Identification and characterization of an immunophilin expressed during the clonal expansion phase of adipocyte differentiation

FK-binding protein 5: Possible relevance to the pathogenesis of metabolic dysfunction and alcohol-associated liver disease

The FK506-binding protein (FKBP5) plays significant roles in mediating stress responses by interacting with glucocorticoids, participating in adipogenesis, and influencing various cellular pathways throughout the body. In this review, we described the potential role of FKBP5 in the pathogenesis of two common chronic liver diseases, metabolic dysfunction-associated steatotic liver disease (MASLD), and alcohol-associated liver disease (ALD). We provided an overview of the FK-binding protein family and elucidated their roles in cellular stress responses, metabolic diseases, and adipogenesis. We explored how FKBP5 may mechanistically influence the pathogenesis of MASLD and ALD and provided insights for further investigation into the role of FKBP5 in these two diseases.

FKBP51 plays an essential role in Akt ubiquitination that requires Hsp90 and PHLPP

FKBP51 plays a relevant role in sustaining cancer cells, particularly melanoma. This cochaperone participates in several signaling pathways. FKBP51 forms a complex with Akt and PHLPP, which is reported to dephosphorylate Akt. Given the recent discovery of a spliced FKBP51 isoform, in this paper, we interrogate the canonical and spliced isoforms in regulation of Akt activation. We show that the TPR domain of FKBP51 mediates Akt ubiquitination at K63, which is an essential step for Akt activation. The spliced FKBP51, lacking such domain, cannot link K63-Ub residues to Akt. Unexpectedly, PHLPP silencing does not foster phosphorylation of Akt, and its overexpression even induces phosphorylation of Akt. PHLPP stabilizes levels of E3-ubiquitin ligase TRAF6 and supports K63-ubiquitination of Akt. The interactome profile of FKBP51 from melanoma cells highlights a relevant role for PHLPP in improving oncogenic hallmarks, particularly, cell proliferation.

Contribution of the co-chaperone FKBP51 in the ventromedial hypothalamus to metabolic homeostasis in male and female mice

Objective

Steroidogenic factor 1 (SF1) expressing neurons in the ventromedial hypothalamus (VMH) have been directly implicated in whole-body metabolism and in the onset of obesity. The co-chaperone FKBP51 is abundantly expressed in the VMH and was recently linked to type 2 diabetes, insulin resistance, adipogenesis, browning of white adipose tissue (WAT) and bodyweight regulation.

Methods

We investigated the role of FKBP51 in the VMH by conditional deletion and virus-mediated overexpression of FKBP51 in SF1-positive neurons. Baseline and high fat diet (HFD)-induced metabolic- and stress-related phenotypes in male and female mice were obtained.

Results

In contrast to previously reported robust phenotypes of FKBP51 manipulation in the entire mediobasal hypothalamus (MBH), selective deletion or overexpression of FKBP51 in the VMH resulted in only a moderate alteration of HFD-induced bodyweight gain and body composition, independent of sex.

Conclusions

Overall, this study shows that animals lacking and overexpressing Fkbp5 in Sf1-expressing cells within the VMH display only a mild metabolic phenotype compared to an MBH-wide manipulation of this gene, suggesting that FKBP51 in SF1 neurons within this hypothalamic nucleus plays a subsidiary role in controlling whole-body metabolism.

•

Loss of FKBP51 in SF1 neurons of the VMH induces a mild metabolic phenotype.

•

Male and female mice develop similar metabolic responses to the loss of FKBP51.

•

VMH-specific overexpression of FKBP51 induces phenotypes comparable to knockout.

•

FKBP51 in the VMH mediates whole-body metabolism in a U-shaped manner.

Relation of adipose tissue and skeletal muscle FKBP5 expression with insulin sensitivity and the regulation of FKBP5 by insulin and free fatty acids

PURPOSE

Recent studies suggest that FK506 binding protein 51 (FKBP51), a negative regulator of glucocorticoid response, encoded by FKBP5, may influence insulin action. The aim of the present study was to assess the relationship between subcutaneous adipose tissue (AT) and skeletal muscle FKBP5 expression in relation to insulin sensitivity in healthy individuals and to study its regulation by insulin and circulating free fatty acid (FFA) elevation.

METHODS

The study group comprised 96 male subjects, 49 normal-weight and 47 overweight/obese. Hyperinsulinemic clamp, subcutaneous AT and skeletal muscle biopsies were performed. In a subgroup of 20 subjects, two 6 h clamps were performed, with and without Intralipid/heparin infusion, and tissue biopsies were obtained before and after each clamp.

RESULTS

AT FKBP5 expression was lower in overweight/obese individuals in comparison with normal-weight individuals (p = 0.004). Muscle FKBP5 expression did not differ between the groups, however, it was inversely related to insulin sensitivity (r = -0.32, p = 0.002). FKBP5 expression decreased in AT (p = 0.003) and increased in muscle (p < 0.0001) after insulin infusion. Intralipid/heparin diminished insulin-induced increase in muscle FKBP5.

CONCLUSION

Our data show that lower AT FKBP5 expression is related to obesity, whereas muscle FKBP5 expression is associated with insulin resistance. AT and muscle FKBP5 expression is differentially regulated by insulin.

FKBP51 and the molecular chaperoning of metabolism

The molecular chaperone FK506-binding protein 51 (FKBP51) is gaining attention as a meaningful biomarker of metabolic dysfunction. This review examines the emerging contributions of FKBP51 in adipogenesis and lipid metabolism, myogenesis and protein catabolism, and glucocorticoid-induced skin hypoplasia and dermal adipocytes. The FKBP51 signaling mechanisms that may explain these metabolic consequences are discussed. These mechanisms are diverse, with FKBP51 independently and directly regulating phosphorylation cascades and nuclear receptors. We provide a discussion of the newly developed compounds that antagonize FKBP51, which may offer therapeutic advantages for adiposity. These observations suggest we are only beginning to uncover the complex nature of FKBP51 and its molecular chaperoning of metabolism.

Focus on FKBP51: A molecular link between stress and metabolic disorders

BACKGROUND

Obesity, Type 2 diabetes (T2D) as well as stress-related disorders are rising public health threats and major burdens for modern society. Chronic stress and depression are highly associated with symptoms of the metabolic syndrome, but the molecular link is still not fully understood. Furthermore, therapies tackling these biological disorders are still lacking. The identification of shared molecular targets underlying both pathophysiologies may lead to the development of new treatments. The FK506 binding protein 51 (FKBP51) has recently been identified as a promising therapeutic target for stress-related psychiatric disorders and obesity-related metabolic outcomes.

SCOPE OF THE REVIEW

The aim of this review is to summarize current evidence of in vitro, preclinical, and human studies on the stress responsive protein FKBP51, focusing on its newly discovered role in metabolism. Also, we highlight the therapeutic potential of FKBP51 as a new treatment target for symptoms of the metabolic syndrome.

MAJOR CONCLUSIONS

We conclude the review by emphasizing missing knowledge gaps that remain and future research opportunities needed to implement FKBP51 as a drug target for stress-related obesity or T2D.

Expression of FK506-binding protein 51 (FKBP51) in Mycosis fungoides

BACKGROUND

Mycosis fungoides (MF) is the major subtype of cutaneous T-cell lymphomas (CTCL). It usually has a prolonged indolent clinical course with a minority of cases acquiring a more aggressive biological profile and resistance to conventional therapies, partially attributed to the persistent activation of nuclear factor-kappa B (NF-κB) pathway. In the last decade, several papers suggested an important role for the FK506-binding protein 51 (FKBP51), an immunophilin initially cloned in lymphocytes, in the control of NF-κB pathway in different types of human malignancies.

