An alternative, human SRC promoter and its regulation by hepatic nuclear factor-1α
An alternative, human SRC promoter and its regulation by hepatic nuclear factor-1α
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DOI：
10.1074/jbc.m004882200
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发表时间：
2000-12-01
影响因子：
4.8
通讯作者：
Boyd, FM
中科院分区：
文献类型：
--
作者：
Bonham, K;Ritchie, SA;Boyd, FM
SRC 基因编码原癌基因 pp60(c-src)，这是一种参与多种信号转导途径的酪氨酸激酶。此外，SRC基因在人类肿瘤中存在差异表达、发育调节且经常过度表达。然而，调节其表达的机制尚未完全探索。在这里，我们描述了新的远端 SRC 启动子和相关外显子的分离，指定为 1 α，我们将其映射到先前描述的 SRC1A 管家启动子上游 1.0 kilobase 的位置。这些启动子及其相关外显子的差异化使用以及随后与共同下游外显子的剪接导致 c-Src 转录物具有不同的 5' 末端但具有相同的编码区。瞬时转染 HepG2 细胞后的启动子分析将最小 1 α 启动子定位到主要转录起始位点上游 145 bp 的区域。该区域包含肝核因子 1 (HNF-1) 的共有结合位点，HNF-1 是一种富含肝脏的转录因子，参与肝脏、肾脏、胃、肠和胰腺中许多基因的调节。随后的迁移率变化测定证实 HNF-1 α 同种型是与启动子的该区域相互作用的主要因子。 HNF-1 位点的突变导致 SRC 启动子活性急剧降低。共转染研究表明，该启动子可以被 HNF-1 α 同工型强烈反式激活，但不能被相关的 HNF-1 β 因子强烈反式激活。与这些结果一致，我们证明源自 SRC1 α 启动子的转录物表现出组织限制的表达模式，在胃、肾和胰腺中存在最高水平。这些结果表明，SRC 转录调控比之前认识的要复杂得多，并且暗示 HNF-1 参与正常组织中 SRC 基因的组织特异性调控和某些人类癌症中 c-Src 的过度表达。
The SRC gene encodes the proto-oncogene pp60(c-src), a tyrosine kinase implicated in numerous signal transduction pathways. In addition, the SRC gene is differentially expressed, developmentally regulated, and frequently overexpressed in human neoplasia. However, the mechanisms regulating its expression have not been completely explored. Here we describe the isolation of a new distal SRC promoter and associated exon, designated 1 alpha, which we mapped to a position 1.0 kilobase upstream of the previously described SRC1A housekeeping promoter. Differential use of these promoters and their associated exons coupled with subsequent splicing to a common downstream exon results in c-Src transcripts with different 5' ends but identical coding regions. Promoter analysis following transient transfections into HepG2 cells mapped the minimal 1 alpha promoter to a region 145 bp upstream of the major transcription start site. This region contained a consensus binding site for hepatic nuclear factor-1 (HNF-1), a liver-enriched transcription factor implicated in the regulation of a number of genes in liver, kidney, stomach, intestine, and pancreas. Subsequent mobility shift assays confirmed that HNF-1 alpha isoform was the predominant factor interacting with this region of the promoter. Mutation of the HNF-1 site resulted in a dramatic reduction in SRC promoter activity. Cotransfection studies demonstrated the promoter could be strongly transactivated by the HNF-1 alpha isoform but not by the related HNF-1 beta factor. Consistent with these results, we demonstrated that transcripts originating from the SRC1 alpha promoter display a tissue restricted pattern of expression with highest levels present in stomach, kidney, and pancreas. These results indicate that SRC transcriptional regulation is much more complex than previously realized and implicates HNF-1 in both the tissue-specific regulation of the SRC gene in normal tissues and the overexpression of c-Src in certain human cancers.