Development of a three-dimensional culture model of prostatic epithelial cells and its use for the study of epithelial-mesenchymal transition and inhibition of PI3K pathway in prostate cancer

Nuclear receptor NURR1 functions to promote stemness and epithelial-mesenchymal transition in prostate cancer via its targeting of Wnt/β-catenin signaling pathway

Dysregulated activation of Wnt/β-catenin signaling pathway is a frequent or common event during advanced progression of multiple cancers. With this signaling activation, it enhances their tumorigenic growth and facilitates metastasis and therapy resistance. Advances show that this signaling pathway can play dual regulatory roles in the control of cellular processes epithelial-mesenchymal transition (EMT) and cancer stemness in cancer progression. Aberrant activation of Wnt/β-catenin signaling pathway is shown to be common in prostate cancer and also castration-resistant prostate cancer (CRPC). However, the transcriptional regulators of this pathway in prostate cancer are still not well characterized. NURR1 (NR4A2) is an orphan nuclear receptor and plays an important role in the development of dopaminergic neurons. Previously, we have shown that NURR1 exhibits an upregulation in isolated prostate cancer stem-like cells (PCSCs) and a xenograft model of CRPC. In this study, we further confirmed that NURR1 exhibited an upregulation in prostate cancer and also enhanced expression in prostate cancer cell lines. Functional and molecular analyses showed that NURR1 could act to promote both in vitro (cancer stemness and EMT) and also in vivo oncogenic growth of prostate cancer cells (metastasis and castration resistance) via its direct transactivation of CTNNB1 (β-catenin) and activation of β-catenin to mediate the activation of Wnt/β-catenin signaling pathway. Moreover, we also demonstrated that NURR1 activity in prostate cancer cells could be modulated by small molecules, implicating that NURR1 could be a potential therapeutic target for advanced prostate cancer management.

Transforming Growth Factor Beta-1 (TGF-β1) Regulates Assembly of Cardiac Spheroids

Cells of all tissues in human body interact with their neighboring cells and components of the extracellular matrix thereby creating a unique 3D microenvironment. These interactions are realized through a complex network of biochemical and mechanical signals that are important in maintaining normal cellular homeostasis. Numerous attempts have been undertaken during the last two decades to develop 3D models for studying their properties and understanding the mechanisms of regulation of cell microenvironment in vivo. Cardiac spheroids (cardiospheres) are one these models of cardiac microenvironment. In this study we demonstrate that unique microenvironment formed in cardiospheres consists of stem/progenitor and mesenchymal cells surrounded by extracellular matrix proteins synthesized by these cells. TGF-β1 participates in the regulation of contraction of cells forming cardiospheres, promotes activation of the epithelial-mesenchymal transition and self-organization of cells, which leads to the formation of larger spheroids. Thereby, the effect of TGF-β1 on the cells of cardiospheres can serve as a model for studying the mechanisms of regulation of cardiac microenvironment.

Three-Dimensional Cell Cultures as an In Vitro Tool for Prostate Cancer Modeling and Drug Discovery

In the last decade, three-dimensional (3D) cell culture technology has gained a lot of interest due to its ability to better recapitulate the in vivo organization and microenvironment of in vitro cultured cancer cells. In particular, 3D tumor models have demonstrated several different characteristics compared with traditional two-dimensional (2D) cultures and have provided an interesting link between the latter and animal experiments. Indeed, 3D cell cultures represent a useful platform for the identification of the biological features of cancer cells as well as for the screening of novel antitumor agents. The present review is aimed at summarizing the most common 3D cell culture methods and applications, with a focus on prostate cancer modeling and drug discovery.

Nuclear receptor HNF4α performs a tumor suppressor function in prostate cancer via its induction of p21-driven cellular senescence

Hepatocyte nuclear factor 4α (HNF4α, NR2A1) is a highly conserved member of the nuclear receptor superfamily. Recent advances reveal that it is a key transcriptional regulator of genes, broadly involved in xenobiotic and drug metabolism and also cancers of gastrointestinal tract. However, the exact functional roles of HNF4α in prostate cancer progression are still not fully understood. In this study, we determined the functional significance of HNF4α in prostate cancer. Our results showed that HNF4α exhibited a reduced expression pattern in clinical prostate cancer tissues, prostate cancer cell lines and xenograft model of castration-relapse prostate cancer. Stable HNF4α knockdown not only could promote cell proliferation and suppress doxorubicin (Dox)-induced cellular senescence in prostate cancer cells, but also confer resistance to paclitaxel treatment and enhance colony formation capacity and in vivo tumorigenicity of prostate cancer cells. On the contrary, ectopic overexpression of HNF4α could significantly inhibit the cell proliferation of prostate cancer cells, induce cell-cycle arrest at G₂/M phase and trigger the cellular senescence in prostate cancer cells by activation of p21 signal pathway in a p53-independent manner via its direct transactivation of CDKN1A. Together, our results show that HNF4α performs a tumor suppressor function in prostate cancer via a mechanism of p21-driven cellular senescence.

Ex-Vivo Model Systems of Cancer-Bone Cell Interactions

This chapter elaborates on the state-of-the-art experimental procedures utilized in ex-vivo model systems of cancer-bone cell interactions under "static and dynamic" culture conditions and their potential use to understand cellular and molecular mechanisms as well as drug testing and discovery. An additional focus of this chapter is to provide details of how to incorporate varying oxygen tension, viz., hypoxic, normoxic, and hyperoxic, in such studies and regulate the bone biology toward dissociation of the bone remodeling stages to achieve only "bone resorption" or "bone formation" individually.

Nuclear receptor ERRα and transcription factor ERG form a reciprocal loop in the regulation of TMPRSS2:ERG fusion gene in prostate cancer

The TMPRSS2:ERG (T:E) fusion gene is generally believed to be mainly regulated by the activated androgen receptor (AR) signaling in androgen-dependent prostate cancer. However, its persistent expression in castration-resistant and neuroendocrine prostate cancers implies that other transcription factors might also regulate its expression. Here, we showed that up-regulation of nuclear receptor estrogen-related receptor alpha (ERRα) was closely associated with the oncogenic transcription factor ERG expression in prostate cancer, and their increased coexpression patterns were closely associated with high Gleason scores and metastasis in patients. Both ERRα and ERG exhibited a positive expression correlation in a castration-resistant prostate cancer (CRPC) xenograft model VCaP-CRPC. We showed that ERRα could directly transactivate T:E fusion gene in both AR-positive and -negative prostate cancer cells via both ERR-binding element- and AR-binding element-dependent manners. Ectopic T:E expression under ERRα regulation could promote both in vitro invasion and in vivo metastasis capacities of AR-negative prostatic cells. Intriguingly, ERG expressed by the T:E fusion could also transactivate the ERRα (ESRRA) gene. Hereby, ERRα and ERG can synergistically regulate each other and form a reciprocal regulatory loop to promote the advanced growth of prostate cancer. Inhibition of ERRα activity by ERRα inverse agonist could suppress T:E expression in prostate cancer cells, implicating that targeting ERRα could be a potential therapeutic strategy for treating the aggressive T:E-positive prostate cancer.