OBJECTIVES

We aimed to investigate the possible value of FKBP51 expression as a new reliable marker of outcome in patients with MF.

METHODS

We assessed by immunohistochemistry (IHC) FKBP51 expression in 44 patients with MF, representative of different stages of the disease. Immunohistochemical results were subsequently confirmed at mRNA level with quantitative PCR (qPCR) in a subset of enrolled patients. In addition, IHC and qPCR served to study the expression of some NF-κB-target genes, including the tumour necrosis factor receptor-associated factor 2 (TRAF2).

RESULTS

Our results show that FKBP51 was expressed in all evaluated cases, with the highest level of expression characterizing MFs with the worst prognosis. Moreover, a significant correlation subsisted between FKBP51 and TRAF2 IHC expression scores.

CONCLUSIONS

We hypothesize a role for FKBP51 as a prognostic marker for MF and suggest an involvement of this immunophilin in deregulated NF-κB pathway of this CTCL.

FKBP51 Null Mice Are Resistant to Diet-Induced Obesity and the PPARγ Agonist Rosiglitazone

FK506-binding protein-51 (FKBP51) is a molecular cochaperone recently shown to be a positive regulator of peroxisome proliferator-activated receptor (PPAR)γ, the master regulator of adipocyte differentiation and function. In cellular models of adipogenesis, loss of FKBP51 not only reduced PPARγ activity but also reduced lipid accumulation, suggesting that FKBP51 knock-out (KO) mice might have insufficient development of adipose tissue and lipid storage ability. This model was tested by examining wild-type (WT) and FKBP51-KO mice under regular and high-fat diet conditions. Under both diets, FKBP51-KO mice were resistant to weight gain, hepatic steatosis, and had greatly reduced white adipose tissue (WAT) but higher amounts of brown adipose tissue. Under high-fat diet, KO mice were highly resistant to adiposity and exhibited reduced plasma lipids and elevated glucose and insulin tolerance. Profiling of perigonadal and sc WAT revealed elevated expression of brown adipose tissue lineage genes in KO mice that correlated increased energy expenditure and a shift of substrate oxidation to carbohydrates, as measured by indirect calorimetry. To directly test PPARγ involvement, WT and KO mice were fed rosiglitazone agonist. In WT mice, rosiglitazone induced whole-body weight gain, increased WAT mass, a shift of substrate oxidation to lipids, and elevated expression of PPARγ-regulated lipogenic genes in WAT. In contrast, KO mice had reduced rosiglitazone responses for these parameters. Our results identify FKBP51 as an important regulator of PPARγ in WAT and as a potential new target in the treatment of obesity and diabetes.

The FKBP5 polymorphism rs1360780 is associated with lower weight loss after bariatric surgery: 26 months of follow-up

BACKGROUND

Bariatric surgery is the most effective treatment choice for severe obesity. Recent literature indicates that FK506-binding protein 51 (FKBP51) could play a role in energy homeostasis, influencing adipogenesis and weight.

OBJECTIVE

To evaluate if the presence of the T allele of the FKBP5 SNP rs1360780, associated with increased FKBP51 expression, could influence weight loss after bariatric surgery.

SETTING

Hospital de Clínicas de Porto Alegre, Brazil.

METHODS

Forty-two patients awaiting bariatric surgery were included, and the presence of the FKBP5 rs1360780 polymorphism was evaluated. During the postoperative period, a 26-month follow-up of weight loss was performed (n = 42, 36, 35, 35, and 30, from the first to fifth postoperative evaluation, respectively; loss to follow-up: 28.6%).

RESULTS

Carriers of the T allele presented significantly lower weight loss compared with patients with the C/C genotype after the 12th to 14th month follow-up period. Differences in weight loss between genotypes ranged from 14.2% to 19.9% of excess weight loss (P = .045 and .004, respectively) and from 7.6% to 9.0% of total weight loss (P = .002 for both comparisons). Furthermore, carriers of the T allele also presented an earlier cessation of weight loss after surgery.

CONCLUSION

The presence of the T allele of the FKBP5 SNP rs1360780 was associated with weight loss after bariatric surgery. Bariatric surgery can interact with genes involved in metabolic regulation, leading to different weight loss outcomes.

Adipogenesis is under surveillance of Hsp90 and the high molecular weight Immunophilin FKBP51

Adipose tissue plays a central role in the control of energy balance as well as in the maintenance of metabolic homeostasis. It was not until recently that the first evidences of the role of heat shock protein (Hsp) 90 and high molecular weight immunophilin FKBP51 have been described in the process of adipocyte differentiation. Recent reports describe their role in the regulation of PPARγ, a key transcription factor in the control of adipogenesis and the maintenance of the adipocyte phenotype. In addition, novel roles have been uncovered for FKBP51 in the organization of the architecture of the nucleus through its participation in the reorganization of the nuclear lamina. Therefore, the aim of this review is to integrate and discuss the recent advances in the field, with special emphasis on the roles of Hsp90 and FKBP51 in the process of adipocyte differentiation.

Pleiotropic roles in cancer biology for multifaceted proteins FKBPs

BACKGROUND

FK506 binding proteins (FKBP) are multifunctional proteins highly conserved across the species and abundantly expressed in the cell. In addition to a well-established role in immunosuppression, FKBPs modulate several signal transduction pathways in the cell, due to their isomerase activity and the capability to interact with other proteins, inducing changes in conformation and function of protein partners. Increasing literature data support the concept that FKBPs control cancer related pathways.

SCOPE OF THE REVIEW

The aim of the present article is to review current knowledge on FKBPs roles in regulation of key signaling pathways associated with cancer.

MAJOR CONCLUSIONS

Some family members appear to promote disease while others are protective against tumorigenesis.

GENERAL SIGNIFICANCE

FKBPs family proteins are expected to provide new biomarkers and small molecular targets, in the near future, increasing diagnostic and therapeutic opportunities in the cancer field. This article is part of a Special Issue entitled Proline-Directed Foldases: Cell Signaling Catalysts and Drug Targets.

Multidomain Peptidyl Prolyl cis/trans Isomerases

BACKGROUND

Peptidyl prolyl cis/trans isomerases (PPIases) assist the folding and restructuring of client proteins by catalysis of the slow rotational motion of peptide bonds preceding a proline residue. Catalysis is performed by relatively small, distinct protein domains of 10 to 18kDa for all PPIase families. PPIases are involved in a wide variety of physiological and pathophysiological processes like signal transduction, cell differentiation, apoptosis as well as viral, bacterial and parasitic infection.

SCOPE OF REVIEW

There are multidomain PPIases consisting of one to up to four catalytic domains of the respective PPIase family supplemented by N- or C-terminal extensions. This review examines the biochemical and functional properties of the members of the PPIase class of enzymes which contain additional protein domains with defined biochemical functions.

MAJOR CONCLUSIONS

The versatile domain architecture of multidomain PPIases is important for the control of enzyme specificity and organelle-specific targeting, the establishment of molecular connections and hence the coordination of PPIase functions across the cellular network.

