The gene encoding hematopoietic cell phosphatase (SHP-1) is structurally and transcriptionally intact in polycythemia vera

Abstract

Polycythemia vera (PV) is an acquired clonal disorder characterized by increased production of mature red cells and growth of erythroid colonies 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 hypersensitive to a number of dierent growth factors. Attention has therefore focused on post-receptor signal transduction pathways. The SHP-1 gene is 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. Secondly, 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 polycythemia in man may result from mutations of the SHP-1 binding domain of the erythropoietin receptor. We have therefore searched for mutations of the SHP-1 gene in genomic DNA from patients with PV. In this disease the majority of peripheral blood lymphocytes are not part of the malignant clone and a variable proportion of myeloid cells may arise from normal progenitors. We have therefore chosen to study DNA from puri®ed peripheral blood granulocytes obtained from nine women in whom the granulocytes were clonally derived. Southern analysis was used to show that the gene was not rearranged and densitometry con®rmed the presence 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 promoters in PV patients was identical to that in three normal controls. Finally, we showed that levels of SHP-1 protein in granulocytes from patients was similar to those from normal controls. These results demonstrate that the SHP-1 gene is structurally and transcriptionally intact in patients with PV.

Increased expression of the INK4a/ARF locus in polycythemia vera

“…19 However, the increase in PTP may represent an effect of the disease rather than a cause. SHP-1 was completely characterized in PV cells and was found to be normal, 19,20 although one group provided evidence for its underexpression. 21 Despite the development of much new knowledge on the control of erythropoiesis, the precise molecular defect that leads to enhanced hematopoiesis in PV is still not apparent.…”

Epigenetic inactivation of suppressors of cytokine signalling in Philadelphia‐negative chronic myeloproliferative disorders

“…In addition to aberrant DNA methylation, genetic inactivation of SOCS1 by somatic mutation has also been reported in Hodgkin lymphoma and primary mediastinal B cell lymphoma (Melzner et al, 2005;Weniger et al, 2006). Methylation of PTPN6 has been reported in myeloma, lymphoma and acute leukaemia, whereas mutational screening of the gene failed to detect structural alterations in CMPD (Chim et al, 2004;Khoury et al, 2004;Johan et al, 2005;Zhao et al, 2005;Asimakopoulos et al, 1997).…”

Polycythemia vera: myths, mechanisms, and management

“…22 Despite claims to the contrary, 23,24 this hypersensitivity does not appear to be the consequence of an abnormality in the negative regulatory hematopoietic phosphatase, SHP-1. 25,26 Indeed, evidence has been obtained for increased activity of a membrane-associated protein tyrosine phosphatase in polycythemia vera erythroid progenitor cells 27 and although overexpression of INK4a and ARF has also been documented in these cells 28 and constitutive phosphorylation of STAT3 has been observed in the granulocytes in a minority of patients, 29 no consistent abnormality of signal transduction or cell cycle regulation has been identified to date in polycythemia vera nor have mutations been identified in p53 or Ras during the chronic phase of the illness. 30 There is evidence for both gain 31,32 and loss 33,34 of suppressor genes in polycythemia vera but exactly which genes and how they might affect erythroid progenitor cell behavior remain unknown.…”