The Roles of ZnT1 and ZnT4 in Glucose-Stimulated Zinc Secretion in Prostate Epithelial Cells

• Published in: Molecular imaging and biology Vol. 23; no. 2; pp. 230 - 240
• Main Authors: Lo, Su-Tang, Parrott, Daniel, Jordan, M. Veronica Clavijo, Joseph, Diya Binoy, Strand, Douglas, Lo, U-Ging, Lin, Ho, Darehshouri, Anza, Sherry, A. Dean
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-04-2021; Springer Nature B.V
• Subjects: Animals; Biotechnology; Cancer surgery; Carcinogenesis; Carcinogens; Cation Transport Proteins - metabolism; Cell Line; Disruption; Efflux; Electron microscopy; Epithelial cells; Epithelial Cells - metabolism; Epithelial Cells - pathology; Exposure; Flow cytometry; Fluorescence; Fluorescent indicators; Glucose; Glucose - administration & dosage; Granular materials; Homeostasis; Humans; Hyperplasia; Imaging; Intracellular; Ions; Lysosomes; Magnetic resonance imaging; Male; Markers; Medicine; Medicine & Public Health; Microscopy; mRNA; Prostate; Prostate - metabolism; Prostate - pathology; Prostate cancer; Prostatectomy; Radiology; Research Article; Secretion; Storage; Sweetening Agents - pharmacology; Tissues; Zinc; Zinc - metabolism; Prostate zinc efflux; Prostate metabolism; Intracellular zinc storage; ZnT1-mediated efflux; Prostate zinc homeostasis; ZnT1 expression; Glucose-stimulated zinc secretion; Lysosomal zinc storage; PNT1A; Zinc-responsive contrast agents
• ISSN: 1536-1632; 1860-2002
• DOI: 10.1007/s11307-020-01557-x

Purpose
We have previously demonstrated by MRI that high glucose stimulates efflux of zinc ions from the prostate. To our knowledge, this phenomena had not been reported previously and the mechanism remains unknown. Here, we report some initial observations that provide new insights into zinc processing during glucose-stimulated zinc secretion (GSZS) in the immortalized human prostate epithelial cell line, PNT1A. Additionally, we identified the subtypes of zinc-containing cells in human benign prostatic hyperplasia (BPH) tissue to further identify which cell types are likely responsible for zinc release
in vivo
.
Procedure
An intracellular fluorescence marker, FluoZin-1-AM, was used to assess the different roles of ZnT1 and ZnT4 in zinc homeostasis in wild type (WT) and mRNA knockdown PNT1A cell lines. Additionally, Bafilomycin A1 (Baf) was used to disrupt lysosomes and assess the role of lysosomal storage during GSZS. ZIMIR, an extracellular zinc-responsive fluorescent marker, was used to assess dynamic zinc efflux of WT and ZnT1 mRNA knockdown cells exposed to high glucose. Electron microscopy was used to assess intracellular zinc storage in response to high glucose and evaluate how Bafilomycin A1 affects zinc trafficking. BPH cells were harvested from transurtheral prostatectomy tissue and stained with fluorescent zinc granule indicator (ZIGIR), an intracellular zinc-responsive fluorescent marker, before being sorted for cell types using flow cytometry.
Results
Fluorescent studies demonstrate that ZnT1 is the major zinc efflux transporter in prostate epithelial cells and that loss of ZnT1
via
mRNA knockdown combined with lysosomal storage disruption results in a nearly 4-fold increase in cytosolic zinc. Knockdown of ZnT1 dramatically reduces zinc efflux during GSZS. Electron microscopy (EM) reveals that glucose stimulation significantly increases lysosomal storage of zinc; disruption of lysosomes
via
Baf or ZnT4 mRNA knockdown increases multi-vesicular body (MVB) formation and cytosolic zinc levels. In human BPH tissue, only the luminal epithelial cells contained significant amounts of zinc storage granules.
Conclusions
Exposure of prostate epithelial cells to high glucose alters zinc homeostasis by inducing efflux of zinc ions
via
ZnT1 channels and increasing lysosomal storage
via
ZnT4. Given that prostate cancer cells undergo profound metabolic changes that result in reduced levels of total zinc, understanding the complex interplay between glucose exposure and zinc homeostasis in the prostate may provide new insights into the development of prostate carcinogenesis.