scholarly journals Phosphorylated HSP27 modulates the association of phosphorylated caldesmon with tropomyosin in colonic smooth muscle

2006 ◽  
Vol 291 (4) ◽  
pp. G630-G639 ◽  
Author(s):  
Sita Somara ◽  
Khalil N. Bitar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Thin Filament ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Contractile Proteins ◽  
Concomitant Increase ◽  
Thin Filament Regulation ◽  
Hsp 27 ◽  
Actomyosin Interaction

Thin-filament regulation of smooth muscle contraction involves phosphorylation, association, and dissociation of contractile proteins in response to agonist stimulation. Phosphorylation of caldesmon weakens its association with actin leading to actomyosin interaction and contraction. Present data from colonic smooth muscle cells indicate that acetylcholine induced a significant association of caldesmon with PKCα and sustained phosphorylation of caldesmon at ser789. Furthermore, acetylcholine induced significant and sustained increase in the association of phospho-caldesmon with heat-shock protein (HSP)27 with concomitant increase in the dissociation of phospho-caldesmon from tropomyosin. At the thin filament level, HSP27 plays a crucial role in acetylcholine-induced association of contractile proteins. Present data from colonic smooth muscle cells transfected with non-phospho-HSP27 mutant cDNA indicate that the absence of phospho-HSP27 inhibits acetylcholine-induced caldesmon phosphorylation. Our results further indicate that the presence of phospho-HSP27 significantly enhances acetylcholine-induced sustained association of phospho-caldesmon with HSP27 with a concomitant increase in acetylcholine-induced dissociation of phospho-caldesmon from tropomyosin. We thus propose a model whereby upon acetylcholine-induced phosphorylation of caldesmon at ser789, the association of phospho-caldesmon (ser789) with phospho-HSP27 results in an essential conformational change leading to dissociation of phospho-caldesmon from tropomyosin. This leads to the sliding of tropomyosin on actin thus exposing the myosin binding sites on actin for actomyosin interaction.

Agonist-induced association of tropomyosin with protein kinase Cα in colonic smooth muscle

2005 ◽  
Vol 288 (2) ◽  
pp. G268-G276 ◽  
Author(s):  
Sita Somara ◽  
Haiyan Pang ◽  
Khalil N. Bitar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Thin Filament ◽  
Regulatory Protein ◽  
Direct Interaction ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Particulate Fraction ◽  
Calcium Dependent

Smooth muscle contraction regulated by myosin light chain phosphorylation is also regulated at the thin-filament level. Tropomyosin, a thin-filament regulatory protein, regulates contraction by modulating actin-myosin interactions. Present investigation shows that acetylcholine induces PKC-mediated and calcium-dependent phosphorylation of tropomyosin in colonic smooth muscle cells. Our data also shows that acetylcholine induces a significant and sustained increase in PKC-mediated association of tropomyosin with PKCα in the particulate fraction of colonic smooth muscle cells. Immunoblotting studies revealed that in colonic smooth muscle cells, there is no significant change in the amount of tropomyosin or actin in particulate fraction in response to acetylcholine, indicating that the increased association of tropomyosin with PKCα in the particulate fraction may be due to acetylcholine-induced translocation of PKCα to the particulate fraction. To investigate whether the association of PKCα with tropomyosin was due to a direct interaction, we performed in vitro direct binding assay. Tropomyosin cDNA amplified from colonic smooth muscle mRNA was expressed as GST-tropomyosin fusion protein. In vitro binding experiments using GST-tropomyosin and recombinant PKCα indicated direct interaction of tropomyosin with PKCα. PKC-mediated phosphorylation of tropomyosin and direct interaction of PKCα with tropomyosin suggest that tropomyosin could be a substrate for PKC. Phosphorylation of tropomyosin may aid in holding the slided tropomyosin away from myosin binding sites on actin, resulting in actomyosin interaction and sustained contraction.

scholarly journals Phosphorylated HSP27 essential for acetylcholine-induced association of RhoA with PKCα

2004 ◽  
Vol 286 (4) ◽  
pp. G635-G644 ◽  
Author(s):  
Suresh B. Patil ◽  
Mercy D. Pawar ◽  
Khalil N. Bitar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Contraction ◽  
Membrane Fraction ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Cell Length ◽  
Sustained Contraction ◽  
Hsp 27

