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 and12EQLPML17 (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 although3DQRDLI8 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. 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 and12EQLPML17 (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 although3DQRDLI8 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. Major histocompatibility complex class II molecules are cell surface molecules that function to bind peptide antigens and present them to CD4+ helper T cells. Newly synthesized major histocompatibility complex class II αβ complexes are targeted to lysosome-like compartments (1Peters P.J. Neefjes J.J. Oorschot V. Ploegh H.L. Geuze H.J. Nature. 1991; 349: 669-676Crossref PubMed Scopus (554) Google Scholar, 2Calafat J. Nijenhuis M. Janssen H. Tulp A. Dusseljee S. Wubbolts R. Neefjes J. J. Cell Biol. 1994; 126: 967-977Crossref PubMed Scopus (83) Google Scholar, 3Fernandez-Borja M. Verwoerd D. Sanderson F. Aerts H. Trowsdale J. Tulp A. Neefjes J. Int. Immunol. 1996; 8: 625-640Crossref PubMed Scopus (40) Google Scholar) by the invariant chain (Ii) 1The abbreviations used are: Iihuman invariant chainCEFchicken embryo fibroblastTftransferrinTRtransferrin receptorTMtransmembrane regionCTcytoplasmic tailINinternalizedSURsurface-associatedWTwild-type.1The abbreviations used are: Iihuman invariant chainCEFchicken embryo fibroblastTftransferrinTRtransferrin receptorTMtransmembrane regionCTcytoplasmic tailINinternalizedSURsurface-associatedWTwild-type. (reviewed in Ref. 4Cresswell P. Annu. Rev. Immunol. 1994; 12: 259-293Crossref PubMed Google Scholar). Upon arrival, Ii is degraded, and αβ chains acquire peptide antigens (5Blum J.S. Cresswell P. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 3975-3979Crossref PubMed Scopus (320) Google Scholar, 6Lotteau V. Teyton L. Peleraux A. Nilsson T. Karlsson L. Schmid S.L. Quaranta V. Peterson P.A. Nature. 1990; 348: 600-605Crossref PubMed Scopus (444) Google Scholar, 7Lamb C.A. Yewdell J.W. Bennick J.R. Cresswell P. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 5998-6002Crossref PubMed Scopus (129) Google Scholar, 8Pieters J. Horstmann H. Bakke O. Griffiths G. Lipp J. J. Cell Biol. 1991; 115: 1213-1223Crossref PubMed Scopus Google Scholar, P. C. Yewdell J. Bakke O. J. PubMed Scopus Google Scholar, J.R. Cresswell P. J. Immunol. Google Scholar, P. M. G. Geuze H.J. Ploegh H.L. J. PubMed Scopus Google Scholar). complexes are to the lysosomal the P. M. G. Geuze H.J. Ploegh H.L. J. PubMed Scopus Google Scholar) the cell are V. Teyton L. Peleraux A. Nilsson T. Karlsson L. Schmid S.L. Quaranta V. Peterson P.A. Nature. 1990; 348: 600-605Crossref PubMed Scopus (444) Google Scholar, P. P. Lipp J. G. J. Biol. 1990; PubMed Google Scholar, P.A. Bakke O. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). and are for of class II to a V. Teyton L. Peleraux A. Nilsson T. Karlsson L. Schmid S.L. Quaranta V. Peterson P.A. Nature. 1990; 348: 600-605Crossref PubMed Scopus (444) Google Scholar, P. M. G. Geuze H.J. Ploegh H.L. J. PubMed Scopus Google Scholar, P.A. Bakke O. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, L. J. Cell Biol. 1994; 126: PubMed Scopus Google for the that Ii is to the of the in the Ii cytoplasmic tail was the cytoplasmic tail J. J. Immunol. Google Scholar). Newly synthesized class II molecules this chimera are to the cell surface and Ii is and class II is J. J. Immunol. Google Scholar). that the cytoplasmic contains a signal M. V. S. 1990; PubMed Scopus Google Scholar, Cell 1990; PubMed Scopus Google is sufficient for of the class II complexes to a lysosome-like and that is Ii cytoplasmic tail targeting signals chimeras T. M. Bakke O. J. Cell Sci. 1994; PubMed Google Scholar) and chimeras L. J. Cell Biol. 1994; 126: PubMed Scopus Google and di-leucine signals were in the and the receptor and to for lysosomal and F. PubMed Scopus Google Scholar, S. J. Biol. PubMed Google Scholar). of two that are by residues F. PubMed Scopus Google Scholar). residues to the are for L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar, L. Teyton L. Peterson P.A. J. Biol. PubMed Scopus Google Scholar, A. G. Bakke O. J. Biol. PubMed Scopus Google suggesting that Ii di-leucine signals those in the and of structural the Ii cytoplasmic tail that the signal a whereas the is a of a A. G. Bakke O. J. Biol. PubMed Scopus Google Scholar). signals to M. V. S. 1990; PubMed Scopus