Cathepsin C Propeptide Interacts with Intestinal Alkaline Phosphatase and Heat Shock Cognate Protein 70 in Human Caco-2 Cells

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  • Hirasaka Katsuya
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Tokuoka Kaori
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Nakao Reiko
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Yamada Chiharu
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Oarada Motoko
    Research Center for Pathogenic Fungi and Microbial Toxicoses, Chiba University
  • Imagawa Takahito
    The Institute for Health Sciences, Tokushima Bunri University
  • Ishidoh Kazumi
    The Institute for Health Sciences, Tokushima Bunri University
  • Okumura Yuushi
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Kishi Kyoichi
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Nikawa Takeshi
    Department of Nutritional Physiology, Institute of Health Biosciences, The University of Tokushima Graduate School

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Abstract

The oligomeric structure and the residual propeptide are distinct characteristics of cathepsin C from other members in the papain superfamily. In this study, we examined the physiological role of the cathepsin C propeptide. The stable overexpression of cathepsin C propeptide significantly decreased the activities of intestinal alkaline phosphatase (IAP) and sucrase in human Caco-2 intestinal epithelial cells, whereas it did not change the proliferation and cathepsin C activity. The overexpression of cathepsin C propeptide significantly decreased the amounts of IAP protein in differentiated Caco-2 cells, compared with the transfection of mock vector, whereas the amounts of IAP transcripts were not changed. Pulse-chase analysis confirmed that the reduction in IAP activity was due to an increase in IAP degradation, but not a decrease in IAP expression. For the mechanism of the enhanced IAP degradation, we identified proteins interacting with cathepsin C propeptide in Caco-2 cells by immunoprecipitation and mass spectrometry. Cathepsin C propeptide interacted with proteins with a molecular mass of approximately 70 kDa, including IAP and heat shock cognate protein 70. Our present results suggest that the propeptide of cathepsin C may stimulate the sorting to the lysosome, at least in part, contributing to the degradation of IAP in Caco-2 cells.<br>

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