Dual androgen-response elements mediate androgen regulation of MMP-2 expression in prostate cancer cells

Sex-Based Differences in the Tumor Microenvironment

Cancers are heterogeneous multifactorial diseases consisting of a major public health issue worldwide. Sex disparities are evidenced in cancer incidence, mortality, expression of prognosis factor, response to treatment, and survival. For both sexes, an interplay of intrinsic and environmental factors influences cancer cells and tumor microenvironment (TME) components. The TME cumulates both supportive and communicative functions, contributing to cancer development, progression, and metastasis dissemination. The frontline topics of this chapter are focused on the contribution of sex, via steroid hormones, such as estrogens and androgens, on the following components of the TME: cancer-associated fibroblasts (CAFs), extracellular matrix (ECM), blood and lymphatic endothelial cells, and immunity/inflammatory system.

The Orphan Nuclear Receptor Gene NR0B2 Is a Favorite Prognosis Factor Modulated by Multiple Cellular Signal Pathways in Human Liver Cancers

BACKGROUND

Liver cancer is a leading cause of cancer death worldwide, and novel prognostic factor is needed for early detection and therapeutic responsiveness monitoring. The orphan nuclear receptor NR0B2 was reported to suppress liver cancer development in a mouse model, and its expression levels were reduced in liver cancer tissues and cell lines due to hypermethylation within its promoter region. However, it is not clear if NR0B2 expression is associated with cancer survival or disease progression and how NR0B2 gene expression is regulated at the molecular level.

METHODS

Multiple cancer databases were utilized to explore NR0B2 gene expression profiles crossing a variety of human cancers, including liver cancers, on several publicly assessable bioinformatics platforms. NR0B2 gene expression with or without kinase inhibitor treatment was analyzed using the qPCR technique, and NR0B2 protein expression was assessed in western blot assays. Two human hepatocellular carcinoma cell lines HepG2 and Huh7, were used in these experiments. NR0B2 gene activation was evaluated using NR0B2 promoter-driven luciferase reporter assays.

RESULTS

NR0B2 gene is predominantly expressed in liver tissue crossing human major organs or tissues, but it is significantly downregulated in liver cancers. NR0B2 expression is mostly downregulated in most common cancers but also upregulated in a few intestinal cancers. NR0B2 gene expression significantly correlated with patient overall survival status in multiple human malignancies, including lung, kidney, breast, urinary bladder, thyroid, colon, and head-neck cancers, as well as liposarcoma and B-cell lymphoma. In liver cancer patients, higher NR0B2 expression is associated with favorite relapse-free and progression-free survival, especially in Asian male patients with viral infection history. In addition, NR0B2 expression negatively correlated with immune infiltration and PIK3CA and PIK3CG gene expression in liver cancer tissues. In HepG2 and Huh7 cells, NR0B2 expression at the transcription level was drastically reduced after MAPK inhibition but was significantly enhanced after PI3K inhibition.

CONCLUSION

NR0B2 gene expression is altered mainly in most human malignancies and significantly reduced in liver cancers. NR0B2 is a prognosis factor for patient survival in liver cancers. MAPK and PI3K oppositely modulate NR0B2 expression, and NR0B2 gene upregulation might serve as a therapeutic responsiveness factor in anti-PI3K therapy for liver cancer.

The Role of the Metzincin Superfamily in Prostate Cancer Progression: A Systematic-Like Review

