A transcriptional switch mediated by cofactor methylation

Protein lysine acetylation in cellular function and its role in cancer manifestation

Lysine acetylation appears to be crucial for diverse biological phenomena, including all the DNA-templated processes, metabolism, cytoskeleton dynamics, cell signaling, and circadian rhythm. A growing number of cellular proteins have now been identified to be acetylated and constitute the complex cellular acetylome. Cross-talk among protein acetylation together with other post-translational modifications fine-tune the cellular functions of different protein machineries. Dysfunction of acetylation process is often associated with several diseases, especially cancer. This review focuses on the recent advances in the role of protein lysine acetylation in diverse cellular functions and its implications in cancer manifestation.

Genes encoding critical transcriptional activators for murine neural tube development and human spina bifida: a case-control study

Background

Spina bifida is a malformation of the neural tube and is the most common of neural tube defects (NTDs). The etiology of spina bifida is largely unknown, although it is thought to be multi-factorial, involving multiple interacting genes and environmental factors. Mutations in transcriptional co-activator genes-Cited2, p300, Cbp, Tfap2α, Carm1 and Cart1 result in NTDs in murine models, thus prompt us to investigate whether homologues of these genes are associated with NTDs in humans.

Methods

Data and biological samples from 297 spina bifida cases and 300 controls were derived from a population-based case-control study conducted in California. 37 SNPs within CITED2, EP300, CREBBP, TFAP2A, CARM1 and ALX1 were genotyped using an ABI SNPlex assay. Odds ratios and 95% confidence intervals were calculated for alleles, genotypes and haplotypes to evaluate the risk for spina bifida.

Results

Several SNPs showed increased or decreased risk, including CITED2 rs1131431 (OR = 5.32, 1.04~27.30), EP300 rs4820428 (OR = 1.30, 1.01~1.67), EP300 rs4820429 (OR = 0.50, 0.26~0.50, in whites, OR = 0.7, 0.49~0.99 in all subjects), EP300 rs17002284 (OR = 0.43, 0.22~0.84), TFAP2A rs3798691 (OR = 1.78, 1.13~2.87 in Hispanics), CREBBP rs129986 (OR = 0.27, 0.11~0.69), CARM1 rs17616105 (OR = 0.41, 0.22~0.72 in whites). In addition, one haplotype block in EP300 and one in TFAP2A appeared to be associated with increased risk.

Conclusions

Modest associations were observed in CITED2, EP300, CREBBP, TFAP2A and CARM1 but not ALX1. However, these modest associations were not statistically significant after correction for multiple comparisons. Searching for potential functional variants and rare causal mutations is warranted in these genes.

Coactivators in PPAR-Regulated Gene Expression

Peroxisome proliferator-activated receptor (PPAR)alpha, beta (also known as delta), and gamma function as sensors for fatty acids and fatty acid derivatives and control important metabolic pathways involved in the maintenance of energy balance. PPARs also regulate other diverse biological processes such as development, differentiation, inflammation, and neoplasia. In the nucleus, PPARs exist as heterodimers with retinoid X receptor-alpha bound to DNA with corepressor molecules. Upon ligand activation, PPARs undergo conformational changes that facilitate the dissociation of corepressor molecules and invoke a spatiotemporally orchestrated recruitment of transcription cofactors including coactivators and coactivator-associated proteins. While a given nuclear receptor regulates the expression of a prescribed set of target genes, coactivators are likely to influence the functioning of many regulators and thus affect the transcription of many genes. Evidence suggests that some of the coactivators such as PPAR-binding protein (PBP/PPARBP), thyroid hormone receptor-associated protein 220 (TRAP220), and mediator complex subunit 1 (MED1) may exert a broader influence on the functions of several nuclear receptors and their target genes. Investigations into the role of coactivators in the function of PPARs should strengthen our understanding of the complexities of metabolic diseases associated with energy metabolism.

CARM1 is required for proper control of proliferation and differentiation of pulmonary epithelial cells

Coactivator-associated arginine methyltransferase I (CARM1; PRMT4) regulates gene expression by multiple mechanisms including methylation of histones and coactivation of steroid receptor transcription. Mice lacking CARM1 are small, fail to breathe and die shortly after birth, demonstrating the crucial role of CARM1 in development. In adults, CARM1 is overexpressed in human grade-III breast tumors and prostate adenocarcinomas, and knockdown of CARM1 inhibits proliferation of breast and prostate cancer cell lines. Based on these observations, we hypothesized that loss of CARM1 in mouse embryos would inhibit pulmonary cell proliferation, resulting in respiratory distress. By contrast, we report here that loss of CARM1 results in hyperproliferation of pulmonary epithelial cells during embryonic development. The lungs of newborn mice lacking CARM1 have substantially reduced airspace compared with their wild-type littermates. In the absence of CARM1, alveolar type II cells show increased proliferation. Electron microscopic analyses demonstrate that lungs from mice lacking CARM1 have immature alveolar type II cells and an absence of alveolar type I cells. Gene expression analysis reveals a dysregulation of cell cycle genes and markers of differentiation in the Carm1 knockout lung. Furthermore, there is an overlap in gene expression in the Carm1 knockout and the glucocorticoid receptor knockout lung, suggesting that hyperproliferation and lack of maturation of the alveolar cells are at least in part caused by attenuation of glucocorticoid-mediated signaling. These results demonstrate for the first time that CARM1 inhibits pulmonary cell proliferation and is required for proper differentiation of alveolar cells.

A-kinase-interacting protein 1 (AKIP1) acts as a molecular determinant of PKA in NF-kappaB signaling

The cAMP-dependent protein kinase (PKA) signaling pathway plays a crucial role in the pathogenesis of many NF-kappaB-related diseases. However, there have been controversial reports with regard to the PKA actions in the regulation of NF-kappaB activity. In this study, we have demonstrated the effect of PKA on NF-kappaB activity in view of AKIP1 action; and in 293 and HeLa cells, where the endogenous AKIP1 expression is minimal, PKA-activating agents inhibited the NF-kappaB-dependent reporter gene expression, blocked the interaction of PKAc and p65 subunit of NF-kappaB, and attenuated PKA-dependent phosphorylation of p65 on Ser-276. This inhibitory function of PKAc in NF-kappaB signaling was reversed by overexpression of AKIP1 in 293 cells. In the breast cancer cell line, MDA-MB231 cells and MCF7 cells, where the endogenous AKIP1 is abundant, the PKA signal was found to be synergized with NF-kappaB activation; PKA-activating agents enhanced NF-kappaB-dependent transcriptional activity and the interaction between p65 and PKAc and augmented the phosphorylation of p65 on Ser-276. After RNAi knockdown of AKIP1 in these breast cancer cells, we observed that PKA-activating agents antagonized NF-kappaB-dependent activation. Meanwhile, PKA inhibitor suppressed NF-kappaB-induced breast cancer cell proliferation and multiple NF-kappaB-dependent anti-apoptotic gene expression. It is likely that expression of AKIP1 determines the relationship between these two signal transduction pathways. These findings explained controversial results from various independent groups regarding the action of PKA signaling on the NF-kappaB activation cascade and suggested a possible therapeutic potential of PKA inhibitor in developing anti-cancer strategies.

