A quantum dot single-photon turnstile device

Quantum communication relies on the availability of light pulses with strong quantum correlations among photons. An example of such an optical source is a single-photon pulse with a vanishing probability for detecting two or more photons. Using pulsed laser excitation of a single quantum dot, a single-photon turnstile device that generates a train of single-photon pulses was demonstrated. For a spectrally isolated quantum dot, nearly 100% of the excitation pulses lead to emission of a single photon, yielding an ideal single-photon source.

Mutations that alter the higher-order structure of its 5' untranslated region affect the stability of chloroplast rps7 mRNA

In this paper, we examine the effects of mutations in the 5'UTR of the chloroplast rps7 transcript of Chlamydomonas reinhardtii that reduce the stability of the mRNA. Five point mutants in the rps7 5'UTR were selected on the basis of their failure to accumulate reporter mRNA in Escherichia coli. Each of these mutations produces alterations in the predicted higher-order structures of the rps7 5'UTR that destabilize the mRNA. Cis-acting suppressors of these mutations have been selected in E. coli and in the C. reinhardtii chloroplast that restore message stability and function. No differences in RNA melting and reannealing profiles have been observed between wild type, original mutant, and suppressor 5'UTRs transcribed in vitro. Proteins of 32 kDa and 47 kDa that bind to the wild-type rps7 5'UTR are not detected by UV cross-linking assays performed with any of the mutant rps7 5'UTRs. However, binding of the 32-kDa protein is restored in the six suppressor mutants examined. This suggests that the 32-kDa protein may be involved in protecting the rps7 5'UTR and the attached coding region from digestion by ribonucleases. Alternatively, the binding site for the 32-kDa protein may be independently lost in the rearranged tertiary structure of the mutant 5'UTR that exposes the RNA to degradation and is restored in the suppressor mutants.

Identification of a novel kidney-specific gene downregulated in acute ischemic renal failure

To gain further insights into the molecular mechanisms involved in acute renal failure, we have isolated a new gene from rat and human, named KSP32 (kidney-specific protein with a molecular mass of 32 kDa). KSP32 encodes a novel gene that shows little homology to other mammalian proteins. It, however, shares extensive homology with several proteins found in the nematode Caenorhabditis elegans and plants. The expression of KSP32 mRNA is highly restricted to kidney. In situ hybidization analysis revealed that the expression of KSP32 mRNA was prominent in the boundary of kidney cortex and outer medulla, exhibiting a raylike formation extending from the medulla into the cortex. Finally, KSP32 mRNA was dramatically downregulated in rat following induction of acute ischemic renal failure. Rapid loss of KSP32 mRNA expression was observed beginning at approximately 5 h following renal injury and mRNA levels remained depressed for at least 96 h. Both KSP32 mRNA levels as well as renal function recovered 14 days after injury. Administration of an endothelin receptor antagonist (SB-209670), known to restore renal function, significantly increased KSP32 expression.

Validating a screening questionnaire for parkinsonism in Australia

Parkinson's disease is a common neurodegenerative disorder in elderly people. Epidemiological studies of the disease can be labour intensive. A two phase design including a screening questionnaire as the first phase has become a popular method in prevalence studies of Parkinson's disease. Such a design has many advantages including less work for assessing physicians and enhanced recruitment of people to be screened. However, its wider application may be questioned because validation has been limited to samples that are drawn from hospitals (or clinics) and may be inappropriate for a community setting. This study assesses whether validating screening questionnaire by using a hospital sample yields the same result as a community based sample. Furthermore, it seeks to establish whether the screening instrument can be simplified to involve less questions. The findings show that some of the questions used in the screening phase yield different responses when comparing a hospital group with a community group. This study also provides a simplified model of questions that may be relevant for screening in the community setting.

