Regulation of Monocarboxylic Acid Transporter 1 Trafficking by the Canonical Wnt/β-Catenin Pathway in Rat Brain Endothelial Cells Requires Cross-talk with Notch Signaling

Zejian Liu,Mary Sneve,Thomas A. Haroldson,Jeffrey P. Smith,Lester R. Drewes

doi:10.1074/jbc.m115.710277

Abstract

The transport of monocarboxylate fuels such as lactate, pyruvate, and ketone bodies across brain endothelial cells is mediated by monocarboxylic acid transporter 1 (MCT1). Although the canonical Wnt/β-catenin pathway is required for rodent blood-brain barrier development and for the expression of associated nutrient transporters, the role of this pathway in the regulation of brain endothelial MCT1 is unknown. Here we report expression of nine members of the frizzled receptor family by the RBE4 rat brain endothelial cell line. Furthermore, activation of the canonical Wnt/β-catenin pathway in RBE4 cells via nuclear β-catenin signaling with LiCl does not alter brain endothelialMct1mRNA but increases the amount of MCT1 transporter protein. Plasma membrane biotinylation studies and confocal microscopic examination of mCherry-tagged MCT1 indicate that increased transporter results from reduced MCT1 trafficking from the plasma membrane via the endosomal/lysosomal pathway and is facilitated by decreased MCT1 ubiquitination following LiCl treatment. Inhibition of the Notch pathway by the γ-secretase inhibitorN-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycinet-butyl ester negated the up-regulation of MCT1 by LiCl, demonstrating a cross-talk between the canonical Wnt/β-catenin and Notch pathways. Our results are important because they show, for the first time, the regulation of MCT1 in cerebrovascular endothelial cells by the multifunctional canonical Wnt/β-catenin and Notch signaling pathways.

Highlights

Monocarboxylic acid transporter 1 (MCT1)-dependent lactate transport is critical for various biological processes, including muscle and colonocyte metabolism, kidney glomerulus function, immune suppression, tumor progression, long-term
In this study, we report that the canonical Wnt/␤-catenin signaling pathway up-regulates MCT1 protein expression on the plasma membrane of RBE4 cells by a mechanism that
Our discovery is consistent with recent studies showing a similar regulatory mechanism that controls MCT1 function by cAMP-dependent signaling in RBE4 cells [49, 52]

Summary

Introduction

Monocarboxylic acid transporter 1 (MCT1)-dependent lactate transport is critical for various biological processes, including muscle and colonocyte metabolism, kidney glomerulus function, immune suppression, tumor progression, long-term. Activation of the canonical Wnt/␤-catenin pathway in RBE4 cells via nuclear ␤-catenin signaling with LiCl does not alter brain endothelial Mct1 mRNA but increases the amount of MCT1 transporter protein. Our results demonstrated the specific requirement of nuclear ␤-catenin-mediated signaling transduction in the observed upregulation of MCT1 by LiCl. treatment of RBE4 cells for 48 h with 5 ␮M SB216763, another commercial GSK-3 ␤ inhibitor, increased MCT1 protein expression by 35% (Fig. 1F).

Results

Conclusion