ABSTRACT
Background: The forkhead box M1 (FOXM1), an important regulator of cell differentiation and proliferation, is overexpressed in a number of aggressive human carcinomas. However, the clinical significance of FOXM1 signaling in human colorectal cancer (CRC) pathogenesis remains unknown. The aim of this study was to evaluate the role of FOXM1 in CRC tumorigenesis. Methods: We investigated FOXM1 expression in 103 cases of primary CRC and matched normal tissue specimens and explored the underlying mechanisms of altered FOXM1 expression and the impact of this altered expression on CRC proliferation and metastasis using in vitro models of CRC. Results: The results showed that high expression of FOXM1 staining was 85.44 % (88/103) in 103 cases of CRC and 20.39 % (21/103) in 103 cases of adjacent noncancerous tissue samples; the difference of FOXM1 expression between two groups was statistically significant (P < 0.001). Silencing of FOXM1 inhibited the proliferation of CRC cells, and the invasion and migration of CRC cells were distinctly suppressed. Furthermore, FOXM1 knockdown led to substantial reductions in VEGF-A levels in CRC cell lines. Conclusions: Our data suggest that the pathogenesis of CRC maybe mediated by FOXM1, and FOXM1 could represent selective targets for the molecularly targeted treatments of CRC
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Subject(s)
Humans , Male , Female , Oncogene Proteins v-fos , Oncogene Proteins v-fos/isolation & purification , Colorectal Neoplasms/diagnosis , Colorectal Neoplasms/therapy , RNA Interference , RNA Interference/radiation effects , RNAi Therapeutics/methods , Cell Proliferation , Cell Proliferation/radiation effectsABSTRACT
The transcription factor c-Fos is a short-lived protein and calpains and ubiquitin-dependent systems have been proposed to be involved in its degradation. In this report, we consider a lysosomal degradation pathway for c-Fos. Using a cell-free assay, we have found that freshly isolated lysosomes can take up and degrade c-Fos with high efficiency. v-Fos, the oncogenic counterpart of c-Fos, can also be taken up by lysosomes, yet the amount of incorporated protein is much lower. c-Fos uptake is independent of its phosphorylation state but it appears to be regulated by dimerization with differentially phosphorylated forms of c-Jun, while v-Fos escapes this regulation. Moreover, we show that c-Fos is immunologically detected in lysosomes isolated from the liver of rats treated with the protease inhibitor leupeptin. Altogether, these results suggest that lysosomes can also participate in the selective degradation of c-Fos in rat liver.
Subject(s)
Liver/metabolism , Lysosomes/metabolism , Oncogene Proteins v-fos/metabolism , Proto-Oncogene Proteins c-fos/metabolism , Animals , Cell Line , Cell-Free System , Electrophoresis, Polyacrylamide Gel , HeLa Cells , Humans , Kinetics , Leupeptins/pharmacology , Lysosomes/drug effects , Oncogene Proteins v-fos/isolation & purification , Phosphorylation , Protease Inhibitors/pharmacology , Proto-Oncogene Proteins c-fos/isolation & purification , Proto-Oncogene Proteins c-jun/isolation & purification , Proto-Oncogene Proteins c-jun/metabolism , Rats , Recombinant Proteins/isolation & purification , Recombinant Proteins/metabolism , Transfection , TrypsinABSTRACT
Viral oncogenes are generally believed to cause transformation through disregulated mimicry of their cellular homologues. However, here we show that FBR v-fos, unlike c-fos, transcriptionally activates unique genes in retrovirally induced chondro-osseous sarcomas. We show that FBR v-fos transactivates the collagen III and stromelysin promoters and that the unique transcriptional properties of transforming FBR depend upon its N-terminal myristylation and the differentiation state of the cell. Deletion or mutation of the myristylation site results in a loss of FBR v-fos transactivation in HeLa and undifferentiated 3T3-L1 preadipocyte cell lines. FBR v-fos transactivation of collagen III maps to a negative regulatory site which binds a key regulator of adipocyte differentiation, C/EBP alpha. Cotransfection of C/EBP alpha abolishes FBR v-fos transactivation of the alpha 1(III) collagen promoter. Furthermore, FBR v-fos cannot transactivate collagen III subsequent to adipocyte differentiation. We also demonstrate that collagen III transcription is reduced during adipocyte differentiation as the transcriptional activity of C/EBP alpha is concomitantly induced. Our results indicate that FBR v-fos transactivation depends upon its cotranslational myristylation and maps to a negative regulatory region which binds C/EBP alpha.
