Distribution of active protein kinase C in smooth muscle

Smooth muscle-protein translocation and tissue function

Smooth muscle (SM) tissue is a complex organization of multiple cell types and is regulated by numerous signaling molecules (neurotransmitters, hormones, cytokines, etc.). SM contractile function can be regulated via expression and distribution of the contractile and cytoskeletal proteins, and activation of any of the second messenger pathways that regulate them. Spatial-temporal changes in the contractile, cytoskeletal or regulatory components of SM cells (SMCs) have been proposed to alter SM contractile activity. Ca(2+) sensitization/desensitization can occur as a result of changes at any of these levels, and specific pathways have been identified at all of these levels. Understanding when and how proteins can translocate within the cytoplasm, or to-and-from the plasmalemma and the cytoplasm to alter contractile activity is critical. Numerous studies have reported translocation of proteins associated with the adherens junction and G protein-coupled receptor activation pathways in isolated SMC systems. Specific examples of translocation of vinculin to and from the adherens junction and protein kinase C (PKC) and 17 kDa PKC-potentiated inhibitor of myosin light chain phosphatase (CPI-17) to and from the plasmalemma in isolated SMC systems but not in intact SM tissues are discussed. Using both isolated SMC systems and SM tissues in parallel to pursue these studies will advance our understanding of both the role and mechanism of these pathways as well as their possible significance for Ca(2+) sensitization in intact SM tissues and organ systems.

Tonic and phasic smooth muscle contraction is not regulated by the PKCα - CPI-17 pathway in swine stomach antrum and fundus

Regulation of myosin light chain phosphatase (MLCP) via protein kinase C (PKC) and the 17 kDa PKC-potentiated inhibitor of myosin light chain phosphatase (CPI-17) has been reported as a Ca²⁺ sensitization signaling pathway in smooth muscle (SM), and thus may be involved in tonic vs. phasic contractions. This study examined the protein expression and spatial-temporal distribution of PKCα and CPI-17 in intact SM tissues. KCl or carbachol (CCh) stimulation of tonic stomach fundus SM generates a sustained contraction while the phasic stomach antrum generates a transient contraction. In addition, the tonic fundus generates greater relative force than phasic antrum with 1 µM phorbol 12, 13-dibutyrate (PDBu) stimulation which is reported to activate the PKCα – CPI-17 pathway. Western blot analyses demonstrated that this contractile difference was not caused by a difference in the protein expression of PKCα or CPI-17 between these two tissues. Immunohistochemical results show that the distribution of PKCα in the longitudinal and circular layers of the fundus and antrum do not differ, being predominantly localized near the SM cell plasma membrane. Stimulation of either tissue with 1 µM PDBu or 1 µM CCh does not alter this peripheral PKCα distribution. There are no differences between these two tissues for the CPI-17 distribution, but unlike the PKCα distribution, CPI-17 appears to be diffusely distributed throughout the cytoplasm under relaxed tissue conditions but shifts to a primarily peripheral distribution at the plasma membrane with stimulation of the tissues with 1 µM PDBu or 1 µM CCh. Results from double labeling show that neither PKCα nor CPI-17 co-localize at the adherens junction (vinculin/talin) at the membrane but they do co-localize with each other and with caveoli (caveolin) at the membrane. This lack of difference suggests that the PKCα - CPI-17 pathway is not responsible for the tonic vs. phasic contractions observed in stomach fundus and antrum.

Auto-align - multi-modality fluorescence microscopy image co-registration

Multi-modality microscopes incorporate multiple microscopy techniques into one module, imaging through a common objective lens. Simultaneous or consecutive image acquisition of a single specimen, using multiple techniques, increases the amount of measurable information available. In order to benefit from each modality, it is necessary to accurately co-register data sets. Intrinsic differences in the image formation process employed by each modality result in images which possess different characteristics. In addition, as a result of using different measurement devices, images often differ in size and can suffer relative geometrical deformations including rotation, scale and translation, making registration a complex problem. Current methods generally rely on manual input and are therefore subject to human error. Here, we present an automated image registration tool for fluorescence microscopy. We show that it successfully registers images obtained via total internal reflection fluorescence (TIRF), or epi-fluorescence, and confocal microscopy. Furthermore, we provide several other applications including channel merging following image acquisition through an emission beam splitter, and lateral stage drift correction. We also discuss areas of membrane trafficking which could benefit from application of Auto-Align. Auto-Align is an essential item in the advanced microscopist's toolbox which can create a synergy of single or multi-modality image data.

