S. Pareek et al., NEURON PROMOTE THE TRANSLOCATION OF PERIPHERAL MYELIN PROTEIN-22 INTOMYELIN, The Journal of neuroscience, 17(20), 1997, pp. 7754-7762
Schwann cells express low levels of myelin proteins in the absence of
neurons. When Schwann cells and neurons are cultured together the prod
uction of myelin proteins is elevated, and myelin is formed. For perip
heral myelin protein 22 (PMP22), the exact amount of protein produced
is critical, because peripheral neuropathies result from its underexpr
ession or overexpression. In this study we examined the effect of neur
ons on Schwann cell PMP22 production in culture and in peripheral nerv
e using metabolic labeling and pulse-chase studies as well as immunocy
tochemistry. Most of the newly synthesized PMP22 in Schwann cells is r
apidly degraded in the endoplasmic reticulum. Only a small proportion
of the total PMP22 acquires complex glycosylation and accumulates in t
he Golgi compartment. This material is translocated to the Schwann cel
l membrane in detectable amounts only when axonal contact and myelinat
ion occur. Myelination does not, however, alter the rapid turnover of
PMP22 in Schwann cells. PMP22 may therefore be a unique myelin protein
in that axonal contact promotes its insertion into the Schwann cell m
embrane and myelin without altering its rapid turnover rate within the
cell.