Google Scholar, A. 1991; PubMed Scopus Google Scholar, C. C. 1991; PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google and to independent structural signal for J. 1991; PubMed Scopus Google Scholar, M. S. J. Biol. PubMed Google Scholar, R. J. J. J. Cell Biol. 1996; PubMed Scopus Google Scholar). signals independent structural is and signals are is to by L. H. J.S. J. Cell Biol. 1996; PubMed Scopus Google Ii is a of wild-type and Ii demonstrate that two wild-type Ii molecules are targeted in J. J. Cell Biol. PubMed Scopus Google that molecules two Ii cytoplasmic the the structural requirements for Ii to the Ii cytoplasmic tail to the transmembrane and domains of the wild-type Ii T. M. Bakke O. J. Cell Sci. 1994; PubMed Google of this was to signals those required for to the of the examined two regions of the Ii that to for targeting to the lysosomal the cytoplasmic tail (CT) and the transmembrane region (TM) L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar). of the that we transferrin and lysosomal targeting by the of the chimeras L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar). and analysis of Ii CT that endocytosis, lysosomal and Analysis of the Ii TM region that two regions the TM were sufficient to lysosomal targeting a without affecting The results demonstrate that the structural requirements for Ii endocytosis and lysosomal targeting are the analyzing chimeras in quantitative we that the two cytoplasmic tail di-leucine signals to that the is for endocytosis and lysosomal whereas the to for lysosomal targeting The between the two signals is by the that of the to in a in whereas of the to a signal to required for the in a in the of chimera that the cell In to the and both di-leucine signals to lysosomal was both in to for L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar, T. M. Bakke O. J. Cell Sci. 1994; PubMed Google Scholar, L. Teyton L. Peterson P.A. J. Biol. PubMed Scopus Google Scholar, G. J. Biol. PubMed Scopus Google Scholar, A. M. Bakke O. J. Cell Sci. PubMed Google were of to lysosomal targeting of that U. J. Cell Biol. PubMed Scopus Google Scholar, I. H. P. J. Cell Biol. PubMed Scopus Google Scholar, I. H. J. Cell Biol. PubMed Scopus Google Scholar, P. V. M. A. I. J. PubMed Scopus Google Scholar, A. S. A. J. Biol. PubMed Google the J. Cell Biol. PubMed Scopus Google Scholar, J. Cell Biol. PubMed Scopus Google Scholar). In the present study, we transferrin a that the endocytosis of the C. J. Cell Biol. PubMed Scopus Google Scholar). to signals lysosomal signals we the of the chimeras a J.J. J. Biol. 1988; PubMed Scopus (40) Google for of are the that of the cell surface L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar) that is is the we the lysosomal targeting was the that the chimera was was The of this chimera was the the was that the for lysosomal targeting is for this by J. J. Biol. 1996; PubMed Scopus Google demonstrated that targeting to the of the of in the J. J. Biol. 1996; PubMed Scopus Google Scholar). demonstrated that was between and that the signal for two were the chimera dramatically the between two a of the Ii without lysosomal targeting and the receptor the that regions of two molecules are required for endocytosis and lysosomal targeting H. J. Cell Biol. 1994; PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google Scholar). that endocytosis of cell surface molecules is a for lysosomal the of chimeras that the cell we that the signal for is for the of that di-leucine signals the cell surface F. PubMed Scopus Google Scholar, S. M. J. Biol. 1994; PubMed Google Scholar) and the S. J. Biol. PubMed Google Scholar, H.J. J. P. J. Biol. PubMed Google Scholar). the two is that the of the signal the tail is J. C. J. 1994; PubMed Scopus Google Scholar). J. C. J. 1994; PubMed Scopus Google Scholar) that di-leucine signals are the to the whereas di-leucine signals for and lysosomal targeting. this the Ii cytoplasmic tail is a the is Quaranta V. J. Immunol. Google Scholar). this the signal to required for both the that the of the signal and is of the of this was to the two di-leucine signals in Ii were was we the were this we substituted the sequence the for the Our results demonstrated that this either targeting suggesting that was the results that di-leucine signals, signals, for the signals in a of both targeting The for this the a peptide corresponding to the Ii cytoplasmic that the residues a whereas the signal is a of a