Epigenetic Downregulation of Secreted Frizzled-Related Proteins In Philadelphia Positive and Philadelphia Negative Myeloproliferative Neoplasms

Hypermethylation of CpG islands in promoter regions is associated with transcriptional inactivation and represents an important mechanism of tumor suppressor gene silencing and plays a role in the pathogenesis of hematopoietic malignancies. Myeloproliferative neoplasms (MPN) constitute a heterogenous group of hematopoietic malignancies and comprise chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). BCR/ABL-negative MPN (Ph-MPN) are often characterized by an autoactivating mutation in the JAK2 tyrosine kinase (JAK2V617F) as well as additional mutations in the JAK-STAT pathway. Secreted Frizzled-related proteins (SFRPs) are antagonists of the Wnt signaling pathway. Consistent with the central role of the Wnt pathway for stem cell maintenance and differentiation of hematopoietic progenitors. Upregulation of Wnt-pathway has been described in haematopoietic malignancies and epigenetic downregulation of SFRPs has been shown in acute leukemia.

We determined the promoter methylation status of SFRP1, -2, -4 and -5 in human cell lines and in 60 samples from MPN patients by methylation-specific PCR (MSP). The JAK2V617F mutation was assessed by allele-specific PCR.

Aberrant methylation among primary MPN samples was 5 % (3/60) for SFRP-1, 24 % (14/60) for SFRP-2, 2% (1/60) for SFRP-4 and 0% (0/60) for SFRP-5. The SFRP-2 promoter was methylated in 0% of CML (0/12), 27% of PV (3/11), 30% of ET (3/10) and 26% of PMF patient samples (7/27). There was no correlation between SFRP-2 hypermethylation and MPN subtype. We detected a trend for a correlation between methylation of the SFRP-2 promoter and presence of JAK2V617F mutation (p = 0,1).

Our data indicate that epigenetic dysregulation of the Wnt signaling pathway is a common event in Ph-MPN with aberrant methylation of at least one SFRP being detected in 30% of the primary patient samples with the most predominant member of the family, SFRP2 being methylated in about one third of the cases. Aberrant methylation of SFRPs may contribute to the pathogenesis of MPN by influencing stem cell maintenance and proliferation of hematopoietic progenitors.

No relevant conflicts of interest to declare.