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Here, plant HAM proteins are shown to physically interact with the transcription factor WUSCHEL and the related WOX proteins, with this interaction driving downstream transcriptional programs and determining the activities of stem cells. Regulation of plant stem cell function Postembryonic development of above-ground tissues and of roots of plants depends on stem cells in the shoot and root apical meristems, respectively. The transcription factor WUSCHEL (WUS) and the related WOX proteins are known to be involved in the specification and maintenance of stem cells within all meristems throughout the plant kingdom. The HAIRY MERISTEM (HAM) family of transcription regulators is known to contribute to shoot stem cell function in certain plant species. The present paper shows that WOX and HAM family proteins act together to control the production of all types of stem cells in diverse niches in Arabidopsis, and that WUS and HAM share some common targets in vivo. Differences in the combined expression patterns of WOX and HAM family members appear to determine the formation of diverse stem cell niche locations. These findings demonstrate how co-operative transcriptional regulators drive common regulatory pathways and point to mechanisms underlying the evolution of stem cell regulation in plants. Plant stem cells in the shoot apical meristem (SAM) and root apical meristem are necessary for postembryonic development of aboveground tissues and roots, respectively, while secondary vascular stem cells sustain vascular development.sup.1,2,3,4. WUSCHEL (WUS), a homeodomain transcription factor expressed in the rib meristem of the Arabidopsis SAM, is a key regulatory factor controlling SAM stem cell populations.sup.5,6, and is thought to establish the shoot stem cell niche through a feedback circuit involving the CLAVATA3 (CLV3) peptide signalling pathway.sup.7. WUSCHEL-RELATED HOMEOBOX 5 (WOX5), which is specifically expressed in the root quiescent centre, defines quiescent centre identity and functions interchangeably with WUS in the control of shoot and root stem cell niches.sup.8. WOX4, expressed in Arabidopsis procambial cells, defines the vascular stem cell niche.sup.9,10,11. WUS/WOX family proteins are evolutionarily and functionally conserved throughout the plant kingdom.sup.12 and emerge as key actors in the specification and maintenance of stem cells within all meristems.sup.13. However, the nature of the genetic regime in stem cell niches that centre on WOX gene function has been elusive, and molecular links underlying conserved WUS/WOX function in stem cell niches remain unknown. Here we demonstrate that the Arabidopsis HAIRY MERISTEM (HAM) family of transcription regulators act as conserved interacting cofactors with WUS/WOX proteins. HAM and WUS share common targets in vivo and their physical interaction is important in driving downstream transcriptional programs and in promoting shoot stem cell proliferation. Differences in the overlapping expression patterns of WOX and HAM family members underlie the formation of diverse stem cell niche locations, and the HAM family is essential for all of these stem cell niches. These findings establish a new framework for the control of stem cell production during plant development., Author(s): Yun Zhou [sup.1] , Xing Liu [sup.1] , Eric M. Engstrom [sup.2] [sup.6] , Zachary L. Nimchuk [sup.1] [sup.3] [sup.6] , Jose L. Pruneda-Paz [sup.4] , Paul T. Tarr [...]

High-fat feeding that induces hyperlipidemia and antherogenesis, stimulates the expression of both PGC-1 beta and sterol responsive element binding protein (SREBP)1c and 1a in liver is described. Unlike SREBP itself, PGC-1beta reduces fat accumulation in the liver while greatly increasing circulating triglycerides and cholesterol in VLDL particles.

Skeletal muscle adapts to chronic physical activity by inducing mitochondrial biogenesis and switching proportions of muscle fibers from type II to type I. Several major factors involved in this process have been identified, such as the calcium/calmodulin-dependent protein kinase IV (CaMKIV), calcineurin A (CNA), and the transcriptional component peroxisome proliferator-activated receptor [gamma] coactivator 1[alpha] (PGC-1[alpha]). Transgenic expression of PGC-1[alpha] recently has been shown to dramatically increase the content of type I muscle fibers in skeletal muscle, but the relationship between PGC-1[alpha] expression and the key components in calcium signaling is not clear. In this report, we show that the PGC-1[alpha] promoter is regulated by both CaMKIV and CnA activity. CaMKIV activates PGC-1[alpha] largely through the binding of cAMP response element-binding protein to the PGC-1[alpha] promoter. Moreover, we show that a positive feedback loop exists between PGC-1[alpha] and members of the myocyte enhancer factor 2 (MEF2) family of transcription factors. MEF2s bind to the PGC-1[alpha] promoter and activate it, predominantly when coactivated by PGC-1[alpha]. MEF2 activity is stimulated further by CnA signaling. These findings imply a unified pathway, integrating key regulators of calcium signaling with the transcriptional switch PGC-1[alpha]. Furthermore, these data suggest an autofeedback loop whereby the calcium-signaling pathway may result in a stable induction of PGC-1[alpha], contributing to the relatively stable nature of muscle fiber-type determination.