GENERAL SIGNIFICANCE

Accessory domains covalently linked to a PPIase domain supply an additional layer of control to the catalysis of prolyl isomerization in specific client proteins. Understanding these control mechanisms will provide new insights into the physiological mode of action of the multidomain PPIases and their ability to form therapeutic targets. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

FKBP51 controls cellular adipogenesis through p38 kinase-mediated phosphorylation of GRα and PPARγ

Glucocorticoid receptor-α (GRα) and peroxisome proliferator-activated receptor-γ (PPARγ) are critical regulators of adipogenic responses. We have shown that FK506-binding protein 51 (FKBP51) represses the Akt-p38 kinase pathway to reciprocally inhibit GRα but stimulate PPARγ by targeting serine 112 (PPARγ) and serines 220 and 234 (GRα). Here, this mechanism is shown to be essential for GRα and PPARγ control of cellular adipogenesis. In 3T3-L1 cells, FKBP51 was a prominent marker of the differentiated state and knockdown of FKBP51 showed reduced lipid accumulation and expression of adipogenic genes. Compared with wild-type (WT), FKBP51 knockout (51KO) mouse embryonic fibroblasts (MEFs) showed dramatic resistance to differentiation, with almost no lipid accumulation and greatly reduced adipogenic gene expression. These features were rescued by reexpression of FKBP51 in 51KO cells. 51KO MEFs exhibited reduced fatty acid synthase activity, increased sensitivity to GRα-induced lipolysis, and reduced PPARγ activity at adipogenic genes (adiponectin, CD36, and perilipin) but elevated GRα transrepression at these same genes. A p38 kinase inhibitor increased lipid content in WT cells and also restored lipid levels in 51KO cells, showing that elevated p38 kinase activity is a major contributor to adipogenic resistance in the 51KO cells. In 51KO cells, the S112A mutant of PPARγ and the triple S212A/S220A/S234A mutant of GRα both increased lipid accumulation, identifying these residues as targets of the FKBP51/p38 axis. Our combined investigations have uncovered FKBP51 as a key regulator of adipogenesis via the Akt-p38 pathway and as a potential target in the treatment of obesity and related disorders.

Expression profiles of key transcription factors involved in lipid metabolism in Beijing-You chickens

Intramuscular fat (IMF) is a crucial factor for the meat quality of chickens. With the aim of studying the molecular mechanisms underlying IMF deposition in chickens, the expression profiles of five candidate transcription factors involved in lipid metabolism in several tissues were examined in Beijing-You (BJY) chickens at five ages (0, 4, 8, 14 and 20 wk). Results showed that accumulation of IMF in breast (IMFbr), thigh (IMFth) and abdominal fat weight increased significantly (P<0.01) after 8 wk. Accumulation of both IMFbr and IMFth from 8 to 14 wk exceeded that from 14 to 20 wk; IMFth was 4-7 times of IMFbr. As for the expression profiles of key transcription factors: 1) expression of C/EBPα and PPARγ in abdominal fat was significantly higher than that in breast and thigh muscles at all ages. The expression of C/EBPα was positively correlated with PPARγ in both breast and thigh muscles, which indicated that both C/EBPα and PPARγ promoted fat deposition and might act through a unified pathway; 2) the expression of SREBP-1 in 0, 4, and 8 wk in thigh muscle was significantly higher than that in breast; 3) expression of C/EBPβ at 4 and 8 wk was significantly higher than that at 14 and 20 wk; and it was positively correlated with IMFth and IMFbr from 0 to 8 wk; 4) expression of PPARα in breast and thigh muscles was significantly higher than that in abdominal fat. Taken together, all five transcription factors studied play roles in lipid metabolism in chickens with C/EBPα and PPARγ being important effectors.

FK506 binding protein 51 positively regulates melanoma stemness and metastatic potential

Melanoma is the most aggressive skin cancer; there is no cure in advanced stages. Identifying molecular participants in melanoma progression may provide useful diagnostic and therapeutic tools. FK506 binding protein 51 (FKBP51), an immunophilin with a relevant role in developmental stages, is highly expressed in melanoma and correlates with aggressiveness and therapy resistance. We hypothesized a role for FKBP51 in melanoma invasive behaviour. FKBP51 promoted activation of epithelial-to-mesenchymal transition (EMT) genes and improved melanoma cell migration and invasion. In addition, FKBP51 induced some melanoma stem cell (MCSC) genes. Purified MCSCs expressed high EMT genes levels, suggesting that genetic programs of EMT and MCSCs overlap. Immunohistochemistry of samples from patients showed intense FKBP51 nuclear signal and cytoplasmic positivity for the stem cell marker nestin in extravasating melanoma cells and metastatic brains. In addition, FKBP51 targeting by small interfering RNA (siRNA) prevented the massive metastatic substitution of liver and lung in a mouse model of experimental metastasis. The present study provides evidence that the genetic programs of cancer stemness and invasiveness overlap in melanoma, and that FKBP51 plays a pivotal role in sustaining such a program.

The prospect of FKBP51 as a drug target

The FK506 binding protein 51 (FKBP51) is best known as an Hsp90-associated co-chaperone that regulates the responsiveness of steroid hormone receptors. In human genetic association studies, FKBP51 has repeatedly been associated with emotion processing and numerous stress-related affective disorders. It has also been implicated in contributing to the glucocorticoid hyposensitivity observed in New World primates. More recently, several research groups have consistently shown a protective effect of FKBP51 knockout or knockdown on stress endocrinology and stress-coping behavior in animal models of depression and anxiety. The principal druggability of FKBP51 is exemplified by the prototypic FKBP ligands FK506 and rapamycin. Moreover, FKBP51 is highly suited for X-ray co-crystallography, which should facilitate the rational drug design of improved FKBP51 ligands. In summary, FKBP51 has emerged as a promising new drug target for stress-related disorders that should be amenable to drug discovery.

Hepatic arterial reconstruction for orthotopic liver transplantation in the rat

BACKGROUND

Orthotopic liver transplantation (OLT) models in rats have been investigated in many studies. The reconstruction of hepatic artery is required for reliable OLT and also requires advanced skills.

METHODS

The hepatic artery reconstructions by a hand-suture technique and a new method using a micro T-tube were investigated in rats with a whole-liver syngeneic graft. Operative time and postoperative patency were compared between the hand-suture and micro T-tube techniques.

RESULTS

Our technique using the micro T-tube shortened the operative time of recipient surgery compared with the hand-suture technique and prolonged the operative time for the donor. The patency ratio was maintained at 24h after OLT with hand suturing but was significantly reduced with the micro T-tube, which had a patency ratio of 0.83 only up to 6h after OLT.

CONCLUSION

The micro T-tube technique may have potential usefulness in the rat OLT model but requires further modification.

The emerging role of large immunophilin FK506 binding protein 51 in cancer

FK506 binding protein 51 (FKBP51) is an immunophilin physiologically expressed in lymphocytes. Very recently, aberrant expression of this protein was found in melanoma; FKBP51 expression correlates with melanoma aggressiveness and is maximal in metastatic lesions. FKBP51 promotes NF-κB activation and is involved in the resistance to genotoxic agents, including anthracyclines and ionizing radiation. FKBP51 is a cochaperone with peptidyl-prolyl isomerase activity that regulates several biological processes through protein-protein interaction. There is increasing evidence that FKBP51 hyperexpression is associated with cancer and this protein has a relevant role in sustaining cell growth, malignancy, and resistance to therapy. There is also evidence that FKBP ligands are potent anticancer agents, in addition to their immunosuppressant activity. In particular, rapamycin and its analogs have shown antitumor activity across a variety of human cancers in clinical trials. Although, classically, rapamycin actions are ascribed to inhibition of mTOR, recent studies indicate FKBP51 is also an important molecular determinant of the drug's anticancer activity. The aim of this article is to review the functions of FKBP51, especially in view of the recent findings that this protein is a potential oncogene when deregulated and a candidate target for signaling therapies against cancer.

