Influence of dihydrotestosterone, epidermal growth factor, and basic fibroblast growth factor on the cell kinetics of the PC3, DU145, and LNCaP prostatic cancer cell lines: relationship with DNA ploidy level

Combination of Arsenic trioxide and Everolimus (Rad001) synergistically induces both autophagy and apoptosis in prostate cancer cells

The inhibitor of PI3K-AKT-mTOR pathway, such as Rad001, has not shown therapeutic efficacy as a single agent in prostate cancer. Arsenic trioxide induces the autophagic pathway in prostate cancer cells. We identified Arsenic trioxide can synergize with Rad001 to induce cytotoxicity of prostate cancer cells. Moreover, we identified synergistic induction of autophagy and apoptosis as the underlying mechanism. This enhanced autophagic cell death is accompanied by increased Beclin1 mRNA stability as well as upregulation of ATG5-ATG12 conjugate, Beclin1, and LC3-2. Rad001 and ATO also can synergistically inhibit tumors in prostate cancer xenograft animal model. These results identify and validate a novel mechanism to enhance and expand the existing targeted therapeutic agent to treat prostate cancer.

Acetylation of androgen receptor enhances coactivator binding and promotes prostate cancer cell growth

Modification by acetylation occurs at epsilon-amino lysine residues of histones and transcription factors. Unlike phosphorylation, a direct link between transcription factor acetylation and cellular growth or apoptosis has not been established. We show that the nuclear androgen receptor (AR), a DNA-binding transcriptional regulator, is acetylated in vivo. The acetylation of the AR is induced by ligand dihydrotestosterone and by histone deacetylase (HDAC) inhibitors in living cells. Direct AR acetylation augmented p300 binding in vitro. Constructs mimicking neutral polar substitution acetylation (AR(K630Q), AR(K630T)) enhanced p300 binding and reduced N-CoR/HDAC/Smad3 corepressor binding, whereas charged residue substitution (AR(K630R)) reduced p300 binding and enhanced corepressor binding. The AR acetylation mimics promoted cell survival and growth of prostate cancer cells in soft agar and in nude mice and augmented transcription of a subset of growth control target gene promoters. Thus, transcription factor acetylation regulates coactivator/corepressor complex binding, altering expression of specific growth control genes to promote aberrant cellular growth in vivo.

REPS2/POB1 is downregulated during human prostate cancer progression and inhibits growth factor signalling in prostate cancer cells

During progression of prostate cancer, cellular changes occur, leading to a transition from androgen-dependent to androgen-independent growth. One aspect of this transition is a switch from androgens to growth factors, like epidermal growth factor (EGF), as primary regulators of proliferation. We examined the involvement of REPS2/POB1 in this process. REPS2/POB1 is an EH domain-containing protein, reported to be involved in signalling via RalBP1 and to play a role in endocytosis of EGF receptors. Furthermore, the protein is relatively highly expressed in androgen-dependent as compared to androgen-independent human prostate cancer cell lines and xenografts. Next to the known REPS2/POB1 protein, an open reading frame encoding REPS2/POB1, with 139 additional amino-acid residues at the NH(2)-terminus, was cloned and found to be expressed in prostate cancer cells. Overexpression, by transient transfection, of both forms of REPS2/POB1 in prostate cancer cell lines, induced apoptosis within 48 h. At shorter time intervals after transfection, signalling towards a TPA response element luciferase reporter was found to be inhibited. From these experiments, it is concluded that REPS2/POB1, through its influence on the Ral signalling pathway, is involved in growth factor signalling. Decreased expression of REPS2/POB1 during progression of prostate cancer may therefore result in loss of control of growth factor signalling and consequently in loss of control of cell proliferation.

5alpha-reductase isozymes and aromatase are differentially expressed and active in the androgen-independent human prostate cancer cell lines DU145 and PC3

BACKGROUND

The presence and possible role of androgen-metabolizing enzymes in androgen-independent prostate carcinoma (CaP) are still unclear. The aim of the present study was: 1) to evaluate the pattern of androgen metabolism (relative production of 5alpha-reduced vs. 17-keto androgens); and 2) to analyze whether one or both the two known 5alpha-reductase isoforms (5alpha-R1 and 5alpha-R2) and the aromatase (Aro) are expressed and active in this pathology.

METHODS

Two different cell lines (DU145 and PC3) were used as a model of androgen-independent human CaP. In these cells, the expression of the two 5alpha-Rs and of Aro were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot, using specific sets of oligoprimers and of [(32)P]-labeled oligoprobes; the enzymatic activities of 5alpha-R and of Aro were evaluated by radioenzymatic methods. The pH optimum for the activity of the two 5alpha-Rs was assessed in cell homogenates at different pH (from 3.5-8), using substrate concentrations similar either to 5alpha-R1 or to 5alpha-R2 Kms.

