Mutation in
fibrillin-2, a major structural component of extracellular microfibrils in connective tissue, results in the autosomal dominant disease
congenital contractural arachnodactyly. This
genetic disease is characterized by dolichostenomelia and
arachnodactyly, in addition to
contractures of the large joints and abnormal pinnae formation, thus indicating the significance of
fibrillin-2 in chondrogenesis. In this study, we investigated the transcriptional regulation of
fibrillin-2 in chondrogenic differentiation. Although
mRNA expression of
fibrillin-1, a highly homologous
protein to
fibrillin-2, remained almost unchanged during chondrogenesis of mouse ATDC5 cells,
fibrillin-2 mRNA expression varied.
Fibrillin-2 was highly expressed at the early stage and declined progressively during differentiation. The 5'-flanking region of the
fibrillin-2 gene contains potential binding sites for E2F, Runx, AP-2, and
Sox transcription factors. The promoter activity of
fibrillin-2 decreased markedly following deletion and mutagenesis of the E2F binding site between -143 and -136 bp. Overexpression of E2F1 resulted in a marked increase in its promoter activity, whereas expression of other
transcription factors including AP-2alpha and Runx2 had no effect. The increase in promoter activity by E2F1 was completely suppressed by the coexpression of E2F4. E2F2 and E2F3 had positive effects on the promoter activity. Although ATDC5 cells expressed transcripts for the E2F family genes at all stages of differentiation, the expression profiles differed. E2F1 expression remained almost unchanged, whereas E2F4 expression increased markedly at the late stage of differentiation. These results indicated that coordinated expression of the E2F family is critical for the transcriptional regulation of
fibrillin-2 during chondrogenesis.