0 7 Genetic genetic JJ 8 16 evidence evidence NN 17 20 for for IN 21 23 an an DT 24 34 additional additional JJ 35 41 factor factor NN 42 50 required require VBN 51 54 for for IN 55 77 erythropoietin-induced erythropoietin-induced JJ 78 84 signal signal NN 85 97 transduction transduction NN 97 98 . . . 100 114 Erythropoietin erythropoietin NN 115 116 ( ( ( 116 119 EPO EPO NNP 119 120 ) ) ) 121 124 and and CC 125 128 its its PRP$ 129 137 receptor receptor NN 138 139 ( ( ( 139 143 EPOR EPOR NNP 143 144 ) ) ) 145 148 are be VBP 149 157 required require VBN 158 161 for for IN 162 165 the the DT 166 177 development development NN 178 180 of of IN 181 187 mature mature JJ 188 200 erythrocytes erythrocyte NNS 200 201 . . . 202 207 After after IN 208 215 binding binding NN 216 218 of of IN 219 225 ligand ligand NN 225 226 , , , 227 230 the the DT 231 235 EPOR epor NN 236 245 activates activate VBZ 246 247 a a DT 248 255 variety variety NN 256 258 of of IN 259 268 signaling signaling NN 269 277 pathways pathway NNS 278 282 that that WDT 283 293 ultimately ultimately RB 294 301 control control VBP 302 310 cellular cellular JJ 311 324 proliferation proliferation NN 324 325 , , , 326 334 survival survival NN 334 335 , , , 336 339 and and CC 340 348 specific specific JJ 349 353 gene gene NN 354 364 expression expression NN 364 365 . . . 366 374 Although although IN 375 384 erythroid erythroid JJ 385 396 progenitors progenitor NNS 397 403 appear appear VBP 404 406 to to TO 407 409 be be VB 410 413 the the DT 414 423 principal principal JJ 424 438 EPO-responsive epo-responsive JJ 439 443 cell cell NN 444 448 type type NN 449 451 in in FW 452 456 vivo vivo FW 457 460 due due JJ 461 463 to to TO 464 467 the the DT 468 478 restricted restricted JJ 479 489 expression expression NN 490 492 of of IN 493 496 the the DT 497 501 EPOR epor NN 501 502 , , , 503 507 many many JJ 508 514 growth growth NN 515 531 factor-dependent factor-dependent JJ 532 536 cell cell NN 537 542 lines line NNS 543 553 expressing express VBG 554 557 the the DT 558 562 EPOR epor NN 563 566 can can MD 567 574 respond respond VB 575 577 to to TO 578 581 EPO EPO NNP 582 584 by by IN 585 595 activating activate VBG 596 600 many many JJ 601 603 or or CC 604 607 all all DT 608 610 of of IN 611 616 these these DT 617 625 pathways pathway NNS 625 626 . . . 627 629 In in IN 630 633 the the DT 634 641 present present JJ 642 647 study study NN 647 648 , , , 649 651 we we PRP 652 656 have have VBP 657 667 identified identify VBN 668 669 a a DT 670 678 cellular cellular JJ 679 686 context context NN 687 688 ( ( ( 688 691 the the DT 692 705 interleukin-2 interleukin-2 NN 706 707 [ [ ( 707 722 IL-2]-dependent il-2]-dependent JJ 723 727 HT-2 ht-2 NN 728 732 line line NN 732 733 ) ) ) 734 736 in in IN 737 742 which which WDT 743 746 the the DT 747 750 EPO EPO NNP 751 762 stimulation stimulation NN 763 765 of of IN 766 769 the the DT 770 774 EPOR epor NN 775 780 fails fail VBZ 781 783 to to TO 784 791 support support VB 792 800 cellular cellular JJ 801 814 proliferation proliferation NN 814 815 , , , 816 822 STAT-5 STAT-5 NNP 823 832 induction induction NN 832 833 , , , 834 836 or or CC 837 841 MAPK MAPK NNP 842 852 activation activation NN 852 853 , , , 854 861 despite despite IN 862 871 efficient efficient JJ 872 887 phosphorylation phosphorylation NN 888 890 of of IN 891 894 the the DT 895 899 EPOR epor NN 900 903 and and CC 904 908 JAK2 jak2 NN 909 912 and and CC 913 923 inhibition inhibition NN 924 926 of of IN 927 936 apoptosis apoptosis NN 937 942 after after IN 943 953 withdrawal withdrawal NN 954 956 of of IN 957 961 IL-2 il-2 NN 961 962 . . . 963 976 Interestingly interestingly RB 976 977 , , , 978 982 when when WRB 983 985 we we PRP 986 991 fused fuse VBD 992 996 HT-2 ht-2 NN 997 1002 cells cell NNS 1003 1013 expressing express VBG 1014 1017 the the DT 1018 1022 EPOR epor NN 1023 1027 with with IN 1028 1033 Ba/F3 ba/f3 NN 1034 1039 cells cell NNS 1040 1042 in in IN 1043 1044 a a DT 1045 1060 complementation complementation NN 1061 1066 assay assay NN 1066 1067 , , , 1068 1071 the the DT 1072 1081 resulting result VBG 1082 1092 hybridomas hybridoma NNS 1093 1105 proliferated proliferate VBD 1106 1109 and and CC 1110 1118 potently potently RB 1119 1128 activated activate VBN 1129 1135 STAT-5 STAT-5 NNP 1136 1139 and and CC 1140 1144 MAPK MAPK NNP 1145 1147 in in IN 1148 1156 response response NN 1157 1159 to to TO 1160 1163 EPO EPO NNP 1163 1164 . . . 1165 1170 These these DT 1171 1175 data datum NNS 1176 1184 indicate indicate VBP 1185 1189 that that IN 1190 1192 an an DT 1193 1205 unidentified unidentified JJ 1206 1214 cellular cellular JJ 1215 1221 factor factor NN 1222 1224 is be VBZ 1225 1231 needed need VBN 1232 1234 to to TO 1235 1242 mediate mediate VB 1243 1252 signaling signaling NN 1253 1255 by by IN 1256 1259 the the DT 1260 1264 EPOR epor NN 1264 1265 . . . 1266 1274 Moreover moreover RB 1274 1275 , , , 1276 1281 Ba/F3 ba/f3 NN 1282 1287 cells cell NNS 1288 1298 apparently apparently RB 1299 1306 express express VBP 1307 1311 this this DT 1312 1321 factor(s) factor(s) NN 1322 1325 and and CC 1326 1333 somatic somatic JJ 1334 1341 fusions fusion NNS 1342 1345 can can MD 1345 1346 , , , 1347 1356 therefore therefore RB 1356 1357 , , , 1358 1364 confer confer VB 1365 1383 EPO-responsiveness epo-responsiveness NN 1384 1386 to to TO 1387 1391 HT-2 ht-2 NN 1392 1397 cells cell NNS 1398 1402 that that WDT 1403 1407 lack lack VBP 1408 1412 this this DT 1413 1419 factor factor NN 1419 1420 . . .