Cloning and characterization of a novel human class I histone deacetylase that functions as a transcription repressor

Histone acetylation alters chromatin state by modifying lysines on histone and plays an important role in modulating gene transcription. A dynamic balance of histone acetylation/deacetylation is maintained by histone acetyltransferases and histone deacetylases. Emerging evidence suggests that a family of histone deacetylases may exist to regulate diverse cellular functions, including chromatin structure, gene expression, cell cycle progression, and oncogenesis. We describe here a novel human histone deacetylase, named HDAC8, cloned from human kidney. HDAC8 encodes 377 amino acid residues and shares extensive homology to several known HDACs, in particular a histone deacetylase from Arabidopsis thaliana. Northern blot analyses revealed that HDAC8 expression pattern for HDAC8 is distinct from that for HDAC1 and HDAC3, and expression of HDAC8 mRNA occurs in multiple organs including heart, lung, kidney, and pancreas. HDAC8 mRNA was also observed in several cell lines derived from cancerous tissues. When expressed in HEK293 cells, HDAC8 exhibited deacetylase activity toward acetylated histone, indicating that this protein is a bona fide histone deacetylase. Its histone deacetylase activity was inhibited by trichostatin and other known histone deacetylase inhibitors. Furthermore, active recombinant HDAC8 was expressed and purified from Escherichia coli. When ectopically expressed in cells, HDAC8 was found to be localized to the nucleus. Co-transfection experiments demonstrated that expression of HDAC8 repressed a viral SV40 early promoter activity. These results indicate that HDAC8 is a novel member of the histone deacetylase family, which may play a role in the development of a broad range of tissues and potentially in the etiology of cancer.

Caltech Faint Galaxy Redshift Survey. XI. The Merger Rate to Redshift 1 from Kinematic Pairs

The rate of mass accumulation due to galaxy merging depends on the mass, density, and velocity distribution of galaxies in the near neighborhood of a host galaxy. The fractional luminosity in kinematic pairs combines all of these effects in a single estimator that is relatively insensitive to population evolution. Here we use a k-corrected and evolution-compensated volume-limited sample having an R-band absolute magnitude of Mk,eR</=-19.8+5logh mag drawing about 300 redshifts from the Caltech Faint Galaxy Redshift Survey and 3000 from the Canadian Network for Observational Cosmology field galaxy survey to measure the rate and redshift evolution of merging. The combined sample has an approximately constant comoving number and luminosity density from redshift 0.1 to 1.1 (OmegaM=0.2, OmegaLambda=0.8); hence, any merger evolution will be dominated by correlation and velocity evolution, not density evolution. We identify kinematic pairs with projected separations less than either 50 or 100 h-1 kpc and rest-frame velocity differences of less than 1000 km s-1. The fractional luminosity in pairs is modeled as fL&parl0;Deltav,rp,Mk,er&parr0;&parl0;1+z&parr0;mL, where &sqbl0;fL,mL&sqbr0; are &sqbl0;0.14+/-0.07,0+/-1.4&sqbr0; and &sqbl0;0.37+/-0.7,0.1+/-0.5&sqbr0; for rp</=50 and 100 h-1 kpc, respectively (OmegaM=0.2, OmegaLambda=0.8). The value of mL is about 0.6 larger if Lambda=0. To convert these redshift-space statistics to a merger rate, we use the data to derive a conversion factor to a physical space pair density, a merger probability, and a mean in-spiral time. The resulting mass accretion rate per galaxy (M1,M2>/=0.2M*) is 0.02+/-0.01&parl0;1+z&parr0;0.1+/-0.5M* Gyr-1. Present-day high-luminosity galaxies therefore have accreted approximately 0.15M* of their mass over the approximately 7 Gyr to redshift 1. Since merging is likely only weakly dependent on the host mass, the fractional effect, deltaM&solm0;M approximately 0.15M*&solm0;M, is dramatic for lower mass galaxies but is, on the average, effectively perturbative for galaxies above 1M*.