HPV16-Immortalized Cells from Human Transformation Zone and Endocervix are More Dysplastic than Ectocervical Cells in Organotypic Culture

A major risk factor for cervical cancer is persistent infection with high-risk human papillomaviruses (HPV) which can cause cervical intraepithelial neoplasia. Greater than 90% of cervical cancers develop in the transformation zone (TZ), a small region of metaplastic squamous epithelium at the squamocolumnar junction between endocervix and ectocervix. However, it is unclear why this region is highly susceptible to malignant progression. We hypothesized that cells from TZ were more susceptible to dysplastic differentiation, a precursor to cervical cancer. We used three-dimensional organotypic culture to compare differentiation of HPV16-immortalized epithelial cell lines derived from ectocervix, TZ, and endocervix. We show that immortal cells from TZ or endocervix form epithelia that are more dysplastic than immortal cells from ectocervix. A higher percentage of immortal cells from TZ and endocervix express the proliferation marker Ki-67 and are positive for phospho-Akt. Immortal cells from TZ and endocervix invade collagen rafts and express increased levels of matrix metalloproteinase-1. Inhibition of MMP-1 or Akt activity blocks invasion. We conclude that HPV16-immortalized cells cultured from TZ or endocervix are more susceptible to dysplastic differentiation, and this might enhance their susceptibility to cervical cancer.

Development of a novel and economical agar-based non-adherent three-dimensional culture method for enrichment of cancer stem-like cells

BACKGROUND

Non-adherent or ultra-low attachment three-dimensional (3D) culture, also called sphere formation assay, has been widely used to assess the malignant phenotype and stemness potential of transformed or cancer cells. This method is also popularly used to isolate the cancer stem-like cells (CSCs) or tumor-initiating cells based on their unique anchorage-independent growth or anoikis-resistant capacity. Different non-adhesive coating agents, such as poly-2-hydroxyethyl methacrylate (poly-HEMA) and synthetic hydrogels, have been used in this non-adherent 3D culture. However, preparation of non-adherent culture-ware is labor-intensive and technically demanding, and also costs of commercial non-adherent culture-ware prepared with various coating agents are relatively expensive and the culture-ware cannot be used repeatedly.

METHODS

In this study, we developed a non-adherent 3D culture method based on agar coating for growing tumor spheres derived from various cancer cell lines and primary prostate cancer tissues under a non-adherent and serum-free condition. The tumor spheres generated by this 3D culture method were analyzed on their expression profiles of CSC-associated markers by reverse transcription quantitative polymerase chain reaction, presence and relative proportion of CSCs by fluorescence-activated cell sorting (CD133⁺/CD44⁺ cell sorting) and also a CSC-visualizing reporter system responsive to OCT4 and SOX2 (SORE6), and in vivo tumorigenicity. The repeated use of agar-coated plates for serial passages of tumor spheres was also evaluated.

RESULTS

Our results validated that the multicellular tumor spheres generated by this culture method were enriched of CSCs, as evidenced by their enhanced expression profiles of CSC markers, presence of CD133⁺/CD44⁺ or SORE6⁺ cells, enhanced self-renewal capacity, and in vivo tumorigenicity, indicating its usefulness in isolation and enrichment of CSCs. The agar-coated plates could be used multiple times in serial passages of tumor spheres.

CONCLUSIONS

The described agar-based 3D culture method offers several advantages as compared with other methods in isolation of CSCs, including its simplicity and low-cost and repeated use of agar-coated plates for continuous passages of CSC-enriched spheres.

Recent advances in prostate cancer research: large-scale genomic analyses reveal novel driver mutations and DNA repair defects

Prostate cancer (PCa) is a disease of mutated and misregulated genes. However, primary prostate tumors have relatively few mutations, and only three genes ( ERG, PTEN, and SPOP) are recurrently mutated in more than 10% of primary tumors. On the other hand, metastatic castration-resistant tumors have more mutations, but, with the exception of the androgen receptor gene ( AR), no single gene is altered in more than half of tumors. Structural genomic rearrangements are common, including ERG fusions, copy gains involving the MYC locus, and copy losses containing PTEN. Overall, instead of being associated with a single dominant driver event, prostate tumors display various combinations of modifications in oncogenes and tumor suppressors. This review takes a broad look at the recent advances in PCa research, including understanding the genetic alterations that drive the disease and how specific mutations can sensitize tumors to potential therapies. We begin with an overview of the genomic landscape of primary and metastatic PCa, enabled by recent large-scale sequencing efforts. Advances in three-dimensional cell culture techniques and mouse models for PCa are also discussed, and particular emphasis is placed on the benefits of patient-derived xenograft models. We also review research into understanding how ETS fusions (in particular, TMPRSS2-ERG) and SPOP mutations contribute to tumor initiation. Next, we examine the recent findings on the prevalence of germline DNA repair mutations in about 12% of patients with metastatic disease and their potential benefit from the use of poly(ADP-ribose) polymerase (PARP) inhibitors and immune modulation. Lastly, we discuss the recent increased prevalence of AR-negative tumors (neuroendocrine and double-negative) and the current state of immunotherapy in PCa. AR remains the primary clinical target for PCa therapies; however, it does not act alone, and better understanding of supporting mutations may help guide the development of novel therapeutic strategies.