A. G. Bakke O. J. Biol. PubMed Scopus Google Scholar). a of the Ii cytoplasmic tail the for of residues 20–29 of the Ii cytoplasmic tail that of residues were required for endocytosis lysosomal targeting. The residues was either of the two this suggesting two of the residues were required for lysosomal the of the two di-leucine regions to the transmembrane region lysosomal targeting. is that a of a signal for lysosomal targeting signals J. A. D. S. J. Cell Biol. 1996; PubMed Scopus Google Scholar). the region of Ii to by the in the in G. J. Biol. PubMed Scopus Google Scholar). Our that this region is necessary for in the of this chimera that the cell surface were the the wild-type Ii analysis of the Ii transmembrane indicates that two regions this residues 11–19 and residues are sufficient to the to lysosomal without affecting the The structural regions that this are demonstrated that the chimeras were that of them were showed that the of the chimeras the The signals to in transmembrane regions are signals (reviewed in Ref. Cell Biol. PubMed Scopus Google Scholar). the of signals to the of residues and when in the of J. Cell Biol. 1991; 115: PubMed Scopus Google Scholar, A. M. Biol. PubMed Scopus Google Scholar). The Ii an of are of the are in the of the A. M. Biol. PubMed Scopus Google Scholar). The is that residues in of complexes the Cell Biol. PubMed Scopus Google Scholar). of the TM chimeras in a the in a of the of the complex of the major histocompatibility complex class II is the of a signal the transmembrane is the between the chains and the Ii is in the and of the Ii is that the transmembrane signal the of Ii are and the chains that the of Ii in the of the chimera when the Ii transmembrane region is L. J. Cell Biol. 1994; 126: PubMed Scopus Google the results that the of the di-leucine signal the Ii cytoplasmic tail is by the of the that chimeras Ii cytoplasmic tail transmembrane signals are to the lysosomal compartment. the required for in the to is signals the two Major histocompatibility complex class II molecules are cell surface molecules that function to bind peptide antigens and present them to CD4+ helper T cells. Newly synthesized major histocompatibility complex class II αβ complexes are targeted to lysosome-like compartments (1Peters P.J. Neefjes J.J. Oorschot V. Ploegh H.L. Geuze H.J. Nature. 1991; 349: 669-676Crossref PubMed Scopus (554) Google Scholar, 2Calafat J. Nijenhuis M. Janssen H. Tulp A. Dusseljee S. Wubbolts R. Neefjes J. J. Cell Biol. 1994; 126: 967-977Crossref PubMed Scopus (83) Google Scholar, 3Fernandez-Borja M. Verwoerd D. Sanderson F. Aerts H. Trowsdale J. Tulp A. Neefjes J. Int. Immunol. 1996; 8: 625-640Crossref PubMed Scopus (40) Google Scholar) by the invariant chain (Ii) 1The abbreviations used are: Iihuman invariant chainCEFchicken embryo fibroblastTftransferrinTRtransferrin receptorTMtransmembrane regionCTcytoplasmic tailINinternalizedSURsurface-associatedWTwild-type.1The abbreviations used are: Iihuman invariant chainCEFchicken embryo fibroblastTftransferrinTRtransferrin receptorTMtransmembrane regionCTcytoplasmic tailINinternalizedSURsurface-associatedWTwild-type. (reviewed in Ref. 4Cresswell P. Annu. Rev. Immunol. 1994; 12: 259-293Crossref PubMed Google Scholar). Upon arrival, Ii is degraded, and αβ chains acquire peptide antigens (5Blum J.S. Cresswell P. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 3975-3979Crossref PubMed Scopus (320) Google Scholar, 6Lotteau V. Teyton L. Peleraux A. Nilsson T. Karlsson L. Schmid S.L. Quaranta V. Peterson P.A. Nature. 1990; 348: 600-605Crossref PubMed Scopus (444) Google Scholar, 7Lamb C.A. Yewdell J.W. Bennick J.R. Cresswell P. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 5998-6002Crossref PubMed Scopus (129) Google Scholar, 8Pieters J. Horstmann H. Bakke O. Griffiths G. Lipp J. J. Cell Biol. 1991; 115: 1213-1223Crossref PubMed Scopus Google Scholar, P. C. Yewdell J. Bakke O. J. PubMed Scopus Google Scholar, J.R. Cresswell P. J. Immunol. Google Scholar, P. M. G. Geuze H.J. Ploegh H.L. J. PubMed Scopus Google Scholar). complexes are to the lysosomal the P. M. G. Geuze H.J. Ploegh H.L. J. PubMed Scopus Google Scholar) the cell are V. Teyton L. Peleraux A. Nilsson T. Karlsson L. Schmid S.L. Quaranta V. Peterson P.A. Nature. 1990; 348: 600-605Crossref PubMed Scopus (444) Google Scholar, P. P. Lipp J. G. J. Biol. 1990; PubMed Google Scholar, P.A. Bakke O. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). and are for of class II to a V. Teyton L. Peleraux A. Nilsson T. Karlsson L. Schmid S.L. Quaranta V. Peterson P.A. Nature. 1990; 348: 600-605Crossref PubMed Scopus (444) Google Scholar, P. M. G. Geuze H.J. Ploegh H.L. J. PubMed Scopus Google Scholar, P.A. Bakke O. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar). invariant chain embryo transferrin transferrin receptor transmembrane region cytoplasmic tail invariant chain embryo transferrin transferrin receptor transmembrane region cytoplasmic tail for the that Ii is to the of the in the Ii cytoplasmic tail was the cytoplasmic tail J. J. Immunol. Google Scholar). Newly synthesized class II molecules this chimera are to the cell surface and Ii is and class II is J. J. Immunol. Google Scholar). that the cytoplasmic contains a signal M. V. S. 1990; PubMed Scopus Google Scholar, Cell 1990; PubMed Scopus Google is sufficient for of the class II complexes to a lysosome-like and that is Ii cytoplasmic tail targeting signals chimeras T. M. Bakke O. J. Cell Sci. 1994; PubMed Google Scholar) and chimeras L. J. Cell Biol. 1994; 126: PubMed Scopus Google and di-leucine signals were in the and the receptor and to for lysosomal and F. PubMed Scopus Google Scholar, S. J. Biol. PubMed Google Scholar). of two that are by residues F. PubMed Scopus Google Scholar). residues to the are for L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar, L. Teyton L. Peterson P.A. J. Biol. PubMed Scopus Google Scholar, A. G. Bakke O. J. Biol. PubMed Scopus Google suggesting that Ii di-leucine signals those in the and of structural the Ii cytoplasmic tail that the signal a whereas the is a of a A. G. Bakke O. J. Biol. PubMed Scopus Google Scholar). signals to M. V. S. 1990; PubMed Scopus Google Scholar, A. 1991; PubMed Scopus Google Scholar, C. C. 1991; PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google and to independent structural signal for J. 1991; PubMed Scopus Google Scholar, M. S. J. Biol. PubMed Google Scholar, R. J. J. J. Cell Biol. 1996; PubMed Scopus Google Scholar). signals independent structural is and signals are is to by L. H. J.S. J. Cell Biol. 1996; PubMed Scopus Google Scholar). Ii is a of wild-type and Ii demonstrate that two wild-type Ii molecules are targeted in J. J. Cell Biol. PubMed Scopus Google that molecules two Ii cytoplasmic the the structural requirements for Ii to the Ii cytoplasmic tail to the transmembrane and domains of the wild-type Ii T. M. Bakke O. J. Cell Sci. 1994; PubMed Google Scholar). The of this was to signals those required for to the of the examined two regions of the Ii that to for targeting to the lysosomal the cytoplasmic tail (CT) and the transmembrane region (TM) L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar). of the that we transferrin and lysosomal targeting by the of the chimeras L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar). and analysis of Ii CT that endocytosis, lysosomal and Analysis of the Ii TM region that two regions the TM were sufficient to lysosomal targeting a without affecting The results demonstrate that the structural requirements for Ii endocytosis and lysosomal targeting are the analyzing chimeras in quantitative we that the two cytoplasmic tail di-leucine signals to that the is for endocytosis and lysosomal whereas the to for lysosomal targeting The between the two signals is by the that of the to in a in whereas of the to a signal to required for the in a in the of chimera that the cell In to the and both di-leucine signals to lysosomal was both in to for L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar, T. M. Bakke O. J. Cell Sci. 1994; PubMed Google Scholar, L. Teyton L. Peterson P.A. J. Biol. PubMed Scopus Google Scholar, G. J. Biol. PubMed Scopus Google Scholar, A. M. Bakke O. J. Cell Sci. PubMed Google were of to lysosomal targeting of that U. J. Cell Biol. PubMed Scopus Google Scholar, I. H. P. J. Cell Biol. PubMed Scopus Google Scholar, I. H. J. Cell Biol. PubMed Scopus Google Scholar, P. V. M. A. I. J. PubMed Scopus Google Scholar, A. S. A. J. Biol. PubMed Google the J. Cell Biol. PubMed Scopus Google Scholar, J. Cell Biol. PubMed Scopus Google Scholar). In the present study, we transferrin a that the endocytosis of the C. J. Cell Biol. PubMed Scopus Google Scholar). to signals lysosomal signals we the of the chimeras a J.J. J. Biol. 1988; PubMed Scopus (40) Google for of are the that of the cell surface