Overexpression of ribonucleotide reductase as a mechanism of resistance to 2,2-difluorodeoxycytidine in the human KB cancer cell line

In this study, human oropharyngeal epidermoid carcinoma KB cells that were resistant to 2,2-difluorodeoxycytidine (dFdCyd) were selected and designated the KB-Gem clone. The KB parental cell line IC50 was 0.3 microM dFdCyd, as compared with the KB-Gem clone IC50 of 32 microM dFdCyd. The KB-Gem clone demonstrated overexpression of ribonucleotide reductase (RR) M2 subunit mRNA (9-fold) and overexpression of M2 protein (2-fold); RR activity was 2.3-fold higher than the KB parental cell line. Both the dATP and dCTP pools of the KB-Gem clone increased 2-fold over the parental cell line, with no change in the dGTP and dTTP pools. Reverse transcriptase-PCR was used to clone the cDNA of deoxycytidine kinase (DCK). Resulting sequences revealed two silent mutations in the KB-Gem clone. The amino acid sequence of the DCK protein and mRNA expression remained unchanged. The KB-Gem clone's DCK enzyme activity was 56% of that of the parental cell line. After the endogenous dNTPs were removed with a G-25 column, no difference was evident between the enzyme activities of the KB-Gem clone and parental cells. Thus, contrary to previous hypotheses, DCK deficiency does not play the primary role in the resistance mechanism of dFdCyd, accepting a secondary role to the overexpression of the target gene, RR, and pool expansion.

DEF-1, a novel Src SH3 binding protein that promotes adipogenesis in fibroblastic cell lines

The Src homology 3 (SH3) motif is found in numerous signal transduction proteins involved in cellular growth and differentiation. We have purified and cloned a novel protein, DEF-1 (differentiation-enhancing factor), from bovine brain by using a Src SH3 affinity column. Ectopic expression of DEF-1 in fibroblasts resulted in the differentiation of a significant fraction of the culture into adipocytes. This phenotype appears to be related to the induction of the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma), since DEF-1 NIH 3T3 cells demonstrated augmented levels of PPARgamma mRNA and, when treated with activating PPARgamma ligands, efficient induction of differentiation. Further evidence for a role for DEF-1 in adipogenesis was provided by heightened expression of DEF-1 mRNA in adipose tissue isolated from obese and diabetes mice compared to that in tissue isolated from wild-type mice. However, DEF-1 mRNA was detected in multiple tissues, suggesting that the signal transduction pathway(s) in which DEF-1 is involved is not limited to adipogenesis. These results suggest that DEF-1 is an important component of a signal transduction process that is involved in the differentiation of fibroblasts and possibly of other types of cells.

Tissue restricted expression of two human Frzbs in preadipocytes and pancreas

Frzb is a newly discovered family of secreted glycoproteins that function to modulate signaling activity of Wnt. Frzb proteins share sequence homology with the extracellular domain of the Wnt receptor (frizzled) and are capable of binding to Wnt. Thus, Frzb functions to antagonize Wnt activity by sequestering Wnt and preventing its binding to the frizzled receptor. Since the initial identification of bovine and human Frzb, several related members of this family have been isolated from rodent and human. In this paper, we describe the cloning and expression of two human frzb homologues termed hFRP-1b and hFRP-2. These human FRPs share significant homology to mouse sFRP-1 and sFRP-2 (55 and 98% identity at amino acid level, respectively). Northern blot experiments revealed that these Frzb homologues have highly restricted tissue distribution. hFRP-1b is exclusively expressed in pancreatic tissue while high levels of hFRP-2 were found in adipose tissue. In addition, low levels of hFRP-2 were also observed in other tissues including heart, pancreas and muscle. Remarkably, FRP-2 is predominantly expressed in un-differentiated preadipocytes in both rodent and man. The expression of FRP-2 is also significantly reduced in fat pads from obese mice. Taken together, these data indicate that distinctive members of the Frzb family exhibit different expression patterns in vivo, suggesting their ability to modulate diverse aspects of Wnt signaling. The expression and dysregulation of sFRP-2 in fat and obesity also suggest a potential roles on the Wnt signaling pathway in the pathology of obesity and related metabolic diseases. Molecular cloning and expression of these Frzbs will allow detailed molecular and biochemical analysis of Wnt-Frzb interaction and their impact on Wnt-Frizzled receptor signal transduction.

