Role of Sp1 and SREBP-1a in the insulin-mediated regulation of glucokinase transcription in the liver of gilthead sea bream (Sparus aurata)

Bayesian Meta-Analysis: Impacts of Eating Habits and Habitats on Omega-3 Long-Chain Polyunsaturated Fatty Acid Composition and Growth in Cultured Fish

Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) such as eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) offer protective benefits against various pathological conditions, including atherosclerosis, obesity, inflammation, and autoimmune diseases. Marine fish and seafood are the primary sources of n-3 LC-PUFAs in the human diet. However, the inclusion of fish oil in aquafeeds is declining due to limited availability, fluctuating prices, sustainability concerns, and replacement with vegetable oils. While comprehensive narrative reviews on the impact of substituting fish oil with vegetable oil in aquafeeds exist, quantitative studies are relatively scarce and mainly focused on comparing the source of vegetable oils. Herein, we employed, for the first time, a Bayesian meta-analysis approach, collecting research data from 81 articles to quantitatively analyze the effects of dietary n-3 LC-PUFA levels on the n-3 LC-PUFA composition and growth performance in cultured fish. Our findings indicate that with the exception of herbivorous fish, dietary n-3 LC-PUFA levels significantly affect the EPA and DHA levels in the livers and muscles of carnivorous, omnivorous, freshwater, and marine fish. Additionally, the growths of freshwater and herbivorous fish were less affected by changes in dietary n-3 LC-PUFA levels compared to that of carnivorous and marine fish.

Chitosan-Based Sustained Expression of Sterol Regulatory Element-Binding Protein 1a Stimulates Hepatic Glucose Oxidation and Growth in Sparus aurata

The administration of a single dose of chitosan nanoparticles driving the expression of sterol regulatory element-binding protein 1a (SREBP1a) was recently associated with the enhanced conversion of carbohydrates into lipids. To address the effects of the long-lasting expression of SREBP1a on the growth and liver intermediary metabolism of carnivorous fish, chitosan-tripolyphosphate (TPP) nanoparticles complexed with a plasmid expressing the N terminal active domain of hamster SREBP1a (pSG5-SREBP1a) were injected intraperitoneally every 4 weeks (three doses in total) to gilthead sea bream (Sparus aurata) fed high-protein-low-carbohydrate and low-protein-high-carbohydrate diets. Following 70 days of treatment, chitosan-TPP-pSG5-SREBP1a nanoparticles led to the sustained upregulation of SREBP1a in the liver of S. aurata. Independently of the diet, SREBP1a overexpression significantly increased their weight gain, specific growth rate, and protein efficiency ratio but decreased their feed conversion ratio. In agreement with an improved conversion of dietary carbohydrates into lipids, SREBP1a expression increased serum triglycerides and cholesterol as well as hepatic glucose oxidation via glycolysis and the pentose phosphate pathway, while not affecting gluconeogenesis and transamination. Our findings support that the periodical administration of chitosan-TPP-DNA nanoparticles to overexpress SREBP1a in the liver enhanced the growth performance of S. aurata through a mechanism that enabled protein sparing by enhancing dietary carbohydrate metabolisation.

Insulin can up-regulate LC-PUFA biosynthesis with the involvement of Srebp-1c and stimulatory protein 1 (Sp1) in marine teleost Siganus canaliculatus

The rabbitfish Siganus canaliculatus is the first marine teleost found to have the biosynthetic ability of long-chain polyunsaturated fatty acids (LC-PUFA) from C₁₈ precursors catalyzed by fatty acyl desaturases (Δ6/Δ5 Fads, Δ4 Fads) and elongases of very long chain fatty acids (Elovls). Previously, we predicted the existence of insulin (INS) response elements (IREs) including nuclear factor Y (NF-Y) and sterol regulatory element (SRE) in the core promoter region of rabbitfish Δ6/Δ5 fads and Δ4 fads. To clarify the potential regulatory effect and mechanism of INS in LC-PUFA biosynthesis, INS responding region was identified at -456 bp to + 51 bp of Δ6/Δ5 fads core promoter, but not in Δ4 fads promoter. Moreover, a unique stimulatory protein 1 (Sp1) element was predicted in the INS responding region of Δ6/Δ5 fads. Subsequently, SRE, NF-Y and Sp1 elements were proved as IREs in Δ6/Δ5 fads promoter. The up-regulation of INS on gene expression of Srebp-1c, Sp1, Δ6/Δ5 fads and elovl5 as well as the LC-PUFA biosynthesis was further demonstrated in S. canaliculatus hepatocyte line (SCHL) cells, but no influence was detected on Δ4 fads. Besides, inhibitors of transcription factors Srebp-1c (Fatostatin, PF-429242) and Sp1 (Mithramycin) could inhibit the gene expression of Srebp-1c, Δ6/Δ5 fads and elovl5, and abolish the up-regulation of INS on these genes' expression and LC-PUFA biosynthesis. These results indicated that INS could up-regulate LC-PUFA biosynthesis with the involvement of Srebp-1c and Sp1 in rabbitfish S. canaliculatus, which is the first report in teleost.

