Matrix metalloproteinase-9 (MMP-9) is a secreted glycoprotein with a major role 
in shaping the extracellular matrix and a detailed understanding of the 
secretory mechanism could help identify methods to correct diseases resulting 
from dysregulation of secretion. MMP-9 appears to follow a canonical secretory 
pathway through a quality control cycle in the endoplasmic reticulum (ER) before 
transport of the properly folded protein to the Golgi apparatus and beyond for 
secretion. Through a complementation assay, we determined that LMAN1, a 
well-studied lectin-carrier protein, interacts with a secretion-competent 
N-glycosylated MMP-9 in the ER while N-glycosylation-deficient 
secretion-compromised MMP-9 does not. In contrast, co-immunoprecipitation 
demonstrated protein interaction between LMAN1 and secretion-compromised 
N-glycosylation-deficient MMP-9. MMP-9 secretion was reduced in the LMAN1 
knockout cell line compared to control cells confirming the functional role of 
LMAN1. These observations support the role of LMAN1 as a lectin-carrier protein 
mediating efficient MMP-9 secretion.