Short-wave cone signal in the red-green detection mechanism

Previous work shows that the red-green (RG) detection mechanism is highly sensitive, responding to equal and opposite long-wave (L) and middle-wave (M) cone contrast signals. This mechanism mediates red-green hue judgements under many conditions. We show that the RG detection mechanism also receives a weak input from the short-wave (S) cones that supports the L signal and equally opposes M. This was demonstrated with a pedestal paradigm, in which weak S cone flicker facilitates discrimination and detection of red-green flicker. Also, a near-threshold +S cone flash facilitates detection of red flashes and inhibits green flashes, and a near-threshold -S cone flash facilitates detection of green flashes and inhibits red flashes. The S contrast weight in RG is small relative to the L and M contrast weights. However, a comparison of our results with other studies suggests that the strength of the absolute S cone contrast contribution to the RG detection mechanism is 1/4 to 1/3 the strength of the S contribution to the blue-yellow (BY) detection mechanism. Thus, the S weight in RG is a significant fraction of the S weight in BY. This has important implications for the 'cardinal' color mechanisms, for it predicts that for detection or discrimination, the mechanisms limiting performance do not lie on orthogonal M-L and S axes within the equiluminant color plane.

Peroxisome proliferator-activated receptor gamma and the control of adipogenesis

The adipose cell is now known to play a complex role in energy homeostasis, storing energy and signaling to other tissues concerning the state of energy balance. The past several years have seen an explosive increase in our knowledge of the transcriptional basis of adipocyte differentiation. This review describes the role of peroxisome proliferator-activated receptor gamma in this process, and describes how other transcription factors may affect adipogenesis by modulating the amount or activity of peroxisome proliferator-activated receptor gamma. Furthermore, peroxisome proliferator-activated receptor gamma and other adipogenic transcription factors provide a focus for beginning to understand how various hormones and metabolites influence the development of this tissue in vivo.

PPAR gamma and the control of adipogenesis

We recently cloned PPAR gamma as a factor that binds to an enhancer which has specificity for adipose cells. When expressed ectopically, PPAR gamma converts fibroblasts into bona fide preadipose cells. Upon application of activators or PPAR gamma ligands, these cells differentiate into fat cells. Most recently, we have been trying to understand the nature of natural ligands that activate PPAR gamma and the protein domains that control adipogenesis. With regards to ligands, we have shown that an unusual prostanoid, 15-deoxy delta 12,14PG J2, can bind to PPAR gamma and activate it. A second transcription factor that is induced early in differentiation, ADD1/SREBP1, appears to promote the formation of PPAR gamma ligands. Transfection of this molecule, a member of the bHLH family, causes the secretion of molecules that can serve as ligands for PPAR gamma. This ligand-like activity is specific for the gamma isoform of PPAR. Current studies are attempting to identify these potentially novel ligands. With regard to structure-function of PPAR gamma, we first analyzed the adipogenic activity of the three isoforms of PPAR: alpha, gamma and delta. Using appropriate activators of each it is clear that PPAR gamma has the most adipogenic action. PPAR alpha can be adipogenic with high levels of the strongest activators and PPAR delta does not stimulate fat cell differentiation. To identify the domain(s) of PPAR gamma responsible for differentiation, chimeras between PPAR gamma and PPAR delta were created and transfected into fibroblasts. This has allowed the isolation of relatively small regions of this molecule that are responsible for differentiation.

Inhibition of adipogenesis through MAP kinase-mediated phosphorylation of PPARgamma

Adipocyte differentiation is an important component of obesity and other metabolic diseases. This process is strongly inhibited by many mitogens and oncogenes. Several growth factors that inhibit fat cell differentiation caused mitogen-activated protein (MAP) kinase-mediated phosphorylation of the dominant adipogenic transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) and reduction of its transcriptional activity. Expression of PPARgamma with a nonphosphorylatable mutation at this site (serine-112) yielded cells with increased sensitivity to ligand-induced adipogenesis and resistance to inhibition of differentiation by mitogens. These results indicate that covalent modification of PPARgamma by serum and growth factors is a major regulator of the balance between cell growth and differentiation in the adipose cell lineage.

