Jak2 Mutation in Myeloproliferative Neoplasms: Is It Just An Exon Episode?.

Abstract 4982

The discovery of the V617F point mutation of JAK2 has revolutionized the understanding of the pathogenesis of BCR-ABL-negative myeloproliferative neoplasms (MPNs). Further discoveries of other JAK2 exon 12-15 and MPL mutations have extended the scope of the research in this field. However, a very small proportion of patients with polycythemia vera (PV) and 50% of patients with essential thrombocythemia (ET), as well as primary myelofibrosis (PMF), are negative for JAK2 or MPL mutations. This indicates that other forms of the mutations may exist and needs further evaluation

Recently, we treated a patient with ET who did not carry JAK2 V617F or JAK2 exon 12 mutations. The genomic DNA of mononuclear cells from heparin-treated bone marrow as well as he gastric tissue from paraffin embedding samples obtained from the patient was extracted using a DNA extraction kit, according to the manufacturer's instruction (Promega, Madison, WI, USA), and stored at -20°C. For mutation analysis of the JAK2 exon 12 and exon 14, genomic DNA was amplified respectively by polymerase chain reaction. And the PCR products either 358bp or 308bp were generated by forward primers within the exon 12 or exon 14 and forward primers within the intron 12 or intron 14(primer sequences and PCR conditions are provided on request). The direct sequencing on ABI-3100-Avant was used for mutation detection.

No mutation was found within JAK2 exon 12 or exon 14. However, a C/T mutation was detected in intron 14 at the position 14 downstream of the exon 14 in bone marrow cells. Informatively, this mutation was not found in genomic DNA of the gastric tissue. Further more, this novel mutation was not found in all samples from 59 MPN patients in our institute, among which 23 were diagnosed with PV, 22 ET, 12 PMF and 2 MPN-U. No such mutation was demonstrated in bone marrow mononuclear cells from 10 normal subjects. Preliminary results by flow cytometric analysis showed that hematopoietic cells including granulocytes, erythrocytes and megakaryocytes all showed elevated tyrosine kinase activity.

We concluded that mutations in JAK2 mRNA splicing region might also contribute to the aberrant signal transduction in hematopoiesis. And direct sequencing for JAK2 whole genomic DNA might be a suitable method for finding novel JAK2 novel mutation in JAK2 negative patients. Further functional study for evaluation of the effect of nucleotide changes within mRNA splicing sequences in wild type and mutated JAK2 cell lines as well as animal models would provide more convincing evidence of the relationship between JAK2 intron mutation and MPNs..