Effects of dietary carbohydrate to lipid ratios on growth, biochemical indicators, lipid metabolism, and appetite in Chinese perch (Siniperca chuatsi)

An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate to lipid (CHO:L) ratios on growth performance, body composition, serum biochemical indexes, lipid metabolism, and gene expression of central appetite regulating factors in Chinese perch (Siniperca chuatsi) (mean initial weight: 12.86 ± 0.10 g). Five isonitrogenous and isoenergetic diets (fish meal, casein as main protein sources) were formulated to contain different graded CHO:L ratio diets ranging from 0.12, 0.86, 1.71, 3.29, and 7.19. Each diet was assigned to triplicate groups of 18 experimental fish. Our results revealed that final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) increased with dietary CHO:L ratio from 0.12 to 1.71 and then decreased with further increases in dietary CHO:L ratio. A two-slope broken-line regression analysis based on WGR showed that the optimal dietary CHO:L level for maximum growth performance of fish was 1.60. Crude lipid and crude protein content in the liver and glycogen concentration in the muscle and liver were significantly influenced by the dietary CHO:L ratios (P < 0.05). The lowest crude lipid content in the liver was observed in fish fed the diet with a CHO:L ratio of 1.71(P < 0.05). Dietary CHO:L ratios significantly induced the glucose concentration of serum (P < 0.05). The relative expression levels of genes involved in lipid metabolism, such as srebp1 and fas in the liver, showed a trend of first decreased and then increased with the increase of dietary CHO:L ratio levels. Appropriate CHO:L ratio in the diet can effectively reduce the accumulation of liver fat. We observed in fish fed the 1.71 CHO:L ratio diet showed higher feed intake, up-regulated mRNA expression of neuropeptide Y (npy) and agouti gene-related protein (agrp), and down-regulated mRNA expression of cocaine- and amphetamine-regulated transcript (cart) and pro-opiomelanocorticoid (pomc) significantly as compared to control group. Thus, these results provide the theoretical basis for feed formulation to determine the appropriate CHO:L ratio requirement of Chinese perch.

Regulation of long-chain polyunsaturated fatty acid biosynthesis in teleost fish

Omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA, C_20-24), including eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), are involved in numerous biological processes and have a range of health benefits. Fish have long been considered as the main source of n-3 LC-PUFA in human diets. However, the capacity for endogenous biosynthesis of LC-PUFA from C₁₈ PUFA varies in fish species based on the presence, expression and activity of key enzymes including fatty acyl desaturases (Fads) and elongation of very long-chain fatty acids (Elovl) proteins. In this article, we review progress on the identified Fads and Elovl, as well as the regulatory mechanisms of LC-PUFA biosynthesis both at transcriptional and post-transcriptional levels in teleosts. The most comprehensive advances have been obtained in rabbitfish Siganus canaliculatus, a marine teleost demonstrated to have the entire pathway for LC-PUFA biosynthesis, including the roles of transcription factors hepatocyte nuclear factor 4α (Hnf4α), liver X receptor alpha (Lxrα), sterol regulatory element-binding protein 1 (Srebp-1), peroxisome proliferator-activated receptor gamma (Pparγ) and stimulatory protein 1 (Sp1), as well as post-transcriptional regulation by individual microRNA (miRNA) or clusters. This research has, for the first time, demonstrated the involvement of Hnf4α, Pparγ and miRNA in the regulation of LC-PUFA biosynthesis in vertebrates. The present review provides readers with a relatively comprehensive overview of the progress made into understanding LC-PUFA biosynthetic systems in teleosts, and some insights into improving endogenous LC-PUFA biosynthesis capacity aimed at reducing the dependence of aquafeeds on fish oil while maintaining or increasing flesh LC-PUFA content and the nutritional quality of farmed fish.

