TorS - Reframing a rational for type 2 diabetes treatment.

The mammalian target of rapamycin complex 1 syndrome (Tors), paradigm implies an exhaustive cohesive disease entity driven by a hyperactive mTORC1, and which includes obesity, type 2 diabetic hyperglycemia, diabetic dyslipidemia, diabetic cardiomyopathy, diabetic nephropathy, diabetic peripheral neuropathy, hypertension, atherosclerotic cardiovascular disease, non-alcoholic fatty liver disease, some cancers, neurodegeneration, polycystic ovary syndrome, psoriasis and other. The TorS paradigm may account for the efficacy of standard-of-care treatments of type 2 diabetes (T2D) in alleviating the glycaemic and non-glycaemic diseases of TorS in T2D and non-T2D patients. The TorS paradigm may generate novel treatments for TorS diseases.

Amyloidogenic light chains impair plasma cell survival.

Systemic light chain amyloidosis (AL) is a clonal plasma cell disorder characterized by the deposition of misfolded immunoglobulin light chains (LC) as insoluble fibrils in organs. The lack of suitable models has hindered the investigation of the disease mechanisms. Our aim was to establish AL LC-producing plasma cell lines and use them to investigate the biology of the amyloidogenic clone. We used lentiviral vectors to generate cell lines expressing LC from patients suffering from AL amyloidosis. The AL LC-producing cell lines showed a significant decrease in proliferation, cell cycle arrest, and an increase in apoptosis and autophagy as compared with the multiple myeloma LC-producing cells. According to the results of RNA sequencing the AL LC-producing lines showed higher mitochondrial oxidative stress, and decreased activity of the Myc and cholesterol pathways. The neoplastic behavior of plasma cells is altered by the constitutive expression of amyloidogenic LC causing intracellular toxicity. This observation may explain the disparity in the malignant behavior of the amyloid clone compared to the myeloma clone. These findings should enable future in vitro studies and help delineate the unique cellular pathways of AL, thus expediting the development of specific treatments for patients with this disorder.

Type 2 diabetes - unmet need, unresolved pathogenesis, mTORC1-centric paradigm.

The current paradigm of type 2 diabetes (T2D) is gluco-centric, being exclusively categorized by glycemic characteristics. The gluco-centric paradigm views hyperglycemia as the primary target, being driven by resistance to insulin combined with progressive beta cells failure, and considers glycemic control its ultimate treatment goal. Most importantly, the gluco-centric paradigm considers the non-glycemic diseases associated with T2D, e.g., obesity, dyslipidemia, hypertension, macrovascular disease, microvascular disease and fatty liver as 'risk factors' and/or 'outcomes' and/or 'comorbidities', rather than primary inherent disease aspects of T2D. That is in spite of their high prevalence (60-90%) and major role in profiling T2D morbidity and mortality. Moreover, the gluco-centric paradigm fails to realize that the non-glycemic diseases of T2D are driven by insulin and, except for glycemic control, response to insulin in T2D is essentially the rule rather than the exception. Failure of the gluco-centric paradigm to offer an exhaustive unifying view of the glycemic and non-glycemic diseases of T2D may have contributed to T2D being still an unmet need. An mTORC1-centric paradigm maintains that hyperactive mTORC1 drives the glycemic and non-glycemic disease aspects of T2D. Hyperactive mTORC1 is proposed to act as double-edged agent, namely, to interfere with glycemic control by disrupting the insulin receptor-Akt transduction pathway, while concomitantly driving the non-glycemic diseases of T2D. The mTORC1-centric paradigm may offer a novel perspective for T2D in terms of pathogenesis, clinical focus and treatment strategy.

Insulin sensitizer prevents and ameliorates experimental type 1 diabetes.

