Elevation of adenylate cyclase activity during leukemic cell differentiation

cAMP inhibits CSF-1-stimulated tyrosine phosphorylation but augments CSF-1R-mediated macrophage differentiation and ERK activation

Macrophage colony stimulating factor (M-CSF) or CSF-1 controls the development of the macrophage lineage through its receptor tyrosine kinase, c-Fms. cAMP has been shown to influence proliferation and differentiation in many cell types, including macrophages. In addition, modulation of cellular ERK activity often occurs when cAMP levels are raised. We have shown previously that agents that increase cellular cAMP inhibited CSF-1-dependent proliferation in murine bone marrow-derived macrophages (BMM) which was associated with an enhanced extracellular signal-regulated kinase (ERK) activity. We report here that increasing cAMP levels, by addition of either 8-bromo cAMP (8BrcAMP) or prostaglandin E(1) (PGE1), can induce macrophage differentiation in M1 myeloid cells engineered to express the CSF-1 receptor (M1/WT cells) and can potentiate CSF-1-induced differentiation in the same cells. The enhanced CSF-1-dependent differentiation induced by raising cAMP levels correlated with enhanced ERK activity. Thus, elevated cAMP can promote either CSF-1-induced differentiation or inhibit CSF-1-induced proliferation depending on the cellular context. The mitogen-activated protein kinase/extracellular signal-related protein kinase kinase (MEK) inhibitor, PD98059, inhibited both the cAMP- and the CSF-1R-dependent macrophage differentiation of M1/WT cells suggesting that ERK activity might be important for differentiation in the M1/WT cells. Surprisingly, addition of 8BrcAMP or PGE1 to either CSF-1-treated M1/WT or BMM cells suppressed the CSF-1R-dependent tyrosine phosphorylation of cellular substrates, including that of the CSF-1R itself. It appears that there are at least two CSF-1-dependent pathway(s), one MEK/ERK dependent pathway and another controlling the bulk of the tyrosine phosphorylation, and that cAMP can modulate signalling through both of these pathways.

Rapid induction of cAMP/PKA pathway during retinoic acid-induced acute promyelocytic leukemia cell differentiation

The second messenger cyclic adenosine monophosphate (cAMP) plays an important role in cell proliferation, differentiation and apoptosis. In the present work, we evaluated the cAMP signaling in acute promyelocytic leukemia (APL) cells in the context of differentiation induced by all-trans retinoic acid (ATRA). There was a marked increase in the intracellular cAMP level within a few minutes after treatment with ATRA in APL cell line NB4 and fresh APL cells, whereas no such phenomenon was observed in NB4-R1 cells that are resistant to ATRA-induced maturation. In addition, the basal level of intracellular cAMP was lower in NB4-R1 than in NB4 cells. Mechanistic study showed that this induction of cAMP was mediated through the activation of adenylate cyclase. Moreover, we found that cAMP-dependent protein kinase (PKA) activity was quickly upregulated in parallel in ATRA-treated NB4 cells, and the phosphorylation of RARalpha by PKA could increase its transactivation effect. Use of H-89, an inhibitor of PKA, could partially suppress the transcriptional expression of ATRA target genes and ATRA-induced differentiation of APL cells. Taken together, we suggested a crosstalk between ATRA-induced cytosolic pathway and nuclear pathway in APL cell differentiation.

Induction of differentiation in human HL-60 cells by 4-hydroxynonenal, a product of lipid peroxidation

4-Hydroxynonenal (HNE) is the major diffusible toxic product generated by lipid peroxidation of cellular membranes. The level of lipid peroxidation and, consequently, the concentration of its products are inversely related to the rate of cell proliferation and directly related to the level of cell differentiation. In the present paper the effects of HNE on the proliferation and differentiation of the HL-60 human promyelocytic cell line have been investigated. Repeated treatment at 45-min intervals with HNE (1 microM) was performed to maintain the cells in the presence of the aldehyde for 7 1/2 or 9 h. The effect of HNE on cell proliferation and differentiation was compared with dimethyl sulfoxide (DMSO)-treated cells. HNE causes a strong inhibition of cell growth without affecting cell viability. Moreover, HL-60 cells acquire the capability to produce chemiluminescence after soluble (phorbol myristate acetate) or corpuscolate (zymosan) stimulation. The phagocytic ability has also been calculated by counting the number of cells that phagocytize opsonized zymosan. Values were 43 and 55% after 10 or 12 HNE treatments, respectively, and 88% in DMSO-treated cells. Myeloperoxidase activity, 5 days after treatment, decreased by 85% in either HNE- or DMSO-treated cells while acid phosphatase activity increased with respect to untreated cells. Results obtained indicate that HNE at concentrations close to those found in the normal tissues can induce inhibition of proliferation and induction of differentiation in the HL-60 cell line.

The differentiating agent, retinoic acid, causes an early inhibition of inositol lipid-specific phospholipase C activity in HL-60 cells

Retinoic acid, a derivative of vitamin A, is shown to inhibit the levels of inositol phosphates and diacylglycerol by 25-30% when added to intact HL-60 cells at concentrations which induce differentiation. The onset of inhibition occurs after 10 min and reaches a maximum at 45 min. To study the mechanism and the site of action of retinoic acid, the activity of the phosphatidylinositol bisphosphate-specific phospholipase C was studied in cells permeabilized with streptolysin O and in membrane preparations. Phospholipase C activity was stimulated either via the guanine nucleotide regulatory protein (G-protein) or directly by Ca2+. Retinoic acid treatment, in a time- and concentration-dependent manner, led to a decrease in phospholipase C activity when stimulated with either GTP gamma S or NaF, both of which activate the enzyme via the G-protein. By contrast, it had no effect on the enzyme activity when stimulated with Ca2+ alone. This indicates that retinoic acid interferes with the coupling of the G-protein and phospholipase C. A relationship between the inhibition of phospholipase C activity and the induction of differentiation by retinoic acid was investigated. Only a small inhibition of GTP gamma S-stimulated phospholipase C activity was observed when an analogue of retinoic acid, etretine or Ro10-1670, with low differentiating activity, was used. Moreover, no inhibition of the GTP gamma S-stimulated phospholipase C activity was observed in an HL-60 sub-line resistant to retinoic acid. These results suggest that phospholipase C inhibition is an important step in the induction of differentiation.