Optomechanics of a quantum-degenerate Fermi gas.

We explore theoretically the optomechanical interaction between a light field and a mechanical mode of ultracold fermionic atoms inside a Fabry-Pérot cavity. The low-lying phonon mode of the fermionic ensemble is a collective density oscillation associated with particle-hole excitations, and is mathematically analogous to the momentum side-mode excitations of a bosonic condensate. The mechanical motion of the fermionic particle-hole system behaves hence as a "moving mirror." We derive an effective system Hamiltonian that has the form of generic optomechanical systems. We also discuss the experimental consequences the optomechanical coupling in optical bistability and in the noise spectrum of the system.

Fermionic stabilization and density-wave ground state of a polar condensate.

We examine the stability of a trapped dipolar condensate mixed with a single-component fermion gas at T=0. Whereas pure dipolar condensates with a small s-wave interaction are unstable even at small dipole-dipole interaction strength, we find that the admixture of fermions can significantly stabilize them, depending on the strength of the boson-fermion interaction. Within the stable regime we find a region where a ground state is characterized by a density wave along the soft trap direction.

Non-involvement of the K-ras mutation in colon carcinogenesis promoted by dietary deoxycholate in azoxymethane-treated rats.

Fisher-344 rats, whose ileum or jejunum had been surgically removed to change the influx of bile acids into the colon, were intraperitoneally administered with azoxymethane and fed on a diet containing deoxycholate for 39 weeks to induce colon cancer. Fecal bile acids in the ileum-resected group were 1.5-times and serum bile acids were about half of those in the jejunum-resected group. As a result, the incidence and number of tumors were higher in the ileum-resected group. In the total of 59 colon tumors (40 were in the ileum-resected group and 19 in the jejunum-resected group), 56 were carcinomas, including two well-differentiated invasive and two mucinous carcinomas found in the ileum-resected rats. However, only three carcinomas, two invasive and one non-invasive, had the K-ras mutation. These results demonstrate that the K-ras mutation was not essentially involved in deoxycholate-promoted colon carcinogenesis.

Soybean resistant proteins interrupt an enterohepatic circulation of bile acids and suppress liver tumorigenesis induced by azoxymethane and dietary deoxycholate in rats.

We found that azoxymethane and dietary deoxycholate induced liver tumors in rats. The incidence and the development of the tumor were closely related to the enterohepatic circulation of bile acids. The feeding of a high-molecular-weight fraction of soy protein digest (HMF) suppressed the tumorigenesis, probably due to the inhibitory effect of soybean resistant protein on reabsorption of bile acids in the intestine.

Antitumorigenic effects of several food proteins in a rat model with colon cancer and their reverse correlation with plasma bile acid concentration.

In order to obtain information on the preventive effects of various food proteins against colonic cancer, six groups of azoxymethane-initiated mature Fischer rats (n = 10) were fed respective diets different in protein sources such as bovine milk casein (casein), high-molecular-weight fraction from protolytic digest of soy protein isolate (soybean HMF), hen's yolk defatted protein (yolk protein), wheat gluten and codfish meat, which had been supplemented with sodium deoxycholate (hereinafter, DCA) as a cancer promoter except for an additional DCA-unfed casein group. All of the living rats at checkpoints during the feeding period were examined by the use of a bronchus fiberscope for colonic tumor incidence at 6 wk intervals between the 10th and 34th wk, from which both blood and feces samples were taken at times of endoscopy. Tumorigenesis in the colon was perceived by endoscopy at wk 22 in the group fed DCA casein only and at wk 28 in the other groups except the DCA-unfed casein group. At wk 34, both soybean HMF and yolk protein groups ranked inferior to the DCA-unfed group in tumor incidence. When plasma steroid or lipid concentration was plotted against tumor incidence at wk 28 or 34, positive correlations were found between plasma bile acid concentration and tumor incidence at both weeks. With the exception of the DCA-unfed casein group, plasma bile acid concentration was reversely correlated to fecal bile acid excretion. Taken altogether, these results suggest that bile acids at higher concentrations in the plasma may serve as risk factors of colon tumor incidence.

