Tali Herzka

MYC Drives Pten/Trp53-Deficient Proliferation and Metastasis due to IL6 Secretion and AKT Suppression via PHLPP2

UNLABELLED We have recently recapitulated metastasis of human PTEN/TP53-mutant prostate cancer in the mouse using the RapidCaP system. Surprisingly, we found that this metastasis is driven by MYC, and not AKT, activation. Here, we show that cell-cell communication by IL6 drives the AKT-MYC switch through activation of the AKT-suppressing phosphatase PHLPP2, when PTEN and p53 are lost together, but not separately. IL6 then communicates a downstream program of STAT3-mediated MYC activation, which drives cell proliferation. Similarly, in tissues, peak proliferation in Pten/Trp53-mutant primary and metastatic prostate cancer does not correlate with activated AKT, but with STAT3/MYC activation instead. Mechanistically, MYC strongly activates the AKT phosphatase PHLPP2 in primary cells and prostate cancer metastasis. We show genetically that Phlpp2 is essential for dictating the proliferation of MYC-mediated AKT suppression. Collectively, our data reveal competition between two proto-oncogenes, MYC and AKT, which ensnarls the Phlpp2 gene to facilitate MYC-driven prostate cancer metastasis after loss of Pten and Trp53. SIGNIFICANCE Our data identify IL6 detection as a potential causal biomarker for MYC-driven metastasis after loss of PTEN and p53. Second, our finding that MYC then must supersede AKT to drive cell proliferation points to MYC inhibition as a critical part of PI3K pathway therapy in lethal prostate cancer.

The nuclear transport receptor Importin-11 is a tumor suppressor that maintains PTEN protein

Phosphatase and tensin homologue (PTEN) protein levels are critical for tumor suppression. However, the search for a recurrent cancer-associated gene alteration that causes PTEN degradation has remained futile. In this study, we show that Importin-11 (Ipo11) is a transport receptor for PTEN that is required to physically separate PTEN from elements of the PTEN degradation machinery. Mechanistically, we find that the E2 ubiquitin-conjugating enzyme and IPO11 cargo, UBE2E1, is a limiting factor for PTEN degradation. Using in vitro and in vivo gene-targeting methods, we show that Ipo11 loss results in degradation of Pten, lung adenocarcinoma, and neoplasia in mouse prostate with aberrantly high levels of Ube2e1 in the cytoplasm. These findings explain the correlation between loss of IPO11 and PTEN protein in human lung tumors. Furthermore, we find that IPO11 status predicts disease recurrence and progression to metastasis in patients choosing radical prostatectomy. Thus, our data introduce the IPO11 gene as a tumor-suppressor locus, which is of special importance in cancers that still retain at least one intact PTEN allele.

Rapid in vivo validation of candidate drivers derived from the PTEN-mutant prostate metastasis genome

Human genome analyses have revealed that increasing gene copy number alteration is a driving force of incurable cancer of the prostate (CaP). Since most of the affected genes are hidden within large amplifications or deletions, there is a need for fast and faithful validation of drivers. However, classic genetic CaP engineering in mouse makes this a daunting task because generation, breeding based combination of alterations and non-invasive monitoring of disease are too time consuming and costly. To address the unmet need, we recently developed RapidCaP mice, which endogenously recreate human PTEN-mutant metastatic CaP based on Cre/Luciferase expressing viral infection, that is guided to Pten(loxP)/Trp53(loxP) prostate. Here we use a sensitized, non-metastatic Pten/Trp53-mutant RapidCaP system for functional validation of human metastasis drivers in a much accelerated time frame of only 3-4months. We used in vivo RNAi to target three candidate tumor suppressor genes FOXP1, RYBP and SHQ1, which reside in a frequent deletion on chromosome 3p and show that Shq1 cooperates with Pten and p53 to suppress metastasis. Our results thus demonstrate that the RapidCaP system forms a much needed platform for in vivo screening and validation of genes that drive endogenous lethal CaP.

Mitochondrial Complex I Inhibitors Expose a Vulnerability for Selective Killing of Pten-Null Cells

SUMMARY A hallmark of advanced prostate cancer (PC) is the concomitant loss of PTEN and p53 function. To selectively eliminate such cells, we screened cytotoxic compounds on Pten−/−;Trp53−/− fibroblasts and their Pten-WT reference. Highly selective killing of Pten-null cells can be achieved by deguelin, a natural insecticide. Deguelin eliminates Pten-deficient cells through inhibition of mitochondrial complex I (CI). Five hundred-fold higher drug doses are needed to obtain the same killing of Pten-WT cells, even though deguelin blocks their electron transport chain equally well. Selectivity arises because mitochondria of Pten-null cells consume ATP through complex V, instead of producing it. The resulting glucose dependency can be exploited to selectively kill Pten-null cells with clinically relevant CI inhibitors, especially if they are lipophilic. In vivo, deguelin suppressed disease in our genetically engineered mouse model for metastatic PC. Our data thus introduce a vulnerability for highly selective targeting of incurable PC with inhibitors of CI.

