IGF2 expression in blood is not associated with its imprinting status in healthy pregnant Chinese women

Loss of Imprinting (LOI) of IGF2 and over-expressed IGF2 are associated with tumorigenesis. Our previous epidemiological study found a relatively high frequency of IGF2 LOI in healthy mid-gestation pregnant women. The aim of this study is to determine whether the expression of IGF2 is associated with its imprinting status in healthy Chinese pregnant women. The IGF2 imprinting status of 300 pregnant women was analyzed. 20 cases of IGF2 LOI and 20 cases of IGF2 retention of imprinting (ROI) were selected randomly for IGF2 expression analysis. The expression pattern of IGF2 between the group with IGF2 ROI and group with IGF2 LOI in healthy Chinese pregnant women was evaluated by real time PCR and western blot. The result showed no significant differences between IGF2 ROI and LOI groups in mRNA and protein levels. These results imply that IGF2 imprinting status has no obvious impact on its expression. There may be some unknown important factors other than imprinting status driving IGF2 expression.

Study on genomic imprinting of IGF2 gene / 中国实用内科杂志

Objective To study the role of genomic imprinting of IGF2 gene in the development of lung cancer.Methods The IGF2 genomic imprinting was studied among 32 patients with lung cancer and the normal lung tissues by using PCR and RFLP.Results Twelve out of the 32 patients were informative(37.5),among whom 10 exhibited biallelic expression,i.e.,LOI(83.3).The matched normal tissues from 4 of these 10 patients also showed weak biallelic expression of IGF2.Conclusion The findings indicate that the loss of IGF2 imprinting is involved in the development of lung cancer.

Epigenetic Alterations and Loss of Imprinting in Colorectal Cancer

Two forms of genomic instability have been described in colorectal cancer: chromosomal (CIN) and microsatellite instability (MIN). Colorectal cancer has been considered to progress through one of these two major pathways. However, recently a CpG island methylator pathway (CIMP) has been established among sporadic MIN cancers. Aberrant methylation of a promoter CpG island is associated with inactivation of tumor suppressor genes and is one of the epigenetic alterations identified to be involved in tumorigenesis. Now, several types of epigenetic alterations appear to play roles complementary to genetic mutations in colorectal carcinogenesis and seem to contribute to the progression of cancer. Epigenetic alterations also increase the probability that genetic changes will lead to cancer initiation. So far, major epigenetic alterations have been categorized into four groups of dysregulations: 1) hypomethylation with oncogene activation and chromosomal instability, 2) hypermethylation with tumor suppressor gene silencing, 3) chromatin modifications, and 4) loss of imprinting (LOI). Especially, LOI is a common epigenetic variant and should have a field effect on the colon, making it more vulnerable to genetic insults. Genomic imprinting is parental-origin-specific allele silencing, a form of gene silencing that is epigenetic in origin and does not involving alterations in the DNA sequence but does involve methylation and other modifications that are heritable during cell division. LOI is the loss of parental-origin-specific marks, leading either to aberrant activation of a normally silent allele of a growth promoter gene or to silencing of the growth inhibitor allele. Most of the attention has been focused on LOI of the IGF2 (insulin-like growth factor II) gene in a Wilms' tumor and colorectal cancer. LOI of IGF2 involves abnormal activation of a normally silent maternally inherited allele and has been associated with personal and family history of colorectal cancer, supporting a role for LOI in carcinogenesis. LOI may be a valuable predictive marker of an individual's risk for colorectal cancer. Now, epigenetics and imprinting are emerging areas in the study of human-cancer genetics.

Cancer Epigenetics / 대한소화기학회지

Knowledge regarding molecular events of cancer development has been rapidly accumulated during the last decade. The discovery of tumor suppressor gene-silencing by aberrant promoter CpG island hypermethylation and histone-directed chromatin remodeling has led epigenetics to its recognition as an important alternative mechanism for carcinogenesis. Epigenetics does not involve changes in nucleotide sequences, but it affects on genetic composition in many ways. Cancer cells integratively co-opt genetic and epigenetic mechanisms to acquire different aspects of carcinogenetic phenotypes. Since epigenetic changes can be reversed with relative ease, the research of cancer epigenetics provides great potential for new therapeutic regimens.

Frequent Biallelic Expression of Insulin-like Growth Factor II (IGF2) in Gynogenetic Ovarian Teratomas: Uncoupling of H19 and IGF2 Imprinting

Human uniparental gestations such as gynogenetic ovarian teratomas provide a model to evaluate the integrity of parent-specific gene expression - i.e. imprinting - in the absence of a complementary parental genetic contribution. The few imprinted genes characterized so far include the insulin-like growth factor-2 gene (IGF2) coding for a fetal growth factor and H19 gene whose normal function is unknown but it is likely to act as an mRNA. IGF2 is expressed by the paternal allele and H19 by the maternal allele. This reciprocal expression is quite interesting because both H19 and IGF2 genes are located close to each other on chromosome 11p15.5. In situ RNA hybridization analysis has shown variable expression of the H19 and IGF2 alleles according to the tissue origin in 11 teratomas. Especially, Skin, derivative of ectoderm, is expressed conspicuously. We examined imprinting of H19 and IGF2 in teratomas using PCR and RT-PCR of exonic polymorphism. H19 and IGF2 transcript could be expressed either biallelically or monoallelically in the teratomas. Biallelic expression (i.e., loss of imprinting) of IGF2 occured in 5 out of 6 mature teratomas and 1 out of 1 immature teratoma. Biallelic expression of H19 occured in 4 out of 10 mature teratomas and 1 out of 1 immature teratoma. Expression levels of H19 and IGF2 transcript using the semi-quantitative RT-PCR had no relation between monoallelic and biallelic expression. Moreover, IGF2 biallelic expression did not affect allele-specificity or levels of H19 expression. These results demonstrate that both genes, H19 and IGF2, can be imprinted, expressed and regulated independently and individually of each other in ovarian teratoma.

Study of loss of imprinting of insulin-like growth factor Ⅱ and H19 genes in cervical carcinoma / 西安交通大学学报(医学版)

Objective To study the loss of imprinting(LOI) of insulin-like growth factor Ⅱ(IGF2) and H19 genes in cervical carcinomas.Methods Polymerase chain reaction(PCR) method was used on DNA samples extracted from 40 cases of cervical carcinoma and 20 cases of normal control tissues to detect the heterozygosity of IGF2 and H19 genes.The LOI of IGF2 and H19 genes was detected by RT-PCR.Results The heterozygous frequency of IGF2 was 52% in cervical cancer samples.Comparatively,in 20 matched normal samples,13 cases showed the heterozygosity(65%).The biallelic expression of IGF2 was detected in 10 cases among the 21 informative cervical cancer samples(47.6%),however,1 case in 13 heterozygous samples of control group(7.7%)((P0.05).Conclusion LOI and LOH of IGF-2 and H19 genes are involved in cervical carcinomas.LOI of IGF2 and H19 may be involved in the initiation stage of carcinogenesis of cervical carcinoma.