Multi-phenotypic Role of Serum Response Factor in the Gastrointestinal System

Serum response factor (SRF) is a master transcription factor of the actin cytoskeleton that binds to highly conserved CArG boxes located within the majority of smooth muscle cell (SMC)-restricted promoters/enhancers. Although most studies of SRF focus on skeletal muscle, cardiac muscle, and vascular SMCs, SRF research has recently expanded into the gastrointestinal (GI) system. Genome scale analyses of GI SMC transcriptome and CArG boxes (CArGome) have identified new SRF target genes. In addition to circular and longitudinal smooth muscle layers, SRF is also expressed in GI mucosa and cancers. In the GI tract, SRF is the central regulator of genes involved in apoptosis, dedifferentiation, proliferation, and migration of cells. Since SRF is the cell phenotypic modulator, it may play an essential role in the development of myopathy, hypertrophy, ulcers, gastric and colon cancers within the GI tract. Given the multi-functional role displayed by SRF in the digestive system, SRF has received more attention emerging as a potential therapeutic target. This review summarizes the findings in SRF research pertaining to the GI tract and provides valuable insight into future directions.

Serum Response Factor Is Essential for Prenatal Gastrointestinal Smooth Muscle Development and Maintenance of Differentiated Phenotype

BACKGROUND/AIMS: Smooth muscle cells (SMCs) characteristically express serum response factor (SRF), which regulates their development. The role of SRF in SMC plasticity in the pathophysiological conditions of gastrointestinal (GI) tract is less characterized. METHODS: We generated SMC-specific Srf knockout mice and characterized the prenatally lethal phenotype using ultrasound biomicroscopy and histological analysis. We used small bowel partial obstruction surgeries and primary cell culture using cell-specific enhanced green fluorescent protein (EGFP) mouse lines to study phenotypic and molecular changes of SMCs by immunofluorescence, Western blotting, and quantitative polymerase chain reaction. Finally we examined SRF change in human rectal prolapse tissue by immunofluorescence. RESULTS: Congenital SMC-specific Srf knockout mice died before birth and displayed severe GI and cardiac defects. Partial obstruction resulted in an overall increase in SRF protein expression. However, individual SMCs appeared to gradually lose SRF in the hypertrophic muscle. Cells expressing low levels of SRF also expressed low levels of platelet-derived growth factor receptor alpha (PDGFRalphalow) and Ki67. SMCs grown in culture recaptured the phenotypic switch from differentiated SMCs to proliferative PDGFRalphalow cells. The immediate and dramatic reduction of Srf and Myh11 mRNA expression confirmed the phenotypic change. Human rectal prolapse tissue also demonstrated significant loss of SRF expression. CONCLUSIONS: SRF expression in SMCs is essential for prenatal development of the GI tract and heart. Following partial obstruction, SMCs down-regulate SRF to transition into proliferative PDGFRalphalow cells that may represent a phenotype responsible for their plasticity. These findings demonstrate that SRF also plays a critical role in the remodeling process following GI injury.

Inhibition effect of N-acetyl-seryl-aspartyl-lysyl-proline on myofibroblast differentiation of MRC-5 human fetal lung fibroblasts inuced by Ang II / 中华劳动卫生职业病杂志

<p><b>OBJECTIVE</b>To explore the inhibition effect of N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) on myofibroblast differentiation of MRC-5 human fetal lung fibroblasts induced by angiotensin (Ang) II.</p><p><b>METHODS</b>The study was divided into 2 step: (1) MRC-5 human fetal lung fibroblasts was induced for 48 h at different dose of Ang II and at different time point by 100 nmol/L Ang II. Then the expression of collagen type I and α-smooth muscle actin (α-SMA) were mesaured by western blot. (2) MRC-5 human fetal lung fibroblasts were divided into 4 group: (1) control, (2) Ang II, (3) Ang II+Ac-SDKP, (4) Ang II+8-Me-cAMP (a specific activator of Epac). The α-SMA expression was observed by immnocytochemical stain. The protein expression of collagen type I, α-SMA, serum response factor (SRF), myocardin-related transcription factor (MRTF)-A, exchange protein directly activated by cAMP (Epac) 1, 2 were measured by Westen blot.</p><p><b>RESULTS</b>Myofibroblast differentiation could be induced by Ang II from MRC-5 cells with a dose- and time-dependent manner. The up-regulation of SRF and MRTF-A were observed in MRC-5 cells induced by Ang II and accompanied with collagen I and α-SMA increased. Pre-treatment with 8-Me-cAMP or Ac-SDKP could attenuated all this changes induced by Ang II, and promoted the expression of Epac1.</p><p><b>CONCLUSION</b>Ac-SDKP can inhibit the myofibroblast differentiation of MRC-5 cells induced by Ang II via Epac1 activating.</p>

