Genetic, physical, and transcript map of the fld region on mouse chromosome 12

Lipin-1 deficiency deteriorates defect of fatty acid β-oxidation and lipid-related kidney damage in diabetic kidney disease

Diabetic lipo-toxicity is a fundamental pathophysiologic mechanism in DM and is now increasingly recognized a key determinant of DKD. Targeting lipid metabolic disorders is an important therapeutic strategy for the treatment of DM and its complications, including DKD. This study aimed to explore the molecular mechanism of lipid metabolic regulation in kidney, especially renal PTECs, and elucidate the role of lipid metabolic related molecule lipin-1 in diabetic lipid-related kidney damage. In this study, lipin-1-deficient db/db mouse model and STZ/HFD-induced T2DM mouse model were used to determine the effect of lipin-1 on DKD development. Then RPTCs and LPIN1 knockdown or overexpressed HK-2 cells induced by PA were used to investigate the mechanism. We found that the expression of lipin-1 increased early and then decreased in kidney during the progression of DKD. Glucose and lipid metabolic disorders and renal insufficiency were found in these 2 types of diabetic mouse models. Interestingly, lipin-1 deficiency might be a pathogenic driver of DKD-to-CKD transition, which could further accelerate the imbalance of renal lipid homeostasis, the dysfunction of mitochondrial and energy metabolism in PTECs. Mechanistically, lipin-1 deficiency resulted in aggravated PTECs injury to tubulointerstitial fibrosis in DKD by downregulating FAO via inhibiting PGC-1α/PPARα mediated Cpt1α/HNF4α signaling and upregulating SREBPs to promote fat synthesis. This study provided new insights into the role of lipin-1 as a regulator for maintaining lipid homeostasis in the kidney, especially PTECs, and its deficiency led to the progression of DKD.

Phosphoproteomics of the developing heart identifies PERM1 - An outer mitochondrial membrane protein

Heart development relies on PTMs that control cardiomyocyte proliferation, differentiation and cardiac morphogenesis. We generated a map of phosphorylation sites during the early stages of cardiac postnatal development in mice; we quantified over 10,000 phosphorylation sites and 5000 proteins that were assigned to different pathways. Analysis of mitochondrial proteins led to the identification of PGC-1- and ERR-induced regulator in muscle 1 (PERM1), which is specifically expressed in skeletal muscle and heart tissue and associates with the outer mitochondrial membrane. We demonstrate PERM1 is subject to rapid changes mediated by the UPS through phosphorylation of its PEST motif by casein kinase 2. Ablation of Perm1 in mice results in reduced protein expression of lipin-1 accompanied by accumulation of specific phospholipid species. Isolation of Perm1-deficient mitochondria revealed significant downregulation of mitochondrial transport proteins for amino acids and carnitines, including SLC25A12/13/29/34 and CPT2. Consistently, we observed altered levels of various lipid species, amino acids, and acylcarnitines in Perm1^-/- mitochondria. We conclude that the outer mitochondrial membrane protein PERM1 regulates homeostasis of lipid and amino acid metabolites in mitochondria.

Consideration of GREB1 as a potential therapeutic target for hormone-responsive or endocrine-resistant cancers

INTRODUCTION

Steroid hormones increase the incidence and promote the progression of many types of cancer. Exogenous estrogens increase the risk of developing breast, ovarian and endometrial cancer and many breast cancers initially respond to estrogen deprivation. Although steroid hormone signaling has been extensively studied, the mechanisms of hormone-stimulated cancer growth have not yet been fully elucidated, limiting opportunities for novel approaches to therapeutic intervention.

AREAS COVERED

This review examines growing evidence for the important role played by the steroid hormone-induced gene called GREB1, or growth regulation by estrogen in breast cancer 1. GREB1 is a critical mediator of both the estrogen-stimulated proliferation of breast cancer cells and the androgen-stimulated proliferation of prostate cancer cells.