Cellular and molecular large-scale features of fetal adipose tissue: is bovine perirenal adipose tissue brown?

Epidemiological and fetal programming studies point to the role of fetal growth in adult adipose tissue (AT) mass in large mammals. Despite the incidence of fetal AT growth for human health and animal production outcomes, there is still a lack of relevant studies. We determined the cellular and large-scale-molecular features of bovine fetal perirenal AT sampled at 110, 180, 210, and 260 days post-conception (dpc) with the aim of identifying key cellular and molecular events in AT growth. The increase in AT weight from 110 to 260 dpc resulted from an increase in adipocyte volume and particularly adipocyte number that were concomitant with temporal changes in the abundance of 142 proteins revealed by proteomics. At 110 and 180 dpc, we identified proteins such as TCP1, FKBP4, or HSPD1 that may regulate adipocyte precursor proliferation by controlling cell-cycle progression and/or apoptosis or delaying PPARγ-induced differentiation. From 180 dpc, the up-regulation of PPARγ-induced proteins, lipogenic and lipolytic enzymes, and adipokine expression may underpin the differentiation and increase in adipocyte volume. Also from 180 dpc, we unexpectedly observed up-regulations in the β-subunit of ATP synthase, which is normally bypassed in brown AT, as well as in aldehyde dehydrogenases ALDH2 and ALDH9A1, which were predominantly expressed in mouse white AT. These results, together with the observed abundant unilocular adipocytes at 180 and 260 dpc, strongly suggest that fetal bovine perirenal AT has much more in common with white than with brown AT.

Proteomic analysis for antiobesity potential of capsaicin on white adipose tissue in rats fed with a high fat diet

It is well recognized that capsaicin increases thermogenesis through enhancement of catecholamine secretion from the adrenal medulla. In the present study of the antiobesity effect of capsaicin, rats (5-week old) received capsaicin (10 mg/kg) along with a high-fat diet (HFD). In comparison with saline-treated rats, body weight of those in the capsaicin-treated group decreased by 8%. We performed differential proteomic analysis using two-dimensional electrophoresis (2-DE) combined with MALDI-TOF mass spectrometry to elucidate the molecular action of capsaicin on the antiobesity effect in epididymal white adipose tissue (WAT). Protein mapping of WAT homogenates using 2-DE revealed significant alterations to a number of proteins: 10 spots were significantly up-regulated and 10 spots were remarkably down-regulated in HFD fed rats treated with capsaicin. Among them, significant down-regulation of heat shock protein 27 (Hsp27) and Steap3 protein, as well as up-regulation of olfactory receptor (Olr1434) in obese WAT was reported for the first time in association with obesity. Most of the identified proteins are associated with lipid metabolism and redox regulation, in which levels of vimentin, peroxiredoxin, and NAD(P)H:quinone oxidoreductase 1 (NQO1) were significantly reduced (>2-fold), whereas aldo-keto reductase, flavoprotein increased with capsaicin treatment. These data demonstrate that thermogenesis and lipid metabolism related proteins were markedly altered upon capsaicin treatment in WAT, suggesting that capsaicin may be a useful phytochemical for attenuation of obesity.

Proteomic analysis of bovine omental, subcutaneous and intramuscular preadipocytes during in vitro adipogenic differentiation

Given the substantial rise in obesity, depot-specific fat accumulation and its associated diseases like diabetes, it is important to understand the molecular basis of depot-specific adipocyte differentiation. Many studies have successfully exploited the adipocyte differentiation, but most of them were not related to depot-specificity, particularly using freshly isolated primary preadipocytes. Using 2-dimensional polyacrylamide gel electrophoresis coupled with sequencing mass spectrometry, we searched and compared the proteins differentially expressed in undifferentiated and differentiated preadipocytes from bovine omental, subcutaneous and intramuscular adipose depots. Our proteome mapping strategy to identify differentially expressed intracellular proteins during adipogenic conversion revealed 65 different proteins that were found to be common for the three depots. Further, we validated the differential expression for a subset of proteins by immunoblotting analyses. The results demonstrated that many structural proteins were down-regulated during differentiation of preadipocytes from all the depots. Most up-regulated proteins like Ubiquinol-cytochrome-c reductase complex core protein I (UQCRC1), ATP synthase D chain, Superoxide dismutase (SOD), Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Sulfotransferase 1A1 (SULT1A1), Carnitine O-palmitoyltransferase 2 (CPT2) and Heat-shock protein beta 1 (HSPB1) across the three depots were found to be associated with lipid metabolism and metabolic activity. Further, all the up-regulated proteins were found to have higher protein expression in omental than subcutaneous or intramuscular depots.

FKBP51 promotes assembly of the Hsp90 chaperone complex and regulates androgen receptor signaling in prostate cancer cells

Prostate cancer progression to the androgen-independent (AI) state involves acquisition of pathways that allow tumor growth under low-androgen conditions. We hypothesized that expression of molecular chaperones that modulate androgen binding to AR might be altered in prostate cancer and contribute to progression to the AI state. Here, we report that the Hsp90 cochaperone FKBP51 is upregulated in LAPC-4 AI tumors grown in castrated mice and describe a molecular mechanism by which FKBP51 regulates AR activity. Using recombinant proteins, we show that FKBP51 stimulates recruitment of the cochaperone p23 to the ATP-bound form of Hsp90, forming an FKBP51-Hsp90-p23 superchaperone complex. In cells, FKBP51 expression promotes superchaperone complex association with AR and increases the number of AR molecules that undergo androgen binding. FKBP51 stimulates androgen-dependent transcription and cell growth, and FKBP51 is part of a positive feedback loop that is regulated by AR and androgen. Finally, depleting FKBP51 levels by short hairpin RNA reduces the transcript levels of genes regulated by AR and androgen. Because the superchaperone complex plays a critical role in determining the ligand-binding competence and transcription function of AR, it provides an attractive target for inhibiting AR activity in prostate cancer cells.

Differential role for c-Rel and C/EBPbeta/delta in TLR-mediated induction of proinflammatory cytokines

TLR stimulation triggers a signaling pathway via MyD88 and IL-1R-associated kinase 4 that is essential for proinflammatory cytokine induction. Although NF-kappaB has been shown to be one of the key transcriptional regulators of these cytokines, evidence suggests that other factors may also be important. In this study, we showed that MyD88-deficient macrophages have defective c-Rel activation, which has been linked to IL-12p40 induction, but not IL-6 or TNF-alpha. We also investigated other transcription factors and showed that C/EBPbeta and C/EBPdelta expression was limited in MyD88- or IL-1R-associated kinase 4-deficient macrophages treated with LPS. Importantly, the absence of both C/EBPbeta and C/EBPdelta resulted in the impaired induction of proinflammatory cytokines stimulated by several TLR ligands. Our results identify c-Rel and C/EBPbeta/delta as important transcription factors in a MyD88-dependent pathway that regulate the induction of proinflammatory cytokines.