Author(s): Jiandie Lin [1]; Hai Wu [2]; Paul T. Tarr [1]; Chen-Yu Zhang [3]; Zhidan Wu [1]; Olivier Boss [3]; Laura F. Michael [1]; Pere Puigserver [1]; Eiji Isotani [4]; [...]

PGC-alpha is a coactivator of nuclear receptors and other transcription factors that regulates several metabolic processes, including mitochondrial biogenesis and respiration, hepatic gluconeogenesis, and muscle fiber-type switching. The central role for PGC-1 alpha in the control of energy metabolism is illustrated.

Cytokinins and ethylene control plant development via sensors from the histidine kinase (HK) family. However, downstream signaling pathways for the key phytohormones are distinct. Here we report that not only cytokinin but also ethylene is able to control root apical meristem (RAM) size through activation of the multistep phosphorelay (MSP) pathway. We found that both cytokinin and ethylene-dependent RAM shortening requires ethylene binding to ETR1 and the HK activity of ETR1. The receiver domain of ETR1 interacts with MSP signaling intermediates acting downstream of cytokinin receptors, further substantiating the role of ETR1 in MSP signaling. We revealed that both cytokinin and ethylene induce the MSP in similar and distinct cell types with ETR1-mediated ethylene signaling controlling MSP output specifically in the root transition zone. We identified members of the MSP pathway specific and common to both hormones and showed that ETR1-regulated ARR3 controls RAM size. ETR1-mediated MSP spatially differs from canonical CTR1/EIN2/EIN3 ethylene signaling and is independent of EIN2, indicating that both pathways can be spatially and functionally separated. Furthermore, we demonstrated that canonical ethylene signaling controls MSP responsiveness to cytokinin specifically in the root transition zone, presumably via regulation of ARR10 , one of the positive regulators of MSP signaling in Arabidopsis. This study shows that ethylene regulates root growth via the multistep phosphorelay (MSP) pathway, typically controlled by cytokinins. The histidine kinase activity of ethylene sensor ETR1 is necessary for ethylene-mediated regulation of the MSP pathway. The downstream components of the MSP pathway involved in the control of root growth are characterized to be some common and some specific to each class of hormone. [ABSTRACT FROM AUTHOR]

The CLAVATA3 (CLV3)-CLAVATA1 (CLV1) ligand-receptor kinase pair negatively regulates shoot stem cell proliferation in plants. clv1 null mutants are weaker in phenotype than clv3 mutants, but the clv1 null phenotype is enhanced by mutations in the related receptor kinases BARELYANYMERISTEM1, 2 and 3 (BAM1, 2 and 3). The basis of this genetic redundancy is unknown. Here, wedemonstrate that the apparent redundancy in the CLV1 clade is in fact due to the transcriptional repression of BAM genes by CLV1 signaling. CLV1 signaling in the rib meristem (RM) of the shoot apical meristem is necessary and sufficient for stem cell regulation. CLV3-CLV1 signaling in the RM represses BAM expression in wild-type Arabidopsis plants. In clv1 mutants, ectopic BAM expression in the RM partially complements the loss of CLV1.BAMregulation by CLV1 is distinct from CLV1 regulation of WUSCHEL, a proposed CLV1 target gene. In addition, quadruple receptor mutants are stronger in phenotype than clv3, pointing to the existence of additional CLV1/BAM ligands. These data provide an explanation for the genetic redundancy seen in the CLV1 clade and reveal a novel feedback operating in the control of plant stem cells. [ABSTRACT FROM AUTHOR]

The Arabidopsis thaliana leucine-rich repeat receptor kinase FLAGELLIN SENSING2 (FLS2) is required for the recognition of bacterial flagellin in innate immunity. Recently, FLS2 was proposed to act as a multispecific receptor recognizing unrelated exogenous and endogenous peptide ligands, including CLAVATA3 (CLV3), a key regulator of shoot meristem stem cell production. Here, we report experimental evidence demonstrating that FLS2 does not recognize CLV3 and that the shoot apical meristem is immune to bacteria independently of CLV3 perception. [ABSTRACT FROM AUTHOR]

