Phos-tag-based analysis of myosin regulatory light chain phosphorylation in human uterine myocytes

Yu-Ping-Feng Formula Ameliorates Alveolar-Capillary Barrier Injury Induced by Exhausted-Exercise via Regulation of Cytoskeleton

Background: Yu-ping-feng powder (YPF) is a compound traditional Chinese medicine extensively used in China for respiratory diseases. However, the role of YPF in alveolar-capillary barrier dysfunction remains unknown. This study aimed to explore the effect and potential mechanism of YPF on alveolar-capillary barrier injury induced by exhausted exercise.

Methods: Male Sprague–Dawley rats were used to establish an exhausted-exercise model by using a motorized rodent treadmill. YPF at doses of 2.18 g/kg was administrated by gavage before exercise training for 10 consecutive days. Food intake-weight/body weight, blood gas analysis, lung water percent content, BALF protein concentration, morphological observation, quantitative proteomics, real-time PCR, and Western blot were performed. A rat pulmonary microvascular endothelial cell line (PMVEC) subjected to hypoxia was applied for assessing the related mechanism.

Results: YPF attenuated the decrease of food intake weight/body weight, improved lung swelling and hemorrhage, alleviated the increase of lung water percent content and BALF protein concentration, and inhibited the impairment of lung morphology. In addition, YPF increased the expression of claudin 3, claudin 18, occludin, VE-cadherin, and β-catenin, attenuated the epithelial and endothelial hyperpermeability in vivo and/or in vitro, and the stress fiber formation in PMVECs after hypoxia. Quantitative proteomics discovered that the effect of YPF implicated the Siah2-ubiquitin-proteasomal pathway, Gng12-PAK1-MLCK, and RhoA/ROCK, which was further confirmed by Western blot. Data are available via ProteomeXchange with identifier PXD032737.

Conclusion: YPF ameliorated alveolar-capillary barrier injury induced by exhausted exercise, which is accounted for at least partly by the regulation of cytoskeleton.

The Evolution of Duplicated Genes of the Cpi-17/Phi-1 (ppp1r14) Family of Protein Phosphatase 1 Inhibitors in Teleosts

The Cpi-17 (ppp1r14) gene family is an evolutionarily conserved, vertebrate specific group of protein phosphatase 1 (PP1) inhibitors. When phosphorylated, Cpi-17 is a potent inhibitor of myosin phosphatase (MP), a holoenzyme complex of the regulatory subunit Mypt1 and the catalytic subunit PP1. Myosin phosphatase dephosphorylates the regulatory myosin light chain (Mlc2) and promotes actomyosin relaxation, which in turn, regulates numerous cellular processes including smooth muscle contraction, cytokinesis, cell motility, and tumor cell invasion. We analyzed zebrafish homologs of the Cpi-17 family, to better understand the mechanisms of myosin phosphatase regulation. We found single homologs of both Kepi (ppp1r14c) and Gbpi (ppp1r14d) in silico, but we detected no expression of these genes during early embryonic development. Cpi-17 (ppp1r14a) and Phi-1 (ppp1r14b) each had two duplicate paralogs, (ppp1r14aa and ppp1r14ab) and (ppp1r14ba and ppp1r14bb), which were each expressed during early development. The spatial expression pattern of these genes has diverged, with ppp1r14aa and ppp1r14bb expressed primarily in smooth muscle and skeletal muscle, respectively, while ppp1r14ab and ppp1r14ba are primarily expressed in neural tissue. We observed that, in in vitro and heterologous cellular systems, the Cpi-17 paralogs both acted as potent myosin phosphatase inhibitors, and were indistinguishable from one another. In contrast, the two Phi-1 paralogs displayed weak myosin phosphatase inhibitory activity in vitro, and did not alter myosin phosphorylation in cells. Through deletion and chimeric analysis, we identified that the difference in specificity for myosin phosphatase between Cpi-17 and Phi-1 was encoded by the highly conserved PHIN (phosphatase holoenzyme inhibitory) domain, and not the more divergent N- and C- termini. We also showed that either Cpi-17 paralog can rescue the knockdown phenotype, but neither Phi-1 paralog could do so. Thus, we provide new evidence about the biochemical and developmental distinctions of the zebrafish Cpi-17 protein family.

