Protein Phosphatase 1 Regulatory Subunit 14A (PPP1R14A) belongs to the PP1 inhibitor family. PPP1R14A is mapped to chromosome 19q13.13-q13.2. PPP1R14A binds directly to protein kinase C and casein kinase I. Meantime, PPP1R14A is a phosphorylation-dependent inhibitor of smooth muscle myosin phosphatase. PPP1R14A is the inhibitor of PPP1CA. When phosphorylated, PPP1R14A has over 1000-fold higher inhibitory activity, creating a molecular switch for regulating the phosphorylation status of PPP1CA substrates and smooth muscle contraction. In addition, inhibition of PPP1R14A also enhances contraction of smooth muscle in the absence of increment of intracellular Ca2+ concentration.