Disease relevance of SRF

• Injection of SRF antisense expression plasmid into gastric ulcers in rats significantly inhibited in vivo angiogenesis in granulation tissue [1].
• Human serum response factor (SRF) bearing a histidine tag was expressed using vaccinia virus [2].
• Recombinant baculoviruses were used to express wild-type serum response factor (SRF) and a mutant, SRF.CKIIA, which lacks all four serine residues in the major casein kinase II (CKII) site at residues 77-90 [3].
• Immediate-early gene induction by the stresses anisomycin and arsenite in human osteosarcoma cells involves MAPK cascade signaling to Elk-1, CREB and SRF [4].
• Because timp-3-null mice develop spontaneous emphysema, our findings suggest that SRF-mediated TIMP-3 inhibition might contribute to the tissue damage seen in LAM [5].

Psychiatry related information on SRF

• Thus, SRF-MYOCD overexpression in small cerebral arteries appears to initiate independently of Abeta a pathogenic pathway mediating arterial hypercontractility and CBF dysregulation, which are associated with Alzheimer's dementia [6].
• In contrast, Id, a natural inhibitor of myogenic bHLH proteins, did not bind SRF in any of the situations tested [7].
• A role in learning for SRF: deletion in the adult forebrain disrupts LTD and the formation of an immediate memory of a novel context [8].
• Based on these results, we have proposed that blockade of SRF may underlie the action of phenytoin, carbamazepine, phenobarbital, valproic acid, and benzodiazepines against generalized tonic-clonic seizures in humans and maximal electroshock seizures in animals [9].

High impact information on SRF

• One of the most exciting recent discoveries was the identification of the serum response factor (SRF) coactivator gene myocardin that appears to be required for expression of many SMC differentiation marker genes, and for initial differentiation of SMC during development [10].
• Hop encodes an unusual homeodomain protein that modulates SRF-dependent cardiac-specific gene expression and cardiac development [11].
• 5. HOP does not bind DNA and acts as an antagonist of serum response factor (SRF), which regulates the opposing processes of proliferation and myogenesis [12].
• We propose that HOP modulates SRF activity during heart development; its absence results in an imbalance between cardiomyocyte proliferation and differentiation with consequent abnormalities in cardiac morphogenesis [12].
• Myocardin belongs to the SAP domain family of nuclear proteins and activates cardiac muscle promoters by associating with SRF [13].

Chemical compound and disease context of SRF

• 4. These findings suggest that the effects of pitavastatin on load-induced cardiac hypertrophy and fibrosis are independent of its cholesterol-lowering action and may be mediated, at least in part, through inhibition of RhoA-ERK-SRF signalling [14].
• Conversely, a dominant-negative mutant form of myocardin, which retains the ability to associate with SRF but is defective in transcriptional activation, blocks cardiomyocyte hypertrophy induced by hypertrophic agonists such as phenylephrine and leukemia inhibitory factor [15].
• Phenobarbital (PB) and the benzodiazepines (BZDs), diazepam (DZP), clonazepam (CZP), and lorazepam (LZP), also reduced SRF, but only at supratherapeutic free serum concentrations achieved in treatment of generalized tonic-clonic status epilepticus [16].

Biological context of SRF

• Here we present a genome-wide view of occupancy of SRF at its binding sites with a focus on those that vary with cell type [17].
• The serum response factor (SRF) is essential for embryonic development and maintenance of muscle cells and neurons [17].
• We also explore possible mechanisms controlling differential binding of SRF in these cell types by assaying cofactor binding, DNA methylation, histone methylation, and histone acetylation at a subset of sites bound preferentially in smooth muscle cells [17].
• We used chromatin immunoprecipitation (ChIP) in combination with human promoter microarrays to identify 216 putative SRF binding sites in the human genome [17].
• Thus, we concluded that at least two distinct classes of coactivator molecules may cooperate to regulate SRF-dependent transactivations in vivo [18].

Anatomical context of SRF

• Together, these data were consistent with a model wherein MKL1 transduces signals from the cytoskeleton to the nucleus in SMCs and regulates SRF-dependent SMC differentiation autonomously or in concert with myocardin [19].
• Genes encoding M1, M2, and M3 were co-expressed in Jurkat T lymphocytes with a reporter gene driven by a mutant serum response element, SRE.L, which responds to SRF activation [20].
• Expression of the dominant negative protein in C2C12 skeletal myoblasts blocked the differentiation-induced expression of the SRF target genes skeletal alpha-actin and alpha-myosin heavy chain and blocked differentiation of the myoblasts to myotubes in vitro [21].
• Transfection of GTPase-deficient Galpha subunits (GalphaQL; constitutively active form) demonstrated that SRF was activated by Galpha(13)QL but only marginally by Galpha(q)QL and Galpha(12)QL in Jurkat cells [20].
• OBJECTIVE: Myocardin is a coactivator of serum response factor (SRF) required for vascular smooth muscle cell (VSMC) differentiation [22].