Clinically relevant concentration of sevoflurane suppresses cervical cancer growth and migration through targeting multiple oncogenic pathways

The biological effects of sevoflurane, a volatile anesthetics, on cancer cells seem to be contradictory and are not fully understood. While some studies demonstrate that sevoflurane promotes tumor growth, other studies report that sevoflurane displays anti-cancer activities. In this work, we systematically investigated the effects of sevoflurane at clinically relevant dose on the multiple biological aspects of cervical cancer cells and analyzed the underlying mechanism. Using a panel of cell lines, we found that sevoflurane significantly inhibited proliferation and migration of cervical cancer cells regardless of cellular origin and genetic background. In contrast, sevoflurane did not affect cervical cancer survival. Additionally, sevoflurane significantly enhanced chemosensitivity of cervical cancer cells. Mechanistically, we show that sevoflurane inhibits Ras and RhoA GTPase activities, leading to the blockade of their downstream signaling pathways, such as Ras/Erk/Akt and Rho/MYPT1/MLC. The rescue studies using Rho activator calpeptin or constitutively active Ras further confirm that Ras and RhoA are the targets of sevoflurane in cervical cancer. Interestingly, we found that the anti-proliferative effect of sevoflurane was via targeting Ras whereas the anti-migratory effect of sevoflurane was mediated via targeting RhoA. Our data clearly demonstrates the anti-cancer effects of sevoflurane. These findings provide preclinical evidence into the potential mechanisms by which sevoflurane may negatively affect cervical cancer growth and metastasis.

Differential Regulation of Myosin Regulatory Light Chain Phosphorylation by Protein Kinase C Isozymes in Human Uterine Myocytes

BACKGROUND

Preterm birth is the most common cause of neonatal morbidity and mortality and a common precedent to lifelong disability. Current treatment has minimal efficacy.

OBJECTIVE

We assessed the role of isozymes of the protein kinase C (PKC) family in regulating the phosphorylation of myosin regulatory light chains (RLCs), which regulate uterine contractility. We also explored the mechanisms through which these isozymes function.

STUDY DESIGN

We used a previously characterized and validated quantitative in-cell Western (ICW) assay to measure site-specific phosphorylations on myosin RLC and CPI-17. Cultures of human uterine myocytes (hUM) were treated with the potent contractile stimulant oxytocin to induce uterine contractility or a pharmacological mimic of diacyl-glycerol to stimulate the conventional and novel isozymes of the PKC family. Combinations of isozyme-selective inhibitors were used to determine the effects of the conventional and novel classes of isozymes.

RESULTS

Stimulation of PKC using phospho-dibutyrate caused immediate, concentration-dependent inhibition of uterine activity ex vivo. Using the ICW assay with hUM, the oxytocin-stimulated increase in the pro-contractile phosphorylations of myosin RLCs at serine¹⁹ and threonine¹⁸ was completely inhibited by prior treatment with phorbol-12-myristate-13-acetate, which stimulates both convention and novel classes of isozymes. Our results suggest that the conventional class of isozymes cause a reduction in phosphorylations at serine¹⁹ and threonine¹⁸ by reducing activity of myosin light chain kinase. The novel class of isozymes has 2 mechanisms of action: the first is activation of CPI-17 through phosphorylation at threonine³⁸, which results in reduced activity of myosin light chain phosphatase and increased levels of activated myosin RLC; the second is increased phosphorylation of the N-terminal region of myosin RLC.

CONCLUSIONS

Specific agonists for the conventional isozymes or inhibitors of the novel isozymes of the PKC family could be useful pharmacological agents for regulation of uterine activity.