EXPERT OPINION

Although its exact function in the cascade of hormone action remains unclear, the ability of GREB1 to modulate tumor progression in models of breast, ovarian and prostate cancer renders this gene an excellent candidate for further consideration as a potential therapeutic target. Research examining the mechanism of GREB1 action will help to elucidate its role in proliferation and its potential contribution to endocrine resistance and will determine whether GREB1 interference may have therapeutic efficacy.

Cardiac lipin 1 expression is regulated by the peroxisome proliferator activated receptor γ coactivator 1α/estrogen related receptor axis

Lipin family proteins (lipin 1, 2, and 3) are bifunctional intracellular proteins that regulate metabolism by acting as coregulators of DNA-bound transcription factors and also dephosphorylate phosphatidate to form diacylglycerol [phosphatidate phosphohydrolase activity] in the triglyceride synthesis pathway. Herein, we report that lipin 1 is enriched in heart and that hearts of mice lacking lipin 1 (fld mice) exhibit accumulation of phosphatidate. We also demonstrate that the expression of the gene encoding lipin 1 (Lpin1) is under the control of the estrogen-related receptors (ERRs) and their coactivator the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α). PGC-1α, ERRα, or ERRγ overexpression increased Lpin1 transcription in cultured ventricular myocytes and the ERRs were associated with response elements in the first intron of the Lpin1 gene. Concomitant RNAi-mediated knockdown of ERRα and ERRγ abrogated the induction of lipin 1 expression by PGC-1α overexpression. Consistent with these data, 3-fold overexpression of PGC-1α in intact myocardium of transgenic mice increased cardiac lipin 1 and ERRα/γ expression. Similarly, injection of the β2-adrenergic agonist clenbuterol induced PGC-1α and lipin 1 expression, and the induction in lipin 1 after clenbuterol occurred in a PGC-1α-dependent manner. In contrast, expression of PGC-1α, ERRα, ERRγ, and lipin 1 was down-regulated in failing heart. Cardiac phosphatidic acid phosphohydrolase activity was also diminished, while cardiac phosphatidate content was increased, in failing heart. Collectively, these data suggest that lipin 1 is the principal lipin protein in the myocardium and is regulated in response to physiologic and pathologic stimuli that impact cardiac metabolism.

E2f6 and Bmi1 cooperate in axial skeletal development

Bmi1 is a Polycomb Group protein that functions as a component of Polycomb Repressive Complex 1 (PRC1) to control axial skeleton development through Hox gene repression. Bmi1 also represses transcription of the Ink4a-Arf locus and is consequently required to maintain the proliferative and self-renewal properties of hematopoietic and neural stem cells. Previously, one E2F family member, E2F6, has been shown to interact with Bmi1 and other known PRC1 components. However, the biological relevance of this interaction is unknown. In this study, we use mouse models to investigate the interplay between E2F6 and Bmi1. This analysis shows that E2f6 and Bmi1 cooperate in the regulation of Hox genes, and consequently axial skeleton development, but not in the repression of the Ink4a-Arf locus. These findings underscore the significance of the E2F6-Bmi1 interaction in vivo and suggest that the Hox and Ink4a-Arf loci are regulated by somewhat different mechanisms.

