Runx2–smad signaling impacts the progression of tumor‐induced bone disease

Abstract

Runx2, a master regulator of osteogenesis, is abnormally expressed in advanced prostate cancer. Here we addressed Runx2 contribution to formation of prostate cancer-related osteolytic and osteoblastic bone lesions by mediating TGFβ/BMP signaling through direct interaction with Smads. Further, we examined involvement of the Runx2-Smad complex in mediating tumor growth and distal metastasis. To identify Runx2-Smad specific mechanisms of prostate tumor activity in bone, we generated PC3 prostate cancer cell lines expressing Runx2-WT or one of two mutant proteins (Runx2-HTY and Runx2-ΔC) that each disrupt the Runx2-Smad interaction, either directly through a point mutation or by deletion of the functional C-terminus, respectively. Intratibial tumors generated from these cells revealed that Runx2-WT expressing cells resulted in predominantly osteolytic disease, while cells expressing mutant proteins exhibited tumors with mixed osteolytic/osteoblastic lesions. Extent of bone loss and of woven bone formation was assessed by radiography and micro-computed tomography. Bioluminescent imaging showed the presence of labeled prostate cancer cells in the lung at the latest time point examined, with Runx2-WT group exhibiting increased incidence of tumor cells in lung. Notably, disruption of the Runx2-Smad interaction significantly reduced incidence and size of lung tumors. Altered expression of Runx2 target genes involved in invasion, growth, adhesion and metastasis supported our findings. Thus, our studies demonstrate that Runx2 in prostate cancer cells plays a significant role in intratibial prostate cancer-related tumor growth and bone loss through mechanisms mediated by the Runx2-Smad signaling pathway. This work expands upon the potential importance of Runx2 as a therapeutic target in cancer.

PACAP and VIP signaling in chondrogenesis and osteogenesis

“…2). BMP signaling pathway is another fundamental regulator of osteogenesis and crosstalk with Runx2 has been reported [82]. Moreover, the TGF␤/BMP pathways are activated by PACAP or VIP [24,83].…”

Dysregulation of Mitochondrial Functions and Osteogenic Differentiation in Cisd2-Deficient Murine Induced Pluripotent Stem Cells

“…as a scaffold for nucleic acids and regulates several essential skeletal-related genes [57]. It acts bidirectionally to target the promoter of Bmp2/Bmp4 and recruit R-Smad to trigger Bmp signaling pathways [43,[58][59][60][61]. Interestingly, nearly all of the genes with the most drastically altered expression function downstream of the Wnt pathway, indicating that Cisd2 is involved in this signaling pathway through an unknown mechanism during the osteogenic process.…”

Expression of the IL‐11 Gene in Metastatic Cells Is Supported by Runx2‐Smad and Runx2‐cJun Complexes Induced by TGFβ1

“…Prostate cancer metastatic bone disease results in predominantly painful bone forming osteoblastic bone lesions, but it is now clinically recognized that osteolysis is also a component of the metastatic disease in the bone microenvironment during progression of prostate tumor growth [Morrissey et al, 2013; Sottnik and Keller, 2013]. Recent studies in mouse models have also identified the osteolytic component of prostate cancer tumor growth in bone [Akech et al, 2010; Dutta et al, 2014; Eswaraka et al, 2014; Fradet et al, 2013; Ortiz and Lin, 2012; Zhang et al, 2015]. TGFβ1 and PTHrP are considered the major factors driving this ‘vicious cycle’ of metastatic bone disease [Buijs et al, 2011; Massague, 2012; Weilbaecher et al, 2011].…”

“…In the TGFβ1 pathway, phosphorylated receptor-regulated R Smads (Smad2/3) form complexes with the co-Smad Smad4, then, enter the nucleus to bind with other transcription factors, such as Runx2 and AP1 factors to regulate gene expression [Ikushima and Miyazono, 2010; Padua and Massague, 2009; Zaidi et al, 2002]. Similar to breast cancer cells, two deregulated osteoytic factors, the Runx2 transcription factor and the osteolytic cytokine IL-11, are highly expressed in metastatic prostate cancer cells [Akech et al, 2010; Pratap et al, 2008; Zhang et al, 2015]. Both these pathologic activities result in woven bone formation and loss of normal bone during progression of tumor growth.…”

“…In response to TGFβ1 Runx2 recruits Smads to unique subnuclear domains forming Runx2-Smad complexes [Javed et al, 2008; Zaidi et al, 2002; Zhang et al, 2000]. Runx2-Smad is critical in facilitating osteolytic disease resulting from orthotopic growth of human breast and prostate tumor cells in the mouse [Akech et al, 2010; Pratap et al, 2008; Zhang et al, 2015]. Studies have further demonstrated a striking reduction of bone resorption by Runx2 RNAi in vivo in the intratibial model of metastatic bone disease [Akech et al, 2010; Pratap et al, 2008].…”