Sun, Lu‐Zhe

Abstract Although the Sonic hedgehog (SHH) signaling pathway has been implicated in promoting malignant phenotypes of prostate cancer, details on how it is activated and exerts its oncogenic role during prostate cancer development and progression is less clear. Here, we show that GLI3, a key SHH pathway effector, is transcriptionally upregulated during androgen deprivation and posttranslationally stabilized in prostate cancer cells by mutation of speckle-type POZ protein (SPOP). GLI3 is a substrate of SPOP-mediated proteasomal degradation in prostate cancer cells and prostate cancer driver mutations in SPOP abrogate GLI3 degradation. Functionally, GLI3 is necessary and sufficient for the growth and migration of androgen receptor (AR)–positive prostate cancer cells, particularly under androgen-depleted conditions. Importantly, we demonstrate that GLI3 physically interacts and functionally cooperates with AR to enrich an AR-dependent gene expression program leading to castration-resistant growth of xenografted prostate tumors. Finally, we identify an AR/GLI3 coregulated gene signature that is highly correlated with castration-resistant metastatic prostate cancer and predictive of disease recurrence. Together, these findings reveal that hyperactivated GLI3 promotes castration-resistant growth of prostate cancer and provide a rationale for therapeutic targeting of GLI3 in patients with castration-resistant prostate cancer (CRPC). Implications: We describe two clinically relevant mechanisms leading to hyperactivated GLI3 signaling and enhanced AR/GLI3 cross-talk, suggesting that GLI3-specific inhibitors might prove effective to block prostate cancer development or delay CRPC.

Objective We aimed to evaluate the contribution of acinar-to-ductal metaplasia (ADM) to the accumulation of cells with a ductal phenotype in cultured human exocrine pancreatic tissues and reveal the underlying mechanism. Methods We sorted and cultured viable cell populations in human exocrine pancreatic tissues with a flow cytometry–based lineage tracing method to evaluate possible mechanisms of ADM. Cell surface markers, gene expression pattern, and sphere formation assay were used to examine ADM. Results A large proportion of acinar cells gained CD133 expression during the 2-dimensional culture and showed down-regulation of acinar markers and up-regulation of ductal markers, assuming an ADM phenotype. In a serum-free culture condition, ADM induction was mainly dependent on transforming growth factor β (TGF-β) secreted from cultured ductal cells. Human acinar cells when cultured alone for a week in a serum-free condition do not undergo ADM. However, serum may contain other factors besides TGF-β to induce ADM in human acinar cells. In addition, we found that TGF-β cannot induce ADM of murine acinar cells. Conclusions Ductal cells are the major source of TGF-β that induces ADM in cultured human exocrine pancreatic tissues. This culture system might be a useful model to investigate the mechanism of ADM in human cells.

Abstract Biomarkers are lacking for identifying the switch of transforming growth factor-beta (TGF-β) from tumor-suppressing to tumor-promoting. Mutated p53 (mp53) has been suggested to switch TGF-β to a tumor promoter. However, we found that mp53 does not always promote the oncogenic role of TGF-β. Here, we show that endogenous mp53 knockdown enhanced cell migration and phosphorylation of ERK in DU145 prostate cancer cells. Further, ectopic expression of mp53 in p53-null PC-3 prostate cancer cells enhanced Smad-dependent signaling, but inhibited TGF-β-induced cell migration by downregulating activated ERK. Reactivation of ERK by the expression of its activator, MEK-1, restored TGF-β-induced cell migration. Since TGF-β is known to activate MAPK/ERK pathway through direct phosphorylation of adaptor protein ShcA and MAPK/ERK signaling is pivotal to tumor progression, we investigated whether ShcA contributed to mp53-induced ERK inhibition and the conversion of TGF-β's role during carcinogenesis. We found that mp53 expression led to decrease of phosphorylated p52ShcA/ERK levels and increase of phosphorylated Smad levels in a panel of mp53-expressing cancer cell lines, and in mammary glands and tumors from mp53 knock-in mice. By manipulating ShcA levels to regulate ERK and Smad signaling in human untransformed and cancer cell lines, we show that TGF-β's role in regulating anchorage-dependent and -independent growth, and migration, can be shifted between growth suppression and migration promotion. Thus, our results, for the first time, suggest that mp53 disrupts ShcA's role in balancing Smad-dependent and -independent signaling activity of TGF-β and that ShcA/ERK signaling is a major pathway regulating the tumor-promoting activity of TGF-β. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1069. doi:1538-7445.AM2012-1069