LRIG1 is a pleiotropic androgen receptor-regulated feedback tumor suppressor in prostate cancer

LRIG1 has been reported to be a tumor suppressor in gastrointestinal tract and epidermis. However, little is known about the expression, regulation and biological functions of LRIG1 in prostate cancer (PCa). We find that LRIG1 is overexpressed in PCa, but its expression correlates with better patient survival. Functional studies reveal strong tumor-suppressive functions of LRIG1 in both AR+ and AR- xenograft models, and transgenic expression of LRIG1 inhibits tumor development in Hi-Myc and TRAMP models. LRIG1 also inhibits castration-resistant PCa and exhibits therapeutic efficacy in pre-established tumors. We further show that 1) AR directly transactivates LRIG1 through binding to several AR-binding sites in LRIG1 locus, and 2) LRIG1 dampens ERBB expression in a cell type-dependent manner and inhibits ERBB2-driven tumor growth. Collectively, our study indicates that LRIG1 represents a pleiotropic AR-regulated feedback tumor suppressor that functions to restrict oncogenic signaling from AR, Myc, ERBBs, and, likely, other oncogenic drivers.

Linking prostate cancer cell AR heterogeneity to distinct castration and enzalutamide responses

Expression of androgen receptor (AR) in prostate cancer (PCa) is heterogeneous but the functional significance of AR heterogeneity remains unclear. Screening ~200 castration-resistant PCa (CRPC) cores and whole-mount sections (from 89 patients) reveals 3 AR expression patterns: nuclear (nuc-AR), mixed nuclear/cytoplasmic (nuc/cyto-AR), and low/no expression (AR-/lo). Xenograft modeling demonstrates that AR+ CRPC is enzalutamide-sensitive but AR-/lo CRPC is resistant. Genome editing-derived AR+ and AR-knockout LNCaP cell clones exhibit distinct biological and tumorigenic properties and contrasting responses to enzalutamide. RNA-Seq and biochemical analyses, coupled with experimental combinatorial therapy, identify BCL-2 as a critical therapeutic target and provide proof-of-concept therapeutic regimens for both AR+/hi and AR-/lo CRPC. Our study links AR expression heterogeneity to distinct castration/enzalutamide responses and has important implications in understanding the cellular basis of prostate tumor responses to AR-targeting therapies and in facilitating development of novel therapeutics to target AR-/lo PCa cells/clones.

NANOG reprograms prostate cancer cells to castration resistance via dynamically repressing and engaging the AR/FOXA1 signaling axis

The pluripotency transcription factor NANOG has been implicated in tumor development, and NANOG-expressing cancer cells manifest stem cell properties that sustain tumor homeostasis, mediate therapy resistance and fuel tumor progression. However, how NANOG converges on somatic circuitry to trigger oncogenic reprogramming remains obscure. We previously reported that inducible NANOG expression propels the emergence of aggressive castration-resistant prostate cancer phenotypes. Here we first show that endogenous NANOG is required for the growth of castration-resistant prostate cancer xenografts. Genome-wide chromatin immunoprecipitation sequencing coupled with biochemical assays unexpectedly reveals that NANOG co-occupies a distinctive proportion of androgen receptor/Forkhead box A1 genomic loci and physically interacts with androgen receptor and Forkhead box A1. Integrative analysis of chromatin immunoprecipitation sequencing and time-resolved RNA sequencing demonstrates that NANOG dynamically alters androgen receptor/Forkhead box A1 signaling leading to both repression of androgen receptor-regulated pro-differentiation genes and induction of genes associated with cell cycle, stem cells, cell motility and castration resistance. Our studies reveal global molecular mechanisms whereby NANOG reprograms prostate cancer cells to a clinically relevant castration-resistant stem cell-like state driven by distinct NANOG-regulated gene clusters that correlate with patient survival. Thus, reprogramming factors such as NANOG may converge on and alter lineage-specific master transcription factors broadly in somatic cancers, thereby facilitating malignant disease progression and providing a novel route for therapeutic resistance.

ATXN7L3 and ENY2 Coordinate Activity of Multiple H2B Deubiquitinases Important for Cellular Proliferation and Tumor Growth

Histone H2B monoubiquitination (H2Bub1) is centrally involved in gene regulation. The deubiquitination module (DUBm) of the SAGA complex is a major regulator of global H2Bub1 levels, and components of this DUBm are linked to both neurodegenerative diseases and cancer. Unexpectedly, we find that ablation of USP22, the enzymatic center of the DUBm, leads to a reduction, rather than an increase, in global H2bub1 levels. In contrast, depletion of non-enzymatic components, ATXN7L3 or ENY2, results in increased H2Bub1. These observations led us to discover two H2Bub1 DUBs, USP27X and USP51, which function independently of SAGA and compete with USP22 for ATXN7L3 and ENY2 for activity. Like USP22, USP51 and USP27X are required for normal cell proliferation, and their depletion suppresses tumor growth. Our results reveal that ATXN7L3 and ENY2 orchestrate activities of multiple deubiquitinating enzymes and that imbalances in these activities likely potentiate human diseases including cancer.

