Transcriptional regulation of the human alpha6 integrin gene by the transcription factor NFI during corneal wound healing.
OBJECTIVE
Wound healing of the corneal epithelium is highly influenced by regulation of integrin gene expression. A recent study demonstrated that laminin (LM), a major constituent of the extracellular matrix (ECM), reduces expression of the human alpha6 integrin subunit gene by altering the properties of the transcription factor (TF) Sp1. In this work, a target site was identified for the TF nuclear factor I (NFI) on the human alpha6 gene, and its regulatory influence was characterized in corneal epithelial cells.


METHODS
Plasmids bearing the alpha6 promoter fused to the CAT gene were transfected into human (HCECs) and rabbit (RCECs) corneal epithelial cells grown on LM. The DNA-binding site for NFI in the alpha6 promoter was identified by DNase I footprinting. Expression and DNA binding of NFI was monitored by Western blot, RT-PCR, and electrophoretic mobility shift assays (EMSAs), and its function was investigated through RNAi and NFI overexpression assays.


RESULTS
All NFI isoforms were found to be expressed in HCECs and RCECs. Transfection analyses revealed that NFI is a repressor of alpha6 expression in both types of cells. LM increases expression of NFI, whereas inhibition of each NFI isoform increases promoter activity suggesting that NFI is a key repressor of alpha6 transcription. In addition, the negative influence of NFI appears to be potentiated by the degradation of Sp1 when cells are grown on LM.


CONCLUSIONS
Repression of alpha6 expression therefore contributes to the final steps of corneal wound healing by both reducing proliferation and allowing attachment of the epithelium to the basal membrane.
Gaudreault
Manon
M
Oncology and Molecular Endocrinology Research Center, Centre Hospitalier Universitaire de Québec, CHUL, Québec, Québec, Canada.
Vigneault
François
F
Gingras
Marie-Eve
ME
Leclerc
Steeve
S
Carrier
Patrick
P
Germain
Lucie
L
Guérin
Sylvain L
SL
D000328:Adult; D000368:Aged; D000818:Animals; D001483:Base Sequence; D002448:Cell Adhesion; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D065306:Corneal Injuries; D017931:DNA Primers; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D019573:Epithelium, Corneal / Q000293:injuries*; D005786:Gene Expression Regulation; D006801:Humans; D008875:Middle Aged; D008969:Molecular Sequence Data; D051839:NFI Transcription Factors / Q000235:genetics*; D010957:Plasmids; D011817:Rabbits; D014158:Transcription, Genetic; D014945:Wound Healing / Q000502:physiology*
D017931:DNA Primers; D051839:NFI Transcription Factors; D015500:Chloramphenicol O-Acetyltransferase