Objective To explore the mechanism by which zinc-regulated transporters, iron-regulated transporter-likeprotein 4 (ZIP4) regulates glycolysis and its impact on tumor progression in cholangiocarcinoma (CCA), providing a theoretical basis for targeted therapy of CCA.

Methods ZIP4 expression in CCA was analyzed using the GEPIA database. Immuno-histochemistry (IHC) was used to detect ZIP4 expression in 20 paired CCA and adjacent non-tumor tissues. Stable ZIP4-overexpressing CCA cell lines (ZIP4-OE) were established. Gene set enrichment analysis was used to screen differentially expressed genes and pathways in ZIP-OE CCA cells. ZIP4, N-myc proto-oncogene protein (MYCN), and histone-lysine N-methyltransferase 2E (KMT2E) were knocked down using small interfering RNAs (siRNAs). The expression of glycolysis-related gene (glucose transporter 1 Glut1, hexokinase 2 HK2, and lactate dehydrogenase A LDHA) was measured by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Glycolytic activity was assessed by measuring the extracellular acidification rate (ECAR). Cell proliferation was evaluated using colony formation assays, and cell migration was assessed using Transwell assays. A xenograft mouse model was constructed to examine CCA tumor growth. Protein levels of ZIP4, KMT2E, H3K4me3 (tri-methylation of lysine 4 on histone H3), and MYCN were detected by Western blotting.

Results GEPIA database analysis and IHC results confirmed significantly higher ZIP4 expression levels in CCA tissues compared to adjacent non-tumor tissues (P＜0.05). Compared to the control group, the ZIP4-OE group exhibited a significantly increased ECAR, along with significantly enhanced proliferation and migration abilities (P＜0.01). Conversely, knockdown of ZIP4 suppressed CCA cells proliferation and migration. GEPIA analysis indicated that ZIP4 upregulates the transcription of oncogene MYCN, as well as glycolysis-related genes. Knockdown of MYCN abolished the ZIP4 overexpression-induced upregulation of Glut1, HK2, and LDHA gene transcription, reduced glycolysis, and significantly inhibited CCA cell proliferation and migration (P＜0.05). Mechanistic studies demonstrated that ZIP4 increases H3K4me3 level via KMT2E, leading to MYCN transcription. Knockdown of KMT2E in CCA cells suppressed the ZIP4 overexpression-induced enhancement in H3K4me3 modification, resulting in MYCN downregulation and significantly reduced CCA cells proliferation and migration (P＜0.05).

Conclusions ZIP4 upregulates H3K4me3 modification through KMT2E, which recruits transcription factors to activate the transcription of MYCN. This subsequently enhances cellular glycolysis and promotes the proliferation and migration of CCA cells.