Protein phosphatase 1 regulatory subunit 12A is an enzyme that in humans is encoded by the PPP1R12Agene.
Myosin phosphatase target subunit 1, which is also called the myosin-binding subunit of myosin phosphatase, is one of the subunits of myosin phosphatase. Myosin phosphatase regulates the interaction of actin and myosin downstream of the guanosine triphosphatase Rho. The small guanosine triphosphatase Rho is implicated in myosin light chain (MLC) phosphorylation, which results in contraction of smooth muscle  and interaction of actin and myosin in nonmuscle cells. The guanosine triphosphate (GTP)-bound, active form of RhoA (GTP.RhoA) specifically interacted with the myosin-binding subunit (MBS) of myosin phosphatase, which regulates the extent of phosphorylation of MLC. Rho-associated kinase (Rho-kinase), which is activated by GTP. RhoA, phosphorylated MBS and consequently inactivated myosin phosphatase. Overexpression of RhoA or activated RhoA in NIH 3T3 cells increased phosphorylation of MBS and MLC. Thus, Rho appears to inhibit myosin phosphatase through the action of Rho-kinase.
^Takahashi N, Ito M, Tanaka J, Nakano T, Kaibuchi K, Odai H, Takemura K (Nov 1997). "Localization of the gene coding for myosin phosphatase, target subunit 1 (MYPT1) to human chromosome 12q15-q21". Genomics. 44 (1): 150–2. doi:10.1006/geno.1997.4859. PMID9286714.
Surks HK, Mochizuki N, Kasai Y, et al. (1999). "Regulation of myosin phosphatase by a specific interaction with cGMP- dependent protein kinase Ialpha.". Science. 286 (5444): 1583–7. doi:10.1126/science.286.5444.1583. PMID10567269.
Feng J, Ito M, Ichikawa K, et al. (2000). "Inhibitory phosphorylation site for Rho-associated kinase on smooth muscle myosin phosphatase.". J. Biol. Chem. 274 (52): 37385–90. doi:10.1074/jbc.274.52.37385. PMID10601309.
Arimura T, Suematsu N, Zhou YB, et al. (2001). "Identification, characterization, and functional analysis of heart-specific myosin light chain phosphatase small subunit.". J. Biol. Chem. 276 (9): 6073–82. doi:10.1074/jbc.M008566200. PMID11067852.
Sebbagh M, Renvoizé C, Hamelin J, et al. (2001). "Caspase-3-mediated cleavage of ROCK I induces MLC phosphorylation and apoptotic membrane blebbing.". Nat. Cell Biol. 3 (4): 346–52. doi:10.1038/35070019. PMID11283607.
Murányi A, Zhang R, Liu F, et al. (2001). "Myotonic dystrophy protein kinase phosphorylates the myosin phosphatase targeting subunit and inhibits myosin phosphatase activity.". FEBS Lett. 493 (2-3): 80–4. doi:10.1016/S0014-5793(01)02283-9. PMID11287000.
Velasco G, Armstrong C, Morrice N, et al. (2002). "Phosphorylation of the regulatory subunit of smooth muscle protein phosphatase 1M at Thr850 induces its dissociation from myosin.". FEBS Lett. 527 (1-3): 101–4. doi:10.1016/S0014-5793(02)03175-7. PMID12220642.
Seko T, Ito M, Kureishi Y, et al. (2003). "Activation of RhoA and inhibition of myosin phosphatase as important components in hypertension in vascular smooth muscle.". Circ. Res. 92 (4): 411–8. doi:10.1161/01.RES.0000059987.90200.44. PMID12600888.