STUDY OF THE ALTERNATIVE ISOFORMS OF PRDM16 PROTEIN AND OF THEIR POSSIBLE ROLE IN LEUKEMOGENESIS

PRDM16 is a member of PRDM gene family, composed of 17 genes. All the PRDM genes so far connected to cancer have (at least) two isoforms, which differ by the presence (PR+) or absence (PR-) of the PR domain that is related to SET domain of histone lysine methyltransferases (HKMTases). In cancer cells, PR+ protein is often disrupted or underexpressed, whereas PR- isoform is present or overexpressed. The presence of the oncogenic PRDM16 PR- isoform together with PRDM16 PR+ has been suggested in Acute Myeloid Leukemia with normal karyotype (AML NK), however the mechanisms through which it is generated remains obscure. We demonstrated that in GDM1 AML cell line both PR- and PR+ isoforms are expressed and PR- transcript is generated by alternative splicing. Considering relative abundance of the two isoforms in AML we wanted to investigate PR+ and PR- protein-genomic binding sites by ChIP-seq technology. Both PRDM16 isoforms bind to the DNA in human cells in thousands of sites. Interestingly, we demonstrated that PRDM16 PR+ binding is dramatically changed when PR- isoform is co-expressed in cells, in respect to the model system when only PR+ protein is present. This is due to PR+/PR- complex formation and displacement of PR+ from its target proximal promoters.