Constitutive expression of the FK506 binding protein 51 (FKBP51) in bone marrow cells and megakaryocytes derived from idiopathic myelofibrosis and non‐neoplastic haematopoiesis

Abstract: Objectives: Overexpression of FK506 binding protein 51 (FKBP51) in megakaryocytic progenitor cells generated from purified CD34+ cells in patients with idiopathic myelofibrosis (IMF) has been demonstrated. It has been suggested that FKBP51 is involved in the dysregulation of the apoptotic programme with consecutive prolongation of cell survival. The knowledge of FKBP51 and its expression in bone marrow cells and mature megakaryocytes in non‐neoplastic haematopoiesis and IMF is sparse. Methods: To evaluate a potential overexpression of FKBP51 in patients with IMF ( n = 37) compared with non‐neoplastic haematopoiesis ( n = 31), total bone marrow cells as well as single megakaryocytes, isolated by laser microdissection, were quantitatively analysed by real‐time reverse transcriptase‐polymerase chain reaction (RT‐PCR). By applying immunohistochemistry, FKBP51 gene expression was correlated with staining pattern and cellular localisation of the corresponding FKBP51 protein. Results: We demonstrated that FKBP51 is constitutively expressed in non‐neoplastic haematopoiesis. FKBP51 gene expression by total bone marrow cells as well as megakaryocytes was not significantly different in IMF. FKBP51 protein expression could be localised to myeloid progenitor cells as well as megakaryocytes. In particular, megakaryocytes were stained almost exclusively nuclear for FKBP51. No differences in expression patterns between both IMF and control cases could be demonstrated. Conclusions: For the first time, FKBP51 expression, in particular gene expression and subcellular localization was described in bone marrow cells of non‐neoplastic and neoplastic haematopoiesis grown in vivo . We conclude that FKBP51 could be temporarily overexpressed in megakaryocytic progenitors rather than contribute to the accumulation of mature megakaryocytes in IMF.