The emerging field of computational morphodynamics aims to understand the changes that occur in space and time during development by combining three technical strategies: live imaging to observe development as it happens; image processing and analysis to extract quantitative information; and computational modelling to express and test time-dependent hypotheses. The strength of the field comes from the iterative and combined use of these techniques, which has provided important insights into plant development. [ABSTRACT FROM AUTHOR]

Summary: Background: Cell numbers in above-ground meristems of plants are thought to be maintained by a feedback loop driven by perception of the glycopeptide ligand CLAVATA3 (CLV3) by the CLAVATA1 (CLV1) receptor kinase and the CLV2/CORYNE (CRN) receptor-like complex []. CLV3 produced in the stem cells at the meristem apex limits the expression level of the stem cell-promoting homeodomain protein WUSCHEL (WUS) in the cells beneath, where CLV1 and WUS RNA are localized. WUS downregulation nonautonomously reduces stem cell proliferation. Overexpression of CLV3 eliminates the stem cells, causing meristem termination [], and loss of CLV3 function allows meristem overproliferation []. There are many questions regarding the CLV3/CLV1 interaction, including where in the meristem it occurs, how it is regulated, and how it is that a large range of CLV3 concentrations gives no meristem size phenotype []. Results: Here we use genetics and live imaging to examine the cell biology of CLV1 in Arabidopsis meristematic tissue. We demonstrate that plasma membrane-localized CLV1 is reduced in concentration by CLV3, which causes trafficking of CLV1 to lytic vacuoles. We find that changes in CLV2 activity have no detectable effects on CLV1 levels. We also find that CLV3 appears to diffuse broadly in meristems, contrary to a recent sequestration model []. Conclusions: This study provides a new model for CLV1 function in plant stem cell maintenance and suggests that downregulation of plasma membrane-localized CLV1 by its CLV3 ligand can account for the buffering of CLV3 signaling in the maintenance of stem cell pools in plants. [ABSTRACT FROM AUTHOR]

Sequence comparisons, biochemical experiments, and studies with mutants in transgenic plants show that the Arabidopsis protein CORYNE, currently thought to be a kinase that acts as part of a receptor kinase complex, is likely to be a pseudokinase and not a kinase. [ABSTRACT FROM AUTHOR]

Abstract: Every cell is separated from its external environment by a lipid membrane. Survival depends on the regulated and selective transport of nutrients, waste products and regulatory molecules across these membranes, a process that is often mediated by integral membrane proteins. The largest and most diverse of these membrane transport systems is the ATP binding cassette (ABC) family of membrane transport proteins. The ABC family is a large evolutionary conserved family of transmembrane proteins (>250 members) present in all phyla, from bacteria to Homo sapiens, which require energy in the form of ATP hydrolysis to transport substrates against concentration gradients. In prokaryotes the majority of ABC transporters are involved in the transport of nutrients and other macromolecules into the cell. In eukaryotes, with the exception of the cystic fibrosis transmembrane conductance regulator (CFTR/ABCC7), ABC transporters mobilize substrates from the cytoplasm out of the cell or into specific intracellular organelles. This review focuses on the members of the ABCG subfamily of transporters, which are conserved through evolution in multiple taxa. As discussed below, these proteins participate in multiple cellular homeostatic processes, and functional mutations in some of them have clinical relevance in humans. [Copyright &y& Elsevier]

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a transcriptional coactivator that regulates multiple aspects of cellular energy metabolism, including mitochondrial biogenesis, hepatic gluconeogenesis, and β-oxidation of fatty acids. PGC-1α mRNA levels are increased in both type-1 and type-2 diabetes and may contribute to elevated hepatic glucose production in diabetic states. We have recently described PGC-1β, a novel transcriptional coactivator that is a homolog of PGC-1α. Although PGC-1β shares significant sequence similarity and tissue distribution with PGC-1α, the biological activities of PGC-1β in the regulation of cellular metabolism is unknown. In this study, we used an adenoviral-mediated expression system to study the function of PGC-1β both in cultured hepatocytes and in the liver of rats. PGC-1β, like PGC-1α, potently induces the expression of an array of mitochondrial genes involved in oxidative metabolism. However, in contrast to PGC-1α, PGC-1β poorly activates the expression of gluconeogenic genes in hepatocytes or liver in vivo, illustrating that these two coactivators play distinct roles in hepatic glucose metabolism. The reduced ability of PGC-1β to induce gluconeogenic genes is due, at least in part, to its inability to physically associate with and coactivate hepatic nuclear receptor 4α (HNF4α) and forkhead transcription factor O1 (FOXO1), two critical transcription factors that mediate the activation of gluconeogenic gene expression by PGC-1α. These data illustrate that PGC-1β and PGC-1α have distinct arrays of activities in hepatic energy metabolism. [ABSTRACT FROM AUTHOR]

