Jensen, Eric D.

Abstract Prostate cancer patients with regional lymph node involvement at radical prostatectomy often experience disease progression to other organs, with the bone as the predominant site. The transcription factor Runx2 plays an important role in bone formation and prostate cancer cell migration, invasion, and metastasis. Here we showed that the forkhead box O (FOXO1) protein, a key downstream effector of the tumor suppressor PTEN, inhibits the transcriptional activity of Runx2 in prostate cancer cells. This inhibition was enhanced by PTEN but diminished by active Akt. FOXO1 bound to Runx2 in vitro and in vivo and suppressed Runx2's activity independent of its transcriptional function. FOXO1 inhibited Runx2-promoted migration of prostate cancer cells, whereas silencing of endogenous FOXO1 enhanced prostate cancer cell migration in a Runx2-dependent manner. Forced expression of FOXO1 also inhibited Runx2-promoted prostate cancer cell invasion. Finally, we found that expression of PTEN and the level of FOXO1 in the nucleus is inversely correlated with expression of Runx2 in a cohort of prostate cancer specimens from patients with lymph node and bone metastasis. These data reveal FOXO1 as a critical negative regulator of Runx2 in prostate cancer cells. Inactivation of FOXO1 due to frequent loss of PTEN in prostate cancer cells may leave the oncogenic activities of Runx2 unchecked, thereby driving promiscuous expression of Runx2 target genes involved in cell migration and invasion and favoring prostate cancer progression. Cancer Res; 71(9); 3257–67. ©2011 AACR.

Abstract HDAC7 associates with Runx2 and represses Runx2 transcriptional activity in a deacetylase-independent manner. HDAC7 suppression accelerates osteoblast maturation. Thus, HDAC7 is a novel Runx2 co-repressor that regulates osteoblast differentiation. Introduction: Runx2 is a key regulator of gene expression in osteoblasts and can activate or repress transcription depending on interactions with various co-factors. Based on previous observations that several histone deacetylases (HDACs) repress Runx2 activity and that HDAC inhibitors accelerate osteoblast differentiation in vitro, we hypothesized that additional HDACs may also affect Runx2 activity. Materials and Methods: A panel of HDACs was screened for repressors of Runx2 activity. Immunofluorescence, co-immunoprecipitation, GST-pulldowns, and chromatin immunoprecipitations were used to characterize the interactions between Runx2 and HDAC7. Expression of osteoblast markers was examined in a C2C12 cell osteoblast differentiation model in which HDAC7 levels were reduced by RNAi. Results: Runx2 activity was repressed by HDAC7 but not by HDAC9, HDRP, HDAC10, or HDAC11. HDAC7 and Runx2 were found co-localized in nuclei and associated with Runx2-responsive promoter elements in osseous cells. A carboxy-terminal domain of Runx2 associated with multiple regions of HDAC7. Although direct interactions with Runx2 were confined to the carboxy terminus of HDAC7, this region was dispensable for repression. In contrast, the amino terminus of HDAC7 bound Runx2 indirectly and was necessary and sufficient for transcriptional repression. Treatment with HDAC inhibitors did not decrease inhibition by HDAC7, indicating that HDAC7 repressed Runx2 by deacetylation-independent mechanism(s). Suppression of HDAC7 expression in C2C12 multipotent cells by RNAi accelerated their BMP2-dependent osteoblast differentiation program. Consistent with this observation, BMP2 decreased nuclear localization of HDAC7. Conclusions: These results establish HDAC7 as a regulator of Runx2's transcriptional activity and suggest that HDAC7 may be an important regulator of the timing and/ or rate of osteoblast maturation.