Prostatic Neoplasms: Xu K

Xu K, Shimelis H, Linn DE, Jiang R, Yang X, Sun F, Guo Z, Chen H, Li W, Chen H, Kong X, Melamed J, Fang S, Xiao Z, Veenstra TD, Qiu Y. · Department of Pharmacology and Experimental Therapeutics and Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, MD 21201, USA. · Cancer Cell. · Pubmed #19345326 No free full text.

Abstract: The androgen receptor (AR) plays a critical role in prostate cancer. We have identified a ubiquitin E3 ligase, RNF6, as an AR-associated protein in a proteomic screen. RNF6 induces AR ubiquitination and promotes AR transcriptional activity. Specific knockdown of RNF6 or mutation of RNF6-induced ubiquitination acceptor sites on AR selectively alters expression of a subset of AR target genes and diminishes recruitment of AR and its coactivators to androgen-responsive elements present in the regulatory region of these genes. Furthermore, RNF6 is overexpressed in hormone-refractory human prostate cancer tissues and required for prostate cancer cell growth under androgen-depleted conditions. Our data suggest that RNF6-induced ubiquitination may regulate AR transcriptional activity and specificity through modulating cofactor recruitment.

Xie Y, Xu K, Linn DE, Yang X, Guo Z, Shimelis H, Nakanishi T, Ross DD, Chen H, Fazli L, Gleave ME, Qiu Y. · Department of Pharmacology and Experimental Therapeutics, University of Maryland, Baltimore 21201, USA. · J Biol Chem. · Pubmed #18056989 links to  free full text

Abstract: We previously showed that the 44-kDa serine/threonine kinase Pim-1 (Pim-1L) can protect prostate cancer cells from apoptosis induced by chemotherapeutic drugs (Xie, Y., Xu, K., Dai, B., Guo, Z., Jiang, T., Chen, H., and Qiu, Y. (2006) Oncogene 25, 70-78). To further explore the mechanisms of Pim-1L-mediated resistance to chemotherapeutic drugs in prostate cancer cells, we employed a yeast two-hybrid screening to identify cellular proteins that were associated with Pim-1L, and we found the ABC transporter BCRP/ABCG2 as one of the potential interacting partners of Pim-1L. We also showed that the expression level of Pim-1L and BCRP was up-regulated in mitoxantrone and docetaxel-resistant prostate cancer cell lines. Pim-1L was co-localized with BCRP on the plasma membrane and induced phosphorylation of BCRP at threonine 362. Knocking-down Pim-1L expression in the drug-resistant prostate cancer cells abolished multimer formation of endogenous BCRP and resensitized the resistant cells to chemotherapeutic drugs suggesting that BCRP phosphorylation induced by Pim-1L was essential for its functionality. This is further corroborated by our finding that the plasma membrane localization and drug-resistant activity of BCRP were compromised by T362A mutation. Our data suggest that Pim-1L may protect prostate cancer cells from apoptosis, at least in part, through regulation of transmembrane drug efflux pump. These findings may provide a potential therapeutic approach by disrupting Pim-1 signaling to reverse BCRP-mediated multidrug resistance.

Guo Z, Dai B, Jiang T, Xu K, Xie Y, Kim O, Nesheiwat I, Kong X, Melamed J, Handratta VD, Njar VC, Brodie AM, Yu LR, Veenstra TD, Chen H, Qiu Y. · Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA. · Cancer Cell. · Pubmed #17045208 No free full text.

Abstract: The androgen receptor (AR) is essential for the growth of prostate cancer cells. Here, we report that tyrosine phosphorylation of AR is induced by growth factors and elevated in hormone-refractory prostate tumors. Mutation of the major tyrosine phosphorylation site in AR significantly inhibits the growth of prostate cancer cells under androgen-depleted conditions. The Src tyrosine kinase appears to be responsible for phosphorylating AR, and there is a positive correlation of AR tyrosine phosphorylation with Src tyrosine kinase activity in human prostate tumors. Our data collectively suggest that growth factors and their downstream tyrosine kinases, which are elevated during hormone-ablation therapy, can induce tyrosine phosphorylation of AR and such modification may be important for prostate tumor growth under androgen-depleted conditions.