Insulin-dependent type-1 diabetes (T1D) is driven by autoimmune ß-cell failure, whereas systemic resistance to insulin is considered the hallmark of insulin-independent type-2 diabetes (T2D). In contrast to this canonical dichotomy, insulin resistance appears to precede the overt diabetic stage of T1D and predict its progression, implying that insulin sensitizers may change the course of T1D. However, previous attempts to ameliorate T1D in animal models or patients by insulin sensitizers have largely failed. Sensitization to insulin by MEthyl-substituted long-chain DICArboxylic acid (MEDICA) analogs in T2D animal models surpasses that of current insulin sensitizers, thus prompting our interest in probing MEDICA in the T1D context. MEDICA efficacy in modulating the course of T1D was verified in streptozotocin (STZ) diabetic rats and autoimmune nonobese diabetic (NOD) mice. MEDICA treatment normalizes overt diabetes in STZ diabetic rats when added on to subtherapeutic insulin, and prevents/delays autoimmune T1D in NOD mice. MEDICA treatment does not improve ß-cell insulin content or insulitis score, but its efficacy is accounted for by pronounced total body sensitization to insulin. In conclusion, potent insulin sensitizers may counteract genetic predisposition to autoimmune T1D and amplify subtherapeutic insulin into an effective therapeutic measure for the treatment of overt T1D.

mTORC1 syndrome (TorS): unified paradigm for diabetes/metabolic syndrome.

'Glucolipotoxicity' and 'insulin resistance' are claimed to drive type 2 diabetes (T2D) and the non-glycemic diseases of the metabolic syndrome (MetS) (obesity, dyslipidemia, hypertension). In line with that, glycemic and/or insulin control are considered to be primary goal in treating T2D/MetS. However, recent standard-of-care (SOC) treatments of T2D, initially designed to control T2D hyperglycemia, appear now to alleviate the cardio-renal and non-glycemic diseases of T2D/MetS independently of glucose lowering and insulin resistance, and in non-T2D patients altogether, calling for an alternative unifying pathophysiology/treatment paradigm for T2D/MetS. This opinion article proposes to replace the current 'glucolipotoxic/insulin-resistance' paradigm of T2D/MetS with an 'mammalian target of rapamycin complex 1 (mTORC1) syndrome' (TorS) paradigm, implying an exhaustive cohesive disease entity driven by an upstream hyperactive mTORC1, and which includes diabetic hyperglycemia, diabetic dyslipidemia, hypertension, diabetic macrovascular and microvascular disease, non-alcoholic fatty liver disease, some cancers, neurodegeneration, polycystic ovary syndrome (PCOS), psoriasis, and others. The TorS paradigm may account for the insulin-resistant glycemic context of TorS, combined with response to insulin of the non-glycemic diseases of TorS. The TorS paradigm may account for the efficacy of current antidiabetic SOC treatments in diabetic and nondiabetic patients. Most importantly, the TorS paradigm may generate novel treatments for TorS.

Suppression of adipose lipolysis by long-chain fatty acid analogs.

Agonist-induced lipolysis of adipose fat is robustly inhibited by insulin or by feedback inhibition by the long-chain fatty acids (LCFA) produced during lipolysis. However, the mode of action of LCFA in suppressing adipose lipolysis is not clear. ß,ß'-Tetramethyl hexadecanedioic acid (Mßß/ EDICA16) is a synthetic LCFA that is neither esterified into lipids nor ß-oxidized, and therefore, it was exploited for suppressing agonist-induced lipolysis in analogy to natural LCFA. Mßß is shown here to suppress isoproterenol-induced lipolysis in the rat in vivo as well as in 3T3-L1 adipocytes. Inhibition of isoproterenol-induced lipolysis is due to decrease in isoproterenol-induced cAMP with concomitant inhibition of the phosphorylation of hormone-sensitive lipase and perilipin by protein kinase A. Suppression of cellular cAMP levels is accounted for by inhibition of the adenylate cyclase due to suppression of Raf1 expression by Mßß-activated AMPK. Suppression of Raf1 is further complemented by induction of components of the unfolded-protein-response by Mßß. Our findings imply genuine inhibition of agonist-induced adipose lipolysis by LCFA, independent of their ß-oxidation or reesterification. Mßß suppression of agonist-induced lipolysis and cellular cAMP levels independent of the insulin transduction pathway may indicate that synthetic LCFA could serve as insulin mimetics in the lipolysis context under conditions of insulin resistance.

