Function In Prostate Cancer Cells Research Articles

Coactivator MYST1 Regulates Nuclear Factor-κB and Androgen Receptor Functions During Proliferation of Prostate Cancer Cells

In prostate cancer (PCa), the functional synergy between androgen receptor (AR) and nuclear factor-κ B (NF-κB) escalates the resistance to therapeutic regimens and promotes aggressive tumor growth. Although the underlying mechanisms are less clear, gene regulatory abilities of coactivators can bridge the transcription functions of AR and NF-κB. The present study shows that MYST1 (MOZ, YBF2 and SAS2, and TIP60 protein 1) costimulates AR and NF-κB functions in PCa cells. We demonstrate that activation of NF-κB promotes deacetylation of MYST1 by sirtuin 1. Further, the mutually exclusive interactions of MYST1 with sirtuin 1 vs AR regulate the acetylation of lysine 16 on histone H4. Notably, in AR-lacking PC3 cells and in AR-depleted LNCaP cells, diminution of MYST1 activates the cleavage of poly(ADP-ribose) polymerase and caspase 3 that leads to apoptosis. In contrast, in AR-transformed PC3 cells (PC3-AR), depletion of MYST1 induces cyclin-dependent kinase (CDK) N1A/p21, which results in G2M arrest. Concomitantly, the levels of phospho-retinoblastoma, E2F1, CDK4, and CDK6 are reduced. Finally, the expression of tumor protein D52 (TPD52) was unequivocally affected in PC3, PC3-AR, and LNCaP cells. Taken together, the results of this study reveal that the functional interactions of MYST1 with AR and NF-κB are critical for PCa progression.

Abstract 1924: Thrombospondin-2 expression is down-regulated in prostate cancer and is associated with inhibition of prostate cancer progression.

Abstract Introduction: Thrombospondin 2 (THBS2 or TSP2) is a secreted glycoprotein associated with tumor growth and angiogenesis inhibition. TSP2 expression levels are altered in many tumors, but, to date, there is no detailed analysis of TSP2 expression and function in prostate cancer (PCa). Objectives: The aim of this work was to characterize TSP2 expression levels in PCa and its potential usefulness for the differential diagnosis between PCa and benign prostatic hyperplasia (BPH), besides characterizing TSP2 functions in PCa. Methods: TSP2 transcript expression levels were analyzed by quantitative real time PCR, in PCa and BPH tissue samples and tumor and non-tumor cell lines. TSP2 protein expression levels were assessed by immunohistochemistry in a tissue microarray platform, containing 204 PCa and 66 BPH tissue samples, using a semi-automated image analysis system. To investigate TSP2 functions in PCa cells, PC3 and DU145 cell lines, were treated with recombinant TSP2 protein (rTSP2) (50 ug/ml) and were subjected to proliferation end point assays and cell cycle analysis. PC3 cells were also subjected to phosphoproteomic analysis using a phospho-antibody array. Results: Our data showed that TSP2 transcript expression levels are down-regulated in PCa tissue samples and cell lines, compared to BPH and non-tumoral samples (p<0.01). Receiving Operating Curve (ROC) analysis demonstrated that TSP2 transcript levels could better distinguish PCa from BPH tissue samples (p<0.01) than serum PSA levels (p=0.299). TSP2 protein expression was observed in the cytoplasm of both PCa and BPH epithelial and stromal cell compartments. TSP2 stromal staining scores were significantly lower in PCa than in BPH tissues (p<0.01), while similar TSP2 epithelial staining patterns were observed. Notably, TSP2 epithelial staining score was positively correlated to vascular invasion and biochemical recurrence in PCa (p<0.05). Treatment of PC3 and DU145 cells with rTSP2 significantly decreased the proliferation rate of these cells, while increased the percentage of cells in sub-G1 phase of the cell cycle. The phosphoproteomic analysis of PC3 cells treated with rTSP2 showed significantly lower phosphorylation levels of ERK and JNK proteins, in contrast to the higher phosphorylation status of p53, p27, paxillin and RSK. Conclusions: Our data indicate that lower TSP2 expression levels in PCa has potential application for the differential diagnosis of PCa and BPH, and suggests possible stromal and epithelial cross talks modulating PCa progression. Additionally, our results point to a putative role of TSP2 on negatively modulating PCa cell proliferation and survival, which could be partially associated with modulation of phosphorylation levels of proteins involved in the MAPK pathway and controlling the cell cycle. Citation Format: Aline R. Matos, Claudia M. Coutinho-Camillo, Eloisio A. Silva, Francisco P. Fonseca, Luiz C S Thuler, Fernando A. Soares, Etel R P Gimba. Thrombospondin-2 expression is down-regulated in prostate cancer and is associated with inhibition of prostate cancer progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1924. doi:10.1158/1538-7445.AM2013-1924

Lamin A/C protein is overexpressed in tissue-invading prostate cancer and promotes prostate cancer cell growth, migration and invasion through the PI3K/AKT/PTEN pathway

