Background: Prostate cancer (PCa) dissemination shows a tendency to develop in the bone, where heme oxygenase 1 (HO-1) plays a critical role in bone remodeling. Previously by LC/ESI-MSMS, we screened for HO-1 interacting proteins and identified annexin 2 (ANXA2). The aim of this study was to analyze the relevance of ANXA2/HO-1 in PCa and bone metastasis. Methods: We assessed ANXA2 levels using a co-culture transwell system of PC3 cells (pre-treated or not with hemin, an HO-1 specific inducer) and the pre-osteoclastic Raw264.7 cell line. Results: Under co-culture conditions, ANXA2 mRNA levels were significantly modulated in both cell lines. Immunofluorescence analysis unveiled a clear ANXA2 reduction in cell membrane immunostaining for Raw264.7 under the same conditions. This effect was supported by the detection of a decrease in Ca²⁺ concentration in the conditioned medium. HO-1 induction in tumor cells prevented both, the ANXA2 intracellular relocation and the decrease in Ca²⁺ concentration. Further, secretome analysis revealed urokinase (uPA) as a key player in the communication between osteoclast progenitors and PC3 cells. To assess the clinical significance of ANXA2/HO-1, we performed a bioinformatics analysis and identified that low expression of each gene strongly associated with poor prognosis in PCa regardless of the clinico-pathological parameters assessed. Further, these genes appear to behave in a dependent manner. Conclusions: ANXA2/HO-1 rises as a critical axis in PCa.

The inflammatory tumor microenvironment is a fertile niche accelerating prostate cancer (PCa). We have reported that heme-oxygenase (HO-1) had a strong anti-tumoral effect in PCa. We previously undertook an in-depth proteomics study to build the HO-1 interactome in PCa. In this work, we used a bioinformatics approach to address the biological significance of HO-1 interactors. Open-access PCa datasets were mined to address the clinical significance of the HO-1 interactome in human samples. HO-1 interactors were clustered into groups according to their expression profile in PCa patients. We focused on the myxovirus resistance gene (MX1) as: (1) it was significantly upregulated under HO-1 induction; (2) it was the most consistently downregulated gene in PCa vs. normal prostate; (3) its loss was associated with decreased relapse-free survival in PCa; and (4) there was a significant positive correlation between MX1 and HMOX1 in PCa patients. Further, MX1 was upregulated in response to endoplasmic reticulum stress (ERS), and this stress triggered apoptosis and autophagy in PCa cells. Strikingly, MX1 silencing reversed ERS. Altogether, we showcase MX1 as a novel HO-1 interactor and downstream target, associated with ERS in PCa and having a high impact in the clinical setting.