EMT/MET at the Crossroad of Stemness, Regeneration and Oncogenesis: The Ying-Yang Equilibrium Recapitulated in Cell Spheroids

The epithelial-to-mesenchymal transition (EMT) is an essential trans-differentiation process, which plays a critical role in embryonic development, wound healing, tissue regeneration, organ fibrosis, and cancer progression. It is the fundamental mechanism by which epithelial cells lose many of their characteristics while acquiring features typical of mesenchymal cells, such as migratory capacity and invasiveness. Depending on the contest, EMT is complemented and balanced by the reverse process, the mesenchymal-to-epithelial transition (MET). In the saving economy of the living organisms, the same (Ying-Yang) tool is integrated as a physiological strategy in embryonic development, as well as in the course of reparative or disease processes, prominently fibrosis, tumor invasion and metastasis. These mechanisms and their related signaling (e.g., TGF-β and BMPs) have been effectively studied in vitro by tissue-derived cell spheroids models. These three-dimensional (3D) cell culture systems, whose phenotype has been shown to be strongly dependent on TGF-β-regulated EMT/MET processes, present the advantage of recapitulating in vitro the hypoxic in vivo micro-environment of tissue stem cell niches and their formation. These spheroids, therefore, nicely reproduce the finely regulated Ying-Yang equilibrium, which, together with other mechanisms, can be determinant in cell fate decisions in many pathophysiological scenarios, such as differentiation, fibrosis, regeneration, and oncogenesis. In this review, current progress in the knowledge of signaling pathways affecting EMT/MET and stemness regulation will be outlined by comparing data obtained from cellular spheroids systems, as ex vivo niches of stem cells derived from normal and tumoral tissues. The mechanistic correspondence in vivo and the possible pharmacological perspective will be also explored, focusing especially on the TGF-β-related networks, as well as others, such as SNAI1, PTEN, and EGR1. This latter, in particular, for its ability to convey multiple types of stimuli into relevant changes of the cell transcriptional program, can be regarded as a heterogeneous "stress-sensor" for EMT-related inducers (growth factor, hypoxia, mechano-stress), and thus as a therapeutic target.

Identification of endonuclease domain-containing 1 as a novel tumor suppressor in prostate cancer

BACKGROUND

Endonuclease domain containing 1 (ENDOD1) is implicated in tumorigenesis and aggressiveness of multiple tumors. In this study, we aimed to investigate the role of ENDOD1 in prostate cancer (PCa).

METHODS

Immunohistochemistry were performed in 30 cases of benign prostatic hyperplasia (BPH) and 50 cases of PCa to identify its association with clinicopathological characteristics. Real-time PCR and western blot were used to detect ENDOD1 mRNA and protein expression in normal prostatic epithelial and PCa cell lines. MTT assays were employed to determine the effect of cell proliferation. Flow cytometry was used to explore the cell cycle distribution and apoptotic effects. Transwell migration and invasion assays were done to evaluate changes in the ability of cell migration and invasion.

RESULTS

Immunoreactivity scores of ENDOD1 showed no statistical difference between BPH and low-grade PCa, whereas lower immunostaining scores were observed in high-grade compared with low-grade PCa. Real-time PCR data indicated that ENDOD1 mRNA expression was markedly increased in LNCaP and 22Rv1 cells and decreased in PC3 and DU145 cells compared to the normal epithelial cells RWPE1. Western blot showed that androgen-sensitive LNCaP cells had the highest protein expression level of ENDOD1, whereas castration-resistant PCa cell lines PC3 and DU145 had significantly lower protein levels. Meanwhile, overexpression of ENDOD1 suppressed cell proliferation, induced G0/G1 cell cycle arrest and inhibited cell migration and invasion. Conversely, siRNA-mediated silencing of ENDOD1 promoted cell proliferation, migration and invasion. No apoptotic effects occurred upon manipulation of ENDOD1 expression.

CONCLUSION

Our results indicate that ENDOD1 is a novel tumor suppressor in PCa, which may be employed as a new drug target of preventing progression to metastatic castration-resistant prostate cancer.

Bone: A Fertile Soil for Cancer Metastasis

Bone is one of the most common and most dangerous sites for metastatic growth across cancer types, and bone metastasis remains incurable. Unfortunately, the processes by which cancers preferentially metastasize to bone are still not well understood. In this review, we summarize the morphological features, physical properties, and cell signaling events that make bone a unique site for metastasis and bone remodeling. The signaling crosstalk between the tumor cells and bone cells begins a vicious cycle - a self-sustaining feedback loop between the tumor cells and the bone microenvironment composed of osteoclasts, osteoblasts, other bone marrow cells, bone matrix, and vasculature to support both tumor growth and bone destruction. Through this crosstalk, bone provides a fertile microenvironment that can harbor dormant tumor cells, sometimes for long periods, and support their growth by releasing cytokines as the bone matrix is destroyed, similar to providing nutrients for a seed to germinate in soil. However, few models exist to study the late stages of bone colonization by metastatic tumor cells. We describe some of the current methodologies used to study bone metastasis, highlighting the limitations of these methods and alternative future strategies to be used to study bone metastasis. While <i>in vivo</i> animal and patient studies may provide the gold standard for studying metastasis, <i>ex vivo</i> models can be used as an alternative to enable more controlled experiments designed to study the late stages of bone metastasis.

Collapsin response mediator protein-1 (CRMP1) acts as an invasion and metastasis suppressor of prostate cancer via its suppression of epithelial-mesenchymal transition and remodeling of actin cytoskeleton organization

The cancer cells can acquire migration and invasion capacities during the metastasis process through the developmental regulatory program epithelial–mesenchymal-transition (EMT), and through its reverse process mesenchymal–epithelial transition cancer cells can recolonize at distant metastatic sites. Among the multifaceted effects exerted by this program, reorganization of actin cytoskeleton is the key mechanical drive for the invasive properties gained by cancer cells. Collapsin response mediator protein-1 (CRMP1) is a cytosolic phosphoprotein and originally characterized as the mediator of semaphorin 3A signaling involved in axon differentiation during neural development. Here we report that CRMP1 can act as a suppressor of tumorigenicity and metastasis in prostate cancer cells. We demonstrated that CRMP1 exhibited a decreased expression pattern in high-grade prostate cancer tissues and many prostate cancer cell lines, and its downregulation in cancer cells was attributed to histone deacetylation and direct repression of its gene by the EMT regulator Snail. Functional analyses revealed that CRMP1 suppressed EMT in prostate cancer cells, as its knockdown could trigger EMT and enhance in vitro invasion capacity, whereas its overexpression could inhibit EMT and suppress both in vitro invasion and in vivo metastasis capacities of prostate cancer cells. Moreover, CRMP1 overexpression could significantly confer resistance to EMT induced by Snail or transforming growth factor-β1 in prostatic epithelial cells and prostate cancer cells. Finally, we demonstrated that CRMP1 could associate with actin and WAVE1, an activator of actin nucleation complex Arp2/3, and also its knockdown could stabilize F-actin and trigger the formation of stress fibers in prostate cancer cells. Together, our study shows that CRMP1 acts an EMT and metastasis suppressor in prostate cancer cells via its regulation of actin polymerization and also suggests that targeting the CRMP1-actin signaling in actin organization could be a potential strategy for management of prostate cancer metastasis.