TbPRMT6 is a type I protein arginine methyltransferase that contributes to cytokinesis in Trypanosoma brucei

Arginine methylation is a widespread posttranslational modification of proteins catalyzed by a family of protein arginine methyltransferases (PRMTs). In Saccharomyces cerevisiae and mammals, this modification affects multiple cellular processes, such as chromatin remodeling leading to transcriptional regulation, RNA processing, DNA repair, and cell signaling. The protozoan parasite Trypanosoma brucei possesses five putative PRMTs in its genome. This is a large number of PRMTs relative to other unicellular eukaryotes, suggesting an important role for arginine methylation in trypanosomes. Here, we present the in vitro and in vivo characterization of a T. brucei enzyme homologous to human PRMT6, which we term TbPRMT6. Like human PRMT6, TbPRMT6 is a type I PRMT, catalyzing the production of monomethylarginine and asymmetric dimethylarginine residues. In in vitro methylation assays, TbPRMT6 utilizes bovine histones as a substrate, but it does not methylate several T. brucei glycine/arginine-rich proteins. As such, it exhibits a relatively narrow substrate specificity compared to other T. brucei PRMTs. Knockdown of TbPRMT6 in both procyclic form and bloodstream form T. brucei leads to a modest but reproducible effect on parasite growth in culture. Moreover, upon TbPRMT6 depletion, both PF and BF exhibit aberrant morphologies indicating defects in cell division, and these defects differ in the two life cycle stages. Mass spectrometry of TbPRMT6-associated proteins reveals histones, components of the nuclear pore complex, and flagellar proteins that may represent TbPRMT6 substrates contributing to the observed growth and morphological defects.

Crosstalk between C/EBPbeta phosphorylation, arginine methylation, and SWI/SNF/Mediator implies an indexing transcription factor code

Cellular signalling cascades regulate the activity of transcription factors that convert extracellular information into gene regulation. C/EBPbeta is a ras/MAPkinase signal-sensitive transcription factor that regulates genes involved in metabolism, proliferation, differentiation, immunity, senescence, and tumourigenesis. The protein arginine methyltransferase 4 PRMT4/CARM1 interacts with C/EBPbeta and dimethylates a conserved arginine residue (R3) in the C/EBPbeta N-terminal transactivation domain, as identified by mass spectrometry of cell-derived C/EBPbeta. Phosphorylation of the C/EBPbeta regulatory domain by ras/MAPkinase signalling abrogates the interaction between C/EBPbeta and PRMT4/CARM1. Differential proteomic screening, protein interaction studies, and mutational analysis revealed that methylation of R3 constraines interaction with SWI/SNF and Mediator complexes. Mutation of the R3 methylation site alters endogenous myeloid gene expression and adipogenic differentiation. Thus, phosphorylation of the transcription factor C/EBPbeta couples ras signalling to arginine methylation and regulates the interaction of C/EBPbeta with epigenetic gene regulatory protein complexes during cell differentiation.

Friend of Prmt1, a novel chromatin target of protein arginine methyltransferases

We describe the isolation and characterization of Friend of Prmt1 (Fop), a novel chromatin target of protein arginine methyltransferases. Human Fop is encoded by C1orf77, a gene of previously unknown function. We show that Fop is tightly associated with chromatin, and that it is modified by both asymmetric and symmetric arginine methylation in vivo. Furthermore, Fop plays an important role in the ligand-dependent activation of estrogen receptor target genes, including TFF1 (pS2). Fop depletion results in an almost complete block of estradiol-induced promoter occupancy by the estrogen receptor. Our data indicate that Fop recruitment to the promoter is an early critical event in the activation of estradiol-dependent transcription.

Biochemical control of CARM1 enzymatic activity by phosphorylation

Coactivator-associated arginine methyltransferase 1 (CARM1) is a dual functional coregulator that facilitates transcription initiation by methylation of Arg(17) and Arg(26) of histone H3 and also dictates the subsequent coactivator complex disassembly by methylation of the steroid receptor coactivator family coactivators and p300/cAMP-response element-binding protein-binding protein. However, the regulation of CARM1 enzymatic activity and substrate specificity remains largely unknown. In this study, we report that CARM1 function is regulated by phosphorylation at Ser(217), a residue completely conserved in the type I protein arginine methyltransferase (PRMT) family of enzymes. Comparative analysis of the published CARM1 crystal structures reveals that the hydroxyl group of Ser(217) forms a strong hydrogen bond with the carbonyl oxygen atom of Tyr(154) to lock the cofactor S-adenosylmethionine inside the binding cavity. Phosphorylation of Ser(217) disrupts this hydrogen bond and subsequently abolishes S-adenosylmethionine binding and its methyltransferase activity. Importantly, Tyr(154) is also conserved in the type I PRMT family of enzymes, suggesting a general role of this hydrogen bond in maintaining the holo structure of the type I PRMT catalytic domain. Moreover, we found that phosphorylation at Ser(217) also promoted CARM1 cytoplasmic localization and that this translocation occurred mainly during mitosis. We propose that phosphorylation at Ser(217) serves as a molecular switch for controlling CARM1 enzymatic activity during the cell cycle.

Protein arginine methyltransferases: nuclear receptor coregulators and beyond

Protein arginine methyltransferases (PRMTs) are a family of enzymes that play a crucial role in diverse cellular functions. Several PRMTs have been associated with gene expression regulation, in which PRMTs act as histone methyltransferases, secondary coregulators of transcription, or facilitate mRNA splicing and stability. Additional functions include modulation of protein localization, ribosomal assembly, and signal transduction. At the organismal level, several PRMTs appear to be important for development and may play an important role in cancer. The relationships between their cellular and organismal functions are poorly understood; at least in part due to the large body of enzymatic substrates for PRMTs and their transcriptional targets that remain to be determined. Specific PRMT inhibitors have been developed in recent years, which should help to shed light on their diverse biological roles. Connecting PRMT cellular functions with their global effects on an organism will facilitate development of novel treatments for human diseases.

