Kockx M, McCabe L, Stein J L, Lian J B, Stein G S
University of Massachusetts Medical Center, Worcester 01655.
J Cell Biochem. 1994 Jan;54(1):47-55. doi: 10.1002/jcb.240540106.
Interrelationships between proliferation and expression of cell growth as well as bone cell-related genes were examined from two standpoints. First, the consequence of downregulating proliferation by DNA synthesis inhibition on expression of a cell cycle-regulated histone gene and genes associated with development of the bone cell phenotype (type I collagen, alkaline phosphatase, osteopontin, and osteocalcin) was investigated. Second, the requirement for stringent growth control to support functional relationships between expression of proliferation and differentiation-related genes was explored. Parameters of cell growth and osteoblast-related gene expression in primary cultures of normal diploid osteoblasts, that initially express proliferation-dependent genes and subsequently postproliferative genes associated with mature bone cell phenotypic properties, were compared to those operative in ROS 17/2.8 osteosarcoma cells that concomitantly express cell growth and mature osteoblast phenotypic genes. Our findings indicate that in both normal diploid osteoblasts and osteosarcoma cells, expression of the cell cycle regulated histone genes is tightly coupled with DNA synthesis and controlled predominantly at a posttranscriptional level. Inhibition of proliferation by blocking DNA synthesis with hydroxyurea upregulates a subset of developmentally expressed genes that postproliferatively support progressive establishment of mature osteoblast phenotypic properties (e.g., alkaline phosphatase, type 1 collagen, and osteopontin). However, the osteocalcin gene, which is expressed during the final stage of osteoblast differentiation when extracellular matrix mineralization occurs, is not upregulated. Variations in the extent to which inhibition of proliferation in normal diploid osteoblasts and in ROS 17/2.8 osteosarcoma cells selectively affects transcription and cellular levels of mRNA transcripts from bone cell-related genes (e.g., osteocalcin) may reflect modifications in proliferation/differentiation interrelationships when stringent growth control is abrogated.
从两个角度研究了细胞增殖与细胞生长表达以及骨细胞相关基因之间的相互关系。首先，研究了通过DNA合成抑制下调增殖对细胞周期调节的组蛋白基因以及与骨细胞表型（I型胶原蛋白、碱性磷酸酶、骨桥蛋白和骨钙素）发育相关基因表达的影响。其次，探讨了严格生长控制对支持增殖与分化相关基因表达之间功能关系的必要性。将正常二倍体成骨细胞原代培养物中细胞生长和与成骨细胞相关基因表达的参数与ROS 17/2.8骨肉瘤细胞中的参数进行了比较。正常二倍体成骨细胞最初表达增殖依赖性基因，随后表达与成熟骨细胞表型特性相关的增殖后基因，而ROS 17/2.8骨肉瘤细胞同时表达细胞生长和成熟成骨细胞表型基因。我们的研究结果表明，在正常二倍体成骨细胞和骨肉瘤细胞中，细胞周期调节的组蛋白基因的表达与DNA合成紧密相关，并且主要在转录后水平受到控制。用羟基脲阻断DNA合成来抑制增殖会上调一部分发育表达的基因，这些基因在增殖后支持成熟成骨细胞表型特性的逐步建立（例如碱性磷酸酶、I型胶原蛋白和骨桥蛋白）。然而，在成骨细胞分化的最后阶段，即细胞外基质矿化发生时表达的骨钙素基因并未上调。正常二倍体成骨细胞和ROS 17/2.8骨肉瘤细胞中增殖抑制对骨细胞相关基因（例如骨钙素）mRNA转录本的转录和细胞水平的选择性影响程度的差异，可能反映了在取消严格生长控制时增殖/分化相互关系的改变。
