Carcinogen and dietary lipid regulate ras expression and localization in rat colon without affecting farnesylation kinetics
Carcinogen and dietary lipid regulate ras expression and localization in rat colon without affecting farnesylation kinetics
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DOI：
10.1093/carcin/20.5.785
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发表时间：
1999-05-01
期刊：
影响因子：
4.7
通讯作者：
Chapkin, RS
中科院分区：
文献类型：
--
作者：
Davidson, LA;Lupton, JR;Chapkin, RS
流行病学和实验数据表明，膳食纤维和脂肪是结直肠癌的主要决定因素。然而，这些饮食成分改变结肠癌发病率的机制尚未阐明，有证据表明，显性功能获得突变使原癌基因短路，并有助于癌症的发病。因此，我们开始剖析在结肠肿瘤发生的起始、促进和进展阶段摄入的膳食脂肪和纤维调控ras p21的定位、表达和突变频率的机制。采用2x2x2因子设计，饲喂玉米油或鱼油、果胶或纤维素加或减致癌物偶氮氧甲烷（AOM）， 34周后处死雄性Sprague-Dawley大鼠（140只）。我们之前的研究表明，玉米油+ AOM的腺癌发病率为70.3%(52/74)，鱼油+ AOM的腺癌发病率为56.1% (37/66)（P < 0.05）。结肠肿瘤中ras的总表达量以及ras膜与细胞质的比值比AOM或盐水注射大鼠粘膜高4- 6倍。饲喂玉米油的动物的ras在粘膜部位的表达量比饲喂鱼油的动物高13% (P < 0.05)，这值得注意，因为ras必须定位于质膜才能发挥作用。肿瘤中ras膜与细胞质比值的升高不是由于法尼基蛋白转移酶活性或戊烯酰化状态的增加，因为几乎所有可检测到的ras都以戊烯酰化形式存在，与AOM和盐水注射的未受损伤大鼠粘膜相比，肿瘤提取物中磷酸化p42和p44丝裂原活化蛋白激酶（ERK）的表达高出两倍（P < 0.05）。不同组间K-ras突变频率无显著差异，但玉米油喂养的大鼠肿瘤突变发生率（85%）高于鱼油喂养的大鼠（58%）。我们的研究结果表明，致癌物诱导的ras表达和膜定位的变化与ERK通路的体内激活有关。膳食n-3多不饱和脂肪酸对肿瘤发展的抑制可能部分是由于对结肠ras表达、膜定位和突变频率的综合影响。
Epidemiological and experimental data suggest that dietary fiber and fat are major determinants of colorectal cancer. However, the mechanisms by which these dietary constituents alter the incidence of colon cancer have not been elucidated, Evidence indicates that dominant gain-of-function mutations short-circuit protooncogenes and contribute to the pathogenesis of cancer. Therefore, we began to dissect the mechanisms whereby dietary fat and fiber, fed during the initiation, promotion and progression stages of colon tumorigenesis, regulate ras p21 localization, expression and mutation frequency. Male Sprague-Dawley rats (140) were provided with corn oil or fish oil and pectin or cellulose plus or minus the carcinogen azoxymethane (AOM) in a 2x2x2 factorial design and killed after 34 weeks. We have previously shown adenocarcinoma incidence in these animals to be 70.3% (52/74) for corn oil + AOM and 56.1% (37/66) for fish oil + AOM (P < 0.05). Total ras expression as well as ras membrane:cytosol ratio was 4- to 6-fold higher in colon tumors than in mucosa from AOM- or saline-injected rats. Expression of ras in the mucosal membrane fraction was 13% higher for animals fed corn oil compared with fish oil feeding (P < 0.05), which is noteworthy since ras must be localized at the plasma membrane to function. The elevated ras membrane:cytosol ratio in tumors was not due to increased farnesyl protein transferase activity or prenylation state, as nearly all detectable ras was in the prenylated form, Phosphorylated p42 and p44 mitogen activated protein kinase (ERK) expression was two-fold higher in tumor extracts compared with uninvolved mucosa from AOM- and saline-injected rats (P < 0.05). The frequency of K-ras mutations was not significantly different between the various groups, but there was a trend toward a greater incidence of mutations in tumors from corn oil fed rats (85%) compared with fish oil fed rats (58%), Our results indicate that the carcinogen-induced changes in ras expression and membrane localization are associated with the in vivo activation of the ERK pathway, In addition, suppression of tumor development by dietary n-3 polyunsaturated fatty acids may be partly due to a combined effect on colonic ras expression, membrane localization, and mutation frequency.