[10] In cell lines derived from human choriocarcinomas, Kopf et al. found that transcription of H19 was under the simultaneous control of both a 5’ upstream and a 3’ downstream region.

[11] Kopf et al. have suggested that this simultaneous and bidirectional regulation of H19 may involve a member of the AP2 transcription factor family.

[15] After many studies, researchers finally concluded that the end product of the H19 gene is a RNA strand for the following reasons: Loss of function and overexpression experiments on H19 have revealed two things: Mice with a loss of H19 function express an overgrowth phenotype similar to babies with BWS.

[14] Brunkow et al. have suggested two reasons for the lethality of H19 overexpression in embryonic mice: In the early placentae (6–8 weeks gestation), both parental H19 alleles (maternal and paternal) are expressed.

[22] A study by Shoshani et al. suggests that H19 is continued to be expressed in high amounts in the liver after birth, specifically in diploid hepatocytes.

[23] Genomic imprinting is surmised to have arisen due to the conflicting interests of maternal and paternal genes within a pregnancy.

[24] However, within the same pregnancy, the mother wants to conserve as much of her resources as possible towards future births without compromising the health of the child(ren) she is currently carrying.

[20] The paternal H19 allele, which is silent postnatally, shows increasing methylation of CpGs in its promoter with gestation time in the fetus.

As well, based on the results from Banet et al., it appears that functional H19 imprinting occurs during early placenta development.

[9] A common characteristic of imprinted genes is asynchronous replication during the DNA synthesis phase of the mitotic cycle.

To determine a possible cause for the downregulation of H19, Gao et al. studied the methylation of 12 CpG sites in the H19 promoter in normal, hyperplasia, adenoma and carcinoma adrenals.

The mean percent methylation of H19 CpGs peaked at sites 9 and 10 in normal, hyperplasia, adenoma and carcinoma adrenals and the lowest mean percent methylation of H19 CpGs dipped at site 7 in normal, hyperplasia, adenoma and carcinoma adrenals.

[19] Surgically removed choriocarcinomas from human patients also exhibited a heavily methylated H19 promoter with enhanced H19 expression.

[30] In in vitro studies, culturing hepatocellular carcinoma cell lines in hypoxic condition upregulated H19 expression.

[29] Verhaugh et al. investigated various polymorphisms in the H19 gene and found that some heterozygous SNP polymorphisms, such as rs2839698 TC, were associated with a decreased risk of developing non-muscle invasive bladder cancer as well as bladder cancer overall; however, this association disappeared for homozygotes (CC).

[21] The expression level of H19 RNA in the epithelial cells of the endometrium increases as tissue differentiation is lost in endometrial cancer.

[38] Studies by Berteaux et al. have also found that the overexpression of H19 in breast cancer cells promotes proliferation.

[38] However, the presence of tumor suppressor protein pRb and transcription factor E2F6 is sufficient to repress H19 expression in breast cancer cells.

[13] In experiments conducted by Doyle et al., it was found that MCF-7, a breast adenomacarcinoma cell line,[39] did not express the H19 gene; however a subline of MCF-7 with a multidrug resistance phenotype, MCF-7/AdrVp, had upregulation of H19.

[34] p95, or NCA-90, is related to carcinoembryonic antigens, which have been found to reduce drug toxicity by Kawaharata et al.[40][41] NCI-H1688, a human lung carcinoma cell line that displays multidrug resistance, also overexpress p95 (NCA-90) and H19.

A previous study conducted by Adriaenssens et al. on H19 correlated an overexpression of H19 with the presence of steroid receptors.

[22] Further studies found that 17-β-estradiol, the dominant form of estrogen, and corticosterone were able to individually stimulate H19 transcription in the uterus, while the presence of progesterone inhibited this effect.

[30] As a result of the functions and signaling pathways that H19 RNA-upregulated genes are involved in, it has been suggested that H19 RNA plays crucial roles in tissue invasion, migration and angiogenesis in tumorigenesis.

[45] Thioredoxin is a protein crucial to the reduction-oxidation reactions involved in metabolism within a cell, and is often found at high levels in cancerous tissues that also overexpress H19 RNA.

[18] This coupled expression is only lost in cases of loss of imprinting (inherited CpG methylated) or promoter mutation.

[47] This indicates that the loss of H19 is not lethal, H19 expression governs IGF2 repression, and the overexpression of IGF2 is responsible for the overgrowth phenotype observed in the maternal inheritance of a deleted H19 gene.

In a double-center, dose escalation Phase I/IIa clinical trial of BC-819 as a treatment for superficial bladder cancer,[52] no severe adverse events related to the plasmid were detected, and tumor responses were observed in more than 70% of patients, including those with a still not-optimized therapeutic dose and regimen.

However, recent studies have discovered the expression of thioredoxin and p95 (NCA-90) in cancer cells when H19 RNA is present in high quantities.