Professor Malcolm Parker
Laboratory of Molecular Endocrinology
Professor Malcolm Parker is Head of the Institute of Reproductive & Developmental Biology and leads the Molecular Endocrinology lab.
Nuclear receptors are a family of ligand dependent transcription factors that control cell differentiation, tissue development and a vast array of physiological processes. They are also implicated in many clinical disorders and may be targeted for therapeutic intervention. The molecular endocrinology laboratory is interested in the role played by nuclear receptors in reproduction, metabolic regulation and cancer, focussing on molecular mechanisms whereby they regulate gene expression.
Nuclear receptors regulate different biological processes by regulating distinct gene networks. This is achieved by the recruitment of transcriptional coactivators and corepressors that form scaffolds for the assembly of chromatin remodelling enzymes. As a consequence, nuclear receptors regulate the epigenetic status of target genes and thereby control transcription from target genes. About ten years ago we discovered a corepressor we called RIP140 (Cavailles et al 1995) and a family of coactivators that we called RIP160 (Heery et al 1997) but which are now known to comprise a family of proteins. RIP140 is essential for female reproduction (White et al 2000) and plays crucial roles in metabolic processes (Leonardssson et al 2004, Powelka et al 2006) that are relevant to obesity and type 2 diabetes.
The RIP140 corepressor is essential for ovulation by controlling nuclear receptor signalling pathways in the ovary. The corepressor is responsible for controlling the expression of approximately 1000 genes, amongst which are gene networks that control cumulus expansion and follicular rupture (Tullet et al 2005). The expression of many of these genes are likely to be regulated by paracrine mechanisms since they are expressed in cumulus cells whereas RIP140 is expressed in mural granulosa cells. We are now in the process of identifying key target genes for nuclear receptor RIP140 signalling in mural cells and will study how they control cumulus cell functions.
Many different types of hormones control cell metabolism and energy homeostasis including fatty acids, thyroid hormone, lipids and vitamins that act through nuclear receptors. Thus nuclear receptor signalling plays a key role in adipogenesis, both energy storage and utilisation in adipose tissue, glucose homeostasis bythe liver and mitochondrial biogenesis and fibre type control in muscle. RIP140 plays a crucial role in many of these processes by controlling networks of genes in adipose tissue and muscle. For example, in white adipose tissue, RIP140 represses genes involved in fatty acid oxidation, oxidative phosphorylation and related metabolic processes (Christian et al 2005; Powelka et al 2006). As a consequence, the absence of RIP140 in mice leads to an activation of these processes, the acquisition of many of the characteristics of brown adipocytes and depletion of stored fat. Thus the RIP140 corepressor appears to play a central role in obesity and diabetes and may serve as a target for therapeutic intervention. Many of these changes can be recapitulated in cultured adipocytes (Christian et al 2005) and in muscle and so we are using them to investigate the molecular mechanism by which RIP140 functions as a corepressor for several gene networks.
- To determine the role of the RIP140 corepressor in ovulation, adipose and muscle biology and cell proliferation.
- To identify and characterise nuclear receptor signalling pathways that are repressed by RIP140.
- To elucidate molecular mechanisms of transcriptional repression by RIP140.
- To identify key target genes regulated by nuclear receptor – RIP140 signalling pathways and determine the epigenetic changes that regulate their transcription.
Future Research Plans
- Characterisation of nuclear receptor-RIP140 signalling pathways that regulate energy homeostasis and ovulation.
Energy homeostasis and ovulation depends on the repression of subsets of genes in metabolic tissues and ovary. Expression profiling has identified differentially expressed genes and our aims are to identify direct RIP140 target genes and characterise the relevant nuclear receptor signalling pathways. To carry out these investigations we have generated adipocyte and muscle cell culture systems with and without RIP140 that recapitulate the behaviour of the tissue in vivo. We are also in the process of generating ovarian granulosa and thecal cell lines.
The identification of RIP140 target genes will be tackled by characterising the promoters of differentially expressed genes in transiently transfected cells and by performing ChIP experiments. Alternatively we will rely on chromatin immunoprecipitation combined with promoter arrays (ChIP-on-chip) to identify the genomic targets of RIP140. To date we have used the candidate gene approach to demonstrate that three differentially expressed genes namely, UCP1, CPT1 and CIDEA are direct targets for RIP140 in adipocytes and have eliminated a number of others. Nuclear receptor signalling pathways will be identified by immunoprecipitation of RIP140 protein complexes followed by mass spectrometry; the use of specific agonists and antagonists; and chromatin immunoprecipitation (ChIP) experiments. The relative contribution of different nuclear receptors will be determined by using siRNA approaches.
- Epigenetic analysis of RIP140 target genes
We are in the process of characterising epigenetic marks in the vicinity of subsets of target promoters in adipocyte and will perform a similar analysis in muscle and ovarian granulosa cells. We have selected genes (i) that are either completely de-repressed or just up-regulated in the absence of RIP140 or (ii) that are subject to activation and repression by nuclear receptors to investigate the interplay between transcriptional coactivators and corepressors. In this way we will establish whether the mechanism by which RIP140 represses target genes is conserved or varies according to the endocrine signal, the nuclear receptor or the target tissue.
- Mechanism of action of the RIP140 corepressor
RIP140 seems to function as a scaffold protein bridging nuclear receptors with chromatin remodelling protein complexes at the promoters of target genes. There are ten nuclear receptor binding motifs which presumably determine which and where receptors bind and four repression domains that seem to function by distinct mechanisms. We are performing structure-function analyses to determine which motifs and repression domains are necessary or sufficient to repress specific genes in different cell types and a proteomic analysis to characterise protein complexes and enzymes that are responsible for the epigenetic changes around target genes.