L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar) that is is the we the lysosomal targeting was the that the chimera was was The of this chimera was the the was that the for lysosomal targeting is for this by J. J. Biol. 1996; PubMed Scopus Google demonstrated that targeting to the of the of in the J. J. Biol. 1996; PubMed Scopus Google Scholar). demonstrated that was between and that the signal for two were the chimera dramatically the between two a of the Ii without lysosomal targeting and the receptor the that regions of two molecules are required for endocytosis and lysosomal targeting H. J. Cell Biol. 1994; PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google Scholar). that endocytosis of cell surface molecules is a for lysosomal the of chimeras that the cell we that the signal for is for the of that di-leucine signals the cell surface F. PubMed Scopus Google Scholar, S. M. J. Biol. 1994; PubMed Google Scholar) and the S. J. Biol. PubMed Google Scholar, H.J. J. P. J. Biol. PubMed Google Scholar). the two is that the of the signal the tail is J. C. J. 1994; PubMed Scopus Google Scholar). J. C. J. 1994; PubMed Scopus Google Scholar) that di-leucine signals are the to the whereas di-leucine signals for and lysosomal targeting. this the Ii cytoplasmic tail is a the is Quaranta V. J. Immunol. Google Scholar). this the signal to required for both the that the of the signal and is of the of this was to the two di-leucine signals in Ii were was we the were this we substituted the sequence the for the Our results demonstrated that this either targeting suggesting that was the results that di-leucine signals, signals, for the signals in a of both targeting The for this the a peptide corresponding to the Ii cytoplasmic that the residues a whereas the signal is a of a A. G. Bakke O. J. Biol. PubMed Scopus Google Scholar). a of the Ii cytoplasmic tail the for of residues 20–29 of the Ii cytoplasmic tail that of residues were required for endocytosis lysosomal targeting. The residues was either of the two this suggesting two of the residues were required for lysosomal the of the two di-leucine regions to the transmembrane region lysosomal targeting. is that a of a signal for lysosomal targeting signals J. A. D. S. J. Cell Biol. 1996; PubMed Scopus Google Scholar). the region of Ii to by the in the in G. J. Biol. PubMed Scopus Google Scholar). Our that this region is necessary for in the of this chimera that the cell surface were the the wild-type Ii analysis of the Ii transmembrane indicates that two regions this residues 11–19 and residues are sufficient to the to lysosomal without affecting the The structural regions that this are demonstrated that the chimeras were that of them were showed that the of the chimeras the The signals to in transmembrane regions are signals (reviewed in Ref. Cell Biol. PubMed Scopus Google Scholar). the of signals to the of residues and when in the of J. Cell Biol. 1991; 115: PubMed Scopus Google Scholar, A. M. Biol. PubMed Scopus Google Scholar). The Ii an of are of the are in the of the A. M. Biol. PubMed Scopus Google Scholar). The is that residues in of complexes the Cell Biol. PubMed Scopus Google Scholar). of the TM chimeras in a the in a of the of the complex of the major histocompatibility complex class II is the of a signal the transmembrane is the between the chains and the Ii is in the and of the Ii is that the transmembrane signal the of Ii are and the chains that the of Ii in the of the chimera when the Ii transmembrane region is L. J. Cell Biol. 1994; 126: PubMed Scopus Google the results that the of the di-leucine signal the Ii cytoplasmic tail is by the of the that chimeras Ii cytoplasmic tail transmembrane signals are to the lysosomal compartment. the required for in the to is signals the two analyzing chimeras in quantitative we that the two cytoplasmic tail di-leucine signals to that the is for endocytosis and lysosomal whereas the to for lysosomal targeting The between the two signals is by the that of the to in a in whereas of the to a signal to required for the in a in the of chimera that the cell In to the and both di-leucine signals to lysosomal was both in to for L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar, T. M. Bakke O. J. Cell Sci. 1994; PubMed Google Scholar, L. Teyton L. Peterson P.A. J. Biol. PubMed Scopus Google Scholar, G. J. Biol. PubMed Scopus Google Scholar, A. M. Bakke O. J. Cell Sci. PubMed Google were of to lysosomal targeting