Nuclear Export of the Oncoprotein v-ErbA Is Mediated by Acquisition of a Viral Nuclear Export Sequence

Abstract

v-ErbA, an oncogenic derivative of the thyroid hormone receptor α (TRα) carried by the avian erythroblastosis virus, contains several alterations including fusion of a portion of avian erythroblastosis virus Gag to its N terminus, N- and C-terminal deletions, and 13 amino acid substitutions. Nuclear export of v-ErbA occurs through a CRM1-mediated pathway. In contrast, nuclear export of TRα and another isoform, TRβ, is CRM1-independent. To determine which amino acid changes in v-ErbA confer CRM1-dependent nuclear export, we expressed a panel of green and yellow fluorescent protein-tagged mutant and chimeric proteins in mammalian cells. The sensitivity of subcellular trafficking of these mutants to leptomycin B (LMB), a specific inhibitor of CRM1, was assessed by fluorescence microscopy. Our data showed that a nuclear export sequence resides within a 70-amino acid domain in the C-terminal portion of the p10 region of Gag, and in vitro binding assays demonstrated that Gag interacts directly with CRM1. However, a panel of ligand-binding domain mutants of v-ErbA lacking the Gag sequence exhibited greater nuclear localization in the presence of LMB, suggesting that the various amino acid substitutions/deletions may cause a conformation shift, unmasking an additional CRM1-dependent nuclear export sequence. In contrast, the altered DNA-binding domain of the oncoprotein did not contribute to CRM1-dependent nuclear export. Heterokaryon experiments revealed that v-ErbA did not undergo nucleocytoplasmic shuttling when the CRM1 export pathway was blocked by LMB treatment, suggesting that the ability to follow the export pathway used by TRα has been lost by the oncoprotein during its evolution. Our findings thus point to the intriguing possibility that acquisition of altered nuclear export capabilities contributes to the oncogenic properties of v-ErbA. v-ErbA, an oncogenic derivative of the thyroid hormone receptor α (TRα) carried by the avian erythroblastosis virus, contains several alterations including fusion of a portion of avian erythroblastosis virus Gag to its N terminus, N- and C-terminal deletions, and 13 amino acid substitutions. Nuclear export of v-ErbA occurs through a CRM1-mediated pathway. In contrast, nuclear export of TRα and another isoform, TRβ, is CRM1-independent. To determine which amino acid changes in v-ErbA confer CRM1-dependent nuclear export, we expressed a panel of green and yellow fluorescent protein-tagged mutant and chimeric proteins in mammalian cells. The sensitivity of subcellular trafficking of these mutants to leptomycin B (LMB), a specific inhibitor of CRM1, was assessed by fluorescence microscopy. Our data showed that a nuclear export sequence resides within a 70-amino acid domain in the C-terminal portion of the p10 region of Gag, and in vitro binding assays demonstrated that Gag interacts directly with CRM1. However, a panel of ligand-binding domain mutants of v-ErbA lacking the Gag sequence exhibited greater nuclear localization in the presence of LMB, suggesting that the various amino acid substitutions/deletions may cause a conformation shift, unmasking an additional CRM1-dependent nuclear export sequence. In contrast, the altered DNA-binding domain of the oncoprotein did not contribute to CRM1-dependent nuclear export. Heterokaryon experiments revealed that v-ErbA did not undergo nucleocytoplasmic shuttling when the CRM1 export pathway was blocked by LMB treatment, suggesting that the ability to follow the export pathway used by TRα has been lost by the oncoprotein during its evolution. Our findings thus point to the intriguing possibility that acquisition of altered nuclear export capabilities contributes to the oncogenic properties of v-ErbA. The v-erbA oncogene is transduced by the avian erythroblastosis virus (AEV) 1The abbreviations used are: AEV, avian erythroblastosis virus; aa, amino acid(s); TRα, thyroid hormone receptor α; TRβ, thyroid hormone receptor β; LMB, leptomycin B; NES, nuclear export sequence; RSV, Rous sarcoma virus; GFP, green fluorescent protein; YFP, yellow fluorescent protein; DAPI, 4′,6-diamidino-2-phenylindole; GST, glutathione S-transferase; N, nuclear; C, cytoplasmic. from the cellular c-erbA protooncogene encoding the thyroid hormone receptor α (TRα), a member of the nuclear receptor superfamily (1Zhang J. Lazar M.A. Annu. Rev. Physiol. 