Phillip J. Iaquinta

Identification of Multipotent Luminal Progenitor Cells in Human Prostate Organoid Cultures

The prostate gland consists of basal and luminal cells arranged as pseudostratified epithelium. In tissue recombination models, only basal cells reconstitute a complete prostate gland, yet murine lineage-tracing experiments show that luminal cells generate basal cells. It has remained challenging to address the molecular details of these transitions and whether they apply to humans, due to the lack of culture conditions that recapitulate prostate gland architecture. Here, we describe a 3D culture system that supports long-term expansion of primary mouse and human prostate organoids, composed of fully differentiated CK5+ basal and CK8+ luminal cells. Organoids are genetically stable, reconstitute prostate glands in recombination assays, and can be experimentally manipulated. Single human luminal and basal cells give rise to organoids, yet luminal-cell-derived organoids more closely resemble prostate glands. These data support a luminal multilineage progenitor cell model for prostate tissue and establish a robust, scalable system for mechanistic studies.

ETS factors reprogram the androgen receptor cistrome and prime prostate tumorigenesis in response to PTEN loss

Studies of ETS-mediated prostate oncogenesis have been hampered by a lack of suitable experimental systems. Here we describe a new conditional mouse model that shows robust, homogenous ERG expression throughout the prostate. When combined with homozygous Pten loss, the mice developed accelerated, highly penetrant invasive prostate cancer. In mouse prostate tissue, ERG markedly increased androgen receptor (AR) binding. Robust ERG-mediated transcriptional changes, observed only in the setting of Pten loss, included the restoration of AR transcriptional output and upregulation of genes involved in cell death, migration, inflammation and angiogenesis. Similarly, ETS variant 1 (ETV1) positively regulated the AR cistrome and transcriptional output in ETV1-translocated, PTEN-deficient human prostate cancer cells. In two large clinical cohorts, expression of ERG and ETV1 correlated with higher AR transcriptional output in PTEN-deficient prostate cancer specimens. We propose that ETS factors cause prostate-specific transformation by altering the AR cistrome, priming the prostate epithelium to respond to aberrant upstream signals such as PTEN loss.

Androgen Receptor Signaling Regulates DNA Repair in Prostate Cancers

UNLABELLED We demonstrate that the androgen receptor (AR) regulates a transcriptional program of DNA repair genes that promotes prostate cancer radioresistance, providing a potential mechanism by which androgen deprivation therapy synergizes with ionizing radiation. Using a model of castration-resistant prostate cancer, we show that second-generation antiandrogen therapy results in downregulation of DNA repair genes. Next, we demonstrate that primary prostate cancers display a significant spectrum of AR transcriptional output, which correlates with expression of a set of DNA repair genes. Using RNA-seq and ChIP-seq, we define which of these DNA repair genes are both induced by androgen and represent direct AR targets. We establish that prostate cancer cells treated with ionizing radiation plus androgen demonstrate enhanced DNA repair and decreased DNA damage and furthermore that antiandrogen treatment causes increased DNA damage and decreased clonogenic survival. Finally, we demonstrate that antiandrogen treatment results in decreased classical nonhomologous end-joining. SIGNIFICANCE We demonstrate that the AR regulates a network of DNA repair genes, providing a potential mechanism by which androgen deprivation synergizes with radiotherapy for prostate cancer.

Identification of Different Classes of Luminal Progenitor Cells within Prostate Tumors

Primary prostate cancer almost always has a luminal phenotype. However, little is known about the stem/progenitor properties of transformed cells within tumors. Using the aggressive Pten/Tp53-null mouse model of prostate cancer, we show that two classes of luminal progenitors exist within a tumor. Not only did tumors contain previously described multipotent progenitors, but also a major population of committed luminal progenitors. Luminal cells, sorted directly from tumors or grown as organoids, initiated tumors of adenocarcinoma or multilineage histological phenotypes, which is consistent with luminal and multipotent differentiation potentials, respectively. Moreover, using organoids we show that the ability of luminal-committed progenitors to self-renew is a tumor-specific property, absent in benign luminal cells. Finally, a significant fraction of luminal progenitors survived in vivo castration. In all, these data reveal two luminal tumor populations with different stem/progenitor cell capacities, providing insight into prostate cancer cells that initiate tumors and can influence treatment response.