Regulation of lipin-1 gene expression by glucocorticoids during adipogenesis

Lipin-1 deficiency in the mouse causes generalized lipodystrophy, characterized by impaired adipose tissue development and insulin resistance. Lipin-1 expression in differentiating preadipocytes is required for normal expression of adipogenic transcription factors, including peroxisome proliferator-activated receptor gamma and CCAAT enhancer binding protein alpha, and for the synthesis of triacylglycerol. The requirement of lipin-1 for adipocyte differentiation can be explained, in part, by its activity as the sole adipocyte phosphatidic acid phosphatase-1 enzyme, which converts phosphatidate to diacylglycerol, the immediate precursor of triacylglycerol. Here we identify glucocorticoids as the stimulus for the induction of lipin-1 expression in differentiating adipocytes, and characterize a glucocorticoid response element (GRE) in the Lpin1 promoter. The Lpin1 GRE binds to the glucocorticoid receptor and leads to transcriptional activation in adipocytes and hepatocytes, as demonstrated by reporter gene transcription, electrophoretic mobility shift, and chromatin immunoprecipitation assays. This represents the first gene regulatory element identified to directly influence lipin-1 expression levels, and may modulate lipin-1 mRNA levels in adipose tissue and liver in conditions associated with increased local glucocorticoid concentrations in vivo, such as obesity and fasting.

GREB 1 is a critical regulator of hormone dependent breast cancer growth

BACKGROUND

Estrogen plays a central role in breast cancer pathogenesis and many potent risk factors for the development of the disease can be explained in terms of increased lifetime exposure to estrogen. Although estrogen regulated genes have been identified, those critically involved in growth regulation remain elusive.METHODS. To identify candidate genes involved in estrogen stimulated breast cancer growth, DNA microarray based gene expression profiles were generated from three estrogen receptor alpha (ER alpha) positive breast cancer cell lines grown under multiple stimulatory and inhibitory conditions.

RESULTS

Only three genes were significantly induced by 17beta-estradiol (E2) relative to control in all three cell lines: GREB 1, stromal cell-derived factor 1 (SDF-1) and trefoil factor 1 (pS2). Quantitative real-time PCR assays confirmed that in all three cell lines, GREB 1 was induced by E2, but not by the antiestrogens tamoxifen (TAM) or ICI 182,780. GREB 1 expression level was strongly correlated with ER alpha positivity in 39 breast cancer cell lines of known ER alpha expression status. GREB 1 induction by E2 was rapid (7.3 fold by 2 h for MCF-7) and mirrored the fraction of cells entering S-phase when released from an estrogen deprivation induced cell arrest. Suppression of GREB 1 using siRNA blocked estrogen induced growth in MCF-7 cells and caused a paradoxical E2 induced growth inhibition.

CONCLUSION

These data suggest that GREB 1 is critically involved in the estrogen induced growth of breast cancer cells and has the potential of being a clinical marker for response to endocrine therapy as well as a potential therapeutic target.

Differential analysis of CD4+ Th memory clones with identical T-cell receptor (TCR)-alphabeta rearrangement (non-transgenic), but distinct lymphokine phenotype, reveals diverse and novel gene expression

This study describes a subtractive hybridization analysis to identify differences in gene expression between sibling Th memory clones, elicited by virus infection and expressing identical T-cell receptor (TCR)-alphabeta rearrangements but distinct lymphokine phenotype: clone Bpp9 secretes interleukin (IL)-4, IL-5 and IL-10; clone Bpp19 secretes interferon (IFN)-gamma, low levels of IL-4, and IL-5 on TCR ligation. cDNA sequencing of difference products (DP) identified both novel and known regulatory (DNA: RNA-binding) or signalling proteins (kinases: phosphatases). Of the 10 novel genes identified, three were putative membrane proteins, one a predicted nuclear protein containing a PEST sequence motif, one a predicted transporter fragment and one contained a zinc-finger motif. One of the membrane proteins was found only in RNA from the activated IFN-gamma-producing clone, i.e. not in other tissues. In addition, a high frequency of granzyme A, B, C and G transcripts (for clone Bpp9) or transcripts for CD94 and NKG2A (for clone Bpp19) were expressed differentially, together with transcripts that mapped to, so far, unassigned regions of the mouse genome that may be further novel genes. The transcriptional profiles presented here may therefore include candidate regulators of Th diversity and effector function.