Alternative splicing of (ppp1r12a/mypt1) in zebrafish produces a novel myosin phosphatase targeting subunit

Myosin phosphatase is an evolutionarily conserved regulator of actomyosin contractility, comprised of a regulatory subunit (Mypt1), and a catalytic subunit (PP1). Zebrafish has become an ideal model organism for the study of the genetic and cell physiological role of the myosin phosphatase in morphogenesis and embryonic development. We identified and characterized a novel splice variant of Mypt1 (ppp1r12a-tv202) from zebrafish, which is widely expressed during early embryonic development. Importantly, mutant alleles and antisense morpholinos that have been used to demonstrate the important role of Mypt1 in early development, not only disrupt the longer splice variants, but also tv202. The protein product of ppp1r12a-tv202 (Mypt1-202) contains the PP1-binding N-terminus, but lacks the regulatory C-terminus, which contains two highly conserved inhibitory phosphorylation sites. We observed that the protein product of tv202 assembled a constitutively active myosin phosphatase uninhibited by kinases such as Zipk. Thus, we propose that Mypt1-202 plays an important role in maintaining baseline Mlc2 dephosphorylation and actomyosin relaxation during early zebrafish development.

Phosphorylation of the regulatory light chain of myosin in striated muscle: methodological perspectives

Phosphorylation of the regulatory light chain (RLC) of myosin modulates cellular functions such as muscle contraction, mitosis, and cytokinesis. Phosphorylation defects are implicated in a number of diseases. Here we focus on striated muscle where changes in RLC phosphorylation relate to diseases such as hypertrophic cardiomyopathy and muscular dystrophy, or age-related changes. RLC phosphorylation in smooth muscle and non-muscle cells are covered briefly where relevant. There is much scientific interest in controlling the phosphorylation levels of RLC in vivo and in vitro in order to understand its physiological function in striated muscles. A summary of available and emerging in vivo and in vitro methods is presented. The physiological role of RLC phosphorylation and novel pathways are discussed to highlight the differences between muscle types and to gain insights into disease processes.

Analysis of phosphorylation of the myosin-targeting subunit of myosin light chain phosphatase by Phos-tag SDS-PAGE

Phosphorylation of the myosin-targeting subunit 1 of myosin light chain phosphatase (MYPT1) plays an important role in the regulation of smooth muscle contraction, and several sites of phosphorylation by different protein Ser/Thr kinases have been identified. Furthermore, in some instances, phosphorylation at specific sites affects phosphorylation at neighboring sites, with functional consequences. Characterization of the complex phosphorylation of MYPT1 in tissue samples at rest and in response to contractile and relaxant stimuli is, therefore, challenging. We have exploited Phos-tag SDS-PAGE in combination with Western blotting using antibodies to MYPT1, including phosphospecific antibodies, to separate multiple phosphorylated MYPT1 species and quantify MYPT1 phosphorylation stoichiometry using purified, full-length recombinant MYPT1 phosphorylated by Rho-associated coiled-coil kinase (ROCK) and cAMP-dependent protein kinase (PKA). This approach confirmed that phosphorylation of MYPT1 by ROCK occurs at Thr(697)and Thr(855), PKA phosphorylates these two sites and the neighboring Ser(696)and Ser(854), and prior phosphorylation at Thr(697)and Thr(855)by ROCK precludes phosphorylation at Ser(696)and Ser(854)by PKA. Furthermore, phosphorylation at Thr(697)and Thr(855)by ROCK exposes two other sites of phosphorylation by PKA. Treatment of Triton-skinned rat caudal arterial smooth muscle strips with the membrane-impermeant phosphatase inhibitor microcystin or treatment of intact tissue with the membrane-permeant phosphatase inhibitor calyculin A induced slow, sustained contractions that correlated with phosphorylation of MYPT1 at 7 to ≥10 sites. Phos-tag SDS-PAGE thus provides a suitable and convenient method for analysis of the complex, multisite MYPT1 phosphorylation events involved in the regulation of myosin light chain phosphatase activity and smooth muscle contraction.