Defining a Population of Stem-like Human Prostate Cancer Cells That Can Generate and Propagate Castration-Resistant Prostate Cancer

PURPOSE

We have shown that the phenotypically undifferentiated (PSA(-/lo)) prostate cancer cell population harbors long-term self-renewing cancer stem cells (CSC) that resist castration, and a subset of the cells within the PSA(-/lo) population bearing the ALDH(hi)CD44(+)α2β1(+) phenotype (Triple Marker(+)/TM(+)) is capable of robustly initiating xenograft tumors in castrated mice. The goal of the current project is to further characterize the biologic properties of TM(+) prostate cancer cell population, particularly in the context of initiating and propagating castration-resistant prostate cancer (CRPC).

EXPERIMENTAL DESIGN

The in vivo CSC activities were measured by limiting-dilution serial tumor transplantation assays in both androgen-dependent and androgen-independent prostate cancer xenograft models. In vitro clonal, clonogenic, and sphere-formation assays were conducted in cells purified from xenograft and patient tumors. qPCR, Western blot, lentiviral-mediated gene knockdown, and human microRNA arrays were performed for mechanistic studies.

RESULTS

By focusing on the LAPC9 model, we show that the TM(+) cells are CSCs with both tumor-initiating and tumor-propagating abilities for CRPC. Moreover, primary patient samples have TM(+) cells, which possess CSC activities in "castrated" culture conditions. Mechanistically, we find that (i) the phenotypic markers are causally involved in CRPC development; (ii) the TM(+) cells preferentially express castration resistance and stem cell-associated molecules that regulate their CSC characteristics; and (iii) the TM(+) cells possess distinct microRNA expression profiles and miR-499-5p functions as an oncomir.

CONCLUSIONS

Our results define the TM(+) prostate cancer cells as a population of preexistent stem-like cancer cells that can both mediate and propagate CRPC and highlight the TM(+) cell population as a therapeutic target. Clin Cancer Res; 22(17); 4505-16. ©2016 AACR.

Dissociated primary human prostate cancer cells coinjected with the immortalized Hs5 bone marrow stromal cells generate undifferentiated tumors in NOD/SCID-γ mice

Reconstitution of tumor development in immunodeficient mice from disaggregated primary human tumor cells is always challenging. The main goal of the present study is to establish a reliable assay system that would allow us to reproducibly reconstitute human prostate tumor regeneration in mice using patient tumor-derived single cells. Using many of the 114 untreated primary human prostate cancer (HPCa) samples we have worked on, here we show that: 1) the subcutaneum represents the most sensitive site that allows the grafting of the implanted HPCa pieces; 2) primary HPCa cells by themselves fail to regenerate tumors in immunodeficient hosts; 3) when coinjected in Matrigel with rUGM (rat urogenital sinus mesenchyme), CAF (carcinoma-associated fibroblasts), or Hs5 (immortalized bone marrow derived stromal) cells, primary HPCa cells fail to initiate serially transplantable tumors in NOD/SCID mice; and 4) however, HPCa cells coinjected with the Hs5 cells into more immunodeficient NOD/SCID-IL2Rγ(-/-) (NSG) mice readily regenerate serially transplantable tumors. The HPCa/Hs5 reconstituted 'prostate' tumors present an overall epithelial morphology, are of the human origin, and contain cells positive for AR, CK8, and racemase. Cytogenetic analysis provides further evidence for the presence of karyotypically abnormal HPCa cells in the HPCa/Hs5 tumors. Of importance, HPCa/Hs5 xenograft tumors contain EpCAM(+) cells that are both clonogenic and tumorigenic. Surprisingly, all HPCa/Hs5 reconstituted tumors are undifferentiated, even for HPCa cells derived from Gleason 7 tumors. Our results indicate that primary HPCa cells coinjected with the immortalized Hs5 stromal cells generate undifferentiated tumors in NSG mice and we provide evidence that undifferentiated HPCa cells might be the cells that possessed tumorigenic potential and regenerated HPCa/Hs5 xenograft tumors.

