Detection of increased icb-1 transcript levels in maturing HL-60 cells: a novel marker for granulocytic and monocytic in vitro differentiation.

Human gene icb-1 was initially described as a gene with increased expression in endometrial tumor cells differentiated in vitro by culture on a reconstituted basement membrane. We provide evidence for a more general involvement of icb-1 gene function in cellular differentiation processes. We report the up-regulation of icb-1 transcript levels in HL-60 promyelocytic leukemia cells during their in vitro differentiation induced by all-trans retinoic acid, vitamin D(3) or DMSO. Increased icb-1 mRNA levels could be observed both in monocytic and granulocytic differentiation. We also report the identification of the novel icb-1 splice variants icb-1beta and gamma, and the spleen-specific isoform icb-1delta. Expression of icb-1 can be used as a novel marker for in vitro differentiation processes of HL-60 cells.