Prostate cancer cell-adipocyte interaction: leptin mediates androgen-independent prostate cancer cell proliferation through c-Jun NH2-terminal kinase

Prostate cancer is one of the leading causes of death among men in the United States, and acquisition of hormone resistance (androgen independence) by cancer cells is a fatal event during the natural history of prostate cancer. Obesity is another serious health problem and has been shown to be associated with prostate cancer. However, little is known about the molecular basis of this association. Here we show that factor(s) secreted from adipocytes stimulate prostate cancer cell proliferation. Leptin is one of the major adipose cytokines, and it controls body weight homeostasis through food intake and energy expenditure. We identify leptin as a novel growth factor in androgen-independent prostate cancer cell growth. Strikingly, leptin stimulates cell proliferation specifically in androgen-independent DU145 and PC-3 prostate cancer cells but not in androgen-dependent LNCaP-FGC cells, although both cell types express functional leptin receptor isoforms. c-Jun NH2-terminal kinase (JNK) has been shown recently to play a crucial role in obesity and insulin resistance. Intriguingly, leptin induces JNK activation in androgen-independent prostate cancer cells, and the pharmacological inhibition of JNK blocked the leptin stimulation of androgen-independent prostate cancer cell proliferation. This suggests that JNK activation is required for leptin-mediated, androgen-independent prostate cancer cell proliferation. Furthermore, other cytokines produced by adipocytes and critical for body weight homeostasis cooperate with leptin in androgen-independent prostate cancer cell proliferation: interleukin-6 and insulin-like growth factor I demonstrate additive and synergistic effects on the leptin stimulation of androgen-independent prostate cancer cell proliferation, respectively. Therefore, adipose cytokines, as well as JNK, are key mediators between obesity and hormone-resistant prostate cancer and could be therapeutic targets.     

Arg(362) and Tyr(365) of the botulinum neurotoxin type a light chain are involved in transition state stabilization

The botulinum neurotoxin type A (BoNT/A) light chain (LC) acts as zinc endopeptidase. The X-ray structure of the toxin demonstrated that Zn(2+) is coordinated by His(222) and His(226) of the Zn(2+) binding motif HisGluXXHis and Glu(261), whereas Glu(223) coordinates the water molecule required for hydrolysis as the fourth ligand. Recent analysis of a cocrystal of the BoNT/B LC and its substrate synaptobrevin 2 suggested that Arg(362) and Tyr(365) of the homologous BoNT/A may be directly involved in catalysis. Their role and that of Glu(350) which is also found in the vicinity to the active site were analyzed by site-directed mutagenesis. Various replacements of Arg(362) and substitution of Tyr(365) with Phe resulted in 79- and 34-fold lower k(cat)/K(m) values, respectively. These changes were provoked by decreased catalytic rates (k(cat)) and not by alterations of ground state substrate binding as evidenced by largely unchanged K(d) and K(m) values. None of these mutations affected the overall secondary structure or zinc content of the LC. These findings suggest that the guanidino group of Arg(362) and the hydroxyl group of Tyr(365) together accomplish transition state stabilization as was proposed for thermolysin, being the prototypical member of the gluzincin superfamily of metalloproteases. Mutation of Glu(350) dramatically diminished the hydrolytic activity which must partly be attributed to an altered active site fine structure as demonstrated by an increased sensitivity toward heat-induced denaturing and a lower Zn(2+) binding affinity. Glu(350) apparently occupies a central position in the active site and presumably positions His(222) and Arg(362).     

Relationship between Aphis gossypii (Homoptera: Aphididae) and sticky lint in cotton

The study was conducted in the northern Texas Rolling Plains in 1999 to define the relationship between number of cotton aphids, Aphis gossypii Glover, and resulting contamination of cotton lint by honeydew. Whole-plot treatments were three furrow irrigation management treatments: cotton grown without supplemental irrigation (dryland), irrigated cotton with last irrigation in mid August, and irrigated cotton with last irrigation in late August. Subplots within each irrigation treatment included an untreated check, a plot treated with lambda-cyhalothrin to stimulate aphid population increase, a plot treated with lambda-cyhalothrin followed by pymetrozine after aphids began to increase, and a plot treated with lambda-cyhalothrin followed by thiamethoxam after aphids began to increase. Cotton aphids were counted on leaves picked from the top and bottom half of the plant. Cotton lint was analyzed for contamination by glucose, fructose, sucrose, and melezitose secreted by cotton aphids, and percentage leaf moisture and nitrogen and leaf sucrose concentrations were determined. The manual sticky cotton thermodetector was used to determine degree of lint stickinesss. There was a significant relationship between thermodetector counts and melezitose contamination on lint, and a melezitose concentration of 90.9 microg/g of lint was associated with a thermodetector count of 10, the threshold for sticky lint problems in textile mills. An equation was developed to estimate melezitose concentration on lint as a function of average numbers of aphids per leaf and the interaction between percentage leaf moisture and nitrogen. The number of aphids per leaf associated with a melezitose concentration of 90.9 microg/g of lint ranged from 11.1 to 50.1, depending on percentage leaf moisture and nitrogen. The threshold for sticky lint problems occurred when aphid numbers ranged between 11.1 and 50.1 per leaf after bolls open.     