Reorganization of the cytoskeleton and association of contractile proteins are important steps in modulating smooth muscle contraction. Heat shock protein (HSP) 27 has significant effects on actin cytoskeletal reorganization during smooth muscle contraction. We investigated the role of phosphorylated HSP27 in modulating acetylcholine-induced sustained contraction of smooth muscle cells from the rabbit colon by transfecting smooth muscle cells with phosphomimic (3D) or nonphosphomimic (3G) HSP27. In 3G cells, the initial peak contractile response at 30 s was inhibited by 25% (24.0 ± 4.5% decrease in cell length, n = 4). The sustained contraction was greatly inhibited by 75% [9.3 ± .9% decreases in cell length ( n = 4)]. Furthermore, in 3D cells, translocation of both PKCα and of RhoA was greatly enhanced and resulted in a greater association of PKCα-RhoA in the membrane fraction. In 3G transfected cells, PKCα and RhoA failed to translocate in response to stimulation with acetylcholine, resulting in an inhibition of association of PKCα-RhoA in the membrane fraction. Studies using GST-RhoA fusion protein indicate that there is a direct association of RhoA with PKCα and with HSP27. The results suggest that phosphorylated HSP27 plays a crucial role in the maintenance of association of PKCα-RhoA in the membrane fraction and in the maintenance of acetylcholine-induced sustained contraction.

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

2009 ◽  
Vol 297 (5) ◽  
pp. G958-G966 ◽  
Author(s):  
Sita Somara ◽  
Robert Gilmont ◽  
Khalil N. Bitar
Keyword(s):  
Smooth Muscle ◽  
Muscle Contraction ◽  
Thin Filament ◽  
Smooth Muscle Contraction ◽  
Regulatory Proteins ◽  
Actin Binding ◽  
Thin Filament Regulation ◽  
Actomyosin Interaction ◽  
Regulation Of Contraction

Coordinated regulation of smooth muscle contraction and relaxation is required for colonic motility. Contraction is associated with phosphorylation of myosin light chain (MLC20) 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 MLC20, relaxation is associated with alterations in thin-filament-mediated regulation that results in termination of contraction.

HSP27 phosphorylation and interaction with actin-myosin in smooth muscle contraction

2002 ◽  
Vol 282 (5) ◽  
pp. G894-G903 ◽  
Author(s):  
Khalil N. Bitar
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Signal Transduction Pathway ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Thin Filament Regulation ◽  
Kinase C ◽  
Hsp27 Phosphorylation ◽  
Myosin Interaction

We have investigated the role of heat shock protein 27 (HSP27) phosphorylation and the association of HSP27 with contractile proteins actin, myosin, and tropomyosin. Smooth muscle cells were labeled with [32P]orthophosphate. C2-ceramide (0.1 μM), an activator of protein kinase C (PKC), induced a sustained increase in HSP27 phosphorylation that was inhibited by calphostin C. C2-ceramide-induced (0.1 μM) sustained colonic smooth muscle cell contraction was accompanied by significant increases in the association of HSP27 with tropomyosin and in the association of HSP27 with actin. The significant increases occurred at 30 s after stimulation and were sustained at 4 min. Contraction was also associated with strong colocalization of HSP27 with tropomyosin and with actin as observed after immunofluorescent labeling of tropomyosin, actin, and HSP27 followed by confocal microscopy. Transfection of smooth muscle cells with HSP27 phosphorylation mutants indicated that phosphorylation of HSP27 could affect myosin association with actin. In conclusion 1) HSP27 phosphorylation appears to be necessary for reorganization of HSP27 inside the cell and seems to be directly correlated with the PKC signal transduction pathway, and 2) agonist-induced phosphorylation of HSP27 modulates actin-myosin interaction through thin-filament regulation of tropomyosin.

