Vascular smooth muscle alpha-actin gene transcription during myofibroblast differentiation requires Sp1/3 protein binding proximal to the MCAT enhancer

Induction of vascular smooth muscle alpha-actin gene transcription in transforming growth factor beta1-activated myofibroblasts mediated by dynamic interplay between the Pur repressor proteins and Sp1/Smad coactivators

The mouse vascular smooth muscle alpha-actin (SMA) gene enhancer is activated in fibroblasts by transforming growth factor beta1 (TGFbeta1), a potent mediator of myofibroblast differentiation and wound healing. The SMA enhancer contains tandem sites for the Sp1 transcriptional activator protein and Puralpha and beta repressor proteins. We have examined dynamic interplay between these divergent proteins to identify checkpoints for possible control of myofibroblast differentiation during chronic inflammatory disease. A novel element in the SMA enhancer named SPUR was responsible for both basal and TGFbeta1-dependent transcriptional activation in fibroblasts and capable of binding Sp1 and Pur proteins. A novel Sp1:Pur:SPUR complex was dissociated when SMA enhancer activity was increased by TGFbeta1 or Smad protein overexpression. Physical association of Pur proteins with Smad2/3 was observed as was binding of Smads to an upstream enhancer region that undergoes DNA duplex unwinding in TGFbeta1-activated myofibroblasts. Purbeta repression of the SMA enhancer could not be relieved by TGFbeta1, whereas repression mediated by Puralpha was partially rescued by TGFbeta1 or overexpression of Smad proteins. Interplay between Pur repressor isoforms and Sp1 and Smad coactivators may regulate SMA enhancer output in TGFbeta1-activated myofibroblasts during episodes of wound repair and tissue remodeling.

Sp and GATA factors are critical for Apolipoprotein AI downstream enhancer activity in human HepG2 cells

The factors that bind to the hepatic-specific human apolipoprotein AI (apoAI) 48-bp downstream enhancer (DSE) were identified and characterized by electrophoretic mobility shift assays. A significant homology was shown between the histone 4 (H4) promoters and the hepatic-specific human apoAI DSE at Sp1 and H4TF2 binding sites. Human HepG2 nuclear extracts were used to form four specific complexes with the DSE (referred to as apoAI DSE-1, -2, -3, and -4). The apoAI DSE-1 and -2 complexes showed similar binding specificity to the Sp/H4TF1 consensus site within the apoAI DSE. The apoAI DSE-1 complex was predominantly recognized by anti-Sp1 and Sp3 sera in gel shift assays, indicating that the DSE was recognized by multiple Sp family members. Nuclear extracts that were prepared from retinoic acid treated HepG2 cells showed increased levels of Sp factors in gel shift and Western blot assays. The apoAI DSE-2 complex was identified as H4TF1 and formed in the absence of magnesium chloride. The apoAI DSE-3 complex bound to a consensus GATA element within the DSE that was recognized by recombinant human GATA-6 as well. The apoAI DSE-3 complex was completely disrupted by a GATA-4 antibody in EMSA. GATA-4 and -6 were detected in nuclear extracts prepared from retinoic acid treated HepG2 cells using Western blot assays. The highest apoAI DSE-3 levels were observed with retinoic acid treated HepG2 cell nuclear extracts in EMSA. ApoAI DSE-4 is a multi-factor complex that includes an Sp/H4TF1 factor and either H4TF2 or apoAI DSE-3. Because apoAI DSE mutations revealed transcription defects in transient transfection assays, we conclude that the entire DSE sequence is required for full apoAI transcriptional activity in HepG2 cells.

