Tissue prostate-specific antigen facilitates refractory prostate tumor progression via enhancing ARA70-regulated androgen receptor transactivation

Despite being well recognized as the best biomarker for prostate cancer, pathophysiologic roles of prostate-specific antigen (PSA) remain unclear. We report here that tissue PSA may be involved in the hormone-refractory prostate cancer progression. Histologic analyses show that the increased tissue PSA levels are correlated with lower cell apoptosis index and higher cell proliferation rate in hormone-refractory tumor specimens. By stably transfecting PSA cDNA into various prostate cancer cell lines, we found that PSA could promote the growth of androgen receptor (AR)-positive CWR22rv1 and high-passage LNCaP (hormone-refractory prostate cancer cells) but not that of AR-negative PC-3 and DU145 cells. Surprisingly, the protease activity of PSA is not crucial for PSA to stimulate growth and promote AR transactivation. We further showed that increased PSA could enhance ARA70-induced AR transactivation via modulating the p53 pathway that results in the decreased apoptosis and increased cell proliferation in prostate cancer cells. Knockdown of PSA in LNCaP and CWR22rv1 cells causes cell apoptosis and cell growth arrest at the G(1) phase. In vitro colony formation assay and in vivo xenografted tumor results showed the suppression of prostate cancer growth via targeting PSA expression. Collectively, our findings suggest that, in addition to being a biomarker, PSA may also become a new potential therapeutic target for prostate cancer. PSA small interfering RNA or smaller molecules that can degrade PSA protein may be developed as alternative approaches to treat the prostate cancer.     

A specific function for phosphatidylinositol 3-kinase alpha (p85alpha-p110alpha) in cell survival and for phosphatidylinositol 3-kinase beta (p85alpha-p110beta) in de novo DNA synthesis of human colon carcinoma cells

We have previously shown an important function of phosphatidylinositol 3-kinase (PI3K)alpha(p85alpha-p110alpha) and PI3Kbeta (p85-alpha-p110beta) for DNA synthesis induced by various mitogens in non transformed fibroblasts and we now report a specific role of these enzymes in human colon cancer cell growth. Using antibodies specific to p110alpha and to p110beta catalytic subunits, increase in PI3Kalpha and PI3Kbeta activities was detected in 15/19 human tumour biopsies relative to adjacent normal mucosa of human colon and bladder. Increase in such activities was also observed in adenocarcinoma cell lines CaCo2, CO115, HCT 116, LS 174T and WiDr relative to non-transformed fibroblasts. Maximal PI3Kalpha activity was observed for LS 174T and PI3Kbeta activity for WiDr cells. This was partly correlated with an increase in p110alpha and p110beta protein levels both in some primary tumours and established cell lines, suggesting that PI3K overexpression is involved in enzymatic deregulation. Functional consequence of such activation was assessed by a microinjection approach. An injection of neutralizing antibody specific to p110beta in WiDr, HCT116 and CO 115 cells inhibited de novo DNA synthesis, whereas antibodies specific to p110gamma had no effect. Neutralizing antibodies specific to p110alpha induced apoptosis, a response that was reverted by treating cells with the caspase inhibitor z-VAD-fmk. However anti-p110beta and anti-p110gamma antibodies did not affect cell survival. We concluded that PI3Kalpha and PI3Kbeta play important roles in human colon cancer cell growth with a specific function for PI3Kbeta in de novo DNA synthesis and an involvement of PI3Kalpha in cell survival.     

