Polycythemia vera is mainly related to JAK2 mutations, whereas a wider mutational spectrum is detected in essential thrombocythemia (ET) with mutations in JAK2, the thrombopoietin (TPO) receptor (MPL), and the calreticulin (CALR) genes.
More importantly, we demonstrated that this MPL Y252H mutant confers increased TPO/MPL-mediated cell growth and increased cell survival upon cytokine withdrawal in BaF3 cells, indicating it is a disease-driving mutation and may contribute to the development of ET in vivo.
Acquired mutations in the juxtamembrane region of MPL (W515L or W515K), the receptor for thrombopoietin, have been reported in patients with primary essential thrombocythemia (ET) or primary myelofibrosis (PMF).
Mpl surface and total protein expression were normal, and TPO levels were mildly increased in the MPLW515L-positive ET patient, while MPL transcripts did not differ from controls in both MPLW515L-positive patients.
Acquired mutations in the juxtamembrane region of MPL (W515K or W515L), the receptor for thrombopoietin, have been described in patients with primary myelofibrosis or essential thrombocythemia, which are chronic myeloproliferative disorders.
PRV-1 (polycythemia rubra vera-1), TPO (thrombopoietin), and c-MPL (myeloproliferative leukemia virus oncogene) genes are candidate ET molecular markers because of their implication in the pathogenesis of ET.
As compared to the published normal sequence of the TPO gene, one allelic base change in a non-coding region of intron 1 was found in all children with ET and ST, but this was reported as a common finding in normal subjects as well.
On the basis of the array results, we characterized apoptosis of normal and ET MKs by time-course evaluation of annexin-V and sub-G1 peak DNA stainings of immature and mature MKs after culture in serum-free medium with an optimal thrombopoietin concentration, and annexin-V-positive MKs only, with decreasing thrombopoietin concentrations.
CD34+ cells from patients with ET, chronic myeloid leukemia (CML), polycythemia vera (PV) and normal individuals were cultured in serum-free medium supplemented with thrombopoietin (TPO).
New insights are emerging into the role of the megakaryocytopoiesis regulator thrombopoietin (TPO) and its receptor, c-Mpl, in ET and related disorders, but TPO-Mpl dynamics appear to be complex.
These results also suggest that the thrombocytosis in ET may be attributed to an alteration of the normal feedback interaction between TPO and its receptor and not as a result of any defect in the structure of TPO or c-mpl.
Although activating mutation in the TPO gene, which leads to overexpression of TPO mRNA, has been reported in familial thrombocythemia, these results suggest that TPO-c-Mpl system may not be directly linked to pathogenesis of sporadic ET.