Abstract 2258: Myc drives Pten/ p53-deficient proliferation and metastasis due to Il6-secretion and Akt-suppression via Phlpp2

The sporadic transition from indolent to metastatic disease is a hallmark of prostate cancer (PC) and frequently involves deletion of PTEN and TP53. We recently recapitulated metastasis of Pten/ Trp53-mutant PC in mouse using the RapidCaP system and surprisingly, we found that it is driven by Myc, rather than Akt activation. Here, we show that cell-cell communication by Il6 drives this Akt-Myc switch through activation of the Akt-inactivating phosphatase Phlpp2. Primary cells revealed that loss of Pten/ Trp53 triggers secretion of the Il6 cytokine when these genes are deleted together, but not separately. Il6 then communicates a downstream program of Stat3-mediated Myc activation, which drives cell proliferation. Abrogation of Myc activity by Myc inhibition with the JQ1 bromodomain inhibitor, Myc-RNAi, and Myc-CRISPR/ Cas9 approaches inhibited proliferation. We validated these findings in vivo, where peak proliferation in Pten/ Trp53 mutant primary and metastatic PC did not correlate with activated Akt, but with Stat3/ Myc activation instead. Most notably, we found that Myc strongly activates the Akt phosphatase Phlpp2 in primary cells and RapidCaP metastasis, and showed genetically that Phlpp2 is essential for dictating proliferation and Myc-mediated suppression of Akt. Collectively, our data reveal competition between two proto-oncogenes: Myc and Akt, which ensnarls the Phlpp2 gene to facilitate Myc-driven metastasis. Citation Format: Dawid G. Nowak, Hyejin Cho, Tali Herzka, Victoria M.Y. Wang, Serif Senturk, Daniel V. DeMarco, David Ding, Christof Fellmann, Tumas Beinortas, David Kleinman, Kaitlin Watrud, Muhan Chen, John E. Wilkinson, Mireia Castillo-Martin, Carlos Cordon-Cardo, Brian D. Robinson, Lloyd C. Trotman. Myc drives Pten/ p53-deficient proliferation and metastasis due to Il6-secretion and Akt-suppression via Phlpp2. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2258. doi:10.1158/1538-7445.AM2015-2258

Abstract 5258: PTEN levels are controlled by a nuclear transport receptor in lung cancer.

The maintenance of PTEN protein levels is critical for tumor suppression. Yet, the ubiquitination system has been shown to affect PTEN levels both adversely through degradation, as well as positively through nuclear import, and it has remained unclear how these two processes are integrated to prevent cancer. Here we show, that a nuclear import receptor is at the heart of a failsafe system that maintains PTEN levels by mediating its nuclear transport. Loss of import receptor function not only leads to cytoplasmic PTEN accumulation but also prompts PTEN degradation through a novel component of the PTEN ubiquitination system. By testing the consequences of importin loss in vivo, we found that hypomorphic mice developed lung adenocarcinoma, which presented with aberrant cytoplasmic PTEN localization and degradation, as predicted by our in vitro findings. Since the corresponding human locus suffers frequent deletion as well as inactivating mutations in lung cancer, we propose that this import receptor is a novel tumor suppressor that antagonizes PI 3-Kinase signaling in settings with at least one intact PTEN gene.

Abstract 4091: RapidCap: A new generation of mouse models for prostate cancer.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Genetically Engineered Mouse Models are the gold standard for functional cancer research. However, the associated time and cost requirements severely limit their application. As a consequence, projects carry typically a high risk, are lengthy, and scientists become ‘locked in’ with a few chosen candidate alterations. To realize the full potential of mouse modeling technology we have developed RapidCaP, a system that relies on surgical gene transfer. Through prostate specific delivery of transgenic virus we can 1) reduce model generation times from several years to a few weeks, 2) test various genetic alterations such as loss or gain of function, alone or in combination, and 3) use non-invasive imaging to monitor disease progression. Using RapidCaP, we show that focal loss of Pten and Trp53 genes triggers prostate lesions within 2 months. Furthermore, we find that this disease responds to castration by strong regression within several weeks, but it later relapses to produce lethal hormone refractory disease. Taken together, our approach establishes a novel platform for basic prostate cancer research and it realizes the goal of carrying out pre-clinical studies in genetically engineered mice. Citation Format: Hyejin Cho, Tali Herzka, Wu Zheng, Mireia Castillo-Martin, Carlos Cordon-Cardo, Lloyd C. Trotman. RapidCap: A new generation of mouse models for prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4091. doi:10.1158/1538-7445.AM2013-4091