Dai B, Kim O, Xie Y, Guo Z, Xu K, Wang B, Kong X, Melamed J, Chen H, Bieberich CJ, Borowsky AD, Kung HJ, Wei G, Ostrowski MC, Brodie A, Qiu Y. · Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, MD 21201, USA. · Cancer Res. · Pubmed #16912182 links to  free full text

Abstract: The nonreceptor tyrosine kinase Etk/BMX was originally identified from the human prostate xenograft CWR22. Here, we report that Etk is up-regulated in human prostate tumor specimens surveyed. Knocking down Etk expression by a specific small interfering RNA (siRNA) in prostate cancer cells attenuates cell proliferation, suggesting an essential role of Etk for prostate cancer cell survival and growth. Targeted expression of Etk in mouse prostate epithelium results in pathologic changes resembling human prostatic intraepithelial neoplasia, indicating that up-regulation of Etk may contribute to prostate cancer development. A marked increase of luminal epithelial cell proliferation was observed in the Etk transgenic prostate, which may be attributed in part to the elevated activity of Akt and signal transducers and activators of transcription 3 (STAT3). More interestingly, the expression level of acetyltransferase cyclic AMP-responsive element binding protein-binding protein (CBP) is also increased in the Etk transgenic prostate as well as in a prostate cancer cell line overexpressing Etk, concomitant with elevated histone 3 acetylation at lysine 18 (H3K18Ac). Down-modulation of Etk expression by a specific siRNA leads to a decrease of H3 acetylation in prostate cancer cell lines. Our data suggest that Etk may also modulate chromatin remodeling by regulating the activity of acetyltransferases, such as CBP. Given that Etk may exert its effects in prostate through modulation of multiple signaling pathways altered in human prostate cancer, the Etk transgenic mouse model may be a useful tool for studying the functions of Etk and identification of new molecular markers and drug targets relevant to human diseases.

Xu K, Ling MT, Wang X, Wong YC. · Department of Anatomy, Laboratory Block, Faculty of Medicine, The University of Hong Kong, Hong Kong, HKSAR, China. · Prostate Cancer Prostatic Dis. · Pubmed #16683014 No free full text.

Abstract: Benign prostate hyperplasia (BPH) is a common disease in elderly men. Although it is a non-malignant disease, it has a significant detrimental impact on the quality of life in patients with late-stage disease. Owing to the lack of specific markers, diagnosis of early-stage BPH has been proven unsuccessful. Recently, using two-dimensional electrophoresis, we identified a group of prostatic secretory proteins that are specifically produced by BPH cells (Xu et al., Electrophoresis 2003; 24: 1311). In this study, we investigated the potential diagnostic value of one of the secretory proteins, alphas1-Casein, in BPH by inmmunohistological staining of normal, BPH and prostate cancer tissues. We found that 90% (20 out of 22) of BPH tissues showed moderate to strong alphas1-Casein protein expression whereas none of the normal tissues (0 out of 10) and less than 10% of the prostate cancer tissues (3 out of 30) showed similar staining intensity. Our results suggest that alphas1-Casein may be a potential biomarker for early identification of BPH patients.

Xie Y, Xu K, Dai B, Guo Z, Jiang T, Chen H, Qiu Y. · Department of Pharmacology & Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, MD 21201, USA. · Oncogene. · Pubmed #16186805 No free full text.

Abstract: Protein kinase Pim-1 has been implicated in the development of hematopoietic and prostatic malignancies. Here, we present the evidence that two isoforms, the 44 and 33 kDa Pim-1, are expressed in all human prostate cancer cell lines examined. The subcellular localization of human 44 kDa Pim-1 is primarily on the plasma membrane, while the 33 kDa isoform is present in both the cytosol and nucleus in PCA cells. The 44 kDa Pim-1 contains the proline-rich motif at the N-terminus and directly binds to the SH3 domain of tyrosine kinase Etk. Such interaction leads to the activation of Etk kinase activity possibly by competing with the tumor suppressor p53. This is corroborated by the fact that overexpression of the 44 kDa Pim-1 in prostate cancer cells confers the resistance to chemotherapeutic drugs. Our results suggest that these two isoforms of Pim-1 kinase may regulate distinct substrates and the 44 kDa Pim-1 may play a more prominent role in drug resistance in prostate cancer cells.

