In vitro-generated stem cell leukaemia showing altered cell cycle progression with distinct signalling of the tyrosine-phosphorylated rasGAP-associated p62(dok) protein

In an attempt to gain more insight into the events of leukaemic transformat ion, a cell line overexpressing MHC class II (DIR) was generated by transfe cting an early CD34-negative haematopoietic progenitor stem cell line with the appropriate constructs. The stable transfection with genes for DR antig ens leads to cellular transformation. The DR+ transformed cell clones expre ss a tyrosine-phosphorylated DR heterodimer and show a significantly differ ent morphology. DR+ clones present the morphology of an immature myeloid ne oplasia expressing alpha -naphthylacetate-esterase (ANAE), but neither myel operoxidase nor CD34. While D064 cells predominately grow adherent as fibro blast-like cells, the DR+ clones display a decrease in adherent growth. Alt hough both cell lines express similar amounts of the interleukin-6 (IL-6) s ignal transducer gp130, the DR-transfected cells still show activation of S TAT factors by IL-6, whereas D064 cells do not. Although the transformed cl ones present acceleration of cell-cycle transition and growth, the G(0)/G(I ) progression inhibitor p27(kip-1), up-regulated, while the expression of p roteins involved in the S/G(2) phase transition, such as cyclin B and cdc2 (p34), is suppressed. Instead cyclin D3, one of the G(0)/G(1) progression f actors, is up-regulated, as well as tyrosine-phosphorylated p62(dok), sugge sting dysregulation of cell cycle-controlling proteins. In addition, DR+ le ukaemia-like cells also overexpress Bcl-2, while bax expression is suppress ed, compared with the wild-type (wt) parental haematopoietic stem cell line . Copyright (C) 2000 John Wiley & Sons, Ltd.