Preventive effect of soybean resistant proteins against experimental tumorigenesis in rat colon.

The insoluble 'high-molecular-weight' fraction (HMF) centrifugally separable after digestion of soy protein isolate with a microbial protease of the exo-type, of which about a quarter is regarded as an indigestible 'resistant protein,' was examined for its preventive effect against colonic tumorigenesis in a model system with male F-344 rats. The rats were intraperitoneally injected with azoxymethane (15 mg/kg BW) once a week for 3 wk and were fed a 20.6% HMF diet (+0.4% DL-Met) or 14.7% casein diet (+0.3% DL-Met) supplemented with 0.2% sodium deoxycholate (DCA) or without supplementation. Twelve wk later, 5 rats of each group were inspected for formation of tumors but no tumors were visible to the naked eye. The DCA-fed casein group was conspicuous for a low count of aberrant crypt foci. At 39 wk, 6 rats of the DCA-fed casein group (n = 10) and 3 rats of the DCA-fed HMF group (n = 9) had a total of 18 tumors with a major axis of 4.0 +/- 0.4 mm and 3 tumors with an axis of 2.0 +/- 0.1 mm, respectively, in contrast to only a single tumor for the DCA-unfed casein group (nil for the DCA-unfed HMF group). The difference in tumor number and size was considered significant between these DCA-fed casein and HMF groups; that is to say, HMF feeding retarded tumor development despite the frequent occurrence of pre-neoplastic lesions. In addition, fecal bile acid excretion was much more elevated by HMF feeding than by casein feeding. It can be assumed from these observations that the antitumorigenicity of HMF is due to the inhibitory effect of soybean resistant proteins on reabsorption as well as the mucosal contact of bile acids in the intestine.

Elimination of Na+-dependent bile acid transporter from small intestine by ileum resection increases [correction of increase] colonic tumorigenesis in the rat fed deoxycholic acid.

Ileal Na+-dependent bile acid transporter (ISBT) constituting a gateway to enterohepatic circulation of bile acids occurs exclusively at the distal site of the small intestine. In the present study, we examined colonic tumorigenesis promoted by deoxycholic acid in relation to the expression of the ISBT. For this purpose, the small intestine of a Fischer-344 rat was resected a length of 20 cm above the ileo-cecal valve (ileal resection) or below the duodenum (jejunal resection). Then, rats were treated with an intraperitoneal injection of azoxymethane (15 mg/kg body wt.) once a week for 3 weeks and fed a 20% casein diet supplemented with 0.2% deoxycholate for 39 weeks. Northern blot analysis demonstrated that the ISBT mRNA was hardly detectable in ileum-resected rats. The excretion of fecal bile acids was 1.5-fold higher in the ileum-resected group than in the jejunum-resected group (P < 0.05). On the contrary, the serum bile acids concentration of ileal-resected rats was about one-half of that of jejunum-resected animals (P < 0.05). The tumor incidence and the total tumor number were significantly higher in the ileum-resected group than in the jejunum-resected one (P < 0.05). Interestingly, no tumor was found at the proximal colon in the jejunum-resected group while tumors developed frequently at the proximal site as well as mid and distal colon in the ileum-resected group. These observations demonstrate that malabsorption of bile acids owing to the lack of ISBT enhanced colon tumorigenesis.

Feeding soybean resistant protein to rats raises fecal bile acid excretion but counteracts a deoxycholate-caused decrease in colonic aberrant crypt foci.

