Deregulation of the phosphatase PP2A in haematopoietic cell lines

Abstract

Haematopoieisis is a long life process, providing different mature functional cells required by physiological demand. In addition to lineage commitment, expansion and differentiation of a specific progenitor pool has to be maintained. This complex process is under the control of transcription factors, growth factors and extrinsic factors. Deregulation of genes results in an imbalance between cell proliferation and differentiation, hence the malignant phenotype. Previous studies using cellular models show the importance of suppressed feedback mechanisms, in particular the regulation of the phosphatase PP2A. The aim of this study was to (1) characterise variations in PP2A transcripts; (2) correlate the PP2A activity with the presence of the mutants using haematopoietic cell lines; and (3) investigate the presence of the resulting mutants/isoforms in a panel of Chronic Myeloid Leukaemia patient samples using cDNA. 6 leukaemia cell lines were used to scan the PPP2CA coding sequence for variations. All nucleotide substitutions identified were silent mutations. A novel splice variant was identified in the PPP2CA as a result of exon 2 skipping, hence called PPP2CAL12 variant. This indicates that interfering with PPP2CA function is not a common event. Interestingly, the BCR-ABL positive cell line, BV173 expressed the PPP2CAL12 variant only. In addition, PPP2CAL12 splice variant was detected at low expression levels in chronic myeloid leukaemia (CML) patient samples.