RUNX2 overexpression and PTEN haploinsufficiency cooperate to promote CXCR7 expression and cellular trafficking, AKT hyperactivation and prostate tumorigenesis

Rationale: The overall success rate of prostate cancer (PCa) diagnosis and therapy has been improved over the years. However, genomic and phenotypic heterogeneity remains a major challenge for effective detection and treatment of PCa. Efforts to better classify PCa into functional subtypes and elucidate the molecular mechanisms underlying prostate tumorigenesis and therapy resistance are warranted for further improvement of PCa outcomes. Methods: We generated Cre⁺;Runx2-cTg;Pten^p/+ (Runx2-Pten double mutant) mice by crossbreeding Cre⁺;Runx2-cTg males with Pten conditional (Pten^p/p) females. By using Hematoxylin and Eosin (H&E) staining, SMA and Masson's Trichrome staining, we investigated the effect of PTEN haploinsufficiency in combination with Runx2 overexpression on prostate tumorigenesis. Moreover, we employed immunohistochemistry (IHC) to stain Ki67 for cell proliferation, cleaved caspase 3 for apoptosis and AKT phosphorylation for signaling pathway in prostate tissues. Chromatin immunoprecipitation coupled quantitative PCR (ChIP-qPCR), reverse transcription coupled quantitative PCR (RT-qPCR), western blot (WB) analyses and immunofluorescence (IF) were conducted to determine the underlying mechanism by which RUNX2 regulates CXCR7 and AKT phosphorylation in PCa cells. Results: We demonstrated that mice with prostate-specific Pten heterozygous deletion and Runx2 overexpression developed high-grade prostatic intraepithelial neoplasia (HGPIN) and cancerous lesions at age younger than one year, with concomitant high level expression of Akt phosphorylation and the chemokine receptor Cxcr7 in malignant glands. RUNX2 overexpression induced CXCR7 transcription and membrane location and AKT phosphorylation in PTEN-deficient human PCa cell lines. Increased expression of RUNX2 also promoted growth of PCa cells and this effect was largely mediated by CXCR7. CXCR7 expression also positively correlated with AKT phosphorylation in PCa patient specimens. Conclusions: Our results reveal a previously unidentified cooperative role of RUNX2 overexpression and PTEN haploinsufficiency in prostate tumorigenesis, suggesting that the defined RUNX2-CXCR7-AKT axis can be a viable target for effective treatment of PCa.