Role of basic region leucine zipper transcription factors cyclic AMP response element binding protein (CREB), CREB2, activating transcription factor 2 and CAAT/enhancer binding protein alpha in cyclic AMP response element-mediated transcription

The transcription factor cAMP response element binding protein (CREB), a member of the basic region leucine zipper (bZIP) family of proteins, is the major cAMP response element (CRE) binding. Other bZIP proteins, including CREB2, activating transcription factor 2 (ATF2), or CAAT/enhancer binding protein (C/EBP) have been reported to transactivate CRE-containing genes or to interfere with transactivation by CREB. We have designed a simple transactivation assay using expression of either a constitutively active CREB mutant or a nuclear targeted mutant of the catalytic subunit of cAMP-dependent protein kinase. In both cases, a striking stimulation of transcription of CRE-containing reporter genes was observed in noradrenergic locus coeruleus-like CATH.a cells. In addition, a constitutively active mutant of ATF2 specifically transactivated a secretogranin II promoter/luciferase reporter gene, but had no effect on the tyrosine hydroxylase promoter. In contrast, CREB2 and C/EBPalpha did not transactivate CRE-containing reporter genes, indicating that these bZIP proteins target distinct genetic elements. Experiments involving dominant-negative bZIP mutants revealed that CREB does not heterodimerize with CREB2, ATF2, c-Jun or C/EBP. Rather, CREB and ATF2 compete for binding to the CRE, and are independently able to up-regulate transcription of genes containing CRE motifs in their regulatory regions.

CEBPα mutations in childhood acute myeloid leukemia

CEBPalpha: mutations have been described in adult acute myeloid leukemia (AML) and conferred a favorable prognosis. However, CEBPalpha mutation has not been reported in children. We investigated 117 children with de novo AML using DNA PCR assay followed by sequencing for each PCR product. CEBPalpha mutations were detected in seven patients, four had FAB M2, two M1 and one M4. CEBPalpha mutations only occurred in patients with intermediate cytogenetics and not in 56 children with AML1-ETO, CBFbeta-MYH11, PML-RARalpha or MLL rearrangements. Five patients had mutations occurred in both N-terminal part and basic-leucine zipper (bZIP) domain, one had an N-terminal frameshift mutation and the remaining one had an inframe insertion in the bZIP domain. Cloning analysis on five samples carrying more than one mutations demonstrated one homozygous combined mutations and four heterozygous biallelic mutations. Four of seven CEBPalpha mutation(+) patients had cooperating mutations with FLT3-ITD or N-ras mutations compared to 27 in 109 CEBPalpha mutation(-) patients. Our results showed that CEBPalpha mutations occurred in 6% of childhood AML and most exhibited combined mutations in both N-terminal part and bZIP domain.

Essential requirement of CCAAT/enhancer binding proteins in embryogenesis

The CCAAT/enhancer binding proteins C/EBPalpha and C/EBPbeta are related transcription factors that are important for the function of various organs in the postnatal mouse. Gene replacement and tissue culture experiments have suggested partial redundancy of both transcription factors. Here we show that mouse embryos deficient of both C/EBPalpha and C/EBPbeta (C/EBPalphabeta(-/-)) die between embryonic day 10 (E10) and E11 and display defective placentas. In situ hybridization revealed that C/EBPalpha and C/EBPbeta are coexpressed in the chorionic plate at E9.5 and later in the trophoblasts of the labyrinthine layer. In C/EBPalphabeta(-/-) placentas, allantoic blood vessels invaded the chorion; however, vessel expansion and development of the labyrinthine layer was impaired. Furthermore, a single copy of either C/EBPalpha in the absence of C/EBPbeta or C/EBPbeta in the absence of C/EBPalpha is sufficient to complete development, suggesting complementation of these C/EBPs during embryogenesis. A single copy of C/EBPalpha in the absence of C/EBPbeta, however, fails to rescue survival after birth, suggesting haploinsufficiency of C/EBPalpha in newborns. Our data thus reveal novel essential, redundant, and dosage dependent functions of C/EBPs.