A response by Adrienne H. K. Roeder and colleagues to a letter to the editor regarding the article "Computational morphodynamics of plants: integrating development over space and time" in the 2011 issue is presented.

The PGC-I family of coactivators stimulates the activity of certain transcription factors and nuclear receptors. Transcription factors in the sterol responsive element binding protein (SREBP) family are key regulators of the lipogenic genes in the liver. We show here that high-fat feeding, which induces hyperlipidemia and atherogenesis, stimulates the expression of both PGC-1β and SREBP1c and 1a in liver. PGC-1β coactiyates the SREBP transcription factor family and stimulates lipogenic gene expression. Further, PGC-1β required for SREBP-mediated lipogenic gene expression. However, unlike SREBP itself, PGC-1 β reduces fat accumulation in the liver while greatly increasing circulating triglycerides and cholesterol in VLDL particles. The stimulation of lipoprotein transport upon PGC-1β expression is likely due to the simultaneous coactivation of the liver X receptor, LXRα, a nuclear hormone receptor with known roles in hepatic lipid transport. These data suggest a mechanism through which dietary saturated fats can stimulate hyperlipidemia and atherogenesis. [ABSTRACT FROM AUTHOR]

PGC-1α is a coactivator of nuclear receptors and other transcription factors that regulates several metabolic processes, including mitochondrial biogenesis and respiration, hepatic gluconeogenesis, and muscle fiber-type switching. We show here that, while hepatocytes lacking PGC-1α are defective in the program of hormone-stimulated gluconeogenesis, the mice have constitutively activated gluconeogenic gene expression that is completely insensitive to normal feeding controls. C/EBPβ is elevated in the livers of these mice and activates the gluconeogenic genes in a PGC-1α-independent manner. Despite having reduced mitochondrial function, PGC-1α null mice are paradoxically lean and resistant to diet-induced obesity. This is largely due to a profound hyperactivity displayed by the null animals and is associated with lesions in the striatal region of the brain that controls movement. These data illustrate a central role for PGC-1α in the control of energy metabolism but also reveal novel systemic compensatory mechanisms and pathogenic effects of impaired energy homeostasis. [Copyright &y& Elsevier]

Summary Coordinated growth of organs requires communication among cells within and between tissues. In plants, leaf growth is largely dictated by the epidermis; here, asymmetric and self-renewing divisions of the stomatal lineage create two essential cell types—pavement cells and guard cells—in proportions reflecting inputs from local, systemic, and environmental cues. The transcription factor SPEECHLESS (SPCH) is the prime regulator of divisions, but whether and how it is influenced by external cues to provide flexible development is enigmatic. Here, we show that the phytohormone cytokinin (CK) can act as an endogenous signal to affect the extent and types of stomatal lineage divisions and forms a regulatory circuit with SPCH. Local domains of low CK signaling are created by SPCH-dependent cell-type-specific activity of two repressive type-A ARABIDOPSIS RESPONSE REGULATORs (ARRs), ARR16 and ARR17, and two secreted peptides, CLE9 and CLE10, which, together with SPCH, can customize epidermal cell-type composition. Graphical Abstract Highlights • Cytokinin promotes asymmetric spacing divisions to increase stomatal production • SPEECHLESS is an effector of CK signaling and can also induce type-A ARR16 • Fine-tuning of CK signaling by cell-type-specific type A-ARRs modulates divisions • Stomatal lineage-specific peptides CLE9 and CLE10 regulate stomatal production Multicellular development requires coordination of systemic signaling with cell-type-specific outputs. Vatén et al. show how the plant hormone cytokinin interfaces with the stomatal transcription factor SPEECHLESS to modulate stem-cell-like asymmetric divisions, thus creating stomata and epidermal cells in appropriate numbers and proportions for leaf performance in fluctuating environments. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptor γ coactivator (PGC)-1α is a coactivator of nuclear receptors and other transcription factors that regulates several components of energy metabolism, particularly certain aspects of adaptive thermogenesis in brown fat and skeletal muscle, hepatic gluconeogenesis, and fiber type switching in skeletal muscle. PGC-1α has been shown to induce mitochondrial biogenesis when expressed in muscle cells, and preliminary analysis has suggested that this molecule may specifically increase the fraction of uncoupled versus coupled respiration. In this paper, we have performed detailed bioenergetic analyses of the function of PGC-1α and its homolog PGC-1β in muscle cells by monitoring simultaneously oxygen consumption and membrane potential. Cells expressing PGC-1α or PGC-1β display higher proton leak rates at any given membrane potential than control cells. However, cells expressing PGC-1α have a higher proportion of their mitochondrial respiration linked to proton leak than cells expressing PGC-1β. Although these two proteins cause a similar increase in the expression of many mitochondrial genes, PGC-1β preferentially induces certain genes involved in the removal of reactive oxygen species, recently recognized as activators of uncoupling proteins. Together, these data indicate that PGC-1α and PGC-1β profoundly alter mitochondrial metabolism and suggest that these proteins are likely to play different physiological functions. [ABSTRACT FROM AUTHOR]