Biochemical analyses of nuclear receptor-dependent transcription with chromatin templates

Chromatin, the physiological template for transcription, plays important roles in gene regulation by nuclear receptors (NRs). It can (1) restrict the binding of NRs or the transcriptional machinery to their genomic targets, (2) serve as a target of regulatory posttranslational modifications by NR coregulator proteins with histone-directed enzymatic activities, and (3) function as a binding scaffold for a variety of transcription-related proteins. The advent of in vitro or "cell-free" systems that accurately recapitulate ligand-dependent transcription by NRs with chromatin templates has allowed detailed analyses of these processes. Biochemical studies have advanced our understanding of the mechanisms of gene regulation, including the role of ligands, coregulators, and nucleosome remodeling. In addition, they have provided new insights about the dynamics of NR-mediated transcription. This chapter reviews the current methodologies for assembling, transcribing, and analyzing chromatin in vitro, as well as the new information that has been gained from these studies.

Arginine methylation regulates IL-2 gene expression: a role for protein arginine methyltransferase 5 (PRMT5)

Arginine methylation is a post-translational modification resulting in the generation of aDMAs (asymmetrical omega-NG, NG-dimethylated arginines) and sDMAs (symmetrical omega-NG, N'G-dimethylated arginines). The role of arginine methylation in cell signalling and gene expression in T lymphocytes is not understood. In the present study, we report a role for protein arginine methylation in regulating IL-2 (interleukin 2) gene expression in T lymphocytes. Leukaemic Jurkat T-cells treated with a known methylase inhibitor, 5'-methylthioadenosine, had decreased cytokine gene expression, as measured using an NF-AT (nuclear factor of activated T-cells)-responsive promoter linked to the luciferase reporter gene. Since methylase inhibitors block all methylation events, we performed RNA interference with small interfering RNAs against the major PRMT (protein arginine methyltransferases) that generates sDMA (PRMT5). The dose-dependent decrease in PRMT5 expression resulted in the inhibition of both IL-2- and NF-AT-driven promoter activities and IL-2 secretion. By using an sDMA-specific antibody, we observed that sDMA-containing proteins are directly associated with the IL-2 promoter after T-cell activation. Since changes in protein arginine methylation were not observed after T-cell activation in Jurkat and human peripheral blood lymphocytes, our results demonstrate that it is the recruitment of methylarginine-specific protein(s) to cytokine promoter regions that regulates their gene expression.

CARM1 but not its enzymatic activity is required for transcriptional coactivation of NF-kappaB-dependent gene expression

Coactivator-associated arginine methyltransferase 1 (CARM1) belongs to the protein arginine methyltransferase family. It was reported to methylate histone as well as non-histone proteins and thus to be involved in transcriptional activation and mRNA degradation/stability. Here we report the genetic complementation of carm1-/- cells with wild-type CARM1 or an enzymatic inactive mutant of CARM1 to investigate the requirement of CARM1 and its enzymatic activity for nuclear factor kappaB (NF-kappaB)-dependent gene expression. Using custom microarray and quantitative reverse transcription PCR, we could define a subset of NF-kappaB target genes that required CARM1 for their proper expression. Although several tumor necrosis factor-alpha- and phorbol-12-myristate-13-acetate/ionomycin-induced NF-kappaB target genes are CARM1 dependent, CARM1 enzymatic activity was dispensable for gene expression. Interestingly, CARM1 was not required for the stimulus-dependent recruitment of RelA/p65 to chromatin, suggesting that CARM1 is rather contributing in protein complex stabilization. Together, our results confirm the importance of CARM1 as transcriptional cofactor without the involvement of its catalytic activity.

Arginine methyltransferase CARM1/PRMT4 regulates endochondral ossification

Background

Chondrogenesis and subsequent endochondral ossification are processes tightly regulated by the transcription factor Sox9 (SRY-related high mobility group-Box gene 9), but molecular mechanisms underlying this activity remain unclear. Here we report that coactivator-associated arginine methyltransferase 1 (CARM1) regulates chondrocyte proliferation via arginine methylation of Sox9.

Results

CARM1-null mice display delayed endochondral ossification and decreased chondrocyte proliferation. Conversely, cartilage development of CARM1 transgenic mice was accelerated. CARM1 specifically methylates Sox9 at its HMG domain in vivo and in vitro. Arg-methylation of Sox9 by CARM1 disrupts interaction of Sox9 with beta-catenin, regulating Cyclin D1 expression and cell cycle progression of chondrocytes.

Conclusion

These results establish a role for CARM1 as an important regulator of chondrocyte proliferation during embryogenesis.

Minireview: role of protein methylation and demethylation in nuclear hormone signaling

Nuclear hormone receptors (NRs) are transcription factors responsible for mediating the biological effects of hormones during development, metabolism, and homeostasis. Induction of NR target genes is accomplished through the assembly of hormone-bound NR complexes at target promoters and coincides with changes in histone modifications that promote transcription. Some coactivators and corepressors of NR can enhance or inhibit NR function by covalently modifying histones. One such modification is methylation, which plays important roles in transcriptional regulation. Histone methylation is catalyzed by histone methyltransferases and reversed by histone demethylases. Recent studies have uncovered the importance of these enzymes in the regulation of NR target genes. In addition to histones, these enzymes have nonhistone substrates and can methylate and demethylate NRs and coregulatory proteins in order to modulate their function. This review discusses recent progress in our understanding of the role of methylation and demethylation of histones, NRs, and their coregulators in NR-mediated transcription.

The protein arginine methyltransferase family: an update about function, new perspectives and the physiological role in humans

Information about the family of protein arginine methyltransferases (PRMTs) has been growing rapidly over the last few years and the emerging role of arginine methylation involved in cellular processes like signaling, RNA processing, gene transcription, and cellular transport function has been investigated. To date, 11 PRMTs gene transcripts have been identified in humans. Almost all PRMTs have been shown to have enzymatic activity and to catalyze arginine methylation. This review will summarize the overall function of human PRMTs and include novel highlights on each family member.

