THE GENE ENCODING HEMATOPOIETIC-CELL PHOSPHATASE (SHP-1) IS STRUCTURALLY AND TRANSCRIPTIONALLY INTACT IN POLYCYTHEMIA-VERA

Polycythemia vera (PV) is an acquired clonal disorder characterized by increased production of mature red cells and growth of erythroid colo nies in the absence of erythropoietin. Mutation of the erythropoietin receptor has been demonstrated to cause familial polycythemia, but no mutations have been found in PV, Moreover, both erythroid and myeloid progenitors from patients with PV have been reported to be hypersensit ive to a number of different growth factors. Attention has therefore f ocused on post-receptor signal transduction pathways, The SHP-1 gene i s an especially attractive candidate gene. Firstly, SHP-1 binds to and negatively regulates signalling from the erythropoietin receptor and is likely to regulate other cytokine receptors in a similar manner, Se condly, absence of SHP-1 protein in the motheaten mouse is accompanied by increased sensitivity of hematopoietic progenitors to a number of cytokines including erythropoietin, Thirdly, familial or sporadic poly cythemia in man may result from mutations of the SHP-1 binding domain of the erythropoietin receptor. We have therefore searched for mutatio ns of the SHP-1 gene in genomic DNA from patients with PV. In this dis ease the majority of peripheral blood lymphocytes are not part of the malignant clone and a variable proportion of myeloid cells may arise f rom normal progenitors. We have therefore chosen to study DNA from pur ified peripheral blood granulocytes obtained from nine women in whom t he granulocytes were clonally derived. Southern analysis was used to s how that the gene was not rearranged and densitometry confirmed the pr esence of two copies of the gene in each DNA sample. Sequencing of the entire coding region and all splice junctions revealed no mutations, Hematopoietic transcription factor binding sites in the SHP-1 promoter region were intact and the methylation status of the two SHP-1 promot ers in PV patients was identical to that in three normal controls, Fin ally, we showed that levels of SHP-1 protein in granulocytes from pati ents was similar to those from normal controls. These results demonstr ate that the SHP-1 gene is structurally and transcriptionally intact i n patients with PV.