Diet-Induced Physiological Responses in the Liver of Atlantic Salmon (Salmo salar) Inferred Using Multiplex PCR Platforms

The simultaneous quantification of several transcripts via multiplex PCR can accelerate research in fish physiological responses to diet and enable the development of superior aquafeeds for farmed fish. We designed two multiplex PCR panels that included assays for 40 biomarker genes representing key aspects of fish physiology (growth, metabolism, oxidative stress, and inflammation) and 3 normalizer genes. We used both panels to assess the physiological effects of replacing fish meal and fish oil by terrestrial alternatives on Atlantic salmon smolts. In a 14-week trial, we tested three diets based on marine ingredients (MAR), animal by-products and vegetable oil (ABP), and plant protein and vegetable oil (VEG). Dietary treatments affected the expression of genes involved in hepatic glucose and lipid metabolism (e.g., srebp1, elovl2), cell redox status (e.g., txna, prdx1b), and inflammation (e.g., pgds, 5loxa). At the multivariate level, gene expression profiles were more divergent between fish fed the marine and terrestrial diets (MAR vs. ABP/VEG) than between the two terrestrial diets (ABP vs. VEG). Liver ARA was inversely related to glucose metabolism (gck)- and growth (igfbp-5b1, htra1b)-related biomarkers and hepatosomatic index. Liver DHA and EPA levels correlated negatively with elovl2, whereas ARA levels correlated positively with fadsd5. Lower hepatic EPA/ARA in ABP-fed fish correlated with the increased expression of biomarkers related to mitochondrial function (fabp3a), oxidative stress (txna, prdx1b), and inflammation (pgds, 5loxa). The analysis of hepatic biomarker gene expression via multiplex PCR revealed potential physiological impacts and nutrient-gene interactions in Atlantic salmon fed lower levels of marine-sourced nutrients.

Chitosan-Based Drug Delivery System: Applications in Fish Biotechnology

Chitosan is increasingly used for safe nucleic acid delivery in gene therapy studies, due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve the solubility and stability of chitosan-nucleic acid polyplexes, and enhance efficient target cell drug delivery, cell uptake, intracellular endosomal escape, unpacking and nuclear import of expression plasmids. As in other fields, chitosan is a promising drug delivery vector with great potential for the fish farming industry. This review highlights state-of-the-art assays using chitosan-based methodologies for delivering nucleic acids into cells, and focuses attention on recent advances in chitosan-mediated gene delivery for fish biotechnology applications. The efficiency of chitosan for gene therapy studies in fish biotechnology is discussed in fields such as fish vaccination against bacterial and viral infection, control of gonadal development and gene overexpression and silencing for overcoming metabolic limitations, such as dependence on protein-rich diets and the low glucose tolerance of farmed fish. Finally, challenges and perspectives on the future developments of chitosan-based gene delivery in fish are also discussed.

The Administration of Chitosan-Tripolyphosphate-DNA Nanoparticles to Express Exogenous SREBP1a Enhances Conversion of Dietary Carbohydrates into Lipids in the Liver of Sparus aurata

In addition to being essential for the transcription of genes involved in cellular lipogenesis, increasing evidence associates sterol regulatory element binding proteins (SREBPs) with the transcriptional control of carbohydrate metabolism. The aim of this study was to assess the effect of overexpression SREBP1a, a potent activator of all SREBP-responsive genes, on the intermediary metabolism of Sparus aurata, a glucose-intolerant carnivorous fish. Administration of chitosan-tripolyphosphate nanoparticles complexed with a plasmid driving expression of the N-terminal transactivation domain of SREBP1a significantly increased SREBP1a mRNA and protein in the liver of S. aurata. Overexpression of SREBP1a enhanced the hepatic expression of key genes in glycolysis-gluconeogenesis (glucokinase and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase), fatty acid synthesis (acetyl-CoA carboxylase 1 and acetyl-CoA carboxylase 2), elongation (elongation of very long chain fatty acids protein 5) and desaturation (fatty acid desaturase 2) as well as reduced nicotinamide adenine dinucleotide phosphate production (glucose-6-phosphate 1-dehydrogenase) and cholesterol synthesis (3-hydroxy-3-methylglutaryl-coenzyme A reductase), leading to increased blood triglycerides and cholesterol levels. Beyond reporting the first study addressing in vivo effects of exogenous SREBP1a in a glucose-intolerant model, our findings support that SREBP1a overexpression caused multigenic effects that favoured hepatic glycolysis and lipogenesis and thus enabled protein sparing by improving dietary carbohydrate conversion into fatty acids and cholesterol.