Caenorhabditis elegans protein arginine methyltransferase PRMT-5 negatively regulates DNA damage-induced apoptosis

Arginine methylation of histone and non-histone proteins is involved in transcription regulation and many other cellular processes. Nevertheless, whether such protein modification plays a regulatory role during apoptosis remains largely unknown. Here we report that the Caenorhabditis elegans homolog of mammalian type II arginine methyltransferase PRMT5 negatively regulates DNA damage-induced apoptosis. We show that inactivation of C. elegans prmt-5 leads to excessive apoptosis in germline following ionizing irradiation, which is due to a CEP-1/p53–dependent up-regulation of the cell death initiator EGL-1. Moreover, we provide evidence that CBP-1, the worm ortholog of human p300/CBP, functions as a cofactor of CEP-1. PRMT-5 forms a complex with both CEP-1 and CBP-1 and can methylate the latter. Importantly, down-regulation of cbp-1 significantly suppresses DNA damage-induced egl-1 expression and apoptosis in prmt-5 mutant worms. These findings suggest that PRMT-5 likely represses CEP-1 transcriptional activity through CBP-1, which represents a novel regulatory mechanism of p53-dependent apoptosis.

Protein arginine methylation is an important posttranslational modification. Aberrant expression of protein arginine methyltransferases (PRMTs) are found in a wide variety of human diseases, especially in many cancers. Given that deregulation of apoptosis is usually related to tumorigenesis, it is not known whether PRMT–mediated protein arginine methylation plays a role in apoptosis. Here we employ the genetic tractable model organism C. elegans to explore the potential regulatory roles of PRMTs in apoptosis. We find that C. elegans PRMTs do not affect developmental cell deaths. However, genetic inactivation of the C. elegans homolog of the mammalian type II protein arginine methyltransferase PRMT5 causes excessive germ cell apoptosis in response to DNA damage. Our genetic analyses indicate that prmt-5–mediated apoptosis is dependent on the C. elegans p53 homolog CEP-1 and requires the core cell death pathway. We further demonstrate that loss of prmt-5 leads to a specific up-regulation of the cell death initiator EGL-1 following DNA damage. Finally, we identify CBP-1, the C. elegans homolog of human p300/CBP, as a CEP-1 cofactor in C. elegans, and we provide genetic and biochemical evidence that PRMT-5 likely functions through CBP-1 to affect CEP-1/p53 transcriptional activity, thereby negatively regulating CEP-1/p53-dependent apoptosis.

Histone arginine methylations: their roles in chromatin dynamics and transcriptional regulation

PRMTs (protein arginine N-methyltransferases) specifically modify the arginine residues of key cellular and nuclear proteins as well as histone substrates. Like lysine methylation, transcriptional repression or activation is dependent upon the site and type of arginine methylation on histone tails. Recent discoveries imply that histone arginine methylation is an important modulator of dynamic chromatin regulation and transcriptional controls. However, under the shadow of lysine methylation, the roles of histone arginine methylation have been under-explored. The present review focuses on the roles of histone arginine methylation in the regulation of gene expression, and the interplays between histone arginine methylation, histone acetylation, lysine methylation and chromatin remodelling factors. In addition, we discuss the dynamic regulation of arginine methylation by arginine demethylases, and how dysregulation of PRMTs and their activities are linked to human diseases such as cancer.

Delineating Anopheles gambiae coactivator associated arginine methyltransferase 1 automethylation using top-down high resolution tandem mass spectrometry

Coactivator-associated arginine methyltransferase 1 (CARM1), originally defined as a coactivator for steroid receptors, is a member of the protein arginine methyltransferases. Here, we report the discovery and characterization of an automethylation event by AgCARM1, a CARM1 homologue in the mosquito Anopheles gambiae, using top-down high resolution tandem mass spectrometry, which allows fine mapping of modifications in the intact protein accurately and quantitatively without priori knowledge. Unexpectedly, we found that AgCARM1 has already been predominantly dimethylated during its expression in Escherichia coli. A single arginine methylation site, R485, was identified which is conserved among CARM1 in insects. No methylation was observed in the intact AgCARM1(R485K) mutant where R485 is mutated to lysine, which confirms that R485 is the only detectable methylation site. Using AgCARM1 methyltransferase defective mutants, we confirmed that this is an automethylation event and show the automethylation of AgCARM1 occurs intermolecularly. This study represents the first comprehensive characterization of an automethylation event by top-down mass spectrometry. The unexpected high percentage of automethylated recombinant AgCARM1 expressed in E. coli may shed light on other bacterially expressed post-translational modifying enzymes, which could be modified but overlooked in biochemical and structural studies. Top-down high resolution tandem mass spectrometry thus provides unique opportunities for revealing unexpected protein modification, localizing specific modification to one amino acid, and delineating molecular mechanism of an enzyme.

The importance of being flexible: the case of basic region leucine zipper transcriptional regulators

Large volumes of protein sequence and structure data acquired by proteomic studies led to the development of computational bioinformatic techniques that made possible the functional annotation and structural characterization of proteins based on their primary structure. It has become evident from genome-wide analyses that many proteins in eukaryotic cells are either completely disordered or contain long unstructured regions that are crucial for their biological functions. The content of disorder increases with evolution indicating a possibly important role of disorder in the regulation of cellular systems. Transcription factors are no exception and several proteins of this class have recently been characterized as premolten/molten globules. Yet, mammalian cells rely on these proteins to control expression of their 30,000 or so genes. Basic region:leucine zipper (bZIP) DNA-binding proteins constitute a major class of eukaryotic transcriptional regulators. This review discusses how conformational flexibility "built" into the amino acid sequence allows bZIP proteins to interact with a large number of diverse molecular partners and to accomplish their manifold cellular tasks in a strictly regulated and coordinated manner.

Intestinal hormones and growth factors: effects on the small intestine

There are various hormones and growth factors which may modify the intestinal absorption of nutrients, and which might thereby be useful in a therapeutic setting, such as in persons with short bowel syndrome. In part I, we focus first on insulin-like growth factors, epidermal and transferring growth factors, thyroid hormones and glucocorticosteroids. Part II will detail the effects of glucagon-like peptide (GLP)-2 on intestinal absorption and adaptation, and the potential for an additive effect of GLP2 plus steroids.

