| First Author | Wang X | Year | 2019 |
| Journal | J Biol Chem | Volume | 294 |
| Issue | 36 | Pages | 13280-13291 |
| PubMed ID | 31315927 | Mgi Jnum | J:281339 |
| Mgi Id | MGI:6369207 | Doi | 10.1074/jbc.RA118.006075 |
| Citation | Wang X, et al. (2019) TIMAP inhibits endothelial myosin light chain phosphatase by competing with MYPT1 for the catalytic protein phosphatase 1 subunit PP1cbeta. J Biol Chem 294(36):13280-13291 |
| abstractText | Transforming growth factor-beta membrane associated protein (TIMAP) is an endothelial cell (EC)-predominant PP1 regulatory subunit and a member of the myosin phosphatase target (MYPT) protein family. The MYPTs preferentially bind the catalytic protein phosphatase 1 subunit PP1cbeta, forming myosin phosphatase holoenzymes. We investigated whether TIMAP/PP1cbeta could also function as a myosin phosphatase. Endogenous PP1cbeta, myosin light chain 2 (MLC2), and myosin IIA heavy chain coimmunoprecipitated from EC lysates with endogenous TIMAP, and endogenous MLC2 colocalized with TIMAP in EC projections. Purified recombinant GST-TIMAP interacted directly with purified recombinant His-MLC2. However, TIMAP overexpression in EC enhanced MLC2 phosphorylation, an effect not observed with a TIMAP mutant that does not bind PP1cbeta. Conversely, MLC2 phosphorylation was reduced in lung lysates from TIMAP-deficient mice and upon silencing of endogenous TIMAP expression in ECs. Ectopically expressed TIMAP slowed the rate of MLC2 dephosphorylation, an effect requiring TIMAP-PP1cbeta interaction. The association of MYPT1 with PP1cbeta was profoundly reduced in the presence of excess TIMAP, leading to proteasomal MYPT1 degradation. In the absence of TIMAP, MYPT1-associated PP1cbeta readily bound immobilized microcystin-LR, an active-site inhibitor of PP1c. By contrast, TIMAP-associated PP1cbeta did not interact with microcystin-LR, indicating that the active site of PP1cbeta is blocked when it is bound to TIMAP. Thus, TIMAP inhibits myosin phosphatase activity in ECs by competing with MYPT1 for PP1cbeta and blocking the PP1cbeta active site. |
