Increased expression of zinc transporter ZIP4, ZIP11, ZnT1, and ZnT6 predicts poor prognosis in pancreatic cancer

Abstract

Introduction: Zinc homeostasis is regulated by SLC39A/ZIP, SLC30A/ZnT, and metallothionein (MT) families in human cells. Zinc dyshomeostasis may affect or be affected by the abnormal behavior of cancer cells. Although decreased serum zinc levels are observed in patients with pancreatic adenocarcinoma (PAAD), limited information is available regarding the expression pattern and prognostic roles of zinc homeostasis-related genes in PAAD.

Objectives: The primary objective of this study was to explore the expression pattern and prognostic roles of zinc homeostasis-related genes in PAAD.

Methods: The expression pattern of 35 known zinc homeostasis-related genes in PAAD was systemically explored based on RNA-sequencing data from the Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) projects. The association between the expression levels of zinc homeostasis-related genes and survival of PAAD patients was evaluated using the Kaplan-Meier method and the log-rank test. Expressional correlation between zinc homeostasis-related genes with potential prognostic value in PAAD and normal pancreatic controls was evaluated using Pearson's correlation analysis. Functional enrichment analyses were performed to elucidate possible mechanisms for the potential prognostic and therapeutic roles of these zinc homeostasis-related genes in PAAD. Effects of ZIP11, ZnT1, or ZnT6 knockdown on the proliferation and the migration of Capan-1 pancreatic cancer cells were assessed by the CCK-8 assay and the wound healing assay respectively.

Results: We demonstrated that the expression levels of ZIP1, ZIP3, ZIP4, ZIP6, ZIP7, ZIP9, ZIP10, ZIP11, ZIP13, ZnT1, ZnT5, ZnT6, ZnT7, and ZnT9 were increased, whereas the expression levels of ZIP5, ZIP14, ZnT2, MT1 G, MT1H, and MT1X were decreased in PAAD tumors compared with normal pancreatic controls. Among these differentially-expressed genes related to zinc homeostasis, higher expression of ZIP4, ZIP11, ZnT1 or ZnT6 predicted poorer prognosis with the possible involvement of several cancer-related processes and pathways in PAAD patients. We further demonstrated that knockdown of ZIP11 attenuated Capan-1 cell proliferation with decreased activation of ERK1/2 pathway; knockdown of ZnT1 attenuated Capan-1 cell proliferation with decreased activation of ERK1/2, p38 MAPK, NF-kB, and mTOR pathways; knockdown of ZnT6 attenuated Capan-1 cell proliferation with decreased activation of ERK1/2, p38 MAPK, and NF-kB pathways.

Conclusions: Higher expression of the zinc transporter ZIP4, ZIP11, ZnT1 or ZnT6 predicted poorer prognosis in patients with PAAD. These findings provide new clues for understanding the complex relationship between zinc homeostasis and pancreatic cancer.

Keywords: Metallothioneins; Pancreatic cancer; Prognosis; Zinc homeostasis; Zinc transporters.