Amelioration of diabesity-induced colorectal ontogenesis by omega-3 fatty acids in mice.

Postnatal intestinal ontogenesis in an animal model of diabesity may recapitulate morphological and transduction features of diabesity-induced intestinal dysplasia and its amelioration by endogenous (n-3) polyunsaturated fatty acids (PUFA). Proliferation, differentiation, and transduction aspects of intestinal ontogenesis have been studied here in obese, insulin-resistant db/db mice, in fat-1 transgene coding for desaturation of (n-6) PUFA into (n-3) PUFA, in db/db crossed with fat-1 mice, and in control mice. Diabesity resulted in increased colonic proliferation and dedifferentiation of epithelial colonocytes and goblet cells, with increased colonic ß-catenin and hepatocyte nuclear factor (HNF)-4α transcriptional activities accompanied by enrichment in HNF-4α-bound (n-6) PUFA. In contrast, in fat-1 mice, colonic proliferation was restrained, accompanied by differentiation of crypt stem cells into epithelial colonocytes and goblet cells and by decrease in colonic ß-catenin and HNF-4α transcriptional activities, with concomitant enrichment in HNF-4α-bound (n-3) PUFA at the expense of (n-6) PUFA. Colonic proliferation and differentiation, the profile of ß-catenin and HNF-4α-responsive genes, and the composition of HNF-4α-bound PUFA of db/db mice reverted to wild-type by introducing the fat-1 gene into the db/db context. Suppression of intestinal HNF-4α activity by (n-3) PUFA may ameliorate diabesity-induced intestinal ontogenesis and offer an effective preventive modality for colorectal cancer.

Gating of the mitochondrial permeability transition pore by long chain fatty acyl analogs in vivo.

The role played by long chain fatty acids (LCFA) in promoting energy expenditure is confounded by their dual function as substrates for oxidation and as putative classic uncouplers of mitochondrial oxidative phosphorylation. LCFA analogs of the MEDICA (MEthyl-substituted DICarboxylic Acids) series are neither esterified into lipids nor beta-oxidized and may thus simulate the uncoupling activity of natural LCFA in vivo, independently of their substrate role. Treatment of rats or cell lines with MEDICA analogs results in low conductance gating of the mitochondrial permeability transition pore (PTP), with 10-40% decrease in the inner mitochondrial membrane potential. PTP gating by MEDICA analogs is accounted for by inhibition of Raf1 expression and kinase activity, resulting in suppression of the MAPK/RSK1 and the adenylate cyclase/PKA transduction pathways. Suppression of RSK1 and PKA results in a decrease in phosphorylation of their respective downstream targets, Bad(Ser-112) and Bad(Ser-155). Decrease in Bad(Ser-112, Ser-155) phosphorylation results in increased binding of Bad to mitochondrial Bcl2 with concomitant displacement of Bax, followed by PTP gating induced by free mitochondrial Bax. Low conductance PTP gating by LCFA/MEDICA may account for their thyromimetic calorigenic activity in vivo.

Gating of the mitochondrial permeability transition pore by thyroid hormone.

