Protein Signatures in Human MDA-MB-231 Breast Cancer Cells Indicating a More Invasive Phenotype Following Knockdown of Human Endometase/Matrilysin-2 by siRNA

New insights into the roles of the FOXO3 and P27Kip1 genes in signaling pathways

Background: The forkhead box O3 (FOXO3) and p27Kip1 are two important genes in breast cancer progression. In the present study we analyzed the effect of simultaneous FOXO3 silencing and p27Kip1 activation on breast cancer cell survival and the potential targets of these changes in cancer molecular pathways. Materials and methods: The present study involved the cloning of FOXO3a shRNA and p27Kip1 genes under the control of the bidirectional survivin promoter to down- and up-regulate FOXO3 and p27Kip1 genes, respectively. After transfection of the recombinant expression vector into the breast cancer cell line, the inhibition of cell growth was assessed by MTS and flow cytometry assays. Following the extraction of total mRNA and protein, the expression of target genes was evaluated by qPCR and Western blotting in both treated and untreated cell lines. Then, the downstream protein responses were examined by 2 D electrophoresis. The differentially expressed proteins were also identified by mass spectrometry. Results: Rates of cell proliferation were significantly inhibited in the transfected cell line 72 h post-transfection. Proteomic profiling of the cell line resulted in the identification of seven novel protein markers in breast cancer responsive to these changes in expression of FOXO3 and p27Kip1. The changes in expression of these markers suggested that certain signaling pathways contribute to the development of breast cancer. Conclusion: Simultaneous silencing of FOXO3 and activation of p27Kip1 in MDA-MB-231 cells caused alterations in the expression level of several genes involved in apoptosis, cell proliferation, cell cycle control, tissue invasion, drug resistance, and metastasis. It seems that the identified genes might serve as useful biomarkers for breast cancer.

Identification of the endoplasmic reticulum localization sequence and N-glycosylation of matrix metalloproteinase 26

Matrix metalloproteinase 26 (MMP-26), also called endometase and matrilysin-2, belongs to the MMP superfamily. Previous studies have focused on its role in tumor invasion and migration but detailed subcellular localization of MMP-26 remains poorly understood. In this study, sequence deletion mutants of MMP-26 revealed that residues 88-123 function to localize MMP-26 to the endoplasmic reticulum (ER). Moreover, using homologous recombination, we show that exchanging residues 88-123 of secretory MMP-7 with the same region in MMP-26 causes localization of this MMP-7 construct to the ER. Moreover, two (N64, N221) of the three possible N-glycosylation sites in MMP-26 were shown to be N-glycosylated, and N-glycosylation is not required for ER localization. These results demonstrate that the 88-123 region of MMP-26 is a noncanonical ER retention signal and MMP-26 is an N-glycosylated protein, thereby providing novel insights into the properties of MMP-26 within the cell.

GRP78 promotes the invasion of pancreatic cancer cells by FAK and JNK

The major characteristics of pancreatic cancer are its excessive local invasion and early systemic dissemination. The glucose-regulated protein is over-expressed in many human cancers including pancreatic cancer and correlated with invasion and metastasis in many cancers. To investigate the effect of Grp78 on the invasion of pancreatic cancer, we used western blot and Transwell assay. We found Grp78 is expressed at lower levels in capan-2 and higher expressed in MiaPaCa-2 cells, and Grp78 expression levels were correlated with the invasion potentials of tumor cells. Then,we increased the expression of Grp78 in capan-2 cells and decreased the expression of Grp78 in MiaPaCa-2 cells. We found that over-expression of Grp78 caused significant increase in the expression of TIMP-1, TIMP-2, MMP-14, MMP-2, and MMP-9 in Capan-2 cells. Consistently, knockdown of Grp78 decreased the expression of them in MiaPaCa-2 cells. Gelatin zymography showed Grp78 over-expression stimulated the activities of MMP-2 and MMP-9, while GRP78 knockdown reduced the activities of MMP-2 and MMP-9. Cytoskeleton staining showed that knockdown of Grp78 caused a marked increase in cytoskeleton F-actin stress fibers in MiaPaCa-2 cells. Consistently, GRP78 knockdown hyperactivated RhoA and inhibited significantly Rac activity. Grp78 over-expression decreases the RhoA and stimulated Rac activity. We also found that Grp78 modulated FAK and JNK signaling pathways. Over-expression of GRP78 in Capan-2 activated FAK and JNK. Finally, we demonstrated that knockdown of FAK by shRNA in combination with blockade of JNK signaling pathway with SP600125 completely inhibited GRP78-induced cancer cell invasion. GRP78 is involved in the regulation of pancreatic cancer invasion. FAK and JNK are the key downstream effectors of GRP78.

Transfection of siRNAs can alter miRNA levels and trigger non-specific protein degradation in mammalian cells

Sequence-non-specific effects of siRNAs that alter the expression of non-targeted genes have been reported, including competition of siRNAs with endogenous RISC components. However, the detailed mechanisms and subsequent effects of such competition are not well documented. Here we analyze the competition of miRNAs in mammalian cells with low concentrations of siRNAs, and found that: 1) transfection of different siRNAs in the low nanomolar range used to deplete target RNAs can reduce the levels of miRNAs in different cell types, 2) siRNA transfection results in rapid reduction of Ago2-associated miRNAs concurrent with accumulation of Ago2-bound siRNAs and a significant change in the expression levels of many miRNAs, 3) competition largely depends on Ago2 and not Dicer, 4) microarray analysis showed that the majority of highly expressed miRNAs are reduced, in a siRNA concentration dependent manner, and low abundant miRNAs may be unchanged or repressed and a few miRNAs appear to have increased levels, and 5) consistent with previous studies, the expression levels of mRNAs that are targeted by highly repressed miRNAs are preferentially increased. As a consequence of such competition, we observed that α-tubulin, a substrate of two up-regulated proteases, granzyme B and granzyme M, was rapidly degraded at the protein level upon siRNA transfection. Our results support a model in which transfection of siRNAs can change the levels of many miRNAs by competition for Ago2, leading to altered expression of many miRNA target genes, which can in turn affect downstream gene expression even at the protein level.

Role of breast cancer metastasis suppressor 1 in digestive system neoplasms

Breast cancer metastasis suppressor 1 (BRMS1) is a tumor metastasis suppressor discovered in breast carcinoma cells in 2000. It can reduce the metastasis potential of tumor cells without affecting the growth of orthotopic tumor. BRMS1 is lowly expressed or not at all in metastases of melanoma, bladder carcinoma, pheochromocytoma, ovarian cancer, non-small cell lung cancer, endometrial cancer, nasal and paranasal sinus carcinoma. Malignant tumors have become one of the most serious diseases endangering human health, and digestive system neoplasms are the most common malignant tumors in China. Elucidation of the role of BRMS1 will certainly provide a potential theoretical basis for the molecular diagnosis, targeted therapy, and prognosis evaluation of tumor metastases. In this review, we will summarize recent progress in understanding the role of BRMS1 in digestive system neoplasms.