Pastori R L, Moskaitis J E, Smith L H, Schoenberg D R
Department of Pharmacology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799.
Biochemistry. 1990 Mar 13;29(10):2599-605. doi: 10.1021/bi00462a024.
Albumin gene expression in Xenopus is regulated by estrogen through changes in the stability of its mRNA. The goal of the present study was to determine whether a similar pathway regulates gamma-fibrinogen. Degenerate oligonucleotides directed to conserved regions of the carboxyl-terminal half (domain D) of human and lamprey gamma-fibrinogen were used to isolate a full-length cDNA clone for Xenopus gamma-fibrinogen. Analysis of codon utilization from the DNA sequence of this clone revealed that Xenopus gamma-fibrinogen mRNA shows the same bias against CG dinucleotides as present in human, but not lamprey, fibrinogen mRNA. Features of the protein shared with the human homologue include all of the cysteine residues, an N-linked glycosylation site at amino acid 50, and 75% sequence identity in domain D. Much of the same region is conserved in lamprey gamma-fibrinogen. There is only a single size mRNA encoding gamma-fibrinogen in Xenopus, unlike rats where two mRNAs of different length are generated by alternate splicing. Administration of estrogen to male Xenopus results in the disappearance of gamma-fibrinogen mRNA from the cytoplasm, with no effect on steady-state levels in the nucleus. This process can be blocked by prior treatment with anti-estrogen, indicating that, like the regulation of serum albumin mRNA, gamma-fibrinogen is regulated posttranscriptionally through an estrogen receptor dependent mechanism. It is postulated that a consensus sequence flanking the AAUAAA polyadenylation signal in gamma-fibrinogen and the 68- and 74-kDa albumin mRNAs, but not vitellogenin or beta-globin mRNA, may play a role in the hormonal regulation of mRNA stability.
非洲爪蟾中白蛋白基因的表达受雌激素调控，其调控方式是通过改变白蛋白mRNA的稳定性。本研究的目的是确定是否存在类似的途径调控γ-纤维蛋白原。针对人及七鳃鳗γ-纤维蛋白原羧基末端一半（结构域D）的保守区域设计的简并寡核苷酸，被用于分离非洲爪蟾γ-纤维蛋白原的全长cDNA克隆。对该克隆DNA序列的密码子使用情况分析表明，非洲爪蟾γ-纤维蛋白原mRNA对CG二核苷酸的偏好与人纤维蛋白原mRNA相同，但与七鳃鳗纤维蛋白原mRNA不同。该蛋白与人同源物共有的特征包括所有半胱氨酸残基、第50位氨基酸处的N-糖基化位点，以及结构域D中75%的序列同一性。七鳃鳗γ-纤维蛋白原中大部分相同区域也保守存在。与大鼠不同，大鼠通过可变剪接产生两种不同长度的mRNA，而非洲爪蟾中仅有一种编码γ-纤维蛋白原的mRNA大小。给雄性非洲爪蟾注射雌激素会导致γ-纤维蛋白原mRNA从细胞质中消失，而对细胞核中的稳态水平没有影响。该过程可被预先用抗雌激素处理阻断，这表明，与血清白蛋白mRNA的调控一样，γ-纤维蛋白原是通过雌激素受体依赖性机制在转录后水平受到调控。据推测，γ-纤维蛋白原以及68 kDa和74 kDa白蛋白mRNA中AAUAAA多聚腺苷酸化信号侧翼的共有序列，而非卵黄蛋白原或β-珠蛋白mRNA中的共有序列，可能在mRNA稳定性的激素调控中发挥作用。