2000; 62: 439-466Crossref PubMed Scopus (581) Google Scholar). During the course of oncogene activation, v-erbA was fused to an AEV gag sequence at its N terminus. In addition, v-erbA acquired two small deletions in the N and C termini and 13 amino acid substitutions interspersed throughout the DNA-binding domain, hinge region, and ligand-binding domain (2Stunnenberg H.G. Garcia-Jimenez C. Betz J.L. Biochim. Biophys. Acta. 1998; 1423: F15-F33Google Scholar, 3Sap J. Munoz A. Damm K. Goldberg Y. Ghysdael J. Leutz A. Beug H. Vennstrom B. Nature. 1986; 324: 635-640Crossref PubMed Scopus (1024) Google Scholar). Studies involving mutant forms of the oncoprotein v-ErbA (also referred to as p75gag-v-erbA) have illustrated the importance of these sequence alterations for its oncogenic properties (4Zenke M. Munoz A. Sap J. Vennstrom B. Beug H. Cell. 1990; 61: 1035-1049Abstract Full Text PubMed Scopus Google Scholar, Munoz A. C. Vennstrom B. Beug H. 1990; Google Scholar, J. Full Text PubMed Google Scholar, M. Cell. Full Text PubMed Scopus Google Scholar, K. A. PubMed Scopus Google Scholar, K. B. A. PubMed Scopus Google Scholar, Google Scholar, 1990; Google Scholar, M. M. Cell. PubMed Scopus Google Scholar). v-ErbA has the to M. Vennstrom B. 2000; PubMed Scopus Google Scholar, J. A. Beug H. J. 2000; Scopus Google has lost hormone binding and and has altered binding J. Munoz A. Damm K. Goldberg Y. Ghysdael J. Leutz A. Beug H. Vennstrom B. Nature. 1986; 324: 635-640Crossref PubMed Scopus (1024) Google Scholar, J. Full Text Full Text PubMed Scopus Google Scholar, 1998; PubMed Scopus Google Scholar, Beug H. M. H.G. J. PubMed Scopus Google Scholar, B. M. Google Scholar, PubMed Scopus Google Scholar, H. Cell. PubMed Scopus Google Scholar, H. M. Cell. PubMed Scopus Google Scholar, A. M. Sap J. Beug H. Vennstrom B. J. PubMed Scopus Google Scholar). TRα a as an of in to thyroid In mammalian and avian v-ErbA in as a of However, a of have a for the oncoprotein K. Nature. PubMed Scopus Google Scholar, A. M. Beug H. M. PubMed Scopus Google Scholar). has been that v-ErbA contributes to by with the of and TRα H.G. PubMed Scopus Google Scholar). v-ErbA with through including a TRα M. Cell. Full Text PubMed Scopus Google Scholar, A. M. Beug H. M. PubMed Scopus Google Scholar, A. J. PubMed Scopus Google Scholar, J. Google of the of by of the C. A. J. A. Google Scholar, M. Google Scholar, C. C. B. J. Cell. Full Text PubMed Scopus Google and of of the for and acid M. Cell. Full Text PubMed Scopus Google Scholar, H. Cell. PubMed Scopus Google Scholar). in the the oncogenic of TRα v-ErbA and the of of in The for by v-ErbA has not been to for binding and and of PubMed Scopus Google Scholar). of oncogenic is the of altered subcellular nuclear localization of as a to A. Annu. Rev. PubMed Scopus Google Scholar, M. M. PubMed Scopus Google Scholar, B. C. C. PubMed Scopus Google Scholar). of the nuclear of v-ErbA, in its nuclear export, may a of its oncogenic v-ErbA subcellular localization and nuclear export from its cellular TRα the and is to the v-ErbA in nuclear and in the B (LMB), a specific inhibitor of the export receptor CRM1 M. Y. PubMed Scopus Google nuclear export of LMB in nuclear localization of v-ErbA, that v-ErbA a CRM1-dependent nuclear export pathway J. PubMed Scopus Google Scholar). In contrast, nucleocytoplasmic shuttling of TRα is not blocked by LMB, that TRα the by a export pathway J. PubMed Scopus Google Scholar). To determine which amino acid changes in v-ErbA confer CRM1-dependent nuclear export, we a panel of v-ErbA mutants and chimeric subcellular trafficking was assessed for sensitivity to