Phosphoinositide 3-kinase signalling pathways in tumor progression, invasion and angiogenesis

AIMS AND BACKGROUND: The PI3 kinase signalling pathway is now accepted as being at least as important as the ras-MAP kinase pathway in cell survival and proliferation, and hence its potential role in cancer is of great interest. The purpose of this review is briefly to examine evidence for an involvement of PI3K in human cancers, discuss the mechanisms by which its activation promotes tumor progression, and consider its utility as a novel target for anticancer therapy. METHODS AND STUDY DESIGN: A Medline review of recent literature concerning the role of PI3 kinase in tumor progression--mechanisms of action and clinical implications. RESULTS: Evidence is presented that misregulation of the PI3 kinase pathway is a feature of many common cancers, either by loss of the suppressor protein PTEN, or by constitutive activation of PI3 kinase isoforms or downstream elements such as AKT and mTOR. This activation potentiates not only cell survival and proliferation, but also cytoskeletal deformability and motility; key elements in tumor invasion. In addition the PI3K pathway is implicated in many aspects of angiogenesis, including upregulation of angiogenic cytokines due to tumor hypoxia or oncogene activation and endothelial cell responses to them. These cytokines signal though receptors such as VEGF-R, FGF-R and Tie-2 and potentiate processes essential for neoangiogenesis including cell proliferation, migration, differentiation into tubules and "invasion" of these capillary sprouts into extracellular matrix (ECM). CONCLUSIONS: A more complete understanding of the role of the PI3 kinase pathway in cancer will lead the way to the development of more potent and selective inhibitors which should be a useful adjunct to conventional therapies, potentially interfering with tumor progression at several pivotal points; in particular cell survival, invasion and angiogenesis.     

Chromosomal localization of human p85 alpha, a subunit of phosphatidylinositol 3-kinase, and its homologue p85 beta.

The human phosphatidylinositol (PI) 3-kinase p85 alpha subunit gene and its homologue p85 beta were assigned to human chromosomes by analysis of their segregation in a panel of somatic cell hybrids using human-specific polymerase chain reaction primers. The p85 alpha locus was only present in hybrids retaining the human chromosome 5q. The presence of the p85 beta locus coincided with the presence of chromosome 19. The precise chromosomal sublocalization of these two genes was then determined by in situ hybridization. We confirmed the localization of the p85 alpha gene at 5q12-q13, as recently described (Cannizzaro, L.A., Skolnik, E.Y., Margolis, B., Croce, C.M., Schlesinger, J. & Huebner, K. (1991). Cancer Res., 51, 3818-3820) and positioned the p85 beta locus at 19q13.2-q13.4.     

The role of alpha(v)beta(3) in prostate cancer progression

Integrin alpha(v)beta(3) is involved in varied cell biological activities, including angiogenesis, cell adhesion, and migration on several extracellular matrix components. Although alpha(v)beta(3) is not typically expressed in epithelial cells, it is expressed in macrophages, activated leukocytes, cytokine-stimulated endothelial cells, osteoclasts, and certain invasive tumors. Interestingly, the adhesion and migration of breast cancer cells on bone matrix are mediated, in part, by alpha(v)beta(3). Similar to breast cancer cells, prostate cancer cells preferentially metastasize to the bone. The biological events that mediate this metastatic pattern of prostate cancer are not well defined. This review discusses the role alpha(v)beta(3) plays in prostate cancer progression, with specific emphasis on bone metastasis and on alpha(v)beta(3) signaling in prostate cancer cells. The data suggest that alpha(v)beta(3), in part, facilitates prostate cancer metastasis to bone by mediating prostate cancer cell adhesion to and migration on osteopontin and vitronectin, which are common proteins in the bone microenvironment. These biological events require the activation of focal adhesion kinase and the subsequent activation of PI-3 kinase/Akt signaling pathway.     