Prostate cancer remains a leading cause of cancer-related morbidity in men. Potentially important regulators of prostate cancer progression are members of the metzincin superfamily of proteases, principally through their regulation of the extracellular matrix. It is therefore timely to review the role of the metzincin superfamily in prostate cancer and its progression to better understand their involvement in this disease. A systematic-like search strategy was conducted. Articles that investigated the roles of members of the metzincin superfamily and their key regulators in prostate cancer were included. The extracted articles were synthesized and data presented in tabular and narrative forms. Two hundred and five studies met the inclusion criteria. Of these, 138 investigated the role of the Matrix Metalloproteinase (MMP) subgroup, 34 the Membrane-Tethered Matrix Metalloproteinase (MT-MMP) subgroup, 22 the A Disintegrin and Metalloproteinase (ADAM) subgroup, 8 the A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTS) subgroup and 53 the Tissue Inhibitor of Metalloproteinases (TIMP) family of regulators, noting that several studies investigated multiple family members. There was clear evidence that specific members of the metzincin superfamily are involved in prostate cancer progression, which can be either in a positive or negative manner. However, further understanding of their mechanisms of action and how they may be used as prognostic indicators or molecular targets is required.

Exogenous testosterone alleviates cardiac fibrosis and apoptosis via Gas6/Axl pathway in the senescent mice

BACKGROUND

Androgen has been implicated in aging-related cardiac remodeling, but its precise role in aging heart remains controversial. We aimed to investigate the role of testosterone in the development of aging-related cardiac remodeling and the mechanisms involved.

METHODS

Wild type and Axl knockout mice (Axl^-/-) were randomized into three groups: the young group (n = 30, 3 months old), the aging group (n = 30, 18 months old), the testosterone undecanoate treatment group (TU, n = 30, 18 months old). Mice in the TU group were given testosterone undecanoate (39 mg/kg) by subcutaneous injection on the back at fifteen-months-old, once a month, a total of three times. The old group received solvent reagent (corn oil) by the same method.

RESULTS

The aging mice exhibited a decrease in serum testosterone, and Gas6 levels and an increase in apoptosis, and manifested cardiac fibrosis. Testosterone injection to wild type mice increased the levels of testosterone and Gas6 in serum and decreased cardiac apoptosis and fibrosis. Axl^-/-mice receiving testosterone injection exhibited no obvious improvement in cardiac remodeling although the levels of testosterone and Gas6 in serum elevated.

CONCLUSIONS

These data indicated that testosterone replacement therapy (TRT) alleviates cardiac fibrosis and apoptosis, at least in part by enhancing Gas6 expression. Moreover, deletion of Axl disables testosterone, which indicated that Axl is an important downstream regulator of testosterone. TRT would improve aging-related cardiac remolding via Gas6/Axl signaling pathway, implicating its therapeutic potential to treat aging-related heart disease.

Androgen Receptor Regulates the Growth of Neuroblastoma Cells in vitro and in vivo

Background: Neuroblastoma is the most common extracranial tumors in children. At present about the true etiology of neuroblastoma is unclear and many studies have tried to find effective treatments for these primary malignant tumors. Although it has been illustrated that androgen receptor (AR) was expressed in neuroblastoma cells in some former reports, the biological role of androgen receptor in the development of neuroblastoma is not fully understood.

Methods: Androgen (R1881) and the antagonists of androgen receptor (MDV3100 and ARN509) were used to study the role of the androgen receptor signaling pathway in vitro and in vivo on SH-SY5Y and Neuro-2a (N2a) cell lines.

Results: We found that AR expression showed an R1881 dose-dependent manner in neuroblastoma cells in vitro and R1881was able to increase, while both antagonists of androgen receptor (MDV3100 and ARN509) significantly decrease, the proliferation, migration, invasion and sphere formation of SH-SY5Y and N2a cells. Moreover, androgen promoted the growth of N2a tumor in vivo. However, when androgen receptor (AR) was effectively knocked down in the two cell lines by siRNA, either promoting or inhibiting effect of the androgen or androgen receptor antagonists, respectively, was attenuated.

Conclusion: Our results suggested that androgen receptor may involve in the progression of neuroblastoma as well as provided insight into a new target for the diagnosis and treatment of neuroblastoma patients.