The Deleted in Liver Cancer 1 (Dlc1) tumor suppressor is haploinsufficient for mammary gland development and epithelial cell polarity

BACKGROUND

Deleted in Liver Cancer 1 (Dlc1) is a tumor suppressor gene, which maps to human chromosome 8p21-22 and is found frequently deleted in many cancers including breast cancer. The promoter of the remaining allele is often found methylated. The Dlc1 gene encodes a RhoGAP protein that regulates cell proliferation, migration and inhibits cell growth and invasion when restored in Dlc1 deficient tumor cell lines. This study focuses on determining the role of Dlc1 in normal mammary gland development and epithelial cell polarity in a Dlc1 gene trapped (gt) mouse.

METHODS

Mammary gland whole mount preparations from 10-week virgin heterozygous Dlc1(gt/+) gene-trapped mice were compared with age-matched wild type (WT) controls. Hematoxylin-Eosin (H&E) and Masson's Trichrome staining of histological sections were carried out. Mammary glands from Dlc1(gt/+) mice and WT controls were enzymatically digested with collagenase and dispase and then cultured overnight to deplete hematopoietic and endothelial cells. The single cell suspensions were then cultured in Matrigel for 12 days. To knockdown Dlc1 expression, primary WT mammary epithelial cells were infected with short hairpin (sh) RNA expressing lentivirus or with a scrambled shRNA control.

RESULTS

Dlc1(gt/+) mice showed anomalies in the mammary gland that included increased ductal branching and deformities in terminal end buds and branch points. Compared to the WT controls, Masson's Trichrome staining showed a thickened stromal layer with increased collagen deposition in mammary glands from Dlc1(gt/+) mice. Dlc1(gt/+) primary mammary epithelial cells formed increased solid acinar spheres in contrast with WT and scrambled shRNA control cells, which mostly formed hollow acinar structures when plated in 3D Matrigel cultures. These solid acinar structures were similar to the acinar structures formed when Dlc1 gene expression was knocked down in WT mammary cells by shRNA lentiviral transduction. The solid acinar structures were not due to a defect in apoptosis as determined by a lack of detectible cleaved caspase 3 antibody staining. Primary mammary cells from Dlc1(gt/+) mice showed increased RhoA activity compared with WT cells.

CONCLUSIONS

The results illustrate that decreased Dlc1 expression can disrupt the normal cell polarization and mammary ductal branching. Altogether this study suggests that Dlc1 plays a role in maintaining normal mammary epithelial cell polarity and that Dlc1 is haploinsufficient.

Candidate tumor suppressor B-cell translocation gene 3 impedes neoplastic progression by suppression of AKT

BTG3 (B-cell translocation gene 3) is a p53 target that also binds and inhibits E2F1. Although it connects two major growth-regulatory pathways functionally and is downregulated in human cancers, whether and how BTG3 acts as a tumor suppressor remain largely uncharacterized. Here we present evidence that BTG3 binds and suppresses AKT, a kinase frequently deregulated in cancers. BTG3 ablation results in increased AKT activity that phosphorylates and inhibits glycogen synthase kinase 3β. Consequently, we also observed elevated β-catenin/T-cell factor activity, upregulation of mesenchymal markers, and enhanced cell migration. Consistent with these findings, BTG3 overexpression suppressed tumor growth in mouse xenografts, and was associated with diminished AKT phosphorylation and reduced β-catenin in tissue specimens. Significantly, a short BTG3-derived peptide was identified, which recapitulates these effects in vitro and in cells. Thus, our study provides mechanistic insights into a previously unreported AKT inhibitory pathway downstream of p53. The identification of an AKT inhibitory peptide also unveils a new avenue for cancer therapeutics development.

Engineered microenvironments provide new insights into ovarian and prostate cancer progression and drug responses

Tissue engineering technologies, which have originally been designed to reconstitute damaged tissue structure and function, can mimic not only tissue regeneration processes but also cancer development and progression. Bioengineered approaches allow cell biologists to develop sophisticated experimentally and physiologically relevant cancer models to recapitulate the complexity of the disease seen in patients. Tissue engineering tools enable three-dimensionality based on the design of biomaterials and scaffolds that re-create the geometry, chemistry, function and signalling milieu of the native tumour microenvironment. Three-dimensional (3D) microenvironments, including cell-derived matrices, biomaterial-based cell culture models and integrated co-cultures with engineered stromal components, are powerful tools to study dynamic processes like proteolytic functions associated with cancer progression, metastasis and resistance to therapeutics. In this review, we discuss how biomimetic strategies can reproduce a humanised niche for human cancer cells, such as peritoneal or bone-like microenvironments, addressing specific aspects of ovarian and prostate cancer progression and therapy response.

Ion channel TRPM8 promotes hypoxic growth of prostate cancer cells via an O2 -independent and RACK1-mediated mechanism of HIF-1α stabilization

The growth adaptation of cancer cells to a hypoxic tumour microenvironment is mostly regulated by hypoxia-induced transcription factor HIF-1. HIF-1 transcriptional activity is strictly controlled by protein levels of the HIF-1α subunit, which is tightly regulated by a well-characterized O2 -dependent ubiquitin ligase-proteasomal degradation pathway. The cold-sensitive Ca(2+) channel protein TRPM8 exhibits increased expression in advanced prostate cancer. However, its exact functional roles in prostate cancer growth regulation are unclear and controversial. In this work, we show that TRPM8 promotes in vitro hypoxic growth capacities, drug resistance, and in vivo tumourigenicity, accompanied with enhanced HIF-1α protein levels. These effects are further potentiated by TRPM8 agonists but suppressed by TRPM8 gene knockdown and blocking with antagonists or TRPM8 antibody. TRPM8-induced suppression of HIF-1α ubiquitination and enhanced HIF-1 transactivation were attenuated by forced RACK1 expression and TRPM8 overexpression reduced phospho-RACK1 levels, thus affecting its dimerization status, and promoted RACK1 binding to HIF-1α and calcineurin. These data indicate that TRPM8-induced increase of HIF-1α protein in hypoxia- or normoxia-exposed prostate cancer cells was mediated through a newly characterized Ca(2+) -dependent but O2 -independent mechanism involving binding of RACK1 to HIF-1α and RACK1-mediated ubiquitination of HIF-1α. Collectively, our study not only provides a mechanistic insight into how TRPM8 promotes the hypoxic growth adaptation of cancer cells via its promotion of RACK1-mediated stabilization of HIF-1α but also suggests a potential therapeutic strategy for prostate cancer by targeting TRPM8.