The crucial role of cyclooxygenase-2 in osteopontin-induced protein kinase C alpha/c-Src/IkappaB kinase alpha/beta-dependent prostate tumor progression and angiogenesis

The regulation of tumor progression towards its malignancy needs the interplay among several cytokines, growth factors, and enzymes, which are controlled in the tumor microenvironment. Here, we report that osteopontin, a small integrin-binding ligand N-linked glycoprotein family of calcified extracellular matrix-associated protein, regulates prostate tumor growth by regulating the expression of cyclooxygenase-2 (COX-2). We have shown that osteopontin stimulates the activation of protein kinase C alpha/nuclear factor-inducing kinase/nuclear factor-kappaB-dependent signaling cascades that induces COX-2 expression, which in turn regulates the prostaglandin E(2) production, matrix metalloproteinase-2 activation, and tumor progression and angiogenesis. We have revealed that suppression of osteopontin-induced COX-2 expression by the nonsteroidal anti-inflammatory drug celecoxib or blocking the EP2 receptor by its blocking antibody resulted in significant inhibition of cell motility and tumor growth and angiogenesis. The data also showed that osteopontin-induced mice PC-3 xenograft exhibits higher tumor load, increased tumor cell infiltration, nuclear polymorphism, and neovascularization. Interestingly, use of celecoxib or anti-EP2 blocking antibody drastically suppressed osteopontin-induced tumor growth that further indicated that suppression of COX-2 or its metabolites could significantly inhibit osteopontin-induced tumor growth. Human clinical prostate cancer specimen analysis also supports our in vitro and animal model studies. Our findings suggest that blockage of osteopontin and/or COX-2 is a promising therapeutic approach for the inhibition of prostate tumor progression and angiogenesis.     

Effect of type I growth factor receptor tyrosine kinase inhibitors on phosphorylation and transactivation activity of the androgen receptor in prostate cancer cells: Ligand-independent activation of the N-terminal domain of the androgen receptor

Although there have been several studies suggesting the involvement of growth factor receptor tyrosine kinases in ligand-independent activation of the androgen receptor (AR) and progression of prostate cancer, limited studies have been reported actually showing the enhancement of phosphorylation of the AR in vivo in response to growth factors or activation of their receptors in prostate cancer cells. In this study, we have demonstrated that overexpression of HER2/Neu enhanced in vivo phosphorylation of the AR and MAP kinase in DU-145 cells, and that the HER2/Neu inhibitor TAK165 reduced the HER2/Neu-enhanced phosphorylated AR and MAP kinase, indicating that the MAP kinase pathway seems to be involved in the phosphorylation of the AR by HER2/Neu. Both HER2/Neu inhibitor TAK165 and EGFR tyrosine kinase inhibitor gefitinib ('Iressa', ZD1839) successfully reduced the HER2/Neu-induced transactivation activity of the AR in PC-3 and DU-145 cells, suggesting that these inhibitors are possible therapeutic drugs for patients with hormone-refractory prostate cancer. The transactivation activity of the AF-1+DBD of the AR was enhanced by HER2/Neu overexpression while that of the AF-2+DBD was not, demonstrating that the enhancement of the AR activity by HER2/Neu was mainly mediated through the AF-1 of the AR.     

HER-2/neu receptor in prostate cancer development and progression to androgen independence

Development of prostate cancer and progression to androgen-independent disease is correlated with increased expression of growth factors and receptors capable of establishing autocrine and/or paracrine growth-stimulatory loops. A thorough review was made of the current literature and recent abstract presentations at scientific meetings focusing on the role of the HER-2/neu (c-erbB2) receptor in prostate cancer and the potential clinical usefulness of its specific inhibitors. In the past 10 years, conflicting results on HER-2/neu expression in prostate cancer have been reported. More recently, four studies have shown experimental evidence of HER-2/neu in the development of prostate cancer and, more specifically, in the progression to a hormone-refractory clinical behavior. Furthermore, it has been proposed that HER-2 family and androgen receptors function synergistically in the absence of androgen, which suggests a cross-talk between the HER-2/neu and androgen receptor pathways. Finally, clinical trials are in progress in prostate cancer patients to test novel agents that selectively interfere with HER-2/neu activity.     