Xu K, Wang X, Xue W, Wang X, Hou S. · Department of Urology, Peking University People's Hospital, Beijing 100044, China. · Beijing Da Xue Xue Bao. · Pubmed #14710249 No free full text.

Abstract: OBJECTIVE: To investigate if downregulation of two mitotic checkpoint proteins, MAD2 and p55CDC, is a frequent event in human prostate cancer and whether decreased expression of these two proteins are associated with progression of prostate cancer. METHODS: Using immunohistochemistry technique, the expressions of MAD2 and p55CDC proteins are examined in 46 benign prostate hyperplasia (BPH) and 65 prostate cancer tissues. Differential expressions were compared first between BPH and prostate cancer specimens, and then among prostate cancer samples with different Gleason grades. RESULTS: We found that down-regulation of MAD2 and p55CDC expressions was significant in prostate cancer (96% and 83%, respectively) compared to BPH (19.5% and 4.3%, respectively) (P<0.001). In addition, decreased expression levels of these two proteins were associated with increased Gleason grade. CONCLUSION: Our results indicate that loss of MAD2 and p55CDC protein expression is a frequent event in prostate carcinoma and the decreased expressions of these two proteins are associated with increased Gleason grade. Our results provide first in vivo evidence to support the hypothesis that down regulation of certain mitotic checkpoint proteins plays an important part in human tumourigenesis.

Xu K, Wang X, Ling PM, Tsao SW, Wong YC. · Department of Urology, People's Hospital, Beijing, China. · Oncol Rep. · Pubmed #12883741 No free full text.

Abstract: Prostate cancer is the second leading cause of cancer-related death in men. Treatment failure in prostate cancer is usually due to the development of androgen independence and resistance to chemotherapeutic drugs at an advanced stage. Recently, it was reported that the alpha1-adrenoceptor antagonist terazosin was able to inhibit prostate cancer cell growth and indicated that it may have an implication in the treatment of prostate cancer. The aim of the present study was to investigate the mechanisms involved in terazosin-induced prostate cancer cell death using two androgen-independent cell lines, PC-3 and DU145. Our results showed that terazosin inhibited not only prostate cancer cell growth but also colony forming ability, which is the main target of chemotherapy. We also found that the sensitivity of these cells to terazosin was not affected by the presence of either functional p53 or Rb, suggesting that the terazosin-induced cell death was independent of p53 and Rb. However, the terazosin-induced cell death was associated with G1 phase cell cycle arrest and up-regulation of p27KIP1. In addition, up-regulation of Bax and down-regulation of Bcl-2 was also observed indicating that these two apoptotic regulators may play important roles in terazosin-mediated cell death pathway. Our results provide evidence for the first time that terazosin may have a therapeutic potential in the treatment of advanced prostate cancer.

Ling MT, Wang X, Ouyang XS, Xu K, Tsao SW, Wong YC. · Cancer Biology Group, Department of Anatomy, Laboratory Block, Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, SAR, China. · Oncogene. · Pubmed #12881706 No free full text.

Abstract: The growth-promoting effect of Id-1 (inhibitor of differentiation/DNA binding) has been demonstrated in a number of human cancers. However, the mechanisms responsible for its action are not clear. In this study, we report that in prostate cancer cells, Id-1 promotes cell survival through activation of nuclear factor-kappaB (NF-kappaB) signalling pathway. After stable expression of Id-1 protein in LNCaP cells, we found that the Id-1 transfectants showed increased resistance to apoptosis induced by TNFalpha through inactivation of Bax and caspase 3. In addition, in the LNCaP cells expressing ectopic Id-1 protein, we also observed increased NF-kappaB transactivation activity and nuclear translocation of the p65 and p50 proteins, which was accompanied by upregulation of their downstream effectors Bcl-xL and ICAM-1. These results indicate that the Id-1-induced antiapoptotic effect may be via NF-kappaB signalling transduction pathway in these cells. In addition, inactivation of Id-1 by its antisense oligonucleotide and retroviral construct in DU145 cells resulted in the decrease of nuclear level of p65 and p50 proteins, which was associated with increased sensitivity to TNFalpha-induced apoptosis. Our results strongly suggest that Id-1 may be one of the upstream regulators of NF-kappaB and activation of NF-kappaB signalling pathway may be essential for Id-1 induced cell proliferation through protection against apoptosis. Our findings also suggest a potential therapeutic strategy in which inactivation of Id-1 may lead to sensitization of prostate cancer cells to chemotherapeutic drug-induced apoptosis.