Our data showed that the Gag region of v-ErbA interacts directly with CRM1 and v-ErbA nuclear export. we showed that the nuclear export sequence resides within a 70-amino acid domain in the C-terminal portion of the p10 region of In contrast, the altered DNA-binding domain of the oncoprotein did not contribute to CRM1-dependent nuclear export, data that the ligand-binding domain of v-ErbA may in CRM1-dependent nuclear export. the CRM1 export pathway was blocked by LMB treatment, nucleocytoplasmic shuttling of v-ErbA was suggesting that the ability to follow the export pathway used by TRα has been lost by the oncoprotein during its evolution. findings point to the intriguing possibility that acquisition of altered nuclear export capabilities contributes to the oncogenic properties of v-ErbA. contains the region for a fusion of TRα with the Gag sequence from v-ErbA fused to amino acid 13 of TRα, the amino of TRα A. M. Sap J. Beug H. Vennstrom B. J. PubMed Scopus Google Scholar). a chimeric in which the DNA-binding domain of v-ErbA was by the DNA-binding domain of TRα H. M. Cell. PubMed Scopus Google Scholar). In the Gag sequence is the N- and C-terminal deletions and the 13 point that v-ErbA from TRα J. 2000; Full Text Full Text PubMed Scopus Google Scholar). The mutants and have substitutions deletions in to in J. 2000; Full Text Full Text PubMed Scopus Google Scholar). the of for the Gag domain the gag sequence was from the of v-erbA through of that region from a J. PubMed Scopus Google Scholar). Gag and v-erbA mutant In addition, the gag sequence from v-erbA was for in vitro for and and for in vitro of TRα and v-ErbA as J. PubMed Scopus Google Scholar, J. Cell. PubMed Scopus Google Scholar). was by the from Google and used for of CRM1 J. J. J. 1998; Full Text Full Text PubMed Scopus Google and mutant J. PubMed Scopus Google To and Gag NES, for the amino of Gag and the CRM1-dependent in the C of Gag the of a the and by of these from To the Rous sarcoma virus p10 sequence was by two with a the and a and the by The was from a and the and and as The was by for and from for and at a was and with the and the and The of was by with an and LMB assays as J. PubMed Scopus Google Scholar). with LMB from M. of from the of In was we have in the of and a as J. PubMed Scopus Google and in in the with was an and a and a a of experiments carried for with of was of LMB of subcellular nuclear localization nuclear localization and nuclear localization was used to determine the of in subcellular the for the v-ErbA mutants in these data to two and nuclear localization and nuclear was carried the and and the Heterokaryon assays as J. PubMed Scopus Google Scholar). in LMB an of as a in for fusion with cells. the in LMB an of for at and for and carried as J. PubMed Scopus Google Scholar). shuttling was by the presence of in the and CRM1 and the Gag domain from v-ErbA, v-ErbA, TRα was by The fusion was expressed in with at and in with was to the The presence of in was by and with Gag, v-ErbA, and TRα in vitro the in the presence of and and expressed in as fusion in proteins and with as J. PubMed Scopus Google Scholar). assays carried in the presence of and of the to the by and as J. PubMed Scopus Google Scholar). The presence of in the from the was by and J. PubMed Scopus Google Scholar). The of was with at and at Nuclear of the Gag of v-ErbA by the course of oncoprotein activation, v-ErbA was fused to a portion of AEV Gag, acquired 13 interspersed amino acid and small deletions in the N and C termini (2Stunnenberg H.G. Garcia-Jimenez C. Betz J.L. Biochim. Biophys. Acta. 1998; 1423: F15-F33Google Scholar, 3Sap J. Munoz A. Damm K. Goldberg Y. Ghysdael J. Leutz A. Beug H. Vennstrom B. Nature. 