The increasing complexity of the oncofetal h19 gene locus: functional dissection and therapeutic intervention

Abstract

The field of the long non-coding RNA (lncRNA) is advancing rapidly. Currently, it is one of the most popular fields in the biological and medical sciences. It is becoming increasingly obvious that the majority of the human transcriptome has little or no-protein coding capacity. Historically, H19 was the first imprinted non-coding RNA (ncRNA) transcript identified, and the H19/IGF2 locus has served as a paradigm for the study of genomic imprinting since its discovery. In recent years, we have extensively investigated the expression of the H19 gene in a number of human cancers and explored the role of H19 RNA in tumor development. Here, we discuss recently published data from our group and others that provide further support for a central role of H19 RNA in the process of tumorigenesis. Furthermore, we focus on major transcriptional modulators of the H19 gene and discuss them in the context of the tumor-promoting activity of the H19 RNA. Based on the pivotal role of the H19 gene in human cancers, we have developed a DNA-based therapeutic approach for the treatment of cancers that have upregulated levels of H19 expression. This approach uses a diphtheria toxin A (DTA) protein expressed under the regulation of the H19 promoter to treat tumors with significant expression of H19 RNA. In this review, we discuss the treatment of four cancer indications in human subjects using this approach, which is currently under development. This represents perhaps one of the very few examples of an existing DNA-based therapy centered on an lncRNA system. Apart from cancer, H19 expression has been reported also in other conditions, syndromes and diseases, where deregulated imprinting at the H19 locus was obvious in some cases and will be summarized below. Moreover, the H19 locus proved to be much more complicated than initially thought. It houses a genomic sequence that can transcribe, yielding various transcriptional outputs, both in sense and antisense directions. The major transcriptional outputs of the H19 locus are presented here.

Figure 1

The increasing complexity of the H19 gene locus: shown is schematic representation of the H19 gene locus showing various transcriptional products produced from both the sense and the antisense strands.

Figure 2

The oncofetal H19 RNA connection: hypoxia, P53 and cancer. (A) Under hypoxic conditions, HIF1-α upregulates H19 RNA expression in p53 mutant cells. H19 induction under hypoxic stress thus contributes to various aspects of tumor progression, including survival, angiogenesis, metastasis and also multidrug resistance; (B) P53 wild-type suppresses H19 RNA upregulation by HIF1-α, probably leading to cell death.