Effect of v-erbA on T3-responsive genes in AML-12 hepatocytes

The v-erbA oncogene belongs to a superfamily of transcription factors called nuclear receptors, which includes the thyroid hormone receptors (TRs) responsible for mediating the effects of thyroid hormone (T3). Nuclear receptors bind to specific DNA sequences in the promoter region of target genes and v-erbA is known to exert a dominant negative effect on the activity of the TRs. The repressor activity of v-erbA has been linked to the development of hepatocellular carcinoma (HCC) in a mouse model. We have used microarray analysis to identify genes differentially expressed in hepatocytes in culture (AML12 cells) stably transfected with v-erbA and exposed to T3. We have found that v-erbA can negatively regulate expression of T3-responsive genes known to have a protective function against tumor development. We have also identified a number of v-erbA- (but not T3-) responsive genes that are known to be involved in carcinogenesis and which may play a role in the development of HCC. AML12 control cells and v-erbA-transfected AML12 cells were exposed to 10 nM T3 for 3h or 24h. Using microarray analysis, we compared gene expression in the presence and absence of v-erbA and identified T3-regulated genes differentially expressed in the presence of v-erbA.

v-erbA癌基因隶属于一类被称为核受体（nuclear receptors）的转录因子超家族，该家族包含介导甲状腺激素（T3）生理效应的甲状腺激素受体（TRs）。核受体可结合靶基因启动子区域的特异性DNA序列，而v-erbA已知可对TRs的活性发挥显性负调控效应。v-erbA的阻遏活性已被证实与小鼠模型中的肝细胞癌（hepatocellular carcinoma, HCC）发生密切相关。本研究采用微阵列分析（microarray analysis）技术，对稳定转染v-erbA并经T3处理的培养肝细胞（AML12细胞）中的差异表达基因进行了鉴定。研究发现，v-erbA可负调控已知具有抗肿瘤发生保护功能的T3应答基因的表达。此外，本研究还鉴定出一批受v-erbA（而非T3）调控的基因，这些基因已被证实参与致癌过程，可能在肝细胞癌的发生发展中发挥作用。实验中将AML12对照细胞与v-erbA转染的AML12细胞分别用10 nM T3处理3小时或24小时。通过微阵列分析，本研究对比了存在与不存在v-erbA时的基因表达谱，最终鉴定出在v-erbA存在条件下差异表达的T3调控基因。