Phosphorylation of the heat shock-related protein, HSP20, mediates cyclic nucleotide-dependent relaxation

Role of Small Heat Shock Proteins in the Remodeling of Actin Microfilaments

Small heat shock proteins (sHsps) play an important role in the maintenance of proteome stability and, particularly, in stabilization of the cytoskeleton and cell contractile apparatus. Cell exposure to different types of stress is accompanied by the translocation of sHsps onto actin filaments; therefore, it is commonly believed that the sHsps are true actin-binding proteins. Investigations of last years have shown that this assumption is incorrect. Stress-induced translocation of sHsp to actin filaments is not the result of direct interaction of these proteins with intact actin, but results from the chaperone-like activity of sHsps and their interaction with various actin-binding proteins. HspB1 and HspB5 interact with giant elastic proteins titin and filamin thus providing an integrity of the contractile apparatus and its proper localization in the cell. HspB6 binds to the universal adapter protein 14-3-3 and only indirectly affects the structure of actin filament. HspB7 interacts with filamin C and controls actin filament assembly. HspB8 forms tight complex with the universal regulatory and adapter protein Bag3 and participates in the chaperone-assisted selective autophagy (CASA) of actin-binding proteins (e.g., filamin), as well as in the actin-depending processes taking place in mitoses. Hence, the mechanisms of sHsp participation in the maintenance of the contractile apparatus and cytoskeleton are much more complicated and diverse than it has been postulated earlier and are not limited to direct interactions of sHsps with actin. The old hypothesis on the direct binding of sHsps to intact actin should be revised and further detailed investigation on the sHsp interaction with minor proteins participating in the formation and remodeling of actin filaments is required.

Heat Shock-Related Protein 20 Peptide Decreases Human Airway Constriction Downstream of β2-Adrenergic Receptor

Severe bronchospasm refractory to β-agonists is a challenging aspect of asthma therapy, and novel therapeutics are needed. β-agonist-induced airway smooth muscle (ASM) relaxation is associated with increases in the phosphorylation of the small heat shock-related protein (HSP) 20. We hypothesized that a transducible phosphopeptide mimetic of HSP20 (P20 peptide) causes relaxation of human ASM (HASM) by interacting with target(s) downstream of the β2-adrenergic receptor (β2AR) pathway. The effect of the P20 peptide on ASM contractility was determined in human and porcine ASM using a muscle bath. The effect of the P20 peptide on filamentous actin dynamics and migration was examined in intact porcine ASM and cultured primary HASM cells. The efficacy of the P20 peptide in vivo on airway hyperresponsiveness (AHR) was determined in an ovalbumin (OVA) sensitization and challenge murine model of allergic airway inflammation. P20 peptide caused dose-dependent relaxation of carbachol-precontracted ASM and blocked carbachol-induced contraction. The β2AR inhibitor, (±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI 118,551), abrogated isoproterenol but not P20 peptide-mediated relaxation. The P20 peptide decreased filamentous actin levels in intact ASM, disrupted stress fibers, and inhibited platelet-derived growth factor-induced migration of HASM cells. The P20 peptide treatment reduced methacholine-induced AHR in OVA mice without affecting the inflammatory response. These results suggest that the P20 peptide decreased airway constriction and disrupted stress fibers through regulation of the actin cytoskeleton downstream of β2AR. Thus, the P20 peptide may be a potential therapeutic for asthma refractory to β-agonists.

Molecular characterization and SNP identification in HSPB6 gene in Karan Fries (Bos taurus x Bos indicus) cattle

Heat shock proteins (HSPs) act as molecular chaperones which are preferentially transcribed in response to severe perturbations of the cellular homeostasis such as heat stress. The present study was undertaken for molecular characterization and detection of genetic polymorphisms of HSPB6 gene in 100 Karan Fries Cattle. HSPB6 gene was mapped on Bos taurus autosome 18 (BTA 18), comprising three exons and two introns. Four sets of primers for HSPB6 gene were designed using Primer3 software (version 0.4.0). For detecting single nucleotide polymorphisms (SNPs), sequence data was analyzed using BioEdit software (version 7.2). Comparative sequence analysis of HSPB6 gene showed five nucleotide polymorphisms, which included three transitions viz. g.161A > G, g.436G > A and g.2152A > G and two transversions viz. g.1743C > G and g.2417A > T compared to B. taurus (NCBI GenBank: AC_000175.1). HSPB6 gene of Karan Fries cattle exhibited a high percentage of nucleotide identity (47.0-100.0%) with the corresponding mammalian homologue. The present study indicated a high degree of genetic variability in the HSPB6 gene in the Karan Fries cattle populations.

Soluble guanylyl cyclase-activated cyclic GMP-dependent protein kinase inhibits arterial smooth muscle cell migration independent of VASP-serine 239 phosphorylation

Coronary artery disease (CAD) accounts for over half of all cardiovascular disease-related deaths. Uncontrolled arterial smooth muscle (ASM) cell migration is a major component of CAD pathogenesis and efforts aimed at attenuating its progression are clinically essential. Cyclic nucleotide signaling has long been studied for its growth-mitigating properties in the setting of CAD and other vascular disorders. Heme-containing soluble guanylyl cyclase (sGC) synthesizes cyclic guanosine monophosphate (cGMP) and maintains vascular homeostasis predominantly through cGMP-dependent protein kinase (PKG) signaling. Considering that reactive oxygen species (ROS) can interfere with appropriate sGC signaling by oxidizing the cyclase heme moiety and so are associated with several CVD pathologies, the current study was designed to test the hypothesis that heme-independent sGC activation by BAY 60-2770 (BAY60) maintains cGMP levels despite heme oxidation and inhibits ASM cell migration through phosphorylation of the PKG target and actin-binding vasodilator-stimulated phosphoprotein (VASP). First, using the heme oxidant ODQ, cGMP content was potentiated in the presence of BAY60. Using a rat model of arterial growth, BAY60 significantly reduced neointima formation and luminal narrowing compared to vehicle (VEH)-treated controls. In rat ASM cells BAY60 significantly attenuated cell migration, reduced G:F actin, and increased PKG activity and VASP Ser239 phosphorylation (pVASP·S239) compared to VEH controls. Site-directed mutagenesis was then used to generate overexpressing full-length wild type VASP (FL-VASP/WT), VASP Ser239 phosphorylation-mimetic (FL-VASP/239D) and VASP Ser239 phosphorylation-resistant (FL-VASP/239A) ASM cell mutants. Surprisingly, FL-VASP/239D negated the inhibitory effects of FL-VASP/WT and FL-VASP/239A cells on migration. Furthermore, when FL-VASP mutants were treated with BAY60, only the FL-VASP/239D group showed reduced migration compared to its VEH controls. Intriguingly, FL-VASP/239D abrogated the stimulatory effects of FL-VASP/WT and FL-VASP/239A cells on PKG activity. In turn, pharmacologic blockade of PKG in the presence of BAY60 reversed the inhibitory effect of BAY60 on naïve ASM cell migration. Taken together, we demonstrate for the first time that BAY60 inhibits ASM cell migration through cGMP/PKG/VASP signaling yet through mechanisms independent of pVASP·S239 and that FL-VASP overexpression regulates PKG activity in rat ASM cells. These findings implicate BAY60 as a potential pharmacotherapeutic agent against aberrant ASM growth disorders such as CAD and also establish a unique mechanism through which VASP controls PKG activity.