ERRα augments HIF-1 signalling by directly interacting with HIF-1α in normoxic and hypoxic prostate cancer cells

Adaptation of cancer cells to a hypoxic microenvironment is important for their facilitated malignant growth and advanced development. One major mechanism mediating the hypoxic response involves up-regulation of hypoxia-inducible factor 1 (HIF-1) expression, which controls reprogramming of energy metabolism and angiogenesis. Oestrogen-related receptor-α (ERRα) is a pivotal regulator of cellular energy metabolism and many biosynthetic pathways, and has also been proposed to be an important factor promoting the Warburg effect in advanced cancer. We and others have previously shown that ERRα expression is increased in prostate cancer and is also a prognostic marker. Here we show that ERRα is oncogenic in prostate cancer and also a key hypoxic growth regulator. ERRα-over-expressing prostate cancer cells were more resistant to hypoxia and showed enhanced HIF-1α protein expression and HIF-1 signalling. These effects could also be observed in ERRα-over-expressing cells grown under normoxia, suggesting that ERRα could function to pre-adapt cancer cells to meet hypoxia stress. Immunoprecipitation and FRET assays indicated that ERRα could physically interact with HIF-1α via its AF-2 domain. A ubiquitination assay showed that this ERRα-HIF-1α interaction could inhibit ubiquitination of HIF-1α and thus reduce its degradation. Such ERRα-HIF-1α interaction could be attenuated by XCT790, an ERRα-specific inverse agonist, resulting in reduced HIF-1α levels. In summary, we show that ERRα can promote the hypoxic growth adaptation of prostate cancer cells via a protective interaction with HIF-1α, suggesting ERRα as a potential therapeutic target for cancer treatment.

Infiltrating macrophages promote prostate tumorigenesis via modulating androgen receptor-mediated CCL4-STAT3 signaling

Infiltrating macrophages are a key component of inflammation during tumorigenesis, but the direct evidence of such linkage remains unclear. We report here that persistent coculturing of immortalized prostate epithelial cells with macrophages, without adding any carcinogens, induces prostate tumorigenesis and that induction involves the alteration of signaling of macrophage androgen receptor (AR)-inflammatory chemokine CCL4-STAT3 activation as well as epithelial-to-mesenchymal transition and downregulation of p53/PTEN tumor suppressors. In vivo studies further showed that PTEN(+/-) mice lacking macrophage AR developed far fewer prostatic intraepithelial neoplasia (PIN) lesions, supporting an in vivo role for macrophage AR during prostate tumorigenesis. CCL4-neutralizing antibody effectively blocked macrophage-induced prostate tumorigenic signaling and targeting AR via an AR-degradation enhancer, ASC-J9, reduced CCL4 expression, and xenografted tumor growth in vivo. Importantly, CCL4 upregulation was associated with increased Snail expression and downregulation of p53/PTEN in high-grade PIN and prostate cancer. Together, our results identify the AR-CCL4-STAT3 axis as key regulators during prostate tumor initiation and highlight the important roles of infiltrating macrophages and inflammatory cytokines for the prostate tumorigenesis.

Endothelial-rich microenvironment supports growth and branching morphogenesis of prostate epithelial cells

BACKGROUND

Development of epithelial organs depends on interaction between the epithelium and the underlying mesenchyme including the vasculature. The aim of this study was to explore the morphogenic effect of endothelial cells on prostate epithelial cell lines in 3D culture and to establish an in vitro model for prostate branching morphogenesis.

METHODS

A panel of eleven cell lines originating in normal or malignant prostate and primary prostate epithelial cells were cultured in reconstituted basement membrane (rBM) matrix with or without non-proliferating but metabolically active endothelial cells. Morphogenesis was evaluated by phase contrast microscopy and further characterized by immunocyto/histocemistry and confocal microscopy.

RESULTS

Endothelial cells induced clonogenic potential of most prostate cell lines and formation of branching and mesenchymal-like colonies. One of the normal-derived cell lines in the panel (PZ-HPV-7) displayed unique properties in rBM culture by forming large and complex branching structures resembling the ductal architecture of the prostate. This ability was highly dependent on epithelial seeding density and soluble factors derived from the endothelial cells. High seeding density suppressed branching of PZ-HPV-7 but survival was compromised at low density in the absence of endothelium.

CONCLUSIONS

We have generated an endothelial-based clonogenic assay to study prostate epithelial morphogenesis in three-dimensional context. This assay will be important tool to study prostate epithelial-endothelial interactions in 3D context and open up possibilities to study molecular regulation of prostate morphogenesis and cancer progression.

Folliculin, the product of the Birt-Hogg-Dube tumor suppressor gene, interacts with the adherens junction protein p0071 to regulate cell-cell adhesion

Birt-Hogg-Dube (BHD) is a tumor suppressor gene syndrome associated with fibrofolliculomas, cystic lung disease, and chromophobe renal cell carcinoma. In seeking to elucidate the pathogenesis of BHD, we discovered a physical interaction between folliculin (FLCN), the protein product of the BHD gene, and p0071, an armadillo repeat containing protein that localizes to the cytoplasm and to adherens junctions. Adherens junctions are one of the three cell-cell junctions that are essential to the establishment and maintenance of the cellular architecture of all epithelial tissues. Surprisingly, we found that downregulation of FLCN leads to increased cell-cell adhesion in functional cell-based assays and disruption of cell polarity in a three-dimensional lumen-forming assay, both of which are phenocopied by downregulation of p0071. These data indicate that the FLCN-p0071 protein complex is a negative regulator of cell-cell adhesion. We also found that FLCN positively regulates RhoA activity and Rho-associated kinase activity, consistent with the only known function of p0071. Finally, to examine the role of Flcn loss on cell-cell adhesion in vivo, we utilized keratin-14 cre-recombinase (K14-cre) to inactivate Flcn in the mouse epidermis. The K14-Cre-Bhd(flox/flox) mice have striking delays in eyelid opening, wavy fur, hair loss, and epidermal hyperplasia with increased levels of mammalian target of rapamycin complex 1 (mTORC1) activity. These data support a model in which dysregulation of the FLCN-p0071 interaction leads to alterations in cell adhesion, cell polarity, and RhoA signaling, with broad implications for the role of cell-cell adhesion molecules in the pathogenesis of human disease, including emphysema and renal cell carcinoma.