Adipocyte differentiation: a transcriptional regulatory cascade

The adipose cell is now known to play a complex role in energy homeostasis, energy storage and signaling to other tissues concerning the state of energy balance. The past few years have seen an explosive increase in our knowledge of the transcriptional basis of adipocyte differentiation. Factors such as peroxisome proliferator-activated receptor gamma, the CCAAT/enhancer binding protein family members, and adipocyte determination- and differentiation-dependent factor 1 play important regulatory roles in this process. Furthermore, these factors provide a focus for beginning to understand how various hormones and metabolites influence the development of adipose tissue in vivo.

Negative regulation of peroxisome proliferator-activated receptor-gamma gene expression contributes to the antiadipogenic effects of tumor necrosis factor-alpha

Recent studies indicate that a peroxisome proliferator-activated receptor, PPAR gamma, functions as an important adipocyte determination factor. In contrast, tumor necrosis factor-alpha (TNF alpha) inhibits adipogenesis, causes dedifferentiation of mature adipocytes, and reduces the expression of several adipocyte-specific genes. Here, we report that treatment of 3T3-L1 adipocytes with TNF alpha resulted in a time- and concentration-dependent decrease in PPAR gamma mRNA expression to the level detected in preadipocytes. PPAR gamma mRNA levels were reduced by 95% with 3 nM TNF alpha treatment for 24 h. Half-maximal effects were seen after 3 h treatment with 3 nM TNF alpha or with 50 pM TNF alpha (24-h exposure). Parallel reductions in PPAR gamma protein levels were also observed after treatment of 3T3-L1 adipocytes with TNF alpha. Using a ribonuclease protection assay, both alternatively spliced PPAR gamma isoforms (gamma 1 and gamma 2) were shown to be negatively regulated by TNF alpha. The down-regulation of PPAR gamma by TNF-alpha preceded the diminution in expression of other adipocyte-specific genes including CCAAT/enhancer binding protein and adipocyte fatty acid-binding protein (aP2). The effect of TNF alpha was specific for the gamma-isoform of PPARs, since the expression of PPAR delta mRNA was not affected by treatment with TNF alpha. Low level constitutive expression of PPAR gamma in 3T3-L1 adipocytes (at levels approximately 2- to 3-fold higher than in preadipocytes) partially blocked the inhibitory effect of TNF alpha on aP2 and adipsin expression. These findings support the following conclusions: 1) PPAR gamma expression is necessary for the maintenance of the adipocyte phenotype. 2) PPAR gamma, but not PPAR delta, expression is sufficient to attenuate TNF alpha-mediated effects on adipocyte phenotype. 3) Reduced PPAR gamma gene expression is likely to represent an important component of the mechanism by which TNF alpha exerts its antiadipogenic effects.

Routine use of unilateral and bilateral radial arteries for coronary artery bypass graft surgery

OBJECTIVES

This study sought to evaluate the routine use of radial artery (RA) grafts in patients undergoing coronary artery revascularization.

BACKGROUND

Previous long-term studies have documented poor patency of saphenous vein grafts compared with internal thoracic artery (ITA) grafts.

METHODS

We performed a prospective review of 175 of 249 consecutive patients.

RESULTS

Fifty-four patients had bilateral RAs harvested. Mean number (+/- SD) of grafts/patient was 3.27 +/- 0.93, with 2.76 +/- 0.97 arterial grafts; a mean of 1.53 +/- 0.68 grafts were performed with the RA. The operative mortality rate was 1.6%. No deaths were related to RA grafts, and there were no RA harvest site hematomas or infections. Transient dysesthesia 1 day to 4 weeks in duration occurred in the distribution of the lateral antebrachial cutaneous nerve in six extremities (2.6%). Elective cardiac catheterization in 60 patients at 12 weeks postoperatively demonstrated a 95.7% patency rate.

CONCLUSIONS

Because of potential benefit of long-term patency associated with arterial grafts, minimal morbidity and mortality associated with use of the RA and excellent short-term patency rates, we cautiously recommend use of one or both RAs as additional conduits to be used concomitantly with the ITA for arterial revascularization of the coronary arteries.

