Autophagy is induced by raptor degradation via the ubiquitin/proteasome system in granular corneal dystrophy type 2

Seung Il Choi, Yong Sun Maeng, Kyu Seo Kim, Tae Im Kim, Eung Kweon Kim

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18 Citations (Scopus)

Abstract

Granular corneal dystrophy type 2 (GCD2) is an autosomal dominant disorder that is caused by a point mutation in transforming growth factor-β-induced gene-h3 (TGFBI), which encodes transforming growth factor-β-induced protein (TGFBIp). Recently, we found that the autophagic clearance of mutant-TGFBIp is delayed in GCD2 corneal fibroblasts; however, any potential correlation between mutant-TGFBIp turnover and autophagy-lysosome pathway remains unknown. Here, we report that mutant-TGFBIp is accumulated and that autophagy, a key clearance pathway for mutant-TGFBIp, is induced in primary cultured GCD2 homozygous (HO) and wild-type (WT) corneal fibroblasts that express exogenously introduced mutant-TGFBIp. Mutant-TGFBI colocalized with LC3-enriched cytosolic vesicles and cathepsin D in primary cultured GCD2 corneal fibroblasts. We also observed reduced levels of raptor (regulatory-Associated protein of the mammalian target of rapamycin [mTOR]) in GCD2 corneal fibroblasts and WT corneal fibroblasts expressing mutant-TGFBIp. Strikingly, treatment with MG132, a ubiquitin/proteasome system inhibitor, significantly increased the levels of both total and ubiquitinated raptor in GCD2 corneal fibroblasts. The levels of the autophagy marker LC3-II were also increased in WT corneal fibroblasts that were treated with shRNA against raptor. However, mutant-TGFBIp accumulated in autophagosomes or/and lysosomes in spite of the significant activation of basal autophagy in GCD2 corneal fibroblasts. These results suggest that an insufficient autophagy-lysosome pathway might be responsible for the intracellular accumulation of mutant-TGFBIp during the pathogenesis of GCD2.

Original languageEnglish
Pages (from-to)1505-1511
Number of pages7
JournalBiochemical and Biophysical Research Communications
Volume450
Issue number4
DOIs
Publication statusPublished - 2014 Aug 8

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All Science Journal Classification (ASJC) codes

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology

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