ABSTRACT
Mutations in the genes for peripheral myelin protein-22 (PMP22) and myelin protein zero (P0) cause human hereditary neuropathies with varying clinical and pathological phenotypes. In this study, we examine the effects of representative disease-causing mutations on the subcellular distribution of their corresponding PMP22- and P0-enhanced green fluorescent protein (EGFP) fusion proteins. In transiently transfected HeLa and 293 cells, we find that wild-type P0-EGFP and PMP22-EGFP are efficiently synthesized and transported through the secretory pathway to the plasma membrane. The P0-EGFP and PMP22-EGFP mutants can be classified into several groups: those that are transported to the plasma membrane as in the majority of P0 mutants; those that are retained in the endoplasmic reticulum as in the majority of PMP22 mutants; and those that are a mixture of the two. In addition, several of these disease-causing mutations are associated with the development of abnormal intracellular cytoplasmic structures that we have previously identified as either intracellular myelin figures or aggresomes. Our studies indicate that different types of PMP22 and P0 mutations are associated with specific intracellular chaperone proteins, including calnexin and BiP, and that these associations can be altered by glycosylation. These findings indicate that the various P0 and PMP22 mutants may exert their pathogenic effects in different subcellular compartments and by different mechanisms in the mammalian cell.
Subject(s)
Charcot-Marie-Tooth Disease/genetics , Charcot-Marie-Tooth Disease/metabolism , Myelin P0 Protein/metabolism , Myelin Proteins/metabolism , Myelin Sheath/genetics , Peripheral Nerves/metabolism , Schwann Cells/metabolism , Cell Compartmentation/genetics , Cell Membrane/genetics , Cell Membrane/metabolism , Endoplasmic Reticulum/genetics , Endoplasmic Reticulum/metabolism , HeLa Cells , Humans , Molecular Chaperones/metabolism , Mutation/genetics , Myelin P0 Protein/genetics , Myelin Proteins/genetics , Myelin Sheath/metabolism , Peripheral Nerves/pathology , Phenotype , Protein Transport/genetics , Recombinant Fusion Proteins , Schwann Cells/pathologyABSTRACT
The gain of function phenotypes exhibited by the heterozygous Tr, Tr-J, and CMT1A mutations indicate that these mutations interfere with more than the function of a single PMP22 allele. The identification of proteins that interact with PMP22 and that are sensitive both to stoichiometry and the effects of the mutations could provide important leads to a unified hypothesis to explain the riddle of the PMP22-related neuropathies.
