Focal adhesion kinase activity is required for bone morphogenetic protein - Smad1 signaling and osteoblastic differentiation in murine MC3T3-E1 cells
Focal adhesion kinase activity is required for bone morphogenetic protein - Smad1 signaling and osteoblastic differentiation in murine MC3T3-E1 cells
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DOI：
10.1359/jbmr.2001.16.10.1772
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发表时间：
2001-10-01
影响因子：
6.2
通讯作者：
Fujita, T
中科院分区：
文献类型：
--
作者：
Tamura, Y;Takeuchi, Y;Fujita, T
通过整合素的细胞-基质相互作用对于成骨细胞分化是必不可少的。我们已经表明，信号激活的α 2 β 1-整合素与I型胶原蛋白的聚集参与成骨细胞MC 3 T3-E1细胞的分化。粘着斑激酶（FAK）是β 1-整联蛋白的直接下游信号，FAK的失活已被证明会破坏成骨细胞分化。为了阐明FAK在成骨细胞中的作用，我们检测了稳定表达反义FAK（asFAK）信使RNA（mRNA）的MC 3 T3-E1细胞。碱性磷酸酶（ALP）的活性，成骨细胞的标志物，没有增加在asFAK细胞与长期培养，直到21天或在响应骨形态发生蛋白2（BMP-2）。用BMP-2处理也未能刺激asFAK细胞中骨钙素的表达。在对照MC 3 T3-E1细胞中，BMP-2诱导Smad 1易位到细胞核中，以刺激含有Smad 1反应元件的Smad 6启动子基因的转录活性。与此相反，BMP-2未能增加Smad 6启动子基因在asFAK细胞中的转录活性，尽管它诱导Smad 1的核转位。这些结果表明，FAK参与Smad 1依赖的转录活性，但不参与Smad 1在成骨细胞的核转位。因此，FAK激活整合素可能收敛转录激活BMP的靶基因在成骨细胞。这些观察结果表明，FAK活性是必不可少的BMP-Smad信号刺激成骨细胞分化。
Cell-matrix interactions via integrins are essential for osteoblastic differentiation. We have shown that signals activated by aggregation of alpha2 beta1-integrin with type I collagen are involved in the differentiation of osteoblastic MC3T3-E1 cells. Focal adhesion kinase (FAK) is an immediate downstream signal of the beta1-integrin, and inactivation of FAK has been shown to disrupt osteoblastic differentiation. To elucidate roles of FAK in osteoblastic cells, we examined MC3T3-E1 cells stably expressing antisense FAK (asFAK) messenger RNA (mRNA). Alkaline phosphatase (ALP) activity, an osteoblastic marker, did not increase in asFAK cells with a long-term culture until 21 days or in response to bone morphogenetic protein 2 (BMP-2). Treatment with BMP-2 also failed to stimulate the expression of osteocalcin in asFAK cells. In control MC3T3-E1 cells, BMP-2 induced translocation of Smad1 into nuclei to stimulate transcriptional activity of the Smad6 promoter gene that contains a Smad1 response element. In contrast, BMP-2 failed to increase transcriptional activity of Smad6 promoter gene in asFAK cells, although it induced nuclear translocation of Smad1. These results indicate that FAK was involved in Smad1-dependent transcriptional activity but not in nuclear translocation of Smad1 in osteoblastic cells. Hence, FAK activation by integrins might converge transcriptional activation by BMP of its target genes in osteoblastic cells. These observations suggest that FAK activity is essential for BMP-Smad signaling to stimulate osteoblastic differentiation.