Gemcitabine and cytosine arabinoside cytotoxicity: association with lymphoblastoid cell expression

Two cytidine analogues, gemcitabine (dFdC) and 1-beta-d-arabinofuranosylcytosine (AraC), show significant therapeutic effect in a variety of cancers. However, response to these drugs varies widely. Evidence from tumor biopsy samples shows that expression levels for genes involved in the cytidine transport, metabolism, and bioactivation pathway contribute to this variation in response. In the present study, we set out to test the hypothesis that variation in gene expression both within and outside of this "pathway" might influence sensitivity to gemcitabine and AraC. Specifically, Affymetrix U133 Plus 2.0 GeneChip and cytotoxicity assays were performed to obtain basal mRNA expression and IC(50) values for both drugs in 197 ethnically defined Human Variation Panel lymphoblastoid cell lines. Genes with a high degree of association with IC(50) values were involved mainly in cell death, cancer, cell cycle, and nucleic acid metabolism pathways. We validated selected significant genes by performing real-time quantitative reverse transcription-PCR and selected two representative candidates, NT5C3 (within the pathway) and FKBP5 (outside of the pathway), for functional validation. Those studies showed that down-regulation of NT5C3 and FKBP5 altered tumor cell sensitivity to both drugs. Our results suggest that cell-based model system studies, when combined with complementary functional characterization, may help to identify biomarkers for response to chemotherapy with these cytidine analogues.

Functional drift of sequence attributes in the FK506-binding proteins (FKBPs)

Diverse members of the FK506-binding proteins (FKBPs) group and their complexes with different macrocyclic ligands of fungal origins such as FK506, rapamycin, ascomycin, and their immunosuppressive and nonimmunosuppressive derivatives display a variety of cellular and biological activities. The functional relatedness of the FKBPs was estimated from the following attributes of their aligned sequences: 1 degrees conservation of the consensus sequence; 2 degrees sequence similarity; 3 degrees pI; 4 degrees hydrophobicity; 5 degrees amino acid hydrophobicity and bulkiness profiles. Analyses of the multiple sequence alignments and intramolecular interaction networks calculated from a series of structures of the FKBPs revealed some variations in the interaction clusters formed by the AA residues that are crucial for sustaining peptidylprolyl cis/trans isomerases (PPIases) activity and binding capacity of the FKBPs. Fine diversification of the sequences of the multiple paralogues and orthologues of the FKBPs encoded in different genomes alter the intramolecular interaction patterns of their structures and allowed them to gain some selectivity in binding to diverse targets (functional drift).

Cloning, expression and characterisation of FKB-6, the sole large TPR-containing immunophilin from C. elegans

We have cloned, expressed, purified and characterised ceFKB-6, the only large tetratricopeptide repeat motif-containing immunophilin in Caenorhabditis elegans which is similar to the human orthologues FKBP51 and FKBP52. It shows increased peptidyl prolyl isomerase activity, the measured k(cat)/K(m) of 1.3 x 10(6) M(-1) s(-1)is twofold greater than that of hFKBP12 and hFKBP51. NMR studies of the interaction between FKB-6 and the C-terminal DAF-21 pentapeptide MEEVD show interactions consistent with those found between the large human immunophilin TPR domains and human Hsp90. In vivo localisation studies show that the fkb-6 gene is expressed in all stages from embryo to adult with predominant expression being noted in the adult dorsal and ventral nerve cords.

Involvement of some large immunophilins and their ligands in the protection and regeneration of neurons: a hypothetical mode of action

The powerful immunosuppressive drugs such as FK506 and its derivatives induce some regeneration and protection of neurons from ischaemic brain injury and some other neurological disorders. The drugs form complexes with diverse FKBPs but apparently the FKBP52/FK506 complex was shown to be involved in the protection and regeneration of neurons. We used several different sequence attributes in searching diverse genomic databases for similar motifs as those present in the FKBPs. A Fortran library of algorithms (Par_Seq) has been designed and used in searching for the similarity of sequence motifs extracted from the multiple sequence alignments of diverse groups of proteins (query motifs) and the target motifs which are encoded in various genomes. The following sequence attributes were used in the establishment of the degree of convergence between: (A) amino acid (AA) sequence similarity (ID) of the query/target motifs and (B) their: (1) AA composition (AAC); (2) hydrophobicity (HI); (3) Jensen-Shannon entropy; and (4) AA propensity to form a particular secondary structure. The sequence hallmark of two different groups of peptidylprolyl cis/trans isomerases (PPIases), namely tetratricopetide repeat (TPR) motifs, which are present in the heat-shock cyclophilins and in the large FK506-binding proteins (FKBPs) were used to search various genomic databases. The Par_Seq algorithm has revealed that the TPR motifs have similar sequence attributes as a number of hydrophobic sequence segments of functionally unrelated membrane proteins, including some of the TMs from diverse G protein-coupled receptors (GPCRs). It is proposed that binding of the FKBP52/FK506 complex to the membranes via the TPR motifs and its interaction with some membrane proteins could be in part responsible for some neuro-regeneration and neuro-protection of the brain during some ischaemia-induced stresses.

Proteomic Analysis of Primary Cultures of Human Adipose-derived Stem Cells

Adipogenesis plays a critical role in energy metabolism and is a contributing factor to the obesity epidemic. This study examined the proteome of primary cultures of human adipose-derived adult stem (ADAS) cells as an in vitro model of adipogenesis. Protein lysates obtained from four individual donors were compared before and after adipocyte differentiation by two-dimensional gel electrophoresis and tandem mass spectroscopy. Over 170 individual protein features in the undifferentiated adipose-derived adult stem cells were identified. Following adipogenesis, over 40 proteins were up-regulated by > or = 2-fold, whereas 13 showed a > or = 3-fold reduction. The majority of the modulated proteins belonged to the following functional categories: cytoskeleton, metabolic, redox, protein degradation, and heat shock protein/chaperones. Additional immunoblot analysis documented the induction of four individual heat shock proteins and confirmed the presence of the heat shock protein 27 phosphoserine 82 isoform, as predicted by the proteomic analysis, as well as the crystallin alpha phosphorylated isoforms. These findings suggest that the heat shock protein family proteome warrants further investigation with respect to the etiology of obesity and type 2 diabetes.

Regulation of adipocyte differentiation and insulin action with rapamycin

Here, we demonstrated that inhibition of mTOR with rapamycin has negative effects on adipocyte differentiation and insulin signaling. Rapamycin significantly reduced expression of most adipocyte marker genes including PPARgamma, adipsin, aP2, ADD1/SREBP1c, and FAS, and decreased intracellular lipid accumulation in 3T3-L1 and 3T3-F442A cells, suggesting that rapamycin would affect both lipogenesis and adipogenesis. Contrary to the previous report that suppressive effect of rapamycin on adipogenesis is limited to the clonal expansion, we revealed that its inhibitory effect persisted throughout the process of adipocyte differentiation. Thus, it is likely that constitutive activation of mTOR might be required for the execution of adipogenic programming. In differentiated 3T3-L1 adipocytes, chronic treatment of rapamycin blunted the phosphorylation of AKT and GSK, which is stimulated by insulin, and reduced insulin-dependent glucose uptake activity. Taken together, these results suggest that rapamycin not only prevents adipocyte differentiation by decrease of adipogenesis and lipogenesis but also downregulates insulin action in adipocytes, implying that mTOR would play important roles in adipogenesis and insulin action.

Hibiscus extract inhibits the lipid droplet accumulation and adipogenic transcription factors expression of 3T3-L1 preadipocytes

OBJECTIVES

This study was designed to investigate the effect of hibiscus (Hibiscus sabdariffa) on adipogenic differentiation of 3T3-L1 cells at the cellular and molecular levels.