Berberine alleviates hyperglycemia by targeting hepatic glucokinase in diabetic db/db mice

Berberine (BBR) is a widely used anti-diabetic agent, and liver glucokinase (GK) has been reported to be involved. However, the mechanisms of BBR in regulating GK are still unknown. Here, we found that BBR upregulated GK immunofluorescence expression in AML12 cells cultured in high glucose and increased glycogen content simultaneously. BBR improved hyperglycemia in db/db mice, and increased liver glucose-6-phosphate/glucose-1-phosphate (G-6-P/G-1-P) was found by analyzing metabolites (serum, liver, and feces) based on gas chromatography-mass spectrometry (GC-MS) metabolomics. Pharmacokinetics-pharmacodynamics (PK-PD) assessment revealed enriched BBR distribution in the liver, and liver G-6-P had the same trend as the concentration-time curve of BBR. G-6-P is solely catalyzed by GK, and GK activity and expression showed a positive correlation with liver BBR levels. In db/db mice, BBR also upregulated GK in liver fractions (cytoplasm and nucleus) and liver glycogen content. GK functionally worked by dissociating from GK regulatory protein (GKRP), and although GKRP expression was not affected, we found a decreased ratio of GK binding with GKRP in BBR treated db/db mice. In conclusion, our study suggests the dissociation of GK from GKRP as the potential mechanism for liver GK increase upon BBR treatment, which contributes to the anti-diabetic effect of BBR.

Fat deposition pattern and mechanism in response to dietary lipid levels in grass carp, Ctenopharyngodon idellus

This study aimed to evaluate the fat deposition pattern and lipid metabolic strategies of grass carp in response to dietary lipid levels. Five isonitrogenous diets (260 g kg^-1 crude protein) containing five dietary lipid levels (0, 20, 40, 60, 80 g kg^-1) were fed to quadruplicate groups of 15 fish with initial weight 200 g, for 8 weeks. The best growth performance and feed utilization was observed in fish fed with lipid level at 40 g kg^-1. MFI and adipose tissue lipid content increased with increasing dietary lipid level up to 40 g kg^-1, and higher lipid level in diet made no sense. Fish adapted to high lipid intake through integrated regulating mechanisms in several related tissues to maintain lipid homeostasis. In the present study, grass carp firstly increased PPARγ and CPT1 expressions in adipose tissue to elevate adipocyte differentiation and lipolysis to adapt to high lipid intake above 40 g kg^-1. In liver, fish elevated hepatic lipid uptake but depressed biosynthesis of hepatic FAs, resulted in no difference in HSI and liver lipid content among the groups. Only in muscle, fish showed a significant fat deposition when the lipid intake above 40 g kg^-1. The excess lipid, derived from enhanced serum TC and TG contents, was more likely to induce deposition in muscle rather than lipid uptake by adipose tissue in grass carp fed with high dietary lipid, indicating the muscle of grass carp might be the main responding organ to high lipid intake.

Nutritional regulation of glucokinase: a cross-species story

The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).

Effects of food-deprivation and refeeding on the regulation and sources of blood glucose appearance in European seabass (Dicentrarchus labrax L.)

