Regulation of Mct1 by cAMP-dependent internalization in rat brain endothelial cells

Abstract

In the cerebrovascular endothelium, monocarboxylic acid transporter 1 (Mct1) controls blood-brain transport of short chain monocarboxylic and keto acids, including pyruvate and lactate, to support brain energy metabolism. Mct1 function is acutely decreased in rat brain cerebrovascular endothelial cells by β-adrenergic signaling through cyclic adenosine monophosphate (cAMP); however, the mechanism for this acute reduction in transport capacity is unknown. In this report, we demonstrate that cAMP induces the dephosphorylation and internalization of Mct1 from the plasma membrane into caveolae and early endosomes in the RBE4 rat brain cerebrovascular endothelial cell line. Additionally, we provide evidence that Mct1 constitutively cycles through clathrin vesicles and recycling endosomes in a pathway that is not dependent upon cAMP signaling in these cells. Our results are important because they show for the first time the regulated and unregulated vesicular trafficking of Mct1 in cerebrovascular endothelial cells; processes which have significance for better understanding normal brain energy metabolism, and the etiology and potential therapeutic approaches to treating brain diseases, such as stroke, in which lactic acidosis is a key component

Glucose deprivation increases monocarboxylate transporter 1 (MCT1) expression and MCT1-dependent tumor cell migration

“…The effect is posttranslational (Figure 1d) and as such may involve a reduced turnover rate of both proteins known to be subject to endosome-dependent recycling. 29,30 These responses to low glucose further explain the metastatic stimulation that can be associated with the use of anti-angiogenic drugs 31 and the higher expression of MCT1 in metastatic lesions compared to primary tumors in patients. 32 Conversely, increased MCT1 expression promotes the anticancer activity of 3-bromopyruvate, 33 an alkylating agent strictly dependent on MCT1 for its uptake, 34 thus offering a new rationale for combination therapy with anti-angiogenic or antivascular drugs.…”

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

“…The Canonical Wnt/␤-Catenin Pathway Increased Expression of MCT1 on the Plasma Membrane of RBE4 Cells-Our previous study revealed an endosomal/lysosomal trafficking pattern for MCT1 that was regulated by the cAMP signaling pathway (49). Furthermore, the MCT1 protein sequence contains several peptide motifs that are highly involved in the endosomal/lysosomal sorting process, such as the dileucine (LI) motif, YXX motif, and acidic clusters (52,55,56) (Fig.…”

“…Cell Culture-RBE4 cells were cultured as described previously (48,49) in a humidified incubator at 37°C with 5% CO 2 . All experiments were conducted when the cells reached 80 -90% confluence.…”

“…Therefore, given the significance of brain endothelial MCT1 for brain functions, the critical role of the canonical Wnt/␤-catenin pathway in BBB development, and the reported interaction between Wnt and Notch pathways, we hypothesized that brain endothelial MCT1 is regulated by the canonical Wnt/␤-catenin pathway and that this regulation requires Notch signaling. To test this hypothesis, we used various agents to activate the Wnt/␤-catenin pathway or block the Notch pathway to characterize MCT1 regulation in an immortalized rat brain endothelial (RBE4) cell line as an in vitro model (9,(47)(48)(49).…”

Gene Therapy for the Nervous System: Challenges and New Strategies

“…Another process, adsorptive endocytosis recycles bound/internalized blood products back into the vessel lumen, which occurs when plasma proteins like heparin, albumin, immunoglobulin G, or wheat germ agglutinin (WGA) interact with the apical plasma membrane and bind to the cell surface or enter the cell within an endosome [163,[171][172][173]. A series of outcomes may arise from adsorptive endocytosis: (1) these endosomes may be recycled back to the apical plasma membrane, where their contents are released back into the circulation; (2) the internalized endosome may fuse with a lysosome, where the endosomal contents will be degraded preventing any unwanted, harmful blood-borne products from contacting the brain parenchyma; (3) adsorptive endocytosis can lead to delivery of materials at the basal plasma membrane and the release of endosomal contents into the CNS; and (4) endosomes may invaginate forming multivesicular bodies which then release EVs (exosomes) containing cell contents into the extracellular space [163,172,174]. Of course, the first two of these endpoints present challenges to delivering therapeutic products to the brain; however, and importantly from the standpoint of a viral vector delivery mechanism, the process of adsorptive endocytosis could offer favorable outcomes considering that this may be the primary method for which blood-borne (a.k.a.…”