The Cutting Edge of Affinity Electrophoresis Technology

Affinity electrophoresis is an important technique that is widely used to separate and analyze biomolecules in the fields of biology and medicine. Both quantitative and qualitative information can be gained through affinity electrophoresis. Affinity electrophoresis can be applied through a variety of strategies, such as mobility shift electrophoresis, charge shift electrophoresis or capillary affinity electrophoresis. These strategies are based on changes in the electrophoretic patterns of biological macromolecules that result from interactions or complex-formation processes that induce changes in the size or total charge of the molecules. Nucleic acid fragments can be characterized through their affinity to other molecules, for example transcriptional factor proteins. Hydrophobic membrane proteins can be identified by means of a shift in the mobility induced by a charged detergent. The various strategies have also been used in the estimation of association/disassociation constants. Some of these strategies have similarities to affinity chromatography, in that they use a probe or ligand immobilized on a supported matrix for electrophoresis. Such methods have recently contributed to profiling of major posttranslational modifications of proteins, such as glycosylation or phosphorylation. Here, we describe advances in analytical techniques involving affinity electrophoresis that have appeared during the last five years.

Neutral Phosphate-Affinity SDS-PAGE system for profiling of protein phosphorylation

In this chapter, we describe a standard protocol for phosphate-affinity SDS-PAGE that uses a dizinc(II) complex of the phosphate-binding molecule Phos-tag in conjunction with a neutral-pH gel system (Zn(2+-)Phos-tag SDS-PAGE) to detect shifts in the mobilities of phosphoproteins. A previous protocol for affinity electrophoresis that uses polyacrylamide-bound Mn(2+)-Phos-tag and Laemmli's buffer system under conditions of alkaline pH has limitations in separating certain phosphoproteins. The current protocol provides major improvements in separation and detection of various phosphorylated protein species. We here introduce two neutral-pH gel systems buffered with Bis-Tris-HCl and Tris-AcOH, respectively, for Zn(2+)-Phos-tag SDS-PAGE, and we also discuss their characteristics on the basis of comparative studies on phosphorylation profiling of proteins with a wide range of molecular masses. Each analytical procedure, from the beginning of gel preparation to the end of electrophoresis, requires 2.5-5 h with either buffer system.

Advances in Phos-tag-based methodologies for separation and detection of the phosphoproteome

This review article describes analytical techniques based on the phosphate-binding tag molecule "Phos-tag", which is an alkoxide-bridged dinuclear metal complex with 1,3-bis(pyridin-2-ylmethylamino)propan-2-olate, for studying the protein phosphorylome. The dinuclear zinc(II) complex forms a stable 1:1 complex with a phosphate monoester dianion in an aqueous solution under conditions of neutral pH. By using a series of functional Phos-tag derivatives, our group has developed novel techniques that are useful in studies on kinomics and phosphoproteomics. Among the derivatives, a series of biotinylated Phos-tag derivatives have been used as molecular tools in applications such as Western blotting for comprehensive detection of phosphorylated proteins and in highly sensitive peptide microarray-based techniques for the detection of kinase activities in biological samples. The review also gives an outline of phosphate affinity electrophoresis, in which immobilized Phos-tag molecules in a general polyacrylamide gel are used to separate proteins and detect differences in their phosphorylation status. This technique permits quantitative analyses of multiple phosphorylation statuses of individual cellular proteins and their time-dependent changes. Conventional mass spectrometry-based shotgun techniques used in phosphoproteomics detect the phosphorylation modification of proteins in peptide fragments, whereas the Phos-tag electrophoresis technique permits the direct analysis of the phosphorylation status of full-length proteins. The technique therefore provides a greater understanding of the detailed properties of particular proteins involved in specific physiological and pathological events. This article is part of a Special Issue entitled: Medical Proteomics.

Toward a systems-level view of dynamic phosphorylation networks

To better understand how cells sense and respond to their environment, it is important to understand the organization and regulation of the phosphorylation networks that underlie most cellular signal transduction pathways. These networks, which are composed of protein kinases, protein phosphatases and their respective cellular targets, are highly dynamic. Importantly, to achieve signaling specificity, phosphorylation networks must be regulated at several levels, including at the level of protein expression, substrate recognition, and spatiotemporal modulation of enzymatic activity. Here, we briefly summarize some of the traditional methods used to study the phosphorylation status of cellular proteins before focusing our attention on several recent technological advances, such as protein microarrays, quantitative mass spectrometry, and genetically-targetable fluorescent biosensors, that are offering new insights into the organization and regulation of cellular phosphorylation networks. Together, these approaches promise to lead to a systems-level view of dynamic phosphorylation networks.

