FLCN, a novel autophagy component, interacts with GABARAP and is regulated by ULK1 phosphorylation

Autophagy. 2014 Oct 1;10(10):1749-60. doi: 10.4161/auto.29640. Epub 2014 Jul 22.

Abstract

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant condition caused by mutations in the FLCN gene and characterized by benign hair follicle tumors, pneumothorax, and renal cancer. Folliculin (FLCN), the protein product of the FLCN gene, is a poorly characterized tumor suppressor protein, currently linked to multiple cellular pathways. Autophagy maintains cellular homeostasis by removing damaged organelles and macromolecules. Although the autophagy kinase ULK1 drives autophagy, the underlying mechanisms are still being unraveled and few ULK1 substrates have been identified to date. Here, we identify that loss of FLCN moderately impairs basal autophagic flux, while re-expression of FLCN rescues autophagy. We reveal that the FLCN complex is regulated by ULK1 and elucidate 3 novel phosphorylation sites (Ser406, Ser537, and Ser542) within FLCN, which are induced by ULK1 overexpression. In addition, our findings demonstrate that FLCN interacts with a second integral component of the autophagy machinery, GABA(A) receptor-associated protein (GABARAP). The FLCN-GABARAP association is modulated by the presence of either folliculin-interacting protein (FNIP)-1 or FNIP2 and further regulated by ULK1. As observed by elevation of GABARAP, sequestome 1 (SQSTM1) and microtubule-associated protein 1 light chain 3 (MAP1LC3B) in chromophobe and clear cell tumors from a BHD patient, we found that autophagy is impaired in BHD-associated renal tumors. Consequently, this work reveals a novel facet of autophagy regulation by ULK1 and substantially contributes to our understanding of FLCN function by linking it directly to autophagy through GABARAP and ULK1.

Keywords: BHD; FLCN; GABARAP; MAP1LC3B; SQSTM1; ULK1; autophagy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Amino Acid Sequence
  • Animals
  • Apoptosis Regulatory Proteins
  • Autophagy*
  • Autophagy-Related Protein-1 Homolog
  • Birt-Hogg-Dube Syndrome / metabolism
  • Birt-Hogg-Dube Syndrome / pathology
  • Carrier Proteins / metabolism
  • Estrone / chemistry
  • Estrone / deficiency
  • Estrone / metabolism*
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Mice
  • Microtubule-Associated Proteins / metabolism*
  • Molecular Sequence Data
  • Phosphorylation
  • Protein Binding
  • Protein-Serine-Threonine Kinases / metabolism*
  • Sequestosome-1 Protein

Substances

  • Adaptor Proteins, Signal Transducing
  • Apoptosis Regulatory Proteins
  • Carrier Proteins
  • FNIP1 protein, human
  • FNIP2 protein, human
  • GABARAP protein, human
  • Intracellular Signaling Peptides and Proteins
  • Microtubule-Associated Proteins
  • SQSTM1 protein, human
  • Sequestosome-1 Protein
  • Estrone
  • Autophagy-Related Protein-1 Homolog
  • Protein-Serine-Threonine Kinases
  • ULK1 protein, human