Dynamic changes in expression of myosin phosphatase in a model of portal hypertension

Abstract

Myosin phosphatase is a target for signaling pathways that modulate calcium sensitivity of force production in smooth muscle. Myosin phosphatase targeting subunit 1 (MYPT1) isoforms are generated by cassette-type alternative splicing of exons in the central and 3' portion of the transcript. Exclusion of the 3' alternative exon, coding for the leucine zipper (LZ)-positive MYPT1 isoform, is associated with the ability to desensitize to calcium (relax) in response to NO/cGMP-dependent signaling. We examined expression of MYPT1 isoforms and smooth muscle phenotype in normal rat vessels and in a prehepatic model of portal hypertension characterized by arteriolar dilation. The large capacitance vessels, aorta, pulmonary artery, and inferior vena cava expressed predominantly the 3' exon-out/LZ-positive MYPT1 isoform. The first-order mesenteric resistance artery (MA1) and portal vein (PV) expressed severalfold higher levels of MYPT1 with predominance of the 3' exon-included/LZ-negative isoform. There was minor variation in the presence of the MYPT1 central alternative exons. Myosin heavy and light chain splice variants in part cosegregated with MYPT1 isoforms. In response to portal hypertension induced by PV ligature, abundance of MYPT1 in PV and MA1 was significantly reduced and switched to the LZ-positive isoform. These changes were evident within 1 day of PV ligature and were maintained for up to 10 days before reverting to control values at day 14. Alteration of MYPT1 expression was part of a complex change in protein expression that can be generalized as a modulation from a phasic (fast) to a tonic (slow) contractile phenotype. Implications of vascular smooth muscle phenotypic diversity and reversible phenotypic modulation in portal hypertension with regards to regulation of blood flow are discussed.

The Role of Rho Kinase and Extracellular Regulated Kinase-Mitogen-Activated Protein Kinase in α2-Adrenoceptor-Mediated Vasoconstriction in the Porcine Palmar Lateral Vein

“…3 and 4). This double band represents different isoforms of MYPT1 as identified by others in vascular tissue (Payne et al, 2004). In segments of porcine palmar lateral vein, contraction with 10 M UK14304 was associated with an increase in the level of MYPT1 phosphorylation at Thr696 (Figs.…”

Calcium Cycling in Synthetic and Contractile Phasic or Tonic Vascular Smooth Muscle Cells

“…This frequency modulation could result from PKA phosphorylation of RyR, PLB and contractile proteins, as it has been established for cardiomyocytes [82][83][84]. Micro-vascular dysfunction, defined as the intrinsic changes in VSMCs contractility (such as reduction of frequency and shortening velocity of phasic contractions), observed in the context of cardiovascular [85,86], may be related to reduced PKA phosphorylation of Ca 2+ handling and contractile proteins, as observed in failing cardiomyocytes [82].…”

Competition of PTB with TIA proteins for binding to a U-rich cis-element determines tissue-specific splicing of the myosin phosphatase targeting subunit 1

“…MP is the primary effector of smooth muscle relaxation and MYPT1 is a key target of signals that regulate smooth muscle tone (for review, see Ito et al 2004). The regulated expression of MP subunits has been proposed as a key determinant of the diversity in smooth muscle contractile properties and in signaling responses in development and disease (Khatri et al 2001;Payne et al 2004).…”