Kanatani Naoko, Fujita Takashi, Fukuyama Ryo, Liu Wenguang, Yoshida Carolina A, Moriishi Takeshi, Yamana Kei, Miyazaki Toshihiro, Toyosawa Satoru, Komori Toshihisa
Department of Developmental and Reconstructive Medicine, Division of Cell Biology, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan.
Dev Biol. 2006 Aug 1;296(1):48-61. doi: 10.1016/j.ydbio.2006.03.039. Epub 2006 Apr 4.
Runx2 and Cbfbeta are essential for skeletal development during the embryonic stage. Runx2 has two isoforms with different N-termini. We examined the functions of the Runx2 isoforms and Cbfbeta in postnatal bone development. On luciferase and electrophoretic mobility shift assays, Runx2-I was less active than Runx2-II in the absence of Cbfb, but the two Runx2 isoforms had similar activity levels in the presence of Cbfb. We generated Runx2-I transgenic mice under the control of Col1a1 promoter and Runx2-I/Cbfb and Runx2-II/Cbfb double transgenic mice. Runx2-I transgenic mice showed less severe osteopenia and fragility than Runx2-II transgenic mice due to milder inhibition of both osteoblast maturation and transition to osteocytes, even though the former mice showed higher transgene expression. However, Runx2-I/Cbfb and Runx2-II/Cbfb double transgenic mice had enhanced inhibition of osteoblast maturation, resulting in similar severity of osteopenia and fragility, although the latter mice had less osteocytes. These findings indicate that (1) Runx2-II more strongly inhibits osteoblast maturation and transition to osteocytes than Runx2-I; (2) Cbfbeta regulates Runx2 function isoform-dependently; and (3) Runx2-I activity is highly dependent on Cbfbeta. These findings demonstrate that Runx2 isoforms exert their functions through at least partly different mechanisms and Cbfbeta regulates bone development by regulating Runx2 function isoform-dependently.
Runx2和Cbfbeta在胚胎期骨骼发育过程中至关重要。Runx2有两种具有不同N端的异构体。我们研究了Runx2异构体和Cbfbeta在出生后骨骼发育中的功能。在荧光素酶和电泳迁移率变动分析中，在没有Cbfb的情况下，Runx2-I的活性低于Runx2-II，但在有Cbfb的情况下，两种Runx2异构体具有相似的活性水平。我们构建了在Col1a1启动子控制下的Runx2-I转基因小鼠以及Runx2-I/Cbfb和Runx2-II/Cbfb双转基因小鼠。Runx2-I转基因小鼠的骨质减少和脆性程度低于Runx2-II转基因小鼠，这是由于对成骨细胞成熟和向骨细胞转变的抑制较轻，尽管前者小鼠的转基因表达较高。然而，Runx2-I/Cbfb和Runx2-II/Cbfb双转基因小鼠对成骨细胞成熟的抑制增强，导致骨质减少和脆性程度相似，尽管后者小鼠的骨细胞较少。这些发现表明：（1）Runx2-II比Runx2-I更强烈地抑制成骨细胞成熟和向骨细胞的转变；（2）Cbfbeta以异构体依赖的方式调节Runx2功能；（3）Runx2-I的活性高度依赖于Cbfbeta。这些发现表明，Runx2异构体至少通过部分不同的机制发挥其功能，并且Cbfbeta通过以异构体依赖的方式调节Runx2功能来调节骨骼发育。