Effect of N-acetyl-seryl-aspartyl-lysyl-proline on differentiation from pulmonary fibroblast to myofibroblast mediated by Rho-associated coiled-coil forming protein kinase pathway / 中华劳动卫生职业病杂志

<p><b>OBJECTIVE</b>To investigate whether N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) can inhibit the differentiation of pulmonary fibroblasts into myofibroblasts by regulating Rho-associated coiled-coil forming protein kinase (ROCK) pathway mediated by transforming growth factor-β1 (TGF-β1).</p><p><b>METHODS</b>Primary culture of pulmonary fibroblasts was performed by trypsinization method. Four generations of pulmonary fibroblasts were divided into control group, TGF-β-induced differentiation group, Y-27632 treatment group, and Ac-SDKP treatment group. The intracellular distributions of ROCK, serum response factor (SRF), and α-smooth muscle actin (α-SMA) were observed by confocal laser scanning microscopy. The protein expression of ROCK, SFR, α-SMA, and type I and type III collagen in pulmonary fibroblasts was measured by Western blot. The mRNA expression of ROCK, SFR, and α-SMA was measured by real-time quantitative PCR.</p><p><b>RESULTS</b>Compared with the control group, the pulmonary fibroblasts stimulated by TGF-β1 had a lot of α-SMA antibody-labeled myofilaments in parallel or cross arrangement, as observed by confocal laser scanning microscopy, and the mRNA and protein expression of ROCK, SRF, and α-SMA and protein expression of type I and type III collagen increased significantly after 6, 12, and 24 h of stimulation (P < 0.05). Compared with the TGF-β1-induced differentiation group, the Y-27632 treatment group and Ac-SDKP treatment group had significantly decreased mRNA and protein expression of ROCK, SRF, and α-SMA and protein expression of type I and type III collagen at the same time point (P < 0.05).</p><p><b>CONCLUSION</b>Ac-SDKP can inhibit the differentiation of pulmonary fibroblasts into myofibroblasts and the synthesis of collagen in rats by regulating the ROCK pathway mediated by TGF-β1. That may be one of the mechanisms by which Ac-SDKP acts against (silicotic) pulmonary fibrosis.</p>

[Hsa-miR-133b expression profile during cardiac progenitor cell differentiation and its inhibitory effect on SRF expression]

Cardiac cell differentiation with the help of miRNAs has recently opened a promising window for the restoration of myocardial infarction. Independent miR-1-2/133a-1 and miR-206/133b clusters are known to be expressed in cardiac and skeletal muscles, respectively. miR-133b differs from miR-133a by only one nucleotide. The sequence similarity of these two miRNAs suggests that they target the same pathways and similar mRNA targets. The present study seeks to determine if miR-133b is expressed during the cardiac cell differentiation and if its expression is in reverse correlation with the SRF and CCND2 [as potential target genes] expression patterns. Human cardiac progenitor cells were prepared from Royan Stem Cell Bank [RSCB] and differentiated into cardiomyocytes. To initiate differentiation, cells were treated with 5-azacytidine as a demethylation factor. Then, ascorbic acid and TGFB1 were added every other day and twice per week, respectively. Differentiation into cardiomyocytes was confirmed by immunocytochemistry [ICC], flow cytometry and realtime PCR for some of the cardiac marker genes. The expression profiles of hsa-miR-133b and two of its potential target genes were also analyzed during the cardiac differentiation. Three weeks after the first differentiation induction, expression level of hsa-miR-133b was approximately five times higher than early stage expression [p<0.05]. During this process, the expression profile of SRF target gene was inversely correlated with hsamiR-133b expression. It is known that SRF is critically involved in the cell cycle. Considering increased miR-133b and decreased SRF expression levels during the late stages of heart cell differentiation, here we speculate that elevated expression of miR-133b blocks SRF expression and decreases cardiomyocytes proliferation in order to induce differentiation with direct targeting of SRF. Taken together, our data suggest that miR-133b along with miR-133a may be involved in cardiomyocytes differentiation.