DESIGN

Various concentrations of hibiscus extract were added to confluent 3T3-L1 preadipocytes at the outset of the differentiation program and further incubated for 36 hours. Cells were maintained in postdifferentiation medium containing insulin with hibiscus extract in complete culture medium.

RESULTS

Hibiscus extract inhibited the adipocyte differentiation of 3T3-L1 preadipocytes induced by insulin, dexamethasone, and isobutylmethylxanthine (IBMX) in a dose-dependent manner. Hibiscus blocked the cytoplasmic lipid accumulation when administered at the onset of differentiation and 4 days after induction of differentiation. The inhibitory effect of hibiscus on adipogenic lipid accumulation of preadipocytes was significant (p < 0.01) between control cells and cells treated with hibiscus. Hibiscus extract significantly attenuated the expression of key adipogenic transcription factors, including CCAAT element binding protein (C/EBP)alpha and peroxisome proliferator-activated receptor (PPAR)gamma at protein levels.

CONCLUSION

These results suggest that hibiscus extract blocks adipogenesis, in part, by its suppression on the expression of adipogenic transcription factors, including C/EBPalpha and PPARgamma.

Structure of the large FK506-binding protein FKBP51, an Hsp90-binding protein and a component of steroid receptor complexes

The ability to bind immunosuppressive drugs such as cyclosporin and FK506 defines the immunophilin family of proteins, and the FK506-binding proteins form the FKBP subfamily of immunophilins. Some FKBPs, notably FKBP12 (the 12-kDa FK506-binding protein), have defined roles in regulating ion channels or cell signaling, and well established structures. Other FKBPs, especially the larger ones, participate in important biological processes, but their exact roles and the structural bases for these roles are poorly defined. FKBP51 (the 51-kDa FKBP) associates with heat shock protein 90 (Hsp90) and appears in functionally mature steroid receptor complexes. In New World monkeys, FKBP51 has been implicated in cortisol resistance. We report here the x-ray structures of human FKBP51, to 2.7 A, and squirrel monkey FKBP51, to 2.8 A, by using multiwavelength anomalous dispersion phasing. FKBP51 is composed of three domains: two consecutive FKBP domains and a three-unit repeat of the TPR (tetratricopeptide repeat) domain. This structure of a multi-FKBP domain protein clarifies the arrangement of these domains and their possible interactions with other proteins. The two FKBP domains differ by an insertion in the second that affects the formation of the progesterone receptor complex.

Positional cloning identifies a novel cyclophilin as a candidate amplified oncogene in 1q21

Gains of 1q21-q23 have been associated with metastasis and chemotherapy response, particularly in bladder cancer, hepatocellular carcinomas and sarcomas. By positional cloning of amplified genes by yeast artificial chromosome-mediated cDNA capture using magnetic beads, we have identified three candidate genes (COAS1, -2 and -3) in the amplified region in sarcomas. COAS1 and -2 showed higher amplification levels than COAS3. Most notably, amplification was very common in osteosarcomas, where in particular COAS2 was highly expressed. COAS1 has multiple repeats and shows no homology to previously described genes, whereas COAS2 is a novel member of the cyclosporin-binding peptidyl-prolyl isomerase family, very similar to cyclophilin A. COAS2 was overexpressed almost exclusively in aggressive metastatic or chemotherapy resistant tumours. Although COAS2 was generally more amplified than COAS1, it was not expressed in well-differentiated liposarcomas, where amplification of this region is very common. All three genes were found to be amplified and over-expressed also in breast carcinomas. The complex nature of the 1q21-23 amplicons and close proximity of the genes make unequivocal determination of the gene responsible difficult. Quite likely, the different genes may give selective advantages to different subsets of tumours.

Calcium- and FK506-independent interaction between the immunophilin FKBP51 and calcineurin

FKBP51 is a member of the immunophilin family having intrinsic peptidyl-prolyl cis-trans-isomerase (PPIase) activity. Its enzymatic activity is inhibited by binding either immunosuppressive agent FK506 or rapamycin. Similar to FKBP12, but at higher concentrations of FK506, FKBP51 has been shown to inhibit the serine/threonine phosphatase activity of calcineurin in the presence of calcium and calmodulin. Here we show that a glutathione S-transferase (GST) fusion protein of FKBP51 on glutathione-Sepharose beads precipitated both purified calcineurin from bovine brain and calcineurin from murine T cell lysates. Surprisingly, the binding of GST-FKBP51 to calcineurin was FK506-independent and independent of a requirement for calcium or exogenous calmodulin. Unlike FKBP12, FKBP51 transiently expressed in COS-7 cells was precipitated by calcineurin bound to calmodulin-Sepharose beads in the absence of either FK506 or rapamycin. Unlike FKBP12, however, overexpression of FKBP51 in Jurkat T cells did not significantly affect the transcriptional activation of nuclear factor of activated T cells (NFAT) upon physiological stimulation, nor did it affect the ability of FK506 to inhibit NFAT-driven transcription. We generated a series of FKBP51 mutations to map the interaction of FKBP51 with calcineurin. Deletion of the aminoterminal, FKBP12-like domain of FKBP51 did not affect the ability of FKBP51 to bind to purified calcineurin, while deletion of the FKBP51 carboxyterminal domain abrogated the ability of FKBP51 to bind to calcineurin. Taken together, these results demonstrate a novel interaction between calcineurin and the immunophilin FKBP51 that is independent of calcium, calmodulin, and drug. The binding site on calcineurin for FKBP51 is separable from the immunophilin PPIase-active and drug-binding site.

Effect of geldanamycin on androgen receptor function and stability

In the ligand-binding inactive state, the steroid receptor heterocomplex contains Hsp90, Hsp70, high-molecular weight immunophilins, and other proteins. Hsp90 acts in association with co-chaperones to maintain the native state of the receptor within the cells. It was reported earlier that Hsp90 might not be as important for the androgen receptor (AR) activity as for the glucocorticoid receptor (GR) and the progesterone receptor (PR) activities. We used the Hsp90 inhibitor geldanamycin (GA) to explore the role of Hsp90 in the function of the AR heterocomplex. GA selectively binds to Hsp90 and inhibits its activity, leading to the loss of steroid receptor activity, and frequently, its degradation. In our study, LNCaP prostate cancer cells were treated with GA for 30 minutes or 24 hours, in the presence of mibolerone, a synthetic androgen. GA reduced the androgen-induced AR protein levels to 15% after 24 hours of treatment. Several androgen up-regulated genes, including immunophilin FKBP51 and prostate specific antigen (PSA), were reduced by GA treatment. In cells treated with GA after transfection with a PSA promoter or an androgen response element-driven reporter gene, AR-mediated transactivation of reporter gene expression was reversibly inhibited by GA. Loss of androgen-binding ability and AR levels was attributed to reduced transcription of AR-regulated gene expression. Degradation rate of 35S-labeled AR was significantly increased by GA in the presence or absence of mibolerone. GA induced the degradation of AR through the proteasomal pathway. AR in cells treated with proteasomal inhibitor lactacystin, was insoluble in Nonidet P-40 (NP40)-based buffer and could not restore the androgen-binding ability. We report here that GA treatment disrupted both hormone-binding activity and receptor protein stability, resulting in a dramatic loss of androgen-induced gene activation. These results show that Hsp90 activity is important for both the chaperone-mediated folding of the AR into a high-affinity ligand-binding conformation and the functional activity of the AR.