Valproic acid inhibits leptin secretion and reduces leptin messenger ribonucleic acid levels in adipocytes

Treatment of epilepsy or bipolar disorder with valproic acid (VPA) induces weight gain and increased serum levels for the satiety hormone, leptin, through an unidentified mechanism. In this study we tested the effects of VPA, a short-chain branched fatty acid (C8:0), on leptin biology and fatty acid metabolism in 3T3-L1 adipocytes. VPA significantly reduced leptin secretion in a dose-dependent manner. Because fatty acid accumulation has been hypothesized to block leptin secretion, we tested the effect of VPA on fatty acid metabolism. Using 14C-radiolabeled VPA, we found that the 14C was mainly incorporated into triacylglycerol. VPA did not alter lipogenesis from acetate, nor did it change the amount of intracellular free fatty acids available for triacylglycerol synthesis. Decreased leptin secretion was accompanied by a reduction in leptin mRNA, even though VPA treatment did not alter the protein levels for known transcription factors affecting leptin transcription including: CCAAT/enhancer binding protein-alpha, peroxisome proliferator-activated receptor-gamma, or steroid regulatory element binding protein 1a. VPA altered levels of leptin mRNA independent of de novo protein synthesis without affecting leptin mRNA degradation. This report demonstrates that VPA decreases leptin secretion and mRNA levels in adipocytes in vitro, suggesting that VPA therapy may be associated with altered leptin homeostasis contributing to weight gain in vivo.

Suppression of C/EBP alpha expression in biliary cell differentiation from hepatoblasts during mouse liver development

BACKGROUND/AIMS

Intrahepatic biliary cell differentiation takes place in periportal hepatoblasts under the influence of the subjacent mesenchyme, which leads to the suppression of mature hepatocyte marker expression. This study was undertaken to analyze C/EBP alpha and beta expression, which may govern transcription of mature hepatocyte marker genes, during mouse liver development with special attention given to biliary differentiation.

METHODS

Expression of C/EBP alpha and beta was immunohistochemically examined. Expression of alpha-fetoprotein, albumin and urea cycle enzymes, the genes of which have CCAAT motifs in their upstream regulatory sequences, was examined immunohistochemically or by using in situ hybridization.

RESULTS

C/EBP alpha started to be expressed in endodermal cells of 9.5-day liver primordium, and continued to be expressed in hepatoblasts and hepatocytes throughout development. Although biliary cell progenitors transiently expressed mature hepatocyte markers, their expression of C/EBP alpha was weak or totally absent. The signals of C/EBP beta in hepatocytes were weak in fetal liver, but became stronger with postnatal development. Differentiated epithelial cells of intrahepatic biliary structures did not express C/EBP alpha.

CONCLUSIONS

These data suggest that the suppression of C/EBP alpha expression may be prerequisite to biliary cell differentiation in the hepatoblast population and one of its earliest signs.

[Effect of Astragalus polysaccharides and berberine on carbohydrate metabolism and cell differentiation in 3T3-L1 adipocytes]

OBJECTIVE

To compare the effects of Astragalus polysaccharides (AP) and berberine (BB) on the adipocyte's carbohydrate metabolism and cell differentiation, for assessing the possible mechanism of them in improving carbohydrate metabolism.

METHODS

Adipocytes were treated with AP or BE, the 3H-glucose up-take rate in them was investigated, those of differentiation phase were stained by oil red O to analyze the degree of cell differentiation by spectrophotography quantitatively. The adipocyte differentiation related expression of PPARgamma mRNA and C/EBPalpha mRNA were determined by RT-PCR.

RESULTS

The 3H-glucose up-take rate in the AP group and BE group were 109.3% and 182.7% of that in the blank control group respectively. AP obviously promoted the cell differentiation and up-regulated expression of PPARgamma mRNA, while BE suppressed the differentiation and expression of PPARgamma and C/EBPalpha mRNA distinctly, all showing significant difference as compared with that in the blank control (P<0.01).

CONCLUSION

AP could promote glucose up-take, cell differentiation and PPARgamma mRNA expression, BB also promote glucose up-take, but suppress the cell differentiation, and inhibit expressions of PPARgamma and C/EBPalpha mRNA in 3T3-L1 adipocytes.