Papaverine Prevents Vasospasm by Regulation of Myosin Light Chain Phosphorylation and Actin Polymerization in Human Saphenous Vein

Objective

Papaverine is used to prevent vasospasm in human saphenous veins (HSV) during vein graft preparation prior to implantation as a bypass conduit. Papaverine is a nonspecific inhibitor of phosphodiesterases, leading to increases in both intracellular cGMP and cAMP. We hypothesized that papaverine reduces force by decreasing intracellular calcium concentrations ([Ca²⁺]_i) and myosin light chain phosphorylation, and increasing actin depolymerization via regulation of actin regulatory protein phosphorylation.

Approach and Results

HSV was equilibrated in a muscle bath, pre-treated with 1 mM papaverine followed by 5 μM norepinephrine, and force along with [Ca²⁺]_i levels were concurrently measured. Filamentous actin (F-actin) level was measured by an in vitro actin assay. Tissue was snap frozen to measure myosin light chain and actin regulatory protein phosphorylation. Pre-treatment with papaverine completely inhibited norepinephrine-induced force generation, blocked increases in [Ca²⁺]_i and led to a decrease in the phosphorylation of myosin light chain. Papaverine pre-treatment also led to increased phosphorylation of the heat shock-related protein 20 (HSPB6) and the vasodilator stimulated phosphoprotein (VASP), as well as decreased filamentous actin (F-actin) levels suggesting depolymerization of actin.

Conclusions

These results suggest that papaverine-induced force inhibition of HSV involves [Ca²⁺]_i-mediated inhibition of myosin light chain phosphorylation and actin regulatory protein phosphorylation-mediated actin depolymerization. Thus, papaverine induces sustained inhibition of contraction of HSV by the modulation of both myosin cross-bridge formation and actin cytoskeletal dynamics and is a pharmacological alternative to high pressure distention to prevent vasospasm.

Contribution of small heat shock proteins to muscle development and function

Investigations undertaken over the past years have led scientists to introduce the concept of protein quality control (PQC) systems, which are responsible for polypeptide processing. The PQC system monitors proteostasis and involves activity of different chaperones such as small heat shock proteins (sHSPs). These proteins act during normal conditions as housekeeping proteins regulating cellular processes, and during stress conditions. They also mediate the removal of toxic misfolded polypeptides and thereby prevent development of pathogenic states. It is postulated that sHSPs are involved in muscle development. They could act via modulation of myogenesis or by maintenance of the structural integrity of signaling complexes. Moreover, mutations in genes coding for sHSPs lead to pathological states affecting muscular tissue functioning. This review focuses on the question how sHSPs, still relatively poorly understood proteins, contribute to the development and function of three types of muscle tissue: skeletal, cardiac and smooth.

Newborn rat response to single vs. combined cGMP-dependent pulmonary vasodilators

Inhaled nitric oxide (NO) and other cGMP- or cAMP-dependent pulmonary vasodilators are often used in combination for the treatment of the persistent pulmonary hypertension of the newborn syndrome. There is in vitro evidence to indicate that NO downregulate the pulmonary vascular response to cGMP-dependent agonists raising concern as to whether a synergistic effect is observed when employing a combined strategy in newborns. Hypothesizing that a synergistic effect is absent, we evaluated newborn and juvenile rat pulmonary arteries to determine the individual and combined vasodilatory effect of cGMP- and cAMP-dependent agonists. In precontracted near-resistance pulmonary arteries, the addition of sildenafil reduced vasorelaxation response to NO donor S-nitroso-N-acetyl penicillamine (SNAP). A similar decrease in SNAP-induced vasodilation was observed in arteries pretreated with BAY 41-2272 (10(-9) M), a soluble guanylate cyclase stimulator cGMP, and its downstream protein kinase activator. cGMP also reduced the vasorelaxant response to the cAMP-dependent forskolin. Inhibition of endogenous vascular NO generation enhanced SNAP-induced relaxation. The present data suggest that the mechanism involved in the cGMP desensitization to other relaxant agonists involves downregulation of the small heat shock protein HSP20 and is evident in rat pulmonary and systemic vascular smooth muscle cells. In newborn rats with chronic hypoxia-induced pulmonary hypertension, the combination of sildenafil and inhaled NO resulted in a lesser reduction in pulmonary vascular resistance compared with their individual effect. These data suggest that clinical exposure to one cGMP-dependent pulmonary vasodilator may affect the response to other cGMP- or cAMP-mediated agonists.

cGMP-dependent protein kinases (cGK)

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes-prkg1 and prkg2-code for cGKs, namely, cGKI and cGKII. In mammals, two isozymes, cGKIα and cGKIβ, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxtaglomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all, signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondral bone growth. This chapter focuses on the involvement of cGKs in cardiovascular and non-cardiovascular processes including cell growth and metabolism.

Systems biology of HBOC-induced vasoconstriction

Vasoconstriction is a major adverse effect of HBOCs. The use of a single drug for attenuating HBOC-induced vasoconstriction has been tried with limited success. Since HBOC causes disruptions at multiple levels of organization in the vascular system, a systems approach is helpful to explore avenues to counteract the effects of HBOC at multiple levels by targeting multiple sites in the system. A multi-target approach is especially appropriate for HBOC-induced vasoconstriction, because HBOC disrupts the cascade of amplification by NO-cGMP signaling and protein phosphorylation, ultimately resulting in vasoconstriction. Targeting multiple steps in the cascade may alter the overall gain of amplification, thereby limiting the propagation of disruptive effects through the cascade. As a result, targeting multiple sites may accomplish a relatively high overall efficacy at submaximal drug doses. Identifying targets and doses for developing a multi-target combination HBOC regimen for oxygen therapeutics requires a detailed understanding of the systems biology and phenotypic heterogeneity of the vascular system at multiple layers of organization, which can be accomplished by successive iterations between experimental studies and mathematical modeling at multiple levels of vascular systems and organ systems. Towards this goal, this article addresses the following topics: a) NO-scavenging by HBOC, b) HBOC autoxidation-induced reactive oxygen species generation and endothelial barrier dysfunction, c) NO- cGMP signaling in vascular smooth muscle cells, d) NO and cGMP-dependent regulation of contractile filaments in vascular smooth muscle cells, e) phenotypic heterogeneity of vascular systems, f) systems biology as an approach to developing a multi-target HBOC regimen.