The calorigenic-thermogenic activity of thyroid hormone (T3) has long been ascribed to uncoupling of mitochondrial oxidative phosphorylation. However, the mode of action of T3 in promoting mitochondrial proton leak is still unresolved. Mitochondrial uncoupling by T3 is reported here to be transduced in vivo in rats and in cultured Jurkat cells by gating of the mitochondrial permeability transition pore (PTP). T3-induced PTP gating is shown here to be abrogated in inositol 1,4,5-trisphosphate (IP(3)) receptor 1 (IP(3)R1)(-/-) cells, indicating that the endoplasmic reticulum IP(3)R1 may serve as upstream target for the mitochondrial activity of T3. IP(3)R1 gating by T3 is due to its increased expression and truncation into channel-only peptides, resulting in IP(3)-independent Ca(2+) efflux. Increased cytosolic Ca(2+) results in activation of protein phosphatase 2B, dephosphorylation and depletion of mitochondrial Bcl2 (S70), and increase in mitochondrial free Bax leading to low-conductance PTP gating. The T3 transduction pathway integrates genomic and nongenomic activities of T3 in regulating mitochondrial energetics and may offer novel targets for thyromimetics designed to modulate energy expenditure.

Suppression of multiple myeloma by mitochondrial targeting.

Treatment of multiple myeloma (MM) aims at inducing cell apoptosis by surpassing the limited capacity of MM cells to cope with oxidative stress. MM cell survival may further be suppressed by limiting cellular cholesterol. Long-chain fatty acid analogs of the MEDICA series promote mitochondrial stress and inhibit cholesterol biosynthesis, thus prompting us to verify their efficacy and mode-of-action in suppressing MM cell survival, in comparison to bortezomib. MEDICA analog is shown here to effectively suppress survival of MM cells, and to inhibit growth of MM xenograft. Suppression of MM cell survival by MEDICA is accompanied by inhibition of the STAT3, MAPK and the mTORC1 transduction pathways due to mitochondrial oxidative stress. MEDICA-induced oxidative stress is abrogated by added exogenous cholesterol. Suppression of MM cell survival by bortezomib is similarly driven by bortezomib-induced oxidative stress, being abrogated by added cholesterol. In line with that, the time-to-best-response of MM patients to bortezomib-based treatment protocols is shown to be positively correlated with their plasma cholesterol level. MEDICA profile may indicate novel therapeutic potential in the management of MM.

Treatment of ErbB2 breast cancer by mitochondrial targeting.

BACKGROUND: ErbB2 breast cancer still remains an unmet need due to primary and/or acquired resistance to current treatment strategies. MEDICA compounds consist of synthetic long-chain α,ω-dicarboxylic acids previously reported to suppress breast cancer in PyMT transgenic mice. METHODS: MEDICA efficacy and mode of action in the ErbB2 context was studied in ErbB2 transgenic mice and human breast cancer cells. RESULTS: MEDICA treatment is shown here to suppress ErbB2 breast tumors and lung metastasis in ErbB2/neu MMTV transgenic mice, to suppress ErbB2/neu xenografts in nod/scid mice, and to suppress survival of AU565 and BT474 human ErbB2 breast cancer cells. Suppression of ErbB2 breast tumors by MEDICA is due to lipid raft disruption with loss of ErbB family members, including EGFR, ErbB2, and ErbB3. In addition, MEDICA inhibits mTORC1 activity, independently of abrogating the ErbB receptors and their signaling cascades. The double hit of MEDICA in abrogating ErbB and mTORC1 is partly accounted for by targeting mitochondria complex I. CONCLUSIONS: Mitochondrial targeting by MEDICA suppresses ErbB2 breast tumors and metastasis due to lipid raft disruption and inhibition of mTORC1 activity. Inhibition of mTORC1 activity by MEDICA avoids the resistance acquired by canonical mTORC1 inhibitors like rapalogs or mTOR kinase inhibitors.

Within brown-fat cells, UCP1-mediated fatty acid-induced uncoupling is independent of fatty acid metabolism.

