Detection of p53, malat1, ki-67 and β-catenin mRNA expression and its significance in molecular diagnosis of colorectal carcinoma

AIM: To detect p53, malat1, ki-67 and β-catenin mRNA expression in colorectal carcinoma and to evaluate its significance in molecular diagnosis of colorectal carcinoma.

METHODS: Real-time RT-PCR was used to detect p53, malat1, ki-67 and β-catenin mRNA expression in samples from 47 colorectal carcinomas, 13 colorectal adenomas and 53 normal colorectal tissues.

RESULTS: The expression levels of p53 and malat1 were significantly different between colorectal carcinoma, colorectal adenoma and normal colorectal tissue (P < 0.05). p53 expression levels showed an average 1.61-fold (P = 0.000) and 2.62-fold (P = 0.000) increase in colorectal adenoma and colorectal carcinoma tissues when compared with normal colorectal tissues respectively, and 1.77-fold (P = 0.026) increase in colorectal carcinoma compared with colorectal adenoma. Similarly, malat1 expression levels were 0.55-fold (P = 0.001), 1.48-fold (P = 0.002) and 1.78-fold (P = 0.034) respectively. However, there were no significant differences among colorectal carcinoma, colorectal adenoma and normal colorectal tissues in ki-67 and β-catenin. The expression levels of p53, malat1, ki-67 and β-catenin mRNA were not associated with the staging of colorectal carcinoma. The AUC (area under curve) of p53 and malat1 were 0.755 and 0.748, respectively. The cut-off value for p53 in colorectal adenoma and colorectal carcinoma was 2.582 and 3.215 respectively; for malat1, 0.925, 1.395 respectively. Logistic regression analysis showed that p53 and malat1 entered the regression equation (P < 0.05). The combined determination showed, the AUC were 0.785, the cut-off values in colorectal adenoma and colorectal carcinoma were 0.750, 0.790 respectively. Thus, the AUC of combined determination was larger than that of single detection for p53 and malat1.

CONCLUSION: The present study demonstrates that p53 and malat1 have certain application value in molecular diagnosis of colorectal carcinoma to identify colorectal carcinoma and colorectal adenoma. Furthermore, the accuracy in diagnosis of colorectal cancer is improved by combined assaying of p53 and malat1.

Effects of down-regulation of p21 by HBx gene on HepG2 cell proliferation and apoptosis

AIM: To establish gene-transfected cell strain HepG2/HBx and study the effect of HBx on cell cycle, proliferation and apoptosis of HepG2 cells as well as the potential regulative role of p21.

METHODS: HBx was transfected into HepG2 cells and G418 selection was used to obtain the positive clones of HepG2/HBx cells. Then HBx mRNA expression and protein expression were detected using RT-PCR and western blot analysis respectively. MTT assay and flow cytometry were adopted to measure the proliferation, cell cycle and apoptosis of HepG2/HBx, HepG2 and HepG2/pcDNA3.1 (HepG2 cells transfected with pcDNA3.1) cells. Semi-quantified RT-PCR was used to evaluate the expression of p21 and p53 in three groups.

RESULTS: The expression of mRNA and protein of HBx in HepG2/HBx cells was confirmed by RT-PCR and western blot respectively. The proliferation of HepG2/HBx cells was accelerated. The proportion of HepG2/HBx cells decreased significantly in G₀/G₁ phase (43.34% ± 3.11% vs 57.69 ± 4.28%, P < 0.01), but increased remarkably in S phase (28.69% ± 1.17% vs 22.41% ± 1.99%, P < 0.05) and the apoptosis rate of HepG2/HBx cells was at a significantly lower level (1.19% ± 0.06% vs 5.43% ± 0.42%, P < 0.001). Compared with HepG2 and HepG2/pcDNA3.1 cells, the expression of p21 mRNA in HepG2/HBx was down-regulated (0.16 ± 0.05 vs 0.78 ± 0.15, P < 0.001), while there was no significant difference in the expression of p53 gene.

CONCLUSION: The HBx gene down-regulates the expression of p21 mRNA, which may play an important role in accelerating cell cycle, improving growth and inhibiting apoptosis of HepG2 cells.

Association between colorectal cancer and tumor suppressor genes: recent research progress

Colorectal cancer is a common high-risk gastrointestinal cancer, and approximately 1.2 million new cases are diagnosed each year worldwide. In recent years, due to the improvement of people's living standards and changes in dietary habits and structure, the incidence and mortality rate of colorectal cancer increase rapidly in China. Moreover, patients have a significantly earlier age of onset. At present, the median age of colorectal cancer onset in China is 58 years old, 12 to 18 years earlier than other countries in Europe and America. The development of colorectal cancer is a complex multi-stage process involving multiple genetic alterations. Many studies have shown that colorectal carcinogenesis involves activation of oncogenes and inactivation of tumor suppressor genes. Tumor suppressor genes associated with colorectal carcinogenesis include p53, APC, DCC, and MMR, and proto-oncogenes include K-ras and c-myc. In this paper, we discuss the association between tumor suppressor genes and colorectal carcinogenesis.

siRNA-mediated knockdown of the SUMO-1 gene down-regulates mutant p53 expression in hepatocellular carcinoma cell line SMMC-7721

AIM: To determine whether the SUMO-1 gene controls the expression of mutant p53 in hepatocellular carcinoma cell line SMMC-7721, and whether siRNA-mediated SUMO-1 knockdown inhibits the proliferation of SMMC-7721 cells.