Cell-permeant peptide inhibitors of vasospasm and intimal hyperplasia

Outcomes from vein graft bypass are limited by graft failure, leading causes of which include intimal hyperplasia and vasospasm. Intimal hyperplasia remains the most common cause of graft failure, but no therapeutic modalities have been shown to prevent intimal hyperplasia in humans. The small heat shock proteins are a class of naturally occurring proteins in vascular smooth muscle. These proteins have an integral role in maintenance of vascular tone and in cellular defense against various stressors. Transduction domains have enabled intracellular therapeutic delivery of peptide analogs of heat shock proteins, as well as peptide inhibitors of the kinases that phosphorylate these proteins. These cell-permeant peptides have been shown to prevent vasospasm and intimal hyperplasia in vitro. Since vascular bypass using vein grafts is analogous to autologous organ transplantation, ex vivo treatment of the vein graft with cell-permeant peptide inhibitors of vasospasm and intimal hyperplasia prior to implantation provides a unique opportunity for targeted treatment of the graft to improve patency.

Cyclic nucleotide-dependent relaxation pathways in vascular smooth muscle

Vascular smooth muscle tone is controlled by a balance between the cellular signaling pathways that mediate the generation of force (vasoconstriction) and release of force (vasodilation). The initiation of force is associated with increases in intracellular calcium concentrations, activation of myosin light-chain kinase, increases in the phosphorylation of the regulatory myosin light chains, and actin-myosin crossbridge cycling. There are, however, several signaling pathways modulating Ca(2+) mobilization and Ca(2+) sensitivity of the contractile machinery that secondarily regulate the contractile response of vascular smooth muscle to receptor agonists. Among these regulatory mechanisms involved in the physiological regulation of vascular tone are the cyclic nucleotides (cAMP and cGMP), which are considered the main messengers that mediate vasodilation under physiological conditions. At least four distinct mechanisms are currently thought to be involved in the vasodilator effect of cyclic nucleotides and their dependent protein kinases: (1) the decrease in cytosolic calcium concentration ([Ca(2+)]c), (2) the hyperpolarization of the smooth muscle cell membrane potential, (3) the reduction in the sensitivity of the contractile machinery by decreasing the [Ca(2+)]c sensitivity of myosin light-chain phosphorylation, and (4) the reduction in the sensitivity of the contractile machinery by uncoupling contraction from myosin light-chain phosphorylation. This review focuses on each of these mechanisms involved in cyclic nucleotide-dependent relaxation of vascular smooth muscle under physiological conditions.

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

The emerging role of HSP20 as a multifunctional protective agent

The small heat shock proteins (sHSPs) are a highly conserved family of molecular chaperones that are ubiquitously expressed throughout nature. They are transiently upregulated in many tissue types following stressful stimuli. Recently, one member of the sHSP family, HSP20 (HspB6), has been shown to be highly effective as a protective mediator against a number of debilitating pathological conditions, including cardiac hypertrophy and Alzheimer's disease. Hsp20 is also an important modulator of vital physiological processes, such as smooth muscle relaxation and cardiac contractility. This review focuses on the molecular mechanisms employed by HSP20 that allow it to act as an innate protector in the context of cardiovascular and neurological diseases. Emerging evidence for a possible role as an anti-cancer agent is also presented.

A novel small molecule target in human airway smooth muscle for potential treatment of obstructive lung diseases: a staged high-throughput biophysical screening

Background

A newly identified mechanism of smooth muscle relaxation is the interaction between the small heat shock protein 20 (HSP20) and 14-3-3 proteins. Focusing upon this class of interactions, we describe here a novel drug target screening approach for treating airflow obstruction in asthma.

Methods

Using a high-throughput fluorescence polarization (FP) assay, we screened a library of compounds that could act as small molecule modulators of HSP20 signals. We then applied two quantitative, cell-based biophysical methods to assess the functional efficacy of these molecules and rank-ordered their abilities to relax isolated human airway smooth muscle (ASM). Scaling up to the level of an intact tissue, we confirmed in a concentration-responsive manner the potency of the cell-based hit compounds.

Results

Among 58,019 compound tested, 268 compounds caused 20% or more reduction of the polarized emission in the FP assay. A small subset of these primary screen hits, belonging to two scaffolds, caused relaxation of isolated ASM cell in vitro and attenuated active force development of intact tissue ex vivo.

Conclusions

This staged biophysical screening paradigm provides proof-of-principle for high-throughput and cost-effective discovery of new small molecule therapeutic agents for obstructive lung diseases.

Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle

Small heat shock proteins HSP27 and HSP20 have been implicated in regulation of contraction and relaxation in smooth muscle. Activation of PKC-α promotes contraction by phosphorylation of HSP27 whereas activation of PKA promotes relaxation by phosphorylation of HSP20 in colonic smooth muscle cells (CSMC). We propose that the balance between the phosphorylation states of HSP27 and HSP20 represents a molecular signaling switch for contraction and relaxation. This molecular signaling switch acts downstream on a molecular mechanical switch [tropomyosin (TM)] regulating thin-filament dynamics. We have examined the role of phosphorylation state(s) of HSP20 on HSP27-mediated thin-filament regulation in CSMC. CSMC were transfected with different HSP20 phosphomutants. These transfections had no effect on the integrity of actin cytoskeleton. Cells transfected with 16D-HSP20 (phosphomimic) exhibited inhibition of acetylcholine (ACh)-induced contraction whereas cells transfected with 16A-HSP20 (nonphosphorylatable) had no effect on ACh-induced contraction. CSMC transfected with 16D-HSP20 cDNA showed significant decreases in 1) phosphorylation of HSP27 (ser78); 2) phosphorylation of PKC-α (ser657); 3) phosphorylation of TM and CaD (ser789); 4) ACh-induced phosphorylation of myosin light chain; 5) ACh-induced association of TM with HSP27; and 6) ACh-induced dissociation of TM from caldesmon (CaD). We thus propose the crucial physiological relevance of molecular signaling switch (phosphorylation state of HSP27 and HSP20), which dictates 1) the phosphorylation states of TM and CaD and 2) their dissociations from each other.

Versatility of the small heat shock protein HSPB6 (Hsp20)

The recently published review by Dreiza et al. (Cell Stress and Chaperones DOI 10.1007/s12192-0090127-8 ) dealing with the functional role of HSPB6 in muscle regulation is critically analyzed. Published data indicate that the chaperone-like activity of HSPB6 is comparable with that of HSPB5 and that phosphorylation of HSPB6 does not affect its oligomeric structure. Different hypotheses concerning the molecular mechanisms of HSPB6 action on smooth muscle contraction and on the reorganization of the cytoskeleton are compared, and it is concluded that although HSPB6 is not a genuine actin-binding protein, it can affect the actin cytoskeleton indirectly. Phosphorylated HSPB6 interacts with 14-3-3 and thereby displaces other binding partners of 14-3-3; among them, certain phosphatases, protein kinases, and various actin-binding proteins, which can participate in the reorganization of the actin cytoskeleton. In addition, HSPB6 seems to regulate the activity of certain protein kinases. All of these processes are dependent on HSPB6 phosphorylation which in turn might be regulated by the formation of heterooligomeric complexes of HSPB6 with other small heat shock proteins.

