Overexpression of JAK2 mRNA in Chronic Myeloproliferative Disease and Its Implication on Mutation Testing and Biology of Disease.

The V617F point mutation in the JAK2 gene is considered the most important molecular abnormality that characterizes patients with non-chronic myeloid leukemia (CML)-myeloproliferative disease (MPD). While it is well-documented that the V617F mutation leads to continuous activation of the JAK2-STAT5 pathway, the levels of JAK2 mRNA expression is not well defined in myeloproliferative diseases. We quantified the levels total JAK2 mRNA as well as V617F mutant mRNA in the plasma of patients with non-CML MPD using RT/PCR, and compared the results with clinical findings and disease behavior. Patients with non-CML MPD (n = 175) had significantly higher levels (P <0.0001) of JAK2 mRNA (median, 1843 pg/ul) than patients with CML (median, 71.53 pg/ul) and normal controls (median, 34.34 pg/ul). In contrast, there was no significant difference (P = 0.15) in DNA levels (copies of JAK2 DNA/ul plasma) between CML patients and non-CML MPD patients. There was no significant difference in JAK2 mRNA levels in the MPD group between patients with or without the V617F mutation. There was no significant difference in JAK2 mRNA levels between patients with polycythemia vera, essential thrombocythemia, or agnogenic myeloid metaplasia, or unclassified MPD (P = 0.09). Survival data was available for only 68 patients; JAK2 mRNA levels in these patients did not correlate with overall survival. In contrast, mutant (V617F) JAK2 mRNA levels in the plasma correlated negatively with overall survival in continuous fashion (P = 0.04) when all patients (with and without the mutation) were considered, as well as when only patients with the mutation were considered (P = 0.03). In contrast, when we quantified levels of mutant JAK2 DNA, 4 of the 68 patients who showed mutation using RNA were negative for the V617F mutation by DNA analysis, and the levels of mutant JAK2 DNA did not correlate with survival. This data suggests that JAK2 mRNA is overexpressed in all patients with non-CML MPD, and levels of mutant JAK2 mRNA may correlate with clinical behavior. Furthermore, when testing for JAK2 mutation, RNA rather than DNA should be used.