Johnson-Pais TL, Leach RJ
Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, 78284
Exp Cell Res. 1996 Jul 10;226(1):67-74.
In this study, a somatic cell genetic approach was used to study the regulation of liversolidusbonesoliduskidney alkaline phosphatase (ALPL) gene expression in osteoblasts. ALPL plays an important role in skeletal mineralization and serves as a good index of bone formation. A series of intertypic hybrids constructed by fusion of the human osteosarcoma TE-85 with the mouse fibrosarcoma La-t- demonstrated a 10-fold reduction of ALPL steady-state mRNA and enzyme activity, a phenomenon termed extinction. Hybrid subclones which reexpressed ALPL contained reduced numbers of fibroblast chromosomes compared to earlier passages. This suggests that a trans-acting negative regulatory factor expressed from the fibroblast genome regulates ALPL expression. Two factors known to influence ALPL expression are 1,25-dihydroxyvitamin D3 (1,25D3) and transforming growth factor-beta1 (TGFbeta1). 1,25D3 is involved in mobilizing bone calcium stores and TGFbeta1 plays a critical role in bone remodeling. The extinguished hybrids were exposed to 1,25D3, TGFbeta1, and a combination of these factors. For two hybrids, the combination induced reexpression of ALPL activity to levels comparable to the TE-85 parent, indicating a competition between the factors and the extinguisher(s). Neither factor alone could induce ALPL reexpression to the levels observed with the combination. In only one hybrid, the combination of factors synergistically increased ALPL expression. These data help define the cis sequence element(s) in the ALPL promoter which are involved in the negative regulation of this gene.
在本研究中，采用体细胞遗传学方法研究成骨细胞中肝/骨/肾碱性磷酸酶（ALPL）基因表达的调控。ALPL在骨骼矿化中起重要作用，是骨形成的良好指标。通过人骨肉瘤TE - 85与小鼠纤维肉瘤La - t融合构建的一系列种间杂种显示ALPL稳态mRNA和酶活性降低了10倍，这种现象称为基因消减。与早期传代相比，重新表达ALPL的杂种亚克隆所含的成纤维细胞染色体数量减少。这表明从成纤维细胞基因组表达的一种反式作用负调控因子调节ALPL的表达。已知影响ALPL表达的两个因子是1,25 - 二羟维生素D3（1,25D3）和转化生长因子 - β1（TGFβ1）。1,25D3参与动员骨钙储备，TGFβ1在骨重塑中起关键作用。将消减的杂种暴露于1,25D3、TGFβ1以及这些因子的组合。对于两个杂种，该组合诱导ALPL活性重新表达至与TE - 85亲本相当的水平，表明这些因子与消减因子之间存在竞争。单独任何一个因子都不能诱导ALPL重新表达至组合处理时观察到的水平。仅在一个杂种中，因子组合协同增加了ALPL的表达。这些数据有助于确定ALPL启动子中参与该基因负调控的顺式序列元件。