Characterization and confocal imaging of calponin in gastrointestinal smooth muscle

1993 ◽  
Vol 265 (5) ◽  
pp. C1371-C1378 ◽  
Author(s):  
M. P. Walsh ◽  
J. D. Carmichael ◽  
G. J. Kargacin
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase ◽  
Smooth Muscle Cells ◽  
Thin Filament ◽  
Muscle Cells ◽  
Biochemical Properties ◽  
Confocal Imaging ◽  
Isolated Cells ◽  
Independent Manner

Calponin isolated from chicken gizzard smooth muscle binds in vitro to actin in a Ca(2+)-independent manner and thereby inhibits the actin-activated Mg(2+)-adenosinetriphosphatase of smooth muscle myosin. This inhibition is relieved when calponin is phosphorylated by protein kinase C or Ca2+/calmodulin-dependent protein kinase II, suggesting that calponin is involved in thin filament-associated regulation of smooth muscle contraction. To further examine this possibility, calponin was isolated from toad stomach smooth muscle, characterized biochemically, and localized in intact isolated cells. Toad stomach calponin had the same basic biochemical properties as calponin from other sources. Confocal immunofluorescence microscopy revealed that calponin in intact smooth muscle cells was localized to long filamentous structures that were colabeled by antibodies to actin or tropomyosin. Preservation of the basic biochemical properties of calponin from species to species suggests that these properties are relevant for its in vivo function. Its colocalization with actin and tropomyosin indicates that calponin is associated with the thin filament in intact smooth muscle cells.

Modulation of smooth muscle contraction by sphingosylphosphorylcholine

1995 ◽  
Vol 269 (3) ◽  
pp. G370-G377 ◽  
Author(s):  
K. N. Bitar ◽  
H. Yamada
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase ◽  
Smooth Muscle Cells ◽  
Map Kinase ◽  
Intracellular Signaling ◽  
Calcium Release ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Mitogen Activated Protein Kinase ◽  
Maximal Response

We have investigated the effect of sphingosylphosphorylcholine (SPC), a synthetic product that was implicated in the sphingomyelin cycle, and have assessed its role in intracellular signaling. SPC induced a dose-dependent contractile effect of smooth muscle cells isolated from the rectosigmoid of the rabbit. Maximal contraction occurred at 10(-6) M. The response started early, 25.4 +/- 6% shortening at 15 s, peaked at 30 s (32.5 +/- 2%), and remained sustained at 8 min (30.0 +/- 3.5%). Preincubation of the cells with thapsigargin had no effect on contraction induced by SPC. The response to a combination of threshold concentrations of inositol 1,4,5-trisphosphate (IP3) and SPC was additive and was significantly different from the maximal response elicited by each agent alone. SPC also induced activation of mitogen-activated protein kinase (MAP kinase). This study demonstrates that SPC is important in cellular signaling of gastrointestinal smooth muscle cells through a mechanism that is independent of IP3-sensitive calcium release and probably through activation of a protein kinase C-mediated activation of MAP kinase.

Spatial dynamics of intracellular calcium in agonist-stimulated vascular smooth muscle cells

1990 ◽  
Vol 259 (4) ◽  
pp. C675-C686 ◽  
Author(s):  
C. B. Neylon ◽  
J. Hoyland ◽  
W. T. Mason ◽  
R. F. Irvine
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Vascular Tissue ◽  
Spatial Dynamics ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
The Novel ◽  
Internal Mammary

Vasoconstrictor agonists stimulate smooth muscle contraction by inducing a rise in intracellular free Ca2+. Digital-imaging microscopy of fura-2 fluorescence from single vascular smooth muscle cells cultured from the human internal mammary artery has allowed us to record the subcellular alterations in Ca2+ that occur immediately after stimulation by receptor agonists. The thrombin-induced rise in cytoplasmic free Ca2+ begins in a discrete region typically located close to the end of the cell. Subsequently, this region of elevated Ca2+ expands until Ca2+ is elevated throughout the cell cytoplasm. The rate of spreading in the region of elevated Ca2+ in a linear direction averaged 10.1 microns/s, enabling it to traverse the length of most cells within approximately 5 s, and involved rises in Ca2+ of between 200 and 500 nM. In some cells, the Ca2+ rise began at both ends and collided midway. Similar dynamic changes in the spatial distribution of Ca2+ were recorded in cells stimulated by acetylcholine. The novel observation that vasoconstrictor agonists induce an elevation of Ca2+ in a localized region which subsequently expands throughout the cytoplasm of single smooth muscle cells may provide new insight into the nature of Ca2+ signaling in vascular tissue.