Differential expression of cytosolic and mitochondrial 3-hydroxy-3-methylglutaryl CoA synthases during adipocyte differentiation

Mitochondrial and cytosolic 3-hydroxy-3-methylglutaryl CoA synthase (m-HMS and c-HMS) genes show high identity at the nucleotide and amino acid level, but no homology has been found in the promoter area. The main regulator for c-HMS is SREBP. The best known transcription factor that regulates m-HMS is PPAR alpha. Three types of PPAR, alpha, gamma and delta have been described in vertebrates. Here we found that they display distinct ligand response profiles in the m-HMS promoter. In some conditions PPAR gamma is a significant activator of m-HMS. Thus, the m-HMS gene is transiently expressed during the clonal expansion phase of 3T3-L1 differentiation. We found that C/EBP delta and PPAR gamma activate the m-HMS promoter in 3T3-L1 cells synergistically. This synergistic effect was only observed in the whole promoter (-1148 to +28). A small construct (-116 to +28) which contains the PPRE did not respond to C/EBP delta and/or PPAR gamma. This suggests that a putative C/EBP site lie somewhere between -1148 and -116 bp. We also show that C/EBP delta was more efficient that C/EBP alpha and C/EBP beta to activate the m-HMS promoter. The time course of c-HMS mRNA expression during 3T3-L1 differentiation was different, with a significant increase at terminal adipogenesis. We found that the transcription factor C/EBP alpha did not activate the c-HMS promoter. The differential pattern of expression shown by these two genes, which have a common ancestor, exemplifies refinements of transcriptional control during evolution.

Regulation of the Hsp90-binding immunophilin, cyclophilin 40, is mediated by multiple sites for GA-binding protein (GABP)

Within steroid receptor heterocomplexes the large tetratricopeptide repeat-containing immunophilins, cyclophilin 40 (CyP40), FKBP51, and FKBP52, target a common interaction site in heat shock protein 90 (Hsp90) and act coordinately with Hsp90 to modulate receptor activity. The reversible nature of the interaction between the immunophilins and Hsp90 suggests that relative cellular abundance might be a key determinant of the immunophilin component within steroid receptor complexes. To investigate CyP40 gene regulation, we have isolated a 5-kilobase (kb) 5'-flanking region of the human gene and demonstrated that a approximately 50 base pair (bp) sequence adjacent to the transcription start site is essential for CyP40 basal expression. Three tandemly arranged Ets sites within this critical region were identified as binding elements for the multimeric Ets-related transcription factor, GA binding protein (GABP). Functional studies of this proximal promoter sequence, in combination with mutational analysis, confirmed these sites to be crucial for basal promoter function. Furthermore, overexpression of both GABP alpha and GABP beta subunits in Cos1 cells resulted in increased endogenous CyP40 mRNA levels. Significantly, a parallel increase in FKBP52 mRNA expression was not observed, highlighting an important difference in the mode of regulation of the CyP40 and FKBP52 genes. Our results identify GABP as a key regulator of CyP40 expression. GABP is a common target of mitogen and stress-activated pathways and may integrate these diverse extracellular signals to regulate CyP40 gene expression.

Sodium salicylate induces the expression of the immunophilin FKBP51 and biglycan genes and inhibits p34cdc2 mRNA both in vitro and in vivo

One of the mechanisms proposed to explain the anti-inflammatory activity of sodium salicylate (NaSal) is based, at least in part, on its ability to inhibit nuclear factor-kappaB activation and inhibition of nuclear factor-kappaB-dependent gene expression. On the other hand, little is known about the ability of NaSal to activate gene expression. By differential display reverse transcription polymerase chain reaction, we identified several genes that are modulated upon treatment of mouse fibroblasts with NaSal. From the various cDNA fragments recovered from autoradiograms, we found that NaSal can increase the levels of mRNA for biglycan, the mouse homologue of the human eIF-3 p47 unit, and immunophilin FKBP51. NaSal-induced expression of these genes was time- and dose-dependent. Moreover, FKBP51 gene expression was augmented in vivo, in mice treated orally or intraperitoneally with NaSal. We also found that treating cells with NaSal can inhibit the expression of the p34(cdc2) kinase. The impact this inhibition on cell cycle was evaluated by measuring the content of DNA during the cell cycle. Treatment of cells with NaSal led to a G(2)/M arrest. By investigating the signaling events that regulate the expression of these genes and their biological activities, we can contribute to the understanding of the mechanism of NaSal.

Leptin-specific patterns of gene expression in white adipose tissue

Leptin is a hormone that regulates body weight by decreasing food intake and increasing energy expenditure. ob/obmice carry leptin mutations and are obese and hyperphagic. Leptin administration to lean and ob/ob mice activates a novel metabolic program that depletes adipose tissue. Although this response is physiologically distinct from that evident after food restriction, the molecular nature of these differences is as yet unknown. Expression monitoring of 6500 genes using oligonucleotide microarrays in wild-type, ob/ob, and transgenic mice expressing low levels of leptin revealed that differences in ambient leptin levels have dramatic effects on the phenotype of white adipose tissue. These data identified a large number of genes that are differentially expressed in ob/ob mice. To delineate the components of the transcriptional program specifically affected by leptin, the level of the same 6500 genes was monitored in wild-type and ob/ob mice at various times after leptin treatment or food restriction. A novel application ofk-means clustering identified 8 clusters of adipose tissue genes whose expression was different between leptin treatment and food restriction in ob/ob mice and 10 such clusters in wild-type experiments. One of the clusters was repressed specifically by leptin in both wild-type and ob/ob mice and included several genes known to be regulated by SREBP–1/ADD1. Further studies confirmed that leptin decreases the levels of SREBP–1/ADD1 RNA and transcriptionally active SREBP–1/ADD1 protein in white adipose tissue. Future studies of the molecular basis for the apparent coordinate regulation of the other clusters of leptin-regulated genes may reveal additional mechanisms by which leptin exerts its weight-reducing effects.

Leptin-specific patterns of gene expression in white adipose tissue

Leptin is a hormone that regulates body weight by decreasing food intake and increasing energy expenditure. ob/ob mice carry leptin mutations and are obese and hyperphagic. Leptin administration to lean and ob/ob mice activates a novel metabolic program that depletes adipose tissue. Although this response is physiologically distinct from that evident after food restriction, the molecular nature of these differences is as yet unknown. Expression monitoring of 6500 genes using oligonucleotide microarrays in wild-type, ob/ob, and transgenic mice expressing low levels of leptin revealed that differences in ambient leptin levels have dramatic effects on the phenotype of white adipose tissue. These data identified a large number of genes that are differentially expressed in ob/ob mice. To delineate the components of the transcriptional program specifically affected by leptin, the level of the same 6500 genes was monitored in wild-type and ob/ob mice at various times after leptin treatment or food restriction. A novel application of k-means clustering identified 8 clusters of adipose tissue genes whose expression was different between leptin treatment and food restriction in ob/ob mice and 10 such clusters in wild-type experiments. One of the clusters was repressed specifically by leptin in both wild-type and ob/ob mice and included several genes known to be regulated by SREBP-1/ADD1. Further studies confirmed that leptin decreases the levels of SREBP-1/ADD1 RNA and transcriptionally active SREBP-1/ADD1 protein in white adipose tissue. Future studies of the molecular basis for the apparent coordinate regulation of the other clusters of leptin-regulated genes may reveal additional mechanisms by which leptin exerts its weight-reducing effects.

