Stromal growth and epithelial cell proliferation in ventral prostates of liver X receptor knockout mice

Abstract

With specific liver X receptor ␣ and ␤ (LXR␣ and LXR␤) antibodies, we found that LXR␣ is strongly expressed in the luminal and basal cells of prostatic epithelium. The ventral prostates (VP) of LXR␣ ؊/؊ mice are characterized by the presence of smooth-muscle actinpositive stromal overgrowth around the prostatic ducts and by numerous fibrous nodules pushing into the ducts and causing obstruction, so that most of the ducts were extremely dilated. BrdU labeling and Ki67 staining revealed epithelial and stromal proliferation in the fibrous nodules. However, the dense stroma surrounding the ducts was not positive for proliferation markers. There was no detectable difference between WT and LXR␣ ؊/؊ mice VP in the expression of the androgen receptor, but there was an increase in nuclear expression of Snail and Smad 2/3, indicating enhanced TGF-␤ signaling. Upon treatment of WT mice for 3 months with the LXR agonist T2320 or for 3 weeks with ␤-sitosterol, LXR␣ was downregulated, and a VP phenotype similar to that of LXR␣ ؊/؊ mice resulted. We conclude that in rodents, LXR␣ seems to control VP stromal growth and that LXR␣ ؊/؊ mice may be a useful model to study prostatic stromal hyperplasia. Because LXR␣ is expressed in the epithelium, the excessive stromal growth in LXR␣ ؊/؊ mice indicates that LXR␣ is essential for epithelial stromal communication.Benign prostatic hyperplasia ͉ liver X receptor ͉ TGF-␤ ͉ mesenchymal transformation ͉ snail L iver X receptor ␣ and ␤ (LXR␣ and LXR␤) are members of the nuclear receptor supergene family of ligandactivated transcription factors (1-3). LXR␣ and -␤ knockout mice have revealed that LXR␣ but not LXR␤ plays an important role in cholesterol homeostasis, whereas LXR␤ has key functions in the immune system, testis, adrenal gland, pancreas, and CNS (4 -12). The endogenous ligands of LXR are oxysterols (13, 14), but they also accept phytosterols, particularly ␤-sitosterol, as ligands (15). Because ␤-sitosterol is thought to be the active ingredient in the over-the-counter preparation used for relief of the symptoms of benign prostatic hyperplasia (BPH) (16), we investigated the role of LXR in the prostate and the possibility that the beneficial effects of ␤-sitosterol are mediated by LXR (17).BPH is a very common disorder in men aged 50 years and is characterized by lower urinary tract disorders that have severe effects on quality of life (18)(19)(20)(21). One of the current theories for the mechanism of BPH is that autocrine and paracrine signaling from stromal cells to epithelium creates a focal area of reawakening of epithelial budding and BPH nodule formation (22). The signaling molecules most commonly implicated in the etiology of BPH are TGF-␤, FGF, EGF, and insulin-like growth factor (22). Current surgical treatments are associated with risk of urinary incontinence, and current pharmacologic intervention is not always effective. Many men try phytotherapy (use of plants and herbs) for relief of the symptoms of BPH. The most popular phytotherapy is ␤-sitosterol and saw palmetto (...

Estrogen-dependent gallbladder carcinogenesis in LXRβ −/− female mice

“…Indeed, in the ventral prostate of LXRα −/− mice, an abnormal stromal overgrowth is accompanied by high expression of SNAIL and SMAD-2/3, markers of an enhanced TGF-β activity (16). A cross-talk between LXRα and TGF-β has been previously hypothesized but still remains poorly understood.…”

“…Anti-LXRα and anti-LXRβ antibodies were developed in our laboratory (16,30) and used in immunohistochemical studies to investigate expression and localization of LXRα and LXRβ in the gallbladders of WT, LXRα −/− , and LXRβ −/− mice. Positive immunoreactivity both for LXRα (Fig.…”

“…Treatment with LXR agonist has an antiproliferative effect in vitro and in vivo (11-15) with a mechanism that seems to involve an increase of the kinase inhibitor p27 (37), suppression of the oncogenic β-catenin (38), and an interplay with TGF-β signaling (16). Indeed, in the ventral prostate of LXRα −/− mice, an abnormal stromal overgrowth is accompanied by high expression of SNAIL and SMAD-2/3, markers of an enhanced TGF-β activity (16).…”

“…Goat polyclonal IgG against LXRα and against LXRβ were prepared in our laboratory as previously described (16,30). The following antibodies were used: rabbit polyclonal to PCNA (GTX22426; GeneTex) at 1:200 dilution; rabbit polyclonal anti-E-cadherin (H-108, sc-7870; Santa Cruz Biotechnology) at 1:200; rabbit anti-pSMAD-2 (AB3849; Chemicon) at 1:100; and rabbit monoclonal to SMAD-4 (Ab40759; Abcam) at 1:100.…”

“…Effects of LXR on regulation of cell cycle have been described in other tissues including the prostate (11), breast cancer cells (12), pancreatic β cells (13,14), and T and B lymphocytes (15). Indeed, the ventral prostate of LXRα −/− mice is affected by a pathological stromal overgrowth positive for pSMAD-2/3 and SNAIL, markers of enhanced TGF-β signaling (16). Moreover, LXR agonist inhibits the growth of prostate tumors in athymic mice inoculated with prostate cancer cells (11) and inhibits estrogen-dependent proliferation of uterine epithelial cells and breast cancer-xenograph growth in nude mice (17).…”