In the present investigation, we have utilized the availability of UCP1(-/-) mice to examine a wide range of previously proposed lipid activators of Uncoupling Protein 1 (UCP1) in its native environment, i.e. in the brown-fat cells. A non-metabolizable fatty acid analogue, beta,beta cent-methyl-substituted hexadecane alpha,omega-dicarboxylic acid (Medica-16) is a potent UCP1 (re)activator in brown-fat cells, despite its bipolar structure. All-trans-retinoic acid activates UCP1 within cells, whereas beta-carotene only does so after metabolism. The UCP1-dependent effects of fatty acids are positively correlated with their chain length. Medium-chain fatty acids are potent UCP1 activators in cells, despite their lack of protonophoric properties in mitochondrial membranes. Thus, neither the ability to be metabolized nor an innate uncoupling/protonophoric ability is a necessary property of UCP1 activators within brown-fat cells.

Inhibition of colorectal cancer by targeting hepatocyte nuclear factor-4alpha.

Hepatocyte nuclear factor-4alpha (HNF-4alpha) serves as target for fatty acid nutrients and xenobiotic amphipathic carboxylates and may account for the differential effects of dietary fatty acids on colorectal cancer (CRC). The putative role played by HNF-4alpha in CRC has been verified here by evaluating the effect of HNF-4alpha antagonists and HNF-4alpha siRNA on CRC growth and proliferation in cultured CRC cells and xenotransplanted nude mice in vivo. HNF-4alpha ligand antagonists of the MEDICA series, namely, beta,beta'-tetramethylhexadecanedioic acid (M16betabeta) and gamma,gamma'-tetramethyloctadocanedioic acid (M18gammagamma) as well as HNF-4alpha siRNA are shown here to inhibit growth and proliferation of HT29 and Caco2 CRC cells, accompanied by increased subG1 cell population, downregulated PCNA, activation of caspase-3, upregulation of Bak and cytoplasmic cytochrome-c, and downregulation of Bcl-2 resulting in apoptotic death. Inhibition of CRC growth with concomitant apoptosis was further confirmed in nude mice xenotransplanted with HT29 CRC cells. CRC suppression by HNF-4alpha ligand antagonists and by HNF-4alpha siRNA was accounted for by suppression of HNF-4alpha transcription and protein expression. alpha,alpha'-tetrachlorotetradecanedioic acid (Cl-DICA), a MEDICA analogue that fails to suppress HNF-4alpha, was ineffective in suppressing growth of cultured or xenotransplanted HT29 CRC cells. Hence, increased transcriptional activity of HNF-4alpha converging onto genes coding for antiapoptotic oncogenes and cytokines may promote CRC development. Suppression of HNF-4alpha activity by natural or xenobiotic HNF-4alpha ligand antagonists or by HNF-4alpha siRNA may offer a treatment mode for CRC.

Modulation of insulin secretion by fatty acyl analogs.

The secretagogue, the incretin-like, and the suppressive activities of long-chain fatty acids (LCFAs) in modulating insulin secretion in vivo and in cultured islets were simulated here by beta,beta'-tetramethyl-hexadecanedioic acid (M16) and alpha,alpha'-tetrachloro-tetradecanedioic acid (Cl-DICA). M16, but not Cl-DICA, serves as a substrate for ATP-dependent CoA thioesterification but is not further metabolized. M16, but not Cl-DICA, acted as a potent insulin secretagogue in islets cultured in basal but not high glucose. Short-term exposure to M16 or Cl-DICA resulted in activation of glucose- but not arginine-stimulated insulin secretion. Long-term exposure to M16, but not to Cl-DICA, resulted in suppression of glucose-, arginine-, and K(+)-stimulated insulin secretion; inhibition of glucose-induced proinsulin biosynthesis; and depletion of islets insulin. beta-Cell mass and islet ATP content remained unaffected. Hence, nonmetabolizable LCFA analogs may highlight discrete LCFA metabolites and pathways involved in modulating insulin secretion, which could be overlooked due to the rapid turnover of natural LCFA.

Negative autoregulation of HNF-4alpha gene expression by HNF-4alpha1.

