ARP2 a novel protein involved in apoptosis of LNCaP cells shares a high degree homology with splicing factor Prp8

The mechanism of apoptosis has been recognized as an important event in processes such as cellular development and homeostasis, as well as degenerative conditions like cancer. Prostate cancer during its advanced stages develops androgen independent cells that ultimately overgrow and promote metastatic events. Our group employing androgen independent LNCaP cells have previously proposed, based on electrophysiological findings, that apoptosis induced cells overexpress a cell death calcium channel-like molecule. Here we report the cloning and expression in Xenopus laevis oocytes of apoptosis regulated protein 2 (ARP2), a protein overexpressed in apoptosis induced LNCaP cells capable to induce calcium inward currents and apoptosis typical morphology changes in oocytes injected with arp2 mRNA. Our results also indicate that clone arp2 cDNA (1.3Kb) shares a 99% homology with a small fragment that corresponds to 18% of the complete sequence of Prp8 cDNA (7.0 Kb), a molecule that codifies for an important protein in the assembly of the spliceosome. We propose that protein ARP2 as a fragment of protein Prp8, corresponds to a molecule with a new function in apoptosis related phenomena.     

Down-regulation of DcR2 sensitizes androgen-dependent prostate cancer LNCaP cells to TRAIL-induced apoptosis

Background

Dysregulation of many apoptotic related genes and androgens are critical in the development, progression, and treatment of prostate cancer. The differential sensitivity of tumour cells to TRAIL-induced apoptosis can be mediated by the modulation of surface TRAIL receptor expression related to androgen concentration. Our previous results led to the hypothesis that downregulation of TRAIL-decoy receptor DcR2 expression following androgen deprivation would leave hormone sensitive normal prostate cells vulnerable to the cell death signal generated by TRAIL via its pro-apoptotic receptors. We tested this hypothesis under pathological conditions by exploring the regulation of TRAIL-induced apoptosis related to their death and decoy receptor expression, as also to hormonal concentrations in androgen-sensitive human prostate cancer, LNCaP, cells.

Results

In contrast to androgen-insensitive PC3 cells, decoy (DcR2) and death (DR5) receptor protein expression was correlated with hormone concentrations and TRAIL-induced apoptosis in LNCaP cells. Silencing of androgen-sensitive DcR2 protein expression by siRNA led to a significant increase in TRAIL-mediated apoptosis related to androgen concentration in LNCaP cells.

Conclusions

The data support the hypothesis that hormone modulation of DcR2 expression regulates TRAIL-induced apoptosis in LNCaP cells, giving insight into cell death induction in apoptosis-resistant hormone-sensitive tumour cells from prostate cancer. TRAIL action and DcR2 expression modulation are potentially of clinical value in advanced tumour treatment.     

Suppressive role of regucalcin in liver cell proliferation: involvement in carcinogenesis

Regucalcin (RGN/SMP30) was discovered in 1978 and is a unique calcium‐binding protein contains no EF‐hand motif calcium‐binding domain. Its name, regucalcin, was proposed as it suppresses activation of enzymes related to calcium signalling. The regucalcin gene (rgn) is localized on the X chromosome. Regucalcin plays its role of suppressor protein in intracellular signalling pathways, including of protein kinases and protein phosphatase activities, protein synthesis, and DNA and RNA synthesis in liver cells. Overexpression of endogenous regucalcin has a suppressive effect on cell proliferation in modelled rat hepatoma H4‐II‐E cells, which are induced by various signalling stimulations in vitro. This suppressive effect is independent of apoptosis. Endogenous regucalcin plays a suppressive role on overproduction of proliferating cells in regenerating rat liver in vivo. Regucalcin mRNA expression is uniquely down‐regulated in development of carcinogenesis in liver of rats in vivo. Regucalcin mRNA and protein expressions are also depressed in human hepatoma HepG2 cells, MCF‐7 breast cancer cells, and prostate cancer LNCaP cells. Depression of regucalcin expression may be associated with activity progression of carcinogens. Regucalcin may be a key molecule suppressor protein in cell proliferation and carcinogenesis.     

