Activation and proliferation signals in murine macrophages: stimulation of Na+,K+-ATPase activity by hemopoietic growth factors and other agents

Na⁺i,K⁺i-Dependent and -Independent Signaling Triggered by Cardiotonic Steroids: Facts and Artifacts

Na⁺,K⁺-ATPase is the only known receptor of cardiotonic steroids (CTS) whose interaction with catalytic α-subunits leads to inhibition of this enzyme. As predicted, CTS affect numerous cellular functions related to the maintenance of the transmembrane gradient of monovalent cations, such as electrical membrane potential, cell volume, transepithelial movement of salt and osmotically-obliged water, symport of Na⁺ with inorganic phosphate, glucose, amino acids, nucleotides, etc. During the last two decades, it was shown that side-by-side with these canonical Na⁺_i/K⁺_i-dependent cellular responses, long-term exposure to CTS affects transcription, translation, tight junction, cell adhesion and exhibits tissue-specific impact on cell survival and death. It was also shown that CTS trigger diverse signaling cascades via conformational transitions of the Na⁺,K⁺-ATPase α-subunit that, in turn, results in the activation of membrane-associated non-receptor tyrosine kinase Src, phosphatidylinositol 3-kinase and the inositol 1,4,5-triphosphate receptor. These findings allowed researchers to propose that endogenous CTS might be considered as a novel class of steroid hormones. We focus our review on the analysis of the relative impact Na⁺_i,K⁺_i-mediated and -independent pathways in cellular responses evoked by CTS.

Ouabain-induced alterations in ABCB1 of mesenteric lymph nodes and thymocytes of rats and mice

Ouabain is a glycoside with immunomodulating properties, and recent studies have suggested its use in adjuvant therapy for cancer treatment. Ouabain is known to modulate the immune system in vitro, and previous studies have revealed that ouabain can modulate the expression and activity of ABCB1, a protein associated with multidrug resistance present in immune system. Therefore, the present study investigated alterations in the expression and activity of ABCB1 in the thymi, peripheral blood monocytes and lymph nodes of Wistar rats and Swiss mice treated acutely or chronically with ouabain. A decrease of almost 45% in the monocyte count and an increase of 55% in the basophil count were observed. A significant decrease (75% reduction) in the amount of cells with ABCB1 activity was found in the thymocytes of ouabain-treated rats and mice. The possible implications of these results for cancer treatment are discussed.

Hematopoietic growth factor receptors

The formation of the cellular constituents of the blood is regulated by a series of endogenous polypeptides with largely paracrine function. A number of these hematopoietic growth factors (HGF's), which include colony stimulating factors, interleukins, and erythropoietin, have been purified to homogeneity and cloned, which in turn has led to extensive investigations of their biochemical properties and biological effects and functions. The HGF's act on target cells by binding to receptors. The kinetics and, to an even larger extent, dynamics of the factor/receptor associations display several intriguing characteristics, most of which are still poorly understood. Herein, the biochemical characteristics of HGF's receptors as well as the binding properties, post-receptor binding events and receptor modulation resulting from the association of HGF's and their target cells are reviewed.

Haemopoietic growth factor regulation of protein kinases and genes associated with cell proliferation

Haemopoietic growth factors stimulate a number of common biochemical and molecular events despite the high specificity of individual ligand-receptor interactions. Analysis of three distinct colony-stimulating factors (CSFs), interleukin 3 (IL-3), granulocyte-CSF and granulocyte macrophage-CSF, and the lymphocytotropic growth factor IL-2 revealed remarkably similar distal subcellular biochemical signals, although the mode of initial membrane signal transduction may differ significantly. Both early progenitor cell growth factors, such as IL-3, and late-acting factors, such as CSF-1, stimulate tyrosine and serine/threonine substrate phosphorylations. One substrate (p68) is phosphorylated in response to many CSFs and to IL-2, suggesting that it plays a highly conserved role in the signal transduction processes of many different receptor(s). The proliferative CSFs and IL-2 also stimulate the expression of many of the same genes, including protooncogenes, the ornithine decarboxylase gene, and members of the phylogenetically ancient family of stress response genes. Thus although initial membrane events may differ among the proliferative stimulants, the biochemical and molecular convergence of signalling pathways on highly conserved cellular substrates and on the programme of gene expression is seen.