Estrogen receptor alpha represses transcription of early target genes via p300 and CtBP1

The regulation of gene expression by nuclear receptors controls the phenotypic properties and diverse biologies of target cells. In breast cancer cells, estrogen receptor alpha (ERalpha) is a master regulator of transcriptional stimulation and repression, yet the mechanisms by which agonist-bound ERalpha elicits repression are poorly understood. We analyzed early estrogen-repressed genes and found that ERalpha is recruited to ERalpha binding sites of these genes, albeit more transiently and less efficiently than for estrogen-stimulated genes. Of multiple cofactors studied, only p300 was recruited to ERalpha binding sites of repressed genes, and its knockdown prevented estrogen-mediated gene repression. Because p300 is involved in transcription initiation, we tested whether ERalpha might be trying to stimulate transcription at repressed genes, with ultimately failure and a shift to a repressive program. We found that estrogen increases transcription in a rapid but transient manner at early estrogen-repressed genes but that this is followed by recruitment of the corepressor CtBP1, a p300-interacting partner that plays an essential role in the repressive process. Thus, at early estrogen-repressed genes, ERalpha initiates transient stimulation of transcription but fails to maintain the transcriptional process observed at estrogen-stimulated genes; rather, it uses p300 to recruit CtBP1-containing complexes, eliciting chromatin modifications that lead to transcriptional repression.

Distinct protein arginine methyltransferases promote ATP-dependent chromatin remodeling function at different stages of skeletal muscle differentiation

Temporal regulation of gene expression is a hallmark of cellular differentiation pathways, yet the mechanisms controlling the timing of expression for different classes of differentiation-specific genes are not well understood. We previously demonstrated that the class II arginine methyltransferase Prmt5 was required for skeletal muscle differentiation at the early stages of myogenesis (C. S. Dacwag, Y. Ohkawa, S. Pal, S. Sif, and A. N. Imbalzano, Mol. Cell. Biol. 27:384-394, 2007). Specifically, when Prmt5 levels were reduced, the ATP-dependent SWI/SNF chromatin-remodeling enzymes could not interact with or remodel the promoter of myogenin, an essential early gene. Here we investigated the requirement for Prmt5 and the class I arginine methyltransferase Carm1/Prmt4 in the temporal control of myogenesis. Both arginine methyltransferases could bind to and modify histones at late-gene regulatory sequences. However, the two enzymes showed sequential requirements for gene expression. Prmt5 was required for early-gene expression but dispensable for late-gene expression. Carm1/Prmt4 was required for late- but not for early-gene expression. The reason for the requirement for Carm1/Prmt4 at late genes was to facilitate SWI/SNF chromatin-remodeling enzyme interaction and remodeling at late-gene loci. Thus, distinct arginine methyltransferases are employed at different times of skeletal muscle differentiation for the purpose of facilitating ATP-dependent chromatin-remodeling enzyme interaction and function at myogenic genes.

Minireview: protein arginine methylation of nonhistone proteins in transcriptional regulation

Endocrine regulation frequently culminates in altered transcription of specific genes. The signal transduction pathways, which transmit the endocrine signal from cell surface to the transcription machinery, often involve posttranslational modifications of proteins. Although phosphorylation has been by far the most widely studied protein modification, recent studies have indicated important roles for other types of modification, including protein arginine methylation. Ten different protein arginine methyltransferase (PRMT) family members have been identified in mammalian cells, and numerous substrates are being identified for these PRMTs. Whereas major attention has been focused on the methylation of histones and its role in chromatin remodeling and transcriptional regulation, there are many nonhistone substrates methylated by PRMTs. This review primarily focuses on recent progress on the roles of the nonhistone protein methylation in transcription. Protein methylation of coactivators, transcription factors, and signal transducers, among other proteins, plays important roles in transcriptional regulation. Protein methylation may affect protein-protein interaction, protein-DNA or protein-RNA interaction, protein stability, subcellular localization, or enzymatic activity. Thus, protein arginine methylation is critical for regulation of transcription and potentially for various physiological/pathological processes.

Biochemical analysis of arginine methylation in transcription

Protein arginine methylation has emerged as an important mechanism for regulating the functions of proteins involved in diverse aspects of gene regulation such as transcriptional activation and repression, mRNA processing and nuclear-cytoplasmic shuttling. This modification is catalyzed by the PRMT family of enzymes which utilize intracellular S-adenosyl methionine as a cofactor to dimethylate-specific arginines found within many target proteins.The establishment of in vitro biochemical assays as well as the development of modification-specific antibodies, and more recently mass spectrometry, have increased our understanding of the mechanism of catalysis of the PRMT family of enzymes. In the following discussion, we present some of the more commonly used in vivo and in vitro techniques which can be utilized to study the mechanism of arginine methylation and its role in transcription.

CBP/p300 and associated transcriptional co-activators exhibit distinct expression patterns during murine craniofacial and neural tube development

Mutations in each of the transcriptional co-activator genes - CBP, p300, Cited2, Cart1 and Carm1 - result in neural tube defects in mice. The present study thus furnishes a complete and comparative temporal and spatial expression map of CBP/p300 and associated transcriptional co-activators, Cited2, Cart1 and Carm1 during the period of murine neural tube development (embryonic days 8.5 to 10.5). Each co-activator except Cart1 was expressed in the dorsal neural folds on E8.5. Although CBP and p300 are functionally interchangeable in vitro, their respective expression patterns diverge during embryogenesis before neural fold fusion is complete. CBP gene expression was lost from the neural folds by E8.75 and was thereafter weakly expressed in the maxillary region and limb buds, while p300 exhibited strong expression in the first branchial arch, limb bud and telencephalic regions on E9.5. Cart1 exhibited strong expression in the forebrain mesenchyme from E9.0 through E10.5. Although CBP, p300, Carm1 and Cited2 share temporal expression on E8.5, these co-activators have different spatial expression in mesenchyme and/or the neuroepithelium. Nevertheless, co-localization to the dorsal neural folds on E8.5 suggests a functional role in elevation and/or fusion of the neural folds. Target genes, and pathways that promote cranial neural tube fusion that are activated by CBP/p300/Carm1/Cited2/Cart1-containing transcriptional complexes await elucidation.

N-Benzyl-1-heteroaryl-3-(trifluoromethyl)-1H-pyrazole-5-carboxamides as inhibitors of co-activator associated arginine methyltransferase 1 (CARM1)

A series of N-benzyl-1-heteroaryl-3-(trifluoromethyl)-1H-pyrazole-5-carboxamides targeting co-activator associated arginine methyltransferase 1 (CARM1) have been designed and synthesized. The potency of these inhibitors was influenced by the nature of the heteroaryl fragment with the thiophene analogues being superior to thiazole, pyridine, isoindoline and benzofuran based inhibitors.

