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Regulatory mechanisms of gene expression of hepatic enzyme by insulin and fructose

胰岛素和果糖对肝酶基因表达的调控机制

基本信息

批准号：
60480499
负责人：
TANAKA Takehiko
金额：
$ 4.42万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

项目摘要

Regulation of the expression of the hepatic L-type pyruvate kinase gene by insulin and fructose was studied in diabetic rats. Insulin stimulated transcription of the pyruvate kinase L gene. Cycloheximide inhibited the induction caused by insulin, suggesting that insulin may stimulate transcription of the pyruvate kinase L gene by stimulating synthesis of some unknown protein. On the other hand, feeding fructose had no effect on transcription of the pyruvate kinase L gene. Since increases in the levels of putative nuclear RNA precursor species of the pyruvate kinase L after fructose feeding preceded changes in the levels of cytosolic pyruvate kinase L mRNA, fructose may increase the levels of pyruvate kinase L mRNA by stabilizing nuclear RNA species. The effect of fructose on pyruvate kinase L was not mediated by hormones such as glucagon, glucocorticoid and thyroid hormones, and thus seems to be directly on the liver.Comparison of the nucleotide sequence of rat R-type isozyme mRNA with that of the L-type isozyme showed that the R-type isozyme mRNA had an identical nucleotide sequence to that of the L-type except in the 5' terminal region including the coding sequence: the sequence upstream of the 5th coding residue of the L-type was replaced by a 98-nucleotide coding sequence plus a 5' untranslated region in the R-type isozyme. By sequence analysis of a genomic clone of LPK30 twelve exons were identified, of which the first and second exons coded the R- and L-specific sequences, respectively. The remaining exons present downstream coded amino acids common to the two isozymes. Thus, we suggest that the two isozyme mRNAs are generated by use of different promoters.

研究了胰岛素和果糖对糖尿病大鼠肝脏L型丙酮酸激酶基因表达的调节作用。胰岛素刺激丙酮酸激酶L基因的转录。放线菌酮抑制胰岛素诱导的丙酮酸激酶L基因的转录，提示胰岛素可能通过刺激某些未知蛋白的合成来刺激丙酮酸激酶L基因的转录。另一方面，喂食果糖对丙酮酸激酶L基因的转录没有影响。由于果糖喂养后丙酮酸激酶L的推定核RNA前体物质水平的增加先于胞质丙酮酸激酶L mRNA水平的变化，因此果糖可通过稳定核RNA物质来增加丙酮酸激酶L mRNA水平。果糖对丙酮酸激酶L的作用不受胰高血糖素、糖皮质激素和甲状腺激素等激素的影响，似乎是直接作用于肝脏。比较大鼠R型同工酶mRNA和L型同工酶mRNA的核苷酸序列，发现R型同工酶mRNA的核苷酸序列与L型同工酶的核苷酸序列完全相同，除了5'端的编码序列：将L型第5个编码残基上游的序列替换为R型同工酶中98个核苷酸的编码序列加上5'非翻译区。通过对LPK 30基因组克隆的序列分析，鉴定了12个外显子，其中第一和第二外显子分别编码R和L特异性序列。其余外显子呈现两种同工酶共有的下游编码氨基酸。因此，我们认为这两种同工酶mRNA是通过使用不同的启动子产生的。