Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex

Abstract

Mutations in LMAN1 (also called ERGIC-53) result in combined deficiency of factor V and factor VIII (F5F8D), an autosomal recessive bleeding disorder characterized by coordinate reduction of both clotting proteins. LMAN1 is a mannose-binding type 1 transmembrane protein localized to the endoplasmic reticulum-Golgi intermediate compartment (ERGIC; refs. 2,3), suggesting that F5F8D could result from a defect in secretion of factor V and factor VIII (ref. 4). Correctly folded proteins destined for secretion are packaged in the ER into COPII-coated vesicles, which subsequently fuse to form the ERGIC. Secretion of certain abundant proteins suggests a default pathway requiring no export signals (bulk flow; refs. 6,7). An alternative mechanism involves selective packaging of secreted proteins with the help of specific cargo receptors. The latter model would be consistent with mutations in LMAN1 causing a selective block to export of factor V and factor VIII. But approximately 30% of individuals with F5F8D have normal levels of LMAN1, suggesting that mutations in another gene may also be associated with F5F8D. Here we show that inactivating mutations in MCFD2 cause F5F8D with a phenotype indistinguishable from that caused by mutations in LMAN1. MCFD2 is localized to the ERGIC through a direct, calcium-dependent interaction with LMAN1. These findings suggest that the MCFD2-LMAN1 complex forms a specific cargo receptor for the ER-to-Golgi transport of selected proteins.

The Cargo Receptors Surf4, Endoplasmic Reticulum-Golgi Intermediate Compartment (ERGIC)-53, and p25 Are Required to Maintain the Architecture of ERGIC and Golgi

“…ERGIC-53 is a hexameric type I membrane protein in complex with the luminal EF-hand protein MCFD2 (Zhang et al, 2003;Nyfeler et al, 2006). This cargo receptor complex cycles between ER and ERGIC (Klumperman et al, 1998;Nyfeler et al, 2006), and it facilitates ER-to-ERGIC transport of the lysosomal enzymes glycoproteins cathepsin C (Vollenweider et al, 1998;Nyfeler et al, 2005), cathepsin Z (Appenzeller et al, 1999), and the blood coagulation factors V and VIII (Nichols et al, 1998;Zhang et al, 2003). MCFD2 is dispensThis article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E07-10 -0989) on February 20, 2008. able for the transport of the lysosomal enzymes, but it required for the transport of factors V and VIII (Nyfeler et al, 2006).…”

Capturing protein interactions in the secretory pathway of living cells

“…The secretion of catC is reduced if a dominant-negative ER-locked form of ERGIC-53 is expressed, but all attempts to show a direct interaction between catC and ERGIC-53 have failed (21). Recently, MCFD2 was identified as an ERGIC-53 interacting protein (22). MCFD2 is a nonglycosylated luminal protein, which contains two EF-hands and binds ERGIC-53 in a calcium-dependent manner, but its precise role in cargo transport is unknown.…”

Mutations in theMCFD2 gene and a novel mutation in theLMAN1 gene in Indian families with combined deficiency of factor V and VIII

“…One of the exceptions is the F5F8D, characterized by defects in genes encoding proteins involved in the intracellular processing of these factors: LMAN1 (previously referred to as ERGIC-53) that acts in the ERGIC compartment as a chaperone in the intracellular transport of both FV and FVIII, and MCFD2 that acts as a cofactor for LMAN1, recruiting correctly folded FV and FVIII in the endoplasmic reticulum [14,18].…”

“…Oligonucleotides and PCR conditions used to amplify the LMAN1 gene have been described in detail [13]. The MCFD2 coding region (exons 2, 3, and 4) and intron-exon boundaries were amplified by PCR using primers kindly provided by Dr. Zhang Bin from Department of Internal Medicine, University of Michigan, Ann Arbor, MI [14].…”

“…It was later reported that mutations in a gene encoding for an ER-Golgi intermediate compartment component (ERGIC-53), now known as lectin mannose binding type 1 (LMAN1), are responsible for a majority of the cases of F5F8D [11][12][13]. Subsequently, a second genetic defect in patients who were not affected by LMAN1 gene mutations, was reported [14]. The product of this gene, known as multiple coagulation factor deficiency 2 (MCFD2), is also known to be a component of ERGIC compartment and interacts with LMAN1.…”