Extracellular matrix effect on RhoA signaling modulation in vascular smooth muscle cells

Morphological adaptations of vascular smooth muscle cells (VSMC) to the mechanically active environment in which they reside, are mediated by direct interactions with the extracellular matrix (ECM) which induces physiological changes at the intracellular level. This study aimed to analyze the effects of the ECM on RhoA-induced mechanical signaling that controls actin organization and focal adhesion formation. VSMC were transfected with RhoA constructs (wild type, dominant negative or constitutively active) and plated on different ECM proteins used as substrate (fibronectin, collagen IV, collagen I, and laminin) or poly-l-lysine as control. Morphological changes of the VSMC were detected by fluorescence confocal microscopy and total internal reflection fluorescence (TIRF) microscopy, and were independently verified using adhesion assays and Western blot analysis. Our results showed that the ECM has an important role in cell spreading, adhesion and morphology with a direct effect on modulating RhoA signaling. RhoA activity significantly affected the stress fibers and focal adhesions reorganization, but in a context imposed by the ECM. Thus, RhoA activity modulation in VSMC induced an increased activation of stress fibers and FA formation at 5h, while a significant inhibition was recorded at 24h after plating on the different ECM. Our findings provide biophysical evidence that ECM modulates VSMC response to mechanical stimuli inducing intracellular biochemical signaling involved in cellular adaptation to the local microenvironment.

Propofol inhibits phorbol 12, 13-dibutyrate-induced, protein kinase C-mediated contraction of rat aortic smooth muscle

BACKGROUND

Propofol induces dose-dependent vasodilation and hypotension in the clinical situation, and protein kinase C (PKC)-mediated Ca2+ sensitization plays an important role in vascular smooth muscle contraction. This study is designed to examine the effects of propofol on the active phorbol ester (phorbol 12, 13-dibutyrate; PDBu)-induced, PKC-mediated contraction of rat aortic smooth muscle.

METHODS

The PDBu-induced contraction of endothelium-denuded rat aortic rings was measured in the presence or absence of PKC inhibitor, bisindolylmaleimide I, or propofol, using isometric force transducers. The PDBu-induced PKC phosphorylation of endothelium-denuded rat aortic strips was detected in the presence or absence of bisindolylmaleimide I or propofol, using Western blotting.

RESULTS

PDBu, but not the inactive phorbol ester, 4-alpha-phorbol 12-myristate-13-acetate, dose-dependently induced both a slowly developing sustained contraction and PKC phosphorylation of rat aortic smooth muscle, reaching the peak level at the concentration of 10(-6) M. The PDBu (10(-6) M)-induced contraction was dose-dependently inhibited by bisindolylmaleimide I with reductions of 6.8 +/- 1.8% (P > 0.05), 39.8 +/- 8.7% (P < 0.01) and 96.7 +/- 1.4% (P < 0.01) in response to concentrations of 5 x 10(-7) M, 10(-6)x M and 5 x 10(-6) M, respectively, and by propofol with decreases of 5.2 +/- 1. 6% (P > 0.05), 9.4 +/- 1.7% (P < 0.05), 65.3 +/- 9.2% (P < 0.01) and 96.2 +/- 1.6% (P < 0.01) in response to concentrations of 5 x 10(-7) M, 10(-6) M, 5 x 10(-6) M and 10(-5) M, respectively. Both bisindolylmaleimide I and propofol also inhibited the PDBu-induced increase in the density of the phosphorylated PKC bands in a dose-dependent manner, with decreases of 6.3 +/- 2.8% (P > 0.05), 42.9 +/- 3.2% (P < 0.01) and 96.6 +/- 3.4% (P < 0.01) in response to 5 x 10(-7) M, 10(-6) M or 5 x 10(-6) M bisindolylmaleimide I, respectively, and with decreases of 4.2 +/- 2.5% (P > 0.05), 13.5 +/- 1.7% (P < 0.05), 69.5 +/- 3.5% (P < 0.01) and 95.3 +/- 4.3% (P < 0.01) in response to 5 x 10(-7) M, 10(-6) M, 5 x 10(-6) M and 10(-5) M propofol, respectively.