1986; 324: 635-640Crossref PubMed Scopus (1024) Google Our have that TRα the by a the nuclear export of v-ErbA is CRM1-dependent J. PubMed Scopus Google Scholar). we to which sequence v-ErbA and TRα CRM1-dependent nuclear export. The of TRα in the of nuclear export by in the as a for TRα that in the export from nuclear export of TRα in a and findings to another of the thyroid hormone we have demonstrated that fusion with is a for subcellular trafficking of TRα and J. PubMed Scopus Google Scholar). TRα fused with in the presence and of In TRα and from the to the that nuclear export is CRM1-independent. To that the LMB used in assays was we the of LMB the shuttling ability of a that a CRM1-mediated export pathway J. PubMed Scopus Google Scholar). nuclear export of was to in the presence of the to the and in the of LMB, in the of the and To which sequence v-ErbA and TRα confer CRM1-dependent nuclear export, we the Gag domain of v-ErbA nuclear export In the Gag the and of virus from the PubMed Scopus Google Scholar). was that Gag proteins directly to the in the of the has been that nuclear and export of the Gag of the pathway A. PubMed Scopus Google Scholar). in we the to to the Gag domain in v-ErbA as to the Gag To the subcellular localization of the AEV Gag domain of v-ErbA, with an encoding its In Gag has a is to nuclear export properties by of the for the nucleocytoplasmic of Gag throughout the and N nuclear localization with a in the N nuclear localization nuclear with N and nuclear localization Gag exhibited a subcellular from that of v-ErbA a and and The of exhibited a with a greater of Gag in the showed nuclear localization of Gag AEV Gag in the that is of nuclear a pathway by through the nuclear The the ability to the To determine Gag a CRM1-dependent nuclear export we the sensitivity of Gag to Gag showed sensitivity to for with LMB in a in nuclear of of the showed nuclear localization of Gag in the of LMB with in the presence of LMB panel and However, v-ErbA in which of the showed nuclear in the presence of LMB panel and Gag was not to the when CRM1 was panel and The presence of a of Gag of that nuclear of the is when is fused to v-ErbA. However, with LMB, was in the of Gag in the not suggesting that the sensitivity to LMB Gag and Gag fused with v-ErbA is not a of altered nuclear to changes in v-ErbA the Gag sequence. in within the for through the of the nuclear J. PubMed Scopus Google is that in the presence of LMB Gag in of the to a v-ErbA at that Gag the CRM1 pathway with altered when not fused to v-ErbA, is a in Gag that is not in to these In these data that the Gag domain of v-ErbA and the and a CRM1-mediated nuclear export pathway. The Gag of v-ErbA with that the AEV Gag sequence that was fused to v-ErbA during interacts directly with CRM1, assays expressed fusion was with in vitro Gag, v-ErbA, TRα and the and binding by and Gag and v-ErbA with CRM1. In contrast, as TRα was in the TRα to CRM1 when a greater of TRα was in the was TRα in the not is used as the of to in vitro nuclear thus the presence of a of in the for specific of CRM1 with The presence of in the was by the of with mutant which the of Gag and v-ErbA with CRM1. of Gag with TRα CRM1-dependent Nuclear the of the AEV Gag domain the subcellular localization and of v-ErbA, with a chimeric fusion of TRα and the Gag sequence from v-ErbA, for nucleocytoplasmic to the exhibited a subcellular localization from that of TRα and v-ErbA TRα, was not to the of exhibited a panel a with panel in to v-ErbA, did not a of showed to nuclear localization panel with panel of with properties of the chimeric and TRα v-ErbA of the in and M. Beug H. H.G. J. 1998; PubMed Scopus Google (4Zenke M. Munoz A. Sap J. Vennstrom B. Beug H. Cell. 1990; 61: 1035-1049Abstract Full Text PubMed Scopus Google Scholar). To determine the Gag sequence is to CRM1-dependent nuclear export of a chimeric we the sensitivity of to for with LMB a in the subcellular localization of with a greater nuclear of showed to nuclear localization in the presence of LMB with in the of LMB panel and data that the AEV Gag sequence is to confer CRM1 the fusion To the of the Gag domain the nuclear export of v-ErbA, with a v-ErbA mutant with a of the Gag and for nucleocytoplasmic The subcellular localization of was from that of TRα and v-ErbA panel and panel with panel was in the with the of to nuclear