Regulation of PPAR gamma gene expression by nutrition and obesity in rodents

The orphan nuclear receptor, peroxisome proliferator-activated receptor (PPAR) gamma, is implicated in mediating expression of fat-specific genes and in activating the program of adipocyte differentiation. The potential for regulation of PPAR gamma gene expression in vivo is unknown. We cloned a partial mouse PPAR gamma cDNA and developed an RNase protection assay that permits simultaneous quantitation of mRNAs for both gamma l and gamma 2 isoforms encoded by the PPAR gamma gene. Probes for detection of adipocyte P2, the obese gene product, leptin, and 18S mRNAs were also employed. Both gamma l and gamma 2 mRNAs were abundantly expressed in adipose tissue. PPAR gamma 1 expression was also detected at lower levels in liver, spleen, and heart; whereas, gamma l and gamma 2 mRNA were expressed at low levels in skeletal muscle. Adipose tissue levels of gamma l and gamma 2 were not altered in two murine models of obesity (gold thioglucose and ob/ob), but were modestly increased in mice with toxigene-induced brown fat ablation uncoupling protein diphtheria toxin A mice. Fasting (12-48 h) was associated with an 80% fall in PPAR gamma 2 and a 50% fall in PPAR gamma mRNA levels in adipose tissue. Western blot analysis demonstrated a marked effect of fasting to reduce PPAR gamma protein levels in adipose tissue. Similar effects of fasting on PPAR gamma mRNAs were noted in all three models of obesity. Insulin-deficient (streptozotocin) diabetes suppressed adipose tissue gamma l and gamma 2 expression by 75% in normal mice with partial restoration during insulin treatment. Levels of adipose tissue PPAR gamma 2 mRNA were increased by 50% in normal mice exposed to a high fat diet. In obese uncoupling protein diphtheria toxin A mice, high fat feeding resulted in de novo induction of PPAR gamma 2 expression in liver. We conclude (a) PPAR gamma 2 mRNA expression is most abundant in adipocytes in normal mice, but lower level expression is seen in skeletal muscle; (b) expression of adipose tissue gamma1 or gamma2 mRNAs is increased in only one of the three models of obesity; (c) PPAR gamma 1 and gamma 2 expression is downregulated by fasting and insulin-deficient diabetes; and (d) exposure of mice to a high fat diet increases adipose tissue expression of PPAR gamma (in normal mice) and induces PPAR gamma 2 mRNA expression in liver (in obese mice). These findings demonstrate in vivo modulation of PPAR gamma mRNA levels over a fourfold range and provide an additional level of regulation for the control of adipocyte development and function.

AdipoQ is a novel adipose-specific gene dysregulated in obesity

Adipose differentiation is accompanied by changes in cellular morphology, a dramatic accumulation of intracellular lipid and activation of a specific program of gene expression. Using an mRNA differential display technique, we have isolated a novel adipose cDNA, termed adipoQ. The adipoQ cDNA encodes a polypeptide of 247 amino acids with a secretory signal sequence at the amino terminus, a collagenous region (Gly-X-Y repeats), and a globular domain. The globular domain of adipoQ shares significant homology with subunits of complement factor C1q, collagen alpha 1(X), and the brain-specific factor cerebellin. The expression of adipoQ is highly specific to adipose tissue in both mouse and rat. Expression of adipoQ is observed exclusively in mature fat cells as the stromal-vascular fraction of fat tissue does not contain adipoQ mRNA. In cultured 3T3-F442A and 3T3-L1 preadipocytes, hormone-induced differentiation dramatically increases the level of expression for adipoQ. Furthermore, the expression of adipoQ mRNA is significantly reduced in the adipose tissues from obese mice and humans. Whereas the biological function of this polypeptide is presently unknown, the tissue-specific expression of a putative secreted protein suggests that this factor may function as a novel signaling molecule for adipose tissue.

