Endocrine Abstracts

Castration-resistant prostate cancer (CRPC) is an androgen-independent subtype of prostate cancer (PCa) that develops in response to androgen deprivation therapy (ADT). In some advanced CRPC cases, tumors can develop the neuroendocrine (NE) phenotype and progress towards an aggressive PCa subtype known as treatment-induced NE PCa (NEPC), which is characterized by an increase in the population of NE cells that secrete neuropeptides promoting cancer progression. A key player in neuropeptide synthesis is peptidylglycine alpha-amidating monooxygenase (PAM), a bifunctional cuproenzyme responsible for the α-amidation-dependent activation of neuropeptides. Due to its use of copper as a co-factor for its activity, PAM is also implicated in copper homeostasis, a process that is dysregulated during PCa development. Given its function in pathways related to NEPC, we hypothesized that PAM may play a role in the maintenance and transition to NEPC. In silico analysis confirmed that PAM expression is upregulated in NEPC tumors. In cell line models for prostate adenocarcinoma and CRPC, we found that PAM expression is differentially regulated by androgen. Further, through in silico analysis, we identified four intronic cis-regulatory elements in the PAM locus that can mediate androgen-dependent differential regulation. To determine the functional role of PAM in PCa progression, we knocked down PAM in various prostate cell models and subjected hormone-refractory PCa cells with PAM knockdown to ADT to model the transition towards NEPC. PAM knockdown led to alterations in the expression of genes involved in NE differentiation and copper homeostasis. Using paracrine signaling and cancer hallmark assays, PAM knockdown reduced the secretion of growth-promoting factors and mitigated the aggressive nature of hormone-refractory and neuroendocrine PCa cells. Overall, our findings demonstrate the coordinated involvement of PAM in neuropeptide synthesis and copper homeostasis and how these two pathways may contribute to the maintenance and transition towards NEPC.