The PSA(-/lo) prostate cancer cell population harbors self-renewing long-term tumor-propagating cells that resist castration

Prostate cancer (PCa) is heterogeneous and contains both differentiated and undifferentiated tumor cells, but the relative functional contribution of these two cell populations remains unclear. Here we report distinct molecular, cellular, and tumor-propagating properties of PCa cells that express high (PSA(+)) and low (PSA(-/lo)) levels of the differentiation marker PSA. PSA(-/lo) PCa cells are quiescent and refractory to stresses including androgen deprivation, exhibit high clonogenic potential, and possess long-term tumor-propagating capacity. They preferentially express stem cell genes and can undergo asymmetric cell division to generate PSA(+) cells. Importantly, PSA(-/lo) PCa cells can initiate robust tumor development and resist androgen ablation in castrated hosts, and they harbor highly tumorigenic castration-resistant PCa cells that can be prospectively enriched using ALDH(+)CD44(+)α2β1(+) phenotype. In contrast, PSA(+) PCa cells possess more limited tumor-propagating capacity, undergo symmetric division, and are sensitive to castration. Altogether, our study suggests that PSA(-/lo) cells may represent a critical source of castration-resistant PCa cells.

Abstract C68: Phenotypic and functional heterogeneity of prostate cancer stem cells

Recent evidence in many tumor systems suggests that there may exist several or even many tumorigenic subpopulations in each tumor. Utilizing 4 xenograft human prostate cancer (PCa) models, including two AR+/PSA+ (LAPC9 and LAPC4) and two AR-/PSA- (Du145 and PC3) xenografts, and by performing exhaustive limiting-dilution tumor regeneration assays in NOD/SCID mice using purified PCa cells based on functional properties (i.e., side population and Aldefluor assays) or preferential expression of surface markers (ABCG2, CD44, or integrin α2β1), we provide evidence for both the phenotypic and functional heterogeneity of PCa stem cells (i.e., PCa cell subpopulations with enhanced tumor-regeneration activity). Our results show that no single marker or assay seems to be able to capture all tumorigenic subsets in all 4 xenografts. We further show that different tumor-initiating subpopulations appear to co-exist in a common tumorigenic pool. We also demonstrate that some tumorigenic PCa cells overexpress stem cell-associated gene expression profiles. Finally, we provide evidence that primary prostate tumors possess subsets of tumor cells that bear similar phenotypic features to those in xenografts. Our results raise the possibility that different PCa patient tumors may harbor CSCs with distinct phenotypic and functional properties.

Note: This abstract was not presented at the conference because the presenter was unable to attend.

Citation Format: Xin Liu, Xin Chen, Brian Laffin, Binglan Yin, Tammy Calhoun-Davis, Feng Wang-Johanning, Dean G. Tang. Phenotypic and functional heterogeneity of prostate cancer stem cells [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 C68.

NANOG promotes cancer stem cell characteristics and prostate cancer resistance to androgen deprivation

Cancer cell molecular mimicry of stem cells (SC) imbues neoplastic cells with enhanced proliferative and renewal capacities. In support, numerous mediators of SC self-renewal have been evinced to exhibit oncogenic potential. We have recently reported that shRNA-mediated knockdown of the embryonic stem cell (ESC) self-renewal gene NANOG significantly reduced the clonogenic and tumorigenic capabilities of various cancer cells. In this study, we sought to test the potential pro-tumorigenic functions of NANOG, particularly, in prostate cancer (PCa). Using quantitative RT-PCR, we first confirmed that PCa cells expressed NANOG mRNA primarily from the NANOGP8 locus on chromosome 15q14. We then constructed a lentiviral promoter reporter in which the -3.8 kb NANOGP8 genomic fragment was used to drive the expression of green fluorescence protein (GFP). We observed that NANOGP8-GFP⁺ PCa cells exhibited cancer stem cell (CSC) characteristics such as enhanced clonal growth and tumor regenerative capacity. To further investigate the functions and mechanisms of NANOG in tumorigenesis, we established tetracycline-inducible NANOG overexpressing cancer cell lines, including both prostate (Du145 and LNCaP) and breast (MCF-7) cancer cells. NANOG induction promoted drug-resistance in MCF-7 cells, tumor regeneration in Du145 cells, and, most importantly, castration-resistant tumor development in LNCaP cells. These pro-tumorigenic effects of NANOG were associated with key molecular changes, including an upregulation of molecules such as CXCR4, IGFBP5, CD133 and ALDH1. The present gain-of-function studies, coupled with our recent loss-of-function work, establish the integral role for NANOG in neoplastic processes and shed light on its mechanisms of action.