A high-molecular-weight fraction after removal of water-soluble peptides from proteinase-treated soybean protein isolate (referred to as HMF) was examined for its effect on preneoplastic lesions in the rat colon. For this purpose, male Fisher-344 rats 7 wk old were divided into 8 groups (n = 5), of which 6 groups received 3 injections of azoxymethane (AOM, 15 mg/kg of body weight) for 3 wk once a week, while all were fed HMF or casein diets supplemented with or without deoxycholic acid (DCA) over a period of 4 wk. Two groups of AOM-treated rats were allowed free access to HMF or casein diets without supplemental DCA, respectively, while the others were pair-fed so as to be well matched in their food intake. There were no significant differences in growth parameters among the pair-fed groups. Feeding HMF diets raised fecal lipid and acidic steroid excretions to a greater extent than feeding casein diets, secondary bile acids being conspicuous among acidic steroids in the excreta irrespective of the presence or absence of DCA supplementation. As a result of observation for colonic aberrant crypt foci (ACF), the intake of HMF proved to reverse the reduction of ACF appearance by DCA. This result implies that secondary bile acids are caught and brought out by HMF, or rather its derivative "resistant protein," so as not to keep contact with colonic mucosae.

Characterization, cDNA cloning, and functional expression of mouse ileal sodium-dependent bile acid transporter.

Mouse ileal sodium dependent bile acid transporter (ISBT) was characterized using isolated enterocytes. Only enterocytes from the most distal portion showed Na+-dependent [3H]taurocholate uptake. Northern blot analysis using a probe against mouse ISBT revealed the expression of mouse ISBT mRNA to be restricted to the distal ileum. The Km and Vmax for Na+-dependent [3H]taurocholate transport into isolated ileocytes were calculated as 27 microM and 360 pmol/mg protein/min, respectively. Uptake of [3H]taurocholate was inhibited by N-ethylmaleimide. We have cloned ISBT cDNA from mouse ileum. The cDNA included the entire open reading frame coding 348 amino acid protein with seven hydrophobic segments and two N-glycosylation sites. COS-7 cells transfected with the expression vector containing this cDNA expressed Na+-dependent [3H]taurocholate uptake activity with a Km of 34 microM.

Soybean curd refuse alleviates experimental tumorigenesis in rat colon.

Adult Fischer-344 rats which underwent administration of azoxymethane were fed diets containing soybean curd refuse (SCR) or a high-molecular-weight fraction of soy protein digest (HMF), or Hammarsten casein (CAS) as a protein source over a period of 34 weeks. All the living rats of each group at 22, 28 or 34 weeks were endoscopically inspected for tumor incidence in the colon. SCR turned out to be comparable to HMF in anti-tumorigenicity, or rather better than HMF.

c-myc mRNA is stabilized by deprivation of amino acids in primary cultured rat hepatocytes.

We investigated whether the expression of growth-related genes could be changed in primary cultured hepatocytes in response to changes in the nutritional environment. Hepatocytes were isolated from the liver of growing rats after collagenase perfusion and cultured in Williams' E medium (WE medium) containing 5% calf serum, 10(-7) M insulin and 10(-6) M dexamethasone for 24 h. When amino acids were removed from the culture, the level of c-myc mRNA increased more than 18-fold within 2-3 h, whereas replenishment of the amino acids to the medium caused rapid decrease in the mRNA level. We found that the half-life of the c-myc mRNA was prolonged more than 6-fold in the absence of amino acids. The mRNA levels of other proteins, such as ornithine decarboxylase, c-Ha-ras and actin, and their half-lives were not affected by amino acids. It is known that a short-lived protein is involved in the degradation of c-myc mRNA. In fact, the addition of cycloheximide to cultured hepatocytes increased the level of c-myc mRNA either in the presence or absence of amino acids, though the levels of other mRNAs were not changed significantly. These results suggest that the synthesis of the short-lived protein is suppressed and the c-myc mRNA is thereby stabilized in the absence of amino acids.

Effects of dietary protein on the induction of DNA synthesis and expression of growth-related genes in liver and kidney of growing rats.

