Fibulin-4 regulates expression of the tropoelastin gene and consequent elastic-fibre formation by human fibroblasts.
Elastic fibres are essential for normal physiology in numerous tissues, including arteries, lungs and skin. Fibulin-4 is an elastic-fibre-associated glycoprotein that is indispensable for elastic-fibre formation in mice. However, the mechanism by which fibulin-4 executes this function remains to be determined. Here, we established an in vitro functional assay system in which fibulin-4 was knocked down in human foreskin fibroblasts using siRNA (small interfering RNA) technology. With two different siRNAs, substantial knockdown of fibulin-4 was achieved, and this suppression was associated with impaired elastic-fibre formation by the fibroblasts. Real-time reverse transcription-PCR analysis showed that knockdown of fibulin-4 expression was accompanied by reduced expression of tropoelastin mRNA. Further analysis showed that this decrease was caused by transcriptional down-regulation of tropoelastin. This effect was selective, since the mRNA level of other elastic-fibre-associated proteins, including fibrillin-1, lysyl oxidase and lysyl oxidase-like-1, was not affected. Moreover, addition of conditioned medium from cultures of CHO (Chinese-hamster ovary) cells overexpressing fibulin-4 stimulated tropoelastin expression and elastic-fibre formation in cultures of Williams-Beuren-syndrome fibroblasts. Knocking down or knocking out fibulin-4 in mice led to a decrease in tropoelastin expression in the aorta. These results indicate that fibulin-4, considered as a structural protein, may also participate in regulating elastic-fibre formation in human cells through an unanticipated mechanism, namely the regulation of tropoelastin expression.
Chen
Qiuyun
Q
Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, OH 44195, USA. chenq3@ccf.org
Zhang
Teng
T
Roshetsky
Joseph F
JF
Ouyang
Zhufeng
Z
Essers
Jeroen
J
Fan
Chun
C
Wang
Qing
Q
Hinek
Aleksander
A
Plow
Edward F
EF
Dicorleto
Paul E
PE
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D002675:Child, Preschool; D006224:Cricetinae; D003412:Cricetulus; D004547:Elastic Tissue / Q000378:metabolism* / Q000502:physiology; D004622:Embryo, Mammalian; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D014333:Tropoelastin / Q000235:genetics* / Q000378:metabolism
C403672:EFEMP2 protein, human; D016326:Extracellular Matrix Proteins; D014333:Tropoelastin