Targeting the relaxin hormonal pathway in prostate cancer

Targeting the androgen signalling pathway has long been the hallmark of anti-hormonal therapy for prostate cancer. However, development of androgen-independent prostate cancer is an inevitable outcome to therapies targeting this pathway, in part, owing to the shift from cancer dependence on androgen signalling for growth in favor of augmentation of other cellular pathways that provide proliferation-, survival- and angiogenesis-promoting signals. This review focuses on the role of the hormone relaxin in the development and progression of prostate cancer, prior to and after the onset of androgen independence, as well as its role in cancers of other reproductive tissues. As the body of literature expands, examining relaxin expression in cancerous tissues and its role in a growing number of in vitro and in vivo cancer models, our understanding of the important involvement of this hormone in cancer biology is becoming clearer. Specifically, the pleiotropic functions of relaxin affecting cell growth, angiogenesis, blood flow, cell migration and extracellular matrix remodeling are examined in the context of cancer progression. The interactions and intercepts of the intracellular signalling pathways of relaxin with the androgen pathway are explored in the context of progression of castration-resistant and androgen-independent prostate cancers. We provide an overview of current anti-hormonal therapeutic treatment options for prostate cancer and delve into therapeutic approaches and development of agents aimed at specifically antagonizing relaxin signalling to curb tumor growth. We also discuss the rationale and challenges utilizing such agents as novel anti-hormonals in the clinic, and their potential to supplement current therapeutic modalities.

Roles of matrix metalloproteinases and their natural inhibitors in prostate cancer progression

Matrix metalloproteinases (MMPs), a group of zinc-dependent endopeptidases involved in the degradation of the extracellular matrix, play an important role in tissue remodeling associated with various physiological processes such as morphogenesis, angiogenesis, and tissue repair, as well as pathological processes including cirrhosis, arthritis and cancer. The MMPs are well established as mediators of tumor invasion and metastasis by breaking down connective tissue barriers. Although there has been a vast amount of literature on the role of MMPs in invasion, metastasis and angiogenesis of various cancers, the role of these endopeptidases in prostate cancer progression has not been systematically reviewed. This overview summarizes findings on the tissue and blood expression of MMPs, their function, regulation and prognostic implication in human prostate cancer, with a focus on MMP-2, -7, -9, MT1-MMP and tissue inhibitor of metalloproteinase 1 (TIMP-1). This review also summarizes the efficacy and failure of early-generation matrix metalloproteinase inhibitors (MMPIs) in the treatment of metastatic prostate cancer and highlights the lessons and challenges for next generation MMPIs.

Genetic analysis of a family with complete androgen insensitivity syndrome

Androgen insensitivity causes impaired embryonic sex differentiation leading to developmental failure of normal male external genitalia in 46 XY genetic men. It results from diminished or absent biological actions of androgens, which is mediated by the androgen receptor (AR) in both the embryo and secondary sexual development. Mutations in the AR located on the X chromosome are responsible for the disease. Almost 70% of affected individuals inherit the mutation from their carrier mother. We hereby report a 10-year-old girl with all the characteristics of complete androgen insensitivity syndrome (CAIS). Similar scenario was observed in 3 maternal aunts, Sequencing of the AR gene in all the family members revealed C 2754 to T transition in exon 6. It was concluded that the C 2754 to T transition rendered the AR incapable of both ligand-binding and activating the transcription and was the cause of CAIS in the patient.

Androgen receptors expressed by prostatic stromal cells obtained from younger versus older males exhibit opposite roles in prostate cancer progression

