The amino terminus of the human AR is target for corepressor action and antihormone agonism

Antiandrogens inhibit the ligand-induced transactivation by the androgen receptor (AR) and have a widespread use in the treatment of prostate cancer but their mode of action is not fully understood. Here we show that the ability of the antiandrogen cyproterone acetate (CPA) to inhibit transactivation by the human AR (hAR) involves the corepressor SMRT (silencing mediator for retinoic acid and thyroid hormone receptor). We detect binding of SMRT to hAR when treating with the antiandrogen CPA, but not with the antihormones casodex or hydroxyflutamide. Interestingly, we find that SMRT binds to the N terminus of the hAR. Thereby, SMRT modulates the activity of hAR in receptor-negative CV1 cells. In addition, we have used receptor point mutants that exhibit normal transactivation potential and unchanged partial agonistic activity when treated with CPA, but lack both SMRT binding and SMRT-mediated inhibition of CPA-bound AR. This indicates that mechanisms involved in hAR-mediated transactivation are distinct from antihormone-induced receptor inactivation. Furthermore, we show that treatment of transfected cells with a cAMP analog or coexpression of the catalytic subunit of PKA, known to activate hAR, inhibits the binding of SMRT to the AR. This suggests that the association of SMRT with hAR is regulated at the level of cross-talk mechanisms and that ligand-independent receptor activation is due to corepressor dissociation. Taken together, we provide novel insights in AR regulation, antihormone action, and functional nuclear receptor-corepressor interaction.     

Effect of high-fiber and high-oil diets on the fecal flora of swine.

Six pairs of pigs were fed a basal diet, a high-fiber diet, and a diet high in corn oil in different sequences to minimize the carry-over effect of diet. After 2 months on each diet, a fecal specimen from each pig was cultured on nonselective medium in roll tubes. Fifty colonies were randomly selected from each fecal sample, and isolates were characterized to identify a representative cross section of the fecal flora. The bacterial composition of the fecal flora differed between basal and high-fiber diets (P = 0.002) and between high-fiber and high-oil diets (P = 0.015). However, the floras were not significantly different between the basal and the high-oil diets (P = 0.135), nor were the floras of the 12 individual pigs (each on all three diets) statistically different (P = 0.103). Only 14 of the 160 observed taxa have been detected in the human fecal flora, and only 159 of 1,871 total isolates (8.5%) were members of described species. The most common isolate was a Streptococcus species similar to that reported by Robinson et al. (I. M. Robinson, S. C. Whipp, J. A. Bucklin, and M. J. Allison, Appl. Environ. Microbiol. 48:964-969, 1984), which was found in 34 of 36 samples and which represented 27.5% of all isolates. Lactobacillus, Fusobacterium, Eubacterium, Bacteroides, and Peptostreptococcus species were the next most common bacteria. Escherichia coli represented 1.7% of all fecal isolates, which is somewhat higher than the 0.1 to 0.6% observed in human feces cultured similarly with prereduced anaerobically sterilized media.(ABSTRACT TRUNCATED AT 250 WORDS)     

The regulation of expression of mouse mammary tumor virus DNA by steroid hormones and growth factors

Mouse mammary tumor virus (MMTV) expression is associated with hyperplastic alveolar growth and subsequent development of mammary cancers in the mouse. The expression of this virus is also controlled by factors involved in the normal proliferation and differentiation of the mammary epithelium. During pregnancy when the mammary gland undergoes massive proliferation, MMTV expression is increased. Steroid hormones and growth factors that play an important role in the proliferation of mammary gland cells are responsible for the increased MMTV expression. In sarcomatous transformation of mouse mammary epithelial cells, MMTV expression is repressed. This repression is due to negative control of MMTV expression by transforming growth factor-beta (TGF beta). This growth factor is produced in high amounts when mammary epithelial cells progress into the transformed state. The expression of MMTV is therefore under multiple control by steroid hormones and growth factors.     

Functionally‐defined compartments of the lordosis neural circuit in the ventromedial hypothalamus in female rats

Sexual behavior in female rats, typified by the lordosis reflex, is dependent upon estrogen action in the ventromedial nucleus of the hypothalamus (VMH) and its surrounding neuropil. However, the synaptic organization of this brain region remains unclear. Pseudorabies virus (PRV) was used to transneuronally label the neural network that innervates the lumbar epaxial muscles that execute the lordosis response. PRV‐labeled neurons were identified within and subjacent to the VMH four days after injection of PRV into the back muscles. The pattern of labeling was defined in relation to three landmarks: the VMH core, as defined by Crystal Violet staining; the shell, as defined by the oxytocin fiber tract; and the cluster of estrogen receptor‐containing cell nuclei. The pattern of PRV labeling in the VMH displayed a striking rostral‐caudal gradient. In general, many of the PRV‐labeled neurons were found in the oxytocin fiber tract, with far fewer in the core of the VMH. Furthermore, PRV‐labeled neurons were rarely found in the cluster of estrogen receptor‐containing neurons, and less than 3% of the PRV‐labeled neurons were double labeled for estrogen receptor. The results suggest that oxytocin may directly influence these lordosis‐relevant VMH projection neurons, whereas estrogen may have transsynaptic effects. © 2000 John Wiley & Sons, Inc. J Neurobiol 45: 1–13, 2000