Genetic characterization of two S-adenosylmethionine-induced ABC transporters reveals their roles in modulations of secondary metabolism and sporulation in Streptomyces coelicolor M145.

S-Adenosylmethionine (SAM) was previously documented to activate secondary metabolism in a variety of Streptomyces spp. and to promote actinorhodin (ACT) and undecylprodigiosin (RED) in Streptomyces coelicolor. The SAM-induced proteins in S. coelicolor include several ABC transporter components (SCO5260 and SCO5477) including BldKB, the component of a well-known regulatory factor for differentiations. In order to assess the role of these ABC transporter complexes in differentiation of Streptomyces, SCO5260 and SCO5476, the first genes from the cognate complex clusters, were individually inactivated by gene replacement. Inactivation of either SCO5260 or SCO5476 led to impaired sporulation on agar medium, with the more drastic defect in the SCO5260 null mutant (ASCO5260). ASCO5260 displayed growth retardation and reduced yields of ACT and RED in liquid cultures. In addition, SAM supplementation failed in promoting the production of ACT and RED in ASCO5260. Inactivation of SCO5476 gave no significant change in growth and production of ACT and RED, but impaired the promoting effect of SAM on ACT production without interfering with the effect on RED production. The present study suggests that SAM induces several ABC transporters to modulate secondary metabolism and morphological development in S. coelicolor.

Dietary trans-10, cis-12 and cis-9,trans-11 conjugated linoleic acids induce apoptosis in the colonic mucosa of rats treated with 1,2-dimethylhydrazine.

We have previously shown that a diet containing a mixture of conjugated linoleic acid (CLA) isomers reduces the incidence of colon tumors in rats treated with 1,2-dimethylhydrazine (DMH). The present study examined which of the two main CLA isomers, trans-10,cis-12 CLA (t10c12) or cis-9,trans-11 CLA (c9t11), decreases colon tumor numbers and the mechanisms for this effect. Six-week-old, male Sprague-Dawley rats were intramuscularly injected with 15 mg/kg of DMH twice per week for 6 weeks and fed a control diet, 1% t10c12, or 1% c9t11 for 30 weeks. The experimental diets were initiated simultaneously with DMH injection. The tumor numbers were decreased and the apoptotic index was significantly increased in the colonic mucosa of the t10c12 and c9t11 groups, when the results were compared with those of the control group. The protein levels of Bcl-2 and cyclooxygenase-2 were significantly decreased, but Bax levels were increased in both of the CLA isomer groups. The thromboxane B(2) levels in colonic mucosa were substantially lower in the two CLA isomer groups than in the control group. However, there was no difference in these parameters between the CLA isomer groups. We have demonstrated that diets containing 1% t10c12 and c9t11 were equally effective in reducing tumor numbers and inducing apoptosis in the colonic mucosa of rats treated with DMH. These results indicate that Bcl-2 family protein levels are associated with CLA-induced apoptosis in the colonic mucosa of DMH-treated rats.

Accumulation of S-adenosylmethionine induced oligopeptide transporters including BldK to regulate differentiation events in Streptomyces coelicolor M145.

S-Adenosylmethionine (SAM), the major methyl donor in diverse biological processes, was recently found to be involved in the regulation of differentiation in streptomycetes. Exogenous SAM, in a quantity as low as 2muM, enhanced antibiotic production and inhibited morphological development of Streptomyces coelicolor M145. Total protein profiling of S. coelicolor M145 revealed that SAM enhanced the expression of oligopeptide-binding components related to ABC transporters that included BldK, a well-known regulatory factor in S. coelicolor differentiation. A radiolabeled SAM feeding experiment verified that exogenous SAM can be imported into the cell, which is under the control of the bld cascade. This study substantiated that BldK serves as a transducer of the SAM signal and uncovered the possible role of oligopeptide import in the regulation of Streptomyces differentiation, particularly in relation to SAM.

trans-10, cis-12 conjugated linoleic acid reduces insulin-like growth factor-II secretion in HT-29 human colon cancer cells.