Benzyldihydroxyoctenone, a novel nonsteroidal antiandrogen, shows differential apoptotic induction in prostate cancer cells in response to their androgen responsiveness

The molecular mechanisms of apoptotic induction by benzyldihydroxyoctenone (BDH), a nonsteroidal antiandrogen, isolated from the culture broth of Streptomyces sp., have been previously published in prostate cancer LNCaP cells. Apoptotic induction of BDH-treated LNCaP cells was associated with downregulation of Bcl-xL that caused, in turn, cytochrome c release from mitochondria, and activation of procaspases and specific proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). The purpose of the present study was to investigate the patterns of apoptotic induction by BDH in non-prostate, ovarian cancer PA-1 (androgen-independent and -insensitive) cells and prostate cancer cells with different androgen responsiveness, such as C4-2 (androgen-independent and -sensitive), 22Rv1 (androgen-dependent and -low sensitive), and LNCaP (androgen-dependent and -high sensitive) cells. We found that BDH-treated LNCaP cell proliferation was significantly inhibited in a time-dependent manner and induced apoptosis via downregulation of the androgen receptor (AR) and prostate-specific antigen (PSA), as well as antiapoptotic Bcl-xL protein. However, the levels of BDH-mediated apoptotic induction and growth inhibition in 22Rv1 cells were apparently lower than those of LNCaP cells. In contrast, the induction of apoptosis and antiproliferative effect in BDH-treated non-prostate cancer PA-1 and hormone refractory C4-2 cells were not detectable and marginal, respectively. Therefore, BDH-mediated differential apoptotic induction and growth inhibition in a cell type seem to be obviously dependent on its androgen responsiveness; primarily on androgen-dependency, and then on androgen sensitivity.     

Androgen Suppresses the Proliferation of Androgen Receptor-Positive Castration-Resistant Prostate Cancer Cells via Inhibition of Cdk2, CyclinA,and Skp2

The majority of prostate cancer (PCa) patient receiving androgen ablation therapy eventually develop castration-resistant prostate cancer (CRPC). We previously reported that androgen treatment suppresses Skp2 and c-Myc through androgen receptor (AR) and induced G1 cell cycle arrest in androgen-independent LNCaP 104-R2 cells, a late stage CRPC cell line model. However, the mechanism of androgenic regulation of Skp2 in CRPC cells was not fully understood. In this study, we investigated the androgenic regulation of Skp2 in two AR-positive CRPC cell line models, the LNCaP 104-R1 and PC-3^AR Cells. The former one is an early stage androgen-independent LNCaP cells, while the later one is PC-3 cells re-expressing either wild type AR or mutant LNCaP AR. Proliferation of LNCaP 104-R1 and PC-3^AR cells is not dependent on but is suppressed by androgen. We observed in this study that androgen treatment reduced protein expression of Cdk2, Cdk7, Cyclin A, cyclin H, Skp2, c-Myc, and E2F-1; lessened phosphorylation of Thr14, Tyr15, and Thr160 on Cdk2; decreased activity of Cdk2; induced protein level of p27^Kip1; and caused G1 cell cycle arrest in LNCaP 104-R1 cells and PC-3^AR cells. Overexpression of Skp2 protein in LNCaP 104-R1 or PC-3^AR cells partially blocked accumulation of p27^Kip1 and increased Cdk2 activity under androgen treatment, which partially blocked the androgenic suppressive effects on proliferation and cell cycle. Analyzing on-line gene array data of 214 normal and PCa samples indicated that gene expression of Skp2, Cdk2, and cyclin A positively correlates to each other, while Cdk7 negatively correlates to these genes. These observations suggested that androgen suppresses the proliferation of CRPC cells partially through inhibition of Cyclin A, Cdk2, and Skp2.     