Phenotypic characterization of prostate cancer LNCaP cells cultured within a bioengineered microenvironment

Biophysical and biochemical properties of the microenvironment regulate cellular responses such as growth, differentiation, morphogenesis and migration in normal and cancer cells. Since two-dimensional (2D) cultures lack the essential characteristics of the native cellular microenvironment, three-dimensional (3D) cultures have been developed to better mimic the natural extracellular matrix. To date, 3D culture systems have relied mostly on collagen and Matrigel™ hydrogels, allowing only limited control over matrix stiffness, proteolytic degradability, and ligand density. In contrast, bioengineered hydrogels allow us to independently tune and systematically investigate the influence of these parameters on cell growth and differentiation. In this study, polyethylene glycol (PEG) hydrogels, functionalized with the Arginine-glycine-aspartic acid (RGD) motifs, common cell-binding motifs in extracellular matrix proteins, and matrix metalloproteinase (MMP) cleavage sites, were characterized regarding their stiffness, diffusive properties, and ability to support growth of androgen-dependent LNCaP prostate cancer cells. We found that the mechanical properties modulated the growth kinetics of LNCaP cells in the PEG hydrogel. At culture periods of 28 days, LNCaP cells underwent morphogenic changes, forming tumor-like structures in 3D culture, with hypoxic and apoptotic cores. We further compared protein and gene expression levels between 3D and 2D cultures upon stimulation with the synthetic androgen R1881. Interestingly, the kinetics of R1881 stimulated androgen receptor (AR) nuclear translocation differed between 2D and 3D cultures when observed by immunofluorescent staining. Furthermore, microarray studies revealed that changes in expression levels of androgen responsive genes upon R1881 treatment differed greatly between 2D and 3D cultures. Taken together, culturing LNCaP cells in the tunable PEG hydrogels reveals differences in the cellular responses to androgen stimulation between the 2D and 3D environments. Therefore, we suggest that the presented 3D culture system represents a powerful tool for high throughput prostate cancer drug testing that recapitulates tumor microenvironment.

MicroRNA-7 inhibits epithelial-to-mesenchymal transition and metastasis of breast cancer cells via targeting FAK expression

Focal adhesion kinase (FAK) is an important mediator of extracellular matrix integrin signaling, cell motility, cell proliferation and cell survival. Increased FAK expression is observed in a variety of solid human tumors and increased FAK expression and activity frequently correlate with metastatic disease and poor prognosis. Herein we identify miR-7 as a direct regulator of FAK expression. miR-7 expression is decreased in malignant versus normal breast tissue and its expression correlates inversely with metastasis in human breast cancer patients. Forced expression of miR-7 produced increased E-CADHERIN and decreased FIBRONECTIN and VIMENTIN expression in breast cancer cells. The levels of miR-7 expression was positively correlated with E-CADHERIN mRNA and negatively correlated with VIMENTIN mRNA levels in breast cancer samples. Forced expression of miR-7 in aggressive breast cancer cell lines suppressed tumor cell monolayer proliferation, anchorage independent growth, three-dimensional growth in Matrigel, migration and invasion. Conversely, inhibition of miR-7 in the HBL-100 mammary epithelial cell line promoted cell proliferation and anchorage independent growth. Rescue of FAK expression reversed miR-7 suppression of migration and invasion. miR-7 also inhibited primary breast tumor development, local invasion and metastatic colonization of breast cancer xenografts. Thus, miR-7 expression is decreased in metastatic breast cancer, correlates with the level of epithelial differentiation of the tumor and inhibits metastatic progression.

Lysophosphatidic acid and sphingosine-1-phosphate promote morphogenesis and block invasion of prostate cancer cells in three-dimensional organotypic models

Normal prostate and some malignant prostate cancer (PrCa) cell lines undergo acinar differentiation and form spheroids in three-dimensional (3-D) organotypic culture. Acini formed by PC-3 and PC-3M, less pronounced also in other PrCa cell lines, spontaneously undergo an invasive switch, leading to the disintegration of epithelial structures and the basal lamina, and formation of invadopodia. This demonstrates the highly dynamic nature of epithelial plasticity, balancing epithelial-to-mesenchymal transition against metastable acinar differentiation. This study assessed the role of lipid metabolites on epithelial maturation. PC-3 cells completely failed to form acinar structures in delipidated serum. Adding back lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) rescued acinar morphogenesis and repressed invasion effectively. Blocking LPA receptor 1 (LPAR1) functions by siRNA (small interference RNA) or the specific LPAR1 inhibitor Ki16425 promoted invasion, while silencing of other G-protein-coupled receptors responsive to LPA or S1P mainly caused growth arrest or had no effects. The G-proteins Gα(12/13) and Gα(i) were identified as key mediators of LPA signalling via stimulation of RhoA and Rho kinases ROCK1 and 2, activating Rac1, while inhibition of adenylate cyclase and accumulation of cAMP may be secondary. Interfering with these pathways specifically impeded epithelial polarization in transformed cells. In contrast, blocking the same pathways in non-transformed, normal cells promoted differentiation. We conclude that LPA and LPAR1 effectively promote epithelial maturation and block invasion of PrCa cells in 3-D culture. The analysis of clinical transcriptome data confirmed reduced expression of LPAR1 in a subset of PrCa's. Our study demonstrates a metastasis-suppressor function for LPAR1 and Gα(12/13) signalling, regulating cell motility and invasion versus epithelial maturation.

