Monocarboxylate transporter 4 promotes the migration of non‑cancerous L929 fibroblast cells by activating the IGF1/IGF1R/PIK3R3/SGK1 axis

The tumor microenvironment (TME) and Warburg effect are critical for the regulation of tumor metastasis. The monocarboxylate transporter (MCT) family members, particularly MCT4, which is encoded by the solute carrier family 16 member 3 gene, play an important role in the regulation of the TME and mediation of the Warburg effect by transporting lactate out of cancer cells. Migration and invasion are two key features of metastasis. Few studies have investigated the mechanism by which MCT4 promotes cell migration, and the suggested mechanisms by which MCT4 promotes migration vary in different tumor cell models. The purpose of the present study was to use non-cancerous cells as a research model to investigate the specific mechanism underlying the promotion of migration by MCT4. In a previous study, murine L929 cells overexpressing human MCT4 (MCT4-L929 cells) were generated and MCT4 was demonstrated to promote the migration and invasion of these non-cancerous cells. In the present study, MCT4-L929 cells and control-L929 cells were used to investigate the potential pathways and mechanisms through which MCT4 promotes cell migration. RNA sequencing analysis revealed 872 differentially expressed genes, comprising 337 and 535 upregulated and downregulated genes, respectively, in the MCT4-L929 cells. Reverse transcription-quantitative analysis and western blotting revealed that MCT4 overexpression increased the transcription and protein levels of insulin-like growth factor 1 (IGF1). In a wound healing assay, the migration of exogenous mouse IGF1-treated control-L929 cells was similar to that of MCT4-L929 cells. Additionally, the inhibition of IGF1 receptor (IGF1R) or serum/glucocorticoid regulated kinase 1 (SGK1), a downstream protein in the IGF1 and phosphoinositide 3-kinase PI3K regulatory subunit 3 (PIK3R3) pathways, in MCT4-L929 cells mitigated the cell migration-promoting effect of MCT4. These novel findings suggest that MCT4 may promote the migration of L929 fibroblast cells via activation of the IGF1/IGF1R/PIK3R3/SGK1 axis.