Trapping and sequence analysis of 1138 putative exons from human chromosome 18

In a search for novel genes on chromosome 18 (HC18), on which several regions have been linked to bipolar disorder, we applied exon trapping to HC18-specific cosmids. Among the 1138 exons trapped, 1052 of them have been mapped to HC18, and the remaining 86 have not been localized. No exons were localized to genomic regions other than HC18. BLAST database search revealed that 190 exons were identical to 98 Unigenes on HC18; 98 identical to additional 82 clusters of ESTs not present in the HC18 Unigene set; 39 homologous to genes from human and other species (e<10(-3)); and the remaining 811 exons had no significant homology to transcripts in public databases. The mapped exons were compared to the 867 annotated genes on HC18 in the Celera databases; 216 exons were identical to 104 Celera 'genes' and the remaining 836 exons were not found in the Celera databases. On average, there were two exons for a matched transcript (known genes and ESTs). Therefore, the 850 novel exons may represent hundreds of novel genes on chromosome 18.

Metabolic lessons from genetically lean mice

Different types of lean mice have been produced by genetic manipulation. Leanness can result from deficiency of stored energy or a lack of adipocytes to store the lipid. Mice lacking functional adipocytes are usually insulin resistant and have fatty livers, and elevated circulating triglyceride levels. Insulin resistance may result from the lack of adipocyte hormones (such as leptin) and increased metabolite (such as triglyceride) levels in nonadipose tissue. Mice with depleted adipocyte triglyceride levels typically are insulin sensitive and have normal or low liver and circulating triglycerides. Mechanisms to produce depleted adipocytes include increased energy expenditure by peripheral tissues, peripheral mechanisms to decrease food intake, and altered central regulation of these processes.

Molecular cloning and characterization of the mouse E2F6 gene

E2F6 is the most recently identified member of the E2F family. In this study, the murine E2F6 gene was cloned and found to consist of eight exons. Analysis of its 5' flanking region revealed two transcription start sites. The proximal promoter region contained no TATA or CAAT box. We also identified a novel E2F6 mRNA containing the alternative exon 2. The E2F6 mRNAs are highly expressed during mouse embryogenesis and are present in all adult tissues examined. Moreover, E2F6 shows a unique expression pattern in synchronized mouse embryonic fibroblasts. E2F6 expression rapidly increases during the G0-G1 transition, reaching its higher level in mid-G1, and remains relatively constant thereafter. These findings suggest that E2F6 may contribute to the regulation of events throughout the cell cycle. Isolation of the murine E2F6 gene is a step toward generation of genetically modified mouse models that will help to understand the functions of E2F6.

Lipodystrophy in the fld mouse results from mutation of a new gene encoding a nuclear protein, lipin

Mice carrying mutations in the fatty liver dystrophy (fld) gene have features of human lipodystrophy, a genetically heterogeneous group of disorders characterized by loss of body fat, fatty liver, hypertriglyceridemia and insulin resistance. Through positional cloning, we have isolated the gene responsible and characterized two independent mutant alleles, fld and fld(2J). The gene (Lpin1) encodes a novel nuclear protein which we have named lipin. Consistent with the observed reduction of adipose tissue mass in fld and fld(2J)mice, wild-type Lpin1 mRNA is expressed at high levels in adipose tissue and is induced during differentiation of 3T3-L1 pre-adipocytes. Our results indicate that lipin is required for normal adipose tissue development, and provide a candidate gene for human lipodystrophy. Lipin defines a novel family of nuclear proteins containing at least three members in mammalian species, and homologs in distantly related organisms from human to yeast.

Mouse models of lipodystrophy

Lipodystrophies are a group of heterogeneous diseases characterized by the loss of adipose tissue and by abnormalities of carbohydrate and lipid metabolism, including insulin resistance, diabetes, and hyperlipidemia. In this review, we describe several mouse models that recapitulate various aspects of the lipodystrophy syndrome, offering insights into the etiology of this condition and potential therapeutic approaches. Studies on these mice suggest that adipose is the primary tissue affected in lipodystrophy, and that secondary leptin deficiency may be responsible for the associated insulin resistance.