Differential intracellular trafficking, secretion and endosomal localization of two IL-15 isoforms.
To analyze the intracellular trafficking of two IL-15 isoforms bearing 48- or 21-amino acid leader peptides (L), we have generated cDNA encoding the two proteins fused at the C terminus with green fluorescent protein (GFP). Confocal microscopy analyses showed that, when transfected in CHO cells, 48L IL-15/GFP was localized in the Golgi apparatus and in early endosomes, while 21L IL-15/GFP was detectable only in the cytosol. The presence of 48L IL-15/GFP in endosomes was confirmed by enzyme-linked immunosorbent assay on endosome-enriched subcellular fractions. Exogenous IL-15 was bound and taken up in endosomes by untransfected CHO cells, indicating that endosomal localization was, at least in part, related to a receptor-mediated uptake. The 48L IL-15/GFP fusion protein was efficiently secreted by COS-7 or CHO cell transfectants, while IL-15 secretion was less efficient in transfectants expressing 21L IL-15/GFP or untagged 48L or 21L IL-15. Treatment with brefeldin A or with inhibitors of N-linked glycosylation further indicated that the 48L IL-15/GFP is secreted through the endoplasmic reticulum/Golgi pathway. Our data suggest a different trafficking of the two IL-15 isoforms and multiple mechanisms controlling IL-15 secretion.
Gaggero
A
A
Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy.
Azzarone
B
B
Andrei
C
C
Mishal
Z
Z
Meazza
R
R
Zappia
E
E
Rubartelli
A
A
Ferrini
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D019556:COS Cells; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D019409:Interleukin-15 / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data
D019409:Interleukin-15; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins