department of pharmacology

Paul MacDonald, Ph.D.

Paul N. MacDonald

Professor and Associate Dean of Graduate Studies

Phone: (216) 368-2466
Fax: 216-368-1300
W309 Wood Building


Vitamin D (Vit D) is required for normal calcium and phosphorus homeostasis and it is essential for the proper development and maintenance of bone. Vit D also exerts profound effects on cellular proliferation and differentiation, effectively inhibiting the proliferation of several breast and prostate tumor-derived, malignant cell lines. The biological effects of vit D are mediated through a nuclear protein termed the vitamin D receptor, or VDR. The VDR is a member of the superfamily of nuclear receptors that function as ligand-activated transcription factors. Thus, vit D and VDR together regulate the expression of specific genes or gene networks in mineral-regulating target organs such as the intestine, bone, kidney, and parathyroid glands. The global objective of my laboratory is to understand the molecular details and signaling mechanisms involved in VDR-mediated gene expression.

The VDR alters gene expression by binding to specific DNA sequences in the promoter region of vitamin D responsive genes. VDR binds these specific DNA sequences as a heterodimer in association with another nuclear receptor termed retinoid X receptor (RXR). Thus, it is the VDR-RXR heterodimer bound to promoter DNA that ultimately controls the level of transcription of a particular vit D responsive gene. The signaling mechanisms that relay communications between the VDR-RXR heterodimer and the transcription complex are not well-understood. One current hypothesis states that additional proteins termed coactivators or corepressors are necessary for the transcriptional response. These coactivator proteins serve as macromolecular bridges between the VDR-RXR heterodimer and RNA polymerase II and a physical interaction of VDR with these transcriptional components is essential for vit D-mediated transcription to ensue. Current efforts in our laboratory are focused on identifying and characterizing the various contacts that occur between VDR and the transcription complex.

We have recently identified two key factors that may play an important role in this communication process. One contact is the interaction of VDR with transcription factor IIB (TFIIB), a component of the RNA polymerase II core transcription complex. This interaction represents a direct physical link between VDR and the polymerase and indeed, we have demonstrated that VDR interaction with TFIIB is an important step in the mechanism of vit D-mediated gene expression. Secondly, we recently cloned a a cDNA encoding a novel nuclear protein that interacts with VDR and participates in vit D-mediated transcription. We have named this factor NCoA-62, for Nuclear receptor Coactivator with a molecular mass of 62,000 Da. Our most recent efforts are directed at understanding the molecular details through which VDR interaction with TFIIB and with NCoA-62 affect vit D-mediated transcription and the potential mechanistic interplay between these various transcription factors.


Selected References:

Ellison, T.E., Dowd, D.R., and MacDonald, P.N. Calmodulin-dependent kinase IV stimulates vitamin D receptor-mediated transcription (2005) Mol. Endocrinol. 19:2309-19.

Sutton, ALM, Zhang, X, Ellison, TI, and MacDonald, PN. The 1,25(OH)2D3-regulated transcription factor MN1 stimulates VDR-mediated-transcription and inhibits osteoblastic cell proliferation (2005) Mol. Endocrinol. 19:2234-44.

Milliken, EL, Zhang, X, Flask, C, Duerk, JL, MacDonald, PN, and Keri, RA. EB1089, a vitamin D receptor agonist, reduces proliferation and decreases tumor growth rate in a mouse model of hormone-induced mammary cancer (2005) Cancer Lett. 229:205-15.

Dhawan P, Peng X, Sutton AL, MacDonald PN , Croniger CM, Trautwein C, Centrella M, McCarthy TL, Christakos S. Functional cooperation between CCAAT/enhancer-binding proteins and the vitamin D receptor in regulation of 25-hydroxyvitamin D3 24-hydroxylase. Mol Cell Biol. 2005 25:472-87.

Skorija K, Cox M, Sisk JM, Dowd DR, Macdonald PN , Thompson CC, Demay MB. Ligand-Independent Actions of the Vitamin D Receptor Maintain Hair Follicle Homeostasis. Mol Endocrinol. 2004 Dec 9; [Epub ahead of print]

MacDonald PN , Dowd DR, Zhang C, Gu C. Emerging insights into the coactivator role of NCoA62/SKIP in Vitamin D-mediated transcription. J Steroid Biochem Mol Biol. 2004 89-90:179-86. Review.

Zhang C, Dowd DR, Staal A, Gu C, Lian JB, van Wijnen AJ, Stein GS, MacDonald PN . Nuclear coactivator-62 kDa/Ski-interacting protein is a nuclear matrix-associated coactivator that may couple vitamin D receptor-mediated transcription and RNA splicing. J Biol Chem. 2003 278:35325-36.

Sutton, A.L.S. and MacDonald, P.N. Vitamin D: More Than a "Bone-a-Fide" Hormone (2003) Mol. Endocrinol. 17: 777-791.

Zhang C, Baudino TA, Dowd DR, Tokumaru H, Wang W, MacDonald PN . Ternary complexes and cooperative interplay between NCoA-62/Ski-interacting protein and steroid receptor coactivators in vitamin D receptor-mediated transcription. J Biol Chem. 2001 ;276:40614-20.

Kraichely DM, MacDonald, P.N. Confirming yeast two-hybrid protein interactions using in vitro glutathione-S-transferase pulldowns. In: Methods in Molecular Biology: Two-Hybrid Systems (MacDonald, P.N., ed.) 2001;177:135-150.

MacDonald PN , Baudino TA, Tokumaru H, Dowd DR, Zhang C. Vitamin D receptor and nuclear receptor coactivators: crucial interactions in vitamin D-mediated transcription. Steroids . 2001 66:171-6. Review

Kraichely, D.M., Collins, J., Delisle, R.K., and MacDonald, P.N. Helix H3 of the vitamin D receptor is required for coactivator interaction and transactivation, J. Biol. Chem. (1999) 274: 14352-14358.

Baudino, T.A., Kraichely, D.M., Jefcoat, S.C., Winchester, S.K., Partridge, N.C., and MacDonald, P.N. Isolation of a novel coactivator, NCoA-62, involved in vitamin D-mediated transcription. J. Biol. Chem. (1998) 273: 16434-16441.