CONCLUSION

Propofol dose-dependently inhibits PDBu-induced, PKC-mediated contraction of rat aortic smooth muscle.

Mechanical stress-activated PKCdelta regulates smooth muscle cell migration

Vascular smooth muscle cells (SMCs) are exposed to altered mechanical stress that may contribute to SMC migration in the development of atherosclerosis. Signal transduction pathways in SMCs activated by mechanical stress that instigate cell migration are undefined. Herein, we provide evidence that mechanical stress enhances SMC migration, which is mediated, at least in part, by protein kinase C (PKC)delta. When rat SMCs cultivated on a flexible membrane were subjected to cyclic strain stress (60 cycles/min, 5, 15, or 20% elongation), PKCdelta was translocated to the Triton-insoluble fraction, whereas PKCalpha was translocated to the membrane, which was confirmed by PKC kinase assays. Immunofluorescence and actin staining revealed a cytoskeleton translocation of PKCdelta in SMCs stimulated by cyclic strain. PKCdelta-deficient SMCs cultivated from PKCdelta-/- mice showed an abnormal cytoskeleton structure, which was related to a diminished phosphorylation of paxillin, focal adhesion kinase, and vinculin in response to mechanical stress. Mechanical stress enhanced SMC migration, which was diminished in PKCdelta-/- SMCs. Taken together, our data demonstrated that mechanical stress activates PKCdelta translocation to the cytoskeleton, which is related to decreased SMC migration and indicates that PKCdelta is a key signal transducer between mechanical stress and cell migration.

Single-cell kinase assays: opening a window onto cell behavior

Recent advances in analytical techniques have made the performance of biochemical assays on individual mammalian cells possible. Of particular interest is the ability to measure the activation of kinases, enzymes with critical roles in virtually every aspect of cell physiology. Single-cell kinase assays promise to deliver a newfound understanding of the molecular mechanisms responsible for cellular control and behavior by revealing the dynamic nature of signal transduction networks in living cells. A recent exciting development is the potential to perform assays of multiple kinases simultaneously in a single cell.

Conventional protein kinase C mediates phorbol-dibutyrate-induced cytoskeletal remodeling in a7r5 smooth muscle cells

Phorbol dibutyrate (PDBu) induced the formation of podosome-like structures together with partial disassembly of actin stress fibers in A7r5 smooth muscle cells. These podosomes contained alpha-actinin, F-actin, and vinculin and exhibit a tubular, column-like structure arising perpendicularly from the bottom of PDBu-treated cells. The conventional protein kinase C (PKC) antagonist, GO6976, inhibited PDBu-induced cytoskeletal remodeling at 0.1 microM, whereas the novel PKC antagonist, rottlerin, was ineffective at 10 microM. PDBu induced the translocation of the conventional PKC-alpha but not the novel PKC-delta to the sites of podosome formation in A7r5 cells. Although partial disassembly of actin stress fibers was observed in both Y-27632- and PDBu-treated cells, focal adhesions were much reduced in number and size only in Y-27632-treated cells. Furthermore, PDBu restored focal adhesions in Y-27632-treated cells. Live video fluorescence microscopy of alpha-actinin GFP revealed a lag phase of about 20 min prior to the rapid formation and dynamic reorganization of podosomes during PDBu treatment. These findings suggest that conventional PKCs mediate PDBu-induced formation of dynamic podosome-like structures in A7r5 cells, and Rho-kinase is unlikely to be the underlying mechanism. The podosome columns could represent molecular scaffolds where PKC-alpha phosphorylates regulatory proteins necessary for Ca(2+) sensitization in smooth muscle cells.

