The Prostate 56:13 ^22 (2003) Prostate Cancer Expression of Runt-Domain Transcription Factor Runx2, a Key Regulator of Osteoblast Differentiation and Function Kristen D. Brubaker, Robert L. Vessella, Lisha G. Brown, and Eva Corey* Department of Urology,University of Washington School of Medicine, Seattle,Washington BACKGROUND. Prostate cancer (CaP) bone metastases express numerous proteins associated with bone cells. Specific transcription factors, including Runx2, regulate the expression of many bone-related factors in osteoblasts. Expression of these transcription factors in CaP may be linked to the ability of CaP bone metastases to influence bone remodeling. METHODS. CaP tissues and cell lines were analyzed for expression of Runx2 mRNA by RT-PCR and in situ hybridization, and protein by immunohistochemistry, Western blotting, and electrophoretic mobility shift assays (EMSA). RESULTS. Runx2 mRNA and protein were detected in CaP tissues and cell lines. A specific Runx2: OSE2 complex could be formed with PC-3 nuclear extracts. CONCLUSIONS. Expression of Runx2 in CaP may be the molecular switch that is associated with expression of various bone-specific factors in CaP. In turn, expression of these factors can influence bone remodeling and possibly play a role in the growth and survival of CaP in bone. Prostate 56: 13–22, 2003. # 2003 Wiley-Liss, Inc. KEY WORDS: prostate cancer; bone metastases; Cbfa1; OSE2; BMP-2 INTRODUCTION Prostate cancer (CaP) is the most commonly diag- nosed malignancy in men and is often associated with bone metastases. CaP bone lesions can be lytic or sclerotic, with the latter predominating. The molecular mechanisms by which CaP alters the balance of normal bone metabolism are poorly understood but it has been hypothesized by Koeneman et al. [1] that CaP cells are osteomimetic in their ability to thrive and grow in the bone milieu. CaP expresses proteins associated with osteoblasts such as osteocalcin [2], receptor activator of NFkB ligand (RANKL) [3], bone sialoproteins [4], osteopontin [5], steoprotegerin (OPG) [3], and bone morphogenetic proteins (BMPs) [6,7]. Expression of several of these proteins is further upregulated in metastatic bone lesions when compared to primary CaP. Increased transcriptional activation of bone- related factors in CaP cells is a candidate mechanism for involvement in the deregulation of bone remodel- ing associated with CaP bone metastases. Runt-domain transcription factor Runx2 (also called Pebp2aA, Cbfa1, AML-3, or Osf2) is a transcription factor essential for osteoblast differentiation [8,9]. Runx2 regulates transcription of many bone-related factors in osteoblasts, including osteocalcin [8], bone sialoproteins [10], osteopontin [11], collagen type I [12], and OPG [13] through an osteoblast-specific cis-acting element termed OSE2. Targeted disruption of runx2 results in complete lack of bone formation [14,15], while mutations are responsible for the genetic disease cleidocranial dysplasia [16,17]. Runx2 gene expression is upregulated early in development in association with mesenchymal condensations and at late stages during bone mineralization [8,18]. Factors involved in osteoblast differentiation, such as the BMPs [19] and Grant sponsor: NIH; Grant number: 5T32DK07779-02; Grant sponsor: NIDDK O’Brien Center; Grant number: DK47656-08; Grant sponsor: Richard M. Lucas Foundation; Grant sponsor: CaPCure Foundation. *Correspondence to: Eva Corey, PhD, Department of Urology, University of Washington, Mailstop 356510, 1959 NE Pacific St. HSB I-340, Seattle, WA 98195. E-mail: ecorey@u.washington.edu Received 16 July 2002; Accepted 9 December 2002 DOI 10.1002/pros.10233 ß 2003 Wiley-Liss, Inc.