HNF-4alpha (hepatocyte nuclear factor-4alpha) is required for tissue-specific expression of many of the hepatic, pancreatic, enteric and renal traits. Heterozygous HNF-4alpha mutants are inflicted by MODY-1 (maturity onset diabetes of the young type-1). HNF-4alpha expression is reported here to be negatively autoregulated by HNF-4alpha1 and to be activated by dominant-negative HNF-4alpha1. Deletion and chromatin immunoprecipitation analysis indicated that negative autoregulation by HNF-4alpha1 was mediated by its association with the TATA-less HNF-4alpha core promoter enriched in Sp1, but lacking DR-1 response elements. Also, negative autoregulation by HNF-4alpha1 was independent of its transactivation function, being similarly exerted by transcriptional-defective MODY-1 missense mutants of HNF-4alpha1, or under conditions of suppressing or enhancing HNF-4alpha activity by small heterodimer partner or by inhibiting histone deacetylase respectively. Negative autoregulation by HNF-4alpha1 was abrogated by overexpressed Sp1. Transcriptional suppression by HNF-4alpha1 independently of its transactivation function may extend the scope of its transcriptional activity to interference with docking of the pre-transcriptional initiation complex to TATA-less promoters.

Suppression of B-Raf(V600E) cancers by MAPK hyper-activation.

B-Raf(V600E) activates MEK/MAPK signalling and acts as oncogenic driver of a variety of cancers, including melanoma, colorectal and papillary thyroid carcinoma. Specific B-Raf(V600E) kinase inhibitors (e.g., Vemurafenib) prove initial efficacy in melanoma followed shortly by acquired resistance, while failing in most other B-Raf(V600E) cancers due to primary resistance. Resistance is due to acquired mutations in the Ras/Raf/MEK/MAPK pathway and/or other oncogenic drivers that bypass B-Raf(V600E). Surprisingly, hyper-activation of MAPK by inhibiting its protein phosphatase 2A by a synthetic long-chain fatty acid analogue (MEDICA), results in oncogene-induced growth arrest and apoptosis of B-Raf(V600E) cancer cells. Growth arrest is accompanied by MAPK-mediated serine/threonine phosphorylation and suppression of a variety of oncogenic drivers that resist treatment by B-Raf(V600E) kinase inhibitors, including ErbB members, c-Met, IGFR, IRS, STAT3 and Akt. The combined activities of mutated B-Raf and MEDICA are required for generating hyper-activated MAPK, growth arrest and apoptosis, implying strict specificity for mutated B-Raf cancer cells.

Modulation of mitochondrial transition pore components by thyroid hormone.

Thyroid hormone (TH) modulates metabolic efficiency by controlling the coupling of mitochondrial oxidative phosphorylation. However, its uncoupling mode of action is still enigmatic. Treatment of Jurkat or GH3 cells with T3 is reported here to result in limited, Cyclosporin A-sensitive mitochondrial depolarization, conforming to low conductance gating of the mitochondrial transition pore (MTP). MTP protein components induced by T3 treatment were verified in T3-treated and hypothyroid rat liver as well as in Jurkat cells. T3 treatment resulted in increase in mitochondrial Bax and Bak together with decreased mitochondrial Bcl2. T3-induced mitochondrial depolarization was aborted by overexpression of Bcl2. In contrast to Bax-Bcl2 family proteins, some other MTP components were either not induced by T3 (e.g. voltage-dependent anion channel) or were induced, but were not involved in Cyclosporin A-sensitive MTP gating (e.g. Cyclophilin D and adenine nucleotide translocase-2) Hence, TH-induced mitochondrial uncoupling may be ascribed to low conductance MTP gating mediated by TH-induced increase in mitochondrial proapoptotic combined with a decrease in mitochondrial antiapoptotic proteins of the Bax-Bcl2 family.

