Overexpression of a novel imprinted gene, PEG10, in human hepatocellular carcinoma and in regenerating mouse livers

The effects of Curcumin on HCT-116 cells proliferation and apoptosis via the miR-491/PEG10 pathway

Paternally expressed gene-10 (PEG10) could participate in several carcinomas and might be regulated by miR-491. To now, miR-491 was found to play an important role in the sensitivity and mechanism of drug usage in the treatment of colorectal cancer, and drug resistance is a key factor to affect the disease healing. In this study, miR-491, PEG10, Wnt1, and β-catenin expression levels and their correlation with colorectal cancer were assessed in cancer tissues and adjacent parts. And the target relationship between PEG10 and miR-491 was verified. Meanwhile, the impaction of Curcumin on miR-491, PEG10, and Wnt/β-catenin signaling pathway were analyzed in HCT-116 cells. The effects of PEG10 and Curcumin on human HCT-116 cells proliferation and apoptosis were investigated by MTT and flow cytometry assay. Results showed that the expression of miR-491 in colon cancer tissues was decreased, but PEG10, Wnt1, and β-catenin were higher than that in adjacent tissues. The PEG10 gene 3' UTR could combine with miR-491 seed sequence and miR-491 overexpression could cause a decrease in PEG10, Wnt1, and β-catenin levels in human HCT-116 cells. Furthermore, PEG10 overexpression increased the expression levels of Wnt1 and β-catenin, thereby promoting cell proliferation and inhibiting apoptosis. In addition, Curcumin could up-regulate miR-491, inhibit PEG10, and Wnt/β-catenin signaling pathway. Consequently, Curcumin reduced HCT-116 cells proliferation and promoted cells apoptosis via the miR-491/PEG10 pathway. In conclusion, PEG10 was a target gene of miR-491, miR-491/PEG10 strengthen the sensitivity of Curcumin in HCT-116 cells proliferation and apoptosis, which might act as an ideal diagnostic biomarker treatment methods.

Gene expression profiling reveals potential biomarkers of human hepatocellular carcinoma

PURPOSE

Hepatocellular carcinoma (HCC), a common cancer worldwide, has a dismal outcome partly due to the poor identification of early-stage HCC. Currently, one third of HCC patients present with low serum alpha-fetoprotein (AFP) levels, the only clinically available diagnostic marker for HCC. The aim of this study was to identify new diagnostic molecular markers for HCC, especially for individuals with low serum AFP.

EXPERIMENTAL DESIGN

We used the microarray technique to determine the expression profiles of 218 HCC specimens from patients with either high or low serum AFP. From the microarray study, we selected five candidate genes (i.e., GPC3, PEG10, MDK, SERPINI1, and QP-C), which were overexpressed in HCCs. Using quantitative real-time PCR analyses, we validated the expression of these five genes in 50 AFP-normal and 8 AFP-positive HCC specimens and 36 cirrhotic noncancerous hepatic specimens, which include 52 independent specimens not used in microarray analysis.

RESULTS

A significant increase in the expression of the five candidate genes could be detected in most of the HCC samples, including those with normal serum AFP and small tumors. GPC3, MDK, and SERPINI1 encode known serum proteins. Consistently, a significant increase in serum midkine, encoded by MDK, was associated with HCC patients, including those with normal serum AFP. Using prediction analysis of microarray, we showed that a combined score of these five genes can accurately classify noncancerous hepatic tissues (100%) and HCC (71%).

CONCLUSIONS

We suggest that a diagnostic signature approach using a combined score of these five biomarkers rather than a single marker may improve the prediction accuracy of HCC patients, including those with normal serum AFP and smaller-sized tumors.

Overexpression of the paternally expressed gene10 (PEG10) from the imprinted locus on chromosome 7q21 in high-risk B-cell chronic lymphocytic leukemia

