MISSENSE MUTATION OF THE ERYTHROPOIETIN RECEPTOR IS A RARE EVENT IN HUMAN ERYTHROID MALIGNANCIES

Human erythroid malignancies (polycythemia vera [PV] and erythroleukem ia) are associated with erythropoietin (Epo)independent growth and dif ferentiation. Missense or nonsense mutations in the Epo receptor (Epo- R) have been recently described in experimental erythroleukemia in mic e and in cases of erythrocytosis in humans. To search for a similar ge netic alteration in erythroleukemia and PV, we entirely sequenced the exons of the Epo-R gene as well as the intron-exon junctions in these disorders using polymerase chain reaction. In 1 of 10 cases of erythro leukemia, a single allele mutation was found in the 8th Epo-R gene exo n that changed asparagine 487 into a serine. No Epo-R gene mutation wa s found in 12 PV cases studied, but the same mutation (N487S) was foun d in 1 patient with polycythemia that did not fulfill the criteria of PV (polycythemia of unknown origin). We did not detect this mutation a fter sequencing part of the 8th exon of the Epo-R gene from 21 other p atients with polycythemia of unknown origin and 51 normal controls, Th e Epo-R mutation was also found in Epstein-Barr virus-derived cell lin es from both cases, suggesting that it is not related to the malignant clone. Therefore, this mutation does not appear to be somatic, althou gh no familial cases were found. The biologic effect of this mutation was subsequently studied. Erythroid progenitors from the polycythemic patient normally responded to Epo, whereas those from the erythroleuke mic patient were Epo-independent due to autocrine stimulation by Epo. The normal and the mutated Epo-R were transfected into the murine Ba/F 3 cell line, Both types of cells displayed the same response to Epo fo r proliferation, differentiation, and inhibition of apoptosis. Althoug h this mutation may destroy a consensus binding site for Grb2, no obvi ous differences either in the pattern of Epo-induced tyrosine phosphor ylated proteins or in the binding of Grb2 to the Epo-R were observed. In conclusion, a somatic Epo-R missense mutation does not appear to be a molecular mechanism involved in the abnormal growth of human erythr oleukemia and PV, However, the Epo-R mutation (N487S) that we describe is located in the same tyrosine sequence beginning at AA 485 as the o ne previously observed (P488S) in a case of polycythemia (Sokol et al, Exp Hematol 22:447, 1994). These results suggest that this phosphopep tide sequence may play an important role in Epo signalling. (C) 1996 b y The American Society of Hematology.