Sources of blood glucose in European seabass (initial weight 218.0±43.0g; mean±S.D., n=18) were quantified by supplementing seawater with deuterated water (5%-(2)H2O) for 72h and analyzing blood glucose (2)H-enrichments by (2)H NMR. Three different nutritional states were studied: continuously fed, 21-day of fast and 21-day fast followed by 3days of refeeding. Plasma glucose levels (mM) were 10.7±6.3 (fed), 4.8±1.2 (fasted), and 9.3±1.4 (refed) (means±S.D., n=6), showing poor glycemic control. For all conditions, (2)H-enrichment of glucose position 5 was equivalent to that of position 2 indicating that blood glucose appearance from endogenous glucose 6-phosphate (G6P) was derived by gluconeogenesis. G6P-derived glucose accounted for 65±7% and 44±10% of blood glucose appearance in fed and refed fish, respectively, with the unlabeled fraction assumed to be derived from dietary carbohydrate (35±7% and 56±10%, respectively). For 21-day fasted fish, blood glucose appearance also had significant contributions from unlabeled glucose (52±16%) despite the unavailability of dietary carbohydrates. To assess the role of hepatic enzymes in glycemic control, activity and mRNA levels of hepatic glucokinase (GK) and glucose 6-phosphatase (G6Pase) were assessed. Both G6Pase activity and expression declined with fasting indicating the absence of a classical counter-regulatory stimulation of hepatic glucose production in response to declining glucose levels. GK activities were basal during fed and fasted conditions, but were strongly stimulated by refeeding. Overall, hepatic G6Pase and GK showed limited capacity in regulating glucose levels between feeding and fasting states.

Effects of alanine aminotransferase inhibition on the intermediary metabolism inSparus auratathrough dietary amino-oxyacetate supplementation

In liver, through the reaction catalysed by alanine aminotransferase (ALT), alanine becomes an effective precursor for gluconeogenesis. In the present study amino-oxyacetate (AOA) was used to evaluate its effect on liver ALT activity of the carnivorous fishSparus aurata. Moreover, the derived metabolic effects on metabolites and other key enzymes of glycolysis, gluconeogenesis and the pentose phosphate pathway were also studied. A dose-effect-dependent inhibition of AOA on hepatic cytosolic and mitochondrial ALT activity was observedin vitro.In vivo, AOA behaved as an inhibitor of hepatic cytosolic ALT activity. A long-term exposure to AOA increased pyruvate kinase activity in the liver irrespective of the composition of the diet supplied to fish.1H NMR studies showed that inclusion of AOA to the diet decreased the hepatic levels of alanine, glutamate and glycogen. Moreover,2H NMR analysis indicated a higher renewal rate for alanine in the liver of fish fed with a high-carbohydrate/low-protein diet, while AOA decreased alanine2H-enrichment irrespective of the diet. The present study indicates that AOA-dependent inhibition of the cytosolic ALT activity could help to increase the use of dietary carbohydrate nutrients.

Hepatocyte nuclear factor 1alpha plays a critical role in PCSK9 gene transcription and regulation by the natural hypocholesterolemic compound berberine

PCSK9 is a natural inhibitor of LDL receptor (LDLR) that binds the extracellular domain of LDLR and triggers its intracellular degradation. PCSK9 and LDLR are coordinately regulated at the transcriptional level by sterols through their promoter-imbedded sterol response elements (SRE) and co-induced by statins. Identification of regulatory networks modulating PCSK9 transcription is important for developing selective repressors of PCSK9 to improve statin efficacy by prolonging the up-regulation of LDLR. Interestingly, the plant-derived hypocholesterolemic compound berberine (BBR) up-regulates LDLR expression while down-regulating PCSK9. In our investigations to define mechanisms underlying the transcriptional suppression of PCSK9 by BBR in HepG2 cells, we have identified a highly conserved hepatocyte nuclear factor 1 (HNF1) binding site residing 28 bp upstream from SRE as a critical sequence motif for PCSK9 transcription and its regulation by BBR. Mutation of the HNF1 site reduced PCSK9 promoter activity >90%. A battery of functional assays identified HNF1α as the predominant trans-activator for PCSK9 gene working through this sequence motif. We further provide evidence suggesting that HNF1 site works cooperatively with SRE as HNF1 mutation significantly attenuated the activity of nuclear SREBP2 to transactivate PCSK9 promoter. Finally, we show that a coordinate modest reduction of HNF1α and nuclear SREBP2 by BBR led to a strong suppression of PCSK9 transcription through these two critical regulatory sequences. This is the first described example of SREBP pairing with HNF1 to control an important regulatory pathway in cholesterol homeostasis. This work also provides a mechanism for how BBR suppresses PCSK9 transcription.

