Structural requirements for major histocompatibility complex class II invariant chain endocytosis and lysosomal targeting.
The invariant chain (Ii) targets newly synthesized major histocompatibility complex class II complexes to a lysosome-like compartment. Previously, we demonstrated that both the cytoplasmic tail (CT) and transmembrane (TM) domains of Ii were sufficient for this targeting and that the CT contains two di-leucine signals, 3DQRDLI8 and 12EQLPML17 (Odorizzi, C. G., Trowbridge, I. S., Xue, L., Hopkins, C. R., Davis, C. D., and Collawn, J. F. (1994) J. Cell Biol. 126, 317-330). In the present study, we examined the relationship between signals required for endocytosis and those required for lysosomal targeting by analyzing Ii-transferrin receptor chimeras in quantitative transport assays. Analysis of the Ii CT signals indicates that although 3DQRDLI8 is necessary and sufficient for endocytosis, either di-leucine signal is sufficient for lysosomal targeting. Deletions between the two signals reduced endocytosis without affecting lysosomal targeting. Transplantation of the DQRDLI sequence in place of the EQLPML signal produced a chimera that trafficked normally, suggesting that this di-leucine sequence coded for an independent structural motif. Structure-function analysis of the Ii TM region showed that when Ii TM residues 11-19 and 20-29 were individually substituted for the corresponding regions in the wild-type transferrin receptor, lysosomal targeting was dramatically enhanced, whereas endocytosis remained unchanged. Our results therefore demonstrate that the structural requirements for Ii endocytosis and lysosomal targeting are different.
Kang
S
S
Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA.
Liang
L
L
Parker
C D
CD
Collawn
J F
JF
D000595:Amino Acid Sequence; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry*; D002642:Chick Embryo; D004705:Endocytosis / Q000502:physiology*; D000949:Histocompatibility Antigens Class II / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008247:Lysosomes / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011990:Receptors, Transferrin / Q000737:chemistry; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013329:Structure-Activity Relationship
D000944:Antigens, Differentiation, B-Lymphocyte; D000949:Histocompatibility Antigens Class II; D008565:Membrane Proteins; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; C045084:invariant chain; D000643:Ammonium Chloride