We previously demonstrated that a mixture of conjugated linoleic acid (CLA) isomers decreases colon cancer incidence in rats treated with 1,2-dimethylhydrazine. Our in vitro studies have also shown that CLA inhibits the growth of HT-29 cells, a human colon cancer cell line. When we compared the individual potencies of the two main isomers found in the mixture of CLA isomers (e.g., cis-9, trans-11 [c9t11] and trans-10, cis-12 [t10c12]), t10c12 CLA decreased viable cell numbers in a dose-dependent manner. By contrast, c9t11 CLA had no effect. Therefore, the present study examined whether the decreased cell growth is related to changes in secretion of insulin-like growth factor (IGF)-II and/or IGF-binding proteins (IGFBPs) that have been shown to regulate HT-29 cell proliferation. Cells were incubated in serum-free medium with various concentrations of the individual CLA isomers, and immunoblot analysis of 24-hour, serum-free, conditioned media using a monoclonal anti-IGF-II antibody was performed. HT-29 cells secreted both mature 7,500 apparent molecular weight (M(r)) and higher-M(r) forms of IGF-II. t10c12 CLA decreased the levels of the higher-M(r) and the mature form of IGF-II in a dose-dependent manner, whereas c9t11 CLA had no effect. Ligand blot analysis of conditioned medium using (125)I-IGF-II revealed that the production of IGFBP-2 and IGFBP-4 was also decreased by t10c12 CLA, whereas c9t11 CLA had no effect. Exogenous IGF-II abrogated the growth inhibition induced by t10c12 CLA. These results indicate that inhibition of HT-29 cell growth by t10c12 CLA may be mediated by decreasing IGF-II secretion in these cells.

Dietary supplementation of conjugated linoleic acid reduces colon tumor incidence in DMH-treated rats by increasing apoptosis with modulation of biomarkers.

OBJECTIVES: We investigated the effects of conjugated linoleic acid (CLA) on tumor incidence, apoptosis, eicosanoid formation, 1,2-diacylglycerol (DAG), and fatty acid profiles of colonic mucosa in 1,2-dimethylhydrazine-treated rats fed different types of dietary fats. METHODS: One hundred twenty male 7-wk-old Sprague-Dawley rats were assigned to a beef tallow (BT) diet or a fish oil (FO) diet; each group was further divided into two groups, one with CLA supplementation (BTC and FOC) and the other without (BT and FO). All groups were fed for 30 wk on experimental diets that contained 12% (w/w) dietary fat (including 1% CLA for the BTC and FOC groups) and were intramuscularly injected with 1,2-dimethylhydrazine for 6 wk, for a total dose of 180 mg/kg of body weight. RESULTS: Rats fed the FOC, BTC, or FO (omega-3 fatty acids, mainly docosahexaenoic acid) showed a reduced incidence of tumors, increased apoptotic index values (P < 0.05), and lower levels of eicosanoids (prostaglandin E(2) and thromboxane B(2)) and DAG in colonic mucosa (P < 0.05). CLA and docosahexaenoic acid were incorporated into membrane phospholipids and significantly reduced the distribution of arachidonic acid in colonic mucosal phospholipids. Because CLA and omega-3 fatty acids reduced tumor incidence and levels of cell response regulators (prostaglandin E(2), thromboxane B(2), and DAG), they may share at least one common path of action in promoting the apoptotic process of colon carcinogenesis. CONCLUSIONS: These results suggested that increased apoptosis by dietary CLA may be attributed, at least in part, to changes in arachidonic acid metabolism in rats. Therefore, CLA may have anticarcinogenic effects by inducing apoptosis through modification of signal transduction in colonic mucosal cells.

Conjugated linoleic acid (CLA) inhibits growth of Caco-2 colon cancer cells: possible mediation by oleamide.

We have previously observed that dietary conjugated linoleic acid (CLA) inhibited colon tumorigenesis induced by 1,2-dimethylhydrazine in rats. The present study was performed to determine the mechanisms by which CLA inhibits colon cancer cell growth. CLA markedly inhibited Caco-2 cell growth, while linoleic acid (LA) slightly increased growth. Both CLA and LA increased the production of material reactive to antibodies against prostaglandin (PG)E2 and leukotriene (LT)B4, estimated by a competitive enzyme immunoassays (EIA), in a dose-dependent manner. However, the magnitude of the increase was markedly higher with CLA than that with LA, suggesting that this material was not PGE2 or LTB4. The active compound was isolated by thin-layer chromatography and the nuclear magnetic resonance and infrared spectra revealed that the structure was identical to that of oleamide. The purified oleamide inhibited cell growth and cross-reacted with the EIA. These results indicate that inhibition of Caco-2 cell growth by CLA may be due in part to increased oleamide production.