RESULTS

The two CaP cell lines DU145 and PC3, although unresponsive to androgens, possess the enzymatic machinery involved in the metabolism of this class of hormonal steroids: 5alpha-Rs, which allow their transformation into 5alpha-reduced steroids (5alpha-dihydrotestosterone, DHT, and 5alpha-androstandione, 5alpha-A), and 17beta-hydroxysteroid-oxidoreductase (17beta-HSD), which interconverts testosterone (T) and androstenedione (ADIONE); however, the two cell lines show differences in the rate of formation of these metabolites. Furthermore, two cell lines expressed the type 1 isoform of 5alpha-R, but only DU145 cells also possess 5alpha-R2. Aro is expressed and active in DU145 as well as in PC3 cells.

CONCLUSIONS

The present findings suggest that T might still be indirectly active in androgen-unresponsive CaP through its local conversion into estrogens by the action of Aro; the biological role played by the two 5alpha-Rs in androgen-independent CaP deserves further investigation.

Androgens are not a direct requirement for the proliferation of human prostatic epithelium in vitro

The androgen receptor pathway is known to be a key regulator of growth in the normal and pathological prostate. However, the precise mechanisms of this signaling pathway with respect to the different cellular compartments of the prostate remain largely unknown. We have used a primary culture system to grow human prostatic epithelial cells of normal, benign, tumor and metastatic origin, as well as immortalized human prostatic epithelial cell lines, to demonstrate the absence of a direct or indirect effect of androgens on cellular proliferation in vitro. In parallel to this observed androgen independence for growth, all cell systems lost significant expression of androgen receptor, prostate-specific antigen and prostatic acid phosphatase. Since the androgen receptor is expressed in the epithelium in situ, our results suggest that the androgen effect on epithelial cells may be one of prostatic differentiation rather than proliferation, and that the androgen receptor/growth factor pathway acts through mesenchymal-epithelial interactions.

Characterization of a 60-kDa cell surface-associated transforming growth factor-beta binding protein that can interfere with transforming growth factor-beta receptor binding

We have characterized a 60-kDa transforming growth factor-beta (TGF-beta) binding protein that was originally identified on LNCaP adenocarcinoma prostate cells by affinity cross-linking of cell surface proteins by using 125I-TGF-beta 1. Binding of 125I-TGF-beta 1 to the 60-kDa protein was competed by an excess of unlabeled TGF-beta 1 but not by TGF-beta 2, TGF-beta 3, activin, or osteogenic protein-1 (OP-1), also termed bone morphogenetic protein-7 (BMP-7). In addition, no binding of 125I-TGF-beta 2 and 125I-TGF-beta 3 to the 60-kDa binding protein on LNCaP cells could be demonstrated by using affinity labeling techniques. The 60-kDa TGF-beta binding protein showed no immunoreactivity with antibodies against the known type I and type II receptors for members of the TGF-beta superfamily. Treatment of LNCaP cells with 0.25 M NaCl, 1 microgram/ml heparin, or 10% glycerol caused a release of the 60-kDa protein from the cell surface. In addition, we found that the previously described TGF-beta type IV receptor on GH3 cells, which does not form a heterometric complex with TGF-beta receptors, could be released from the cell surface by these same treatments. This suggests that the 60-kDa protein and the similarly sized TGF-beta type IV receptor are related proteins. The eluted 60-kDa LNCaP protein was shown to interfere with the binding of TGF-beta to the TGF-beta receptors. Thus, the cell surface-associated 60-kDa TGF-beta binding protein may play a role in regulating TGF-beta binding to TGF-beta receptors.

In vitro characterization of prolactin-induced effects on proliferation in the neoplastic LNCaP, DU145, and PC3 models of the human prostate

BACKGROUND

Proliferation of normal and tumoral prostate tissue is regulated by androgens and various growth factors. We characterized the in vitro proliferative influence of prolactin (PRL) in androgen-sensitive and androgen-insensitive human prostate cancers.

METHODS

The biologic models employed included the androgen-sensitive LNCaP and the androgen-insensitive DU145 and PC3 cell lines. PRL-induced influences (0.1-10 mIU/ml of medium) on proliferation were assessed using the colorimetric methylthiotetrazole assay. Androgen sensitivity in the three cell lines was determined by assessing the proliferative influence of dihydrotestosterone (DHT) (0.1-10 nM). PRL-induced modifications in PC3 cell kinetics were assessed using Feulgen-stained nuclear image cytometry.

RESULTS

Although DHT markedly stimulated LNCaP proliferation, it had no proliferative effect on the DU145 and PC3 cell lines. By contrast, PRL significantly modulated the proliferation of the DU145 and PC3 lines, but exerted weak, if any, effect on the proliferation of the LNCaP cell line. PRL increased the percentage of PC3 proliferating cells (i.e., cells in the S/G2 phases of the cell cycle) at low doses (0.1 mIU/mL) and decreased this percentage at high doses (10 mIU/ml).

CONCLUSIONS

Proliferation of androgen-insensitive human prostate cell lines can be significantly modulated by prolactin.