Jiang Y H, Lupton J R, Chapkin R S
Faculty of Nutrition, Molecular and Cell Biology Group, Texas A&M University, College Station 77843-2471, USA.
Carcinogenesis. 1997 Feb;18(2):351-7. doi: 10.1093/carcin/18.2.351.
In order to elucidate the influence of dietary constituents on colonic intracellular signal transduction, the effect of different fats on rat colonic epithelial protein kinase C (PKC) alpha (classical), delta (novel) and lambda-zeta (atypical) expression was determined in carcinogen-treated animals. Sprague-Dawley rats were provided with one of two fats (corn oil and fish oil); plus or minus the carcinogen azoxymethane (AOM) and killed at two time points (15 and 37 weeks) in a 2x2x2 factorial design. At 5 and 6 weeks of age, animals were injected s.c. with either AOM at a dose of 15 mg/kg body weight or saline once a week for 2 weeks and continued on the same diet until termination of the study. At 15 and 37 weeks after the second injection, 10 rats from each treatment group were killed. Colonic PKC alpha, delta and lambda-zeta steady-state protein and mRNA levels were determined using immunoblotting and relative quantitative polymerase chain reaction, respectively. Colonic mucosa from rats injected with AOM had significantly suppressed membrane and cytosolic PKC alpha and cytosolic lambda-zeta protein levels (P < 0.05) as compared to saline-injected control animals at both time points. In contrast, rats fed fish oil diets had significantly higher (P < 0.05) cytosolic PKC delta and lambda-zeta protein levels relative to animals fed corn oil diets. However, the effect of diet and AOM on the steady-state expression of PKC alpha, delta and zeta mRNA was not consistent with changes in the respective isozyme protein levels, suggesting regulation at the post-transcriptional level. These data demonstrate that dietary fish oil blocks the carcinogen-induced decrease in the steady-state levels of colonic mucosal PKC delta and lambda-zeta, which may in part explain why this fat source protects against colon cancer development.
为了阐明饮食成分对结肠细胞内信号转导的影响，在致癌物处理的动物中测定了不同脂肪对大鼠结肠上皮蛋白激酶C（PKC）α（经典型）、δ（新型）和λ-ζ（非典型）表达的影响。给斯普拉格-道利大鼠提供两种脂肪（玉米油和鱼油）中的一种；加上或减去致癌物偶氮甲烷（AOM），并在2×2×2析因设计的两个时间点（15周和37周）处死动物。在5和6周龄时，给动物皮下注射剂量为15mg/kg体重的AOM或生理盐水，每周一次，共2周，并继续相同饮食直至研究结束。在第二次注射后15周和37周，处死每个治疗组的10只大鼠。分别使用免疫印迹和相对定量聚合酶链反应测定结肠PKCα、δ和λ-ζ的稳态蛋白和mRNA水平。与两个时间点注射生理盐水的对照动物相比，注射AOM的大鼠结肠黏膜中膜和胞质PKCα以及胞质λ-ζ蛋白水平显著降低（P<0.05）。相反，与喂食玉米油的动物相比，喂食鱼油饮食的大鼠胞质PKCδ和λ-ζ蛋白水平显著更高（P<0.05）。然而，饮食和AOM对PKCα、δ和ζ mRNA稳态表达的影响与各自同工酶蛋白水平的变化不一致，表明在转录后水平存在调控。这些数据表明，饮食中的鱼油可阻止致癌物诱导的结肠黏膜PKCδ和λ-ζ稳态水平降低，这可能部分解释了这种脂肪来源预防结肠癌发生的原因。