We report high expression of the maternally imprinted gene PEG10 in high-risk B-CLL defined by high LPL mRNA expression. Differential expression was initially identified by microarray analysis and confirmed by real time PCR in 42 B-CLL patients. mRNA expression ranged from 0.3- to 375.4-fold compared to normal peripheral blood mononuclear cells (PBMNC). Expression levels in CD19+ B-CLL cells were 100-fold higher than in B-cells from healthy donors. PEG10 expression levels in B-CLL patient samples remained stable over time even after chemotherapy. High PEG10 expression correlated with high LPL expression (p=0.001) and a positive Coombs' test (p=0.04). Interestingly, similar expression patterns were observed for the neighbouring imprinted gene sarcoglycan-epsilon (SGCE). Monoallelic expression and maintained imprinting of PEG10 were found by allele- or methylation-specific PCR. The intensity of intracellular staining of PEG10 protein corresponded to mRNA levels as confirmed by immunofluorescence staining. Short term knock-down of PEG10 in B-CLL cells and HepG2 cells was not associated with changes in cell survival but resulted in a significant change in the expression of 80 genes. However, long term inhibition of PEG10 led to induction of apoptosis in B-CLL cells. Our data indicate (i) a prognostic value of PEG10 in B-CLL patients; (ii) specific deregulation of the imprinted locus at 7q21 in high-risk B-CLL; (iii) a potential functional and biological role of PEG10 protein expression. Altogether, PEG10 represents a novel marker in B-CLL.

PEG10 Is a c-MYC Target Gene in Cancer Cells

The product of the imprinted gene paternally expressed gene-10 (PEG10) has been reported to support proliferation in hepatocellular carcinomas, but how this gene is regulated has been an open question. We find that MYC knockdown by RNA interference suppresses PEG10 expression in Panc1 pancreatic carcinoma and HepG2 hepatocellular carcinoma cells and that knockdown of PEG10 inhibits the proliferation of Panc1, HepG2, and Hep3B cells. Conversely, PEG10 was up-regulated by inducing c-MYC expression in a B-lymphocyte cell line. Chromatin immunoprecipitation from Panc1 cells showed c-MYC bound to an E-box-containing region in the PEG10 first intron and site-directed mutagenesis showed that the most proximal E-box is essential for promoter activity. In a mouse mammary tumor virus (MMTV)-MYC transgenic mouse model of breast cancer, most but not all of the mammary carcinomas had strongly increased Peg10 mRNA compared with normal mammary gland. By immunohistochemistry, normal human breast and prostate epithelium was negative for the major isoform [reading frame-1 (RF1)] of PEG10 protein, but this cytoplasmic protein was strongly expressed in a subset of breast carcinomas in situ and invasive ductal carcinomas ( approximately 30%) and in a similar percentage of prostate cancers. As in the mouse model, we found positive, but not absolute, correlations between PEG10 and c-MYC in tissue arrays containing 161 human breast cancers (P < 0.002) and 30 prostate cancers (P = 0.014). Immunostaining of human placenta showed PEG10 and c-MYC proteins coexpressed in proliferating cytotrophoblast and coordinately lost in postmitotic syncytiotrophoblast. These findings link cancer genetics and epigenetics by showing that a classic proto-oncogene, MYC, acts directly upstream of a proliferation-positive imprinted gene, PEG10.

Specificity and significance of expression of imprinted gene PEG10 in hepatocellular carcinoma

AIM: To study the specificity and significance of the expression of imprinted gene PEG10 in hepatocellular carcinoma (HCC) and to evaluate the feasibility for PEG10 as a novel molecular target of gene therapy for HCC.

METHODS: The total RNA was extracted from different tumor cell lines (liver cancer HepG2, gastric cancer SGC7901, colorectal cancer Lovo, pancreatic cancer PC3, melanoma A375 and T lymphoma Jurkat cells), normal human fetal liver cell line L02, human HCC (n = 32) and the corresponding cancer-adjacent tissues (n = 32), benign liver tissues (n = 10) and peripheral blood cells (n = 10). Then the expression of PEG10 was detected by reverse transcription polymerase chain reaction (RT-PCR). Simultaneously, AFP expression was detected in human HCC and the corresponding cancer-adjacent tissues.

RESULTS: After amplification, the length of PEG10 and AFP fragment was 455 bp and 140 bp respectively. PEG10 was markedly expressed in HepG2 cells, and weakly expressed in SGC7901, PC3, Lovo cells. PEG10 expression was found negative in L02 and other tumor cell lines. The positive rates of PEG10 expression in HCC and the corresponding tissues were 78.1% and 0%, but the ones for AFP were 93.8% and 59.4% respectively. There was no significant difference between PEG10 and AFP expression in HCC tissues (P>0.05), whereas the expression of AFP (19/32) was significantly higher than that of PEG10 in cancer-adjacent tissues (0/32) (c²_0.01,1 = 17.05, P<0.01). PEG10 wasn't detected in benign liver tissues and normal peripheral blood cells.

CONCLUSION: PEG10 is more specifically expressed in HCC than AFP, which provides evidence for PEG10 as a novel molecular target of gene therapy for HCC.