Suppression of NF-kappaB-dependent gene expression by a hexamethylene bisacetamide-inducible protein HEXIM1 in human vascular smooth muscle cells.
BACKGROUND
Neointima formation is a characteristic feature of atherosclerosis and post-angioplasty restenosis, in which various soluble factors and mechanical injury stimulate signalling pathways in vascular smooth muscle cells (VSMC), promoting their migration and proliferation, and the eventual formation of the neointima. The transcription factor NF-kappaB has been shown to play a pivotal role in this process. Hexamethylene bisacetamide, an inhibitor of VSMC proliferation, induces the mRNA expression of HEXIM1 (hexamethylene bisacetamide-inducible protein 1). However, the protein expression and function of HEXIM1 remain unknown.


RESULTS
In the present study, we demonstrated that HEXIM1 localizes in the cytoplasm and nucleus, and its nuclear expression is restricted to discrete speckled areas. Treatment of VSMC with hexamethylene bisacetamide up-regulated HEXIM1 expression, not only in mRNA but also protein levels. Moreover, HEXIM1 is shown to suppress the transcriptional activity of NF-kappaB via its C-terminal leucine-rich domain. A glutathione-S-transferase pull down assay indicated that HEXIM1 interacts with the p65 subunit of NF-kappaB. In VSMC, treatment with hexamethylene bisacetamide resulted in a down-modulation of the transcription of NF-kappaB target genes.


CONCLUSIONS
We may therefore conclude that HEXIM1 plays an inhibitory role in NF-kappaB-dependent gene expression in VSMC and is the candidate of a novel therapeutic target for inhibition of VSMC proliferation.
Ouchida
Rika
R
Division of Clinical Immunology, Advanced Clinical Research Center, Institute of Medical Science, University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Kusuhara
Masatoshi
M
Shimizu
Noriaki
N
Hisada
Tetsuya
T
Makino
Yuichi
Y
Morimoto
Chikao
C
Handa
Hiroshi
H
Ohsuzu
Fumitaka
F
Tanaka
Hirotoshi
H
D000081:Acetamides / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter / Q000187:drug effects; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D014157:Transcription Factors
D000081:Acetamides; C476123:HEXIM1 protein, human; D016328:NF-kappa B; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D005982:Glutathione Transferase; C014026:hexamethylene bisacetamide