Aging is a major risk factor for prostate cancer (PCa), and prostatic stromal cells may also promote PCa progression. Accordingly, stromal cells do not equally promote PCa in older males and younger males. Therefore, it is also possible that the expression of androgen receptors (ARs) by prostatic stromal cells in older versus younger males plays different roles in PCa progression. Using a gene knockdown technique and coculture system, we found that the knockdown of the AR in prostatic stromal cells obtained from younger males could promote the invasiveness and metastasis of cocultured PC3/LNCaP cells in vitro. By contrast, the invasiveness and metastasis of LNCaP cells was inhibited when cocultured with prostatic stromal cells from older males that when AR expression was knocked down. Moreover, after targeting AR expression with small hairpin RNA (shRNA), matrix metalloproteinase (MMP) expression in stromal cells was observed to increase in the younger group, but decreased or remained unchanged in the older group. One exception, however, was observed with MMP9. In vivo, after knocking down AR expression in prostatic stromal cells, the incidence of metastatic lymph nodes was observed to increase in the younger age group, but decreased in the older age group. Together, these data suggest that the AR in prostatic stromal cells played opposite roles in PCa metastasis for older versus younger males. Therefore, collectively, the function of the AR in prostatic stromal cells appears to change with age, and this may account for the increased incidence of PCa in older males.

Oral contraceptive containing chlormadinone acetate and ethinylestradiol reduces plasma concentrations of matrix metalloproteinase-2 in women with polycystic ovary syndrome

Biochemical markers of cardiovascular disease, including matrix metalloproteinases (MMPs), are altered in women with polycystic ovary syndrome (PCOS), with many of these alterations thought to be due to excess androgen concentrations. Despite oral contraceptives (OCs) being the first-line pharmacological treatment in women with PCOS and the importance of MMPs in many physiological conditions and pathological states, including cardiovascular diseases, no study has yet evaluated whether OCs alter plasma concentrations of MMPs. We therefore assessed whether treatment with an OC containing the anti-androgenic progestogen alters MMP profiles in women with PCOS. We analysed 20 women with PCOS who wanted hormonal contraception (OC-PCOS group), 20 ovulatory women who required hormonal contraception (OC-control group) and 20 ovulatory women who wanted non-hormonal contraception (non-OC-control group). OC consisted of cyclic use of 2 mg chlormadinone acetate/30 μg ethinylestradiol for 6 months. Plasma concentrations of MMP-2, MMP-9, TIMP-1 and TIMP-2 were measured by gelatin zymography or enzyme-linked immunoassays. OC treatment for 6 months significantly reduced plasma MMP-2 concentrations in the OC-control and OC-PCOS groups and TIMP-2 and TIMP-1 concentrations levels in the OC-control group (all p < 0.05), but had no effects on MMP-9 concentrations or on MMP-2/TIMP-2 and MMP-9/TIMP-1 ratios in any group (all p > 0.05). These findings indicated that long-term treatment with an OC containing chlormadinone acetate plus ethinylestradiol reduced plasma MMP-2 concentrations in both healthy and PCOS women. As the latter have imbalances in circulating matrix MMPs, treatment of these women with an OC may be beneficial.

The association between inflammation-related genes and serum androgen levels in men: the prostate, lung, colorectal, and ovarian study

BACKGROUND

Androgens and inflammation have been implicated in the etiology of several cancers, including prostate cancer. Serum androgens have been shown to correlate with markers of inflammation and expression of inflammation-related genes.

METHODS

In this report, we evaluated associations between 9,932 single nucleotide polymorphisms (SNPs) marking common genetic variants in 774 inflammation-related genes and four serum androgen levels (total testosterone [T], bioavailable T [BioT]; 5α-androstane-3α, 17β-diol glucuronide [3αdiol G], and 4-androstene-3,17-dione [androstenedione]), in 560 healthy men (median age 64 years) drawn from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Baseline serum androgens were measured by radioimmunoassay. Genotypes were determined as part of the Cancer Genetic Markers of Susceptibility Study genome-wide scan. SNP-hormone associations were evaluated using linear regression of hormones adjusted for age. Gene-based P values were generated using an adaptive rank truncated product (ARTP) method.