Oxytocin: its mechanism of action and receptor signalling in the myometrium

Oxytocin is a nonapeptide hormone that has a central role in the regulation of parturition and lactation. In this review, we address oxytocin receptor (OTR) signalling and its role in the myometrium during pregnancy and in labour. The OTR belongs to the rhodopsin-type (Class 1) of the G-protein coupled receptor superfamily and is regulated by changes in receptor expression, receptor desensitisation and local changes in oxytocin concentration. Receptor activation triggers a number of signalling events to stimulate contraction, primarily by elevating intracellular calcium (Ca(2+) ). This includes inositol-tris-phosphate-mediated store calcium release, store-operated Ca(2+) entry and voltage-operated Ca(2+) entry. We discuss each mechanism in turn and also discuss Ca(2+) -independent mechanisms such as Ca(2+) sensitisation. Because oxytocin induces contraction in the myometrium, both the activation and the inhibition of its receptor have long been targets in the management of dysfunctional and preterm labours, respectively. We discuss current and novel OTR agonists and antagonists and their use and potential benefit in obstetric practice. In this regard, we highlight three clinical scenarios: dysfunctional labour, postpartum haemorrhage and preterm birth.

Rho-kinase mediates diphosphorylation of myosin regulatory light chain in cultured uterine, but not vascular smooth muscle cells

Phosphorylation of myosin regulatory light chain (RLC) triggers contraction in smooth muscle myocytes. Dephosphorylation of phosphorylated RLC (pRLC) is mediated by myosin RLC phosphatase (MLCP), which is negatively regulated by rho-associated kinase (ROK). We have compared basal and stimulated concentrations of pRLC in myocytes from human coronary artery (hVM), which has a tonic contractile pattern to myocytes from human uterus (hUM), which has a phasic contractile pattern. Our studies reveal fundamental differences between hVM and hUM regarding the mechanisms regulating phosphorylation RLC. Whereas hVM responded to stimulation by phosphorylation of RLC at S19, hUM responded by forming diphosphorylated RLC (at T18 and S19; ppRLC), which, compared to pRLC, causes two to threefold greater activation of myosin ATPase that provides energy to power the contraction. Importantly, the conversion of pRLC to ppRLC is mediated by ROK. In hUM, MLCP has high activity for ppRLC and this is inhibited by ROK through phosphorylation of the substrate targeting subunit (MYPT1) at T853. Inhibitors of ROK significantly reduce contractility in both hVM and hUM. We demonstrated that inhibition of ppRLC in phasic myocytes (hUM) is 100-fold more sensitive to ROK inhibitors than is pRLC in tonic myocytes (hVM). We speculate that these differences in phosphorylation of RLC might reflect evolution of different contractile patterns to perform distinct physiological functions. Furthermore, our data suggest that low concentrations of ROK inhibitors might inhibit uterine contractions with minimal effects on vascular tone, thus posing a novel strategy for prevention or treatment of conditions such as preterm birth.

Protein phosphatase 1 β paralogs encode the zebrafish myosin phosphatase catalytic subunit

Background

The myosin phosphatase is a highly conserved regulator of actomyosin contractility. Zebrafish has emerged as an ideal model system to study the invivo role of myosin phosphatase in controlling cell contractility, cell movement and epithelial biology. Most work in zebrafish has focused on the regulatory subunit of the myosin phosphatase called Mypt1. In this work, we examined the critical role of Protein Phosphatase 1, PP1, the catalytic subunit of the myosin phosphatase.

Methodology/Principal Findings

We observed that in zebrafish two paralogous genes encoding PP1β, called ppp1cba and ppp1cbb, are both broadly expressed during early development. Furthermore, we found that both gene products interact with Mypt1 and assemble an active myosin phosphatase complex. In addition, expression of this complex results in dephosphorylation of the myosin regulatory light chain and large scale rearrangements of the actin cytoskeleton. Morpholino knock-down of ppp1cba and ppp1cbb results in severe defects in morphogenetic cell movements during gastrulation through loss of myosin phosphatase function.

