Abstract
β-catenin plays an important role as regulatory hub in several cellular processes including cell adhesion, metabolism, and epithelial mesenchymal transition. This is mainly achieved by its dual role as structural component of cadherin-based adherens junctions, and as a key nuclear effector of the Wnt pathway. For this dual role, different classes of proteins are differentially regulated via β-catenin dependent mechanisms. Here, we applied a liquid chromatography-mass spectrometry (LC-MS/MS) approach to identify proteins modulated after β-catenin knockdown in the breast cancer cell line MCF-7. We used a label free analysis to compare trypsin-digested proteins from CTR (shCTR) and β-catenin knockout cells (shβcat). This led to the identification of 98 differentially expressed proteins, 53 of them were up-regulated and 45 down-regulated. Loss of β-catenin induced morphological changes and a significant modulation of the expression levels of proteins associated with primary metabolic processes. In detail, proteins involved in carbohydrate metabolism and tricarboxylic acid cycle were found to be down-regulated, whereas proteins associated to lipid metabolism were found up-regulated in shβcat compared to shCTR. A loss of mitochondrial mass and membrane potential was also assessed by fluorescent probes in shβcat cells with respect to the controls. These data are consistent with the reduced expression of transcriptional factors regulating mitochondrial biogenesis detected in shβcat cells. β-catenin driven metabolic reprogramming resulted also in a significant modulation of lipogenic enzyme expression and activity. Compared to controls, β-catenin knockout cells showed increased incorporation of [1-14C]acetate and decreased utilization of [U-14C]glucose for fatty acid synthesis. Our data highlight a role of β-catenin in the regulation of metabolism and energy homeostasis in breast cancer cells.
Highlights
We investigated the expression of peroxisome proliferator-activated receptor coactivator-1α (PGC-1α), a key transcriptional regulator of cellular energy metabolism and mitochondrial biogenesis (Liang and Ward, 2006)
We found a reduced expression of CAV1 and CD36 genes in shβcat, this may result in a reduction of the uptake of lipids with a consequent lower synthesis of triacylglycerol and reduced mobilization of monoacylglycerols by monoacyl glycerol lipase (MGL), whose expression resulted down-regulated after βcat knockdown
Cellular functions and processes regulated by β-catenin appear to be closely related to a specific proteogenomics landscape. This is true for colon cancer cells where a cell-specific protein networks modulate Wnt signaling (Song et al, 2014), and for breast cancer where alterations of β-catenin levels drive the progression of the basal category of ErbB2-positive breast cancer (Tung et al, 2017)
Summary
Β-catenin is a multifunctional protein localized at multiple subcellular regions, including adherents junctions, cytoplasm and/or nucleus. β-catenin plays an essential role in the maintenance of adult tissue homeostasis. Suppression of Wnt/β-catenin signaling results in reduced migration in vitro and in vivo, reduced tumor growth, and reduced expression of stem cell markers (Jang et al, 2015) Overall, these findings depict a key role of β-catenin in the regulation of tumor initiation and progression, stemness, proliferation and invasion. Analysis of KEGG pathways/functions revealed that up- or down-regulations of β-catenin lead to altered regulation of actin cytoskeleton, insulin signaling and metabolism (Herbst et al, 2014), though the molecular mechanisms underlying these associations appear still unclear. In this scenario, the complexity of the β-catenin network can be fully addressed by experimental approaches that allow managing thousands of molecules simultaneously. We gained insight into the mechanisms that link β-catenin to modifications of metabolic proteins, and we described in our model a metabolic reprogramming accompanied by alterations in mitochondrial function and lipid metabolism
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