Lysophosphatidic acid induces early growth response gene 1 expression in vascular smooth muscle cells: CRE and SRE mediate the transcription.
OBJECTIVE
Lysophosphatidic acid (LPA), one component of oxidized low-density lipoprotein, is a potent bioactive phospholipid. Early growth response gene-1 (Egr-1), an important transcription factor, regulates expression of an array of genes involved in vascular diseases. Whether and how LPA regulates the transcriptional machinery of Egr-1 gene is unknown and is addressed in this study.


RESULTS
We found that LPA markedly induces Egr-1 mRNA and protein in aortic smooth muscle cells (SMCs). RNA stability and nuclear run-on assays reveal that LPA-induced Egr-1 gene expression is controlled at the transcriptional level. Reporter gene analyses have shown that the -141 to +20 nt region of the Egr-1 promoter contains regulatory elements. Electrophoretic mobility shift assays reveal that the DNA-binding activities of both CREB and SRF to the CRE and SRE motifs of the Egr-1 promoter are markedly elevated in response to LPA. The increased binding activity depends on the phosphorylation of CREB and SRF. Luciferase assays of a series of deleted or mutated Egr-1 promoter-reporter gene constructs, along with dominant negative CREB transfection analysis revealed that the 2 CRE sites and the 2 proximal SRE sites in the Egr-1 promoter are required for maximal LPA-induced Egr-1 gene expression.


CONCLUSIONS
Our data reveal that LPA regulates Egr-1 expression via transcription factors CREB and SRF. These results establish a novel role for CREB in mediating LPA-induced gene expression. Our results imply that elevated LPA levels may, through activation of Egr-1, which regulates an array of atherogenic genes, exacerbate atheromatous lesions.
Department of Pathobiology, The University of Tennessee, Knoxville, TN, USA. cuim@utk.edu
Mei-Zhen
MZ
Cui
Essam
E
Laag
Longsheng
L
Sun
Mingqi
M
Tan
Guojun
G
Zhao
Xuemin
X
Xu
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects*; D008246:Lysophospholipids / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020218:Response Elements / Q000502:physiology*; D027602:Serum Response Element / Q000502:physiology*; D026362:Serum Response Factor / Q000502:physiology; D015398:Signal Transduction; D014158:Transcription, Genetic
D017362:Cyclic AMP Response Element-Binding Protein; D051766:Early Growth Response Protein 1; D008246:Lysophospholipids; D012333:RNA, Messenger; D026362:Serum Response Factor; D000242:Cyclic AMP; C032881:lysophosphatidic acid