The androgen receptor and stem cell pathways in prostate and bladder cancers (review)

Bladder cancer is three times more common in men than in women. However, the physiological basis of the male predominance of bladder cancer remains poorly understood. A higher than expected association of prostate and bladder cancers has also been reported which may indicate a common mechanism of carcinogenesis. Consistent with this, androgens and the androgen receptor (AR) play essential roles in prostate carcinogenesis and are believed to play a role in bladder carcinogenesis. There is also evidence implicating cancer stem cells in prostate and bladder cancers. Indeed putative prostate and bladder cancer stem cells share some common molecular features. We highlight key proteins (CD49f, CD133, PTEN, CD44) which are implicated in both prostate and bladder cancers and are enriched in putative prostate and bladder cancer stem cells. We examine published chromatin immuno-precipitation studies analyzing the genome-wide distribution of the AR to identify AR association with, and by inference potential AR-regulation of, these loci. We discuss recent evidence indicating a role for the AR in the splicing of the key urological stem cell protein CD44. We propose a model whereby aberrant AR regulation of these putative stem cell proteins contributes to malignant transformation of prostate and bladder cells. For these reasons we propose that the relationship between androgens and cancer stem cell associated proteins warrants further investigation.     

Inhibition of tumor growth and progression of LNCaP prostate cancer cells in athymic mice by androgen and liver X receptor agonist

Androgen-dependent human LNCaP 104-S tumor xenografts progressed to androgen-independent relapsed tumors (104-Rrel) in athymic mice after castration. The growth of 104-Rrel tumors was suppressed by testosterone. However, 104-Rrel tumors adapted to androgen and regrew as androgen-stimulated 104-Radp tumors. Androgen receptor expression in tumors and serum prostate-specific antigen increased during progression from 104-S to 104-Rrel but decreased during transition from 104-Rrel to 104-Radp. Expression of genes related to liver X receptor (LXR) signaling changed during progression. LXRalpha, LXRbeta, ATP-binding cassette transporter A1 (ABCA1), and sterol 27-hydroxylase decreased during progression from 104-S to 104-Rrel. These coordinated changes in LXR signaling in mice during progression are consistent with our previous findings that reduction of ABCA1 gene expression stimulates proliferation of LNCaP cells. To test if attenuation of LXR signaling may enhance prostate cancer progression from an androgen-dependent state to an androgen-independent state, castrated mice carrying 104-S tumors were given the synthetic LXR agonist T0901317 by gavage. T0901317 delayed progression from 104-S to 104-Rrel tumors. Based on our in vivo model, androgen is beneficial for the treatment of androgen-independent androgen receptor-rich prostate cancer and modulation of LXR signaling may be a potentially useful therapy for prostate cancer.     

Clinical significance of expression of estrogen receptor alpha and beta mRNAs in ovarian cancers

Novel human estrogen receptor (ER)-beta was identified in cDNA libraries from human testis. ER-beta specifically expresses in testis, ovary, thymus, spleen, osteoblasts and fetus. ER-beta might not conserve the same physiological functions as does ER-alpha. Therefore, the clinical significance of the expression of ER-alpha and ER-beta mRNAs in ovarian cancers was investigated. The percentage of ER-beta mRNA to ER-alpha mRNA ranged from 1.5 to 10% in normal ovaries. On the other hand, the ratios of ER-beta mRNA to ER-alpha mRNA were in a wide range in ovarian cancers. There was no significant difference in the ratios among ovarian cancers classified according to histological types or clinical stages. In a 48-month survival rate, the patient prognosis in ovarian cancers with a low or high ratio of ER-beta mRNA to ER-alpha mRNA (<1.5 or >10% of ER-beta mRNA to ER-alpha mRNA) was significantly worse than that in ovarian cancers with a medium ratio (>==1.5 to <==10% of ER-beta mRNA to ER-alpha mRNA). In conclusion, the intact synchronized expression of ER-beta mRNA interacting with ER-alpha mRNA might be damaged in some ovarian cancers, which might lead to poor patient prognosis.