The small heat shock protein, HSPB6, in muscle function and disease

The small heat shock protein, HSPB6, is a 17-kDa protein that belongs to the small heat shock protein family. HSPB6 was identified in the mid-1990s when it was recognized as a by-product of the purification of HSPB1 and HSPB5. HSPB6 is highly and constitutively expressed in smooth, cardiac, and skeletal muscle and plays a role in muscle function. This review will focus on the physiologic and biochemical properties of HSPB6 in smooth, cardiac, and skeletal muscle; the putative mechanisms of action; and therapeutic implications.

Role of thin-filament regulatory proteins in relaxation of colonic smooth muscle contraction

Coordinated regulation of smooth muscle contraction and relaxation is required for colonic motility. Contraction is associated with phosphorylation of myosin light chain (MLC(20)) and interaction of actin with myosin. Thin-filament regulation of actomyosin interaction is modulated by two actin-binding regulatory proteins: tropomyosin (TM) and caldesmon (CaD). TM and CaD are known to play crucial role in actomyosin interaction promoting contraction. Contraction is associated with phosphorylation of the small heat shock protein HSP27, concomitant with the phosphorylation of TM and CaD. Phosphorylation of HSP27 is attributed as being the prime modulator of thin-filament regulation of contraction. Preincubation of colonic smooth muscle cells (CSMC) with the relaxant neurotransmitter vasoactive intestinal peptide (VIP) showed inhibition in phosphorylation of HSP27 (ser78). Attenuation of HSP27 phosphorylation can result in modulation of thin-filament-mediated regulation of contraction leading to relaxation; thus the role of thin-filament regulatory proteins in a relaxation milieu was investigated. Preincubation of CSMC with VIP exhibited a decrease in phosphorylation of TM and CaD. Furthermore, CSMC preincubated with VIP showed a reduced association of TM with HSP27 and with phospho-HSP27 (ser78) whereas there was reduced dissociation of TM from CaD and from phospho-CaD. We thus propose that, in addition to alteration in phosphorylation of MLC(20), relaxation is associated with alterations in thin-filament-mediated regulation that results in termination of contraction.

The role of the calponin homology domain of smoothelin-like 1 (SMTNL1) in myosin phosphatase inhibition and smooth muscle contraction

In this study, we provide further insight into the contribution of the smoothelin-like 1 (SMTNL1) calponin homology (CH)-domain on myosin light chain phosphatase (SMPP-1M) activity and smooth muscle contraction. SMTNL1 protein was shown to have inhibitory effects on SMPP-1M activity but not on myosin light chain kinase (MLCK) activity. Treatment of beta-escin permeabilized rabbit, ileal smooth muscle with SMTNL1 had no effect on the time required to reach half-maximal force (t(1/2)) during stimulation with pCa6.3 solution. The addition of recombinant SMTNL1 protein to permeabilized, smooth muscle strips caused a significant decrease in contractile force. While the calponin homology (CH)-domain was essential for maximal SMTNL1-associated relaxation, it alone did not cause significant changes in force. SMTNL1 was poorly dephosphorylated by PP-1C in the presence of the myosin targeting subunit (MYPT1), suggesting that phosphorylated SMTNL1 does not possess "substrate trapping" properties. Moreover, while full-length SMTNL1 could suppress SMPP-1M activity toward LC(20) in vitro, truncated SMTNL1 lacking the CH-domain was ineffective. In summary, our findings suggest an important role for the CH-domain in mediating the effects of SMTNL1 on smooth muscle contraction.

Evidence that a protein kinase A substrate, small heat-shock protein 20, modulates myometrial relaxation in human pregnancy

For a successful human pregnancy, the phasic smooth muscle of the myometrium must remain quiescent until labor. Activation of cAMP/cAMP-dependent protein kinase A (PKA) pathways contributes to this quiescence. The small heat-shock protein 20 (HSP20) is a target of PKA, and phosphorylated HSP20 (pHSP20) modulates relaxation of tonic vascular smooth muscle via interaction with actin, independent of myosin dephosphorylation. Our objective was to determine whether relaxation in human myometrium is associated with changes in phosphorylation of HSP20. Myometrium was obtained at elective cesarean. Elevating cAMP with forskolin or rolipram (a phosphodiesterase inhibitor) caused substantial relaxation of spontaneously contracting human myometrial strips, of 92 +/- 4% (mean +/- sem, n = 10) and 84 +/- 7% (n = 6), respectively. Subsequent two-dimensional electrophoresis with immunoblotting of strip extracts showed a significant 2.6- and 2.1-fold increase in phosphorylated HSP20 (pHSP20) after forskolin (P < 0.01; n = 5) or rolipram treatment (P < 0.05; n = 4). Noncyclic-nucleotide-mediated relaxation, induced by the calcium channel blocker nifedipine, did not alter pHSP20. Inhibition of PKA with H89 significantly attenuated rolipram-induced relaxation (P < 0.01; n = 4), and partially reduced rolipram-stimulated pHSP20. Total and pHSP20 protein was unchanged in term laboring and nonlaboring myometria. Coimmunoprecipitation studies revealed a specific association of HSP20 with alpha-smooth muscle actin and HSP27, a key regulator of actin filament dynamics. Finally, coimmunofluorescence demonstrated moderate colocalization of HSP20 with alpha-smooth muscle actin in the cytoplasm of laboring myometria. Our data support a novel role for pHSP20 in the modulation of cyclic-nucleotide-mediated myometrial relaxation, through interaction with actin. pHSP20 represents an important new target for future tocolytic therapy.

Cell permeant peptide analogues of the small heat shock protein, HSP20, reduce TGF-beta1-induced CTGF expression in keloid fibroblasts

A growing body of evidence suggests the involvement of connective tissue growth factor (CTGF) in the development and maintenance of fibrosis and excessive scarring. As the expression of this protein requires an intact actin cytoskeleton, disruption of the cytoskeleton represents an attractive strategy to decrease CTGF expression and, consequently, excessive scarring. The small heat-shock-related protein (HSP20), when phosphorylated by cyclic nucleotide signaling cascades, displaces phospho-cofilin from the 14-3-3 scaffolding protein leading to activation of cofilin as an actin-depolymerizing protein. In the present study, we evaluated the effect of AZX100, a phosphopeptide analogue of HSP20, on transforming growth factor-beta-1 (TGF-beta1)-induced CTGF and collagen expression in human keloid fibroblasts. We also examined the effect of AZX100 on scar formation in vivo in dermal wounds in a Siberian hamster model. AZX100 decreased the expression of CTGF and type I collagen induced by TGF-beta1, endothelin, and lysophosphatidic acid. Treatment with AZX100 decreased stress fiber formation and altered the morphology of human dermal keloid fibroblasts. In vivo, AZX100 significantly improved collagen organization in a Siberian hamster scarring model. Taken together, these results suggest the potential use of AZX100 as a strategy to prevent excessive scarring and fibrotic disorders.

