ASSEMBLED IGG MOLECULES ARE EXPORTED FROM THE ENDOPLASMIC-RETICULUM IN MYELOMA CELLS DESPITE THE RETENTION SIGNAL SEKDEL

The KDEL retention signal, when added at the C-terminal of the constan t region of light and heavy chains of immunoglobulins is able to effic iently retain assembled immunoglobulins only in cells of nonlymphoid o rigin. In transfected myeloma cells the wild type and the KDEL-Ig muta nts are secreted with the same efficiency. This phenomenon is not due to a proteolytic cleavage of the KDEL signal nor to a lack of intermol ecular disulfide bond formation and is not due to an impaired recognit ion of the KDEL signal in myeloma cells. Thus, the constitutive secret ion of assembled immunoglobulins, currently considered to follow a def ault process, appears to be regulated by a mechanism that is able to o vercome an efficient ER retention system. (C) 1998 Academic Press.