Androgen receptor protein is down-regulated by basic fibroblast growth factor in prostate cancer cells

Abstract

Interactions between polypeptide growth factors and the androgen receptor (AR) are important for regulation of cellular events in carcinoma of the prostate. Basic fibroblast growth factor (bFGF), the prototype of heparin-binding growth factors, and the AR are commonly expressed in prostate cancer. bFGF diminished prostate-specific antigen protein in the supernatants of androgen-stimulated human prostate cancer cells LNCaP by 80%. In the present study, we asked whether the bFGF effect on prostate-specific antigen is preceded by action on AR expression. LNCaP cells were treated with bFGF and AR protein expression was determined by immunoblotting and ligand binding assay. bFGF down-regulated AR protein in a dose-dependent manner showing a maximal effect at 50 ng ml −1 both in the presence or absence of dihydrotestosterone. Down-regulation of AR protein expression occurred already after 8 h of bFGF treatment and a maximal inhibition was observed 24 h after addition of bFGF to culture media. As AR expression can be reduced by an increase in intracellular calcium levels, we investigated whether the bFGF effect on AR protein is mediated by this mechanism. Calcium release from intracellular stores and store-operated calcium influx after treatment with either bFGF or calcium ionophore A 23187 were measured by single cell fluorescence technique. The ionophore A 23187 was able to induce calcium influx and an increase in cytoplasmic calcium concentration in LNCaP cells. In contrast, bFGF was incapable of eliciting a similar effect. In contrast to AR protein, AR mRNA levels were not affected by bFGF as shown by semiquantitative reverse transcription polymerase chain reaction. In summary, these studies show that bFGF is a potent negative regulator of AR protein expression in the human prostate cancer cell line LNCaP. © 2000 Cancer Research Campaign

The Transcriptional Co-Activator cAMP Response Element-Binding Protein-Binding Protein Is Expressed in Prostate Cancer and Enhances Androgen- and Anti-Androgen-Induced Androgen Receptor Function

“…15 In LNCaP cells, however, androgenic hormones enhance AR expression by protein stabilization even when neither co-activator is overexpressed. 42,43 This would compromise interpretation of results of any immunoblot experiments similar to those performed in DU-145 cells.…”

Nitric oxide-mediated inhibition of androgen receptor activity: possible implications for prostate cancer progression

“…Nonspecific binding was blocked by incubation with 5% non-fat dry milk in PBS. Subsequently, membranes were incubated with AR-specific rabbit antibody PG-21 (1:500; Upstate, Lake Placid, NY, USA) and with mouse monoclonal anti-beta actin antibody (1:50 000; ab6276; Abcam) (Cronauer et al, 2000(Cronauer et al, , 2004. Immunoreactive bands were detected with peroxidase-labeled mouse anti-rabbit or anti-mouse antibodies (1:5000) and visualized by enhanced chemiluminescence (Amersham Pharmacia).…”

Degradation and beyond: Control of androgen receptor activity by the proteasome system

“…Ligand-independent AR degradation occurs in response to growth factors and cytokine stimulation. AR signalling has been shown to be inhibited by IL-6 [37], basic fibroblast growth factor (bFGF) [38], and insulin-like growth factor 1 (IGF-1) [23,39]. Growth factors and cytokines activate the PI3K/Akt kinase pathway which promotes AR phosphorylation (see Fig.…”