E50K-OPTN-induced retinal cell death involves the Rab GTPase-activating protein, TBC1D17 mediated block in autophagy

PLoS One. 2014 Apr 21;9(4):e95758. doi: 10.1371/journal.pone.0095758. eCollection 2014.

Abstract

The protein optineurin coded by OPTN gene is involved in several functions including regulation of endocytic trafficking, autophagy and signal transduction. Certain missense mutations in the gene OPTN cause normal tension glaucoma. A glaucoma-causing mutant of optineurin, E50K, induces death selectively in retinal cells. This mutant induces defective endocytic recycling of transferrin receptor by causing inactivation of Rab8 mediated by the GTPase-activating protein, TBC1D17. Here, we have explored the mechanism of E50K-induced cell death. E50K-OPTN-induced cell death was inhibited by co-expression of a catalytically inactive mutant of TBC1D17 and also by shRNA mediated knockdown of TBC1D17. Endogenous TBC1D17 colocalized with E50K-OPTN in vesicular structures. Co-expression of transferrin receptor partially protected against E50K-induced cell death. Overexpression of the E50K-OPTN but not WT-OPTN inhibited autophagy flux. Treatment of cells with rapamycin, an inducer of autophagy, reduced E50K-OPTN-induced cell death. An LC3-binding-defective mutant of E50K-OPTN showed reduced cell death, further suggesting the involvement of autophagy. TBC1D17 localized to autophagosomes and inhibited autophagy flux dependent on its catalytic activity. Knockdown of TBC1D17 rescued cells from E50K-mediated inhibition of autophagy flux. Overall, our results suggest that E50K mutant induced death of retinal cells involves impaired autophagy as well as impaired transferrin receptor function. TBC1D17, a GTPase-activating protein for Rab GTPases, plays a crucial role in E50K-induced impaired autophagy and cell death.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Autophagy / drug effects*
  • Cell Line
  • Electrophoresis, Polyacrylamide Gel
  • Eye Proteins / genetics
  • Eye Proteins / metabolism
  • Eye Proteins / pharmacology*
  • Fluorescent Antibody Technique, Indirect
  • GTPase-Activating Proteins / genetics
  • GTPase-Activating Proteins / metabolism*
  • Genetic Vectors
  • Mice
  • Microscopy, Confocal
  • rab GTP-Binding Proteins

Substances

  • Eye Proteins
  • GTPase-Activating Proteins
  • TBC1D17 protein, human
  • RAB8A protein, human
  • rab GTP-Binding Proteins

Grants and funding

This work was supported by a grant to GS from the Department of Biotechnology, Government of India [grant number BT/PR10130/BRB/10/614/2008]. GS gratefully acknowledges the Department of Science and Technology, Government of India for J C Bose National Fellowship. MLC gratefully acknowledges Department of Science and Technology for funding under the Women Scientist Scheme (SR/WOS-A/LS-28/2010). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.