Comparison of macrophage responses to oxidized low-density lipoprotein and macrophage colony-stimulating factor (M-CSF or CSF-1)

Modification of low-density lipoprotein (LDL), for example by oxidation, could be involved in foam cell formation and proliferation observed in atherosclerotic lesions. Macrophage colony-stimulating factor (CSF-1 or M-CSF) has been implicated in foam cell development. It has been reported previously that oxidized LDL (ox.LDL) and CSF-1 synergistically stimulate DNA synthesis in murine bone-marrow-derived macrophages (BMM). The critical signal-transduction cascades responsible for the proliferative response to ox.LDL, as well as their relationship to those mediating CSF-1 action, are unknown. We report here that ox.LDL stimulated extracellular signal-regulated protein kinase (ERK)-1, ERK-2 and phosphoinositide 3-kinase activities in BMM but to a weaker extent than optimal CSF-1 concentrations at the time points examined. Inhibitor studies suggested at least a partial role for these kinases, as well as p70 S6-kinase, in ox.LDL-induced macrophage survival and DNA synthesis. For the DNA synthesis response to CSF-1, the degree of inhibition by PD98059, wortmannin and rapamycin was significant at low CSF-1 concentrations but was reduced as the CSF-1 dose increased. Using BMM from CSF-1-deficient mice (op/op) and a neutralizing antibody approach, we found no evidence for an essential role for endogenous CSF-1 in ox.LDL-mediated survival or DNA synthesis; likewise, with the same approaches, no evidence was obtained for an essential role for endogenous granulocyte/macrophage-CSF in ox.LDL-mediated macrophage survival and, in contrast with the literature, ox.LDL-induced macrophage DNA synthesis.

MRL/lpr and MRL+/+ Macrophage DNA Synthesis in the Absence and the Presence of Colony-Stimulating Factor-1 and Granulocyte-Macrophage Colony-Stimulating Factor

Macrophage accumulation and proliferation as well as altered macrophage properties have been observed in autoimmune MRL mice. To determine whether there might be innate differences in the proliferative responses, we examined the DNA synthesis responses of peritoneal macrophages and macrophages derived in vitro from bone marrow precursors (bone marrow-derived macrophages (BMM)). Murine peritoneal exudate macrophages normally require the addition of macrophage CSF (CSF-1) to enter cell cycle in vitro. In contrast, we have found that many thioglycollate-induced adherent peritoneal macrophages, but not resident peritoneal macrophages, from both MRL/lpr and MRL+/+ mice atypically underwent DNA synthesis even in the absence of added CSF-1. They also responded very well to granulocyte-macrophage CSF. These findings may help to explain the appearance of increased macrophage numbers in MRL lesions. In contrast to a previous report, it was found that MRL/lpr and MRL+/+ BMM did not have an enhanced response to CSF-1 and that modulation of CSF-1 receptor expression was not more rapid in MRL BMM. We also found no evidence for abnormal CSF-1 internalization and degradation or for the lpr mutation to have any enhanced effect on BMM survival in the absence of CSF-1. TNF-α lowered the DNA synthesis response to CSF-1 of MRL/lpr BMM rather than enhanced it, as has been reported. Our data suggest that the enhanced accumulation of macrophages in the MRL/lpr kidney cannot be explained by a proposed model of enhanced responsiveness of MRL/lpr BMM to CSF-1, including a contribution by TNF-α.

Proliferation-independent induction of macrophage cyclin D2, and repression of cyclin D1, by lipopolysaccharide

D-type cyclins are induced in response to mitogens and are essential and rate-limiting for G1 phase progression in normal mammalian cells. Macrophages proliferating in response to colony-stimulating factor-1 (CSF-1) express cyclin D1 and to a lesser extent cyclin D2 but not cyclin D3. Previously we showed that the macrophage-activating agent lipopolysaccharide (LPS) blocks CSF-1-induced proliferation and cyclin D1 expression in macrophages. Here we report upon the effect of LPS on expression of cyclin D2 in normal mouse bone marrow-derived macrophages (BMM). Unexpectedly we found that this anti-mitogen raised levels of CSF-1-stimulated cyclin D2 mRNA and protein. Furthermore, LPS alone induced cyclin D2 but not cyclin D1. Inhibition of the MEK/ERK (MAPK/ERK kinase/extracellular signal-regulated kinase) mitogen-activated protein kinase pathway repressed LPS-induced cyclin D2 mRNA, whereas inhibition of the p38 mitogen-activated protein kinase enhanced expression. However, in contrast to cyclin D1, cyclin D2 in bone marrow-derived macrophages did not appear to be regulated by protein kinase A pathways. The present data (a) show elevation of a D-type cyclin in the absence of proliferation, (b) demonstrate inverse regulation of two distinct D-type cyclins under identical conditions, and (c) suggest that cyclin D2 plays a role in macrophage activation by LPS.