Transdifferentiation of myoblasts by the adipogenic transcription factors PPAR gamma and C/EBP alpha

Skeletal muscle and adipose tissue development often has a reciprocal relationship in vivo, particularly in myodystrophic states. We have investigated whether determined myoblasts with no inherent adipogenic potential can be induced to transdifferentiate into mature adipocytes by the ectopic expression of two adipogenic transcription factors, PPAR gamma and C/EBP alpha. When cultured under optimal conditions for muscle differentiation, murine G8 myoblasts expressing PPAR gamma and C/EBP alpha show markedly reduced levels of the myogenic basic helix-loop-helix proteins MyoD, myogenin, MRF4, and myf5 and are completely unable to differentiate into myotubes. Under conditions permissive for adipogenesis including a PPAR activator, these cells differentiate into mature adipocytes that express molecular markers characteristic of this lineage. Our results demonstrate that a developmental switch between these two related but highly specialized cell types can be controlled by the expression of key adipogenic transcription factors. These factors have an ability to inhibit myogenesis that is temporally and functionally separate from their ability to stimulate adipogenesis.

Regulation of adipocyte gene expression and differentiation by peroxisome proliferator activated receptor gamma

Peroxisome proliferator activated receptor (PPAR)gamma is an orphan member of the nuclear hormone receptor superfamily and is expressed at high levels specifically in adipose tissue. Recent data suggest that this factor is a central regulator of adipocyte gene expression and differentiation. Fibroblastic cell lines that express PPARgamma ectopically can be induced to differentiate into fat cells by a variety of lipids and lipid-like activators of PPARs, suggesting that this protein may function to link adipogenesis with systemic lipid metabolism.

PPAR gamma 2 regulates adipose expression of the phosphoenolpyruvate carboxykinase gene

Phosphoenolpyruvate carboxykinase (PEPCK) is expressed at high levels in liver, kidney, and adipose tissue. This enzyme catalyzes the rate-limiting step in hepatic and renal gluconeogenesis and adipose glyceroneogenesis. The regulatory factors important for adipose expression of the PEPCK gene are not well defined. Previous studies with transgenic mice established that the region between bp -2086 and -888 is required for expression in adipose tissue but not for expression in liver or kidney tissue. We show here that a DNA fragment containing this region can function as an enhancer and direct differentiation-dependent expression of a chloramphenicol acetyltransferase gene from a heterologous promoter in cultured 3T3-F442A preadipocytes and adipocytes. We further demonstrate that the adipocyte-specific transcription factor PPAR gamma 2, previously identified as a regulator of the adipocyte P2 enhancer, binds in a heterodimeric complex with RXR alpha to the PEPCK 5'-flanking region at two sites, termed PCK1 (bp -451 to -439) and PCK2 (bp -999 to -987). Forced expression of PPAR gamma 2 and RXR alpha activates the PEPCK enhancer in non-adipose cells. This activation is potentiated by peroxisome proliferators and fatty acids but not by 9-cis retinoic acid. Mutation of the PPAR gamma 2 binding site (PCK2) abolishes both the activity of the enhancer in adipocytes and its ability to be activated by PPAR gamma 2 and RXR alpha. These results establish a role for PPAR gamma 2 in the adipose expression of the PEPCK gene and suggest that this factor functions as a coordinate regulator of multiple adipocyte-specific genes.

Stimulation of adipogenesis in fibroblasts by PPAR gamma 2, a lipid-activated transcription factor

Peroxisome proliferator-activated receptor gamma 2 (PPAR gamma 2) is an adipocyte-specific nuclear hormone receptor that has recently been identified as a key regulator of two fat cell enhancers. Transcriptional activation by PPAR gamma 2 is potentiated by a variety of lipids and lipid-like compounds, including naturally occurring polyunsaturated fatty acids. We demonstrate here that retroviral expression of PPAR gamma 2 stimulates adipose differentiation of cultured fibroblasts. PPAR activators promote the differentiation of PPAR gamma 2-expressing cells in a dose-dependent manner. C/EBP alpha, a second transcription factor induced during adipocyte differentiation, can cooperate with PPAR gamma 2 to stimulate the adipocyte program dramatically. Our results suggest that the physiologic role of PPAR gamma 2 is to regulate development of the adipose lineage in response to endogenous lipid activators and that this factor may serve to link the process of adipocyte differentiation to systemic lipid metabolism.