of that U. J. Cell Biol. PubMed Scopus Google Scholar, I. H. P. J. Cell Biol. PubMed Scopus Google Scholar, I. H. J. Cell Biol. PubMed Scopus Google Scholar, P. V. M. A. I. J. PubMed Scopus Google Scholar, A. S. A. J. Biol. PubMed Google the J. Cell Biol. PubMed Scopus Google Scholar, J. Cell Biol. PubMed Scopus Google Scholar). In the present study, we transferrin a that the endocytosis of the C. J. Cell Biol. PubMed Scopus Google Scholar). to signals lysosomal signals we the of the chimeras a J.J. J. Biol. 1988; PubMed Scopus (40) Google for of are the that of the cell surface L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar) that is is the we the lysosomal targeting was the that the chimera was was The of this chimera was the the was that the for lysosomal targeting is for this by J. J. Biol. 1996; PubMed Scopus Google demonstrated that targeting to the of the of in the J. J. Biol. 1996; PubMed Scopus Google Scholar). demonstrated that was between and that the signal for two were the chimera dramatically the between two a of the Ii without lysosomal targeting and the receptor the that regions of two molecules are required for endocytosis and lysosomal targeting H. J. Cell Biol. 1994; PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google Scholar). that endocytosis of cell surface molecules is a for lysosomal targeting. the of chimeras that the cell we that the signal for is for the of that di-leucine signals the cell surface F. PubMed Scopus Google Scholar, S. M. J. Biol. 1994; PubMed Google Scholar) and the S. J. Biol. PubMed Google Scholar, H.J. J. P. J. Biol. PubMed Google Scholar). the two is that the of the signal the tail is J. C. J. 1994; PubMed Scopus Google Scholar). J. C. J. 1994; PubMed Scopus Google Scholar) that di-leucine signals are the to the whereas di-leucine signals for and lysosomal targeting. this the Ii cytoplasmic tail is a the is Quaranta V. J. Immunol. Google Scholar). this the signal to required for both the that the of the signal and is of the of this was to the two di-leucine signals in Ii were was we the were this we substituted the sequence the for the Our results demonstrated that this either targeting suggesting that was the results that di-leucine signals, signals, for the signals in a of both targeting The for this the a peptide corresponding to the Ii cytoplasmic that the residues a whereas the signal is a of a A. G. Bakke O. J. Biol. PubMed Scopus Google Scholar). a of the Ii cytoplasmic tail the for of residues 20–29 of the Ii cytoplasmic tail that of residues were required for endocytosis lysosomal targeting. The residues was either of the two this suggesting two of the residues were required for lysosomal the of the two di-leucine regions to the transmembrane region lysosomal targeting. is that a of a signal for lysosomal targeting signals J. A. D. S. J. Cell Biol. 1996; PubMed Scopus Google Scholar). the region of Ii to by the in the in G. J. Biol. PubMed Scopus Google Scholar). Our that this region is necessary for in the of this chimera that the cell surface were the the wild-type Ii Our analysis of the Ii transmembrane indicates that two regions this residues 11–19 and residues are sufficient to the to lysosomal without affecting the The structural regions that this are demonstrated that the chimeras were that of them were showed that the of the chimeras the The signals to in transmembrane regions are signals (reviewed in Ref. Cell Biol. PubMed Scopus Google Scholar). the of signals to the of residues and when in the of J. Cell Biol. 1991; 115: PubMed Scopus Google Scholar, A. M. Biol. PubMed Scopus Google Scholar). The Ii an of are of the are in the of the A. M. Biol. PubMed Scopus Google Scholar). The is that residues in of complexes the Cell Biol. PubMed Scopus Google Scholar). of the TM chimeras in a the in a of the of the complex of the major histocompatibility complex class II is the of a signal the transmembrane is the between the chains and the Ii is in the and of the Ii is that the transmembrane signal the of Ii are and the chains that the of Ii in the of the chimera when the Ii transmembrane region is L. J. Cell Biol. 1994; 126: PubMed Scopus Google Scholar). In the results that the of the di-leucine signal the Ii cytoplasmic tail is by the of the that chimeras Ii cytoplasmic tail transmembrane signals are to the lysosomal compartment. the required for in the to is signals the two C. for of the and and for and for of the