PDF file - 80K, Myogenic differentiation is impaired in RD cells devoid of PDGF activity. RD cells were cultured for 72 hours under conditions facilitating myogenic differentiation. A, quantification of SA-βgal-positive senescent cells in the presence of CP-673,451 or vehicle. B, cell elongation as a morphological sign of myogenic differentiation in the presence of CP-673,451 or vehicle. C, qRT-PCR analysis for the two myogenic transcripts MYL1 and MYOGENIN and the myogenic repressor HEY-1, a mediator of Notch signaling, in the presence of CP-673,451 or vehicle (0.1% DMSO) (left panel). The right panel shows expression of the same myogenic transcripts in non-differentiated cells and in cells where differentiatiation was induced in the absence of vehicle. All expression values were normalized to the expression in non-differentiated cells (right panel, left bar). Data are presented � SD (*P<0.05, ***P<0.001, Student's t test).
ARTICLE ABSTRACT
Platelet-derived growth factor receptors (PDGFR) α and β have been suggested as potential targets for treatment of rhabdomyosarcoma, the most common soft tissue sarcoma in children. This study identifies biologic activities linked to PDGF signaling in rhabdomyosarcoma models and human sample collections. Analysis of gene expression profiles of 101 primary human rhabdomyosarcomas revealed elevated PDGF-C and -D expression in all subtypes, with PDGF-D as the solely overexpressed PDGFRβ ligand. By immunohistochemistry, PDGF-CC, PDGF-DD, and PDGFRα were found in tumor cells, whereas PDGFRβ was primarily detected in vascular stroma. These results are concordant with the biologic processes and pathways identified by data mining. While PDGF-CC/PDGFRα signaling associated with genes involved in the reactivation of developmental programs, PDGF-DD/PDGFRβ signaling related to wound healing and leukocyte differentiation. Clinicopathologic correlations further identified associations between PDGFRβ in vascular stroma and the alveolar subtype and with presence of metastases. Functional validation of our findings was carried out in molecularly distinct model systems, where therapeutic targeting reduced tumor burden in a PDGFR-dependent manner with effects on cell proliferation, vessel density, and macrophage infiltration. The PDGFR-selective inhibitor CP-673,451 regulated cell proliferation through mechanisms involving reduced phosphorylation of GSK-3α and GSK-3β. Additional tissue culture studies showed a PDGFR-dependent regulation of rhabdosphere formation/cancer cell stemness, differentiation, senescence, and apoptosis. In summary, the study shows a clinically relevant distinction in PDGF signaling in human rhabdomyosarcoma and also suggests continued exploration of the influence of stromal PDGFRs on sarcoma progression. Cancer Res; 73(7); 2139–49. ©2013 AACR.