Glut4 storage vesicles without Glut4: transcriptional regulation of insulin-dependent vesicular traffic

Two families of transcription factors that play a major role in the development of adipocytes are the CCAAT/enhancer-binding proteins (C/EBPs) and the peroxisome proliferator-activated receptors (PPARs), in particular PPAR gamma. Ectopic expression of either C/EBP alpha or PPAR gamma in NIH 3T3 fibroblasts results in the conversion of these cells to adipocyte-like cells replete with fat droplets. NIH 3T3 cells ectopically expressing C/EBP alpha (NIH-C/EBP alpha) differentiate into adipocytes and exhibit insulin-stimulated glucose uptake, whereas NIH 3T3 cells ectopically expressing PPAR gamma (NIH-PPAR gamma) differentiate but do not exhibit any insulin-stimulated glucose uptake, nor do they express any C/EBP alpha. The reason for the lack of insulin-responsive glucose uptake in the NIH-PPAR gamma cells is their virtual lack of the insulin-responsive glucose transporter, Glut4. The NIH-PPAR gamma cells express functionally active components of the insulin receptor-signaling pathway (the insulin receptor, IRS-1, phosphatidylinositol 3-kinase, and Akt2) at levels comparable to those in responsive cell lines. They also express components of the insulin-sensitive vesicular transport machinery, namely, VAMP2, syntaxin-4, and IRAP, the last of these being the other marker of insulin-regulated vesicular traffic along with Glut4. Interestingly, the NIH-PPAR gamma cells show normal insulin-dependent translocation of IRAP and form an insulin-responsive vesicular compartment as assessed by cell surface biotinylation and sucrose velocity gradient analysis, respectively. Moreover, expression of a Glut4-myc construct in the NIH-PPAR gamma cells results in its insulin-dependent translocation to the plasma membrane as assessed by immunofluorescence and Western blot analysis. Based on these data, we conclude that major role of C/EBP alpha in the context of the NIH-PPAR gamma cells is to regulate Glut4 expression. The differentiated cells possess a large insulin-sensitive vesicular compartment with negligible Glut4, and Glut4 translocation can be reconstituted on expression of this transporter.

The leukemic fusion gene AML1-MDS1-EVI1 suppresses CEBPA in acute myeloid leukemia by activation of Calreticulin

The leukemic fusion gene AML1-MDS1-EVI1 (AME) encodes a chimeric transcription factor that results from the t(3,21)(q26;q22) translocation seen in patients with acute myeloid leukemia, with therapy-related myelodysplastic syndrome, or with chronic myeloid leukemia in blast crisis. The myeloid transcription factor CEBPA is crucial for normal granulopoiesis. Here, we found that conditional expression of AME suppresses CEBPA protein by 90.8% and DNA-binding activity by 93.9%. In contrast, CEBPA mRNA levels remained unchanged. In addition, we detected no differences in CEBPA mRNA levels in leukemic blasts of patients carrying the AME translocation (n = 8) compared to acute myeloid leukemia patients with a normal karyotype (n = 9). CEBPA protein and binding activity, however, were reduced significantly (100% and 92.1%, respectively) in AME patient samples. Furthermore, we observed that calreticulin (CRT), a putative inhibitor of CEBPA translation, was strongly activated after induction of AME in the cell-line system (14.8-fold) and in AME patient samples (12.2-fold). Moreover, inhibition of CRT by small interfering RNA powerfully restored CEBPA levels. These results identify CEBPA as a key target of the leukemic fusion protein AME and suggest that modulation of CEBPA by CRT may represent a mechanism involved in the differentiation block in AME leukemias.