PI3K, Erk signaling in BMP7-induced epithelial-mesenchymal transition (EMT) of PC-3 prostate cancer cells in 2- and 3-dimensional cultures

We reported previously that bone morphogenetic protein 7 (BMP7) could induce epithelial-mesenchymal transition (EMT) in PC-3 prostate cancer cells grown in tissue culture plates. In this study, we examined BMP7-induced morphological and molecular expression changes that are characteristic of EMT using these cells under both two- (2D) and three-dimensional (3D) culture conditions. Filamentous outgrowths from spheroid structures that were formed from PC-3 cells in 3D cultures were strikingly evident when the spheroids were exposed to extracellular BMP7. This morphological change in 3D was accompanied by down-regulation of E-cadherin, which is an essential adhesion molecule for the integrity of epithelial phenotype. Invasiveness of the cancer cells was significantly enhanced with BMP7 treatment along with activation and up-regulation of proteases such as MMP1, MMP13, and urokinase plasminogen activator. Signal transduction of EMT conversion was examined by the use of certain pathway-specific inhibitors. Of the chemical inhibitors tested, inhibitors of PI3 kinase and Erk were found to suppress BMP-induced morphological changes both in 2D and 3D conditions. These results suggest that, besides the Smad signaling pathways, BMP-induced activation of PI3K and Erk contribute to EMT morphologic conversion of the PC-3 prostate cancer cells. Together, the results support the notion that the complexity of EMT may be better evaluated in terms of both spatial and temporal processes in 3D cell culture models that are physiologically more relevant than the cell growth in tissue culture plates.

Three-dimensional cancer-bone metastasis model using ex-vivo co-cultures of live calvarial bones and cancer cells

One of the major limitations of studying cancer-bone metastasis has been the lack of an appropriate ex-vivo model which can be used under defined conditions that simulates closely the in vivo live bone microenvironment in response to cancer-bone interactions. We have developed and utilized a three-dimensional (3D) cancer-bone metastasis model using free-floating live mouse calvarial bone organs in the presence of cancer cells in a roller tube system. In such co-cultures under hypoxia and a specifically defined bone remodeling stage, viz., resorption system, cancer cells showed a remarkable affinity and specificity for the "endosteal side" of the bone where they colonize and proliferate. This was concurrent with differentiation of resident stem/progenitor cells to osteoclasts and bone resorption. In contrast, under bone formation conditions this model revealed different pathophysiology where the breast cancer cells continued to induce osteoclastic bone resorption whereas prostate cancer cells led to osteoblastic bone formation. The current 3D model was used to demonstrate its application to studies involving chemical and biochemical perturbations in the absence and presence of cancer cells and cellular responses. We describe proof-of-principle with examples of the broad versatility and multi-faceted application of this model that adds another dimension to the ongoing studies in the cancer-bone metastasis arena.

TGF-β1-induced EMT of non-transformed prostate hyperplasia cells is characterized by early induction of SNAI2/Slug

BACKGROUND

Epithelial-mesenchymal transition (EMT) underlying cancer cell invasion and metastasis has been thoroughly studied in prostate cancer. Although EMT markers have been clinically observed in benign prostate hyperplasia, molecular events underlying the onset and progression of EMT in benign prostate cells have not been described.

METHODS

EMT in BPH-1 cells was induced by TGF-β1 treatment and the kinetics of expression of EMT markers, regulators, and selected miRNAs was assessed by western blotting and quantitative RT-PCR.

RESULTS

EMT in BPH-1 cells was accompanied by rapid up-regulation of SNAI2/Slug and ZEB1 transcription factors, while changes in expression levels of ZEB2 and miR-200 family members were observed after extended time intervals. Invasive phenotype with EMT hallmarks, characterizing tumorigenic clones derived from BPH-1 cells, was associated with increased mRNA levels of SNAI2, ZEB1, and ZEB2, but was not associated with significant changes in basal levels of miR-200 family members. RNA interference revealed that SNAI2/Slug is crucial for TGF-β1-induced vimentin up-regulation and migration of BPH-1 cells.

CONCLUSIONS

This study suggests that in BPH-1 cells the transcription factor SNAI2/Slug is important for EMT initiation, while the ZEB family of transcription factors in cooperation with the miR-200 family may oppose the reversal of the EMT phenotype.

Epithelial-to-mesenchymal transition in prostate cancer: paradigm or puzzle?

The lethal consequences of prostate cancer are related to its metastasis to other organ sites. Epithelial-to-mesenchymal transition (EMT) has received considerable attention as a conceptual paradigm to explain invasive and metastatic behavior during cancer progression. EMT is a normal physiologic process by which cells of epithelial origin convert into cells bearing mesenchymal characteristics. It has been proposed that EMT is co-opted by cancer cells during their metastatic dissemination from a primary organ to secondary sites, but the extent to which this recapitulates physiologic EMT remains uncertain. However, there is ample evidence that EMT-like states occur in, and may contribute to, prostate cancer progression and metastasis, and so has become a very active area of research. Here we review this evidence and explore recent studies that have aimed to better define the role and mechanisms of EMT in prostate cancer. While definitive evidence of something akin to physiologic EMT is still lacking in human prostate cancer, this area of research has nonetheless provided new avenues of investigation into the longstanding puzzles of metastasis, therapeutic resistance, and prognostic biomarkers.

Estrogen-initiated transformation of prostate epithelium derived from normal human prostate stem-progenitor cells

The present study sought to determine whether estrogens with testosterone support are sufficient to transform the normal human prostate epithelium and promote progression to invasive adenocarcinoma using a novel chimeric prostate model. Adult prostate stem/early progenitor cells were isolated from normal human prostates through prostasphere formation in three-dimensional culture. The stem/early progenitor cell status and clonality of prostasphere cells was confirmed by immunocytochemistry and Hoechst staining. Normal prostate progenitor cells were found to express estrogen receptor α, estrogen receptor β, and G protein-coupled receptor 30 mRNA and protein and were responsive to 1 nm estradiol-17β with increased numbers and prostasphere size, implicating them as direct estrogen targets. Recombinants of human prostate progenitor cells with rat urogenital sinus mesenchyme formed chimeric prostate tissue in vivo under the renal capsule of nude mice. Cytodifferentiation of human prostate progenitor cells in chimeric tissues was confirmed by immunohistochemistry using epithelial cell markers (p63, cytokeratin 8/18, and androgen receptor), whereas human origin and functional differentiation were confirmed by expression of human nuclear antigen and prostate-specific antigen, respectively. Once mature tissues formed, the hosts were exposed to elevated testosterone and estradiol-17β for 1-4 months, and prostate pathology was longitudinally monitored. Induction of prostate cancer in the human stem/progenitor cell-generated prostatic tissue was observed over time, progressing from normal histology to epithelial hyperplasia, prostate intraepithelial neoplasia, and prostate cancer with local renal invasion. These findings provide the first direct evidence that human prostate progenitor cells are estrogen targets and that estradiol in an androgen-supported milieu is a carcinogen for human prostate epithelium.