GRIP1-associated SET-domain methyltransferase in glucocorticoid receptor target gene expression

Transcriptional regulators such as the glucocorticoid receptor (GR) recruit multiple cofactors to activate or repress transcription. Although most cofactors are intrinsically bifunctional, little is known about the molecular mechanisms dictating the specific polarity of regulation. Furthermore, chromatin modifications thought to be confined to silent loci appear in actively transcribed genes suggesting that similar enzymatic activities may mediate constitutive and transient chromatin states. GRIP1, a GR ligand-dependent coregulator of the p160 family can potentiate or inhibit transcription but the molecular contexts and mechanisms that enable GRIP1 corepressor activity are poorly understood. In a yeast 2-hybrid screen with GRIP1 repression domain (RD)-containing fragment, we repeatedly isolated the C-terminal region of a SET domain-containing protein subsequently identified as histone H4 lysine 20 trimethyltransferase, Suv4-20h1. We cloned a full-length Suv4-20h1 and dissected its interaction with GRIP1 in yeast, in vitro, and in mammalian cells. Strict nuclear localization and high salt concentration required for Suv4-20h1 extraction were consistent with its tight association with chromatin. Overexpression of Suv4-20h1 in human U2OS and A549 cells expressing integrated and endogenous GR, respectively, antagonized ligand-dependent induction of a subset of GR target genes, whereas Suv4-20h1 siRNA-mediated depletion had a reciprocal effect. Inhibition of GR transactivation required both the GRIP1 interacting region of Suv4-20h1 and its catalytic activity. Thus, Suv4-20h1 known exclusively as a factor involved in constitutive heterochromatin maintenance, actively participates in hormone-dependent transcriptional regulation affecting GR target gene expression in a promoter- and cell type-specific manner.

Transcriptional activation of human matrix metalloproteinase-9 gene expression by multiple co-activators

Matrix metalloproteinase-9 (MMP-9), a proteolytic enzyme for matrix proteins, chemokines and cytokines, is a major target in cancer and autoimmune diseases, since it is aberrantly upregulated. To control MMP-9 expression in pathological conditions, it is necessary to understand the regulatory mechanisms of MMP-9 expression. MMP-9 gene expression is regulated primarily at the transcriptional level. In this study, we investigated the role of multiple co-activators in regulating MMP-9 transcription. We demonstrate that multiple transcriptional co-activators are involved in MMP-9 promoter activation, including CBP/p300, PCAF, CARM1 and GRIP1. Furthermore, enhancement of MMP-9 promoter activity requires the histone acetyltransferase activity of PCAF but not that of CBP/p300, and the methyltransferase activity of CARM1. More importantly, these co-activators are able to activate MMP-9 promoter activity independently, and function in a synergistic manner. Significant synergy was observed among CARM1, p300 and GRIP1, which is dependent on the interaction of p300 and CARM1 with the AD1 and AD2 domains of GRIP1, respectively. This suggests the formation of a ternary co-activator complex on the MMP-9 promoter. Chromatin immunoprecipitation assays demonstrate that these co-activators associate with the endogenous MMP-9 promoter, and that siRNA knockdown of expression of these co-activators reduces endogenous MMP-9 expression. Taken together, these studies demonstrate a new level of transcriptional regulation of MMP-9 expression by the cooperative action of co-activators.

Arginine methylation of FOXO transcription factors inhibits their phosphorylation by Akt

Forkhead box O (FOXO) transcription factors, the key regulators of cell survival, are negatively controlled through the PI3K-Akt signaling pathway. Phosphorylation of FOXO by Akt leads to cytoplasmic localization and subsequent degradation via the ubiquitin-proteasome system. Here we show a paradigm of FOXO1 regulation by the protein arginine methyltransferase PRMT1. PRMT1 methylated FOXO1 at conserved Arg248 and Arg250 within a consensus motif for Akt phosphorylation; this methylation directly blocked Akt-mediated phosphorylation of FOXO1 at Ser253 in vitro and in vivo. Silencing of PRMT1 by small interfering RNA enhanced nuclear exclusion, polyubiquitination, and proteasomal degradation of FOXO1. PRMT1 knockdown led to a decrease in oxidative-stress-induced apoptosis depending on the PI3K-Akt signaling pathway. Furthermore, stable expression of enzymatic inactive PRMT1 mutant increased resistance to apoptosis, whereas this effect was reversed by expression of phosphorylation-deficient FOXO1. Our findings predict a role for arginine methylation as an inhibitory modification against Akt-mediated phosphorylation.

Folding of the KIX domain: characterization of the equilibrium analog of a folding intermediate using 15N/13C relaxation dispersion and fast 1H/2H amide exchange NMR spectroscopy

The KIX domain of the transcription co-activator CBP is a three-helix bundle protein that folds via rapid accumulation of an intermediate state, followed by a slower folding phase. Recent NMR relaxation dispersion studies revealed the presence of a low-populated (excited) state of KIX that exists in equilibrium with the natively folded form under non-denaturing conditions, and likely represents the equilibrium analog of the folding intermediate. Here, we combine amide hydrogen/deuterium exchange measurements using rapid NMR data acquisition techniques with backbone (15)N and (13)C relaxation dispersion experiments to further investigate the equilibrium folding of the KIX domain. Residual structure within the folding intermediate is detected by both methods, and their combination enables reliable quantification of the amount of persistent residual structure. Three well-defined folding subunits are found, which display variable stability and correspond closely to the individual helices in the native state. While two of the three helices (alpha(2) and alpha(3)) are partially formed in the folding intermediate (to approximately 50% and approximately 80%, respectively, at 20 degrees C), the third helix is disordered. The observed helical content within the excited state exceeds the helical propensities predicted for the corresponding peptide regions, suggesting that the two helices are weakly mutually stabilized, while methyl (13)C relaxation dispersion data indicate that a defined packing arrangement is unlikely. Temperature-dependent experiments reveal that the largest enthalpy and entropy changes along the folding reaction occur during the final transition from the intermediate to the native state. Our experimental data are consistent with a folding mechanism where helices alpha(2) and alpha(3) form rapidly, although to different extents, while helix alpha(1) consolidates only as folding proceeds to complete the native state-structure.

Pyrazole inhibitors of coactivator associated arginine methyltransferase 1 (CARM1)

This study reports the identification and Hits to Leads optimization of inhibitors of coactivator associated arginine methyltransferase (CARM1). Compound 7b is a potent, selective inhibitor of CARM1.