A novel preadipocyte cell line established from mouse adult mature adipocytes

We have established a novel preadipocyte cell line from mouse adult mature adipocytes. The mature adipocytes were isolated from fat tissues by taking only the floating population of mature fat cells. The isolated mature adipocytes were de-differentiated into fibroblast-like cells. The in vitro studies showed that the cells could re-differentiate into mature adipocytes after over 20 passages. The in vivo transplantation study also demonstrated that the cells had the full potential to differentiate into mature adipocytes, which has not been shown for the 3T3-L1 preadipocyte cell line derived from mouse embryo. We have further analyzed the expression profile of key fat regulatory genes such as the peroxisome proliferator-activated receptorgamma or CCAAT/enhancer-binding protein gene families. We conclude that our cell line could be used as a preferred alternative to 3T3-L1, potentially reflecting the characteristics of mature adipocytes more, since the cell line is actually derived from adult mature adipocytes.

Hepatic CCAAT/enhancer binding protein alpha mediates induction of lipogenesis and regulation of glucose homeostasis in leptin-deficient mice

CCAAT/enhancer binding protein alpha (C/EBP alpha) is a critical factor in glucose metabolism in the neonate as revealed by conventional C/EBP alpha-null mice that do not survive beyond the first day after birth because of severe hypoglycemia and a deficiency in hepatic glycogen accumulation. To elucidate the function of C/EBP alpha in leptin-deficient mouse (ob/ob) liver, a C/EBP alpha-liver null mouse on an ob/ob background (ob/ob-C/EBP alpha/Cre(+)) was produced using a floxed C/EBP alpha allele and Cre recombinase under control of the albumin promoter (AlbCre). The C/EBP alpha-deficient liver in ob/ob mice had significantly decreased triglyceride content compared with equivalent mice lacking the AlbCre transgene (ob/ob-C/EBP alpha/Cre(-)). Expression of genes involved in lipogenesis including fatty acid synthase, acetyl-coenzyme A carboxylase, stearoyl-coenzyme A desaturase 1 and ATP-citrate lyase dramatically decreased in ob/ob-C/EBP alpha/Cre(+) mouse liver. Induction of these lipogenic genes by a high-carbohydrate diet caused an exacerbation in the development of fatty liver and an increase in liver size, hepatic triglyceride, and cholesterol contents in ob/ob-C/EBP alpha/Cre(-) mice but not in ob/ob-C/EBP alpha/Cre(+) mice. Deficiency in hepatic C/EBP alpha expression caused an exacerbation of hyperglycemia because of decreased insulin secretion. Taken together, these results indicate that hepatic C/EBP alpha plays a critical role in the acceleration of lipogenesis in ob/ob mice and in glucose homeostasis by the indirect regulation of insulin secretion.

Effect of a C/EBP gene replacement on mitochondrial biogenesis in fat cells

CCAAT/enhancer-binding proteins, C/EBPalpha and C/EBPbeta, are required for fat cell differentiation and maturation. Previous studies showed that replacement of C/EBPalpha with C/EBPbeta, generating the beta/beta alleles in the mouse genome, prevents lipid accumulation in white adipose tissue (WAT). In this study, beta/beta mice lived longer and had higher energy expenditure than their control littermates due to increased WAT energy oxidation. The WAT of beta/beta mice was enriched with metabolically active, thermogenic mitochondria known for energy burning. The beta/beta allele exerted its effect through the elevated expression of the G protein alpha stimulatory subunit (Galphas) in WAT. Galphas, when overexpressed in fat-laden 3T3-L1 cells, stimulated mitochondrial biogenesis similar to that seen in the WAT of beta/beta mice, and effectively diminished the stored lipid pool.

Dysfunctional interaction of C/EBPalpha and the glucocorticoid receptor in asthmatic bronchial smooth-muscle cells

BACKGROUND

Increased proliferation of bronchial smooth-muscle cells may lead to increased muscle mass in the airways of patients with asthma. The antiproliferative effect of glucocorticoids in bronchial smooth-muscle cells in subjects without asthma is mediated by a complex of the glucocorticoid receptor and the CCAAT/enhancer binding protein alpha (C/EBPalpha). We examined the signaling pathway controlling the inhibitory effect of glucocorticoids on cell proliferation and interleukin-6 synthesis in bronchial smooth-muscle cells of subjects with asthma and those without asthma.