Superoxide anion impairs contractility in cultured aortic smooth muscle cells

2002 ◽  
Vol 283 (1) ◽  
pp. H382-H390 ◽  
Author(s):  
Chiwaka Kimura ◽  
Wei Cheng ◽  
Kazunari Hisadome ◽  
Yi-Ping Wang ◽  
Tetsuya Koyama ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Superoxide Anion ◽  
Collagen Gel ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Aortic Smooth Muscle Cells ◽  
Aortic Smooth Muscle ◽  
A 23187 ◽  
High K

We examined the effects of superoxide anion (O[Formula: see text]) generated by xanthine plus xanthine oxidase (X/XO) on the intracellular Ca2+ concentration ([Ca2+]i) and muscle contractility in cultured bovine aortic smooth muscle cells (BASMC). Cells were grown on collagen-coated dish for the measurement of [Ca2+]i. Pretreatment with X/XO inhibited ATP-induced Ca2+ transient and Ca2+release-activated Ca2+ entry (CRAC) after thapsigargin-induced store depletion, both of which were reversed by superoxide dismutase (SOD). In contrast, Ca2+ transients induced by high-K+ solution and Ca2+ ionophore A-23187 were not affected by X/XO. BASMC-embedded collagen gel lattice, which was pretreated with xanthine alone, showed contraction in response to ATP, thapsigargin, high-K+ solution, and A-23187. Pretreatment of the gel with X/XO impaired gel contraction not only by ATP and thapsigargin, but also by high-K+ solution and A-23187. The X/XO-treated gel showed normal contraction; however, when SOD was present during the pretreatment period. These results indicate that O[Formula: see text] attenuates smooth muscle contraction by impairing CRAC, ATP-induced Ca2+ transient, and Ca2+ sensitivity in BASMC.

Regulation of smooth muscle contraction in rabbit internal anal sphincter by protein kinase C and Ins(1,4,5)P3

1991 ◽  
Vol 260 (4) ◽  
pp. G537-G542 ◽  
Author(s):  
K. N. Bitar ◽  
C. Hillemeier ◽  
P. Biancani ◽  
K. J. Balazovich
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Smooth Muscle Contraction ◽  
Threshold Concentration ◽  
Maximal Contraction ◽  
Calmodulin Antagonist ◽  
Kinase C

We have examined the role of protein kinase C (PKC)-beta II and its functional relationship to inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and intracellular Ca2+ in the contraction of smooth muscle cells from the rabbit internal and sphincter (IAS). PKC-beta (0.1-100 U/ml) and Ins(1,4,5)P3 (10(-9) to 10(-6) M) caused concentration-dependent contraction of IAS smooth muscle cells permeabilized by saponin. The combination of threshold concentrations of Ins(1,4,5)P3 (10(-9) M) and PKC (0.1 U/ml) was more than additive, causing near maximal shortening (28.2 +/- 2.1% decrease in cell length from control). The response to high concentrations of Ins(1,4,5)P3 and PKC used in combination was not greater than the response to either agent alone. The calmodulin antagonist W-7 (10(-9) M) inhibited the maximal contraction induced by Ins(1,4,5)P3 but not contraction caused by PKC, whereas the PKC antagonist H-7 (10(-6) M) inhibited the maximal contraction induced by PKC but not contraction caused by Ins(1,4,5)P3. Threshold doses of the ionophores A23187 (10(-9) M) and ionomycin (0.2 ng/ml) caused little contraction by themselves, but they potentiated the response elicited by a threshold concentration of PKC (0.1 U/ml), inducing maximal contraction. Preincubation of IAS cells with 4 mM Sr2+, which inhibits the release of intracellular Ca2+, abolished the potentiating effect of Ins(1,4,5)P3 and calcium ionophores on PKC, but the calmodulin antagonist W-7 did not. These data suggest that the contractile effect of maximally effective doses of PKC is independent of the effects of Ins(1,4,5)P3. At submaximal concentrations, however, PKC-dependent contraction is potentiated by Ins(1,4,5)P3 or by ionophore-mediated release of intracellular Ca2+ without requiring calmodulin activation.

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