Actin cytoskeletal dynamics in smooth muscle: a new paradigm for the regulation of smooth muscle contraction

A growing body of data supports a view of the actin cytoskeleton of smooth muscle cells as a dynamic structure that plays an integral role in regulating the development of mechanical tension and the material properties of smooth muscle tissues. The increase in the proportion of filamentous actin that occurs in response to the stimulation of smooth muscle cells and the essential role of stimulus-induced actin polymerization and cytoskeletal dynamics in the generation of mechanical tension has been convincingly documented in many smooth muscle tissues and cells using a wide variety of experimental approaches. Most of the evidence suggests that the functional role of actin polymerization during contraction is distinct and separately regulated from the actomyosin cross-bridge cycling process. The molecular basis for the regulation of actin polymerization and its physiological roles may vary in diverse types of smooth muscle cells and tissues. However, current evidence supports a model for smooth muscle contraction in which contractile stimulation initiates the assembly of cytoskeletal/extracellular matrix adhesion complex proteins at the membrane, and proteins within this complex orchestrate the polymerization and organization of a submembranous network of actin filaments. This cytoskeletal network may serve to strengthen the membrane for the transmission of force generated by the contractile apparatus to the extracellular matrix, and to enable the adaptation of smooth muscle cells to mechanical stresses. Better understanding of the physiological function of these dynamic cytoskeletal processes in smooth muscle may provide important insights into the physiological regulation of smooth muscle tissues.

Small heat shock proteins in smooth muscle

The small heat shock proteins (HSPs) HSP20, HSP27 and alphaB-crystallin are chaperone proteins that are abundantly expressed in smooth muscles are important modulators of muscle contraction, cell migration and cell survival. This review focuses on factors regulating expression of small HSPs in smooth muscle, signaling pathways that regulate macromolecular structure and the biochemical and cellular functions of small HSPs. Cellular processes regulated by small HSPs include chaperoning denatured proteins, maintaining cellular redox state and modifying filamentous actin polymerization. These processes influence smooth muscle proliferation, cell migration, cell survival, muscle contraction and synthesis of signaling proteins. Understanding functions of small heat shock proteins is relevant to mechanisms of disease in which dysfunctional smooth muscle causes symptoms, or is a target of drug therapy. One example is that secreted HSP27 may be a useful marker of inflammation during atherogenesis. Another is that phosphorylated HSP20 which relaxes smooth muscle may prove to be highly relevant to treatment of hypertension, vasospasm, asthma, premature labor and overactive bladder. Because small HSPs also modulate smooth muscle proliferation and cell migration they may prove to be targets for developing effective, novel treatments of clinical problems arising from remodeling of smooth muscle in vascular, respiratory and urogenital systems.

The small heat shock-related protein, HSP20, is a cAMP-dependent protein kinase substrate that is involved in airway smooth muscle relaxation

Activation of the cAMP/cAMP-dependent PKA pathway leads to relaxation of airway smooth muscle (ASM). The purpose of this study was to examine the role of the small heat shock-related protein HSP20 in mediating PKA-dependent ASM relaxation. Human ASM cells were engineered to constitutively express a green fluorescent protein-PKA inhibitory fusion protein (PKI-GFP) or GFP alone. Activation of the cAMP-dependent signaling pathways by isoproterenol (ISO) or forskolin led to increases in the phosphorylation of HSP20 in GFP but not PKI-GFP cells. Forskolin treatment in GFP but not PKI-GFP cells led to a loss of central actin stress fibers and decreases in the number of focal adhesion complexes. This loss of stress fibers was associated with dephosphorylation of the actin-depolymerizing protein cofilin in GFP but not PKI-GFP cells. To confirm that phosphorylated HSP20 plays a role in PKA-induced ASM relaxation, intact strips of bovine ASM were precontracted with serotonin followed by ISO. Activation of the PKA pathway led to relaxation of bovine ASM, which was associated with phosphorylation of HSP20 and dephosphorylation of cofilin. Finally, treatment with phosphopeptide mimetics of HSP20 possessing a protein transduction domain partially relaxed precontracted bovine ASM strips. In summary, ISO-induced phosphorylation of HSP20 or synthetic phosphopeptide analogs of HSP20 decreases phosphorylation of cofilin and disrupts actin in ASM, suggesting that one possible mechanism by which HSP20 mediates ASM relaxation is via regulation of actin filament dynamics.

MYOMETRIAL ACTIVATION – COORDINATION, CONNECTIVITY AND CONTRACTILITY

One of the most important stages of pregnancy is the activation of uterine contractions that result in the expulsion of the fetus. The timely onset of labour is clearly important for a healthy start to life but incomplete understanding of the precise mechanisms regulating labour onset have prohibited the development of effective and safe treatments for preterm labour. This review explores the activation of the myometrium at labour onset, focussing on mechanisms of uterine contractility, including those proteins that play an important role in smooth muscle contractility. The review primarily focuses on human work but in the absence of human data describes animal studies. A broad overview of myometrial contraction mechanisms is provided before discussing more detailed aspects and identifying areas where uncertainty remains. Also discussed is the recent application of ‘omics’ based approaches to parturition research, which has facilitated an increase in the understanding of myometrial activation.

Phosphorylation and activation of a transducible recombinant form of human HSP20 in Escherichia coli

Protein-based cellular therapeutics have been limited by getting molecules into cells and the fact that many proteins require post-translational modifications for activation. Protein transduction domains (PTDs), including that from the HIV TAT protein (TAT), are small arginine rich peptides that carry molecules across the cell membrane. We have shown that the heat shock-related protein, HSP20 is a downstream-mediator of cyclic nucleotide-dependent relaxation of vascular smooth muscle and is activated by phosphorylation. In this study, we co-expressed in Escherichia coli the cDNAs encoding the catalytic subunit of protein kinase G and a TAT-HSP20 fusion protein composed of the TAT PTD (-YGRKKRRQRRR-) fused to the N-terminus of human HSP20. Immunoblot and HPLC-ESI-MS/MS analysis of the purified TAT-HSP20 demonstrated that it was phosphorylated at serine 40 (equivalent to serine 16 in wild-type human HSP20). This phosphorylated TAT-HSP20 was physiologically active in intact smooth muscles in that it inhibited 5-hydroxytryptamine-induced contractions by 57%+/-4.5. The recombinant phosphorylated protein also led to changes in actin cytoskeletal morphology in 3T3 cells. These results delineate strategies for the expression and activation of therapeutic molecules for intracellular protein based therapeutics.

Cyclic nucleotide signaling in cavernous smooth muscle

INTRODUCTION

Penile erection depends on cavernous smooth muscle relaxation that is principally regulated by cyclic nucleotide signaling. It is hoped that a comprehensive review of publications relevant to this subject will be helpful to both scientists and clinicians who are interested in the sciences of erectile function/dysfunction. AIMS. To review the roles of extracellular signaling molecules, their receptors, intracellular effectors, and phosphodiesterases in cyclic nucleotide signaling that leads to cavernous smooth muscle relaxation. The involvement of these molecules in the development of erectile dysfunction and the possibility of using them as therapeutic agents or targets are also discussed.

METHODS

Entrez, the search engine for life sciences, was used to search for publications relevant to the topics of this review. Keywords used in the searches included vascular, cavernous, penis, smooth muscle, signaling molecules (adenosine, nitric oxide, etc.), and key elements in the cyclic nucleotide signaling pathways (cAMP, cGMP, cyclases, PKG, PKA, etc.). Articles that are dedicated to the study of erectile function/dysfunction were prioritized for citation.