RESULTS

Suggestive associations were observed for two inflammation-related genes and circulating androgen levels (false discovery rate [FDR] q-value <0.1) in both SNP and gene-based tests. Specifically, T was associated with common variants in MMP2 and CD14, with the most significant SNPs being rs893226G > T in MMP2 and rs3822356T > C in CD14 (FDR q-value = 0.09 for both SNPs). Other genes implicated in either SNP or gene-based tests were IK with T and BioT, PRG2 with T, and TNFSF9 with androstenedione.

CONCLUSION

These results suggest possible cross-talk between androgen levels and inflammation pathways, but larger studies are needed to confirm these findings and to further clarify the interrelationship between inflammation and androgens and their effects on cancer risk.

Intronic DNA elements regulate androgen-dependent expression of the murine Nkx3.1 gene

Nkx3.1 is a well-conserved homeobox gene that is involved in development, differentiation and maintenance of prostate epithelial cells. Nkx3.1 expression is induced by androgen in prostate epithelia and, as such, our interest is to understand the mechanism(s) for this androgen-dependent expression in normal epithelial cells. In this report, we show that the region of DNA sequence 2.7 kilobases in front of the mouse Nkx3.1 gene drives enhanced transcription in prostate epithelia cells; however, this segment was not capable of androgen-directed regulation. Among the multiple, potential androgen response elements (AREs) identified by scanning sequences near and within the gene, two sequences within the intron of the murine Nkx3.1 gene were demonstrated to confer androgen-dependent transcription in reporter gene transfection experiments. Each of the elements, termed ARE A and ARE B, contained a 6-base pair core sequence, TGTTCT, that has been described as an androgen receptor half-site binding sequence, separated by 498 base pairs of DNA. Both of the intronic half-sites bind activated androgen receptor from a variety of sources, albeit with different apparent affinities. This region of the Nkx3.1 gene demonstrates a high degree of conservation among diverse species and mutagenesis experiments demonstrated that both elements are required for androgen stimulation. Taken together, our study shows that androgen-dependent transcription of the mouse Nkx3.1 gene is conferred through a noncanonical element within the intron of the gene.

Regulation of mRNAs encoding MMP-9 and MMP-2, and their inhibitors TIMP-1 and TIMP-2 by androgens in the rat ventral prostate

The relative activities of matrix metalloproteinases (MMPs) and their natural inhibitors (tissue inhibitors of matrix metalloproteinases, TIMPs) determine the extent of matrix degradation in any tissue. Their identification and characterization is key towards understanding remodeling of the prostate in the context of both castration induced atrophy and tumor invasion and metastasis. Although the expression of MMPs and TIMPs in prostate tumors has been reported, their regulation by androgens has not been studied. Here, we show that androgen ablation by castration increases the steady state mRNA levels of MMP-9, MMP-2, TIMP-1 and TIMP-2. Blockade of the androgen receptor using flutamide, however, has differential effects on the steady state mRNA expressions of these genes. We also show that both castration and flutamide treatment cause enhanced expression of a high molecular weight gelatinolytic activity in the rat ventral prostate (RVP). Actinomycin D does not affect the increase in steady state mRNA levels of MMP-9 and TIMP-1. Furthermore we show that actinomycin D alone enhances the steady state mRNA and protein levels of these genes. Using RNA gel shift assay with 3'-UTR of TIMP-1, we show that an RNA binding protein is induced following castration. Taken together our data suggest that the induction of MMP-2, MMP-9, TIMP-1 and TIMP-2 mRNAs post-castration could be at least in part due to post-transcriptional stabilization.