Quantitative studies in plant developmental biology require monitoring and measuring the changes in cells and tissues as growth gives rise to intricate patterns. The success of these studies has been amplified by the combined strengths of two complementary techniques, namely live imaging and computational image analysis. Live imaging records time-lapse images showing the spatial-temporal progress of tissue growth with cells dividing and changing shape under controlled laboratory experiments. Image processing and analysis make sense of these data by providing computational ways to extract and interpret quantitative developmental information present in the acquired images. Manual labeling and qualitative interpretation of images are limited as they don't scale well to large data sets and cannot provide field measurements to feed into mathematical and computational models of growth and patterning. Computational analysis, when it can be made sufficiently accurate, is more efficient, complete, repeatable, and less biased. In this chapter, we present some guidelines for the acquisition and processing of images of sepals and the shoot apical meristem of Arabidopsis thaliana to serve as a basis for modeling. We discuss fluorescent markers and imaging using confocal laser scanning microscopy as well as present protocols for doing time-lapse live imaging and static imaging of living tissue. Image segmentation and tracking are discussed. Algorithms are presented and demonstrated together with low-level image processing methods that have proven to be essential in the detection of cell contours. We illustrate the application of these procedures in investigations aiming to unravel the mechanical and biochemical signaling mechanisms responsible for the coordinated growth and patterning in plants., (Copyright © 2012 Elsevier Inc. All rights reserved.)

ABCG1 and ABCG4 are highly homologous members of the ATP binding cassette (ABC) transporter family that regulate cellular cholesterol homeostasis. In adult mice, ABCG1 is known to be expressed in numerous cell types and tissues, whereas ABCG4 expression is limited to the central nervous system (CNS). Here, we show significant differences in expression of these two transporters during development. Examination of beta-galactosidase-stained tissue sections from Abcg1(-/-)LacZ and Abcg4(-/-)LacZ knockin mice shows that ABCG4 is highly but transiently expressed both in hematopoietic cells and in enterocytes during development. In contrast, ABCG1 is expressed in macrophages and in endothelial cells of both embryonic and adult liver. We also show that ABCG1 and ABCG4 are both expressed as early as E12.5 in the embryonic eye and developing CNS. Loss of both ABCG1 and ABCG4 results in accumulation in the retina and/or brain of oxysterols, in altered expression of liver X receptor and sterol-regulatory element binding protein-2 target genes, and in a stress response gene. Finally, behavioral tests show that Abcg4(-/-) mice have a general deficit in associative fear memory. Together, these data indicate that loss of ABCG1 and/or ABCG4 from the CNS results in changes in metabolic pathways and in behavior.