Macrophage Lineage Cells in Inflammation: Characterization by Colony-Stimulating Factor-1 (CSF-1) Receptor (c-Fms), ER-MP58, and ER-MP20 (Ly-6C) Expression

Macrophage populations resident in tissues and at sites of inflammation are heterogeneous and with local proliferation sometimes evident. Using the convenient murine peritoneal cavity as an inflammation model, the appearance of macrophage lineage cells was followed with time in both thioglycollate- and sodium periodate-induced exudates. The cells were characterized by their proliferative response in vitro in response to colony-stimulating factor-1 (CSF-1) (or macrophage colony-stimulating factor [M-CSF]), particularly by their ability to form colonies in agar, in combination with flow cytometry (surface marker expression and forward and side scatter characteristics). We propose that c-Fms (CSF-1 receptor), unlike other markers, is a uniformly expressed and specific marker suitable for the detection of macrophage-lineage cells in tissues, both in the steady state and after the initiation of an inflammatory reaction. It was shown that the bone marrow myeloid precursor markers, ER-MP58 and ER-MP20 (Ly-6C), but not ER-MP12 (PECAM-1), are expressed by a high proportion of macrophage-lineage cells in the inflamed peritoneum. The macrophage colony-forming cells (M-CFCs) in a 16-hour thioglycollate-induced exudate were phenotyped as c-Fms+ERMP12−20+58+, properties consistent with their being more mature than bone marrow M-CFCs. It is proposed that ER-MP58, as well as ER-MP20, may be a useful marker for distinguishing inflammatory macrophage-lineage cells from the majority of those residing normally in tissues.

© 1998 by The American Society of Hematology.

Macrophage Lineage Cells in Inflammation: Characterization by Colony-Stimulating Factor-1 (CSF-1) Receptor (c-Fms), ER-MP58, and ER-MP20 (Ly-6C) Expression

Macrophage populations resident in tissues and at sites of inflammation are heterogeneous and with local proliferation sometimes evident. Using the convenient murine peritoneal cavity as an inflammation model, the appearance of macrophage lineage cells was followed with time in both thioglycollate- and sodium periodate-induced exudates. The cells were characterized by their proliferative response in vitro in response to colony-stimulating factor-1 (CSF-1) (or macrophage colony-stimulating factor [M-CSF]), particularly by their ability to form colonies in agar, in combination with flow cytometry (surface marker expression and forward and side scatter characteristics). We propose that c-Fms (CSF-1 receptor), unlike other markers, is a uniformly expressed and specific marker suitable for the detection of macrophage-lineage cells in tissues, both in the steady state and after the initiation of an inflammatory reaction. It was shown that the bone marrow myeloid precursor markers, ER-MP58 and ER-MP20 (Ly-6C), but not ER-MP12 (PECAM-1), are expressed by a high proportion of macrophage-lineage cells in the inflamed peritoneum. The macrophage colony-forming cells (M-CFCs) in a 16-hour thioglycollate-induced exudate were phenotyped as c-Fms+ERMP12−20+58+, properties consistent with their being more mature than bone marrow M-CFCs. It is proposed that ER-MP58, as well as ER-MP20, may be a useful marker for distinguishing inflammatory macrophage-lineage cells from the majority of those residing normally in tissues.

© 1998 by The American Society of Hematology.

