A 30-KDA ALTERNATIVE TRANSLATION PRODUCT OF THE CCAAT ENHANCER-BINDING PROTEIN-ALPHA MESSAGE - TRANSCRIPTIONAL ACTIVATOR LACKING ANTIMITOTIC ACTIVITY
A 30-KDA ALTERNATIVE TRANSLATION PRODUCT OF THE CCAAT ENHANCER-BINDING PROTEIN-ALPHA MESSAGE - TRANSCRIPTIONAL ACTIVATOR LACKING ANTIMITOTIC ACTIVITY
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DOI：
10.1073/pnas.90.20.9606
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发表时间：
1993-10-15
影响因子：
11.1
通讯作者：
LANE, MD
中科院分区：
文献类型：
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作者：
LIN, FT;MACDOUGALD, OA;LANE, MD
全长(42 KDa)CCAAT/增强子结合蛋白α(C/EBPalpha)(P42)参与了3T3-L1前脂肪细胞分化过程中包括422(AP2)和C/EBPalpha基因在内的脂肪细胞基因的转录激活。我们已经确定了一个30 kDa的C/EBPalpha亚型(P30)，它在3T3-L1脂肪细胞、小鼠脂肪组织和大鼠肝脏中表达。在体外翻译野生型C/EBPalpha mRNA或瞬时转染野生型C/EBPalpha载体后，P42和P30的表达水平相似。突变分析表明，P30是C/EBPalpha信息的第三个框内蛋氨酸密码子起始的另一种翻译产物。P30C/EBPalpha与422(AP2)和C/EBPalpha基因启动子驱动的C/EBP位点结合并激活报告基因的表达。虽然将p30C/EBPalpha表达载体导入3T3-L1前脂肪细胞不足以诱导分化，但p30C/EBPalpha载体可促进分化。与抑制细胞增殖的p42C/EBPalpha不同，p30C/EBPalpha不是抗核分裂的。因此，全长C/EBPalpha的N端12 kDa片段包含一个抗分裂活性所必需的氨基酸序列。在3T3-L1前脂肪细胞分化和肝细胞发育过程中，细胞p42C/EBPalpha/p30C/EBPalpha的比例发生变化，增加了调节作用的可能性。
Full-length (42 kDa) CCAAT/enhancer binding protein alpha (C/EBPalpha) (p42) has been implicated in the transcriptional activation of adipocyte genes including the 422(aP2) and C/EBPalpha genes during differentiation of 3T3-L1 preadipocytes. We have identified a 30-kDa isoform (p30) of C/EBPalpha that is expressed by 3T3-L1 adipocytes, mouse adipose tissue, and rat liver. In vitro translation of wild-type C/EBPalpha mRNA or transient transfection with a wild-type C/EBPalpha vector gave rise to similar levels of p42 and p30. Mutational analysis revealed that p30 is an alternative translation product initiated at the third in-frame methionine codon of the C/EBPalpha message. p30C/EBPalpha binds to the C/EBP sites within and activates reporter gene expression driven by the 422(aP2) and C/EBPalpha gene promoters. Although transfection of 3T3-L1 preadipocytes with a strong p30C/EBPalpha expression vector is insufficient to induce differentiation, this vector advances the differentiation program. Unlike p42C/EBPalpha, which inhibits cell proliferation, p30C/EBPalpha is not antimitotic. Thus, the N-terminal 12-kDa segment of full-length C/EBPalpha contains an amino acid sequence necessary for antimitotic activity. During differentiation of 3T3-L1 preadipocytes and during hepatocyte development, the cellular p42C/EBPalpha/p30C/EBPalpha ratio changes, raising the possibility of a regulatory role.