NF-kappa B (p65/RelA) as a regulator of TNF alpha-mediated ML-1 cell differentiation

ML-1 human myeloblastic leukemia cells, suspended in serum-depleted medium, proliferate when the insulin-like growth factor-1 (IGF-I) and transferrin (Tf) are supplied, but differentiate to monocytes when these factors are re placed by the tumor necrosis factor-alpha (TNF-alpha). Induction of differe ntiation, but not of proliferation, involved the selective activation of di verse members of the NF-kappaB family of proteins. In differentiation-induc ed cells, NF-kappaB (p65) was translocated from the cytoplasm to the nucleu s, whereas NF-kappaB (p75) remained localized to the cytoplasm. In contrast , NF-kappaB (p52) was present in the nuclei of proliferation- as well as of differentiation-induced ML-1 cells. The differentiation-specific transloca tion of NF-kappaB (p65) from the cytoplasm to the nucleus was mediated by a n increase in the level of NIK, the NF-kappaB-inducing kinase which, throug h phosphorylation of I kappaB kinase alpha (I kappak alpha), causes a decre ase in the level of I kappaB alpha, allowing p65 to move from the cytoplasm to the nucleus. The p52/p65 heterodimer formed in the nucleus, bound speci fically to the promoter of the tumor suppressor protein p53, effecting a 25 to 30-fold increase in the level of this protein. As we reported previousl y (Li et al, Cancer Res 1998; 58: 4282-4287), that increase led to the decr eased expression of proliferating cell nuclear antigen (PCNA) and to the lo ss of proliferation-associated DNA synthesis. The ensuing uncoupling of gro wth from differentiation was followed by the initiation of the monocyte-spe cific differentiation program.