Antisecretory effects of somatostatin and vasopressin in the rat colon descendens in vitro

The effects of two hormones, vasopressin and somatostatin (SOM), on ion secretion in rat colon descendens were compared. Three modes for induction of epithelial secretion were used: neuronally mediated secretion due to electric field stimulation (EFS), Ca2+-dependent secretion elicited by carbachol, and cAMP-dependent secretion evoked either by a receptor-mediated mechanism elicited by vasoactive intestinal peptide (VIP) or by a direct activation of the adenylate cyclase by means of forskolin. Somatostatin inhibited ion secretion evoked by EFS (55-65%), carbachol (80%) and VIP (95%) in a dose-dependent manner. Maximal inhibition by SOM was observed at 10(-7) M. Somatostatin had, however, no effect on the secretory response to forskolin. The inhibition of the VIP effect could be attenuated by pretreatment with pertussis toxin. In contrast, vasopressin in concentrations as low as 0.025-0.25 U/liter decreased the secretory effects of EFS (55-75%) and carbachol (85%), but had no effect on cAMP-dependent secretion elicited either by VIP or forskolin. The results suggest that the antisecretory effect of vasopressin is mediated only by a block in the Ca2+ pathway, whereas SOM inhibits Ca2+-dependent secretion as well as receptor-mediated cAMP-dependent secretion. The interaction with the cAMP pathway is located at the step between stimulation of the receptor and activation of the adenylate cyclase and probably involves an Ni-protein.     

Evolution of cytochrome P-450 proteins [published erratum appears in Mol Biol Evol 1988 Mar;5(2):199]

Thirty-four cytochrome P-450 sequences from one bacterial and six vertebrate species have been aligned with the aid of a computer alignment algorithm. Phylogenetic trees were constructed using the unweighted-pair-group and neighbor-joining methods. The two trees differed at only a single branch point near the base of the tree. The cytochrome P-450 superfamily of proteins clustered into eight families and contained 16 gene-duplication events. The first gene duplication occurred approximately 1,360 Myr before the present (Mybp) and gave rise to cytochrome P-450s found in two different cellular organelles, the mitochondria and the endoplasmic reticulum. Both groups utilize cholesterol or its metabolites as substrates, implying that cholesterol existed greater than 1,360 Mybp. The fourth gene duplication (approximately 900 Mybp) gave rise to the drug-metabolizing P-450s. These proteins aid in the detoxification of foreign chemicals, as opposed to the metabolism of endogenous compounds. The importance of the capacity to metabolize drugs is reflected in 11 further gene duplications occurring in this lineage. The first occurred approximately 800 Mybp and gave rise to the two major P-450 families, the phenobarbital and 3-methylcholanthrene families. An apparent increase in the rate of cytochrome P-450 evolution is noted between the bird-mammal divergence (300 Mybp) and the mammalian radiation (75 Mybp).      

Single chloride channels in colon mucosa and isolated colonic enterocytes of the rat

Summary Chloride channels from rat colonic enterocytes were studied using the patch-clamp technique. After removal of mucus, inside-out patches were excised from the apical membrane of intact epithelium located at the luminal surface. They contained spontaneously switching Cl^– channels with a conductance of 35–40 pS. The channels were blocked reversibly by anthracene-9-carboxylic acid (1mm).In excised patches from single enterocytes, isolated by calcium removal, the Cl^– channels were studied in more detail. TheI–V relation was linear between ±80 mV. The selectivity was I^–>Br^–>Cl^–=NO ₃ ^– >F^–=HCO ₃ ^– .Thirty pS Cl^– channels were also found on the basolateral membrane of crypts isolated by brief calcium removal. TheI–V curve of these Cl^– channels was also linear.The results provide direct evidence for the existence of Cl^– channels in the apical membrane of surface cells in colonic mucosa. The properties of these channels are similar to those previously observed when incorporating membrane vesicles into planar lipid bilayers. Both results support the validity of the theoretical models describing intestinal secretion.     

The valency state of absorbed iron appearing in the portal blood and ceruloplasmin substitution

Summary (1) Attempts to determine the redox-state of the absorbed iron, which appeared in the portal blood when the free iron-binding capacity was previously saturated, indicate that about 30–90% of this iron was in the ferrous state. This effect was particularly prominent after luminal administration of ferrous iron, but was also seen when iron was given in the ferric state. (2) Total iron absorption is significantly higher in ceruloplasmin-substituted copper-deficient animals as compared to copper-deficient controls. (3) The appearance rate of absorbed iron in the portal blood of copper-deficient animals increased several times immediately after the intravenous infusion of ceruloplasmin. (5) The distribution of absorbed iron was changed due to the ceruloplasmin substitution: it was increased in the reticulocytes (+66%), plasma (+400%) and the body (+ 112%), whereas in the liver it was decreased by about 78%. (5) In iron-deficient rats intravenously injected ceruloplasmin did not increase iron absorption. (6) The conclusion was drawn that, as for the entrance into the mucosa from the luminal side, also for the release at the contraluminal side into the portal blood, the ferrous state of iron is favoured and that ceruloplasmin accelerates the release into the portal blood by catalyzing the oxidation of ferrous iron due to its high Fe(II):oxygen oxidoreductase (EC 1.16.3.1) activity.