Interference with transforming growth factor-beta/ Smad3 signaling results in accelerated healing of wounds in previously irradiated skin

Transforming growth factor (TGF)-beta regulates many aspects of wound repair including inflammation, chemotaxis, and deposition of extracellular matrix. We previously showed that epithelialization of incisional wounds is accelerated in mice null for Smad3, a key cytoplasmic mediator of TGF-beta signaling. Here, we investigated the effects of loss of Smad3 on healing of wounds in skin previously exposed to ionizing radiation, in which scarring fibrosis complicates healing. Cutaneous wounds made in Smad3-null mice 6 weeks after irradiation showed decreased wound widths, enhanced epithelialization, and reduced numbers of neutrophils and myofibroblasts compared to wounds in irradiated wild-type littermates. Differences in breaking strength of wild-type and Smad3-null wounds were not significant. As shown previously for neutrophils, chemotaxis of primary dermal fibroblasts to TGF-beta required Smad3, but differentiation of fibroblasts to myofibroblasts by TGF-beta was independent of Smad3. Previous irradiation-enhanced induction of connective tissue growth factor mRNA in wild-type, but not Smad3-null fibroblasts, suggested that this may contribute to the heightened scarring in irradiated wild-type skin as demonstrated by Picrosirius red staining. Overall, the data suggest that attenuation of Smad3 signaling might improve the healing of wounds in previously irradiated skin commensurate with an inhibition of fibrosis.

Potential action of IL-4 and IL-13 as fibrogenic factors on lung fibroblasts in vitro

BACKGROUND

Asthma is characterized by chronic inflammation of the airway with the presence of Th2 cytokines. Airway remodeling in asthma is closely related to clinical manifestations. Lung myofibroblasts play a critical role in the airway remodeling and Th2 cytokines may modulate their behavior. We examined the effect of two major Th2 cytokines, IL-4 and IL-13, on differentiation of lung fibroblasts to myofibroblasts. We hypothesized that these cytokines would stimulate fibroblast proliferation in association with decreased prostaglandin E(2) (PGE(2)).

METHODS

Lung fibroblasts were incubated with IL-4 and IL-13 with or without Th1 cytokine interferon-gamma (IFN-gamma) in vitro. Differentiation of lung fibroblasts to myofibroblasts was characterized by the expression of alpha-smooth muscle actin (alpha-SMA) as well as a morphological and immunohistochemical analysis. Fibroblast proliferation stimulated by IL-4 and IL-13 was assessed with the MTT assay. We also investigated the effect of these cytokines on cyclooxygenase (COX) gene expression and PGE(2) production.

RESULTS

IL-4 and IL-13 increased alpha-SMA expression and myofibroblastic differentiation. This effect was attenuated by IFN-gamma and dexamethasone failed to have an influence on differentiation. IL-4 and IL-13 stimulated fibroblast proliferation. These cytokines downregulated the expression of both COX-1 and COX-2 genes and decreased the production of PGE(2).

CONCLUSIONS

IL-4 and IL-13 induce differentiation of fibroblasts to myofibroblasts and this response is attenuated by IFN-gamma. IL-4 and IL-13 stimulate fibroblast proliferation and this effect is at least partly due to suppressed COX gene expressions and subsequently decreased PGE(2) production. These findings suggest that IL-4 and IL-13 directly act on lung fibroblast to induce a fibrogenic response.

Cell-type-specific activation of PAK2 by transforming growth factor beta independent of Smad2 and Smad3

Transforming growth factor beta (TGF-beta) causes growth arrest in epithelial cells and proliferation and morphological transformation in fibroblasts. Despite the ability of TGF-beta to induce various cellular phenotypes, few discernible differences in TGF-beta signaling between cell types have been reported, with the only well-characterized pathway (the Smad cascade) seemingly under identical control. We determined that TGF-beta receptor signaling activates the STE20 homolog PAK2 in mammalian cells. PAK2 activation occurs in fibroblast but not epithelial cell cultures and is independent of Smad2 and/or Smad3. Furthermore, we show that TGF-beta-stimulated PAK2 activity is regulated by Rac1 and Cdc42 and dominant negative PAK2 or morpholino antisense oligonucleotides to PAK2 prevent the morphological alteration observed following TGF-beta addition. Thus, PAK2 represents a novel Smad-independent pathway that differentiates TGF-beta signaling in fibroblast (growth-stimulated) and epithelial cell (growth-inhibited) cultures.

