McCabe L R, Banerjee C, Kundu R, Harrison R J, Dobner P R, Stein J L, Lian J B, Stein G S
Department of Cell Biology, University of Massachusetts Medical Center, Worcester 01655, USA.
Endocrinology. 1996 Oct;137(10):4398-408. doi: 10.1210/endo.137.10.8828501.
Developmental studies of oncogene expression implicate the Fos and Jun family of transcription factors in the regulation of bone growth and differentiation. Promoters of many developmentally regulated genes, including osteocalcin, a marker of osteoblast differentiation, contain AP-1 sites that bind Fos/Jun dimers. Here, we demonstrate that the selective expression of fos- and jun-related genes is functionally related to the stage of osteoblast growth and differentiation in vitro. During osteoblast proliferation, nuclear protein levels of all seven activating protein-1 (AP-1) members are maximal. Subsequently, during the period of extracellular matrix maturation, levels decline. In fully differentiated osteoblasts, Fra-2 and (to a lesser extent) Jun D are the principal AP-1 members detectable by Western blot analysis. AP-1 complex composition and binding activity also exhibit developmental changes. All Fos and Jun family members are involved in AP-1 complex formation in proliferating cells, whereas Fra-2 and Jun D predominate in AP-1 complexes in differentiated osteoblasts. Overexpression of Fos and Jun family members in ROS 17/2.8 cells markedly affects the expression of an osteocalcin promoter-chloramphenicol acetyltransferase construct. Coexpression of only one AP-1 pair, Fra-2 and Jun D, stimulated reporter expression, whereas coexpression of other AP-1 pairs down-regulated expression (i.e. c-jun and any Fos family member) or had no effect (i.e. Fra-1 and Jun B). Promoter deletion analyses indicate that these effects are site specific. Consequential effects of Fra-2 on osteoblast differentiation are further demonstrated by antisense studies in which osteoblast differentiation and the development of a bone tissue-like organization were suppressed. Consistent with recent findings suggesting that AP-1 complex composition can selectively regulate gene transcription, our findings demonstrate that differential expression of Fos and Jun family members could play a role in the developmental regulation of bone-specific gene expression and, as a result, may be functionally significant for osteoblast differentiation.
癌基因表达的发育研究表明，转录因子Fos和Jun家族参与骨生长和分化的调控。许多受发育调控基因的启动子，包括成骨细胞分化标志物骨钙素的启动子，都含有能结合Fos/Jun二聚体的AP-1位点。在此，我们证明fos和jun相关基因的选择性表达在功能上与体外成骨细胞生长和分化阶段相关。在成骨细胞增殖期间，所有七种激活蛋白-1（AP-1）成员的核蛋白水平最高。随后，在细胞外基质成熟期间，水平下降。在完全分化的成骨细胞中，Fra-2和（程度较轻的）Jun D是通过蛋白质印迹分析可检测到的主要AP-1成员。AP-1复合物组成和结合活性也表现出发育变化。所有Fos和Jun家族成员都参与增殖细胞中AP-1复合物的形成，而Fra-2和Jun D在分化的成骨细胞的AP-1复合物中占主导地位。Fos和Jun家族成员在ROS 17/2.8细胞中的过表达显著影响骨钙素启动子-氯霉素乙酰转移酶构建体的表达。仅一对AP-1，Fra-2和Jun D的共表达刺激报告基因表达，而其他AP-1对的共表达下调表达（即c-jun和任何Fos家族成员）或无作用（即Fra-1和Jun B）。启动子缺失分析表明这些作用是位点特异性的。Fra-2对成骨细胞分化的相应作用通过反义研究进一步证明，其中成骨细胞分化和骨组织样组织的发育受到抑制。与最近表明AP-1复合物组成可选择性调节基因转录的研究结果一致，我们的研究结果表明Fos和Jun家族成员的差异表达可能在骨特异性基因表达的发育调控中起作用，因此可能对成骨细胞分化具有功能意义。
