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Prostate cancer that recurs following androgen-deprivation therapy is termed castration-resistant, which is incurable and is marked by reactivation of androgen receptor (AR) signaling. KIF20A, a kinesin with unique structural features, is overexpressed in human castration-resistant prostate cancer (CRPC) compared to androgen-dependent PC and benign tissue. KIF20A has well-described roles in mitotic processes, but it has a less characterized function in vesicle fission and trafficking within Golgi-driven secretory pathways. Stable expression of KIF20A in androgen-dependent PC cells promoted progression to CRPC through the activation of AR signaling in vitro and in vivo. KIF20A expression resulted in the secretion of autocrine factors in the conditioned media that activated AR and caused castration-resistant proliferation of naïve androgen-dependent cells. Pharmacologic disruption of vesicle biogenesis blocked KIF20A-driven castration-resistant proliferation of androgen-dependent PC. KIF20A depletion or treatment with the KIF20A-specific inhibitor, paprotrain, reduced CRPC. These data are the first to establish KIF20A as a driver of CRPC progression through AR activation and as a promising therapeutic target against CRPC., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Most prostate cancer cases remain indolent for long periods of time, but metastatic progression quickly worsens the prognosis and leads to mortality. However, little is known about what promotes the metastasis of prostate cancer and there is a lack of effective prognostic indicators, making it immensely difficult to manage options for treatment or surveillance. Arginyltransferase 1 (Ate1) is the enzyme mediating post-translational protein arginylation, which has recently been identified as a master regulator affecting many cancer-relevant pathways including stress response, cell cycle checkpoints, and cell migration/adhesion. However, the precise role of Ate1 in cancer remains unknown. In this study, we found the occurrence of metastasis of prostate cancer is inversely correlated with the levels of Ate1 protein and mRNA in the primary tumor. We also found that metastatic prostate cancer cell lines have a reduced level of Ate1 protein compared to non-metastatic cell lines, and that a depletion of Ate1 drives prostate cancer cells towards more aggressive pro-metastatic phenotypes without affecting proliferation rates. Furthermore, we demonstrated that a reduction of Ate1 can result from chronic stress, and that shRNA-reduced Ate1 increases cellular resistance to stress, and drives spontaneous and stress-induced genomic mutations. Finally, by using a prostate orthotropic xenograft mouse model, we found that a reduction of Ate1 was sufficient to enhance the metastatic phenotypes of prostate cancer cell line PC-3 in vivo. Our study revealed a novel role of Ate1 in suppressing prostate cancer metastasis, which has a profound significance for establishing metastatic indicators for prostate cancer, and for finding potential treatments to prevent its metastasis.

Deregulation of microRNAs (miRs) contributes to progression and metastasis of prostate and other cancers. miR-23b and -27b, encoded in the same miR cluster (miR-23b/-27b), are downregulated in human metastatic prostate cancer compared with primary tumors and benign tissue. Expression of miR-23b/-27b decreases prostate cancer cell migration, invasion and results in anoikis resistance. Conversely, antagomiR-mediated miR-23b and -27b silencing produces the opposite result in a more indolent prostate cancer cell line. However, neither miR-23b/-27b expression or inhibition impacts prostate cancer cell proliferation suggesting that miR-23b/-27b selectively suppresses metastasis. To examine the effects of miR-23b/-27b on prostate cancer metastasis in vivo, orthotopic prostate xenografts were established using aggressive prostate cancer cells transduced with miR-23b/-27b or non-targeting control miRNA. Although primary tumor formation was similar between miR-23b/-27b-transduced cells and controls, miR-23b/-27b expression in prostate cancer cells decreased seminal vesicle invasion and distant metastases. Gene-expression profiling identified the endocytic adaptor, Huntingtin-interacting protein 1-related (HIP1R) as being downregulated by miR-23b/-27b. Increased HIP1R expression in prostate cancer cells inversely phenocopied the effects of miR-23b/-27b overexpression on migration, invasion and anchorage-independent growth. HIP1R rescued miR-23b/-27b-mediated repression of migration in prostate cancer cells. HIP1R mRNA levels were decreased in seminal vesicle tissue from mice bearing miR-23b/-27b-transduced prostate cancer cell xenografts compared with scrambled controls, suggesting HIP1R is a key functional target of miR-23b/-27b. In addition, depletion of HIP1R led to a more rounded, less mesenchymal-like cell morphology, consistent with decreased metastatic properties. Together, these data demonstrate that the miR-23b/-27b cluster functions as a metastasis-suppressor by decreasing HIP1R levels in pre-clinical models of prostate cancer.

Increased androgen receptor (AR) transcriptional activity mediated by coactivator proteins may drive castration-resistant prostate cancer (CRPC) growth. Vav3, a Rho GTPase guanine nucleotide exchange factor (GEF), is overexpressed in human prostate cancers, particularly in models of CRPC progression. Vav3 coactivates AR in a Vav3 pleckstrin homology (PH) domain-dependent but GEF-independent manner. Ectopic expression of Vav3 in androgen-dependent human prostate cancer cells conferred robust castration-resistant xenograft tumor growth. Vav3 but not a Vav3 PH mutant greatly stimulated interaction between the AR amino and carboxyl termini (N-C interaction), which is required for maximal receptor transcriptional activity. Vav3 was distributed between the cytoplasm and nucleus with nuclear localization-dependent on the Vav3 PH domain. Membrane targeting of Vav3 abolished Vav3 potentiation of AR activity, whereas nuclear targeting of a Vav3 PH mutant rescued AR coactivation, suggesting that nuclear localization is an important function of the Vav3 PH domain. A nuclear role for Vav3 was further demonstrated by sequential chromatin immunoprecipitation assays, which revealed that Vav3 and AR were recruited to the same transcriptional complexes of an AR target gene enhancer. These data demonstrate the importance of Vav3 in CRPC and define a novel nuclear function of Vav3 in regulating AR activity.

Abnormally suppressed levels of cyclin-dependent kinase inhibitors (CKIs) are associated with aggressive androgen-independent prostate cancer and contribute to uncontrolled proliferation. The androgen-independent human prostate cancer cell lines, LNCaP-104R1, ALVA31 and PC-3, express low levels of the CKI, p21(CIP1), compared to the less-malignant, androgen-dependent LNCaP cells. We investigated the mechanism underlying this suppression by examining the role of Rho GTPases, signaling proteins that play important roles in cell cycle progression, at least in part through regulation of CKIs. Inhibition of Rac1 induced p21 expression in androgen-independent lines but had no effect on the higher p21 levels characteristic of LNCaP cells. This induction of p21 was functionally significant as evidenced by inhibition of cyclin-dependent kinase 2 activity and decreased cell proliferation. Conversely, overexpression of constitutively active Rac1 suppressed the higher p21 levels seen in LNCaP cells. Thus, Rac1 activity is both necessary and sufficient for suppression of p21 in prostate cancer cells. Furthermore, Rac1 activity was significantly higher in all three androgen-independent cell lines compared to LNCaP cells. Thus in three models of aggressive human prostate cancer, hyperactivity of Rac1 corresponds to suppressed levels of p21. These results are unique in describing a role for Rac1 in p21 regulation and may implicate the Rac1 signaling pathway as a potential therapeutic target for controlling prostate cancer cell growth following progression to androgen independence.