Molecular Mechanisms To Regulate Phospholipid Scramblase 1 Gene Expression And Its Role In Leukemic Cell Differentiation

Phospholipid scramblase 1 (PLSCR1) is a multiply palmitoylated, calcium-binding type II transmembrane protein. Unpalmitoylated PLSCR1 was also found to localize into the nucleus where it binds to genomic DNA. However, exact mechanisms of regulation of PLSCR1 gene expression and its biological functions remain largely unclear. Based on the discovery that proliferation and terminal differentiation of myeloid precursor cells in response to selective growth factors are impaired in PLSCR1-/-knock-out mice, in the present work, we try to analyze whether and how differentiation-inducing agents influence the expression of PLSCR1 gene in acute myeloid leukemia (AML) cells and the potential roles of PLSCR1 in leukemic cell differentiation. Towards this end, the following original and interesting results were gotten: (1) all-trans retinoic acid (ATRA) and phorbol 12-myristate 13-acetate(PMA), but not other differentiation-inducing agents dimethyl sulfoxide (DMSO), sodium butyrate or vitamin D3, can upregulate the expression of PLSCR1 gene in AML cell lines NB4,HL60 and U937 regardless of differentiation towards granulocyte or monocyte. (2) Based on the facts that both ATRA and PMA result in phosphorylation of protein kinase Cδ(PKCδ), we find that PKCδ-specific inhibitor rottlerin nearly eliminates the ATRA-and PMA-induced PLSCR1 expression while ectopic expression of a constitutively active form of PKCδdirectly increases PLSCR1 expression, suggesting that PKCδmediates the expression of PLSCR1 induced by ATRA and PMA. (3) It has been reported that interferons (IFNs) can upregulate PLSCR1 expression and activate PKCδ. Here we show that pretreatment of rottlerin and transfection of dominant negative mutant of PKCδcan significantly antagonize IFNα2a-induced PLSCR1 expression, indicating that IFNα2a upregulates PLSCR1 also via action of PKCδ. (4) With IFNα2a-upregulated PLSCR1 expression as a model to figure out the molecular mechanisms by which PKCδmodulates PLSCR1 expression, we first reveal that IFNα2a...