Effects of wortmannin and rapamycin on CSF-1-mediated responses in macrophages

There are differing views regarding the roles of phosphatidylinositol 3-kinases (PI3-kinases) and p70 S6 kinase (p70s6k) in growth factor-induced cellular responses. One approach that is widely employed to investigate these roles is to use the inhibitors, wortmannin and rapamycin, respectively. This approach is used here to study the responses in macrophages to colony stimulating factor-1 (CSF-1). Wortmannin (> or = 30 nM) and rapamycin (> or = 3 nM) both weakly inhibited CSF-1-stimulated DNA synthesis in murine bone marrow-derived macrophages (BMM), suggesting that there are PI3-kinase- and p70s6k-independent pathways required for the onset of S phase; interestingly the combination of the drugs gave dramatic suppression. Inhibition of DNA synthesis by rapamycin on the BMM was much less than that observed with the CSF-1-dependent cell line, BAC1.2F5. In BMM, wortmannin suppressed CSF-1-stimulated increase in p70s6k activity indicating that PI3-kinase activity may lie upstream. In contrast to some other growth factor/cell systems, no evidence was obtained using the inhibitors for the involvement of PI3-kinase or p70s6k in CSF-1-mediated induction of c-fos mRNA expression or Erk-1 activity; in addition, no evidence was found for an involvement in the CSF-1-mediated increase in cyclin D1 expression or STAT activation. The findings reinforce the need to study the signal transduction cascades relevant to each individual growth factor and preferably not in cell lines.

Serum transcriptionally regulates Na(+)-K(+)-ATPase gene expression in vascular smooth muscle cells

The present study was designed to examine the effects of serum on Na(+)-K(+)-ATPase alpha 1- and beta 1-subunit gene expression in cultured vascular smooth muscle cells (VSMC) from rat thoracic aortas. Addition of 10% serum to VSMC for 24 h increased Na(+)-K(+)-ATPase activity 1.5-fold and alpha 1- and beta 1-subunit protein levels 1.9-fold. Serum (10%) caused a 3.5-fold increase in alpha 1-mRNA levels and a 6.7-fold increase in beta 1-mRNA levels, with peak elevations at 12 h. The protein synthesis inhibitor cycloheximide abolished serum-mediated beta 1-mRNA induction but did not affect serum-mediated alpha 1-mRNA induction. Protein kinase C (PKC) inhibitors (staurosporine A or calphostin C) or tyrosine kinase (TK) inhibitors (genistein or herbimycin A) significantly reduced serum-mediated beta 1-mRNA induction but had no effect on serum-mediated alpha 1-mRNA induction. Transfection experiments with the 5'-flanking sequences of the alpha 1- or beta 1-subunit genes linked to the luciferase reporter gene revealed that 10% serum caused 2.8- and 6.5-fold increases in luciferase activity, respectively. Among growth factors, only basic fibroblast growth factor (FGF) enhanced luciferase activities for the alpha 1- and beta 1-subunit genes. We conclude that 1) serum stimulates alpha 1- and beta 1-mRNA expression, alpha 1- and beta 1-subunit protein accumulation, and Na(+)-K(+)-ATPase activity; 2) serum-mediated beta 1-mRNA induction partly requires de novo synthesis of intermediate regulatory proteins and activation of PKC and TK, whereas serum-mediated alpha 1-mRNA induction occurs through PKC- and TK-independent mechanisms; 3) the 5'-flanking regions of the alpha 1- and beta 1-subunit genes are serum responsive; and 4) FGF mimics stimulatory effects of serum on promoter activities for the alpha 1- and beta 1-subunit genes.

Phenotypic effects of aldosterone and dexamethasone in a SV40-transformed mammalian cortical ascending limb cell line exhibiting mineralocorticoid receptors