RESULTS

More than 1,000 articles were identified, many of which are studies of the vascular system and are therefore reviewed but not cited. Studies on erectile function have identified both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways in cavernous smooth muscle. Many signaling molecules of these two pathways have been shown capable of inducing erection when administered intracavernously. However, for sexually induced erection, nitric oxide (NO) is the responsible signaling molecule and it passes on the signal through soluble guanyl cyclase (sGC), cGMP, and protein kinase G (PKG).

CONCLUSIONS

The NO/sGC/cGMP/PKG pathway is principally responsible for sexually stimulated erection. Detumescence is mainly carried out by the degradation of cGMP by phosphodiesterase 5. Both cAMP and cGMP signaling pathways are susceptible to genetic and biochemical alterations in association with erectile dysfunction. Several key elements along these pathways are potential therapeutic targets.

Convergence of Ca2+-desensitizing mechanisms activated by forskolin and phenylephrine pretreatment, but not 8-bromo-cGMP

Contractile stimuli can sensitize myosin to Ca2+ by activating RhoA kinase (ROK) and PKC that inhibit myosin light chain phosphatase (MLCP) activity. Relaxant stimuli, acting through PKA and PKG (cyclic nucleotide-dependent protein kinases), and pretreatment with contractile agents such as phenylephrine (PE), can desensitize myosin to Ca2+. It is unknown precisely how these stimuli cause Ca2+ desensitization. To test the hypothesis that PKA, PKG, and PE pretreatment signaling systems converge to cause relaxation by inhibition of ROK in intact, isolated tissues, we examined the effects of forskolin (FSK; PKA activation), 8-bromo-cGMP (8br-cGMP; PKG activation), and PE pretreatment on KCl-induced force maintenance in rabbit arteries, a response nearly completely dependent on ROK activation. PE pretreatment and agents activating PKA and PKG caused Ca2+ desensitization by inhibiting KCl-induced tonic force and MLC phosphorylation without inhibiting intracellular [Ca2+]. At pCa 5 in beta-escin-permeabilized muscle, FSK and 8b-cGMP accelerated the relaxation rate when tissues were returned to pCa 9, suggesting that both agents can elevate MLCP activity. However, a component of the Ca2+ desensitization attributed to PKG activation in intact tissues appeared to involve a MLC phosphorylation-independent component. Inhibition of KCl-induced tonic force by the ROK inhibitor, Y-27632, and by PE pretreatment, were synergistically potentiated by 8b-cGMP, but not FSK. FSK and PE pretreatment, but not 8b-cGMP, inhibited the KCl-induced increase in site-specific myosin phosphatase target protein-1 phosphorylation at Thr853. These data support the hypothesis that PKA and PE pretreatment converge on a common Ca2+-desensitization pathway, but that PKG can act by a mechanism different from that activated by PKA and PE pretreatment.

Structure, properties, and probable physiological role of small heat shock protein with molecular mass 20 kD (Hsp20, HspB6)

This review is devoted to critical analysis of data concerning the structure and functions of small heat shock proteins with apparent molecular mass 20 kD (Hsp20). We describe the structure of Hsp20, its phosphorylation by different protein kinases, interaction of Hsp20 with other small heat shock proteins, and chaperone activity of Hsp20. The distribution of Hsp20 in different animal tissues and the factors affecting expression of Hsp20 are also described. Data on the possible involvement of Hsp20 in regulation of platelet aggregation and glucose transport are presented and analyzed. Special attention is paid to literature data describing probable regulatory effect of Hsp20 on contraction of smooth muscle. Two hypotheses postulating direct effect of Hsp20 on actomyosin interaction or its effect on cytoskeleton are compared and analyzed. The most recent data on the effect of Hsp20 on apoptosis and contractile activity of cardiomyocytes are also presented.

Small heat shock protein with apparent molecular mass 20 kDa (Hsp20, HspB6) is not a genuine actin-binding protein

The interaction of recombinant human small heat shock protein with apparent molecular mass 20 kDa (Hsp20, HspB6) with actin was investigated. Wild type Hsp20 and its S16D mutant mimicking phosphorylation of Hsp20 by cyclic nucleotide-dependent protein kinases do not affect the rate and extent of actin polymerization. Ultracentrifugation of the mixture of Hsp20 (or its S16D mutant) with isolated F-actin or F-actin containing tropomyosin, calponin or alpha-actinin resulted in co-sedimentation of less than 0.04 mol of Hsp20 monomer per mol of actin. Myofibrils of skeletal, cardiac or smooth muscle bound less than 0.04 mol of Hsp20 monomer per mol of actin and this stoichiometry was independent of phosphorylation or mutation of Ser16 of Hsp20. Since Hsp20 is not a genuine actin-binding protein, the earlier described correlation between Hsp20 phosphorylation and smooth muscle relaxation cannot be explained by direct interaction of Hsp20 with actin.

Role of the small heat shock proteins in regulating vascular smooth muscle tone

BACKGROUND

Vasospasm occurs in conduits used for vascular reconstructions. The small heat shock proteins, HSP20 and HSP27, coordinately regulate vascular smooth muscle tone. Phosphorylated HSP20 is associated with vasorelaxation, and phosphorylated HSP27 inhibits the phosphorylation of HSP20 and relaxation. We hypothesized that the relationship between the phosphorylated states of these two proteins might dictate the tone of a vessel and may contribute to vasospasm.

STUDY DESIGN

Sodium nitroprusside relaxation of vascular smooth muscle was recorded using pig coronary artery and human saphenous vein. Segments were frozen and homogenized, and extracted proteins were separated by one- and two-dimensional gel electrophoresis, transferred to Immobilon (Millipore), and probed with anti-cGMP-dependent protein kinase (anti-PKG), -HSP20, -HSP27, and -phosphoHSP27 antibodies. Band intensity was estimated using densitometry.

RESULTS

Pig coronary artery completely relaxed (100%) with SNP (10(-7)M), but human saphenous vein only partially relaxed (20%). The levels of cGMP-dependent protein kinase and HSP20 were similar in the two tissue types. Human saphenous vein had significantly higher levels of HSP27 versus pig coronary artery (30.14 +/- 0.8 versus 6.62 +/- 0.2 pixels/mg; p < or = 0.001) and phosphoHSP27 (8.29 +/- 3.43 versus 0.012 +/- 0.008 pixels/mg; p < or = 0.001).

CONCLUSIONS

Human saphenous vein contained significantly higher levels of HSP27 and pHSP27. Increased levels of phosphorylated HSP27 might contribute to vasospasm in human saphenous vein.