localization and To determine nuclear export of v-ErbA is CRM1-dependent in the of Gag, we the sensitivity of to with LMB the subcellular of in the presence and of LMB, of exhibited to nuclear localization of the mutant and data that the AEV Gag sequence nuclear export of v-ErbA. in the p10 of AEV AEV acquired the sequence was at the encoding the Gag a of a portion of the gag sequence was fused with the c-erbA additional gag K. Beug H. Vennstrom B. J. PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar). the portion of the AEV gag sequence that is fused with v-erbA and the region for the Gag of sequence the Gag is the proteins and A. PubMed Scopus Google Scholar). the sequence fused with v-ErbA the portion of Gag as the p10 region, which a sequence demonstrated to have properties in A. PubMed Scopus Google The CRM1 nuclear export receptor in the virus, and the inhibitor M. M. M. Cell. Full Text Full Text PubMed Scopus Google Scholar, K. C. K. Cell. Full Text Full Text PubMed Scopus Google Scholar, B. C. PubMed Scopus Google Scholar). of in the of p10 is to confer the properties A. PubMed Scopus Google Scholar). To a CRM1-dependent was in the p10 region in AEV Gag, we a of for fusion fused to the C-terminal portion of the p10 region from AEV Gag the In addition, we fused a 70-amino acid region from the N of Gag to to as a and the p10 domain for a for nucleocytoplasmic in the presence of LMB, to the for and which with LMB the subcellular of In the and presence of LMB, of and of showed a nuclear localization and suggesting that these small proteins to throughout the and that nuclear export is CRM1-independent. did not have the as not did fusion a greater in the the of these to is to that the amino of AEV Gag may of these of v-ErbA. In addition, in the to have a greater with at In to and in the of LMB the fusion proteins p10 and to the and in of cells. of the CRM1 inhibitor in a in nuclear suggesting that the confer CRM1-dependent nuclear export In the presence of LMB, p10 and showed a to that of with of a nuclear localization The presence of a is to the small of these which in through the of the nuclear and and these data that the p10 region of AEV Gag contains an that is to CRM1-dependent nuclear export of a The p10 of AEV Gag CRM1-dependent of Gag and that the p10 domain of AEV Gag is for CRM1-dependent nuclear export of Gag and v-ErbA, we two and which the C-terminal portion of the AEV p10 region, and subcellular with of and for In the of LMB, and nuclear and in subcellular with of a localization and and of LMB in a in the nuclear of and with a of the of nuclear localization and and and and In contrast, the subcellular of the and in the presence of LMB and and that when the C-terminal portion the Gag domain is these showed an altered nuclear nuclear to in as as to of v-ErbA data that the p10 region of AEV Gag contains an that is and for CRM1-mediated nuclear export. of in the of v-ErbA CRM1-mediated Nuclear the AEV Gag sequence and Gag fused with v-ErbA have sensitivity to LMB, we to additional sequence changes in v-ErbA contribute to its ability to the by a CRM1-mediated pathway. with mutants with deletions substitutions in the ligand-binding domain and for nucleocytoplasmic to the of the mutants of and exhibited with the to nuclear in with LMB altered the of of the mutants for and was a greater nuclear the of exhibited a in was for did not greater nuclear in the presence of LMB, and of a nuclear localization in the presence and of LMB, In these data that the ligand-binding domain of v-ErbA may of the oncoprotein with CRM1. The DNA-binding of v-ErbA to CRM1-dependent Nuclear that TRα, which a for CRM1, may an in a acid sequence the two of its DNA-binding domain Full Text Full Text PubMed Scopus Google Scholar). domain is in the nuclear receptor superfamily and is to directly with the a nuclear export receptor Cell. PubMed Scopus Google Scholar). The DNA-binding domain of v-ErbA has two amino acid changes with TRα To determine the altered DNA-binding domain of v-ErbA a in CRM1-dependent nuclear