METHODS

Lines of bronchial smooth-muscle cells were established from cells from 20 subjects with asthma, 8 subjects with emphysema, and 26 control subjects. Cell proliferation was determined by means of cell counts and [3H]thymidine incorporation. Signal transduction was studied by means of an electrophoretic DNA mobility-shift assay, a supershift electrophoretic-mobility assay, immunoblotting, use of C/EBPalpha antisense oligonucleotides, and use of a human C/EBPalpha expression vector. Interleukin-6 release was determined by means of an enzyme-linked immunosorbent assay.

RESULTS

Glucocorticoids activated the glucocorticoid receptor and inhibited serum-induced secretion of interleukin-6 in bronchial smooth-muscle cells from both subjects with asthma and those without asthma; however, glucocorticoids inhibited proliferation only in bronchial smooth-muscle cells from subjects without asthma. C/EBPalpha protein was detected by immunoblotting in all bronchial smooth-muscle cells from subjects without asthma but not in those with asthma, whereas the protein was expressed in lymphocytes from both groups of subjects. C/EBPalpha antisense oligonucleotides or the glucocorticoid-receptor inhibitor mifepristone reversed the antiproliferative effect of glucocorticoids in bronchial smooth-muscle cells from subjects without asthma. When bronchial smooth-muscle cells from subjects with asthma were transiently transfected with an expression vector for human C/EBPalpha, two forms of the protein were expressed, and subsequent administration of glucocorticoids inhibited cell proliferation.

CONCLUSIONS

We hypothesize that a cell-type-specific absence of C/EBPalpha is responsible for the enhanced proliferation of bronchial smooth-muscle cells derived from subjects with asthma and that it explains the failure of glucocorticoids to inhibit proliferation in vitro.

Altered fat differentiation and adipocytokine expression are inter-related and linked to morphological changes and insulin resistance in HIV-1-infected lipodystrophic patients

OBJECTIVE

To achieve a better understand of the pathophysiology of HIV-related lipoatrophy, we compared the mRNA expression of adipocytokines in fat samples from patients and healthy HIV-seronegative controls together with fat morphology and we studied the relationship between changes in fat morphology, adipocytokine expression, markers of adipose tissue differentiation and whole body insulin sensitivity.

DESIGN

Cross-sectional analytical study.

SUBJECTS AND METHODS

The mRNA expression of adipocytokines and transcriptional factors in fat samples from 26 patients with peripheral lipoatrophy (all under anti-retroviral therapy associating protease inhibitor and nucleoside-analogue reverse transcriptase inhibitors) and from 16 non-HIV-infected controls was measured by real time quantitative RT-PCR. Fat morphology was assessed histologically on a subgroup of 10 patients and six controls: collagen fibres by Sirius Red staining, apoptosis by the TUNEL technique, vessels by smooth muscle alpha-actin staining and macrophages by CD68 staining. Insulin resistance was assessed by using the homeostasis model assessment.

RESULTS

The patients' fat showed higher values of apoptosis (P=0.005), fibrosis (P<0.05), vessel density (P=0.001) and macrophage infiltration (P<0.05) than the controls' fat, together with lower adiponectin and leptin mRNA levels and higher interleukin (IL)-6 and tumour necrosis factor (TNF)alpha mRNA levels. TNFa and IL-6 expression correlated positively with the level of apoptosis (P=0.05 and P<0.05, respectively) and negatively with CCAAT-enhancer binding protein (C/EBP)alpha (P<0.001 and P<0.05, respectively). Apoptosis correlated negatively with the expression level of sterol-regulatory-element-binding-protein-1c (SREBP1c) (P=0.01) and C/EBPalpha (P=0.01) whilst the vessel density correlated negatively with SREBP1c (P<0.005), C/EBPalpha (P=0.001) and beta (P=0.001). Adiponectin and leptin expression correlated positively with each other, and also with adipogenic marker expression and overall insulin sensitivity. These relationships were also present when the patient group was studied separately. Finally, fat morphological abnormalities correlated positively with whole body insulin resistance.

CONCLUSIONS

Adipose tissue from patients with HIV-1-related lipoatrophy shows increased apoptosis, together with decreased adipocyte differentiation. Increased TNFalpha and IL-6 expression could be a major phenomenon linking these alterations. Decreased adiponectin and leptin expression, which may result from decreased adipocyte differentiation, could be involved in the observed whole body insulin resistance.