Avaliação de colesterol e triglicerídeos séricos em cães saudáveis suplementados com ômega n-3 / Evaluation of serum cholesterol and triglycerides in healthy dogs supplemented with ômega-3 N

A análise da concentração sérica de colesterol e triglicerídeos foi realizada em 20 cães, sem raça definida, saudáveis, 10 machos e 10 fêmeas, previamente e após a suplementação por 30 dias com ácidos graxos poli-insaturados de cadeia longa derivados do ômega n-3 (497mg ácido docosa-hexaenoico e 780mg ácido eicosapentanoico). A concentração sérica de colesterol apresentou redução significativa após a suplementação em ambos os sexos (271,6±79,8mg/dL; 236,2±67,6mg/dL, antes e após suplementação, respectivamente). Em relação à concentração sérica de triglicerídeos, houve redução apenas nas fêmeas (57,8±12,1mg/dL; 45,2±7,8mg/dL, antes e após suplementação, respectivamente), não havendo efeito da suplementação nos machos.

The analysis of serum cholesterol and triglycerides was performed in 20 healthy mongrel dogs, 10 male and 10 female, before and after supplementation for 30 days with fatty acids of long chain polyunsaturated derived from omega-3 n (497mg docosahexaenoic acid and 780mg eicosapentaenoic acid). The serum cholesterol presented a significant reduction after supplementation in both sexes (271.6±79.8mg/dL; 236,2±67,6mg/dL, before and after supplementation respectively). Regarding serum triglycerides, there was a reduction only in females (57.8±12,1mg/dL; 45.2±7,8mg/dL, before and after supplementation respectively), with no effect of supplementation in males.

Expression and Prognostic Significance of Serum Response Factor in Cholangiocarcinoma

BACKGROUND: Serum response factor (SRF) is a transcriptional factor that plays an important role in cell growth and differentiation for several types of cells. The expression of SRF in cholangiocarcinoma (CC) and its potential role has not been examined. The aim of this study was to determine the relationship between the expression of SRF in CC and the clinicopathological parameters, as well as patient survival. METHODS: We analyzed the expression of SRF in 84 surgically resected cases of CC (33 cases of intrahepatic CC [ICC] and 51 cases of extrahepatic CC [ECC]) by using immunohistochemistry. RESULTS: The positive expression of SRF was detected in 48.8% of the cases of CC (42.4% in ICC, 52.9% in ECC). SRF was predominantly expressed in the CC cells with intense labeling in the nucleus. A SRF expression was significantly associated with the cell proliferation rate (Ki-67 labeling index, p=0.046) and poor patient survival (p=0.002). The tumor differentiation (p=0.038), the T category (p<0.001), lymph node and distant metastasis (p<0.001, p=0.009) and nerve and vessel invasion (p=0.010, p=0.012) were also found to be significantly associated with a poor CC prognosis. CONCLUSIONS: These results suggest that the SRF may play a role in the tumor cell proliferation of CC, and its expression in tumor cells can provide additional prognostic information.

Rac1 accelerates endothelial cell senescence induced by hypoxia in vitro / 生理学报

To investigate the role and mechanism of Rac1 protein in the process of the human umbilical vein endothelial cell (HUVEC) senescence, we used hypoxia as a model for modulating HUVECs entering replicative senescence in vitro. Premature senescence of HUVECs was evidenced by detecting the SA-beta-Gal activity and PAI-1 expression. Meanwhile, cell cycle distribution and cell proliferation rate were investigated by flow cytometry assay and BrdU staining. The results indicated that the HUVECs became enlarged and flattened, both SA-beta-Gal activity and PAI-1 expression increased obviously, while cell proliferation was inhibited and G(1) phase cell cycle arresting occurred when HUVECs were treated with continued hypoxia for 96 h. Accompanied with these changes, the expression of activated Rac1 increased obviously in cells after hypoxia. All these observations suggested that endothelial senescence could be induced by continued hypoxia and it might correlate with the activity of Rac1. To further define the relationship between Rac1 and HUVEC senescence, HUVECs were transiently infected with the constitutively active form of Rac1 (V12Rac1) or dominant negative form of Rac1 (N17Rac1) using retrovirus vector pLNCX-V12Rac1 or pLNCX-N17Rac1. We observed the changes of these three kinds of HUVECs (HUVECs, N17Rac1-HUVECs, V12Rac1-HUVECs) after hypoxia for 48 h and 96 h, the expression and localization of serum response factor (SRF), which is one of the downstream signal molecules of Rac1, were also investigated. The results obtained indicated that after continued hypoxia for 48 h, HUVECs infected by V12Rac1 showed obvious senescence accompanied with SA-beta-Gal activation, PAI-1 expression increase, G(1) phase arrest and cell proliferation inhibition which were similar to HUVECs after continued 96-hour hypoxia treatment, while the senescence of HUVECs infected by N17Rac1 was significantly inhibited even if the cells were exposed to hypoxia for more than 96 h. All the results identified that the activation of Rac1 might accelerate HUVEC senescence induced by hypoxia and that inactivation of Rac1 could partly block the cell senescence. To further investigate the mechanism of HUVEC senescence induced by Rac1, we detected the expression of total SRF (tSRF) and nuclear SRF (nSRF) in these three kinds of HUVECs by immunofluorescent analysis and Western blot assay after hypoxia. The results showed that the expression of nSRF decreased obviously and the nuclear translocation of SRF was inhibited in HUVECs infected by V12Rac1 compared with those in the normal HUVECs. In contrast, the expression of nSRF increased obviously in the HUVECs infected by N17Rac1. These results suggest that activation of Rac1 accelerates endothelial cell senescence and inhibition of Rac1 activity prevents HUVECs from entering senescence induced by hypoxia, while the nuclear translocation of SRF regulated by Rac1 might play an important role in the process of senescence.