We have analyzed the functional and morphological effects of corticosteroid hormones in a SV40-transformed rabbit cortical-ascending-limb (CAL) cell line (RC.SV2, Vandewalle et al., 1989) having mineralocorticoid (MR) and glucocorticoid (GR) receptors (Rafestin-Oblin et al., 1993). Both aldosterone and dexamethasone (5 x 10(-8) M) induced a marked increase in (3H)ouabain binding (used to quantify membrane Na(+)-K+ ATPase) detectable as early as 6 hours and maximal at 24 hours (+56-57%) (due to a 1.6-1.8-fold increase in cell membrane binding sites without Kd alteration), and significantly augmented the ouabain-sensitive component of Rb+ influx. Triiodothyronine (T3, 10(-9) M) also stimulated ouabain binding by 21% but was not permissive for steroid action, whereas 5 micrograms/ml insulin had no effect. Both steroid hormones, T3 and insulin induced the formation of domes that was tightly correlated with ouabain binding (r = 0.949) except for insulin. The effects of aldosterone and dexamethasone on cell monolayers and cell ultrastructure were, however, strikingly different as aldosterone induced a marked amplification of basolateral areas with appearance of large intercellular spaces, reminiscent of the changes observed in deoxycorticosterone-treated rats, whereas dexamethasone predominantly influenced cell height. This discrepancy might be due to specific occupancy of MR and GR by aldosterone and dexamethasone, respectively, and/or to nongenomic effects of dexamethasone. We have thus characterized a cell culture model making it possible to analyze the actions of mineralocorticoid and glucocorticoid hormones in the mammalian kidney.

K+ fluxes mediated by Na(+)-K(+)-Cl- cotransport and Na(+)-K(+)-ATPase pumps in renal tubule cell lines transformed by wild-type and temperature-sensitive strains of Simian virus 40

The relative contributions of Na(+)-K(+)-ATPase pumps and Na(+)-K(+)-Cl- cotransport to total rubidium (Rb+) influx into primary cultures of renal tubule cells (PC.RC) and cells transformed either with the wild-type or a temperature-sensitive mutant of the simian virus 40 (SV40), were measured under various growth conditions. The Na(+)-K(+)-ATPase-mediated component represented 74% and 44-48% of total Rb+ influx into PC.RC and SV40-transformed cells, respectively. Proliferating transformed cells showed substantial ouabain-resistant bumetanide-sensitive (Or-Bs) Rb+ influx (41-45% of total) which indicated the presence of a Na(+)-K(+)-Cl- cotransport. The Or-Bs component of Rb+ influx was greatly reduced when temperature-sensitive transformed renal cells (RC.SVtsA58) grown in Petri dishes or on permeable filters were shifted from the permissive (33 degrees C) to the restrictive temperature (39.5 degrees C) to arrest cell growth. The ouabain-sensitive Rb+ influx mediated by the Na(+)-K(+)-ATPase, the total and amiloride-sensitive Na+ uptakes were not modified following inhibition of cell proliferation. A similar fall in the Or-Bs influx was obtained when renal tubule cells transformed by the wild-type SV40 (RC.SV) were incubated with the K+ channel blocker, tetraethylammonium (TEA) ion, which we had previously shown to arrest cell growth without affecting cell viability (Teulon et al.: J. Cell. Physiol., 151:113-125, 1992). Reinitiation of cell growth by removal of TEA or return to 33 degrees C of the temperature-sensitive cells restored the Or-Bs component of Rb influx. Taken together, these results indicate that the Na(+)-K(+)-Cl- cotransport activity is critically dependent on cell growth conditions.

Macrophage colony stimulating factor activates phosphatidylcholine hydrolysis by cytoplasmic phospholipase A2

The macrophage colony stimulating factor (M-CSF) is required for the proliferation and differentiation of monocytes. Previous studies have demonstrated that M-CSF stimulation is associated with phosphatidylcholine (PC) hydrolysis and increased formation of both diacylglycerol (DAG) and phosphorylcholine. The present work extends those results by demonstrating that treatment of human monocytes with M-CSF is associated with increases in a cytoplasmic Ca(2+)-dependent activity which hydrolyzes 1-palmitoyl,2-arachidonoyl PC to arachidonic acid. The finding that this hydrolysis of PC is associated with increases in production of lysophosphatidylcholine indicates that M-CSF stimulates a cytoplasmic phospholipase A2 (cPLA2) activity. These results are supported by the demonstration that M-CSF induces cPLA2 gene expression. M-CSF-induced increases in cPLA2 mRNA levels were biphasic and corresponded with rapid (30-60 min) and delayed (24-72 h) increases in cPLA2 activity. The results demonstrate that this effect of M-CSF on cPLA2 expression is controlled at least in part by post-transcriptional stabilization of cPLA2 transcripts. The finding that M-CSF treatment is also associated with phosphorylation of the cPLA2 protein further suggests that expression of this enzyme is regulated at multiple levels. Finally, the stimulation of cPLA2 activity and arachidonate release is supported by increases in prostaglandin (PG) synthesis. In this regard, levels of both PGE2 and PGF2 alpha were increased in response to M-CSF. Taken together, these results indicate that M-CSF stimulates PC hydrolysis in human monocytes by inducing cPLA2 activity and thereby formation of eicosanoids.