- Biological role of RIP140 in energy homeostasis and ovulation
Our previous work has relied on phenotypic analysis of constitutive RIP140 null mice. The metabolic effects of RIP140 are complicated by systemic effects in which the function of one tissue may result in alteration in other tissues and vice-versa. To overcome these problems we are generating conditional knockout with the aim of determining the function of RIP140 specifically in adipose, muscle ovarian granulosa cells. In addition, we are generating transgenic mice expressing exogenous RIP140 (i) to allow a structure–function analysis of the corepressor in vivo by crossing such mice with RIP140 null mice (ii) to test the hypothesis that RIP140 may contribute to physical features observed in infants with partial tetrasomy 21q22.1 some of which are found in individuals with Downs syndrome.
- Cavailles, V., Dauvois, S., L'Horset, F., Lopez, G., Hoare, S., Kushner, P.J. & Parker, M.G. (1995) Nuclear factor RIP140 modulates transcriptional activation by the estrogen receptor. EMBO J. 14, 3741-3751
- Heery, D.M., Kalkhoven, E., Hoare, S. & Parker, M.G. (1997) A signature motif in transcriptional co-activators mediates binding to nuclear receptors. Nature 387, 733-736.
- White, R., Leonardsson, G., Rosewell, I., Jacobs, M.A., Milligan, S. and Parker, M.G. (2000) The nuclear receptor corepressor RIP140 is essential for female fertility. Nature Medicine 6 1368-1374.
- Leonardsson, G., Steel, J., Christian, M., Pocock V, Debevec, D., Bell, J., So P-W, Medina-Gomez G., Vidal-Puig A., White R. and Parker M. (2004) The Nuclear Receptor Corepressor RIP140 Regulates Fat accumulation, Proc. Nat. Acad. Sci. 101, 8437-8442
- Tullet, J.M., Pocock, V., Steel. J.H., White, R., Milligan, S., Parker, M.G..(2005) Multiple signalling defects in the absence of RIP140 impair both cumulus expansion and follicle rupture. Endocrinology 146, 4127-4137.
- Christian, M., Kiskinis, K., Debevec, D., Leonardsson, G., White, R. and Parker, M. G. (2005) RIP140-targetted repression of gene expression in adipocytes. Mol. & Cell.Biol. 25, 9383-9391
- Powelka AM, Seth A, Virbasius JV, Kiskinis E, Nicoloro SM, Guilherme A, Tang X, Straubhaar J, Cherniack AD, Parker MG, Czech MP. Suppression of oxidative metabolism and mitochondrial biogenesis by the transcriptional corepressor RIP140 in mouse adipocytes. J Clin Invest. 2006 Jan; 116:125-36
- Christian M, White R and Parker MG. Metabolic regulation by the nuclear receptor corepressor RIP140 Trends Endocrinol Metab. 2006 Aug;17 (6):243-50
- Debevec D, Christian M, Morganstein D, Seth A, Herzog B, Parker M and White R. Receptor interacting protein 140 regulates expression of uncoupling protein 1 in adipocytes through specific peroxisome proliferator activated receptor isoforms and estrogen-related receptor alpha. Mol Endocrinol. 2007 Jul;21(7):1581-92
- Herzog B, Hallberg M, Seth A, Woods A, White R and Parker MG. The Nuclear Receptor Cofactor RIP140 is required for the Regulation of Hepatic Lipid and Glucose Metabolism by LXR. Mol Endocrinol. 2007 Aug 7;
- Seth A, Steel JH, Nichol D, Pocock V, Kumaran MK, Fritah A, Mobberley M, Ryder TA, Rowlerson A, Scott J, Poutanen M, White R and Parker M. The Transcriptional Corepressor RIP140 Regulates Oxidative Metabolism in Skeletal Muscle. Cell Metab. 2007 Sep;6(3):236-45
- Kiskinis E; Hallberg M; Christian M; Olofsson M; Dilworth SM; White R; Parker MG. (Nov 2007). RIP140 directs histone and DNA methylation to silence Ucp1 expression in white adipocytes. EMBO J. 26:4831-4840.
Morganstein D.L., Christian M., Turner J.J., Parker M.G and White R. (2008) Conditionally immortalized white preadipocytes: a novel adipocyte model. J Lipid Res. Mar;49(3):679-85
Zschiedrich I., Hardeland U., Krones-Herzig A., Berriel Diaz M., Vegiopoulos A., Müggenburg J., Sombroek D., Hofmann T.G., Zawatzky R., Yu X., Gretz N., Christian M., White R., Parker M.G., Herzig S. (2008) Coactivator function of RIP140 for NFkappaB/RelA-dependent cytokine gene expression. Blood. Jul 15;112(2):264-76
Hallberg M., Morganstein D.L., Kiskinis E., Shah K., Kralli A., Dilworth S.M., White R., Parker M.G. and Christian M. (2008) A functional interaction between RIP140 and PGC-1alpha regulates the expression of the lipid droplet protein CIDEA. Mol & Cell Biol. Nov;28(22):6785-95
Dr Jenny Steel (Wellcome Trust funded)
Dr Marius Jones (BBSRC funded)
Dr Jaya Nautiyal (Wellcome Trust funded)
Michelle Percharde (BBSRC funded)