Radiopotentiation of enzalutamide over human prostate cancer cells as assessed by real-time cell monitoring

AimTo evaluate the radiopotentiation of enzalutamide in human prostate cancer cells.BackgroundWhile radiotherapy is the first line of treatment for prostate cancer, androgen blockade therapies are demonstrating significant survival benefit as monotherapies. As androgen blockade can cause cell death by apoptosis, it is likely that androgen blockade will potentiate the cytotoxic activities of radiotherapy.Materials and methodsHere, we tested the potential synergistic effects of these two treatments over two human metastatic prostate cancer cells by real-time cell analysis (RTCA), androgen-sensitive LNCaP cells (Lymph Node Carcinoma of the Prostate) and androgen-independent PC-3. Both cell lines were highly resistant to high doses of radiotherapy.ResultsA pre-treatment of LNCaP cells with IC50 concentrations of enzalutamide significantly sensitized them to radiotherapy through enhanced apoptosis. In contrast, enzalutamide resistant PC-3 cells were not sensitized to radiotherapy by androgen blockade.ConclusionsThese results provide evidence that the enzalutamide/radiotherapy combination could maximize therapeutic responses in patients with enzalutamide-sensitive prostate cancer.     

1H, 13C and 15N resonance assignments of a ribonucleoprotein complex consisting of Prp24-RRM2 bound to a fragment of U6 RNA

Saccharomyces cerevisiae Prp24 is an essential RNA binding protein involved in pre-mRNA splicing. Nearly complete backbone and side chain resonance assignments have been obtained for the second RNA recognition motif (RRM) of Prp24 (RRM2, residues M114-E197) both in isolation and bound to a six nucleotide fragment of U6 RNA (AGAGAU). In addition, nearly complete backbone assignments have been made for a Prp24 construct spanning the second and third RRMs (RRM23, residues M114-K290), both free and bound to AGAGAU.     

A protein in rat prostatic interacting with androgen regulated gene

2M NaCl-insoluble fraction of rat ventral prostatechromatin(residual proteins)contain proteins able tointeract specifically with androgen-receptor complex andis,therefore,a part of the acceptor complex.Amongresidual proteins,a 97 KDa protein has been found whichbinds signifieantly to a genomic fragment containingan androgen-regulated gene coding for a 22 KDa protein.The biological significance of this binding in androgenaction need to be further studied. A mini-plasmid clone containing 22 KDa proteincoding sequence was cloned into Charon 4A genomiclibrary from which a 5.7 Kb genomic fragment wasisolated,identified by hybridization with a 5' and a 3'cDNA probes,and shown to contain the 5' flankingsequence.Restriction enzyme treatment of this fragmentyielded a 4.7 Kb restriction fragment representingthe 5' upstream region and a 1.0 Kb containing part ofthe coding sequence.Deletion studies indicated that the97 KDa protein bound only to a subclone of about 300 bpsegment.Furthermore,gel shifting experiment supportedits DNA-prptein binding.     

Pentafluorophenyl Substitution of Natural Di(indol‐3‐yl)methane Strongly Enhances Growth Inhibition and Apoptosis Induction in Various Cancer Cell Lines

Di(indol‐3‐yl)methane (=3,3′‐methanediyldi(1H‐indole), DIM, 1 ) is a known weakly antitumoral compound formed by digestion of indole‐3‐carbinol (=1H‐indol‐3‐ylmethanol), an ingredient of various Brassica vegetables. Out of a series of nine fluoroaryl derivatives of 1 , three pentafluorophenyl derivatives 2c , 2h , and 2i were identified that exhibited a two to five times greater anti‐proliferative effect and an increased apoptosis induction when compared with 1 in the following carcinoma cell lines: BxPC‐3 pancreas, LNCaP prostate, C4‐2B prostate, PC3 prostate and the triple‐negative MDA‐MB‐231 breast carcinoma. Compound 2h was particularly efficacious against androgen‐refractory C4‐2B prostate cancer cells (IC₅₀=6.4 μm ) and 2i against androgen‐responsive LNCaP cells (IC₅₀=6.2 μm ). In addition, 2c and 2h exhibited distinct activity in three cancer cell lines resistant to 1 .     