ERF mutations reveal a balance of ETS factors controlling prostate oncogenesis

Half of all prostate cancers are caused by the TMPRSS2–ERG gene-fusion, which enables androgens to drive expression of the normally silent E26 transformation-specific (ETS) transcription factor ERG in prostate cells. Recent genomic landscape studies of such cancers have reported recurrent point mutations and focal deletions of another ETS member, the ETS2 repressor factor ERF. Here we show these ERF mutations cause decreased protein stability and mostly occur in tumours without ERG upregulation. ERF loss recapitulates the morphological and phenotypic features of ERG gain in normal mouse prostate cells, including expansion of the androgen receptor transcriptional repertoire, and ERF has tumour suppressor activity in the same genetic background of Pten loss that yields oncogenic activity by ERG. In the more common scenario of ERG upregulation, chromatin immunoprecipitation followed by sequencing indicates that ERG inhibits the ability of ERF to bind DNA at consensus ETS sites both in normal and in cancerous prostate cells. Consistent with a competition model, ERF overexpression blocks ERG-dependent tumour growth, and ERF loss rescues TMPRSS2–ERG-positive prostate cancer cells from ERG dependency. Collectively, these data provide evidence that the oncogenicity of ERG is mediated, in part, by competition with ERF and they raise the larger question of whether other gain-of-function oncogenic transcription factors might also inactivate endogenous tumour suppressors.

Deletion of 3p13-14 locus spanning FOXP1 to SHQ1 cooperates with PTEN loss in prostate oncogenesis

A multigenic locus at 3p13-14, spanning FOXP1 to SHQ1, is commonly deleted in prostate cancer and lost broadly in a range of cancers but has unknown significance to oncogenesis or prognosis. Here, we report that FOXP1-SHQ1 deletion cooperates with PTEN loss to accelerate prostate oncogenesis and that loss of component genes correlates with prostate, breast, and head and neck cancer recurrence. We demonstrate that Foxp1-Shq1 deletion accelerates prostate tumorigenesis in mice in combination with Pten loss, consistent with the association of FOXP1-SHQ1 and PTEN loss observed in human cancers. Tumors with combined Foxp1-Shq1 and Pten deletion show increased proliferation and anaplastic dedifferentiation, as well as mTORC1 hyperactivation with reduced Akt phosphorylation. Foxp1-Shq1 deletion restores expression of AR target genes repressed in tumors with Pten loss, circumventing PI3K-mediated repression of the androgen axis. Moreover, FOXP1-SHQ1 deletion has prognostic relevance, with cancer recurrence associated with combined loss of PTEN and FOXP1-SHQ1 genes.Although the locus at 3p13-14 is commonly deleted in prostate cancer, the identity of the potential driver genes is still unclear. Here, the authors, using a PTEN loss-driven prostate cancer mouse model, show that a multigenic FOXP1-SHQ1 deletion is a driver event with prognostic value.

Abstract LB-018: Loss of function mutations of an ETS repressor expand the ETS positive subset of prostate cancer

Recent genomic profiling of both primary and metastatic prostate cancers has revealed novel loss-of-function point mutations and copy number deletions of the gene ERF, an ETS transcriptional repressor with a nearly identical DNA-binding domain to the TMPRSS2-ERG oncogene product. Furthermore, ERF homozygous loss or point mutations occur exclusive of the ERG upregulation that occurs in 50% of prostate cancers following fusion of androgen-regulated upstream genomic elements of TMPRSS2 to the ERG gene. We characterized the function of ERF, as well as its relationship to ERG using CRISPR and shRNA technology to investigate both normal prostate- and patient tumor-derived organoid cultures, as well as existing TMPRSS2-ERG positive models. In both normal prostate and tumor models lacking upregulated ERG, inhibition of the ERF repressor leads to an expansion of the androgen transcriptome, and recapitulates phenotypic features seen with ERG upregulation. Cistromic analysis reveals that ERF occupies androgen-receptor (AR) associated chromatin, overlapping with potential ERG sites. Accordingly, in the presence of the upregulated ERG oncogene, ERF is now unable to bind any AR associated chromatin, and the AR transcriptome is expanded. CRISPR-mediated loss of ERG in TMPRSS2-ERG positive models leads to a halt of tumor cell growth, but concomitant loss of the ERF repressor partially restores cellular proliferation. We conclude that ERF is an endogenous repressor of androgen signaling in normal prostatic tissue and a potential tumor suppressor in prostate cancer. It occupies chromatin associated with AR-regulated genes and inhibits their transcriptional regulation. Loss of ERF function, either by mutation or more frequently by competition with the TMPRSS2-ERG gene product, leads to an expansion of the androgen transcriptome. Thereby, the ETS positive subtype of prostate cancer, currently defined by an activating ETS fusion event (e.g. TMPRSS2-ERG) should be expanded to encompass genomic loss of a repressive ETS factor. Citation Format: Rohit Bose, Wassim Abida, Wouter Karthaus, Joshua Armenia, Phillip Iaquinta, John Wongvipat, Michael Doran, Haley Hieronymus, Philip Watson, Patrick Sullivan, Yupu Liang, Nikolaus Schultz, Charles Sawyers. Loss of function mutations of an ETS repressor expand the ETS positive subset of prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-018.