Sequential gene promoter interactions of C/EBPbeta, C/EBPalpha, and PPARgamma during adipogenesis

Treatment of 3T3-L1 preadipocytes with differentiation inducers triggers a cascade in which C/EBPbeta is rapidly expressed, followed by C/EBPalpha and PPARgamma. C/EBPalpha and PPARgamma then activate the expression of adipocyte genes that produce the differentiated phenotype. Circumstantial evidence indicates that C/EBPbeta activates transcription of the C/EBPalpha and PPARgamma genes, both of which possess C/EBP regulatory elements in their proximal promoters. Although C/EBPbeta is expressed immediately upon induction of differentiation, acquisition of DNA binding activity is delayed for approximately 14h. Chromatin immunoprecipitation (ChIP) analysis conducted 24h after induction revealed that C/EBPbeta binds to C/EBP regulatory elements in the proximal promoters of the C/EBPalpha and PPARgamma genes. After an additional delay ChIP analysis showed that C/EBPalpha binds to its own promoter and to the promoters of the PPARgamma and 422/aP2 genes. These findings support the view that once expressed, C/EBPalpha is responsible for maintaining the expression of PPARgamma and C/EBPalpha, as well as adipocyte proteins (e.g., 422/aP2) in the terminally differentiated state. Together these findings provide compelling evidence that C/EBPbeta, C/EBPalpha, and PPARgamma participate in a cascade during adipogenesis.

Interleukin 11 treatment alters the protein content of Galpha(i2) and adipogenic transcription factors in 3T3-L1 adipocytes

Exposure of fully differentiated 3T3-L1 adipocytes to 5 nM interleukin 11 (IL-11) resulted in an increase (1.9+/-0.5 fold) in the protein content for the heterotrimeric G protein Galpha(i2). This G protein has been suggested to be involved in the control of the insulin responsive glucose transporter (GLUT4) translocation to the plasma membrane. Conversely, IL-11 had no effect on the content of three other G proteins, involved in insulin action. The alteration in Galpha(i2) protein corresponds to and provides a molecular rationale for our previously described IL-11 induced increase in plasma membrane glucose transporter content and increased rate of glucose transport. In addition, treatment with the cytokine altered the protein content of several transcription factors, C/EBPalpha and CHOP-10 decreased while PPARgamma and C/EBPbeta increased. These changes in transcription factor content are consistent with an alteration of phenotype with the cells reverting to an earlier stage of the differentiation process in response to IL-11.

Reciprocal roles of MSX2 in regulation of osteoblast and adipocyte differentiation

Mice deficient in the Msx2 gene manifest defects in skull ossification and a marked reduction in bone formation associated with decreases in osteoblast numbers, thus suggesting that Msx2 is involved in bone formation. However, the precise role of Msx2 during osteoblast differentiation is not fully understood. In the present study, we investigated the role of Msx2 in the regulation of osteoblast differentiation in the multipotent mesenchymal cell lines C3H10T1/2 and C2C12 and in murine primary osteoblasts. Introduction of Msx2 induced alkaline phosphatase activity in C3H10T1/2 and C2C12 cells and promoted the calcification of murine primary osteoblasts. This effect of Msx2 was also observed in mesenchymal cells isolated from Runx2-deficient mice. Interestingly the expression of Msx2 was induced by bone morphogenetic protein 2 treatment in Runx2-deficient mesenchymal cells. In contrast, Msx2 diminished peroxisome proliferator-activated receptor gamma (PPARgamma) expression and adipogenesis of the preadipocytic cell line 3T3-F442A. Moreover Msx2 inhibited the transcriptional activity of PPARgamma, CCAAT/enhancer-binding protein beta (C/EBPbeta), and C/EBPdelta and blocked adipocyte differentiation of mesenchymal cells induced by overexpression of PPARgamma, C/EBPalpha, C/EBPbeta, or C/EBPdelta. These data indicate that Msx2 promotes osteoblast differentiation independently of Runx2 and negatively regulates adipocyte differentiation through inhibition of PPARgamma and the C/EBP family.