To investigate molecular mechanisms of growth control by protein nutrition, we examined whether nutritive quality of protein affects the induction of DNA synthesis in liver and kidney of growing rats in relation to expression of growth-related genes such as c-myc, c-fos, c-Ha-ras, and ornithine decarboxylase (ODC). Rats were adapted to 2-h meal feeding schedule at first with laboratory chow for 10 days and then with a protein-free diet for 3 days prior to experiments. When protein-free diet was fed to the rats, the levels of c-myc, ODC and c-Ha-ras mRNAs increased in the liver within 2 days. However, substantial changes in the levels of those mRNAs were not observed in the kidney. The level of c-fos mRNA in these tissues was too low to detect by our method. Feeding of casein diet to rats that had been maintained on protein-free diet for 3 days caused a rapid decrease in the level of c-myc mRNA and induced DNA synthesis in the liver. On the other hand, zein diet, which lacks tryptophan and lysine, did not lower the c-myc mRNA level nor induced DNA synthesis in the liver. However, if zein diet was supplemented with tryptophan and lysine, a decrease in c-myc mRNA level and an induction of DNA synthesis were observed. The levels of ODC and c-Ha-ras mRNAs were not changed by feeding of casein or zein diet. Neither casein nor zein induced DNA synthesis and changed the levels of the mRNA in the kidney. The amount of food intake during the 2-h feeding period was not different among the diets. These results suggest that the liver cells are arrested in G1 phase during the feeding of protein-free diet and good quality of protein is required to progress the cell cycle to enter S phase.

Expressions of c-myc and insulin-like growth factor-1 mRNA in the liver of growing rats vary reciprocally in response to changes in dietary protein.

To investigate molecular mechanisms of growth control by diets, we examined the effects of nutrition on the expression of c-myc and insulin-like growth factor-1 (IGF-1) genes in the liver of growing rats. In the first study, rats were fed either a 24% casein, 24% zein or protein-free diet, or were starved for 3 d. The levels of the two mRNAs in the tissues were then determined by Northern blot hybridization. In the liver, levels of the two mRNAs varied in a reciprocal anner in response to changes in either quantity or quality of diet. The expression of c-myc mRNA was greatly enhanced by consumption of the protein-free diet or by starvation, whereas the IGF-1 mRNA levels were reduced markedly by consumption of the zein diet or the protein-free diet or by starvation. In another study, the casein and zein diets were fed to rats that had been adapted to a 2-h meal-feeding pattern, first with nonpurifled diet for 10 d and then with the protein-free diet for 3 d before the experiment. In rats fed casein, the level of c-myc mRNA decreased 75% within 8 h after consumption of the casein diet, whereas the IGF-1 mRNA level increased 100% during that period. Consumption of the zein diet did not affect the level of either mRNA. Because quantity of food intake did not differ between the rats fed casein and those fed zein, expression of the two genes in the liver was affected by the quality of the protein consumed. These results indicate that quality and quantity of diets changed the expression of c-myc and IGF-1 genes and thus demonstrate the possibility that nutrition not only supplies material for body components but also affects the signal transduction for growth in young growing rats.

Spermidine-induced destabilization of ornithine decarboxylase (ODC) is mediated by accumulation of antizyme in ODC-overproducing variant cells.

The mechanism of spermidine-induced destabilization of ornithine decarboxylase (ODC) was examined in newly isolated ODC-overproducing variant cells by use of an in vitro ODC degrading system. The cells accumulated ODC protein in the presence of alpha-difluoromethylornithine. Addition of spermidine to the medium accelerated degradation of ODC protein concomitantly with induction of antizyme, a regulatory protein that binds to ODC, inhibiting its activity. Both the acceleration of ODC degradation and the induction of antizyme were inhibited by cycloheximide, but not by actinomycin D. ODC was degraded rapidly in extracts from spermidine-treated cells. The rate of ODC degradation correlated with the amount of antizyme in the extracts, and the degradation activity was abolished by treatment of the extracts with anti-antizyme antibody. Thus, antizyme induced by spermidine was essential for the accelerated degradation of ODC in the cells. ODC was phosphorylated in the cells, probably at serine residue 303 in the first internal PEST region. ODC phosphorylation occurred even when its new synthesis was inhibited by cycloheximide. Antizyme accelerated the degradations of both dephosphorylated ODC and native ODC.

