PIASxbeta is a key regulator of osterix transcriptional activity and matrix mineralization in osteoblasts.
We recently reported that tensile stress induces osteoblast differentiation and osteogenesis in the mouse calvarial suture in vitro. Using this experimental system, we identified PIASxbeta, a splice isoform of Pias2, as one of the genes most highly upregulated by tensile stress. Further study using cell culture revealed that this upregulation was transient and was accompanied by upregulation of other differentiation markers, including osterix, whereas expression of Runx2 was unaffected. Runx2 and osterix are the two master proteins controlling osteoblast differentiation, with Runx2 being upstream of osterix. Targeted knockdown of PIASxbeta by small interfering RNA (siRNA) markedly suppressed osteoblastic differentiation and matrix mineralization, whereas transient overexpression of PIASxbeta caused the exact opposite effects. Regardless of PIASxbeta expression level, Runx2 expression remained constant. Reporter assays demonstrated that osterix enhanced its own promoter activity, which was further stimulated by PIASxbeta but not by its sumoylation-defective mutant. NFATc1 and NFATc3 additionally increased osterix transcriptional activity when co-transfected with PIASxbeta. Because osterix has no consensus motif for sumoylation, other proteins are probably involved in the PIASxbeta-mediated activation and NFAT proteins may be among such targets. This study provides the first line of evidence that PIASxbeta is indispensable for osteoblast differentiation and matrix mineralization, and that this signaling molecule is located between Runx2 and osterix.
Ali
Md Moksed
MM
Division of Cell Biology and Molecular Pharmacology, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Niigata-city, Niigata 951-8514, Japan.
Yoshizawa
Tatsuya
T
Ishibashi
Osamu
O
Matsuda
Akio
A
Ikegame
Mika
M
Shimomura
Junko
J
Mera
Hisashi
H
Nakashima
Kazuhisa
K
Kawashima
Hiroyuki
H
D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D003393:Cranial Sutures; D005786:Gene Expression Regulation; D051379:Mice; D050778:NFATC Transcription Factors / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D009924:Organ Culture Techniques; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis; D050828:Protein Inhibitors of Activated STAT / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D000076182:Sp7 Transcription Factor; D013314:Stress, Mechanical; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D044767:Ubiquitin-Protein Ligases; D015854:Up-Regulation
D050659:Core Binding Factor Alpha 1 Subunit; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D050828:Protein Inhibitors of Activated STAT; D034741:RNA, Small Interfering; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; C485521:Miz1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D000469:Alkaline Phosphatase