Associations of SRF with chemical compounds

• However, calcineurin inhibitors and the tyrosine kinase inhibitor genistein selectively suppressed SRF activation by M1, but not by Galpha(13)QL, indicating the presence of separate pathways [20].
• Steroid receptor coactivator-1 (SRC-1) specifically bound to serum response factor (SRF), as demonstrated by glutathione S-transferase pull down assays, and the yeast and mammalian two-hybrid tests [18].
• Substitution of this target lysine for alanine did not affect the translocation of SRF to PML-nuclear bodies [23].
• Western blotting analysis showed that the expressions of the ERalpha and SRF protein decreased significantly with genistein treatment (P<0.05) [24].
• The ribosomal S6 kinase pp90rsk, a growth factor-inducible kinase, phosphorylates SRF in vitro at serine 103, the site that becomes newly phosphorylated upon growth factor stimulation in vivo [25].

Physical interactions of SRF

• Indeed, 90% of SRF sites also bound by ELK4 were common to all three cell types [17].
• We mapped the region in the SRF that interacts with PML to the C-terminal transactivation domain [26].
• Immunoprecipitation assays showed that HERP1 physically interacts with SRF [22].
• Using a yeast interaction assay, we find that SRF binds the RAP74 subunit of TFIIF and that SRF's transcriptional activation domain is the region involved in this binding [27].
• An ATF6-VP16 chimera activated expression of an SRE reporter gene in HeLa cells, suggesting that ATF6 can interact with endogenous SRF [28].

Enzymatic interactions of SRF

• Casein kinase II (CKII) phosphorylates the mammalian transcription factor serum response factor (SRF) on a serine residue(s) located within a region of the protein spanning amino acids 70 to 92, thereby enhancing its DNA-binding activity in vitro [29].
• All the glycosylation sites identified in SRF are situated in a relatively short region of the primary sequence close to or within the transcriptional activation domain which is distant from the major sites of phosphorylation catalyzed by casein kinase II [30].

Regulatory relationships of SRF

• HERP1 inhibits myocardin-induced vascular smooth muscle cell differentiation by interfering with SRF binding to CArG box [22].
• These results suggest that neuronal MKL1 contributes to SRF-regulated gene expression induced by BDNF or synaptic activity [31].
• Specifically, overexpression of SRF in human lung fibroblasts upregulated urokinase-type plasminogen activator (uPA) and its substrate Plg, whereas it downregulated plasminogen activator inhibitor (PAI)-1 [32].
• Mutant forms of p116Rip that fail to oligomerize or bind to MBS are still capable of inhibiting SRF activity [33].
• SAP-1 and Elk-1 are members of a large group of eukaryotic transcription factors that contain a conserved ETS DNA binding domain and that cooperate with the serum response factor (SRF) to activate transcription of the c-fos protooncogene [34].

Other interactions of SRF

• Megakaryoblastic leukemia 1, a potent transcriptional coactivator for serum response factor (SRF), is required for serum induction of SRF target genes [35].
• PML modulates SRF-mediated c-fos promoter activities upon addition of serum to cells or expression of constitutively active Rho family GTPases [26].
• Here, we report that SRF is modified by SUMO-1 chiefly at lysine(147) within the DNA-binding domain [23].
• HERP1 protein interfered with the SRF/CArG-box interaction in vivo and in vitro [22].
• Knockdown of SRF protein levels in human and rat endothelial cells abolished VEGF-induced in vitro angiogenesis, impaired endothelial cell migration and proliferation, and inhibited VEGF-induced actin polymerization and immediate early gene expression [1].

Analytical, diagnostic and therapeutic context of SRF

• Using real time RT-PCR, we have shown that HSP and SRF mRNA were both regulated by genistein in a time- and dose-dependent manner; however, it appears that only the effect of genistein on SRF mRNA, but not HSP mRNA expression, can be partially abolished by cotreatment with estrogen antagonist ICI 182,780 [24].
• Here, we report the identification, purification, and molecular cloning of a human protein that promotes the formation of stable higher-order complexes of SRF and Phox1 [36].
• Direct, competition, and supershift electrophoretic mobility shift assays revealed highly enriched specific binding activity at the betaA/T-rich element that was antigenically distinct from GATA-4, MEF2A-D, SRF, and Oct-1, nuclear proteins that were previously shown to bind A/T-rich elements [37].
• Strikingly, in both the mammalian two-hybrid assay and in vivo coimmunoprecipitations, the association of SRF and p35-C/EBPbeta but not p20-C/EBPbeta is dramatically stimulated by activated Ras [38].
• TIMP-3 inhibition was further confirmed by reverse transcriptase/polymerase chain reaction, immunoblotting, and immunostaining of human lung fibroblasts transfected with SRF fused to DsRed2 (a red variant of green fluorescent protein) [5].

References