Cracking the coregulator codes

The study of the genetic code has collectively revealed that the biochemical basis of heredity is uniform for nearly all known forms of life. Genetic approaches have generated a much better appreciation and understanding of many aspects of biological processes-and in some cases provided strategies for the treatment of human diseases. Still, the enormous and undoubtedly impressive amount of information gathered on gene sequences, their myriad expression patterns and translation into proteins is insufficient to answer seemingly simpler questions such as to what sets us humans apart from much more undemanding species while sharing almost the same sets of genes. Regulation of the proteome by post-translational modifications (PTMs) is beginning to be understood as a major contributing factor to the structural and functional diversity in biology and for defining cellular mechanisms in particular. Covalent, PTMs provide an astonishingly rich and specific basis for an ultrafast regulation of cellular processes, many of which converge to transcription units to control gene expression. With this essay we intend to share with the reader the rapid growth of our knowledge of the many conjunctions that exist between PTMs and key cellular processes that have emerged by studying the nuclear receptors (NRs) and their transcriptional coregulators.

Drosophila arginine methyltransferase 1 (DART1) is an ecdysone receptor co-repressor

Histone arginine methylation is an epigenetic marker that regulates gene expression by defining the chromatin state. Arginine methyltransferases, therefore, serve as transcriptional co-regulators. However, unlike other transcriptional co-regulators, the physiological roles of arginine methyltransferases are poorly understood. Drosophila arginine methyltransferase 1 (DART1), the mammalian PRMT1 homologue, methylates the arginine residue of histone H4 (H4R3me2). Disruption of DART1 in Drosophila by imprecise P-element excision resulted in low viability during metamorphosis in the pupal stages. In the pupal stage, an ecdysone hormone signal is critical for developmental progression. DART1 interacted with the nuclear ecdysone receptor (EcR) in a ligand-dependent manner, and co-repressed EcR in intact flies. These findings suggest that DART1, a histone arginine methyltransferase, is a co-repressor of EcR that is indispensable for normal pupal development in the intact fly.

Histone modifications and chromatin dynamics: a focus on filamentous fungi

The readout of the genetic information of eukaryotic organisms is significantly regulated by modifications of DNA and chromatin proteins. Chromatin alterations induce genome-wide and local changes in gene expression and affect a variety of processes in response to internal and external signals during growth, differentiation, development, in metabolic processes, diseases, and abiotic and biotic stresses. This review aims at summarizing the roles of histone H1 and the acetylation and methylation of histones in filamentous fungi and links this knowledge to the huge body of data from other systems. Filamentous fungi show a wide range of morphologies and have developed a complex network of genes that enables them to use a great variety of substrates. This fact, together with the possibility of simple and quick genetic manipulation, highlights these organisms as model systems for the investigation of gene regulation. However, little is still known about regulation at the chromatin level in filamentous fungi. Understanding the role of chromatin in transcriptional regulation would be of utmost importance with respect to the impact of filamentous fungi in human diseases and agriculture. The synthesis of compounds (antibiotics, immunosuppressants, toxins, and compounds with adverse effects) is also likely to be regulated at the chromatin level.

A novel methyltransferase methylates Cucumber mosaic virus 1a protein and promotes systemic spread

In mammalian and yeast systems, methyltransferases have been implicated in the regulation of diverse processes, such as protein-protein interactions, protein localization, signal transduction, RNA processing, and transcription. The Cucumber mosaic virus (CMV) 1a protein is essential not only for virus replication but also for movement. Using a yeast two-hybrid system with tobacco plants, we have identified a novel gene encoding a methyltransferase that interacts with the CMV 1a protein and have designated this gene Tcoi1 (tobacco CMV 1a-interacting protein 1). Tcoi1 specifically interacted with the methyltransferase domain of CMV 1a, and the expression of Tcoi1 was increased by CMV inoculation. Biochemical studies revealed that the interaction of Tcoi1 with CMV 1a protein was direct and that Tcoi1 methylated CMV 1a protein both in vitro and in vivo. The CMV 1a binding activity of Tcoi1 is in the C-terminal domain, which shows the methyltransferase activity. The overexpression of Tcoi1 enhanced the CMV infection, while the reduced expression of Tcoi1 decreased virus infectivity. These results suggest that Tcoi1 controls the propagation of CMV through an interaction with the CMV 1a protein.

The protein arginine methyltransferases CARM1 and PRMT1 cooperate in gene regulation

Protein arginine methyltransferases (PRMT) have been implicated in the regulation of transcription. They are recruited to promoters via interaction with transcription factors and exert their coactivator function by methylating arginine residues in histones and other chromatin proteins. Here, we employ an unbiased approach to identify novel target genes, which are under the control of two members of the enzyme family, PRMT1 and CARM1/PRMT4 (coactivator associated arginine methyltransferase 1). By using cDNA microarray analysis, we find that the siRNA-mediated single knockdown of neither CARM1 nor PRMT1 causes significant changes in gene expression. In contrast, double knockdown of both enzymes results in the deregulated expression of a large group of genes, among them the CITED2 gene. Cytokine-stimulated expression analysis indicates that transcriptional activation of CITED2 depends on STAT5 and the coactivation of both PRMTs. ChIP analysis identifies the CITED2 gene as a direct target gene of STAT5, CARM1 and PRMT1. In reporter gene assays, we show that STAT5-mediated transcription is cooperatively enhanced by CARM1 and PRMT1. Interaction assays reveal a cytokine-induced association of STAT5 and the two PRMTs. Our data demonstrate a widespread cooperation of CARM1 and PRMT1 in gene activation as well as repression and that STAT5-dependent transcription of the CITED2 gene is a novel pathway coactivated by the two methyltransferases.

Protein arginine methyltransferase 1 coactivates NF-kappaB-dependent gene expression synergistically with CARM1 and PARP1

Nuclear factor kappa B (NF-kappaB) plays an important role in the transcriptional regulation of genes involved in inflammation and cell survival. Transcriptional coactivators that methylate histones become increasingly important. Recently, we provided evidence that coactivator-associated arginine methyltransferase 1 (CARM1) is a transcriptional coactivator of NF-kappaB and functions as a promoter-specific regulator of NF-kappaB recruitment to chromatin. Here, we show that protein arginine methyltransferase 1 (PRMT1) synergistically coactivates NF-kappaB-dependent gene expression at the macrophage inflammatory protein 2 and human immunodeficiency virus 1 long terminal repeat promoters in concert with the transcriptional coactivators p300/CREB binding protein, CARM1, and poly(ADP-ribose) polymerase 1. PRMT1 formed a complex with poly(ADP-ribose) polymerase 1 and NF-kappaB in vivo and interacted directly with the NF-kappaB subunit p65 in vitro. The methyltransferase activity of PRMT1 appeared essential for its coactivator function in context with CARM1 and p300/CREB binding protein. These results suggest that the cooperative action between PRMT1 and CARM1 is required for NF-kappaB-dependent gene expression.

