Vernucci M, Cerrato F, Besnard N, Casola S, Pedone P V, Bruni C B, Riccio A
Centro di Endocrinologia ed Oncologia Sperimentale 'G Salvatore', CNR; Dipartimento di Biologia e Patologia Cellulare e Molecolare 'L Califano', Università di Napoli 'Federico II', Napoli, Italy.
Oncogene. 2000 Dec 14;19(54):6376-85. doi: 10.1038/sj.onc.1204024.
The expression of the linked but reciprocally imprinted Igf2 and H19 genes is activated in adult liver in the course of tumor development. By in situ hybridization analysis we have shown that both the Igf2 and H19 RNAs are expressed in the majority of the neoplastic nodules, and that hepatocellular carcinomas are developed in an experimental model of liver carcinogenesis. H19 is also highly activated in smaller and less distinct hyperplastic regions. The few neoplastic areas showing Igf2 but no H19 RNA display loss of the maternally inherited allele at the Igf2/H19 locus. These data are compatible with the existence of a common activation mechanism of these two genes during liver carcinogenesis and with a stronger H19 induction in the pre-neoplastic lesions. By using mice carrying a deletion of the H19 endodermal enhancer, we show that this regulatory element is necessary for the activation of the Igf2 and H19 genes upon induction of liver carcinogenesis. Furthermore, multiple sites of the H19 endodermal enhancer region become hypersensitive to DNase I when the carcinogenesis process is induced. Lastly, liver tumors developed in mice paternally inheriting the H19 enhancer deletion are found to have marked growth delays, increased frequency of apoptotic nuclei, and lack of Igf2 mRNA expression, thus indicating that this regulatory element plays a major role in the progression of liver carcinogenesis, since it is required for the activation of the anti-apoptotic Igf2 gene.
在肿瘤发生过程中，连锁但相互印记的Igf2和H19基因的表达在成年肝脏中被激活。通过原位杂交分析，我们发现Igf2和H19 RNA在大多数肿瘤结节中均有表达，并且在肝癌发生的实验模型中出现了肝细胞癌。H19在较小且不太明显的增生区域也被高度激活。少数显示Igf2但无H19 RNA的肿瘤区域在Igf2/H19位点表现出母系遗传等位基因的缺失。这些数据与这两个基因在肝癌发生过程中存在共同激活机制以及在癌前病变中H19诱导更强相一致。通过使用携带H19内胚层增强子缺失的小鼠，我们表明该调控元件对于肝癌发生诱导时Igf2和H19基因的激活是必需的。此外，当诱导致癌过程时，H19内胚层增强子区域的多个位点对DNase I变得高度敏感。最后，在父系遗传H19增强子缺失的小鼠中发生的肝肿瘤被发现具有明显的生长延迟、凋亡核频率增加以及缺乏Igf2 mRNA表达，因此表明该调控元件在肝癌发生进展中起主要作用，因为它是抗凋亡Igf2基因激活所必需的。