Development of novel metastatic prostate cancer cell lines by “organoid” in vitro culture technology.

33 Background: The inability to propagate patient-derived prostate cancer cells in vitro is a major impediment in the mechanistic understanding of tumorigenesis and therapeutic response. In order to generate accurate in vitro models that represent the diversity of in situ prostate cancer, we have developed a three-dimensional “organoid” system to culture metastasis samples and integrated it into our precision medicine workflow of attaining and characterizing pre-treatment biopsies. Methods: Biopsy samples of prostate cancer metastases, both soft tissue and bone, acquired at the time of therapeutic or diagnostic interventions following informed consent and institutional review board approval were obtained from two institutions. Samples were digested in Type II Collagenase (Gibco) and re-suspended in growth factor reduced Matrigel (BD), plated on plastic, and overlaid with prostate culture media (PCM). PCM consists of serum free Advanced DMEM/F12 (Gibco) with multiple growth factors optimized to propagate b...

Abstract PR3: The snoRNP assembly factor SHQ1 is a novel prostate cancer tumor suppressor gene

Approximately 50% of prostate tumors harbor the TMPRSS2-ERG translocation, but precisely how this mutation contributes to prostate cancer initiation and progression is unclear. In an effort to identify other causative mutations involved in prostate cancer, we previously performed an integrated genomic analysis of < 200 primary and advanced human prostate cancer samples and cell lines, including assessment of genomic copy-number alterations, mRNA expression, and focused exon sequencing. We identified a recurrent genomic loss, a focal region of chromosome 3p14.1-p13, which was significantly associated with TMPRSS2-ERG translocation. Comparison of copy-number and mRNA expression data implicated at least three genes in this region ( FOXP1, RYBP , and SHQ1 ) as potential cooperative tumor suppressors, which may function in concert with TMPRSS2-ERG translocation. In addition to the genomic loss of SHQ1 , we identified point mutations in both SHQ1 and its interacting partner DKC1/dyskerin in primary prostate tumors, leading us to focus on this SHQ1-dyskerin pathway as a potential tumor-suppressive mechanism. SHQ1 is a critical assembly factor for H/ACA-class snoRNA-containing snoRNPs (small nucleolar ribonucleoproteins), of which the core component is the RNA-modifying enzyme DKC1/dyskerin. Downstream targets of dyskerin-containing snoRNPs include the ribosome, splicesome, and telomerase RNPs. DKC1/dyskerin is mutated in the human syndrome dyskeratosis congenita (DC), a disease also caused by mutations in the telomerase complex, which results in bone marrow failure and increased incidence of various neoplasias. We found that, in both human prostate cancer cell lines and mouse fibroblasts in vitro, knockdown of SHQ1 led to increased growth and partial transformation, as evidenced by loss of anchorage-dependence. Additionally, loss of either SHQ1 or dyskerin in vitro led to a global impairment of snoRNA levels, confirming that snoRNA maturation is a major downstream target of the SHQ1-dyskerin pathway in prostate cancer cells. Strikingly, in a mouse model of prostate regeneration by sub-renal capsule implantation, SHQ1-loss in conjunction with ERG expression, but not SHQ1-loss alone, led to development of prostate intraepithelial neoplasia and a low incidence of invasive cancer. Finally, in an in vitro interaction assay, prostate cancer-derived mutations in either SHQ1 or dyskerin impaired their association, to a degree similar to that seen with mutations in dyskerin found in DC. These data, along with the identification of point mutations in both SHQ1 and DKC1/dyskerin in other human cancers, strongly implicate SHQ1 as a novel prostate cancer tumor suppressor gene, potentially acting via disruption of snoRNA maturation. This abstract is also presented as Poster C60. Citation Format: Phillip J. Iaquinta, Chee Wai Chua, Rosario Machado-Pinilla, Haley Hieronymus, John Wongvipat, U. Thomas Meier, Michael Shen, Charles L. Sawyers. The snoRNP assembly factor SHQ1 is a novel prostate cancer tumor suppressor gene [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr PR3.