Abstract 476: Defining two populations of prostate cancer cells with distinct molecular, biological, and tumor-propagating properties

Prostate cancer (PCa) is a heterogeneous malignancy containing different types of tumor cells. The cellular basis underlying PCa cell heterogeneity and functional importance of different PCa cell populations in maintaining tumor homeostasis and mediating castration-resistant progression remain poorly understood. By whole-genome microarray analysis, time-lapse videomicroscopy, serial tumor transplantations, and other functional assays, here we report the distinct molecular, cell biological, and tumor-propagating properties of PCa cells that express high (i.e., PSA+) and low (PSA−/lo) levels of PSA. PSA−/lo PCa cells are relatively quiescent and resistant to multiple stresses, exhibit high clonogenic potential, and possess long-term tumor-propagating capacity in intact male mice. They preferentially express stem cell-associated genes and epigenetic profiles and can generate PSA+ cells by either asymmetric or symmetric cell division. Of great clinic significance, PSA−/lo PCa cells can initiate robust tumor development in fully castrated hosts and survive experimental androgen-deprivation therapy. In contrast, PSA+ PCa cells, despite being highly tumorigenic in androgen-proficient hosts, possess more limited tumor-propagating capacity, mainly undergo symmetric division, and are sensitive to castration. Our data together suggest that the two populations of PCa cells appear to play differential roles in tumor maintenance and PSA−/lo cells may represent an important source of castration-resistant PCa cells. Our findings have important implications in understanding PCa cell heterogeneity, tumor response to the mainstay antiandrogen therapies, and emergence of castration-resistant PCa.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 476. doi:10.1158/1538-7445.AM2011-476

Functional evidence that the self-renewal gene NANOG regulates human tumor development

Tumor development has long been known to resemble abnormal embryogenesis. The embryonic stem cell (ESC) self-renewal gene NANOG is purportedly expressed by some epithelial cancer cells but a causal role in tumor development has remained unclear. Here, we provide compelling evidence that cultured cancer cells, as well as xenograft- and human primary prostate cancer cells express a functional variant of NANOG. NANOG mRNA in cancer cells is derived predominantly from a retrogene locus termed NANOGP8. NANOG protein is detectable in the nucleus of cancer cells and is expressed higher in patient prostate tumors than matched benign tissues. NANOGP8 mRNA and/or NANOG protein levels are enriched in putative cancer stem/progenitor cell populations. Importantly, extensive loss-of-function analysis reveals that RNA interference-mediated NANOG knockdown inhibits tumor development, establishing a functional significance for NANOG expression in cancer cells. Nanog short hairpin RNA transduced cancer cells exhibit decreased long-term clonal and clonogenic growth, reduced proliferation and, in some cases, altered differentiation. Thus, our results demonstrate that NANOG, a cell-fate regulatory molecule known to be important for ESC self-renewal, also plays a novel role in tumor development.

Critical and distinct roles of p16 and telomerase in regulating the proliferative life span of normal human prostate epithelial progenitor cells

Normal human prostate (NHP) epithelial cells undergo senescence in vitro and in vivo, but the underlying molecular mechanisms remain obscure. Here we show that the senescence of primary NHP cells, which are immunophenotyped as intermediate basal-like cells expressing progenitor cell markers CD44, alpha2beta1, p63, hTERT, and CK5/CK18, involves loss of telomerase expression, up-regulation of p16, and activation of p53. Using genetically defined manipulations of these three signaling pathways, we show that p16 is the primary determinant of the NHP cell proliferative capacity and that hTERT is required for unlimited proliferative life span. Hence, suppression of p16 significantly extends NHP cell life span, but both p16 inhibition and hTERT are required to immortalize NHP cells. Importantly, immortalized NHP cells retain expression of most progenitor markers, demonstrate gene expression profiles characteristic of proliferating progenitor cells, and possess multilineage differentiation potential generating functional prostatic glands. Our studies shed important light on the molecular mechanisms regulating the proliferative life span of NHP progenitor cells.