Serum response factor participates in RhoA-induced endothelial cell F-actin rearrangements / 生理学报

RhoA is one of the main members of RhoGTPase family involved in cell morphology, smooth muscle contraction, cytoskeletal microfilaments and stress fiber formation. It has been demonstrated that RhoA modulates endothelial cell permeability by its effect on F-actin rearrangement, but the molecular mechanism of rearrangement of actin cytoskeleton remains unclear. Recent studies prove that RhoA/Rho kinase regulates smooth muscle specific actin dynamics by activating serum response factor (SRF)-dependent transcription. To further investigate the molecular mechanism of the rearrangement of vascular endothelial cell actin cytoskeleton, we explored the relationship between the activation of SRF and F-actin rearrangement induced by RhoA in human umbilical vein endothelial cells (HUVECs). HUVECs were infected with the constitutively active forms of RhoA (Q63LRhoA) or the dominant negative forms of RhoA(T19NRhoA) using retrovirus vector pLNCX-Q63LRhoA or pLNCX-T19NRhoA, the positive clone was obtained by G418 selection. The expression and distribution of SRF in normal and infected cells were evaluated by immunohistochemistry and Western blot in complete medium and in serum-free medium. The effect of F-actin polymerization was detected by Rhodamine-Phalloidine staining. Infection of PLNCX-Q63LRhoA induced F-actin rearrangement and stress fiber formation in HUVECs, as well as enhanced the expression of SRF in the nuclei. In contrast, the cells infected with T19NRhoA showed no distinct changes. With serum deprivation, the expression of SRF increased obviously in both normal and infected HUVECs, but the subcellular localization of SRF was evidently different. In HUVECs, the localization of SRF was in the nuclei after 3 d with serum deprivation, but it was redistributed outside the nuclei after 5 d with serum deprivation. In cells infected with Q63LRhoA, the immunolocalization of SRF was always in the nuclei compared with HUVECs infected with T19NRhoA, which was almost always localized in the cytoplasm. In HUVECs, the rearrangement of F-actin and formation of stress fiber increased after 3 d with serum deprivation, but appeared decreased and unpolymerized after 5 d with serum deprivation. The polymerization of F-actin and the formation of stress fiber in HUVECs infected with Q63LRhoA kept during the period of serum-free culture, whereas the rearrangement of F-actin in cells infected with T19NRhoA was not found. These results suggest that RhoA influences endothelial F-actin rearrangement in part by regulating the expression and subcellular localization of SRF.

Study of the role of serum blocking factors on the immune response of patients with cancer larynx and/or hypopharynx

Twenty-two patients with cancer larynx and/or hypopharynx were subjected to surgery. The effect of sera, taken from the patients and control individuals, on normal lymphocytes was assessed in the presence of non specific stimulant [PHA] and tumour antigen as speciuc stimulant. Higher proliferation of lymphocytes was noticed in response to control sera, compared to cancer patients. Also, a significant increase in lymphocyte biastogenesis in response to PHA and T.A. was noticed postoperatively. Patients with cancer larynx and/or hypopharynx have blocking serum factors in their sera which cause reduction in response of normal lymphocytes. These serum factors were significantly decreased or almost disappeared after one and half months postoperatively