Diehl A M, Yang S Q
Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205.
Hepatology. 1994 Feb;19(2):447-56.
CCAAT/enhancer binding proteins are a family of basic zipper DNA binding proteins that regulate transcription of several liver-specific genes and certain growth-related genes. Growth-related variations in the nuclear expression of one or more of the CCAAT/enhancer binding proteins may regulate the transition from the nonproliferative, differentiated phenotype of adult liver to the proliferative phenotype of regenerating liver. To evaluate this possibility, we used Northern- and Western-blot analyses to profile the expression of selected CCAAT/enhancer binding proteins in regenerating liver. Variations in CCAAT/enhancer binding protein expression were then correlated with changes in binding to the CCAAT/enhancer binding protein site of the c-fos promoter. Expression of both CCAAT/enhancer binding protein alpha and CCAAT/enhancer binding protein beta increases after partial hepatectomy. Steady-state levels of CCAAT/enhancer binding protein alpha mRNA increase 30% within an hour of partial hepatectomy (p < 0.05). This is followed by a transient increase in nuclear levels of CCAAT/enhancer binding protein alpha protein at 3 hr after partial hepatectomy (p = 0.08). In contrast, increases in CCAAT/enhancer binding protein beta mRNA and protein are more sustained. Levels of CCAAT/enhancer binding protein beta mRNA increase 400% to 500% within an hour of partial hepatectomy and remain increased throughout most of the prereplicative period (p < 0.01). Nuclear levels of CCAAT/enhancer binding protein beta protein are 200% to 300% greater than prehepatectomy levels at 3 hr (p < 0.001) to 6 hr (p < 0.05) and do not approach basal levels until 24 hr after partial hepatectomy. Gel mobility shift assays of nuclear extracts from regenerating livers indicate that these increases in nuclear protein expression are associated with increased DNA binding of CCAAT/enhancer binding protein alpha-beta heterodimers and beta-beta homodimers. These results demonstrate growth-related variations in the expression and DNA binding of both CCAAT/enhancer binding protein alpha and beta during liver regeneration and support the theory that altered CCAAT/enhancer binding protein DNA binding may contribute to regeneration-associated changes in liver cell phenotype.
CCAAT/增强子结合蛋白是一类碱性拉链DNA结合蛋白家族，可调节多种肝脏特异性基因和某些生长相关基因的转录。一种或多种CCAAT/增强子结合蛋白的核表达中与生长相关的变化，可能调节成年肝脏从非增殖、分化表型向再生肝脏增殖表型的转变。为评估这种可能性，我们使用Northern印迹和Western印迹分析来描绘再生肝脏中选定的CCAAT/增强子结合蛋白的表达情况。然后将CCAAT/增强子结合蛋白表达的变化与c-fos启动子的CCAAT/增强子结合蛋白位点的结合变化相关联。部分肝切除术后，CCAAT/增强子结合蛋白α和CCAAT/增强子结合蛋白β的表达均增加。部分肝切除术后一小时内，CCAAT/增强子结合蛋白α mRNA的稳态水平增加30%（p<0.05）。随后在部分肝切除术后3小时，CCAAT/增强子结合蛋白α蛋白的核水平出现短暂增加（p = 0.08）。相比之下，CCAAT/增强子结合蛋白β mRNA和蛋白的增加更为持久。部分肝切除术后一小时内，CCAAT/增强子结合蛋白β mRNA的水平增加400%至500%，并在大部分复制前期保持增加（p<0.01）。CCAAT/增强子结合蛋白β蛋白的核水平在3小时（p<0.001）至6小时（p<0.05）比肝切除术前水平高200%至300%，直到部分肝切除术后24小时才接近基础水平。对再生肝脏核提取物的凝胶迁移率变动分析表明，这些核蛋白表达的增加与CCAAT/增强子结合蛋白α-β异二聚体和β-β同二聚体的DNA结合增加有关。这些结果证明了肝脏再生过程中CCAAT/增强子结合蛋白α和β在表达和DNA结合方面与生长相关的变化，并支持这样一种理论，即改变的CCAAT/增强子结合蛋白DNA结合可能导致肝细胞表型的再生相关变化。
