Ganglioside GM2 induces epithelial–mesenchymal transition (EMT) in cancer cells in a MEK/ERK/Egr1-dependent transcriptional program

Ganglioside GM2 plays a critical role in cancer cell migration and invasion, although the intricate molecular mechanism remains elusive. This study provides a novel insight on the underlying signaling pathways and their cross talk involved in GM2-mediated tumorigenesis. Transcriptome sequencing displayed differential expression of ERK (extracellular signal-regulated kinase) target genes in GM2-treated HeLa cells. Results further showed significant upregulation of the ERK target gene expression in HeLa, MCF7 and SK-RC-45 cells in the presence of exogenous GM2. Inhibition of the MAPKK (mitogen-activated protein kinase kinase), MEK pathway with small molecule inhibitor U0126 abrogated target gene expression through the reduction in the phosphorylation level of ERK1/2 and caused functional reduction of GM2-induced migration and invasion of HeLa cells. CRISPR-Cas9-mediated knockout of ERK1 and ERK2 in HeLa cells rendered the downregulation of ERK-target gene expression in response to exogenous GM2, confirming the involvement of MEK/ERK pathway in the regulation of GM2-mediated oncogenesis. Moreover, functional knockout of Egr1 (early growth response protein 1, an ERK-target) caused significant reduction in the GM2-mediated migration/invasion of HeLa cells and induction in expression of its targets, Tgfβ1 (transforming growth factor beta 1) and Pai-1 (plasminogen activator 1). Finally, Egr1 KO in HeLa cells further reduced the induction of mesenchymal marker expression in the presence of GM2, thereby confirming the role of Egr1 in GM2-induced epithelial-mesenchymal transition (EMT) process. Taken together, this study identified MEK-ERK-Egr1 axis as an important regulatory signaling in GM2-mediated EMT and pro-tumorigenic functions.