The role of S100A4 in Acute Myeloid Leukaemia

Nuclear mislocalization of proteins can interfere with normal cellular function and cooperatively drive tumour development. To understand how this process mediates AML development, the nuclear proteome of AML blasts was analyzed in comparison with normal human CD34+ cells to identify misregulated nuclear proteins. This study identified that S100A4 as the most significant and fold changing protein in AML blasts which has not been previously associated with AML. S100A4 belongs to the S100 multigene family of calcium-binding proteins of the EF-hand type and has been implicated in tumour progression and metastasis in many solid tumours but little is known of its role in haematological malignancy. Using western blotting, S100A4 protein expression was observed in the nucleus of AML blasts FAB M1 (83%; 24/33) and 44% FAB M4 (4/9) whilst normal CD34+ or CD14+ differentiated monocytic controls have shown only cytosolic expression of S100A4. An independent dataset (TCGA) supports the overexpression of S100A4 mRNA in AML and suggests that overexpression may confer a poor prognosis (p=0.0118). To determine whether ectopic expression of nuclear S100A4 can affect the growth and survival of normal hematopoietic cells, CD34+ cells were infected with lentiviral vectors expressing nuclear-targeted S100A4. Overexpression of nuclear S100A4 could not be demonstrated in transduced CD34+ cells or in normal differentiated cells (probably due to rapid degradation of ectopically expressed S100A4 in these cells). To examine functional significance of S100A4 expression on normal and leukaemic cells, S100A4 expression was knocked down. In CD34+ cells, no significant effects were observed on the growth or lineage development of these cells suggesting S100A4 is not required for normal hematopoiesis. Conversely, knocking down S100A4 expression in AML lines (NOMO-1, TF-1, THP-1, and OCIAML2) showed significant reduction in growth and induced cell death through apoptosis suggesting that AML cells are dependent on S100A4 for their growth and survival. Further, to identify the binding partners of S100A4 through which mediates its functions, a co immunoprecipitation coupled with LC/MS was performed on cytoplasmic and nuclear extract of AML cell line (ME-1) under Ca2+ enriched conditions. Heterogeneous nuclear Ribonucleoprotein M (hnRNPM) was identified as novel binding partner of S100A4 AML. These findings suggest that therapeutically targeting S100A4 would be an effective strategy in AML while sparing normal hematopoietic cells