Roles For Eukaryotic Initiation Factor 3g In Malignant Phenotype Of Breast Cancer

The eukaryotic initiation factor 3 (eIF3) is a multiprotein complex containing at least 13 nonidentical subunits,that plays a central role in translation initiation. Recent studies shown that various subunits of eIF3 such as eIF3a,eIF3f have abnormal expression in human cancers,some subunits also closely related to the malignant phenotype and prognosis of cancer,and individual overexpression of some subunits promotes malignant transformation of immortal fibroblast cells. eIF3g, the p42 subunit of the eIF3 complex,has been reported to strongly associate with eIF2 and eIF5 in translation initiation. Moreover, eIF3g may play crucial roles by binding directly apoptosis-inducing factor(AIF) and protein 4.1R.In our previous work, we found that K562/ADR cells and MCF-7/ADR cells have higher expression of eIF3g with comparision to the parental K562 cells and MCF-7 cells by the result of 2-dimensional gel-electrophoresis(2D-GE) and western blot, this difference between the two patterns might provide clues to the relationship between eIF3g and the multidrug resistance or other malignant phenotype of cancer.In order to evaluate roles for eIF3g in malignant phenotype of breast cancer,we obtained a stable eIF3g expressing single clones Bcap37/eIF3g and contrasted changes of malignant phenotype of human breast cancer Bcap37 cells, designed and constructed artificial microRNA targeting eIF3g gene, transfected eIF3g-microRNA to Bcap37 cells to further confirm the roles of eIF3g,used immunohistochemistry method to analyze the expression and clinical significance of eIF3g in breast cancers.The details are listed below. 1 Influence of up-regulation of eIF3g expression to the malignant phenotype of breast cancerWestern blot was used to obtain a stable eIF3g expressing single clone Bcap37/eIF3g,and MTT assay,FCM, scratch assay, transwell assay, were used to valuate roles for eIF3g in cell proliferation, motility,cell cycle,and drug resistance of Bcap37 cells. MTT assay results showed that the proliferation rate of Bcap37/eIF3g cells was significantly higher than that of the cells of two control groups (P<0.05). Nude mice model showed that the tumor volume of nude mice in over-expression group were higher than those in tumour control groups (P<0.05). The results of scratch assay and transwell assay showed significantly promoted motility for Bcap37/eIF3g cells compared to the cells of the two control groups (P<0.01). Flow cytometry analysis of cell cycle revealed that the fraction of cells in S phase in stable eIF3g expressing cell line cells was significantly higher compared to that of the two control groups. MTT assay results showed that the ADR IC50 value of stable eIF3g expressing cell line was higher and the VCR IC50 value was lower than the two control groups(P<0.05),but the IC50 value of 5-fluorouracil and paclitaxel had no difference between stable cell line and control groups.2 Influence of inhibition of eIF3g expression to the malignant phenotype of breast cancerArtificial microRNA targeting eIF3g gene was constructed and inserted into the pcDNA3.1(+) expression vector, the expression vector was transfected into human breast cancer Bcap37 cell, the MTT assay and scratch assay were used to valuate roles for eIF3g in cell proliferation and motility. Western blot confirmed that artificial microRNA can effectively inhibit eIF3g expression in Bcap37 cell. MTT assay results showed that the microRNA began to inhibit cells proliferation at 48h after transfection and got to the highest inhibition at 72h. (P<0.05),and scratch assay showed that down-regulation of eIF3g expression may decrease cell motility. 3 The expression of eIF3g in tissues of breast cancer and its association with clinicopathological features.The immunohistochemistry method was used to analyze the expression and clinical significance of eIF3g in 54 cases of breast cancer,10 cases of breast benign neoplasm and 10 cases of normal breast samples. Results showed that in 20 cases of breast cancers with the lymph node metastasis, the high expression of eIF3g were 65 %, but in 34 cases of breast cancers without the lymph node metastasis, the high expression of eIF3g were only 20.6%(P<0.01). Moreover,23 cases of breast cancer with chemotherapy before operation were detected by immunohistochemistry to analyze the relationship between the expression of eIF3g and the the sensitivity to chemotherapeutic drugs. Results showed that 10 cases of breast cancers with good chemotherapy effectiori all had low expression(P<0.05).Conclusion1 Overexpression of eIF3g in Bcap37 cells can promote cell proliferation and motility, increase S phase percentage,reduce G2/M phase percentage, enhance drug resistance to ADR.Inhibition of eIF3g in Bcap37 cells can also inhibit cell proliferation. and mobility.2 The results of immunohistochemistry showed that the expression of eIF3g was high in breast cancers with the lymph node metastasis and low in breast cancers with good chemotherapy effection.