A surfactant protein C precursor protein BRICHOS domain mutation causes endoplasmic reticulum stress, proteasome dysfunction, and caspase 3 activation

Am J Respir Cell Mol Biol. 2005 Jun;32(6):521-30. doi: 10.1165/rcmb.2005-0009OC. Epub 2005 Mar 18.


BRICHOS is a domain found in several proteins consisting of approximately 100 amino acids with sequence and structural similarities. Mutations in BRICHOS domain have been associated with both degenerative and proliferative diseases in several nonpulmonary organs, although the pathogenic mechanisms are largely undefined. Recently, several mutations in surfactant protein C (SP-C) mapping to the BRICHOS domain located within the proprotein (proSP-C) have been linked to interstitial lung diseases. In vitro expression of one of these BRICHOS mutants, the exon 4 deletion (hSP-CDeltaexon4), promotes a dominant-negative perinuclear aggregation of the protein. The present study characterizes the trafficking behavior and pathogenic consequences resulting from hSP-CDeltaexon4 expression. Time-lapse and co-localization microscopy studies demonstrated enhanced green fluorescent protein (EGFP)/hSP-CDeltaexon4 expression in calnexin-positive (endoplasmic reticulum [ER]) compartment with subsequent time- and concentration-dependent development of ubiquitinated perinuclear inclusion bodies followed by apoptosis. Compared with controls, EGFP/hSP-CDeltaexon4 promoted upregulation of multiple ER stress species, activated caspase 3, and induced annexin V binding. Furthermore, in GFP-u cells, hSP-CDeltaexon4 directly inhibited proteasome activity. These results support a model whereby proSP-C BRICHOS mutations induce a dynamic toxic gain-of-function, causing apoptotic cell death both by early ER accumulation leading to an exaggerated unfolded protein response and by enhanced deposition of cellular aggregates associated with proteasome dysfunction.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Apoptosis / physiology
  • Caspase 3
  • Caspases / metabolism*
  • Cell Line
  • Endoplasmic Reticulum / metabolism*
  • Gene Expression
  • Humans
  • Kidney / cytology
  • Molecular Sequence Data
  • Mutagenesis
  • Proteasome Endopeptidase Complex / metabolism*
  • Protein Precursors / chemistry
  • Protein Precursors / genetics
  • Protein Precursors / metabolism
  • Protein Structure, Tertiary
  • Protein Transport
  • Pulmonary Surfactant-Associated Protein C / chemistry*
  • Pulmonary Surfactant-Associated Protein C / genetics*
  • Pulmonary Surfactant-Associated Protein C / metabolism
  • Respiratory Mucosa / cytology
  • Respiratory Mucosa / metabolism
  • Ubiquitin / metabolism


  • Protein Precursors
  • Pulmonary Surfactant-Associated Protein C
  • Ubiquitin
  • CASP3 protein, human
  • Caspase 3
  • Caspases
  • Proteasome Endopeptidase Complex