Identification of a novel beta-cell glucokinase (GCK) promoter mutation (-71G>C) that modulates GCK gene expression through loss of allele-specific Sp1 binding causing mild fasting hyperglycemia in humans

OBJECTIVE

Inactivating mutations in glucokinase (GCK) cause mild fasting hyperglycemia. Identification of a GCK mutation has implications for treatment and prognosis; therefore, it is important to identify these individuals. A significant number of patients have a phenotype suggesting a defect in glucokinase but no abnormality of GCK. We hypothesized that the GCK beta-cell promoter region, which currently is not routinely screened, could contain pathogenic mutations; therefore, we sequenced this region in 60 such probands.

RESEARCH DESIGN AND METHODS

The beta-cell GCK promoter was sequenced in patient DNA. The effect of the identified novel mutation on GCK promoter activity was assessed using a luciferase reporter gene expression system. Electrophoretic mobility shift assays (EMSAs) were used to determine the impact of the mutation on Sp1 binding.

RESULTS

A novel -71G>C mutation was identified in a nonconserved region of the human promoter sequence in six apparently unrelated probands. Family testing established cosegregation with fasting hyperglycemia (> or = 5.5 mmol/l) in 39 affected individuals. Haplotype analysis in the U.K. family and four of the Slovakian families demonstrated that the mutation had arisen independently. The mutation maps to a potential transcriptional activator binding site for Sp1. Reporter assays demonstrated that the mutation reduces promoter activity by up to fourfold. EMSAs demonstrated a dramatic reduction in Sp1 binding to the promoter sequence corresponding to the mutant allele.

CONCLUSIONS

A novel beta-cell GCK promoter mutation was identified that significantly reduces gene expression in vitro through loss of regulation by Sp1. To ensure correct diagnosis of potential GCK-MODY (maturity-onset diabetes of the young) cases, analysis of the beta-cell GCK promoter should be included.

Distinct gene-expression profiles characterize mammary tumors developed in transgenic mice expressing constitutively active and C-terminally truncated variants of STAT5

Background

Stat5 is a latent transcription factor that regulates essential growth and survival functions in normal cells. Constitutive activity of Stat5 and the involvement of its C-terminally truncated variant have been implicated in blood cell malignancies and mammary or breast cancer. To distinguish the individual contributions of the Stat5 variants to mammary tumorigenesis, global gene-expression profiling was performed on transgenic STAT5-induced tumors.

Results

We identified 364 genes exhibiting differential expression in mammary tumors developed in transgenic mice expressing constitutively active STAT5 (STAT5ca) vs. its C-terminally truncated variant (STAT5Δ750). These genes mediate established Stat5 effects on cellular processes such as proliferation and cell death, as well as yet-unrelated homeostatic features, e.g. carbohydrate metabolism. A set of 14 genes linked STAT5Δ750 expression to the poorly differentiated carcinoma phenotype and STAT5ca to the highly differentiated papillary adenocarcinoma.

Specifically affected genes exhibited differential expression in an individual tumor set vs. its counterpart and the intact mammary gland: 50 genes were specifically affected by STAT5ca, and 94% of these were downregulated, the latter involved in suppression of tumor suppressors and proliferation antagonistics. This substantial downregulation distinguishes the STAT5ca-induced tumorigenic consequences from the relatively equal effect of the STAT5Δ750 on gene expression, which included significant elevation in the expression of oncogenes and growth mediators.

STAT5Δ750 mRNA expression was below detection levels in the tumors and the amount of STAT5ca transcript was not correlated with the expression of its specifically affected genes. Interestingly, we identified several groups of three to eight genes affected by a particular STAT5 variant with significant correlated expression at distinct locations in the clustergram.

Conclusion

The different gene-expression profiles in mammary tumors caused by the STAT5Δ750 and STAT5ca variants, corroborated by the absence of a direct link to transgenic STAT5 expression, imply distinct metabolic consequences for their oncogenic role which probably initiate early in tumor development. Tumorigenesis may involve induction of growth factor and oncogenes by STAT5Δ750 or suppression of tumor suppressors and growth antagonists by STAT5ca. The list of genes specifically affected by the STAT5 variants may provide a basis for the development of a marker set for their distinct oncogenic role.