Expression of P62, A Putative Collagen Receptor, on Human Megakaryocytic Leukemia Cells

Megakaryocytic leukemia and platelet factor 4

The de novo megakaryocytic leukemia fulfilling the FAB criteria is still an uncommonly recognized variant of acute leukemia. Many studies have shown that the megakaryocytic leukemic events may occur at a pluripotent stem cell level and clinical observations reveal that the megakaryocytic leukemias are diverse entities. The immunophenotyping using monoclonal antibodies against platelet specific surface antigens and the ultrastructural detection of platelet peroxidase reaction do not provide sufficiently useful information to determine whether a megakaryocytic leukemia is chronic, acute, therapy-responsive or therapy-unresponsive. More sophisticated techniques are required to further characterize megakaryocytic leukemic cells. In this review, we emphasize that megakaryocytic leukemic cells can be categorized into two groups; one with the PF4 mRNA, and the other without it, and that the expression of PF4 mRNA in the blasts could be a useful marker for the identification of mature megakaryoblasts. It seems that the patients with blasts expressing PF4 mRNA will have a longer survival and a better response to chemotherapy than those without PF4. We further discuss the fact that the detection of mRNAs of the IL-6 receptor, PDGF A- and B-chains, and TGF beta 1 in megakaryocytic leukemic cells will be useful to clarify the mechanisms involved in the proliferation of megakaryocytic leukemic cells and fibroblasts in the bone marrow. Furthermore, we reviewed data showing that megakaryocytic erythroid, and mast cell lineages share the nuclear transcription factor known as GF-1 (NF-E1 or Erf-1). We suggest that characterization of megakaryocytic leukemia should be performed using monoclonal antibodies against erythroid, megakaryocytic and mast cell lineages.

Detection of platelet-specific protein mRNAs in different megakaryoblasts using the reverse transcriptase polymerase chain reaction

The short segments of cDNA encoding glycoprotein (GP)Ib alpha, GPIIb, GPIIIa and platelet factor (PF) 4 were amplified using reverse transcriptase-polymerase chain reaction (RT-PCR) in order to characterize various types of megakaryoblasts. Cell lines with megakaryocytic features (K562, CMK and HEL) were tested. GPIb alpha, GPIIb and GPIIIa mRNAs were found to be present in K562, CMK and HEL cells, while only HEL cells expressed PF4 or mRNA. These results suggested that megakaryoblastic cell lines could be categorized into two groups, one with the PF4 transcript and the other without it. PF4 mRNA was present in the cells obtained from one Down's syndrome patient with transient myeloproliferative disorder and in one patient with primary myelofibrosis and megakaryoblastosis. On the other hand, one patient with acute megakaryoblastic leukemia transformed from refractory anemia had a poor prognosis with megakaryoblastic leukemia cells which expressed no PF4 mRNA. These observations suggested that the expression of PF4 mRNA in peripheral blood megakaryoblasts may indicate the absence of a true leukemic process.