Regulatory elements for the tissue-specific expression of the rat serine dehydratase-encoding gene.

L-Serine dehydratase (SDH; EC 4.2.1.13), the key enzyme for serine utilization in the rat, is synthesized primarily in the liver. Cis-acting DNA elements required for liver-specific expression of the SDH gene were identified by two approaches: (1) transient expression assays in primary cultured rat hepatocytes, and in rat fibrosarcoma and normal rat kidney epithelial (NRK-52E) cell lines; and (2) in vitro transcription assays with nuclear extracts prepared from rat liver and spleen. Deletion analyses of the 5' flanking sequences of the gene have defined two functionally different regions: (a) a cell-type-specific promoter located between positions -62 and +10, which is sufficient for liver-specific expression; and (b) a distal promoter region between bp -133 and -63 containing positive cis-acting elements that regulate the promoter activity in a non-tissue-specific fashion. No other cis-acting elements essential for liver-specific expression were found in the region of -134 to 2.1 kb upstream relative to the cap site of SDH.

Translational control mechanism of ornithine decarboxylase by asparagine and putrescine in primary cultured hepatocytes.

Asparagine stimulated the translation of ornithine decarboxylase (ODC) mRNA more than 10-fold in cultured hepatocytes which had been pretreated with glucagon in simple salt/glucose medium. Putrescine suppressed the increase in the rate of ODC synthesis caused by asparagine without significant change in the amount of ODC mRNA, suggesting that putrescine inhibited the effect of asparagine at least in part at the level of translation. Polysomal distribution of ODC mRNA was analyzed to examine the site of translational regulation by these effectors. In uninduced hepatocytes, most of the ODC mRNA was sedimented slightly after the 40 S ribosomal subunit. This ODC mRNA was sequestered from translational machinery since it was not shifted to the polysome fraction when peptide elongation was specifically inhibited by a low concentration of cycloheximide. In asparagine-treated cells, 40% of total ODC mRNA was in the polysomal fraction and formed heavier polysomes, indicating that asparagine stimulated both recruitment of ODC mRNA from the untranslatable pool and the initiation steps of translation. Putrescine did not change the distribution pattern of ODC mRNA on polysomes significantly. Thus, 30% of ODC mRNA remained on polysomes even when ODC synthesis was completely inhibited by putrescine. Paradoxically more than 70% of ODC mRNA was shifted into polysomes by putrescine in the presence of low concentrations of cycloheximide. These results, together with changes in the polysome profile, suggested that putrescine nonspecifically stimulated the recruitment of ODC mRNA from the untranslatable pool, whereas it specifically inhibited its translation at both the initiation and the elongation steps.

Hormonal regulation of serine dehydratase gene expression in liver and kidney of the adrenalectomized rat.

We have previously demonstrated that glucagon but not dexamethasone could induce serine dehydratase (SDH: EC.4.2.1.13) in liver, and either glucagon or dexamethasone could induce the enzyme in kidney of normal rats. The mechanism(s) of the hormonal regulation of SDH gene expression in liver and kidney was further studied using adrenalectomized rats. Simultaneous administration of glucagon and dexamethasone induced the activity, rate of SDH synthesis, and accumulation of SDH mRNA in both liver and kidney of the rat. The increased SDH activity was reflected by changes in the amount of enzyme protein and in the rate of SDH protein synthesis, both parameters closely paralleling the changes in the levels of SDH mRNA. The rates of transcription of the SDH gene as measured in run-on experiments with isolated nuclei were also increased by the administration of these hormones. These results indicate that the expression of the SDH gene was regulated primarily at the transcriptional level under these conditions. When glucagon or dexamethasone was injected separately into adrenalectomized rats, significant increases in the levels of SDH mRNA and the rate of SDH gene transcription were observed in liver. Although glucagon was more effective than dexamethasone, both hormones were required for the maximal induction of SDH gene transcription in liver. In contrast, dexamethasone alone effectively increased the rate of SDH gene transcription in kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutritional regulation and tissue-specific expression of the serine dehydratase gene in rat.