Conclusions/Significance

Our work demonstrates that zebrafish have two genes encoding PP1β, both of which can interact with Mypt1 and assemble an active myosin phosphatase. In addition, both genes are required for convergence and extension during gastrulation and correct dosage of the protein products is required.

Nonmuscle myosin IIB links cytoskeleton to IRE1α signaling during ER stress

Here we identify and characterize a cytoskeletal myosin protein required for IRE1α oligomerization, activation, and signaling. Proteomic screening identified nonmuscle myosin heavy chain IIB (NMHCIIB), a subunit of nonmuscle myosin IIB (NMIIB), as an ER stress-dependent interacting protein specific to IRE1α. Loss of NMIIB compromises XBP1s and UPR target gene expression with no effect on the PERK pathway. Mechanistically, NMIIB is required for IRE1α aggregation and foci formation under ER stress. The NMIIB-mediated effect on IRE1α signaling is in part dependent on the phosphorylation of myosin regulatory light chain and the actomyosin contractility of NMIIB. Biologically, the function of NMIIB in ER stress response is conserved as both mammalian cells and C. elegans lacking NMIIB exhibit hypersensitivity to ER stress. Thus, optimal IRE1α activation and signaling require concerted coordination between the ER and cytoskeleton.

The uterine myocyte as a target for prevention of preterm birth

Preterm birth (PTB) remains the most common cause of neonatal morbidity and mortality as well as long-term disability. Current strategies to prevent or arrest spontaneous preterm labor (SPTL) have limited success. For almost three decades, there have been no novel pharmacological agents used clinically to address this important obstetrical complication. In this review, we focus on the uterine myocyte as a target for prevention of spontaneous PTB. After presenting an overview of intracellular signaling pathways that are important in regulation of smooth muscle contractility, we discuss previous and current pharmacological approaches to manage SPTL. We also present recent evidence from our own laboratories suggesting a potentially novel and uterine-specific approach to maintain or impose uterine relaxation. Finally, we briefly discuss extrinsic systems that might affect uterine activity and reinforce the concept that SPTL represents a syndrome that is the end result of a variety of pathophysiologic etiologies leading to PTB. We conclude by emphasizing the need for much more research to provide sufficient understanding of the mechanisms of SPTL and to make inroads towards reducing the incidence and adverse consequences of this common and serious syndrome.

Phos-tag SDS-PAGE systems for phosphorylation profiling of proteins with a wide range of molecular masses under neutral pH conditions

We have previously reported a neutral-pH gel system buffered with Bis-Tris hydrochloride (Bis-Tris-HCl) in Zn(2+)-Phos-tag SDS-PAGE for advanced profiling of phosphoproteins with molecular masses of 10-200 kDa. In the current work, we describe characteristics of two neutral-pH gel systems, Bis-Tris-HCl and Tris-acetic acid (Tris-AcOH), based on comparative studies of the separation of a wide range of proteins with molecular masses from 10 to 350 kDa. For 10-200 kDa cellular proteins, the Bis-Tris-HCl system showed a higher resolving power in a 2-D fluorescence DIGE analysis of certain phosphoproteins, e.g. histone H3 (15 kDa) and elongation factor 2 (95 kDa). Furthermore, there was a large difference in the 1-D migration patterns of phosphorylated species of extracellular signal-regulated kinases 1 and 2 (ERK1/2, 44/42 kDa), which arise from changes in the phosphorylation status of the Thr-202 and Tyr-204, in the two buffer systems at the same concentration of Zn(2+)-Phos-tag. In contrast, shifts in the mobility of various phosphorylated species of a high-molecular-mass protein, ataxia telangiectasia-mutated kinase (ATM, 350 kDa), could only be detected in the Tris-AcOH system with a 3% w/v polyacrylamide gel strengthened with 0.5% w/v agarose.