Musculoskeletal Biology and Pathology
A main focus of our research for several decades has been exploration of molecular mechanisms that regulate skeletal development and remodeling. These studies center on commitment of mesenchymal stem cells to the osteoblast lineage, and the subsequent growth and differentiation of pre-committed osteoblasts. Our lab has identified several unique parameters of transcriptional control that regulate phenotype-restricted gene expression in the context of nuclear architecture (see Nuclear Structure and Function). We identified nuclear matrix protein 2 (NMP2) as an osteoblast-restricted, nuclear matrix-associated, transcription factor. NMP2, identified by other labs as AML3 or Cbfa1 (and later designated Runx2), is essential for bone formation in vivo and is mutated in Cleidocranial Dysplasia, an autosomal bone disorder.
We have since continued our quest to identify biological roles of Runx2 in osteoblast proliferation and differentiation and have demonstrated its central place in balancing growth with differentiation in osteoblasts. Using genomics, we have discovered many target genes for Runx2, and through proteomic approaches, we have identified several co-regulatory proteins that contribute to Runx2-mediated gene expression. Of direct clinical relevance is our discovery that Runx2 is highly expressed in breast and prostate cancer cells metastasizing to bone. Exploration of these new dimensions to Runx-mediated control of gene expression represents a major focus of our research group.
We have also established the essential role of microRNAs in the bone-lineage using a conditional Dicer null mouse model which has a high bone mass phenotype. We have examined the biological function of microRNAs at multiple stages during differentiation in various mesenchymal lineages (e.g., osteoblasts, chondrocytes and myoblasts), as well as identified a network of microRNAs that controls the osteoblast-related master regulator Runx2 ( see Genetic and Epigenetic Regulation of Gene Expression).
- Gordon JA, Hassan MQ, Saini S, Montecino M, van Wijnen AJ, Stein GS, Stein JL, Lian JB. Pbx1 represses osteoblastogenesis by blocking Hoxa10-mediated recruitment of chromatin remodeling factors. Mol Cell Biol. 2010 Jul;30(14):3531-41.
- Gaur T, Hussain S, Mudhasani R, Parulkar I, Colby JL, Frederick D, Kream BE, van Wijnen AJ, Stein JL, Stein GS, Jones SN, Lian JB. Dicer inactivation in osteoprogenitor cells compromises fetal survival and bone formation, while excision in differentiated osteoblasts increases bone mass in the adult mouse. Dev Biol. 2010 Apr 1;340(1):10-21.
- Li Z, Hassan MQ, Volinia S, van Wijnen AJ, Stein JL, Croce CM, Lian JB, Stein GS. A microRNA signature for a BMP2-induced osteoblast lineage commitment program. Proc Natl Acad Sci U S A. 2008 Sep 16;105(37):13906-11.
- Hassan MQ, Tare RS, Lee SH, Mandeville M, Morasso MI, Javed A, van Wijnen AJ, Stein JL, Stein GS, Lian JB. BMP2 commitment to the osteogenic lineage involves activation of Runx2 by DLX3 and a homeodomain transcriptional network. J Biol Chem. 2006 Dec 29;281(52):40515-26.
- Galindo M, Pratap J, Young DW, Hovhannisyan H, Im HJ, Choi JY, Lian JB, Stein JL, Stein GS, van Wijnen AJ. The bone-specific expression of Runx2 oscillates during the cell cycle to support a G1-related antiproliferative function in osteoblasts. J Biol Chem. 2005 May 27;280(21):20274-85.
- Hassan MQ, Javed A, Morasso MI, Karlin J, Montecino M, van Wijnen AJ, Stein GS, Stein JL, Lian JB. Dlx3 transcriptional regulation of osteoblast differentiation: temporal recruitment of Msx2, Dlx3, and Dlx5 homeodomain proteins to chromatin of the osteocalcin gene. Mol Cell Biol. 2004 Oct;24(20):9248-61.
- Pratap J, Galindo M, Zaidi SK, Vradii D, Bhat BM, Robinson JA, Choi JY, Komori T, Stein JL, Lian JB, Stein GS, van Wijnen AJ. Cell growth regulatory role of Runx2 during proliferative expansion of preosteoblasts. Cancer Res. 2003 Sep 1;63(17):5357-62.
- Shen J, Hovhannisyan H, Lian JB, Montecino MA, Stein GS, Stein JL, Van Wijnen AJ. Transcriptional induction of the osteocalcin gene during osteoblast differentiation involves acetylation of histones h3 and h4. Mol Endocrinol. 2003 Apr;17(4):743-56.
- Banerjee C, Javed A, Choi JY, Green J, Rosen V, van Wijnen AJ, Stein JL, Lian JB, Stein GS. Differential regulation of the two principal Runx2/Cbfa1 n-terminal isoforms in response to bone morphogenetic protein-2 during development of the osteoblast phenotype. Endocrinology. 2001 Sep;142(9):4026-39.
- Javed A, Gutierrez S, Montecino M, van Wijnen AJ, Stein JL, Stein GS, Lian JB. Multiple Cbfa/AML sites in the rat osteocalcin promoter are required for basal and vitamin D-responsive transcription and contribute to chromatin organization. Mol Cell Biol. 1999 Nov;19(11):7491-500.
- Hou Z, Nguyen Q, Frenkel B, Nilsson SK, Milne M, van Wijnen AJ, Stein JL, Quesenberry P, Lian JB, Stein GS. Osteoblast-specific gene expression after transplantation of marrow cells: implications for skeletal gene therapy. Proc Natl Acad Sci U S A. 1999 Jun 22;96(13):7294-9.
- Lian JB, Shalhoub V, Aslam F, Frenkel B, Green J, Hamrah M, Stein GS, Stein JL. Species-specific glucocorticoid and 1,25-dihydroxyvitamin D responsiveness in mouse MC3T3-E1 osteoblasts: dexamethasone inhibits osteoblast differentiation and vitamin D down-regulates osteocalcin gene expression. Endocrinology. 1997 May;138(5):2117-27.Banerjee C, Hiebert SW, Stein JL, Lian JB, Stein GS. An AML-1 consensus sequence binds an osteoblast-specific complex and transcriptionally activates the osteocalcin gene. Proc Natl Acad Sci U S A. 1996 May 14;93(10):4968-73.
- Montecino M, Lian J, Stein G, Stein J. Changes in chromatin structure support constitutive and developmentally regulated transcription of the bone-specific osteocalcin gene in osteoblastic cells. Biochemistry. 1996 Apr 16;35(15):5093-102.
- Owen TA, Bortell R, Shalhoub V, Heinrichs A, Stein JL, Stein GS, Lian JB. Postproliferative transcription of the rat osteocalcin gene is reflected by vitamin D-responsive developmental modifications in protein-DNA interactions at basal and enhancer promoter elements. Proc Natl Acad Sci U S A. 1993 Feb 15;90(4):1503-7.
- Owen TA, Aronow M, Shalhoub V, Barone LM, Wilming L, Tassinari MS, Kennedy MB, Pockwinse S, Lian JB, Stein GS. Progressive development of the rat osteoblast phenotype in vitro: reciprocal relationships in expression of genes associated with osteoblast proliferation and differentiation during formation of the bone extracellular matrix. J Cell Physiol. 1990 Jun;143(3):420-30.
- Marks SC Jr, Mackowiak S, Shaloub V, Lian JB, Stein GS. Proliferation and differentiation of osteoblasts in osteopetrotic rats: modification in expression of genes encoding cell growth and extracellular matrix proteins. Connect Tissue Res. 1989;21(1-4):107-13; discussion 114-6.