Transduction of phosphorylated heat shock-related protein 20, HSP20, prevents vasospasm of human umbilical artery smooth muscle

Activation of cyclic nucleotide-dependent signaling pathways inhibits agonist-induced contraction of most vascular smooth muscles except human umbilical artery smooth muscle (HUASM). This impaired vasorelaxation may contribute to complications associated with preeclampsia, intrauterine growth restriction, and preterm delivery. Cyclic nucleotide-dependent signaling pathways converge at the phosphorylation of the small heat shock-related protein HSP20, causing relaxation of vascular smooth muscle. We produced recombinant proteins containing a protein transduction domain linked to HSP20 (rTAT-HSP20). Pretreatment of HUASM with in vitro phosphorylated rTAT-HSP20 (rTAT-pHSP20) significantly inhibited serotonin-induced contraction, without a decrease in myosin light chain phosphorylation. rTAT-pHSP20 remained phosphorylated upon transduction into isolated HUASM as demonstrated by two-dimensional gel electrophoresis. Transduction of peptide analogs of phospho-HSP20 containing the phosphorylation site on HSP20 and phosphatase-resistant mimics of the phosphorylation site (S16E) also inhibited HUASM contraction. These data suggest that impaired relaxation of HUASM may result from decreased levels of phosphorylated HSP20. Protein transduction can be used to restore intracellular expression levels and the associated physiological response. Transduction of posttranslationally modified substrate proteins represents a proteomic-based therapeutic approach that may be particularly useful when the expression of downstream substrate proteins is downregulated.

Involvement of p38-mitogen-activated protein kinase in adenosine receptor-mediated relaxation of coronary artery

The purpose of this study was to explore the involvement of adenosine receptor(s) in porcine coronary artery (PCA) relaxation and to define the role of MAPK signaling pathways. Isometric tensions were recorded in denuded PCA rings. 5'-(N-ethylcarboxamido)adenosine (NECA), a nonselective adenosine receptor agonist, induced a concentration-dependent relaxation (EC(50) = 16.8 nM) of PGF(2alpha) (10 microM)-preconstricted arterial rings. NECA-induced relaxation was completely blocked by 0.1 microM SCH-58261 (A(2A) antagonist) at lower doses (1-40 nM) but not at higher doses (80-1,000 nM). MRS-1706 (1 microM, A(2B) antagonist) was able to shift the NECA concentration-response curve to the right. CGS-21680 (selective A(2A) agonist) induced responses similarly to NECA, whereas N(6)-cyclopentyladenosine (A(1) agonist) and Cl-IB-MECA (A(3) agonist) did not. Furthermore, the effect of NECA was attenuated by the addition of SB-203580 (10 microM, p38 MAPK inhibitor) but not by PD-98059 (10 microM, MEK inhibitor). Interestingly, SB-203580 had no effect on CGS-21680-induced relaxation. Western blot analysis demonstrated that PGF(2alpha) and adenosine agonists stimulated p38 MAPK at a concentration of 40 nM in PCA smooth muscle cells. MRS-1706 (1 microM) significantly reduced NECA-induced p38 MAPK phosphorylation. Addition of NECA and SB-203580 alone or in combination inhibited PGF(2alpha)-induced p38 MAPK. Western blot data were further confirmed by p38 MAPK activity measurement using activating transcription factor-2 assay. Our results suggest that the adenosine receptor subtype involved in causing relaxation of porcine coronary smooth muscle is mainly A(2A) subtype, although A(2B) also may play a role, possibly through p38 MAPK pathway.

Transducible heat shock protein 20 (HSP20) phosphopeptide alters cytoskeletal dynamics

Activation of cyclic nucleotide dependent signaling pathways leads to relaxation of smooth muscle, alterations in the cytoskeleton of cultured cells, and increases in the phosphorylation of HSP20. To determine the effects of phosphorylated HSP20 on the actin cytoskeleton, phosphopeptide analogs of HSP20 were synthesized. These peptides contained 1) the amino acid sequence surrounding the phosphorylation site of HSP20, 2) a phosphoserine, and 3) a protein transduction domain. Treatment of Swiss 3T3 cells with phosphopeptide analogs of HSP20 led to loss of actin stress fibers and focal adhesion complexes as demonstrated by immunocytochemistry, interference reflection microscopy, and biochemical quantitation of globular-actin. Treatment with phosphopeptide analogs of HSP20 also led to dephosphorylation of the actin depolymerizing protein cofilin. Pull-down assays demonstrated that 14-3-3 proteins associated with phosphopeptide analogs of HSP20 (but not peptide analogs in which the serine was not phosphorylated). The binding of 14-3-3 protein to phosphopeptide analogs of HSP20 prevented the association of cofilin with 14-3-3. These data suggest that HSP20 may modulate actin cytoskeletal dynamics by competing with the actin depolymerizing protein cofilin for binding to the scaffolding protein 14-3-3. Interestingly, the entire protein was not needed for this effect, suggesting that the association is modulated by phosphopeptide motifs of HSP20. These data also suggest the possibility that cyclic nucleotide dependent relaxation of smooth muscle may be mediated by a thin filament (actin) regulatory process. Finally, these data suggest that protein transduction can be used as a tool to elucidate the specific function of peptide motifs of proteins.

Transducible recombinant small heat shock-related protein, HSP20, inhibits vasospasm and platelet aggregation

BACKGROUND

Human saphenous vein (HSV) is the autologous conduit of choice for peripheral vascular reconstruction. Injury during harvest leads to vasospasm and a thrombogenic endoluminal surface. A proteomic transduction approach was developed to prevent vein graft vasospasm and thrombosis.

METHODS

Recombinant HSP20 protein linked to the TAT protein transduction domain was generated in a bacterial expression system (TAT-HSP20). The effect of this protein on the inhibition of smooth muscle contraction was determined using rings of rabbit aorta and HSV in a muscle bath. In addition, the effects of TAT-HSP20 on platelet aggregation were determined in vitro using human citrated whole blood.

RESULTS

Recombinant TAT-HSP20 inhibited norepinephrine-induced contraction of rabbit aortic and HSV segments. Similarly, TAT-HSP20 induced smooth muscle relaxation in HSV segments precontracted with norepinephrine. In human-citrated whole blood, platelet aggregation was significantly inhibited by TAT-HSP20 in a dose-dependent manner.

CONCLUSIONS

The results of this study demonstrate that recombinant TAT-HSP20 inhibits vascular smooth muscle contraction and platelet aggregation. This suggests that HSP20 may be an ideal effector molecule to target as a proteomic approach to enhance early vein graft patency rates by preventing acute vasospasm and thrombosis.

Transduction of peptide analogs of the small heat shock-related protein HSP20 inhibits intimal hyperplasia

BACKGROUND

Human saphenous vein (HSV) is the autologous conduit of choice for peripheral vascular reconstructions. However, vasospasm can lead to early graft failure. The leading cause of delayed graft failure is intimal hyperplasia.

OBJECTIVE

To develop a proteomic approach to prevent vein-graft spasm and intimal hyperplasia.

METHODS

Biomimetic peptide analogs of the small heat shock-related protein HSP20, containing a protein transduction domain (PTD), a phosphorylated serine, and a sequence of HSP20 surrounding the phosphorylation site (PTD-pHSP20), or a scrambled sequence of the same amino acids surrounding the phosphorylation site (PTD-scHSP20) were synthesized. The peptides were used in muscle bath and organ culture experiments with human saphenous vein (HSV) segments. Cultured smooth muscle cell lines were used to determine the effect of the peptides on proliferation and migration.

