The Mycotoxin Patulin Decreases Expression of Density-Enhanced Phosphatase-1 by Down-Regulating PPARγ in Human Colon Cancer Cells

The Mycotoxin Patulin Decreases Expression of Density-Enhanced Phosphatase-1 by Down-Regulating PPARγ in Human Colon Cancer Cells

AKIHIRO KATSUYAMA,¹ TOMOMI KONNO,¹ SHUJI SHIMOYAMA² and HIDEAKI KIKUCHI^1,2

¹Department of Biochemistry and Molecular Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Aomori, Japan
²Science of Bioresources, The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate, Japan

Patulin is a mycotoxin that is found mainly in apple products and causes symptoms such as bleeding from the digestive tract and diarrhea. Efforts to elucidate the mechanism of its toxicity have focused on protein tyrosine phosphatases (PTPs), which regulate the function of tight junctions (TJs) in colon epithelial cells. Patulin reacts with the conserved cysteine residues in the catalytic domains of PTP isoforms. Treatment of Caco-2 human colon cancer cells, used as a colon epithelial model, with 50 μM patulin decreased the level of density-enhanced phosphatase-1 (DEP-1) protein to 30% of the control level after 6 h. The level of DEP-1 mRNA was also decreased during 24 h after treatment with patulin. Moreover, knockdown of DEP-1 increased the level of phosphorylated claudin-4. Destruction of TJs by patulin treatment was observed by immunostaining with an antibody against zonula occludens (ZO)-1. To better understand the mechanistic basis of the decrease in DEP-1 mRNA levels, we searched for a cis-element upstream of the DEP-1 gene and found an element responsive to the peroxisome proliferator-activated receptor gamma (PPARγ) protein. Using a PPARγ-specific antibody, we showed a decrease in PPARγ abundance to 42% of the control level within 6 h after treatment with patulin. PPARγ has four cysteine residues that are involved in zinc finger formation. Our data suggest that DEP-1 affects TJ function and that PPARγ might control DEP-1 expression. Therefore, the toxicity of patulin to cellular functions might be attributable to its ability to down-regulate the expression of DEP-1 and PPARγ.

keywords —— claudin-4; density-enhanced phosphatase-1; patulin; peroxisome proliferator-activated receptor gamma; tight junction

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Tohoku J. Exp. Med., 2014, 233, 265-274

Correspondence: Hideaki Kikuchi, Department of Biochemistry and Molecular Biology, Faculty of Agriculture and Life Science, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.

e-mail: hkikuchi@cc.hirosaki-u.ac.jp