Calponin is required for agonist-induced signal transduction--evidence from an antisense approach in ferret smooth muscle

1. The present study was undertaken to determine whether calponin (CaP) participates in the regulation of vascular smooth muscle contraction and, if so, to investigate the mechanism. 2. By PCR homology cloning, the cDNA sequence of ferret basic (h1) CaP was determined and phosphorothioate antisense and random oligonucleotides were synthesized and introduced into strips of ferret aorta by a chemical loading procedure. 3. Treatment of ferret aorta with CaP antisense oligonucleotides resulted in a decrease in protein levels of CaP to 54% of that in random sequence-loaded muscles, but no change in the protein levels of caldesmon (CaD), actin, desmin or extracellular regulated protein kinase (ERK). 4. Contraction in response to phenylephrine or a phorbol ester was significantly decreased in antisense-treated muscles compared to random sequence-loaded controls. Neither basal intrinsic tone nor the contraction in response to 51 mM KCl was significantly affected by antisense treatment. 5. During phenylephrine contractions, phospho-ERK levels increased, as did myosin light chain (LC20) phosphorylation. Phenylephrine-induced ERK phosphorylation and CaD phosphorylation at an ERK site were significantly decreased by CaP antisense. Increases in myosin light chain phosphorylation were unaffected. 6. The data indicate that CaP plays a significant role in the regulation of contraction and suggest that in a tonically active smooth muscle CaP may function as a signalling protein to facilitate ERK-dependent signalling, but not as a direct regulator of actomyosin interactions at the myofilament level.

Leiomodin and tropomodulin in smooth muscle

Evidence is accumulating to suggest that actin filament remodeling is critical for smooth muscle contraction, which implicates actin filament ends as important sites for regulation of contraction. Tropomodulin (Tmod) and smooth muscle leiomodin (SM-Lmod) have been found in many tissues containing smooth muscle by protein immunoblot and immunofluorescence microscopy. Both proteins cofractionate with tropomyosin in the Triton-insoluble cytoskeleton of rabbit stomach smooth muscle and are solubilized by high salt. SM-Lmod binds muscle tropomyosin, a biochemical activity characteristic of Tmod proteins. SM-Lmod staining is present along the length of actin filaments in rat intestinal smooth muscle, while Tmod stains in a punctate pattern distinct from that of actin filaments or the dense body marker α-actinin. After smooth muscle is hypercontracted by treatment with 10 mM Ca2+, both SM-Lmod and Tmod are found near α-actinin at the periphery of actin-rich contraction bands. These data suggest that SM-Lmod is a novel component of the smooth muscle actin cytoskeleton and, furthermore, that the pointed ends of actin filaments in smooth muscle may be capped by Tmod in localized clusters.

Inhibition of PKCalpha and rhoA translocation in differentiated smooth muscle by a caveolin scaffolding domain peptide

Receptor-coupled contraction of smooth muscle involves recruitment to the plasma membrane of downstream effector molecules PKCalpha and rhoA but the mechanism of this signal integration is unclear. Caveolins, the principal structural proteins of caveolar plasma membrane invaginations, have been implicated in the organization and regulation of many signal transducing molecules. Thus, using laser scanning confocal immunofluorescent microscopy, we tested the hypothesis that caveolin is involved in smooth muscle signaling by investigating caveolin isoform expression and localization, together with the effect of a peptide inhibitor of caveolin function, in intact differentiated smooth muscle cells. All three main caveolin isoforms were identified in uterine, stomach, and ileal smooth muscles and assumed a predominantly plasma membranous localization in myometrial cells. Cytoplasmic introduction of a peptide corresponding to the caveolin-1 scaffolding domain-an essential region for caveolin interaction with signaling molecules--significantly inhibited agonist-induced translocation of both PKCalpha and rhoA. Translocation was unimpaired by a scrambled peptide and was unaltered in sham-treated cells. The membranous localization of caveolins, and direct inhibition of receptor-coupled PKCalpha and rhoA translocation by the caveolin-1 scaffolding domain, supports the concept that caveolins can regulate the integration of extracellular contractile stimuli and downstream intracellular effectors in smooth muscle.