Prostate cancer (PC) remains the second most common cause of cancer-related death in Western countries. A previous proteomics study suggested that the nuclear membrane protein lamin A/C to be a maker to discriminate low- and high-Gleason score tumors and to identify high-risk cancers. To characterize its function in PC cells, we performed a detailed expression analysis in PC tissue and explored the consequences of down or upregulation of lamin A/C in PC cells. Our results confirm an increased lamin A/C protein expression in high-risk cancers and show association of expression with tumor cell formations at the invasion fronts of tumors and in invasion 'spearheading' tumor cell clusters. In the prostate tumor cell lines, LNCaP, DU145, and PC3 small hairpin RNA knockdown or overexpression of lamin A/C resulted in inhibition or stimulation, respectively, of cell growth, colony formation, migration and invasion. Further mechanism studies suggested that the lamin A/C-related malignant behavior is regulated through modulation of the phosphoinositide 3-kinase (PI3K)/AKT/PTEN signaling pathway. Western blot results indicated that knockdown or overexpression of lamin A/C decreased or increased, respectively, protein levels of the PI3K subunits p110 and p85 in all three cell lines; phosphor-AKT in the PTEN-negative cell lines LNCaP and PC3, and, increased or decreased, respectively, PTEN protein levels in PTEN-positive DU145 cells. Together, our data suggest that lamin A/C proteins are positively involved in malignant behavior of PC cells through the PI3K/AKT/PTEN pathway. Lamin A/C may represent a new oncogenic factor and a novel therapeutic target for PC.

Androgens Induce Functional CXCR4 through ERG Factor Expression in TMPRSS2-ERG Fusion-Positive Prostate Cancer Cells

TMPRSS2-ERG fusion transcripts have been shown to be expressed in a majority of prostate cancer (PC) patients because of chromosomal translocations or deletions involving the TMPRSS2 gene promoter and the ERG gene coding sequence. These alterations cause androgen-dependent ERG transcription factor expression in PC patients. We and others have shown that chemokine receptor CXCR4 expression is upregulated in PC tumor cells, and its ligand, CXCL12, is expressed in bone stromal cells. The CXCL12/CXCR4 axis functions in PC progression to enhance invasion and metastasis. To address the regulation of CXCR4 expression, we identified several putative ERG consensus-binding sites in the promoter region of CXCR4. We hypothesized that androgen-dependent regulation of the ERG transcription factor could induce CXCR4 expression in PC cells. Results of the current study show that 1) prostate tumor cells coexpress higher ERG and CXCR4 compared with benign tissue, 2) CXCR4 expression is increased in the TMPRSS2-ERG fusion-positive cell line, 3) ERG transcription factor binds to the CXCR4 gene promoter, 4) synthetic androgen (81881) upregulates both ERG and CXCR4 in TMPRSS2-ERG fusion-positive VCaP cells, 5) small interfering RNA-mediated down-regulation of ERG resulted in the loss of androgen-dependent regulation of CXCR4 expression in VCaP cells, and 6) 81881-activated TMPRSS2-ERG expression functionally activates CXCR4 in VCaP cells. These findings provide a link between TMPRSS2-ERG translocations and enhanced metastasis of tumor cells through CXCR4 function in PC cells.

Heat shock protein 27 mediates repression of androgen receptor function by protein kinase D1 in prostate cancer cells

We have previously shown that protein kinase D1 (PKD1), charter member of PKD protein family, is downregulated in advanced prostate cancer (PC) and influences androgen receptor (AR) function in PC cells. Other independent studies showed that serine 82 residue in heat shock protein 27 (Hsp27) undergoes substrate phosphorylation by PKD1 and is associated with nuclear transport of AR resulting in increased AR transcriptional activity. In this study, we show that PKD1 interacts and phosphorylates Hsp27 at Ser82 in PC cells, which is mediated by p38-dependent mitogen-activated protein kinase pathway and is necessary for PKD1 repression of AR transcriptional activity and androgen-dependent proliferation of PC cells. The study provides first in vivo evidence that Hsp27 is a mediator of repression of AR function by PKD1 in PC cells, thereby linking the data in the published literature.

Protein kinase D1 (PKD1) influences androgen receptor (AR) function in prostate cancer cells

Protein kinase D1 (PKD1), founding member of PKD protein family, is down-regulated in advanced prostate cancer (PCa). We demonstrate that PKD1 and androgen receptor (AR) are present as a protein complex in PCa cells. PKD1 is associated with a transcriptional complex which contains AR and promoter sequence of the Prostate Specific Antigen (PSA) gene. Ectopic expression of wild type PKD1 and the kinase dead mutant PKD1 (K628W) attenuated the ligand-dependent transcriptional activation of AR in prostate cancer cells and yeast cells indicating that PKD1 can affect AR transcription activity, whereas knocking down PKD1 enhanced the ligand-dependent transcriptional activation of AR. Co-expression of kinase dead mutant with AR significantly inhibited androgen-mediated cell proliferation in both LNCaP and DU145 PC cells. Our data demonstrate for the first time that PKD1 can influence AR function in PCa cells.

Is prostate-specific membrane antigen a multifunctional protein?

Prostate-specific membrane antigen (PSMA) is a metallopeptidase expressed predominantly in prostate cancer (PCa) cells. PSMA is considered a biomarker for PCa and is under intense investigation for use as an imaging and therapeutic target. Although the clinical utility of PSMA in the detection and treatment of PCa is evident and is being pursued, very little is known about its basic biological function in PCa cells. The purpose of this review is to highlight the possibility that PSMA might be a multifunctional protein. We suggest that PSMA may function as a receptor internalizing a putative ligand, an enzyme playing a role in nutrient uptake, and a peptidase involved in signal transduction in prostate epithelial cells. Insights into the possible functions of PSMA should improve the diagnostic and therapeutic values of this clinically important molecule.