RESUMO
Often described as a mediator of cell cycle arrest or as a pro-apoptotic factor in stressful conditions, the MAP3K ZAK (Sterile alpha motif and leucine zipper-containing kinase) has also been proven to positively regulate epidermal growth factor receptor (EGFR) and WNT signaling pathways, cancer cell proliferation and cellular neoplastic transformation. Here, we show that both isoforms of ZAK, ZAK-α and ZAK-ß are key factors in cancer cell migration. While ZAK depletion reduced cell motility of HeLa and HCT116 cells, its overexpression triggered the activation of all three mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK), c-JUN N-terminal kinase (JNK) and p38, as well as an increase in cell motion. On the contrary, the kinase-dead mutants, ZAK-α K45M and ZAK-ß K45M, were not able to provoke such events, and instead exerted a dominant-negative effect on MAPK activation and cell migration. Pharmacological inhibition of ZAK by nilotinib, preventing ZAK-autophosphorylation and thereby auto-activation, led to the same results. Activated by epidermal growth factor (EGF), we further showed that ZAK constitutes an essential element of the EGF/ERK-dependent cell migration pathway. Using public transcriptomic databases and tissue microarrays, we finally established that, as strong factors of the EGFR signaling pathway, ZAK-α and/or ZAK-ß transcripts and protein(s) are frequently upregulated in colorectal adenoma and carcinoma patients. Notably, gene set enrichment analysis disclosed a significant correlation between ZAK+ colorectal premalignant lesions and gene sets belonging to the MAPK/ERK and motility-related signaling pathways of the reactome database, strongly suggesting that ZAK induces such pro-tumoral reaction cascades in human cancers.
