The Transcriptional Coactivator DRIP/Mediator Complex Is Involved in Vitamin D Receptor Function and Regulates Keratinocyte Proliferation and Differentiation

Department of Medicine and Endocrinology, University of California, San Francisco and Veterans Affairs Medical Center San Francisco, San Francisco, California 94121, USA.
Journal of Investigative Dermatology (Impact Factor: 7.22). 10/2010; 130(10):2377-88. DOI: 10.1038/jid.2010.148
Source: PubMed


Mediator is a multisubunit coactivator complex that facilitates transcription of nuclear receptors. We investigated the role of the mediator complex as a coactivator for vitamin D receptor (VDR) in keratinocytes. Using VDR affinity beads, the vitamin D receptor interacting protein (DRIP)/mediator complex was purified from primary keratinocytes, and its subunit composition was determined by mass spectrometry. The complex included core subunits, such as DRIP205/MED1 (MED1), that directly binds to VDR. Additional subunits were identified that are components of the RNA polymerase II complex. The functions of different mediator components were investigated by silencing its subunits. The core subunit MED1 facilitates VDR activity and regulating keratinocyte proliferation and differentiation. A newly described subunit MED21 also has a role in promoting keratinocyte proliferation and differentiation, whereas MED10 has an inhibitory role. Blocking MED1/MED21 expression caused hyperproliferation of keratinocytes, accompanied by increases in mRNA expression of the cell cycle regulator cyclin D1 and/or glioma-associated oncogene homolog. Blocking MED1 or MED21 expression also resulted in defects in calcium-induced keratinocyte differentiation, as indicated by decreased expression of differentiation markers and decreased translocation of E-cadherin to the membrane. These results show that keratinocytes use the transcriptional coactivator mediator to regulate VDR functions and control keratinocyte proliferation and differentiation.

Download full-text


Available from: Alma L Burlingame, Jun 04, 2014
  • Source
    • "Our previous study of Med1 ablation in the epidermal keratinocytes of the skin also demonstrates that an aberrant differentiation in the hair follicle cycle is accelerated into anagen (growth phases of the cycle), perhaps due to the activation of bulge HF-SC, but mature hair follicles capable of producing hair shafts do not develop [17]. In vitro Med1 silencing increased proliferation but decreased the formation of the E-cadherin/β-catenin complex that is critical for both cell adhesion and keratinocyte differentiation [15]. When the niche specific ECM protein Col17a1 is deleted from bulge HF-SCs [40], the hair follicle cycle is shifted to anagen with a skin phenotype similar to that of Med1 null mice [17]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cell fates are determined by specific transcriptional programs. Here we provide evidence that the transcriptional coactivator, Mediator 1 (Med1), is essential for the cell fate determination of ectodermal epithelia. Conditional deletion of Med1 in vivo converted dental epithelia into epidermal epithelia, causing defects in enamel organ development while promoting hair formation in the incisors. We identified multiple processes by which hairs are generated in Med1 deficient incisors: 1) dental epithelial stem cells lacking Med 1 fail to commit to the dental lineage, 2) Sox2-expressing stem cells extend into the differentiation zone and remain multi-potent due to reduced Notch1 signaling, and 3) epidermal fate is induced by calcium as demonstrated in dental epithelial cell cultures. These results demonstrate that Med1 is a master regulator in adult stem cells to govern epithelial cell fate.
    Full-text · Article · Jun 2014 · PLoS ONE
  • Source
    • "The VDR forms a heterodimer with the retinoid X receptor (RXR), and binds to vitamin D response elements (VDRE), specific DNA sequences located within the promoters of target genes. Co-regulator complexes link the VDR-RXR heterodimer to the transcriptional machinery and provide an additional regulation in vitamin D-mediated gene transcription (5). In dermal keratinocytes, 1,25(OH)2D3 inhibits proliferation and enhances differentiation (6). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The secosteroidal hormone 1,25-dihyroxyvitamin D [1,25(OH)2D3] and its receptor, the vitamin D receptor (VDR), are crucial regulators of epidermal proliferation and differentiation. However, the effects of 1,25(OH)2D3-directed signaling on oral keratinocyte pathophysiology have not been well studied. We examined the role of 1,25(OH)2D3 in regulating proliferation and differentiation in cultured oral keratinocytes and on the oral epithelium in vivo. Using lentiviral-mediated shRNA to silence VDR, we generated an oral keratinocyte cell line with stable knockdown of VDR expression. VDR knockdown significantly enhanced proliferation and disrupted calcium- and 1,25(OH)2D3-induced oral keratinocyte differentiation, emphasizing the anti-proliferative and pro-differentiation effects of 1,25(OH)2D3 in oral keratinocytes. Using vitamin D3-deficient diets, we induced chronic vitamin D deficiency in mice as evidenced by decreased serum 25-hydroxyvitamin D (25OHD) concentrations. The vitamin D-deficient mice manifested increased proliferation of the tongue epithelium, but did not develop any morphological or histological abnormalities in the oral epithelium, suggesting that vitamin D deficiency alone is insufficient to alter oral epithelial homeostasis and provoke carcinogenesis. Immunohistochemical analyses of human and murine oral squamous cell carcinomas showed increased VDR expression. Overall, our results provide strong support for a crucial role for vitamin D signaling in oral keratinocyte pathophysiology.
    Full-text · Article · Mar 2014 · International Journal of Oncology
  • Source
    • "These co-regulatory complexes are necessary for the VDR-RXR heterodimer to either induce or suppress gene transcription and include ATPase-containing nucleosomal remodeling capabilities, enzymes with chromatin histone modifying abilities (e.g., acetyl- or methyl-transferases), and proteins involved in recruitment of RNA polymerase II (Pike et al., 2012). GRIP1 (Issa et al., 2001), RAC3 (Issa et al., 2001), SRC-1 (Masuyama et al., 1997a), TIF-1 (vom et al., 1996), ACTR (Chen et al., 1997), pCIP (Torchia et al., 1997), and Mediator (Oda et al., 2010) are some of the described co-activator proteins and co-activator complexes to date. These co-activators all regulate VDR function through co-assembling with VDR but they modulate VDR activity via distinct mechanisms. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The vitamin D receptor (VDR) is a nuclear, ligand-dependent transcription factor that in complex with hormonally active vitamin D, 1,25(OH)2D3, regulates the expression of more than 900 genes involved in a wide array of physiological functions. The impact of 1,25(OH)2D3-VDR signaling on immune function has been the focus of many recent studies as a link between 1,25(OH)2D3 and susceptibility to various infections and to development of a variety of inflammatory diseases has been suggested. It is also becoming increasingly clear that microbes slow down immune reactivity by dysregulating the VDR ultimately to increase their chance of survival. Immune modulatory therapies that enhance VDR expression and activity are therefore considered in the clinic today to a greater extent. As T cells are of great importance for both protective immunity and development of inflammatory diseases a variety of studies have been engaged investigating the impact of VDR expression in T cells and found that VDR expression and activity plays an important role in both T cell development, differentiation and effector function. In this review we will analyze current knowledge of VDR regulation and function in T cells and discuss its importance for immune activity.
    Full-text · Article · Jun 2013 · Frontiers in Immunology
Show more