Johnson-Pais T L, Leach R J
Department of Cellular, University of Texas Health Science Center at San Antonio 78284, USA.
Exp Cell Res. 1995 Dec;221(2):370-6. doi: 10.1006/excr.1995.1387.
Intratypic osteosarcoma hybrids were constructed by fusing the human osteoblast-like osteosarcoma SaOS-2 with the rat osteoblast-like osteosarcoma UMR-106. Both of these osteosarcomas express liver/bone/kidney alkaline phosphatase (ALPL), but only the UMR-106 cell line expresses osteopontin (OPN), a gene expressed during later stages of osteoblast differentiation. Analysis of osteoblast gene expression in these hybrids demonstrated that ALPL continued to be expressed; however, OPN steady-state mRNA levels were dramatically reduced in four hybrids. Quantitative measurements indicated that OPN steady-state mRNA levels were extinguished by a factor of 20- to 1000-fold. Since SaOS-2 chromosomes are preferentially lost from these hybrids, subclones of extinguished hybrids were isolated that reexpressed OPN mRNA at levels similar to the UMR-106 parental line. These data indicate that trans-acting negative regulatory factors, expressed from the SaOS-2 genome, are responsible for OPN extinction. This report provides the first demonstration of the negative regulation of OPN gene expression and also provides additional evidence that extinction plays a role in the regulation of osteoblast gene expression.
通过将人成骨细胞样骨肉瘤SaOS-2与大鼠成骨细胞样骨肉瘤UMR-106融合，构建了同型骨肉瘤杂交细胞系。这两种骨肉瘤均表达肝/骨/肾碱性磷酸酶（ALPL），但只有UMR-106细胞系表达骨桥蛋白（OPN），该基因在成骨细胞分化后期表达。对这些杂交细胞系中成骨细胞基因表达的分析表明，ALPL持续表达；然而，在四个杂交细胞系中，OPN稳态mRNA水平显著降低。定量测量表明，OPN稳态mRNA水平降低了20至1000倍。由于SaOS-2染色体在这些杂交细胞系中优先丢失，因此分离出了OPN表达熄灭的杂交细胞系的亚克隆，这些亚克隆重新表达的OPN mRNA水平与UMR-106亲代细胞系相似。这些数据表明，由SaOS-2基因组表达的反式作用负调控因子是OPN表达熄灭的原因。本报告首次证明了OPN基因表达的负调控，也提供了额外的证据表明基因表达熄灭在成骨细胞基因表达调控中起作用。
