Transcriptional regulation of the HOX4C gene by basic fibroblast growth factor on rheumatoid synovial fibroblasts.
OBJECTIVE
To examine the expression of genes of the HOX D cluster in the synovial tissue of patients with rheumatoid arthritis (RA), and to determine whether basic fibroblast growth factor (bFGF) influences the expression and transcriptional regulation of the gene.


METHODS
The expression of genes of the HOX D cluster, including HOX4C, HOX4D, HOX4H, and HOX4I, was determined in the synovium of 4 patients with RA and 4 with osteoarthritis (OA) by in situ reverse transcription (RT) and RT-polymerase chain reaction (RT-PCR). The induction of HOX4C messenger RNA (mRNA) by bFGF was determined by RT-PCR. The binding activity of a transcriptional regulator of the HOX4C gene, C2, was analyzed by the mobility shift assay. NIH-3T3 cells transfected with a construct containing C2 binding sequence were incubated with bFGF, and the activity of the reporter was measured by luciferase assay.


RESULTS
Using an in situ RT assay, specific expression of HOX4C mRNA was detected in 3 of 4 RA synovial samples, whereas none of the OA synovia expressed HOX4C. HOX4D, HOX4H, and HOX4I genes were expressed in all synovial samples from RA and OA patients. The presence of HOX4C mRNA was also confirmed by RT-PCR and Southern blotting. Treatment with bFGF increased the expression of HOX4C mRNA in RA fibroblasts. The mobility shift assay and luciferase assay showed that bFGF enhanced C2 binding activity and significantly increased the transcriptional activity on RA fibroblasts.


CONCLUSIONS
Our findings suggest that HOX4C is involved in synovial hyperplasia, and that the transcriptional regulation of HOX4C genes by bFGF may play a crucial role in the pathogenesis of RA.
Xue
C
C
St. Marianna University School of Medicine, Kawasaki, Japan.
Hasunuma
T
T
Asahara
H
H
Yin
W
W
Maeda
T
T
Fujisawa
K
K
Dong
Y
Y
Sumida
T
T
Nishioka
K
K
D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D001665:Binding Sites; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D018398:Homeodomain Proteins; D006801:Humans; D009363:Neoplasm Proteins; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D013583:Synovial Membrane / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics
D017931:DNA Primers; D004268:DNA-Binding Proteins; C088822:HOXD9 protein, human; D018398:Homeodomain Proteins; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D016222:Fibroblast Growth Factor 2