Expression of the estrogen receptor-associated immunophilins, cyclophilin 40 and FKBP52, in breast cancer

The estrogen receptor alpha (ER alpha) is implicated in the development of breast cancer. The immunophilins, cyclophilin 40 (CyP40) and FKBP52, are associated with ER alpha and other steroid receptors in mutually exclusive heterocomplexes and may differentially modulate receptor activity. Since previous studies have not assessed the levels of these immunophilins in breast cancer, we examined 10 breast cancer cell lines for mRNA and protein expression of CyP40 and FKBP52 and for amplification of the CyP40 gene. In addition, 26 breast carcinomas, including seven with matched normal breast tissue, were examined for mRNA expression of both immunophilins. CyP40 and FKBP52 were ubiquitously expressed in breast cancer cell lines, but there were significant differences in their pattern of expression. FKBP52 protein levels were generally an order of magnitude greater than those for CyP40. FKBP52 mRNA expression correlated strongly with protein expression and was significantly higher in ER alpha-positive compared with ER alpha-negative cell lines. However, CyP40 mRNA expression did not correlate with protein expression, nor did expression of this immunophilin correlate with ER alpha status. Relatively high expression of CyP40 in one cell line (BT-20) could be attributed to amplification of the CyP40 gene. Both immunophilins were also ubiquitously expressed in breast carcinomas, and we demonstrate for the first time that both CyP40 and FKBP52 mRNA are overexpressed in breast tumors compared to matched normal breast controls. The overexpression of CyP40 and FKBP52, coupled with relative differences in their expression in tumors, may have important functional implications for ER alpha and other steroid receptors in breast cancer.

Transforming growth factor-beta enhances and pro-inflammatory cytokines inhibit ob gene expression in 3T3-L1 adipocytes

Leptin is a protein which is encoded by the obese (ob) gene. It is synthesized by adipocytes and binds to receptors in the hypothalamus, thereby suppressing appetite and increasing the metabolic rate. When mouse 3T3-L1 cells are induced to differentiate into adipocytes, they begin to constitutively express low levels of ob mRNA. Using reverse transcription and a semi-quantitative polymerase chain reaction, the experiments described herein demonstrate that the anti-inflammatory cytokine transforming growth factor-beta increases steady state ob mRNA. Conversely, treatment of 3T3-L1 adipocytes with the pro-inflammatory cytokines interleukin-1 beta, interleukin-6, interleukin-11, and tumor necrosis factor-alpha results in a decrease in ob transcripts. When considered in the context of animal studies showing that interleukin-1 and tumor necrosis factor-alpha induce leptin and ob mRNA, these results suggest that pro-inflammatory cytokines induce ob gene transcription in vivo via secondary mediators such as transforming growth factor-beta.

Novel progesterone target genes identified by an improved differential display technique suggest that progestin-induced growth inhibition of breast cancer cells coincides with enhancement of differentiation

Progesterone is an important regulator of normal and malignant breast epithelial cells. In addition to stimulating development of normal mammary epithelium, it can be used to treat hormone-dependent breast tumors. However, the mechanism of growth inhibition by progestins is poorly understood, and only a limited number of progesterone target genes are known so far. We therefore decided to clone such target genes by means of differential display polymerase chain reaction. In this paper, we describe an improved differential display strategy that eliminates false positives, along with the identification of nine positive (TSC-22, CD-9, Na+/K+-ATPase alpha1, desmoplakin, CD-59, FKBP51, and three unknown genes) and one negative progesterone target genes (annexin-VI) from the mammary carcinoma cell line T47D, which is growth-inhibited by progestins. None of these genes have been reported before to be progesterone targets. Regulation of desmoplakin, CD-9, CD-59, Na+/K+-ATPase alpha1, and annexin-VI by the progestin suggests that progesterone induces T47D cells to differentiate. Three of these genes were repressed by estradiol and up-regulated by the progestin. Estradiol treatment of T47D cells also leads to formation of lamellipodia and delocalization of two cell adhesion proteins, E-cadherin and alpha-catenin. All these effects were reversed by the progestin. These data suggest that estradiol dedifferentiates T47D cells, while progestins have the opposite effect. This may be linked to the capacity of progestins to inhibit tumor growth.

Steroid receptor interactions with heat shock protein and immunophilin chaperones

We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

Tissue distribution and abundance of human FKBP51, and FK506-binding protein that can mediate calcineurin inhibition

We previously described the isolation of an FK506-binding protein, FKBP51, that is predominantly expressed in murine T cells and is capable of mediating drug-dependent calcineurin inhibition in vitro. In addition, the gene for FKBP51 is induced by glucocorticoids. Screening of a human thymus cDNA library resulted in the identification of the human homologue of FKBP51. Expression of the 3.7 kb mRNA corresponding to FKBP51 is induced by glucocorticoids in the human T cell line, C7TK.4. The 51.2 kDa protein encoded by this gene shares 87% identity to murine FKBP51 and demonstrates a similar IC50 value for the FK506-mediated inhibition of calcineurin phosphatase in vitro. The distribution and abundance of FKBP51 and FKBP12 in seventeen human tissues were compared by Western analysis. Unlike its murine counterpart, the human FKBP51 is abundantly expressed in numerous tissues and in many cases, is in molar excess over FKBP12.

Molecular cloning of human FKBP51 and comparisons of immunophilin interactions with Hsp90 and progesterone receptor

A cDNA for human FKBP51 has been cloned and sequenced, and protein products have been expressed in both in vitro and bacterial systems. The deduced amino acid sequence for human FKBP51 is 90% identical to sequences of recently described murine proteins and is 55% identical to the sequence of human FKBP52. Human FKBP51 mRNA is expressed in a wide range of tissues, and the protein has peptidylprolyl isomerase activity that is inhibited by FK506 but not cyclosporine. FKBP51 is the same as a previously described progesterone receptor-associated immunophilin that, similar to FKBP52 and cyclophilin 40, is an Hsp90-binding protein and appears in functionally mature steroid receptor complexes along with Hsp90 and p23. Each of the three receptor-associated immunophilins displays interactions with progesterone receptor that are more dynamic than Hsp90-receptor interactions. Whereas FKBP52 and FKBP51 compete about equally well for binding to Hsp90 in a purified system, FKBP51 accumulates preferentially in progesterone receptor complexes assembled in a cell-free system. This observation provides a precedent for differential interactions between Hsp90-associated immunophilins and target proteins such as steroid receptors.

Rapamycin inhibits clonal expansion and adipogenic differentiation of 3T3-L1 cells

Differentiating 3T3-L1 cells express an immunophilin early during the adipocyte conversion program as described in this issue [Yeh, W.-C., Li, T.-K., Bierer, B. E. & McKnight, S. L. (1995) Proc. Natl. Acad. Sci. USA 92, 11081-11085]. The temporal expression profile of this protein, designated FK506-binding protein (FKBP) 51, is concordant with the clonal-expansion period undertaken by 3T3-L1 cells after exposure to adipogenic hormones. Having observed FKBP51 synthesis early during adipogenesis, we tested the effects of three immunosuppressive drugs--cyclosporin A, FK506, and rapamycin--on the terminal-differentiation process. Adipocyte conversion was not affected by either cyclosporin A or FK506 and yet was significantly reduced by rapamycin at drug concentrations as low as 10 nM. Clonal expansion was impeded in drug-treated cultures, as was the accumulation of cytoplasmic lipid droplets normally seen late during differentiation. Rapamycin treatment likewise inhibited the expression of CCAAT/enhancer binding protein alpha, a transcription factor required for 3T3-L1 cell differentiation. All three of these effects were reversed by high FK506 concentrations, indicating that the operative inhibitory event was mediated by an immunophilin-rapamycin complex.