Here, we describe the initial characterization of Abcg4(-/-) mice and identify overlapping functions of ABCG4 and ABCG1 in the brain. Histological examination of tissues from Abcg4(+/-)/nlsLacZ and Abcg1(+/-)/nlsLacZ mice demonstrates that coexpression of Abcg4 and Abcg1 is restricted to neurons and astrocytes of the central nervous system (CNS). Interestingly, Abcg4 mRNA is undetectable outside the CNS, in contrast with the broad tissue and cellular expression of Abcg1. We also used primary astrocytes, microglia, neurons, and macrophages to demonstrate that the expression of Abcg1, but not Abcg4, is induced after the activation of liver X receptor. Cellular localization studies demonstrated that both proteins reside in RhoB-positive endocytic vesicle membranes. Furthermore, overexpression of either ABCG1 or ABCG4 increased the processing of sterol-regulatory element binding protein 2 (SREBP-2) to the transcriptionally active protein, thus accounting for the observed increase in the expression of SREBP-2 target genes and cholesterol synthesis. Consistent with these latter results, we show that the expression levels of the same SREBP-2 target genes are repressed in the brains of Abcg1(-/-) and, to a lesser extent, Abcg4(-/-) mice. Based on the results of the current study, we propose that ABCG1 and ABCG4 mediate the intracellular vesicular transport of cholesterol/sterols within both neurons and astrocytes to regulate cholesterol transport in the brain.

Peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) is a transcriptional coactivator that regulates multiple aspects of cellular energy metabolism, including mitochondrial biogenesis, hepatic gluconeogenesis, and beta-oxidation of fatty acids. PGC-1alpha mRNA levels are increased in both type-1 and type-2 diabetes and may contribute to elevated hepatic glucose production in diabetic states. We have recently described PGC-1beta, a novel transcriptional coactivator that is a homolog of PGC-1alpha. Although PGC-1beta shares significant sequence similarity and tissue distribution with PGC-1alpha, the biological activities of PGC-1beta in the regulation of cellular metabolism is unknown. In this study, we used an adenoviral-mediated expression system to study the function of PGC-1beta both in cultured hepatocytes and in the liver of rats. PGC-1beta, like PGC-1alpha, potently induces the expression of an array of mitochondrial genes involved in oxidative metabolism. However, in contrast to PGC-1alpha, PGC-1beta poorly activates the expression of gluconeogenic genes in hepatocytes or liver in vivo, illustrating that these two coactivators play distinct roles in hepatic glucose metabolism. The reduced ability of PGC-1beta to induce gluconeogenic genes is due, at least in part, to its inability to physically associate with and coactivate hepatic nuclear receptor 4alpha (HNF4alpha) and forkhead transcription factor O1 (FOXO1), two critical transcription factors that mediate the activation of gluconeogenic gene expression by PGC-1alpha. These data illustrate that PGC-1beta and PGC-1alpha have distinct arrays of activities in hepatic energy metabolism.

The multidrug resistance-associated protein 2 (MRP2, ABCC2), mediates the efflux of several conjugated compounds across the apical membrane of the hepatocyte into the bile canaliculi. We identified MRP2 in a screen designed to isolate genes that are regulated by the farnesoid X-activated receptor (FXR, NR1H4). MRP2 mRNA levels were induced following treatment of human or rat hepatocytes with either naturally occurring (chenodeoxycholic acid) or synthetic (GW4064) FXR ligands. In addition, we have shown that MRP2 expression is regulated by the pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3). Thus, treatment of rodent hepatocytes with PXR or CAR agonists results in a robust induction of MRP2 mRNA levels. The dexamethasone- and pregnenolone 16alpha-carbonitrile-dependent induction of MRP2 expression was not evident in hepatocytes derived from PXR null mice. In contrast, induction of MRP2 by phenobarbital, an activator of CAR, was comparable in wild-type and PXR null mice. An unusual 26-bp sequence was identified 440 bp upstream of the MRP2 transcription initiation site that contains an everted repeat of the AGTTCA hexad separated by 8 nucleotides (ER-8). PXR, CAR, and FXR bound with high affinity to this element as heterodimers with the retinoid X receptor alpha (RXRalpha, NR2B1). Luciferase reporter gene constructs containing 1 kb of the rat MRP2 promoter were prepared and transiently transfected into HepG2 cells. Luciferase activity was induced in a PXR-, CAR-, or FXR-dependent manner. Furthermore, the isolated ER-8 element was capable of conferring PXR, CAR, and FXR responsiveness on a heterologous thymidine kinase promoter. Mutation of the ER-8 element abolished the nuclear receptor response. These studies demonstrate that MRP2 is regulated by three distinct nuclear receptor signaling pathways that converge on a common response element in the 5'-flanking region of this gene.