| 61. |
- Zhu, Baoyi, et al.
(författare)
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Antagonistic relationship between the unfolded protein response and myocardin-driven transcription in smooth muscle
- 2020
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Ingår i: Journal of Cellular Physiology. - : Wiley. - 0021-9541 .- 1097-4652. ; 235:10, s. 7370-7382
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Tidskriftsartikel (refereegranskat)abstract
- Smooth muscle cells (SMCs) are characterized by a high degree of phenotypic plasticity. Contractile differentiation is governed by myocardin-related transcription factors (MRTFs), in particular myocardin (MYOCD), and when their drive is lost, the cells become proliferative and synthetic with an expanded endoplasmic reticulum (ER). ER is responsible for assembly and folding of secreted proteins. When the load on the ER surpasses its capacity, three stress sensors (activating transcription factor 6 [ATF6], inositol-requiring enzyme 1α [IRE1α]/X-box binding protein 1 [XBP1], and PERK/ATF4) are activated to expand the ER and increase its folding capacity. This is referred to as the unfolded protein response (UPR). Here, we hypothesized that there is a reciprocal relationship between SMC differentiation and the UPR. Tight negative correlations between SMC markers (MYH11, MYOCD, KCNMB1, SYNPO2) and UPR markers (SDF2L1, CALR, MANF, PDIA4) were seen in microarray data sets from carotid arterial injury, partial bladder outlet obstruction, and bladder denervation, respectively. The UPR activators dithiothreitol (DTT) and tunicamycin (TN) activated the UPR and reduced MYOCD along with SMC markers in vitro. The IRE1α inhibitor 4μ8C counteracted the effect of DTT and TN on SMC markers and MYOCD expression. Transfection of active XBP1s was sufficient to reduce both MYOCD and the SMC markers. MRTFs also antagonized the UPR as indicated by reduced TN and DTT-mediated induction of CRELD2, MANF, PDIA4, and SDF2L1 following overexpression of MRTFs. The latter effect did not involve the newly identified MYOCD/SRF target MSRB3, or reduced production of either XBP1s or cleaved ATF6. The UPR thus counteracts SMC differentiation via the IRE1α/XBP1 arm of the UPR and MYOCD repression.
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| 62. |
- Zhu, Baoyi, et al.
(författare)
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Cavin-3 (PRKCDBP) deficiency reduces the density of caveolae in smooth muscle
- 2017
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Ingår i: Cell and Tissue Research. - : Springer Science and Business Media LLC. - 0302-766X .- 1432-0878. ; 368:3, s. 591-602
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Tidskriftsartikel (refereegranskat)abstract
- Cavins belong to a family of proteins that contribute to the formation of caveolae, which are membrane organelles with functional roles in muscle and fat. Here, we investigate the effect of cavin-3 ablation on vascular and urinary bladder structure and function. Arteries and urinary bladders from mice lacking cavin-3 (knockout: KO) and from controls (wild type: WT) were examined. Our studies revealed that the loss of cavin-3 resulted in ∼40% reduction of the caveolae protein cavin-1 in vascular and bladder smooth muscle. Electron microscopy demonstrated that the loss of cavin-3 was accompanied by a reduction of caveolae abundance by 40-45% in smooth muscle, whereas the density of caveolae in endothelial cells was unchanged. Vascular contraction in response to an α1-adrenergic agonist was normal but nitric-oxide-dependent relaxation was enhanced, in parallel with an increased relaxation on direct activation of soluble guanylyl cyclase (sGC). This was associated with an elevated expression of sGC, although blood pressure was similar in WT and KO mice. Contraction of the urinary bladder was not affected by the loss of cavin-3. The proteomic response to outlet obstruction, including STAT3 phosphorylation, the induction of synthetic markers and the repression of contractile markers were identical in WT and KO mice, the only exception being a curtailed induction of the Golgi protein GM130. Loss of cavin-3 thus reduces the number of caveolae in smooth muscle and partly destabilizes cavin-1 but the functional consequences are modest and include an elevated vascular sensitivity to nitric oxide and slightly disturbed Golgi homeostasis in situations of severe cellular stress.
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| 63. |
- Zhu, Baoyi, et al.
(författare)
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Nexilin/NEXN controls actin polymerization in smooth muscle and is regulated by myocardin family coactivators and YAP
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Nexilin, encoded by the NEXN gene, is expressed in striated muscle and localizes to Z-discs, influencing mechanical stability. We examined Nexilin/NEXN in smooth muscle cells (SMCs), and addressed if Nexilin localizes to dense bodies and dense bands and whether it is regulated by actin-controlled coactivators from the MRTF (MYOCD, MKL1, MKL2) and YAP/TAZ (YAP1 and WWTR1) families. NEXN expression in SMCs was comparable to that in striated muscles. Immunofluorescence and immunoelectron microscopy suggested that Nexilin localizes to dense bodies and dense bands. Correlations at the mRNA level suggested that NEXN expression might be controlled by actin polymerization. Depolymerization of actin using Latrunculin B repressed the NEXN mRNA and protein in bladder and coronary artery SMCs. Overexpression and knockdown supported involvement of both YAP/TAZ and MRTFs in the transcriptional control of NEXN. YAP/TAZ and MRTFs appeared equally important in bladder SMCs, whereas MRTFs dominated in vascular SMCs. Expression of NEXN was moreover reduced in situations of SMC phenotypic modulation in vivo. The proximal promoter of NEXN conferred control by MRTF-A/MKL1 and MYOCD. NEXN silencing reduced actin polymerization and cell migration, as well as SMC marker expression. NEXN targeting by actin-controlled coactivators thus amplifies SMC differentiation through the actin cytoskeleton, probably via dense bodies and dense bands.
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| 64. |
- Zhu, Baoyi, et al.
(författare)
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Similar regulatory mechanisms of caveolins and cavins by myocardin family coactivators in arterial and bladder smooth muscle
- 2017
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Caveolae are membrane invaginations present at high densities in muscle and fat. Recent work has demonstrated that myocardin family coactivators (MYOCD, MKL1), which are important for contractile differentiation and cell motility, increase caveolin (CAV1, CAV2, CAV3) and cavin (CAVIN1, CAVIN2, CAVIN3) transcription, but several aspects of this control mechanism remain to be investigated. Here, using promoter reporter assays we found that both MKL1/MRTF-A and MKL2/MRTF-B control caveolins and cavins via their proximal promoter sequences. Silencing of MKL1 and MKL2 in smooth muscle cells moreover reduced CAV1 and CAVIN1 mRNA levels by well over 50%, as did treatment with second generation inhibitors of MKL activity. GATA6, which modulates expression of smooth muscle-specific genes, reduced CAV1 and CAV2, whereas the cavins were unaffected or increased. Viral overexpression of MKL1 and myocardin induced caveolin and cavin expression in bladder smooth muscle cells from rats and humans and MYOCD correlated tightly with CAV1 and CAVIN1 in human bladder specimens. A recently described activator of MKL-driven transcription (ISX) failed to induce CAV1/CAVIN1 which may be due to an unusual transactivation mechanism. In all, these findings further support the view that myocardin family coactivators are important transcriptional drivers of caveolins and cavins in smooth muscle.
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