Phosphoinositide 3-OH kinase p85alpha and p110beta are essential for androgen receptor transactivation and tumor progression in prostate cancers

Phosphoinositide 3-OH kinases (PI3Ks) are a group of major intracellular signaling molecules. In our previous study, we found that inhibition of PI3K activity suppressed the androgen receptor (AR)-mediated gene expression in prostate cancer cells. The AR has been considered as a critical determinant for the development and progression of human prostate cancers. In this study, we sought to identify the PI3K isoforms involved in AR transactivation. Using a gene-specific small interference RNA (siRNA) approach, we determined that the regulatory isoform p85alpha and the catalytic isoform p110beta, but not p110alpha, were required for androgen-stimulated AR transactivation and cell proliferation in prostate cancer cells. Consistently, overexpression of wild-type p110beta but not p110alpha gene led to androgen-independent AR transactivation. Silencing p110beta gene in prostate cancer cells abolished tumor growth in nude mice. Of the dual (lipid and protein) kinase activities, p110beta's lipid kinase activity was required for AR transactivation. Further analysis by a chromatin immunoprecipitation assay showed that p110beta is indispensable for androgen-induced AR-DNA interaction. Finally, gene expression analysis of clinical specimens showed that both p85alpha and p110beta were highly expressed in malignant prostate tissues compared to the nonmalignant compartments, and their expression levels correlated significantly with disease progression. Taken together, our data demonstrated that p85alpha and p110beta are essential for androgen-stimulated AR transactivation, and their aberrant expression or activation might play an important role in prostate cancer progression.

Androgen receptor-dependent regulation of Bcl-xL expression: Implication in prostate cancer progression

BACKGROUND

Recently we reported that silencing the androgen receptor (AR) gene reduced Bcl-xL expression that was associated with a profound apoptotic cell death in prostate cancer cells. In this study we further investigated AR-regulated Bcl-xL expression.

METHODS

Prostate cancer cell line LNCaP and its sublines, LNCaP/PURO and LNCaP/Bclxl, were used for cell proliferation assay and xenograft experiments in nude mice. Luciferase gene reporters driven by mouse or human bcl-x gene promoter were used to determine androgen regulation of Bcl-xL expression. RT-PCR and Western blot assays were conducted to assess Bcl-xL gene expression. Chromatin immunoprecipitation assay was performed to determine AR interaction with Bcl-xL promoter. Bcl-xL-induced alteration of gene expression was examined using cDNA microarray assay.

RESULTS

In cultured prostate cancer LNCaP cells, androgen treatment significantly increased Bcl-xL expression at mRNA and protein levels via an AR-dependent mechanism. Promoter analyses demonstrated that the AR mediated androgen-stimulated bcl-x promoter activation and that the AR interacted with bcl-x promoter. Enforced expression of Bcl-xL gene dramatically increased cell proliferation in vitro and promoted xenograft tumor growth in vivo. Genome-wide gene profiling analysis revealed that Bcl-xL expression was significantly higher in metastatic and castration-resistant diseases compared to normal prostate tissues or primary cancers. Bcl-xL overexpression significantly increased the expression of cyclin D2, which might be responsible for Bcl-xL-induced cell proliferation and tumor growth.

CONCLUSIONS

Taken together, our data strongly suggest that androgen stimulates Bcl-xL expression via the AR and that increased Bcl-xL expression plays a versatile role in castration-resistant progression of prostate cancer.

Androgens influence expression of matrix proteins and proteolytic factors during cutaneous wound healing

Excessive proteolytic activity is a feature of chronic wounds such as venous ulcers, in which resolution of the inflammatory response fails and restorative matrix accumulation is delayed as a consequence. The inflammatory actions of native androgens during the healing of acute skin wounds have lately been characterized. We have now investigated the hypothesis that such activities may impact upon the balance between anabolic and catabolic processes during wound healing. We report that wound deposition of both type I collagen and fibronectin is increased in castrated rats compared with control animals. This response is accompanied by early increases and later decreases in overall wound levels of the key collagenolytic enzymes, matrix metalloproteinase (MMP)-1 and MMP-13. Moreover, the activities of MMP-2 and MMP-9, two further enzymes that contribute to collagen digestion during venous ulceration, were significantly decreased in the wounds of castrated rats. Additional analyses provide evidence that androgens directly stimulate dermal fibroblast collagen production, which supports the suggestion that increased wound collagen deposition in androgen-deprived rats results from reduced matrix degradation (as opposed to enhanced matrix protein biosynthesis). Androgen-mediated dysregulation of the parallel processes of collagen deposition and turnover may underscore the delayed healing of cutaneous wounds in elderly male patients and further contribute to the increased incidence of non-healing wounds in this population.

