Brain fatty acid-binding protein (FABP7) and PAX6 are both expressed in radial glial cells and have been implicated in neurogenesis and glial cell differentiation. FABP7 and PAX6 have also been postulated to play a role in malignant glioma cell growth and invasion. Here, we address the role of PAX6 in regulating FABP7 gene expression in malignant glioma cells. We report that PAX6 and FABP7 RNA are generally co-expressed in malignant glioma cell lines, tumors and tumor neurospheres. Using the CAT reporter gene assay, we show that FABP7 promoter activity is upregulated by PAX6. Sequential deletion analysis of the FABP7 promoter, combined with gel shift and supershift assays demonstrate the presence of a PAX6 responsive region located upstream of the FABP7 gene, at -862 to -1033 bp. Inclusion of sequences between -1.2 and -1.8 kb reduced CAT activity, suggesting the presence of a repressor element within this region. While PAX6 overexpression did not induce endogenous FABP7 expression in FABP7-negative cells, knock-down of PAX6 in PAX6-positive malignant glioma cells resulted in reduced FABP7 levels. These data provide the first evidence of direct transactivation of the FABP7 proximal promoter by PAX6 and suggest a synergistic mechanism for PAX6 and other co-factor(s) in regulating FABP7 expression in malignant glioma.
[Show abstract][Hide abstract] ABSTRACT: Malignant gliomas are the most common adult brain cancers. In spite of aggressive treatment, recurrence occurs in the great majority of patients and is invariably fatal. Polyunsaturated fatty acids are abundant in brain, particularly ω-6 arachidonic acid (AA) and ω-3 docosahexaenoic acid (DHA). Although the levels of ω-6 and ω-3 polyunsaturated fatty acids are tightly regulated in brain, the ω-6:ω-3 ratio is dramatically increased in malignant glioma, suggesting deregulation of fundamental lipid homeostasis in brain tumor tissue. The migratory properties of malignant glioma cells can be modified by altering the ratio of AA:DHA in growth medium, with increased migration observed in AA-rich medium. This fatty acid-dependent effect on cell migration is dependent on expression of the brain fatty acid binding protein (FABP7) previously shown to bind DHA and AA. Increased levels of enzymes involved in eicosanoid production in FABP7-positive malignant glioma cells suggest that FABP7 is an important modulator of AA metabolism. We provide evidence that increased production of eicosanoids in FABP7-positive malignant glioma growing in an AA-rich environment contributes to tumor infiltration in the brain. We discuss pathways and molecules that may underlie FABP7/AA-mediated promotion of cell migration and FABP7/DHA-mediated inhibition of cell migration in malignant glioma.
Progress in lipid research 08/2013; 52(4). DOI:10.1016/j.plipres.2013.08.004 · 10.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Paired box 6 (PAX6), a highly conserved transcriptional factor, has been implicated in tumorigenesis.
We aimed to explore the roles and molecular mechanisms of PAX6 and microRNA (miR-7) in colorectal cancer cells.
Tissue microarray immunohistochemistry and Western blot were applied to examine the PAX6 expression. Real-time RT-PCR and Western blot were performed to determine the expression of miR-7 and PAX6. Luciferase reporter assay was used to determine whether PAX6 was a target of miR-7. Effects of miR-7 and PAX6 on colorectal cell proliferation, cell cycle progression, colony formation and invasion were then investigated. Western blot was used to determine the activities of the ERK and PI3K signal pathways, as well as the protein expression of MMP2 and MMP9.
The protein levels of PAX6 were gradually increased, while the expression of miR-7 was gradually reduced with malignancy of colorectal cancer. PAX6 was further identified as a target of miR-7, and its protein expression was negatively regulated by miR-7 in human colorectal cancer cells. Overexpression of PAX6 in Caco-2 and SW480 cells enhanced cellular proliferation, cell cycle progression, colony formation, and invasion, while miR-7 upregulation repressed these biological processes. Furthermore, the activities of ERK and PI3K signal pathways, as well as the protein levels of MMP2 and MMP9, were upregulated in PAX6-overexpressed Caco-2 and SW480 cells but deregulated in miR-7-overexpressed Caco-2 and SW480 cells.
Our study suggests that as a novel target of miR-7, PAX6 may serve as a promising therapeutic target for colorectal cancer.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study is to review recent evidence for the role of the cytosolic fatty acid binding proteins (FABPs) as central regulators of whole-body metabolic control.
Dysregulated FABPs have been associated with a number of diseases, including obesity and nonalcoholic fatty liver disease (FABP1, FABP2, FABP4), cardiovascular risk (FABP3) and cancer (FABP5, FABP7). As underlying mechanisms become better understood, FABPs may represent novel biomarkers for therapeutic targets. In addition, the role of FABPs as important signalling molecules has also been highlighted in recent years; for example, FABP3 may act as a myokine, matching whole-body metabolism to muscular energy demands and FABP4 functions as an adipokine in regulating macrophage and adipocyte interactions during inflammation.
In addition to their traditional role as fatty acid trafficking proteins, increasing evidence supports the role of FABPs as important controllers of global metabolism, with their dysregulation being linked to a host of metabolic diseases.
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