Androgens, lipogenesis and prostate cancer.

Both experimental and epidemiological data indicate that androgens are among the main factors controlling the development, maintenance and progression of prostate cancer. Identifying the genes that are regulated by androgens represents a major step towards the elucidation of the mechanisms underlying the impact of androgens on prostate cancer cell biology and is an attractive approach to find novel targets for prostate cancer therapy. Among the genes that have been identified thus far, several genes encode lipogenic enzymes.

Identification of an androgen response element in intron 8 of the sterol regulatory element-binding protein cleavage-activating protein gene allowing direct regulation by the androgen receptor.

Sterol regulatory element-binding proteins (SREBPs) are transcription regulators that play a pivotal role in intracellular lipid homeostasis. They are synthesized as inactive precursor proteins in the endoplasmic reticulum, where they are retained by SREBP cleavage-activating protein (SCAP), a sterol sensing protein that in turn is linked to a retention protein complex. Low intracellular sterol concentrations weaken the interaction of SCAP with its retention proteins and allow translocation of the SREBP.

A Sertoli cell-selective knockout of the androgen receptor causes spermatogenic arrest in meiosis.

Androgens control spermatogenesis, but germ cells themselves do not express a functional androgen receptor (AR). Androgen regulation is thought to be mediated by Sertoli and peritubular myoid cells, but their relative roles and the mechanisms involved remain largely unknown. Using Cre/loxP technology, we have generated mice with a ubiquitous knockout of the AR as well as mice with a selective AR knockout in Sertoli cells (SC) only.

Epigallocatechin-3-gallate is a potent natural inhibitor of fatty acid synthase in intact cells and selectively induces apoptosis in prostate cancer cells.

Chemical inhibitors of fatty acid synthase (FAS) inhibit growth and induce apoptosis in several cancer cell lines in vitro and in tumor xenografts in vivo. Recently the green tea component epigallocatechin-3-gallate (EGCG) was shown to act as a natural inhibitor of FAS in chicken liver extracts. Here we investigated whether EGCG inhibits FAS activity in cultured prostate cancer cells and how this inhibition affects endogenous lipid synthesis, cell proliferation and cell viability.

Androgens stimulate coordinated lipogenic gene expression in normal target tissues in vivo.

In prostate cancer cell lines in culture androgens cause a marked and coordinated upregulation of the expression of several lipogenic genes. Here, using castrated male Wistar rats as an experimental paradigm, we investigated whether coordinated androgen stimulation of lipogenic gene expression represents a more general physiological regulation in non-cancerous androgen-responsive cells as well. In typical target tissues for androgen action such as the ventral prostate and the lacrimal gland, androgen deprivation resulted in a marked reduction in the mRNA and protein levels of genes involved in fatty acid (fatty acid synthase and acetyl-CoA-carboxylase) and cholesterol synthesis (HMG-CoA-reductase and farnesyl diphosphate synthase).

RNA interference-mediated silencing of the fatty acid synthase gene attenuates growth and induces morphological changes and apoptosis of LNCaP prostate cancer cells.

Fatty acid synthase (FASE), a key enzyme in the biosynthesis of fatty acids, is markedly overexpressed in many human epithelial cancers, rendering it an interesting target for antineoplastic therapy. Here, using the potent and highly sequence-specific mechanism of RNA interference (RNAi), we have silenced the expression of FASE in lymph node carcinoma of the prostate (LNCaP) cells. RNAi-mediated down-regulation of FASE expression resulted in a major decrease in the synthesis of triglycerides and phospholipids and induced marked morphological changes, including a reduction in cell volume, a loss of cell-cell contacts, and the formation of spider-like extrusions.

Fatty acid synthase drives the synthesis of phospholipids partitioning into detergent-resistant membrane microdomains.

Fatty acid synthase (FAS) is a key metabolic enzyme catalyzing the synthesis of long-chain saturated fatty acids. It plays a central role in the production of surfactant in fetal lungs, in the supply of fatty components of milk, and in the conversion and storage of energy in liver and adipose tissue. Remarkably high levels of FAS expression are found in the majority of human epithelial cancers.

Coactivation of an endogenous progesterone receptor by TIF2 in COS-7 cells.

Transfection experiments, a powerful tool to study the function of steroid hormone receptors and their coregulators, are often performed in COS-7 cells, because of high transfection efficiencies and expression levels. Here we report on the presence in COS-7 cells of an endogenous steroid hormone receptor, which is highly responsive to progesterone and the synthetic steroids R1881 and ORG2058, but not to 5 alpha-DHT. A 10-fold excess of the progesterone antagonist RU486 abolishes the stimulation by progesterone, while cotransfection with the coactivator TIF2 increases its activity 6- to 7-fold.

Overexpression of fatty acid synthase is an early and common event in the development of prostate cancer.

The expression of fatty acid synthase (FAS), a key lipogenic enzyme and potential target for antineoplastic therapy, was analyzed in 87 frozen needle biopsies of prostate cancer using a highly sensitive immunohistochemical detection technique (Envision). In comparison to normal or benign, hyperplastic glandular structures, which were all negative for FAS staining, immunohistochemical signal was evident in 24/25 low grade prostatic epithelial neoplasia (PIN) lesions, in 26/26 high grade PIN lesions and in 82/87 invasive carcinomas. Staining intensity tended to increase from low grade to high grade PIN to invasive carcinoma.

Role of the phosphatidylinositol 3'-kinase/PTEN/Akt kinase pathway in the overexpression of fatty acid synthase in LNCaP prostate cancer cells.

One of the most common molecular changes in cancer cells is the overexpression of fatty acid synthase (FAS), a key metabolic enzyme catalyzing the terminal steps in the synthesis of long chain saturated fatty acids. As part of our efforts to elucidate the mechanisms responsible for FAS overexpression, we have addressed the question whether overexpression of FAS may be linked to the frequently observed inactivation of PTEN and subsequent activation of the phosphatidylinositol 3'-kinase (PI3k) pathway. Using LNCaP prostate cancer cells as an experimental paradigm of FAS-overexpressing PTEN-null cancer cells, we demonstrate that LY294002, an inhibitor of the PI3k pathway causes a dramatic decrease in FAS protein expression.