The propeptide of macrophage inhibitory cytokine (MIC-1), a TGF-beta superfamily member, acts as a quality control determinant for correctly folded MIC-1.
Macrophage inhibitory cytokine (MIC-1), a divergent member of the transforming growth factor-beta (TGF-beta) superfamily and activation associated cytokine, is secreted as a 28 kDa dimer. To understand its secretion, we examined its processing in MIC-1-transfected Chinese hamster ovary cells. Mature MIC-1 dimer arises post-endoplasmic reticulum (ER) by proteolytic cleavage of dimeric pro-MIC-1 precursor at a furin-like site. Unlike previously characterized TGF-beta superfamily members, MIC-1 dimers are also secreted in constructs lacking the propeptide. A clue to the function of the propeptide came from the observation that a range of proteasome inhibitors, including lactacystin and MG132, cause major increases in levels of undimerized pro-MIC-1 precursor. There was no effect of proteasome inhibitors on cells expressing mature MIC-1 without the propeptide, suggesting that the propeptide can signal misfolding of MIC-1, leading to proteasomal degradation. Deletion mutagenesis showed the N-terminal 28 amino acids of the propeptide are necessary for proteasomal degradation. This is the first demonstration, to our knowledge, of a quality control function in a propeptide domain of a secretory protein and represents an additional mechanism to ensure correct folding of proteins leaving the ER.
Bauskin
A R
AR
Centre for Immunology, St Vincent's Hospital and University of New South Wales, Sydney, NSW 2010, Australia. a.bauskin@cfi.unsw.edu.au
Zhang
H P
HP
Fairlie
W D
WD
He
X Y
XY
Russell
P K
PK
Moore
A G
AG
Brown
D A
DA
Stanley
K K
KK
Breit
S N
SN
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D016207:Cytokines / Q000737:chemistry* / Q000378:metabolism; D006031:Glycosylation; D055436:Growth Differentiation Factor 15; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D016212:Transforming Growth Factor beta / Q000737:chemistry* / Q000378:metabolism
D016207:Cytokines; D055436:Growth Differentiation Factor 15; D009097:Multienzyme Complexes; D016212:Transforming Growth Factor beta; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex