Aberrant integrin αv and α5 expression in prostate adenocarcinomas and bone-metastases is consistent with a bone-colonizing phenotype

Background Collaborative signaling between fibronectin-binding αv and α5 integrins has been implicated in the lethal dissemination of prostate cancer in the bone-metastatic niche, the major source of morbidity and mortality in the disease. Methods We assessed the frequency and pattern of expression of these integrins in primary high-grade adenocarcinomas and bone metastases compared to the physiological gland. Formalin-fixed paraffin-embedded (FFPE) radical prostatectomy (RP) samples (n=25) containing ≥ Gleason grade 4 cancer and decalcified surgical or diagnostic bone metastatic samples from 10 patients were stained for integrin αv (ITGAV) and integrin α5 (ITGA5) expression. Antibody optimization and antigen-retrieval was performed beforehand. Results ITGAV was exclusively expressed in the basal layer of physiological prostate glands whereas αv expression was invariably recapitulated in the malignant gland and bone metastases (100%) in multiple distinct patterns: epithelial membranous, basilar/luminal membranous, punctate cytoplasmic, intense foci as single cells or clusters, and rim stromal layers. The luminal/basilar layer of ITGAV expression was striking in cribriform carcinomas, suggestive of a role in molecular pathogenesis. ITGA5 infrequently highlighted the basal layer of the physiological gland, was absent in primary adenocarcinoma, but was expressed with ITGAV exclusively in bone metastases (71%). Conclusions We conclude that ITGAV expression is aberrantly expressed in high frequency in high-grade prostatic adenocarcinomas in patterns suggestive of recapitulated basal cell functions, consistent with a stem-regulatory role that has been proposed. Co-expression and enrichment of αv and α5 in osseous metastases supports their proposed collaborative role in colonization of the bone microenvironment and as candidate targets for therapy.