The Anti-Aging and Tumor Suppressor Protein Klotho Enhances Differentiation of a Human Oligodendrocytic Hybrid Cell Line
Journal of Molecular Neuroscience (Impact Factor: 2.34). 06/2014; 55(1). DOI: 10.1007/s12031-014-0336-1
Klotho functions as an aging suppressor, which, in mice, extends lifespan when overexpressed and accelerates development of aging-like phenotypes when disrupted. Klotho is mainly expressed in brain and kidney and is secreted into the serum and CSF. We have previously shown that Klotho is reduced in brains of old monkeys, rats, and mice. We further reported the ability of Klotho to enhance oligodendrocyte differentiation and myelination. Here, we examined the signaling pathways induced by Klotho in MO3.13, a human oligodendrocytic hybrid cell line. We show that exogenous Klotho affects the ERK and Akt signaling pathways, decreases the proliferative abilities and enhances differentiation of MO3.13 cells. Furthermore, microarray analysis of Klotho-treated MO3.13 cells reveals a massive change in gene expression with 80 % of the differentially expressed genes being downregulated. Using gene set enrichment analysis, we predicted potential transcription factors involved in regulating Klotho-treated MO3.13 cells and found that these cells are highly enriched in the gene sets, that are similarly observed in cancer, cardiovascular disease, stress, aging, and hormone-related chemical and genetic perturbations. Since Klotho is downregulated in all brain tumors tested to date, enhancing Klotho has therapeutic potential for treating brain and other malignancies.
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ABSTRACT: Membrane protein shedding is a critical step in many normal and pathological processes. The anti-aging protein Klotho (KL), mainly expressed in kidney and brain, is secreted into the serum and CSF, respectively. KL is proteolytically released, or shed, from the cell surface by ADAM10 and ADAM17, which are the α-secretases that also cleave the amyloid precursor protein and other proteins. The transmembrane KL is a co-receptor with the FGF receptor for FGF23, while the shed form acts as a circulating hormone. However, the precise cleavage sites in KL are unknown. KL contains two major cleavage sites: one close to the juxtamembrane region and another between the KL1 and KL2 domains. We identified the cleavage site involved in KL release by mutating potential sheddase(s) recognition sequences and examining the production of the KL extracellular fragments in transfected COS-7 cells. Deletion of amino acids T958 and L959 results in a 50-60% reduction in KL shedding, and an additional P954E mutation results in further reduction of KL shedding by 70-80%. Deletion of amino acids 954-962 resulted in a 94% reduction in KL shedding. This mutant also had moderately decreased cell surface expression, yet had overall similar subcellular localization as WT KL as demonstrated by immunofluorescence. Cleavage-resistant mutants could function as a FGFR co-receptor for FGF23, but lost activity as a soluble form of KL in proliferation and transcriptional reporter assays. Cleavage between the KL1 and KL2 domains is dependent on juxtamembrane cleavage. Our results shed light into mechanisms underlying KL release from the cell membrane and provide a target for potential pharmacologic interventions aiming at regulating KL secretion.Biochemistry 08/2014; 53(34). DOI:10.1021/bi500409n · 3.02 Impact Factor
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ABSTRACT: Invasive ductal carcinoma of the breast is the most common cancer affecting women worldwide. The marked heterogeneity of breast cancer is matched only with the heterogeneity in its associated or causative factors. Breast cancer in Saudi Arabia is apparently an early onset with many of the affected females diagnosed before they reach the age of 50 years. One possible rationale underlying this observation is that consanguinity, which is widely spread in the Saudi community, is causing the accumulation of yet undetermined cancer susceptibility mutations. Another factor could be the accumulation of epigenetic aberrations caused by the shift toward a Western-like lifestyle in the past two decades. In order to shed some light into the molecular mechanisms underlying breast cancer in the Saudi community, we identified KLOTHO (KL) as a tumor-specific methylated gene using genome-wide methylation analysis of primary breast tumors utilizing the MBD-seq approach. KL methylation was frequent as it was detected in 55.3 % of breast cancer cases from Saudi Arabia (n = 179) using MethyLight assay. Furthermore, KL is downregulated in breast tumors with its expression induced following treatment with 5-azacytidine. The involvement of KL in breast cancer led us to investigate its relationship in the context of breast cancer, with one of the protagonists of its function, fibroblast growth factor receptor 4 (FGFR4). Overexpression of FGFR4 in breast cancer is frequent in our cohort and this overexpression is associated with poor overall survival. Interestingly, FGFR4 expression is higher in the absence of KL methylation and lower when KL is methylated and presumably silenced, which is suggestive of an intricate relationship between the two factors. In conclusion, our findings further implicate "metabolic" genes or pathways in breast cancer that are disrupted by epigenetic mechanisms and could provide new avenues for understanding this disease in a new context.Tumor Biology 07/2015; DOI:10.1007/s13277-015-3733-3 · 3.61 Impact Factor
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