Structure/function analysis of mouse Purbeta, a single-stranded DNA-binding repressor of vascular smooth muscle alpha-actin gene transcription

Plasticity of smooth muscle alpha-actin gene expression in fibroblasts and vascular smooth muscle cells is mediated by opposing effects of transcriptional activators and repressors. Among these factors, three single-stranded DNA-binding proteins, Puralpha, Purbeta, and MSY1, have been implicated as coregulators of a cryptic 5'-enhancer module. In this study, a molecular analysis of Purbeta, the least well characterized member of this group, was conducted. Southwestern and Northwestern blotting of purified Purbeta deletion mutants using smooth muscle alpha-actin-derived probes mapped the minimal single-stranded DNA/RNA-binding domain to a conserved region spanning amino acids 37-263. Quantitative binding assays indicated that the relative affinity and specificity of Purbeta for single-stranded DNA were influenced by purine/pyrimidine content; by non-conserved regions outside amino acids 37-263; and by cell-derived proteins, specifically MSY1. When overexpressed in A7r5 vascular smooth muscle cells, Purbeta (but not Puralpha) inhibited transcription of a smooth muscle-specific mouse alpha-actin promoter transgene. Structural domains required for Purbeta repressor activity included the minimal DNA-binding region and a C-terminal domain required for stabilizing high affinity protein and nucleic acid interactions. Purbeta inhibitory activity in transfected A7r5 cells was potentiated by MSY1, but antagonized by serum response factor, reinforcing the idea that interplay among activators and repressors may account for phenotypic changes in smooth muscle alpha-actin-expressing cell types.

Specific protein-1 is a universal regulator of UDP-glucose dehydrogenase expression: its positive involvement in transforming growth factor-beta signaling and inhibition in hypoxia

UDP-glucose dehydrogenase (UGDH) is a key enzyme of the unique pathway for the synthesis of UDP-glucuronate, the substrate for the numerous glucuronosyl transferases, which act on the synthesis of glycosaminoglycans and glucuronidation reaction of xeno- and endobiotics. Using the bacterial artificial chromosome approach, we have cloned and characterized the human UGDH promoter. The core promoter of -644 nucleotides conferred reporter gene activity in transient transfection assay of a variety of cell types, including MRC5 fibroblasts and the HepG2 hepatoma cell line. The minimal promoter of -100 nucleotides contains a functional inverted TATA box. No consensus CAAT sequence was found up to -2133 nucleotides. The expression of UGDH was up- and down-regulated by transforming growth factor (TGF)-beta and hypoxia, respectively. TGF-beta enhanced the activity of all the deletion constructs, except the minimal promoter. Hypoxia slightly increased the activity of the short promoter-containing constructs but decreased that of the -374 nucleotides and core promoter constructs. The core promoter contained numerous GC-rich sequences for the binding of Sp1 transcription factor. Bisanthracycline, an anti-Sp1 compound, decreased UGDH mRNA expression and inhibited the core promoter constructs activity. Gel mobility shift and supershift assays after TGF-beta stimulation demonstrated an increased DNA binding of the nuclear extract proteins to the two Sp1 sequences located in the -374-bp promoter. By contrast, nuclear extract proteins from hypoxia-treated cells demonstrated a decreased binding of the consensus Sp1 sequence. These results indicate that numerous Sp1 cis-acting sequences of the UGDH core promoter are responsible for up- and down-regulation of the gene after TGF-beta stimulation and in hypoxic conditions, respectively.

MLL-mediated transcriptional gene regulation investigated by gene expression profiling

The human mixed lineage leukemia (MLL) gene is involved in about 50 different chromosomal translocations, associated with the disease phenotype of acute leukemia. However, the normal function of MLL is less understood. Homozygous knockouts of murine Mll were embryonal lethal, while heterozygous disruption led to aberrant hox gene expression associated with skeletal malformations, growth retardation, and impaired hematopoiesis. To understand MLL functions on the molecular level, gene expression profiling experiments were performed with a pair of murine cell lines (MLL(+/+) and MLL(-/-)). Microarray hybridization experiments revealed 197 potential target genes that are differentially expressed, providing new and important clues about MLL functions.