Dual roles for the Notch target gene Hes-1 in the differentiation of 3T3-L1 preadipocytes

The process of adipogenesis involves a complex program of gene expression that includes down-regulation of the gene encoding Hes-1, a target of the Notch signaling pathway. To determine if Notch signaling affects adipogenesis, we exposed 3T3-L1 preadipocytes to the Notch ligand Jagged1 and found that differentiation was significantly reduced. This effect could be mimicked by constitutive expression of Hes-1. The block was associated with a complete loss of C/EBPalpha and peroxisome proliferator-activated receptor gamma (PPARgamma) induction and could be overcome by retroviral expression of either C/EBPalpha or PPARgamma2. Surprisingly, small interfering RNA (siRNA)-mediated reduction of Hes-1 mRNA in 3T3-L1 cells also inhibited differentiation, suggesting an additional, obligatory role for Hes-1 in adipogenesis. This role may be related to our observation that both Notch signaling and Hes-1 down-regulate transcription of the gene encoding DLK/Pref-1, a protein known to inhibit differentiation of 3T3-L1 cells. The results presented in this study establish a new target downstream of the Notch-Hes-1 pathway and suggest a dual role for Hes-1 in adipocyte development.

Regulatory potential scores from genome-wide three-way alignments of human, mouse, and rat

We generalize the computation of the Regulatory Potential (RP) score from two-way alignments of human and mouse to three-way alignments of human, mouse, and rat. This requires overcoming technical challenges that arise because the complexity of the models underlying the score increases exponentially with the number of species. Despite the close evolutionary proximity of rat to mouse, we find that adding the rat sequence increases our ability to predict genomic sites that regulate gene transcription. A variant of the RP scoring scheme that accounts for local variation in neutral mutational patterns further improves our predictions.

Sequential gene promoter interactions by C/EBPβ, C/EBPα, and PPARγ during adipogenesis

Treatment of 3T3-L1 preadipocytes with differentiation inducers triggers a cascade in which C/EBPbeta is rapidly expressed, followed by C/EBPalpha and PPARgamma. C/EBPalpha and PPARgamma then activate the expression of adipocyte genes that produce the differentiated phenotype. Circumstantial evidence indicates that C/EBPbeta activates transcription of the C/EBPalpha and PPARgamma genes, both of which possess C/EBP regulatory elements in their proximal promoters. Although C/EBPbeta is expressed immediately upon induction of differentiation, acquisition of DNA binding activity is delayed for approximately 14h. Chromatin immunoprecipitation (ChIP) analysis conducted 24h after induction revealed that C/EBPbeta binds to C/EBP regulatory elements in the proximal promoters of the C/EBPalpha and PPARgamma genes. ChIP analysis showed that after an additional delay C/EBPalpha binds to its own promoter and to the promoters of the PPARgamma and 422/aP2 genes. These findings support the view that once expressed, C/EBPalpha is responsible for maintaining the expression of PPARgamma, and C/EBPalpha, as well as adipocyte proteins (e.g., 422/aP2) in the terminally differentiated state. Together these findings provide compelling evidence that C/EBPbeta, C/EBPalpha, and PPARgamma participate in a cascade during adipogenesis.

[Expression of CCAAT/enhancer-binding protein in cultured rat hepatic stellate cells and its significance]

OBJECTIVE

The expression of C/EBPalpha protein and mRNA during automatically activation process in primary cultures of HSCs were observed in order to explore its possible association with the proliferation and activation of HSCs.

METHODS

Immunocytochemistry, Western blot and RT-PCR were used to evaluated the expression of C/EBPalpha protein and mRNA; as well as the expression of alpha-SMA, Desmin, MMP2, type I procollagen (alpha1). The eukaryotic vector harboring the full length cDNA of C/EBPalpha was transfected into activated HSC, then immunocytochemistry was applied to confirm the transfection and evaluate the effect of transfection on the proliferation of HSC by calculating the PCNA-positive cells. The morphological changes of HSC were observed by use of phase-contrast microscope.