Characterization of protein arginine methyltransferases in porcine brain

Protein arginine methylation is a posttranslational modification involved in various cellular functions including cell signaling, protein subcellular localization and transcriptional regulation. We analyze the protein arginine methyltransferases (PRMTs) that catalyze the formation of methylarginines in porcine brain. We fractionated the brain extracts and determined the PRMT activities as well as the distribution of different PRMT proteins in subcellular fractions of porcine brain. The majority of the type I methyltransferase activities that catalyze the formation of asymmetric dimethylarginines was in the cytosolic S3 fraction. High specific activity of the methyltransferase was detected in the S4 fraction (high-salt stripping of the ultracentrifugation precipitant P3 fraction), indicating that part of the PRMT was peripherally associated with membrane and ribosomal fractions. The amount and distribution of PRMT1 are consistent with the catalytic activity. The elution patterns from gel filtration and anion exchange chromatography also indicate that the type I activity in S3 and S4 are mostly from PRMT1. Our results suggest that part of the type I arginine methyltransferases in brains, mainly PRMT1, are sequestered in an inactive form as they associated with membranes or large subcellular complexes. Our biochemical analyses confirmed the complex distribution of different PRMTs and implicate their regulation and catalytic activities in brain.

Communication between the synapse and the nucleus in neuronal development, plasticity, and disease

Sensory experience is critical for the proper development and plasticity of the brain throughout life. Successful adaptation to the environment is necessary for the survival of an organism, and this process requires the translation of specific sensory stimuli into changes in the structure and function of relevant neural circuits. Sensory-evoked activity drives synaptic input onto neurons within these behavioral circuits, initiating membrane depolarization and calcium influx into the cytoplasm. Calcium signaling triggers the molecular mechanisms underlying neuronal adaptation, including the activity-dependent transcriptional programs that drive the synthesis of the effector molecules required for long-term changes in neuronal function. Insight into the signaling pathways between the synapse and the nucleus that translate specific stimuli into altered patterns of connectivity within a circuit provides clues as to how activity-dependent programs of gene expression are coordinated and how disruptions in this process may contribute to disorders of cognitive function.

Protein arginine methylation in health and disease

Protein arginine methylation is a rapidly growing field of biomedical research that holds great promise for extending our understanding of developmental and pathological processes. Less than ten years ago, fewer than two dozen proteins were verified to contain methylarginine. Currently, however, hundreds of methylarginine proteins have been detected and many have been confirmed by mass spectrometry and other proteomic and molecular techniques. Several of these proteins are products of disease genes or are implicated in disease processes by recent experimental or clinical observations. The purpose of this chapter is twofold; (1) to re-examine the role of protein arginine methylation placed within the context of cell growth and differentiation, as well as within the rich variety of cellular metabolic methylation pathways and (2) to review the implications of recent advances in protein methylarginine detection and the analysis of protein methylarginine function for our understanding of human disease.

The transcriptional coactivator and acetyltransferase p300 in fibroblast biology and fibrosis

The transcriptional coactivator p300 is a ubiquitous nuclear phosphoprotein and transcriptional cofactor with intrinsic acetyltransferase activity. p300 controls the expression of numerous genes in cell-type and signal-specific manner, and plays a pivotal role in cellular proliferation, apoptosis, and embryogenesis. By catalyzing acetylation of histones and transcription factors, p300 plays a significant role in epigenetic regulation. Recent evidence suggests that abnormal p300 function is associated with deregulated target gene expression, and is implicated in inflammation, cancer, cardiac hypertrophy, and genetic disorders such as the Rubinstein-Taybi syndrome. The activity of p300 is regulated at multiple levels, including developmental stage-specific expression, post-translational modifications, subcellular localization, and cell-type and gene-specific interactions with transcription factors. Although p300 has been investigated extensively in epithelial and hematopoietic cells, its role in fibroblast biology and tissue repair has received little attention to date. Recent studies implicate p300 in the regulation of collagen synthesis by transforming growth factor-beta (TGF-beta). Both the acetyltransferase activity of p300 and its inducible interaction with Smad3 are essential for mediating TGF-beta-induced stimulation of collagen synthesis. As a signal integrator whose availability for intracellular interactions with transcription factors is strictly limiting, p300 mediates the antagonistic regulation of TGF-beta-induced collagen synthesis by IFN-gamma and TNF-alpha via intracellular competition for limiting amount of p300. Significantly, p300 is itself a direct transcriptional target of TGF-beta in normal fibroblasts, and its levels are significantly elevated in fibrotic lesions as well as in experimental models of fibrosis. The emerging appreciation of the importance of p300 in extracellular matrix (ECM) remodeling and fibrosis and novel insights concerning the regulation, mechanism of action, and significance of p300 in fibroblast biology are discussed in this minireview.

The 44-kDa Pim-1 kinase phosphorylates BCRP/ABCG2 and thereby promotes its multimerization and drug-resistant activity in human prostate cancer cells

We previously showed that the 44-kDa serine/threonine kinase Pim-1 (Pim-1L) can protect prostate cancer cells from apoptosis induced by chemotherapeutic drugs (Xie, Y., Xu, K., Dai, B., Guo, Z., Jiang, T., Chen, H., and Qiu, Y. (2006) Oncogene 25, 70-78). To further explore the mechanisms of Pim-1L-mediated resistance to chemotherapeutic drugs in prostate cancer cells, we employed a yeast two-hybrid screening to identify cellular proteins that were associated with Pim-1L, and we found the ABC transporter BCRP/ABCG2 as one of the potential interacting partners of Pim-1L. We also showed that the expression level of Pim-1L and BCRP was up-regulated in mitoxantrone and docetaxel-resistant prostate cancer cell lines. Pim-1L was co-localized with BCRP on the plasma membrane and induced phosphorylation of BCRP at threonine 362. Knocking-down Pim-1L expression in the drug-resistant prostate cancer cells abolished multimer formation of endogenous BCRP and resensitized the resistant cells to chemotherapeutic drugs suggesting that BCRP phosphorylation induced by Pim-1L was essential for its functionality. This is further corroborated by our finding that the plasma membrane localization and drug-resistant activity of BCRP were compromised by T362A mutation. Our data suggest that Pim-1L may protect prostate cancer cells from apoptosis, at least in part, through regulation of transmembrane drug efflux pump. These findings may provide a potential therapeutic approach by disrupting Pim-1 signaling to reverse BCRP-mediated multidrug resistance.