The mechanism of dietary regulation and tissue-specific expression of the serine dehydratase gene in rat has been studied. The hepatic serine dehydratase activity and its mRNA showed a parallel increase with increasing protein content in the diet. However, when rats that had been maintained on a high protein diet were fed a protein-free diet, the mRNA level rapidly decreased to 0.5 in 3 h, whereas the enzyme activity gradually fell to a low level over a period of 5 days. With animals maintained on a high protein diet or on a protein-free diet, we examined the sites hypersensitive to DNase I in the 5'-flanking region of serine dehydratase gene in the liver chromatins. A series of DNase I-hypersensitive sites were located within 10.5 kilobase pairs upstream of the transcription start site. The DNA regions at -3050 and -3180 (region II) and -3600 to -3850 (region III) were more susceptible to the nuclease in the expressing than in the nonexpressing liver. A reverse situation obtained at -100 (region I). Kidney contained serine dehydratase mRNA at a level of 5% of liver as determined by Northern blotting. The kidney chromatin was found to be susceptible to DNase I only at region I. No conspicuous DNase I-hypersensitive sites were observed in the relevant regions of chromatins from brain and lung, in which serine dehydratase mRNA was scarcely transcribed. These results suggest that nutritional control and tissue-specific expression of the serine dehydratase gene is closely associated with the alteration of DNase I hypersensitivity at specific sites of the 5'-flanking region of the gene.

Effects of glucose, insulin, and cAMP on transcription of the serine dehydratase gene in rat liver.

Starvation and diabetes both caused a dramatic induction of hepatic L-serine dehydratase (SDH) (EC 4.2.1.13) in rats. Increases in the activity of the enzyme which had been demonstrated in several previous studies were found to be associated with increases in the amount of SDH protein and its mRNA in our studies reported herein. Nuclear run-on experiments with isolated liver nuclei demonstrated that the increases in SDH activity were mainly the result of increases in the rate of SDH gene transcription. Refeeding of glucose to starved rats or the administration of insulin to diabetic rats caused a marked reduction in the amount of SDH mRNA. The rates of transcription as measured in isolated nuclei were reduced to uninduced levels within 30 min of either treatment. Following the administration of Bt2-cAMP, the transcription rates of the SDH gene returned to the original induced rates within 40 min both in glucose-refed rats and in diabetic rats administered insulin. The results of these experiments indicate that the induction of SDH in rat liver in vivo is controlled predominantly at the level of gene transcription by the reciprocal action of cAMP and insulin.

Analyses of ornithine decarboxylase antizyme mRNA with a cDNA cloned from rat liver.

Ornithine decarboxylase antizyme is a unique inhibitory protein induced by polyamines and involved in the regulation of ornithine decarboxylase. A cDNA was isolated from a rat liver cDNA library by the screening with monoclonal antibodies to rat liver antizyme as probes. The expression products of the cDNA in bacterial systems inhibited rat ornithine decarboxylase activity in a manner characteristic of antizyme and rabbit antisera raised against its direct expression product reacted to rat liver antizyme, confirming the authenticity of the cDNA. On RNA blot analysis with the cDNA probe, an antizyme mRNA band of 1.3 kb was detected in rat tissues. Antizyme mRNA did not increase upon administration of putrescine, an inducer of antizyme, and its half-life after actinomycin D treatment was as long as 12 h in rat liver, suggesting that antizyme mRNA is constitutively expressed and antizyme synthesis is regulated at the translational level. Similar-sized mRNAs hybridizable to the cDNA were also found in various mammalian and non-mammalian vertebrate tissues under physiological conditions. In addition, chicken and frog antizymes showed immunocrossreactivity with rat antizyme. The ubiquitous presence and the evolutionally conserved structure of antizyme in vertebrate tissues suggest that it has an important function.