(A) Meta-analysis using public datasets showed that ERRα mRNA expression is higher in CRPC patients in GSE6919 (Student's t-test P = 0.0172). (B) ERRα was also found to be higher in CRPC compared to androgen-sensitive PCa, as well as in primary tumors from CRPC patients that developed metastases to bone compared to other sites or normal prostate tissues in GSE21034 (One way ANOVA, bonferri post-hoc test : P < 0,05, normal (n = 22) versus CRPC (n = 41); P < 0.0005, normal (n = 22) versus CRPC bone mets (n = 5); P < 0.005, PCa (n = 104) versus CRPC bone mets (n = 5)) and (C) PCa versus CRPC (that all had developed bone metastases) in GSE32269 (Student's t-test P = 0.0178): *P < 0.05, **P < 0.005, ***P < 0.0005. (D) Visualization of ERRα protein expression by IHC on sections of prostate primary tumor (a) and the associated bone metastatic lesions (b) from the same patient. (E) Assessment of ERRα expression by Western blotting and (F) real-time RT-PCR on triplicate samples and normalized against the ribosomal protein gene L32 (ANOVA, Student's t-tests P < 0.0001) in PC3 control (CT-1-3) and PC3-ERRα (ERRα-1–3) overexpressing ERRα clones. (G) Increased expression of VEGF-A mRNA in PC3-ERRα (ANOVA, Student's t-tests P < 0.0001). (H) Increase of ERRα protein expression in PC3c-ERRα (ERRα(c)) overexpressing ERRα shown by Western blot and (I) by real-time RT-PCR for VEGF-A expression (Student's t-tests P = 0.001). (J) Assessment of ERRα expression by Western blotting in an ACE-1 empty-vector CT clone, an ACE-ERRα and a clone overexpressing the dominant negative ERRα with AF2 domain deletion (AF2). (K) VEGF-A mRNA expression was also increased in ACE-ERRα cells (Student's t-tests P = 0.0001). Bar = 200 μm, T: Tumor; Ost: osteocytes; BM: Bone Matrix