Combination effect of PectaSol and Doxorubicin on viability, cell cycle arrest and apoptosis in DU-145 and LNCaP prostate cancer cell lines

The effect of PectaSol on Dox (Doxorubicin) cytotoxicity in terms of apoptosis and cell cycle changes in PCa (prostate cancer) cell lines (DU‐145 and LNCaP) has been investigated. Combination of PectaSol and Dox resulted in a viability of 29.4 and 32.6% (P<0.001) in DU‐145 and LNCaP cells. The IC₅₀ values decreased 1.5‐fold and 1.3‐fold in the DU‐145 and LNCaP cells respectively. In the DU‐145 cells, combination of PectaSol and Dox resulted in a reduction in p27 gene and protein expression (P<0.001). In LNCaP cells, this combination increased p53, p27 and Bcl‐2 expression. Treatment with both drugs in DU‐145 cells led to an increase in sub‐G₁ arrest (54.6% compared with 12.2% in Dox). In LNCaP cells, combination of the drugs led to an increased in G₂/M arrest (61.7% compared with 53.6% in Dox). Based on these findings, progressive cytotoxicity effect of Dox and PectaSol together rapidly induce cell death in DU‐145 through apoptosis and in LNCaP cells through cell cycle arrest (G₂/M arrest).     

Castration-induced prostate epithelial cell apoptosis results from targeted oxidative stress attack of M1142-macrophages

Prostate development and function are regulated by androgens. Epithelial cell apoptosis in response to androgen deprivation is caspase-9-dependent and peaks at Day 3 after castration. However, isolated epithelial cells survive in the absence of androgens. Znf142 showed an on-off expression pattern in intraepithelial CD68-positive macrophages, with the on-phase at Day 3 after castration. Rats treated with gadolinium chloride to deplete macrophages showed a significant drop in apoptosis, suggesting a causal relationship between macrophages and epithelial cell apoptosis. Intraepithelial M1-polarization was also limited to Day 3, and the inducible nitric oxide synthase (iNOS) knockout mice showed significantly less apoptosis than wild-type controls. The epithelial cells showed focal DNA double-strand breaks (DSB), 8-oxoguanine, and protein tyrosine-nitrosylation, fingerprints of exposure to peroxinitrite. Cultured epithelial cells induced M1-polarization and showed focal DSB and underwent apoptosis. The same phenomena were reproduced in LNCaP cells cocultured with Raw 264.7 macrophages. In conclusion, the M1 ₁₄₂-macrophage (named after Znf142) attack causes activation of the intrinsic apoptosis pathway in epithelial cells after castration.     

Pterostilbene-Isothiocyanate Conjugate Suppresses Growth of Prostate Cancer Cells Irrespective of Androgen Receptor Status

Chemotherapy and anti-hormonal therapies are the most common treatments for non-organ-confined prostate cancer (PCa). However, the effectiveness of these therapies is limited, thus necessitating the development of alternative approaches. The present study focused on analyzing the role of pterostilbene (PTER)-isothiocyanate (ITC) conjugate – a novel class of hybrid compound synthesized by appending an ITC moiety on PTER backbone – in regulating the functions of androgen receptor (AR), thereby causing apoptosis of PCa cells. The conjugate molecule caused 50% growth inhibition (IC₅₀) at 40±1.12 and 45±1.50 μM in AR positive (LNCaP) and negative (PC-3) cells, respectively. The reduced proliferation of PC-3 as well as LNCaP cells by conjugate correlated with accumulation of cells in G2/M phase and induction of caspase dependent apoptosis. Both PI3K/Akt and MAPK/ERK pathways played an important and differential role in conjugate-induced apoptosis of these PCa cells. While the inhibitor of Akt (A6730) or Akt-specific small interference RNA (siRNA) greatly sensitized PC-3 cells to conjugate-induced apoptosis, on the contrary, apoptosis was accelerated by inhibition of ERK (by PD98059 or ERK siRNA) in case of LNCaP cells, both ultimately culminating in the expression of cleaved caspase-3 protein. Moreover, anti-androgenic activity of the conjugate was mediated by decreased expression of AR and its co-activators (SRC-1, GRIP-1), thus interfering in their interactions with AR. All these data suggests that conjugate-induced inhibition of cell proliferation and induction of apoptosis are partly mediated by the down regulation of AR, Akt, and ERK signaling. These observations provide a rationale for devising novel therapeutic approaches for treating PCa by using conjugate alone or in combination with other therapeutics.     