export, a chimeric fusion in which the DNA-binding domain of v-ErbA was with the DNA-binding domain of TRα, was with and for nucleocytoplasmic to the showed a of subcellular and including nuclear nuclear and nuclear localization In with nuclear showed a panel with localization to with an showed a localization to The of these to To determine nuclear export of v-ErbA CRM1-dependent in the presence of the TRα NES, we the sensitivity of to with LMB altered the subcellular of In the presence of LMB, to the In contrast, in the of LMB, of showed a findings that the CRM1-dependent within the AEV Gag p10 domain is to the TRα the Gag sequence was the of to a nuclear with a with LMB did not the subcellular of In the presence of LMB, of showed to nuclear localization of with in the of LMB data of the importance of the AEV Gag domain in v-ErbA CRM1-dependent nuclear export and v-ErbA the CRM1 the presence of LMB, v-ErbA to in the suggesting that the oncoprotein the CRM1-mediated nuclear export pathway. However, v-ErbA in nucleocytoplasmic not in a to determine v-ErbA nucleocytoplasmic shuttling in the presence of LMB, assays In the of v-ErbA has a thus in the of LMB showed and nuclear the presence of v-ErbA in the of a shuttling of the and the In in which was v-ErbA in the panel in with and the showed an of v-ErbA panel v-ErbA did not in the when the for the that a of shuttling did not nucleocytoplasmic findings that v-ErbA not the and the when the CRM1 pathway is suggesting that the ability to follow the export pathway used by TRα has been lost by the oncoprotein v-ErbA during its evolution. To for oncogenic of the ability to follow the TRα export we the nucleocytoplasmic shuttling properties of by the fusion of with cells. In the of LMB, was in and panel as for v-ErbA, to of a and not the DNA-binding domain the TRα NES, did not when CRM1 was blocked by with LMB panel data that the oncoprotein has lost the ability to the TRα export receptor to fusion with Gag and to sequence and that the altered DNA-binding domain of the oncoprotein not an in v-ErbA export. of a CRM1-dependent by an oncogenic derivative of a TRα carried by AEV, the capabilities of the virus through of the and The oncogenic of v-ErbA in from with we findings suggesting in addition, the altered subcellular localization of v-ErbA a in its oncogenic the oncoprotein v-ErbA the by a CRM1-dependent its cellular TRα a nuclear export pathway J. PubMed Scopus Google Scholar). In addition, we that another of the thyroid hormone TRβ, a nuclear export pathway. that export occurs by a CRM1-mediated pathway J. Full Text Full Text PubMed Scopus Google Scholar). the data not we for The fusion of a portion of the AEV Gag including the p10 domain, to the N of v-ErbA the oncoprotein to directly with CRM1 and its CRM1-mediated export. In addition, the point that nuclear and export of the Gag may of importance for AEV A. PubMed Scopus Google Scholar). The region that is to the sequence with properties and the CRM1-mediated export of v-ErbA the sequence for the CRM1-dependent B. C. PubMed Scopus Google Scholar, J. Cell. PubMed Scopus Google and a of the sequence for of an with CRM1. a of these altered export the subcellular of v-ErbA has from the nuclear localization of its cellular to a of the oncoprotein to that the Gag and amino acid of the p10 domain, is for with CRM1, sequence v-ErbA and TRα may the ability of the oncoprotein to follow the CRM1-mediated nuclear export pathway. The of nuclear localization of the Gag sequence in the presence of LMB, a specific inhibitor of CRM1, that nuclear of Gag may with the that nuclear localization of the Gag is A. PubMed Scopus Google Scholar). the of nuclear localization of in with LMB that the chimeric receptor not CRM1-mediated export pathway is that the Gag sequence to follow the CRM1-dependent export pathway in to the export pathway by is with the of the TRα in its DNA-binding domain Full Text Full Text PubMed Scopus Google a sequence that is in the fusion However, when the DNA-binding domain of v-ErbA was with