RESULTS

In HSV rings precontracted with norepinephrine, PTD-pHSP20 but not PTD-scHSP20 led to relaxation. There was no significant difference in smooth muscle cell proliferation in cells treated with PTD-pHSP20 compared with PTD-scHSP20. Treatment with PTD-pHSP20 significantly inhibited cellular migration compared with PTD-scHSP20. Control, untreated, and PTD-scHSP20-treated saphenous veins had significant increases in intimal thickness after culture. This intimal thickening was completely inhibited by treatment with PTD-pHSP20.

CONCLUSIONS

Protein transduction of biologically active motifs of HSP20 can affect pathologic and physiologic responses of HSV and represents a novel proteomic-based therapeutic approach.

CLINICAL RELEVANCE

We have been a part of the genomics era and are now viewing the emergence of "proteomics." The genome is linear and relatively easy to examine; however the proteome is much more complex and dynamic. In essence, the purpose of gene therapy is to manipulate the genome to produce a particular protein. This manuscript describes a new proteomic approach in which the biologically active part of a protein is directly introduced into vascular cells. Peptides were synthesized which contained a total of 24 amino acids, 11 of which represent a protein transduction domain or "carrier" while the other 13 are the biologically active "cargo." These synthetic peptides prevent spasm (contraction) and intimal hyperplasia in segments of human saphenous vein treated ex vivo. Preclinical development is currently underway to develop these molecules as a proteomic-based vein harvest solution to enhance vein-graft patency.

Small Heat-Shock Protein Hsp20 Phosphorylation Inhibits β-Agonist-Induced Cardiac Apoptosis

Activation of the sympathetic nervous system is a common compensatory feature in heart failure, but sustained β-adrenergic activation induces cardiomyocyte death, leading to cardiac remodeling and dysfunction. In mouse cardiomyocytes, we recently reported that prolonged exposure to β-agonists is associated with transient increases in expression and phosphorylation of a small heat-shock protein, Hsp20. To determine the functional significance of Hsp20, we overexpressed this protein and its constitutively phosphorylated (S16D) or nonphosphorylated (S16A) mutant in adult rat cardiomyocytes. Hsp20 protected cardiomyocytes from apoptosis triggered by activation of the cAMP-PKA pathway, as indicated by decreases in the number of pyknotic nuclei, terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling, and DNA laddering, which were associated with inhibition of caspase-3 activity. These protective effects were further increased by the constitutively phosphorylated Hsp20 mutant (S16D), which conferred full protection from apoptosis. In contrast, the nonphosphorylatable mutant (S16A) exhibited no antiapoptotic properties. Immunostaining studies and immunoprecipitations with Hsp20 or actin antibodies demonstrated that Hsp20 translocated to cytoskeleton and associated with actin on isoproterenol stimulation. These findings suggest that Hsp20 and its phosphorylation at Ser16 may provide cardioprotection against β-agonist-induced apoptosis. Thus, Hsp20 may represent a novel therapeutic target in the treatment of heart failure.

Sildenafil-induced vasorelaxation is associated with increases in the phosphorylation of the heat shock-related protein 20 (HSP20)

PURPOSE

Sildenafil is an oral phosphodiesterase type 5 inhibitor that is a vasodilator used in the treatment of erectile dysfunction. Cyclic nucleotide-dependent vasorelaxation is associated with increases in the phosphorylation of the heat shock related protein 20 (HSP20). The purpose of this study was to determine if sildenafil-induced vasorelaxation is associated with increases in the phosphorylation of HSP20.

MATERIALS AND METHODS

Peptides containing an 11 amino acid enhanced protein transduction domain (PTD) and the functional 13 amino acid sequence of HSP20 with a phosphoserine (PTD-pHSP20) were synthesized using F-MOC technology. Rings of porcine coronary artery were suspended in a muscle bath and sub-maximally contracted with serotonin. Increasing concentrations of sodium nitroprusside (SNP; 0.01-10 microM), sildenafil (0.01-100 microM), or PTD-pHSP20 (0.1-1.0 mM) were added to the baths and the percent relaxation was recorded. To determine if sildenafil-induced vasorelaxation was associated with increases in the phosphorylation of HSP20, rings of porcine coronary artery were untreated (control) or treated with SNP (10 microM) or sildenafil (100 microM) for 2, 5, and 10 min and then snap frozen. Extracted proteins were then separated using two-dimensional SDS-PAGE, transferred to a membrane, and probed for HSP20.

RESULTS

Sildenafil induced vasorelaxation of pre-contracted coronary artery in a dose-dependent manner. Sildenafil-induced vasorelaxation was associated with an increase in the phosphorylation of HSP20. Transduction of peptide analogues of pHSP20 led to a dose-dependent relaxation of pre-contracted porcine coronary artery.

CONCLUSIONS

These findings suggest that sildenafil-induced vasorelaxation is associated with increases in the phosphorylation of HSP20 and that transduction of phosphopeptide analogues of HSP20 is sufficient for relaxation of vascular smooth muscle.

Some properties of human small heat shock protein Hsp20 (HspB6)

Human heat shock protein of apparent molecular mass 20 kDa (Hsp20) and its mutant, S16D, mimicking phosphorylation by cyclic nucleotide-dependent protein kinases, were cloned and expressed in Escherichia coli. The proteins were obtained in a homogeneous state without utilization of urea or detergents. On size exclusion chromatography at neutral pH, Hsp20 and its S16D mutant were eluted as symmetrical peaks with an apparent molecular mass of 55-60 kDa. Chemical crosslinking resulted in the formation of dimers with an apparent molecular mass of 42 kDa. At pH 6.0, Hsp20 and its S16D mutant dissociated, and were eluted in the form of two peaks with apparent molecular mass values of 45-50 and 28-30 kDa. At pH 7.0-7.5, the chaperone activity of Hsp20 (measured by its ability to prevent the reduction-induced aggregation of insulin or heat-induced aggregation of yeast alcohol dehydrogenase) was similar to or higher than that of commercial alpha-crystallin. Under these conditions, the S16D mutant of Hsp20 possessed lower chaperone activity than the wild-type protein. At pH 6.0, both alpha-crystallin and Hsp20 interacted with denatured alcohol dehydrogenase; however, alpha-crystallin prevented, whereas Hsp20 either did not affect or promoted, the heat-induced aggregation of alcohol dehydrogenase. The mixing of wild-type human Hsp27 and Hsp20 resulted in a slow, temperature-dependent formation of hetero-oligomeric complexes, with apparent molecular mass values of 100 and 300 kDa, which contained approximately equal amounts of Hsp27 and Hsp20 subunits. Phosphorylation of Hsp27 by mitogen activated protein kinase-activated protein kinase 2 was mimicked by replacing Ser15, 78 and 82 with Asp. A 3D mutant of Hsp27 mixed with Hsp20 rapidly formed a hetero-oligomeric complex with an apparent molecular mass of 100 kDa, containing approximately equal quantities of two small heat shock proteins.