Serum bone turnover markers (PINP and ICTP) for the early detection of bone metastases in patients with prostate cancer: a longitudinal approach

PURPOSE

An increase in bone turnover markers in patients with prostate cancer may predict bone metastases but it can also reflect the effects of androgen deprivation treatment. To assess the diagnostic efficacy of early detection of skeletal metastases we retrospectively performed serial measurements of a bone formation marker (PINP) and a bone resorption marker (ICTP) in serum of patients with prostate cancer.

MATERIALS AND METHODS

Residual serum samples from 64 patients with prostate cancer treated between 1999 and 2004 were selected from our prostate specific antigen serum archive, and divided into 3 groups of patients with no metastases (N0M0), with lymph node metastases only (N1M0) and with skeletal metastases (M1). In the M1 group the T(1) sample was collected near the first positive bone scintigraph.

RESULTS

The N1M0 and M1 groups showed increased PINP levels (ANOVA T(0) p = 0.035, T(1) p <0.001). The PINP levels in the M1 group increased further (paired t test p = 0.028), while no increase was found in the other groups. There was no significant difference between the number of patients receiving androgen deprivation therapy in the N1M0 and the M1 groups. Increased PINP levels in the M1 group were detectable 8 months before the first positive bone scintigraph. The increase in ICTP in the M1 group differed significantly from the other groups (the Student t test in 45 patients p = 0.029). The increases in PINP and ICTP differentiated between patients with or without skeletal metastases (AUC 0.71, p = 0.002 and AUC 0.64, p = 0.045, respectively).

CONCLUSIONS

Followup measurement of serum PINP and ICTP is useful in the early assessment of skeletal metastases in patients with prostate cancer regardless of the confounding role of androgen deprivation treatment. The bone formation marker is the most indicative.

Lithium suppresses cell proliferation by interrupting E2F-DNA interaction and subsequently reducing S-phase gene expression in prostate cancer

BACKGROUND

Lithium is an existing drug for bipolar disorder and its uptake was recently linked to reduced tumor incidence compared to the general population. The major target of lithium action is glycogen synthase kinase 3 (GSK-3). Since GSK-3 expression and activation are associated with prostate cancer progression, the anti-cancer potential of lithium on prostate cancer was investigated in this study.

METHODS

Multiple prostate cancer cell lines were treated with lithium chloride (LiCl). Cell proliferation and cell cycle distribution were analysed. DNA replication was determined using BrdU labeling assay. Genome-wide screening of gene expression was performed using cDNA microarray assay. GSK-3beta gene-specific silencing was conducted using small interferencing RNA (siRNA) transfection. E2 factor (E2F) transactivation was evaluated using reporter gene assay and E2F-DNA interaction was determined with chromatin-immunoprecipitation assay (ChIP).

RESULTS

LiCl significantly inhibited cell proliferation, which was associated with reduced DNA replication and S-phase cell cycle arrest. LiCl significantly decreased the expression of multiple DNA replication-related genes, including cell division cycle 6 (cdc6), cyclin A, cyclin E, and cdc25C, which are regulated by E2F factor during cell cycle. A novel GSK-3-specific inhibitor TDZD-8 and GSK-3beta siRNA also suppressed the expression of these E2F target genes, indicating that LiCl-induced anti-cancer effect was associated with GSK-3beta inhibition. Furthermore, LiCl suppressed E2F transactivation by interrupting the interaction of E2F1 factor with its target gene promoter.

CONCLUSIONS

These data indicated that LiCl suppresses cancer cell proliferation by disrupting E2F-DNA interaction and subsequent E2F-mediated gene expression in prostate cancer.