Ling MT, Wang X, Ouyang XS, Lee TK, Fan TY, Xu K, Tsao SW, Wong YC. · Cancer Biology Laboratory, Department of Anatomy, Faculty of Medicine, The University of Hong Kong, Hong Kong, SAR, China. · Oncogene. · Pubmed #12466969 links to  free full text

Abstract: The helix-loop-helix protein Id-1 has been suggested to play a positive role in cell proliferation and tumorigenesis of many types of human cancers. However, little is known about the molecular mechanism involved in the function of Id-1. In this study, using four stable Id-1 transfectant clones, we investigated the involvement of MAPK signaling pathway in the Id-1 induced serum independent prostate cancer cell growth. Our results demonstrated that both transient and stable ectopic Id-1 expression in prostate cancer LNCaP cells led to activation of the Raf/MEK1/2 signaling pathway. In addition, inhibition of MEK1/2 phosphorylation by one of its inhibitors, PD098059, resulted in the decreased cell cycle S phase fraction and cell growth rate, suggesting that activation of MAPK signaling pathway is essential for Id-1 induced prostate cancer cell proliferation. Furthermore, treatment with antisense oligonucleotide complementary to Id-1 mRNA in PC-3 and DU145 cells resulted in a decreased Id-1 expression which was accompanied by decreased Egr-1 protein. Our results suggest for the first time that the function of Id-1 is associated with MAPK signaling pathway activation and indicate a possible novel mechanism in which Id-1 regulates prostate cancer cell growth and tumorigenesis.

Ouyang X, Wang X, Xu K, Jin DY, Cheung AL, Tsao SW, Wong YC. · Department od Anatomy, Faculty of Medicine, University of Hong Kong, SAR, PR China. · Biochim Biophys Acta. · Pubmed #11755215 No free full text.

Abstract: Chromosomal instability (CIN) is one of the common features in prostate cancer, especially in advanced stages. Recently, the involvement of p53 in CIN through the regulation of centrosome amplification has been proposed in certain tumor types. In this study, we investigated the relationship between p53 and centrosome amplification in prostate cancer cells. Increased centrosome number and size were observed in DU145 and PC3 containing nonfunctional p53 compared to LNCap which expressed wild-type p53. Transfection of p53 into PC3 cells resulted in a decreased cell growth rate, G2/M arrest and decreased centrosome abnormalities. We provide the first evidence on a correlation between loss of p53 function and centrosome amplification in prostate cancer cells. Our results indicate that p53 may play a role in the regulation of centrosome amplification and loss of p53 may be one of the mechanisms involving CIN in prostate cancer cells.

Xu K, Wang X, Ling M, Wong Y. · Department of Urology, People's Hospital, Peking University, Beijing 100044, China. · Chin Med J (Engl). · Pubmed #14642133 links to  free full text

Abstract: OBJECTIVE: To study the effects of an alpha(1)-adrenoceptor antagonist, terazosin on the androgen-independent prostate cancer cell lines PC-3 and DU145. METHODS: Two androgen independent cell lines, PC-3 and DU145, were used to determine cell viability, colony-forming ability, as well as cell cycle distribution, after exposure to terazosin. Western blot analysis was used to determine the expression of p21WAF1 and p27KIP1. RESULTS: This study shows that terazosin inhibits not only prostate cancer cell growth but also its colony forming ability, both of which are main targets of clinical treatment. In addition, terazosin is shown to inhibit cell growth through G1 phase cell cycle arrest and the up-regulation of p27(KIP1). CONCLUSION: This study provides evidence that the alpha(1)-adrenoceptor antagonist terazosin may have therapeutic potential in the treatment of advanced hormone refractory prostate cancer.