highly methylated 71 in CRC (relative to normal) is the promoter region of PP1R16B (protein phosphatase 1 regulatory subunit 16B), which codes for a membrane protein that regulates protein phosphatase 1 in endothelial cells. 72 The locus of GDF6 (growth differentiation factor 6), a gene that has a role in vascular stabilization, 73 is also highly methylated 74 in CRC. CLIP4 (CAP-Gly domain-containing linker protein family member 4), whose function is largely unknown, has been reported to be hypermethylated in gastric cancer.…”