METHODS: Synthetic SUMO-1 siRNA was transfected into SMMC-7721 cells to silence the expression of the SUMO-1 gene. The expression level of mutant p53 in SMMC-7721 cells was detected by RT-PCR and Western blot experiments after SUMO-1 down-regulation. SMMC-7721 cell proliferation was examined by MTT assay at 24, 48 and 72 h after siRNA transfection.

RESULTS: Both SUMO-1 and mutant p53 were highly expressed in SMMC-7721 cells. The expression of mutant p53 was down-regulated coincidentally with SUMO-1 silencing in SMMC-7721 cells. The expression of mutant p53 in SMMC-7721 cells at 24, 48 and 72 h after siRNA transfection decreased by 5.73% ± 0.61%, 69.43% ± 1.22% and 57.71% ± 0.94%, respectively. SUMO-1 knockdown inhibits the proliferation of SMMC-7721 cells. The reduced rates of cell proliferation at 24, 48 and 72 h after siRNA transfection were 70.96%, 71.57% and 81.56%, respectively.

CONCLUSION: SUMO-1 controls SMMC-772 cell proliferation possibly by regulating the expression of mutant p53 at the transcriptional level.

Transfection of the wild-type xeroderma pigmentosum group D gene alters the biological behavior of human cholangiocarcinoma cell line QBC939

AIM: To investigate the impact of tranfection of the wild-type xeroderma pigmentosum group D (XPD) gene on the biological behavior of human cholangiocarcinoma cell line QBC939.

METHODS: Empty plasmid pEGFP-N2 and recombinant plasmid pECFP-N2-XPD were digested with KPN I, BGI II and SPH I for plasmid identification. Cells were divided into four groups: pEGFP-N2-XPD group, pEGFP-N2 group, Lipofectamine (Lip) group, and blank control group. Cells were transfected with Lipofectamine. The expression of green fluorescent protein (GFP) was observed under a fluorescence microscope. The mRNA expression of wild-type XPD, p53, cyclin D1 and c-myc was detected by reverse transcription-polymerase chain reaction (RT-PCR). Flow cytometry (FCM) was employed for examining the cell cycle of transfected QBC939 cells. Cell proliferation was detected by methyl thiazolyl tetrazolium (MTT) assay.

RESULTS: The relative expression level of XPD mRNA in the pEGFP-N2-XPD group was significantly higher than those in the pEGFP-N2 group, Lip group and blank control group (0.778 ± 0.018 vs 0.561 ± 0.039, 0.544 ± 0.035 and 0.542 ± 0.034, respectively; all P < 0.01). The relative expression level of p53 mRNA in the pEGFP-N2-XPD group was also significantly higher than those in the pEGFP-N2 group, Lip group and blank control group (0.421 ± 0.019 vs 0.256 ± 0.014, 0.267 ± 0.015 and 0.274 ± 0.018, respectively; all P < 0.01). The relative expression level of cyclin D1 mRNA in the pEGFP-N2-XPD group was significantly lower than those in the pEGFP-N2 group, Lip group and blank control group (0.339 ± 0.041 vs 0.560 ± 0.039, 0.558 ± 0.050 and 0.560 ± 0.041, respectively; all P < 0.01). The relative expression level of c-myc mRNA in the pEGFP-N2-XPD group was also significantly lower than those in the pEGFP-N2 group, Lip group and blank control group (0.355 ± 0.045 vs 0.570 ± 0.075, 0.560 ± 0.041 and 0.537 ± 0.050, respectively; all P < 0.01). FCM results showed that the percentage of cells in G₁ phase was significantly higher (81.65% vs 65.54%, 56.61% and 63.26%, respectively; all P < 0.05) and that in S1 phase was significantly lower (11.83% vs 24.10%, 29.52% and 27.28%; all P < 0.05) in the pEGFP-N2-XPD group than in the pEGFP-N2 group, Lip group and blank control group. MTT assay revealed that the growth rate of cells in the pEGFP-N2-XPD group was significantly lower than those in the other three groups (all P < 0.01).

CONCLUSION: Transfection of the wild-type XPD gene can inhibit the proliferation of human QBC939 cells in vitro, down-regulate the expression of cyclin D1 and c-myc mRNAs, and up-regulate the expression of p53 mRNA.

Research progress in roles of murine double minute 2 gene in the gastrointestinal tumor

Murine double minute 2 (MDM2), an oncogene discovered in recent years, can enhance cell survival activity, prolong cell survival duration, promote cell proliferation and stimulate tumor growth. In recent years, it was shown that MDM2 participated in the genesis and development of various tumors. In addition, MDM2 is associated with the invasion, metastasis and poor prognosis of malignant tumors, especially gastrointestinal tumors such as esophageal cancer, gastric cancer, colon cancer, liver cancer, etc. So it is significant to study the relationship between MDM2 and gastrointestinal tumors for tumor prevention and treatment. In combination with domestic and overseas literatures, this article provides a brief review of the research progress in the roles of MDM2 in the genesis, development and metastasis of gastrointestinal tumors.