Interactions between human osteoblasts and prostate cancer cells in a novel 3D in vitro model

Cell-cell and cell-matrix interactions play a major role in tumor morphogenesis and cancer metastasis. Therefore, it is crucial to create a model with a biomimetic microenvironment that allows such interactions to fully represent the pathophysiology of a disease for an in vitro study. This is achievable by using three-dimensional (3D) models instead of conventional two-dimensional (2D) cultures with the aid of tissue engineering technology. We are now able to better address the complex intercellular interactions underlying prostate cancer (CaP) bone metastasis through such models. In this study, we assessed the interaction of CaP cells and human osteoblasts (hOBs) within a tissue engineered bone (TEB) construct. Consistent with other in vivo studies, our findings show that intercellular and CaP cell-bone matrix interactions lead to elevated levels of matrix metalloproteinases, steroidogenic enzymes and the CaP biomarker, prostate specific antigen (PSA); all associated with CaP metastasis. Hence, it highlights the physiological relevance of this model. We believe that this model will provide new insights for understanding of the previously poorly understood molecular mechanisms of bone metastasis, which will foster further translational studies, and ultimately offer a potential tool for drug screening.

Protein kinase D1 suppresses epithelial-to-mesenchymal transition through phosphorylation of snail

Cancer cells undergo epithelial-mesenchymal transition (EMT) as a program of increased invasion and metastasis during cancer progression. Here, we report that a novel regulator of EMT in cancer cells is protein kinase D1 (PKD1), which is downregulated in advanced prostate, breast, and gastric cancers. Ectopic reexpression of PKD1 in metastatic prostate cancer cells reversibly suppressed expression of mesenchyme-specific genes and increased epithelial markers such as E-cadherin, whereas small interfering RNA-mediated knockdown of PKD1 increased expression of mesenchyme markers. Further, PKD1 inhibited tumor growth and metastasis in a tumor xenograft model. PKD1 phosphorylates Ser(11) (S11) on transcription factor Snail, a master EMT regulator and repressor of E-cadherin expression, triggering nuclear export of Snail via 14-3-3σ binding. Snail S11 mutation causes acquisition of mesenchymal traits and expression of stem cell markers. Together, our results suggest that PKD1 functions as a tumor and metastasis suppressor, at least partly by regulating Snail-mediated EMT, and that loss of PKD1 may contribute to acquisition of an aggressive malignant phenotype.

A comprehensive panel of three-dimensional models for studies of prostate cancer growth, invasion and drug responses

Prostate epithelial cells from both normal and cancer tissues, grown in three-dimensional (3D) culture as spheroids, represent promising in vitro models for the study of normal and cancer-relevant patterns of epithelial differentiation. We have developed the most comprehensive panel of miniaturized prostate cell culture models in 3D to date (n = 29), including many non-transformed and most currently available classic prostate cancer (PrCa) cell lines. The purpose of this study was to analyze morphogenetic properties of PrCa models in 3D, to compare phenotypes, gene expression and metabolism between 2D and 3D cultures, and to evaluate their relevance for pre-clinical drug discovery, disease modeling and basic research. Primary and non-transformed prostate epithelial cells, but also several PrCa lines, formed well-differentiated round spheroids. These showed strong cell-cell contacts, epithelial polarization, a hollow lumen and were covered by a complete basal lamina (BL). Most PrCa lines, however, formed large, poorly differentiated spheroids, or aggressively invading structures. In PC-3 and PC-3M cells, well-differentiated spheroids formed, which were then spontaneously transformed into highly invasive cells. These cell lines may have previously undergone an epithelial-to-mesenchymal transition (EMT), which is temporarily suppressed in favor of epithelial maturation by signals from the extracellular matrix (ECM). The induction of lipid and steroid metabolism, epigenetic reprogramming, and ECM remodeling represents a general adaptation to 3D culture, regardless of transformation and phenotype. In contrast, PI3-Kinase, AKT, STAT/interferon and integrin signaling pathways were particularly activated in invasive cells. Specific small molecule inhibitors targeted against PI3-Kinase blocked invasive cell growth more effectively in 3D than in 2D monolayer culture, or the growth of normal cells. Our panel of cell models, spanning a wide spectrum of phenotypic plasticity, supports the investigation of different modes of cell migration and tumor morphologies, and will be useful for predictive testing of anti-cancer and anti-metastatic compounds.

Monocyte chemoattractant protein-1 (MCP-1)/CCL2 secreted by hepatic myofibroblasts promotes migration and invasion of human hepatoma cells

The aim of our study was to investigate whether myofibroblasts and the chemokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 may play a role in hepatocellular carcinoma progression. We observed that hepatic myofibroblast LI90 cells express MCP-1/CCL2 mRNA and secrete this chemokine. Moreover, myofibroblast LI90 cell-conditioned medium (LI90-CM) induces human hepatoma Huh7 cell migration and invasion. These effects are strongly reduced when a MCP-1/CCL2-depleted LI90-CM was used. We showed that MCP-1/CCL2 induces Huh7 cell migration and invasion through its G-protein-coupled receptor CCR2 and, to a lesser extent, through CCR1 only at high MCP-1/CCL2 concentrations. MCP-1/CCL2's chemotactic activities rely on tyrosine phosphorylation of focal adhesion components and depend on matrix metalloproteinase (MMP)-2 and MMP-9. Furthermore, we observed that Huh7 cell migration and invasion induced by the chemokine are strongly inhibited by heparin, by beta-D-xyloside treatment of cells and by anti-syndecan-1 and -4 antibodies. Finally, we developed a 3-dimensional coculture model of myofibroblast LI90 and Huh7 cells and demonstrated that MCP-1/CCL2 and its membrane partners, CCR1 and CCR2, may be involved in the formation of mixed hepatoma-myofibroblast spheroids. In conclusion, our data show that human liver myofibroblasts act on hepatoma cells in a paracrine manner to increase their invasiveness and suggest that myofibroblast-derived MCP-1/CCL2 could be involved in the pathogenesis of hepatocellular carcinoma.