RESULTS

Constitutive expression of mRNA and protein of C/EBPalpha were detected in primarily cultured HSCs, and the protein was seen in both nuclei and cytoplasm with the latter being dominant. Their expression levels reached highest at day 2 of the culture, then decreased gradually when continually cultured to the day 4, 7, 10, on the other hand, the expression of alpha-SMA, MMP2 and ColI(alpha1) increased steadily. Transient transfection was verified by the fact that much more and stronger C/EBPalpha stain was observed in transfected HSCs than in void-vector transfected cells. In C/EBPalpha gene transfected HSCs, the number of PCNA-positive cells dramatically decreased compared with the void-vector transfected cells 24h after transfection. In addition, the C/EBPalpha gene transfected HSCs died 36 h after transfection, a few surviving cells became longer and thinner in morphology, however the void-vector transfected cells almost all remained alive.

CONCLUSIONS

C/EBPalpha was likely involved in the HSCs activation, and over-expressed C/EBPalpha by transfection had inhibitory influence on the proliferation of cultured rat HSCs.

Lipin expression preceding peroxisome proliferator-activated receptor-gamma is critical for adipogenesis in vivo and in vitro

We recently identified mutations in the lipin gene, Lpin1, as the cause of lipodystrophy in the fatty liver dystrophy (fld) mouse. Here we identify impaired adipocyte differentiation as the basis for lipodystrophy in lipin-deficient mice and demonstrate that lipin is required for normal induction of the adipogenic gene transcription program. We found that the reduced adiposity in chow fed fld mice and resistance to obesity in fld mice fed a high-fat diet is associated with reduced adipogenic gene expression. Using primary mouse embryonic fibroblasts isolated from fld mice, we confirmed that lipin deficiency prevents normal lipid accumulation and induction of key adipogenic genes, including peroxisome proliferator-activated receptor (PPAR)gamma and CCAAT enhancer-binding protein (C/EBP)alpha. However, our previous studies of daily gene expression in differentiating 3T3-L1 preadipocytes indicated that lipin expression is undetectable until about day 3 of differentiation, at a point after PPARgamma and C/EBPalpha gene expression is established. This paradox was resolved by examining gene expression at 10-h intervals during 3T3-L1 cell differentiation, leading to detection of transient lipin expression at 10 h into the differentiation program, prior to the induction of PPARgamma and C/EBPalpha. Consistent with a requirement for lipin expression upstream of PPARgamma, differentiation of lipin-deficient mouse embryonic fibroblasts could be rescued by ectopic expression of PPARgamma. Thus, we conclude that lipin expression is required prior to PPARgamma during adipocyte differentiation.

Roles of fibroblast growth factor 10 (Fgf10) in adipogenesis in vivo

The development of white adipose tissue (WAT) of Fgf10-/- mouse embryos was greatly impaired. Here, we examined the mechanism of Fgf10 action in adipogenesis in vivo. The proliferative activity in the WAT of Fgf10-/- embryos was greatly decreased. We also examined the expression of transcription factors, C/EBPbeta, C/EBPalpha and PPARgamma, that are important for adipogenesis. Although the expression of C/EBPbeta and PPARgamma in the WAT of Fgf10-/- embryos was greatly decreased, the expression of C/EBPalpha was essentially unchanged. Therefore, we examined their expression in the WAT of C/EBPalpha-/- embryos. Although the expression of C/EBPbeta and PPARgamma in the WAT was greatly decreased, the expression of Fgf10 was essentially unchanged. As these results in vivo appeared to be contradictory to a transcriptional cascade model in vitro that C/EBPbeta induces the expression of PPARgamma and C/EBPalpha reported, we also examined their expression in the WAT of wild type embryos at different developmental stages. The expression of Fgf10 and C/EBPalpha was followed by that of C/EBPbeta and PPARgamma. The present findings indicate that Fgf10 but not C/EBPalpha is required for the proliferation of preadipocytes. In contrast, both Fgf10 and C/EBPalpha acting synergistically in separate, parallel pathways are required for the differentiation. Unexpectedly, the transcriptional cascade of adipogenesis in vivo described here is distinct from the cascade in vitro previously reported.