TY - JOUR
T1 - The Erythropoietin Receptor Transmembrane Domain Mediates Complex Formation with Viral Anemic and Polycythemic gp55 Proteins
AU - Constantinescu, Stefan N.
AU - Keren, Tzvia
AU - Russ, William P.
AU - Ubarretxena-Belandia, Iban
AU - Malka, Yaniv
AU - Kubatzky, Katharina F.
AU - Engelman, Donald M.
AU - Lodish, Harvey F.
AU - Henis, Yoav I.
PY - 2003/10/31
Y1 - 2003/10/31
N2 - Erythropoietin receptor (EpoR) activation is crucial for mature red blood cell production. The murine EpoR can also be activated by the envelope protein of the polycythemic (P) spleen focus forming virus (SFFV), gp55-P. Due to differences in the TM sequence, gp55 of the anemic (A) strain SFFV, gp55-A, cannot efficiently activate the EpoR. Using antibody-mediated immunofluorescence co-patching, we show that the majority of EpoR forms hetero-oligomers at the cell surface with gp55-P and, surprisingly, with gp55-A. The EpoR TM domain is targeted by gp55-P and -A, as only chimeric receptors containing EpoR TM sequences oligomerized with gp55 proteins. Both gp55-P and gp55-A are homodimers on the cell surface, as shown by co-patching. However, when the homomeric interactions of the isolated TM domains were assayed by TOXCAT bacterial reporter system, only the TM sequence of gp55-P was dimerized. Thus, homo-oligomerization of gp55 proteins is insufficient for full EpoR activation, and a correct conformation of the dimer in the TM region is required. This is supported by the failure of gp55-A→P, a mutant protein whose TM domain can homo-oligomerize, to fully activate EpoR. As unliganded EpoR forms TM-dependent but inactive homodimers, we propose that the EpoR can be activated to different extents by homodimeric gp55 proteins, depending on the conformation of the gp55 protein dimer in the TM region.
AB - Erythropoietin receptor (EpoR) activation is crucial for mature red blood cell production. The murine EpoR can also be activated by the envelope protein of the polycythemic (P) spleen focus forming virus (SFFV), gp55-P. Due to differences in the TM sequence, gp55 of the anemic (A) strain SFFV, gp55-A, cannot efficiently activate the EpoR. Using antibody-mediated immunofluorescence co-patching, we show that the majority of EpoR forms hetero-oligomers at the cell surface with gp55-P and, surprisingly, with gp55-A. The EpoR TM domain is targeted by gp55-P and -A, as only chimeric receptors containing EpoR TM sequences oligomerized with gp55 proteins. Both gp55-P and gp55-A are homodimers on the cell surface, as shown by co-patching. However, when the homomeric interactions of the isolated TM domains were assayed by TOXCAT bacterial reporter system, only the TM sequence of gp55-P was dimerized. Thus, homo-oligomerization of gp55 proteins is insufficient for full EpoR activation, and a correct conformation of the dimer in the TM region is required. This is supported by the failure of gp55-A→P, a mutant protein whose TM domain can homo-oligomerize, to fully activate EpoR. As unliganded EpoR forms TM-dependent but inactive homodimers, we propose that the EpoR can be activated to different extents by homodimeric gp55 proteins, depending on the conformation of the gp55 protein dimer in the TM region.
UR - http://www.scopus.com/inward/record.url?scp=0242384797&partnerID=8YFLogxK
U2 - 10.1074/jbc.M302974200
DO - 10.1074/jbc.M302974200
M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???
AN - SCOPUS:0242384797
SN - 0021-9258
VL - 278
SP - 43755
EP - 43763
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 44
ER -