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_5 label "Selventa" provenance.
_4 value "5. Myosin (de)phosphorylation and muscle contraction The contractile function of actomyosin culminates in muscle tissue. Phosphorylation of the myosin regulatory light chains is sufficient to trigger contraction in smooth muscle (192). This phosphorylation is promoted by raising the concentration of Ca2+, which activates MLCK. The Ca2+-independent net increase in phosphorylation of the regulatory light chains induced by Rho-kinase (139), ILK (264), ZIPK (264), and ZIPK-like kinase (55, 231) sensitizes muscles to Ca2+. Muscle contractility is also influenced by variations in the composition of myosin phosphatase. Thus the sensitivity of vascular smooth muscles to regulation by nitric oxide via the activation of cGMPdependent protein kinase 1-alpha depends on the presence of leucine zippers in the splice variants of the large and small Mypt that are expressed in this tissue (339). In chicken gizzard, a developmental switch between leucine zipperpositive and -negative Mypts correlates with the loss of cGMP-mediated myosin relaxation at hatching (203). Other forms of splice variance of the Mypt1-encoding gene have also been implicated in the developmental regulation of muscle contractility (108). The importance of the enzymes that control the contractility of smooth muscles in arteries (193), airways (182), and corpora carvenosa (381) makes them potential targets in the treatment of cardiac and cerebral vascular spasms, asthma, and erectile dysfunction. In striated muscle, contraction is triggered by membrane depolarization. Even though phosphorylation of the myosin regulatory light chain is not required for contraction, it does positively affect the speed and force of contraction (346). Thus a gradient of myosin regulatory light chain phosphorylation correlates with the pattern of cardiac contraction (99). The role of the Mypt2-based myosin phosphatase in the contraction of striated muscle has been poorly studied. C. Scd5-Associated PP1 Fungi lack Mypt or Neurabin homologs, yet in budding yeast PP1 has also been implicated in the organization of cortical actin. Thus, after shifting of the temperature- sensitive PP1 mutant glc7-10 to a restrictive temperature, the actin ring at the bud neck disappeared, actin cables became rare, and actin no longer showed its typical polarized localization (16). This mutant was also de- ficient in vacuolar fusion and in secretory and endocytotic vesicular transport (292). Strikingly similar phenotypes were observed after the functional disruption of Scd5, Rvs167, or Sla2 (32, 59, 167, 259, 277). Scd5 has been identified as a PP1-binding protein in various screens (173, 372, 374), and recently, it was found that disruption of the RVXF motif of Scd5 that mediates the interaction with PP1 severely disturbed endocytosis and actin organization (78). Rvs167 and Sla2 interact physically and genetically with Scd5 (32, 59, 167, 259). Also, mutation of either Rvs167 or Sla2, like that of PP1, compromised the integrity of the cell wall at high temperatures, presumably because of a disruption in the transport of vesicles with cargoes required for the construction of the cell wall (16, 59, 259). Collectively, the available data indicate that PP1, Scd5, Rvs167, and Sla2 function together in a signaling pathway that regulates vesicular transport and the polarized distribution of actin patches. Possibly, Scd5 targets PP1 to actin patches and vesicles. Potential substrates of Scd5-associated PP1 include the phosphoproteins Sla2, Sla1, and Pan1. The latter two proteins have both been found to interact with PP1 in yeast two-hybrid screens (372, 374) and to be components of a complex involved in actin organization, endocytosis, and cell wall morphogenesis (357). Because homologs of various proteins introduced in this section have been identified in animals, where they have also been implicated in actin organization and endocytosis (167), it is tempting to speculate..." provenance.
_4 wasQuotedFrom 14715909 provenance.
assertion hadPrimarySource 14715909 provenance.
large_corpus.bel title "BEL Framework Large Corpus Document" provenance.
large_corpus.bel description "Approximately 61,000 statements." provenance.
assertion wasDerivedFrom large_corpus.bel provenance.
assertion wasDerivedFrom _4 provenance.
large_corpus.bel authoredBy _5 provenance.
large_corpus.bel version "1.4" provenance.