CAMKK2 promotes prostate cancer progression through an alternative pathway involving CAMKI-CREB-mediated cholesterol metabolism

Castration-resistant prostate cancer (CRPC) remains an incurable disease driven predominantly by aberrant androgen receptor AR signaling, suggesting that processes downstream of AR represent viable alternative targets for the treatment of CRPC. CAMKK2 (encoding calcium/calmodulin-dependent protein kinase kinase 2) is a direct AR target that is highly expressed during prostate cancer progression, a functional driver of the disease and hence, emerging therapeutic target. To date, CAMKK2’s oncogenic effects in prostate cancer have been attributed to its activation of AMP-activated protein kinase (AMPK), but recent reports suggest that CAMKK2 may also facilitate tumorigenesis through AMPK-independent mechanisms. Here, we demonstrate that AR-mediated CAMKK2 signaling promotes prostate cancer growth through an alternative downstream pathway involving calcium/calmodulin-dependent protein kinase I (CAMKI) and cAMP response element-binding protein (CREB). Unbiased transcriptomics identified CREB-mediated transcription as a CAMKK2-regulated process, findings that were validated using diverse molecular, genetic and pharmacological approaches in vitro and in vivo. CAMKK2 promoted CREB serine-133 phosphorylation and activation through CAMKIa independently of AMPK, CAMKIV or other CAMKI isoforms. Functionally, CREB activity was required for maximal CRPC growth. The CREB family members CREB1 and ATF1 exhibited close redundancy, necessitating co-targeting for optimal anti-tumor efficacy. Pharmacologically, a small molecule inhibitor of CREB1/ATF1, 666-15, blocked CRPC growth with minimal side effects in vitro and in vivo including in patient-derived xenograft models of enzalutamide resistance. Mechanistically, CAMKK2-mediated CREB increased prostate cancer growth through augmenting cholesterol metabolism. Together, these findings identified a novel oncogenic pathway in prostate cancer that could be exploited for the treatment of CRPC.