Difference in Protein Expression Profile and Chemotherapy Drugs Response of Different Progression Stages of LNCaP Sublines and Other Human Prostate Cancer Cells

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, 80-90% of the patients who receive androgen ablation therapy ultimately develop recurrent tumors in 12-33 months after treatment with a median overall survival time of 1-2 years after relapse. LNCaP is a commonly used cell line established from a human lymph node metastatic lesion of prostatic adenocarcinoma. We previously established two relapsed androgen receptor (AR)-rich androgen-independent LNCaP sublines 104-R1 (androgen depleted for 12 months) and 104-R2 cells (androgen depleted for 24 months) from AR-positive androgen-dependent LNCaP 104-S cells. LNCaP 104-R1 and 104-R2 mimics the AR-positive hormone-refractory relapsed tumors in patients receiving androgen ablation therapy. Androgen treatment stimulates proliferation of 104-S cells, but causes growth inhibition and G1 cell cycle arrest in 104-R1 and 104-R2 cells. We investigated the protein expression profile difference between LNCaP 104-S vs. LNCaP 104-R1, 104-R2, PC-3, and DU-145 cells as well as examined the sensitivity of these prostate cancer cells to different chemotherapy drugs and small molecule inhibitors. Compared to 104-S cells, 104-R1 and 104-R2 cells express higher protein levels of AR, PSA, c-Myc, Skp2, BCL-2, P53, p-MDM2 S166, Rb, and p-Rb S807/811. The 104-R1 and 104-R2 cells express higher ratio of p-Akt S473/Akt, p-EGFR/EGFR, and p-Src/Src, but lower ratio of p-ERK/ERK than 104-S cells. PC-3 and DU-145 cells express higher c-Myc, Skp2, Akt, Akt1, and phospho-EGFR but less phospho-Akt and phospho-ERK. Overexpression of Skp2 increased resistance of LNCaP cells to chemotherapy drugs. Paclitaxel, androgen, and inhibitors for PI3K/Akt, EGFR, Src, or Bcl-2 seem to be potential choices for treatment of advanced prostate cancers. Our study provides rationale for targeting Akt, EGFR, Src, Bcl-2, and AR signaling as a treatment for AR-positive relapsed prostate tumors after hormone therapy.     

Ursolic acid overcomes Bcl‐2‐mediated resistance to apoptosis in prostate cancer cells involving activation of JNK‐induced Bcl‐2 phosphorylation and degradation

Androgen‐independent prostate cancers express high levels of Bcl‐2, and this over‐expression of Bcl‐2 protects prostate cancer cells from undergoing apoptosis. Ursolic acid (UA) has demonstrated an anti‐proliferative effect in various tumor types. The aim of this study is to evaluate the difference between UA‐induced apoptosis in androgen‐dependent prostate cancer cell line LNCaP cells and androgen‐independent prostate cancer cell line LNCaP‐AI cells and to reveal the molecular mechanisms underlying the apoptosis. We found that UA treatment in vitro can effectively induce apoptosis in LNCaP and LNCaP‐AI cells. UA can overcome Bcl‐2‐mediated resistance to apoptosis in LNCaP‐AI cells. Intrinsic apoptotic pathways can be triggered by UA treatment because c‐Jun N‐terminal kinase (JNK) is activated and subsequently provokes Bcl‐2 phosphorylation and degradation, inducing activation of caspase‐9. Although further evaluation is clearly needed, the present results suggest the potential utility of UA as a novel therapeutic agent in advanced prostate cancer. J. Cell. Biochem. 109: 764–773, 2010. © 2009 Wiley‐Liss, Inc.