1Center for Prostate Disease Research (CPDR), Department of Surgery, Uniformed
Services University of the Health Sciences,
Rockville, Maryland, MD 20852, USA;
2Affymetrix Gene Array Laboratory, Division of Retrovirology, Walter Reed Army Institute of Research, Rockville, Maryland, MD 20850, USA;
3Department of Genitourinary Pathology, Armed Forces Institute of Pathology, Washington, DC 20307, USA; 4Urology Service, Walter Reed Army Medical Center, Washington, DC 20307-5001, USA
Evaluations of androgen regulated gene (ARG) repertoire
provide new insights into the androgen receptor (AR) mediated signaling
at the transcriptional level. Definition of ARGs having critical functions
in the biology of normal and malignant prostate should aid in identifying
new bio-markers and therapeutic targets for prostate cancer (CaP). Using
Affymetrix HuGene FL oligonucleotide arrays, temporal expression profiles
of ARGs in widely used hormone responsive LNCaP cells, were analysed by
hierarchical clustering methods and functional classification. ARGs in
response to different androgen concentrations showed temporal co-regulation
of genes involved in specific biochemical pathways. This study focuses
on our new observations of the coordinated androgen induction of genes
(NDRG1, PDIR, HERPUD1, ORP150) involved in the endoplasmic reticulum (ER)
stress response pathway. Expression analysis of the two selected ER stress
responsive genes, NDRG1 and HERPUD1 in primary CaPs revealed a significantly
reduced tumor associated expression. Intri- guing linkage of the androgen
signaling to ER stress responsive genes, a protective response to protein
unfolding or protein damage resulting from cellular stress signals, suggests
that androgens may induce such stress signals in CaP cells. Decreased
CaP associated expression of two ER stress responsive genes also suggests
that possible abrogation of this pathway in prostate tumorigenesis.
Since Huggins' seminal discovery showing that growth of the prostate gland depends on male sex hormones, androgen deprivation therapy has been the gold standard for the treatment of advanced prostate cancer (CaP) (Huggins and Hodges, 1941). However, the vast majority of the patients eventually relapse after a period of initial response to hormone therapy. Molecular mechanisms involved in the cell proliferation and differentiation of the prostate by androgen, as well as androgen ablation mediated prostate cell death and emergence of androgen independent cancers are under active investigations (Coffey, 1992; Hakimi et al., 1996; Augustus et al., 1999; Tindall and Scardino, 1999; Grossmann et al., 2001).
Biologic effects of androgen on target cells, e.g., prostatic epithelial are in part mediated by transcrip- tional regulation of ARGs by the androgen receptor (AR) (Coffey, 1992; Hakimi et al., 1996; Augustus et al., 1999; Tindall and Scardino, 1999; Grossmann et al., 2001). Gain of AR functions is believed to play some role in prostate tumorigenesis. Alterations of the AR gene by mutations in the hormone-binding domain have been reported in a subset advanced stage of CaP (Tilley et al., 1996; Grossmann et al., 2001). Amplifica- tions of the AR gene in hormone refractory CaP represent yet another scenario where gain of AR functions may be associated with tumor progression (Visakorpi et al., 1995). Germ-line alterations of CAG repeat length in AR may influence the risk of CaP (Hakimi et al., 1996; Hardy et al., 1996; Stanford et al., 1997). Growth factors commonly involved in cell proliferation and tumorigenesis, e.g., IGF I, EGF and KGF have been shown to activate the transcrip- tion transactivation functions of the AR (Culig et al., 1994). Recent studies analysing expression of ARGs in hormone sensitive and refractory CWR22 nude mice xenograft model have also shown sustained expression of some ARGs in AR positive recurrent tumors following castration suggesting constitutive activation of AR signaling in these tumors (Nagabhushan et al., 1996; Amler et al., 2000; Mousses et al., 2002). Thus androgen regulation of critical target genes may play a role in normal prostate growth and prostate tumor- igenesis.
Therefore, systematic and comprehensive analysis of the ARGs should provide the reporters for androgen signaling in CaP. These reporters may serve as potential biomarkers for predisposition/initiation/ progression of prostate cancers (Xu et al., 2001; Vaarala et al., 2000; Amler et al., 2000). Towards this aim, we are analysing the ARG repertoire in prostate cancer cells using high-throughput approaches and evaluating their signi®cance in human CaP (Xu et al., 2000a, 2001). The objective of this study is to define biochemical pathway(s) regulated by androgen signal- ing by analysing coordinated expression of genes linked to specific pathway(s) and further evaluate the role of such pathway(s) in human prostate tumorigenesis. We have determined the temporal expression profiles of ARGs in widely used hormone responsive LNCaP cells (Horoszewicz et al., 1983). Our results show coordi- nated regulation of ARGs in distinct and specific biochemical pathways and this report focuses on our new observations on the coordinated regulation of genes in ER stress response. Further, significantly decreased expression of two selected ER stress responsive genes, NDRG1 and HERPUD1, were noted in cancer cells when laser capture microdissected (LCM) paired normal and cancer cells from prostate cancer patients were analysed. Abrogation of regula- tion of ER stress responsive genes, e.g., NDRG1 and HERPUD1 may contribute in prostate tumorigenesis.