Prostate cancer at advanced stages including metastatic and castration-resistant cancer remains incurable due to the lack of effective therapies.The CAMK2N1 gene, cloned and characterized as an inhibitor of CaMKII (calcium/calmodulin-dependent protein kinase Ⅱ), has been shown to affect tumor genesis and tumor growth.However, it is still unknown whether CAMK2N1 plays a role in prostate cancer development.We first examined the protein and mRNA levels of CAMK2N1 and observed a significant decrease in human prostate cancers comparing to normal prostate tissues.Re-expression of CAMK2N1 in prostate cancer cells reduced cellular proliferation, arrested cells in G0/G1 phases, and induced apoptotic cell death accompanied by down-regulation of IGF-1, ErbB2, and VEGF downstream kinases PI3K/AKT, as well as the MEK/ ERK-mediated signaling pathways.Conversely, knockdown of CAMK2N1 had a significant opposite effects on these phenotypes.Our analyses suggest that CAMK2N1 plays a tumor suppressive role in prostate cancer cells.Reduced CAMK2N1 expression correlates to human prostate cancer progression and predicts poor clinical outcome, indicating that CAMK2N1 may serve as a biomarker.The inhibition of tumor growth by expressing CAMK2N1 established a role of CAMK2N1 as a therapeutic target.