A regulatory role for tumor necrosis factor (TNF) in ML-1 human myeloblastic leukemia cell maturation

Upregulation of TLR1, TLR2, TLR4, and IRAK-2 Expression During ML-1 Cell Differentiation to Macrophages: Role in the Potentiation of Cellular Responses to LPS and LTA

12-O-tetradecanoylphorbol 13-acetate (TPA) induces the differentiation of human myeloid ML-1 cells to macrophages. In the current study, the expression, responsiveness, and regulation of toll-like receptors (TLRs) in TPA-induced ML-1-derived macrophages were investigated. We have found that TPA-induced differentiation of ML-1 cells was accompanied by the upregulation of TLR1, TLR2, TLR4, and CD14 expression at both the mRNA and protein levels. Interestingly, TLR1 and TLR4 protein expression on ML-1 cells could be blocked by pretreatment with U0126, suggesting the role of an Erk1/2-induced differentiation signal in this process. In addition, the expression of IRAK-2, a key member of the TLR/IRAK-2/NF-κB-dependent signaling cascade was also induced in response to TPA. Accordingly, we demonstrated an increased cellular release of inflammatory cytokines (TNF-α and various interleukins) upon stimulation with LPS and LTA ligands for TLR4 and TLR2, respectively. Furthermore, using luminol-dependent chemiluminescence, addition of LPS and LTA induces a sustained DPI-inhibitable generation of reactive oxygen species (ROS) by the differentiated ML-1 cells. Together, these data suggest that the increase in the responsiveness of TPA-treated ML-1 cells to LPS and LTA occurs in response to the upregulation of their respective receptors as well as an induction of the IRAK-2 gene expression.

NF-kappaB (p65/RelA) as a regulator of TNFalpha-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-1) and transferrin (Tf) are supplied, but differentiate to monocytes when these factors are replaced by the tumor necrosis factor-alpha (TNF-alpha). Induction of differentiation, but not of proliferation, involved the selective activation of diverse members of the NF-kappaB family of proteins. In differentiation-induced cells, NF-kappaB (p65) was translocated from the cytoplasm to the nucleus, 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 translocation of NF-kappaB (p65) from the cytoplasm to the nucleus was mediated by an increase in the level of NIK, the NF-kappaB-inducing kinase which, through phosphorylation of IkappaB kinase alpha (Ikappakalpha), causes a decrease in the level of IkappaBalpha, allowing p65 to move from the cytoplasm to the nucleus. The p52/p65 heterodimer formed in the nucleus, bound specifically 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 previously (Li et al, Cancer Res 1998; 58: 4282-4287), that increase led to the decreased expression of proliferating cell nuclear antigen (PCNA) and to the loss of proliferation-associated DNA synthesis. The ensuing uncoupling of growth from differentiation was followed by the initiation of the monocyte-specific differentiation program.

Induction of differentiation and down-regulation of c-myb gene expression in ML-1 human myeloblastic leukemia cells by the clinically effective anti-leukemia agent meisoindigo

Meisoindigo, a second generation derivative of indirubin, is an effective chemotherapeutic agent with very low toxicity used in the treatment of chronic myeloid leukemia. To determine the nature of this activity, the effect of a nontoxic concentration (0.72 micrograms/mL) of this compound on ML-1 human myeloblastic leukemic cells was examined. At such a concentration, differentiation induction was found to be the most pronounced drug effect. During the 3-day drug incubation period, the viable cell number remained essentially constant, with approximately 48% of the cells demonstrating a mature phenotype with increased acid phosphatase activity and nitroblue tetrazolium dye reduction. As observed with other DNA-specific agents, induction of ML-1 differentiation by meisoindigo was accompanied by the down-regulation of c-myb gene expression. These data suggest that induction of leukemic cell differentiation associated with decreased c-myb expression may be one of the mechanisms of the antitumor action of meisoindigo.

Serum TNF-alpha, gamma-INF, G-CSF and GM-CSF levels in neutropenic children with acute leukemia treated with short-course, high-dose methylprednisolone

High-dose methylprednisolone (HDMP, 20-30 mg/kg/day po) treatment has been shown to increase the number of bone marrow and peripheral blood CD34 positive progenitors and serum granulocyte-macrophage colony-stimulating factor (GM-CSF) levels in patients with ALL and AML. To investigate the effect of HDMP on some other hematopoietic regulatory cytokines, tumor necrosis factor-alpha (TNF-alpha), gamma-interferon (gamma-INF), granulocyte colony-stimulating factor (G-CSF) and interleukin-6 (IL-6) were studied by microplate ELISA technique in 15 chemotherapy-induced neutropenic episodes of 14 children with acute leukemia (eight with ALL and six with AML) in whom HDMP was given alone (30 mg/kg/day po) for 4 days. The absolute neutrophil counts increased significantly in all neutropenic episodes on the fourth day of HDMP treatment. The TNF-alpha was 93.5 +/- 161 pg/ml in ALL and 78.3 +/- 61.4 pg/ml in AML before treatment and 76.1 +/- 160 pg/ml in ALL and 19.1 +/- 39.8 pg/ml in AML after treatment. The gamma-INF was 204.1 +/- 210.3 pg/ml in ALL and 130.8 +/- 138.3 pg/ml in AML before treatment and 28.6 +/- 50.5 pg/ml in ALL and 23.3 +/- 20.4 pg/ml in AML after treatment (P<0.05). Serum G-CSF and GM-CSF levels increased in all episodes (100%). The GM-CSF levels increased from 12.2 +/- 10.9 pg/ml to 36 +/- 24.7 pg/ml after treatment in ALL (P<0.05) and from 13.3 +/- 4 pg/ml to 45 +/- 48.1 pg/ml in AML (P<0.05). Serum G-CSF levels increased from 13.3 +/- 11.7 pg/ml to 83.3 +/- 86.8 pg/ml after treatment in ALL (P<0.05) and from 6.6 +/- 12.1 pg/ml to 28.3 +/- 11.3 pg/ml in AML (P<0.05). However, IL-6 levels were undetectable in all patients before and after therapy. These preliminary data suggest that short-course HDMP treatment could decrease serum TNF-alpha and gamma-INF and increase G-CSF and GM-CSF levels.

Tumor necrosis factor activities and cancer therapy--a perspective

Tumor necrosis factor (TNF) is a multifunctional cytokine which has excited and fascinated numerous investigators and commercial entities due to its promise as a therapeutic agent against cancer and as a target for drugs treating septic shock. TNF is a protein having cytotoxic, cytostatic, immunomodulatory as well as several other activities and is also involved in septic shock. This review covers the structure of TNF and its receptors, various in vitro activities and in vivo activities based on studies in animal model systems. The role of TNF as an anticancer therapeutic agent, based on various phase I and phase II clinical studies, has also been considered. The review concludes with several considerations for increasing the therapeutic utility of TNF in terms of targeting, toxicity and half-life.