the DNA-binding domain of TRα, chimeric was not to follow a export suggesting that when fused with v-ErbA sequence and changes the ability to to the export receptor and confer properties the Gag the CRM1 export pathway nucleocytoplasmic shuttling of v-ErbA, suggesting that the oncoprotein the nuclear export pathway by TRα and that the CRM1-dependent nuclear export pathway is the export pathway used by v-ErbA. the of v-ErbA a in CRM1-dependent Nuclear importance of the ligand-binding domain is illustrated by the nuclear export properties of v-ErbA which to the ligand-binding The nucleocytoplasmic of these mutants was at the of we a greater nuclear of these mutants the Gag sequence. However, the of the in the ligand-binding domain, is with of the importance of region for nuclear A. J. 62: PubMed Google J. 2000; Full Text Full Text PubMed Scopus Google and with (4Zenke M. Munoz A. Sap J. Vennstrom B. Beug H. Cell. 1990; 61: 1035-1049Abstract Full Text PubMed Scopus Google Scholar, Munoz A. C. Vennstrom B. Beug H. 1990; Google Scholar). showed in subcellular in the presence of In contrast, of the mutants of v-ErbA exhibited greater nuclear localization in the presence of LMB, suggesting that these nuclear follow a CRM1-mediated export pathway. the of at the possibility that these mutants may the by another export pathway when CRM1 is these v-ErbA ligand-binding domain which the Gag NES, follow the CRM1-dependent export is that the various amino acid cause a conformation shift, unmasking an additional that is not in is by the export properties of the mutant the amino acid of a conformation the sequence deletions in the in a with CRM1. for a involving a is illustrated by a of proteins that undergo CRM1-dependent nuclear export, including of the the the the and J. PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, M. J. Full Text Full Text PubMed Scopus Google Scholar, Y. Y. A. 1998; PubMed Scopus Google Scholar, M. J. J. PubMed Scopus Google Scholar). of nuclear export through and unmasking of is to as another of of The in the ligand-binding domain of v-ErbA is as a for an additional that the altered nuclear export of v-ErbA. is by the of CRM1 of the mutant which changes of these to an In addition, mutants with the not within the region and the CRM1 suggesting that to the may the However, the not the additional with the to with CRM1. The mutant which region, follow the CRM1 nuclear export pathway. and which from the CRM1 In to sequence alterations in the ligand-binding domain, is that amino acid substitutions in the hinge region, which changes to to of the oncoprotein with CRM1. In these data two for CRM1 in to the with the AEV Gag sequence. acid substitutions acquired during the of the oncoprotein by a through the of amino these cause a conformation that in of the Gag with CRM1. for the and of a of v-ErbA, which to a of fusion with a NES, has for the of of v-ErbA. for a of binding and and of in oncoprotein of PubMed Scopus Google Scholar). in addition, the acquisition of altered nuclear export by the oncoprotein v-ErbA may a in its and that altered subcellular localization another of for in from the of altered nuclear export in of its J. PubMed Scopus Google is from the in J. PubMed Scopus Google and of the B virus CRM1 in the suggesting that the of the CRM1-mediated pathway may an during M. M. J. Full Text Full Text PubMed Scopus Google Scholar). The acquired of CRM1-mediated nuclear export by v-ErbA in its to the which may directly is that of v-ErbA is for its oncogenic C. C. Sap J. J. H. Beug H. M. PubMed Scopus Google Scholar). v-ErbA may to the to its to that to with In that CRM1-dependent nuclear export of v-ErbA is by an within a 70-amino acid region in the C of the AEV Gag p10 sequence and to the possibility that amino acid changes in of v-ErbA a in CRM1-mediated nuclear export. is to the of these and in CRM1-dependent nuclear export. findings that fusion of the Gag sequence with v-ErbA was a in the of the properties of M. for with the to A. M. J. and J. for the of and M. for the of