MEDICA 16 inhibits hepatic acetyl-CoA carboxylase and reduces plasma triacylglycerol levels in insulin-resistant JCR: LA-cp rats.

Intracellular triacylglycerol (TG) content of liver and skeletal muscle contributes to insulin resistance, and a significant correlation exists between TG content and the development of insulin resistance. Because acetyl-CoA carboxylase (ACC) is the rate-limiting enzyme for liver fatty acid biosynthesis and a key regulator of muscle fatty acid oxidation, we examined whether ACC plays a role in the accumulation of intracellular TG. We also determined the potential role of 5'-AMP-activated protein kinase (AMPK) in this process, since it can phosphorylate and inhibit ACC activity in both liver and muscle. TG content, ACC, and AMPK were examined in the liver and skeletal muscle of insulin-resistant JCR:LA-cp rats during the time frame when insulin resistance develops. At 12 weeks of age, there was a threefold elevation in liver TG content and a sevenfold elevation in skeletal muscle TG content. Hepatic ACC activity was significantly elevated in 12-week-old JCR:LA-cp rats compared with lean age-matched controls (8.75 +/- 0.53 vs. 3.30 +/- 0.18 nmol. min(-1). mg(-1), respectively), even though AMPK activity was also increased. The observed increase in hepatic ACC activity was accompanied by a 300% increase in ACC protein expression. There were no significant differences in ACC activity, ACC protein expression, or AMPK activity in the skeletal muscle of the 12-week JCR:LA-cp rats. Treatment of 12-week JCR:LA-cp rats with MEDICA 16 (an ATP-citrate lyase inhibitor) resulted in a decrease in hepatic ACC and AMPK activities, but had no effect on skeletal muscle ACC and AMPK. Our data suggest that alterations in ACC or AMPK activity in muscle do not contribute to the development of insulin resistance. However, increased liver ACC activity in the JCR:LA-cp rat appears to contribute to the development of lipid abnormalities, although this increase does not appear to occur secondary to a decrease in AMPK activity.

Transcriptional suppression of human microsomal triglyceride transfer protein by hypolipidemic insulin sensitizers.

Microsomal triglyceride transfer protein (MTP) catalyzes the assembly and secretion of liver triglyceride-rich lipoproteins. The human MTP (hMTP) promoter activity is reported here to be suppressed by HNF-4alpha ligand antagonists (e.g., Medica analogs) or by PPARgamma ligand agonists (e.g., thiazolidinediones), thus accounting for their hypolipidemic activity in humans. Suppression of liver hMTP by Medica analogs or by thiazolidinediones was mediated by the TAAA sequence that serves as non-canonical TATA box of the hMTP core promoter. MTP suppression was evident in the specific context of the wild type hMTP core promoter, but not in the context of the mutated rodent-conforming hMTP core promoter governed by a canonical TATA box conjoined with its proximal (-50/-38)DR-1 element. hMTP suppression by Medica analogs or thiazolidinediones mediated by hMTP TAAA was independent of HNF-4alpha or PPARgamma. hMTP suppression by Medica analogs, but not by thiazolidinediones, was further complemented by inhibition of HNF-4alpha transcriptional activity transduced by the distal (-83/-70)DR-1 element of hMTP promoter. hMTP promoter activity was unaffected by PPARalpha activation. Furthermore, in contrast to hMTP, the promoter activity of the rodent-conforming hMTP was robustly activated by Wy-14,643-activated PPARalpha or by thiazolidinedione-activated PPARgamma. Transcriptional activation by PPARalpha or PPARgamma of the rodent-conforming, but not the wild type hMTP gene promoter, resulted from the species-specific context of the respective proximal DR-1 elements. Hence, suppression of hMTP transcription by hypolipidemic insulin sensitizers requires the specific context of hMTP core promoter. In light of the species-specific context of MTP core promoters, the rodent MTP promoter may not substitute for the human promoter when searching for hypolipidemic MTP suppressors.