PC3 human prostate carcinoma cell holoclones contain self-renewing tumor-initiating cells

Primary keratinocytes exhibit three typical clonal morphologies represented by holoclones, meroclones, and paraclones, with holoclones containing self-renewing stem cells, and meroclones and paraclones containing more mature and differentiated cells. Interestingly, long-term-cultured human epithelial cancer cells in clonal cultures also form holoclones, meroclones, and paraclones, and tumor cell holoclones have been hypothesized to harbor stem-like cells or cancer stem cells. However, the key question of whether tumor cell holoclones genuinely contain tumor-initiating cells has not been directly addressed. Here, using PC3 human prostate carcinoma cells as a model, we provide direct experimental evidence that tumor cell holoclones contain stem-like cells that can initiate serially transplantable tumors. Importantly, holoclones derived from either cultured PC3 cells or holoclone-initiated tumors can be serially passaged and regenerate all three types of clones. In contrast, meroclones and paraclones cannot be continuously propagated and fail to initiate tumor development. Phenotypic characterizations reveal high levels of CD44, alpha(2)beta(1) integrin, and beta-catenin expression in holoclones, whereas meroclones and paraclones show markedly reduced expression of these stem cell markers. The present results have important implications in understanding morphologic heterogeneities and tumorigenic hierarchies in human epithelial cancer cells.

Evidence that senescent human prostate epithelial cells enhance tumorigenicity: cell fusion as a potential mechanism and inhibition by p16INK4a and hTERT

Normal human prostate (NHP) epithelial cells undergo senescence in vitro and in vivo but the potential role of senescent NHP cells in prostate tumorigenesis remain unclear. Here we show that senescent NHP cells enhance the in vivo tumorigenicity of low-tumorigenic LNCaP prostate cancer and low/non-tumorigenic subset of cells (called L cells) isolated from multiple bulk-cultured prostate (and other) cancer cell lines. Subsequent studies suggest cell-cell fusion as a potential mechanism for senescent NHP cell-enhanced tumor development. Using fluorescently tagged tumor cells and/or NHP cells, we find that NHP cells, like fibroblasts, can undergo fusion with unfractionated tumor cells or the L cells. Using 293T-L cells as the model cell system, we verify NHP and 293T-L cell fusion by using differential RT-PCR, karyotyping, and gene expression analyses. Further experiments demonstrate that senescent NHP cells that have lost progenitor markers, accumulated p16INK4a (p16) protein expression, and acquired the AR mRNA expression, appear to be the preferential fusion targets. Strikingly, the tumorigenicity of the NHP/293T-L hybrid cells was inhibited by exogenous p16 as well as hTERT. Chromosomal analyses revealed that hTERT probably inhibited the in vivo tumorigenicity by maintaining genomic stability. These results suggest that senescent NHP cells, like senescent fibroblasts, may promote tumor development and that one of the mechanisms underlying the senescent NHP cell-enhanced tumorigenicity could be through cell fusion.

Hierarchical organization of prostate cancer cells in xenograft tumors: the CD44+alpha2beta1+ cell population is enriched in tumor-initiating cells

Prostate cancer cells are heterogeneous in their tumorigenicity. For example, the side population cells isolated from LAPC9 xenografts are 100 to 1,000 times more tumorigenic than the corresponding non-side population cells. Highly purified CD44(+) prostate cancer cells from several xenografts are also enriched in prostate cancer stem/progenitor cells. Because the CD44(+) prostate cancer cell population is still heterogeneous, we wonder whether we could further enrich for tumorigenic prostate cancer cells in this population using other markers. Integrin alpha2beta1 has been proposed to mark a population of normal human prostate stem cells. Therefore, we first asked whether the alpha2beta1(+/hi) cells in prostate tumors might also represent prostate cancer stem cells. Highly purified (> or =98%) alpha2beta1(+/hi) cells from three human xenograft tumors, Du145, LAPC4, and LAPC9, show higher clonal and clonogenic potential than the alpha2beta1(-/lo) cells in vitro. However, when injected into the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse prostate or s.c., the alpha2beta1(+/hi) prostate cancer cells are no more tumorigenic than the alpha2beta1(-/lo) cells. Immunofluorescence studies reveal that CD44 and alpha2beta1 identify an overlapping and inclusive population of prostate cancer cells in that approximately 70% of alpha2beta1(+/hi) cells are CD44(+) and 20% to 30% of CD44(+) cells are distributed in the alpha2beta1(-/lo) cell population. Subsequently, we sorted out CD44(+)alpha2beta1(+/hi), CD44(+)alpha2beta1(-/lo), CD44(-)alpha2beta1(+/hi), and CD44(-)alpha2beta1(-/lo) cells from LAPC9 tumors and carried out tumorigenicity experiments. The results revealed a hierarchy in tumorigenic potential in the order of CD44(+)alpha2beta1(+/hi) approximately CD44(+)alpha2beta1(-/lo) > CD44(-)alpha2beta1(+/hi) >> CD44(-)alpha2beta1(-/lo). These observations together suggest that prostate cancer cells are organized as a hierarchy.