Protein kinase C has both stimulatory and suppressive effects on macrophage superoxide production

Unlike resident peritoneal macrophages (RPM) or tumor necrosis factor alpha (TNF alpha)-primed bone marrow-derived macrophages (BMM), unprimed BMM do not generate superoxide in response to the protein kinase C (PKC) activator, phorbol myristate acetate (PMA). However, these cells do contain significant levels of PKC activity. In contrast to PMA, zymosan induces the generation of superoxide in unprimed BMM, as well as in TNF alpha-primed BMM and RPM. Staurosporine, a potent PKC inhibitor, failed to affect the zymosan-induced production of superoxide by unprimed and TNF alpha-primed BMM and RPM, in spite of substantial inhibition of PMA-induced superoxide production by the primed BMM and RPM. However, when PKC was depleted from unprimed BMM by prolonged (24 h) treatment with phorbol dibutyrate (PdBt) (10(-7) M) the ability of zymosan to induce the production of superoxide was greatly diminished. Such a result could be interpreted as suggesting a role for PKC in the zymosan-induced response, a conclusion which contrasts with the inhibitor data. However, PKC depletion, in this case, is achieved via the PdBt-induced activation of PKC. It is thus possible that it is the initial activation of PKC, rather than its depletion, that suppresses superoxide production. Consistent with this interpretation, the co-stimulation of unprimed BMM with both zymosan and PMA resulted in a reduced superoxide release compared to zymosan alone. The activation of PKC therefore appears to have a suppressive effect on the generation of superoxide by unprimed cells. We thus conclude that PKC is not required for zymosan-induced superoxide production by either primed or unprimed macrophages and suggest that PKC may be involved in regulatory mechanisms restricting superoxide production by macrophages. However, since PMA alone can initiate the release of superoxide from primed BMM and RPM, it would appear that PKC can mediate both stimulatory and suppressive signals for macrophage superoxide production.

Biochemical events accompanying macrophage activation and the inhibition of colony-stimulating factor-1-induced macrophage proliferation by tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide

Agents that can arrest cellular proliferation are now providing insights into mechanisms of growth factor action and how this action may be controlled. It is shown here that the macrophage activating agents tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), and lipopolysaccharide (LPS) can maximally inhibit colony stimulating factor-1 (CSF-1)-induced, murine bone marrow-derived macrophage (BMM) DNA synthesis even when added 8-12 h after the growth factor, a period coinciding with the G1/S-phase border of the BMM cell cycle. This inhibition was independent of autocrine PGE2 production or increased cAMP levels. In order to compare the mode of action of these agents, their effects on a number of other BMM responses in the absence or presence of CSF-1 were examined. All three agents stimulated BMM protein synthesis; TNF alpha and LPS, but not IFN gamma, stimulated BMM Na+/H+ exchange and Na+,K(+)-ATPase activities, as well as c-fos mRNA levels. IFN gamma did not inhibit the CSF-1-induced Na+,K(+)-ATPase activity. TNF alpha and LPS inhibited both CSF-1-stimulated urokinase-type plasminogen activator (u-PA) mRNA levels and u-PA activity in BMM, whereas IFN gamma lowered only the u-PA activity. In contrast, LPS and IFN gamma, but not TNF alpha, inhibited CSF-1-induced BMM c-myc mRNA levels, the lack of effect of TNF alpha dissociating the inhibition of DNA synthesis and decreased c-myc mRNA expression for this cytokine. These results indicate that certain biochemical responses are common to both growth factors and inhibitors of BMM DNA synthesis and that TNF alpha, IFN gamma, and LPS, even though they all have a common action in suppressing DNA synthesis, activate multiple signaling pathways in BMM, only some of which overlap or converge.

Macrophage growth arrest by cyclic AMP defines a distinct checkpoint in the mid-G1 stage of the cell cycle and overrides constitutive c-myc expression

Proliferation of a murine macrophage cell line (BAC1.2F5) in response to colony-stimulating factor 1 (CSF-1) is inhibited by prostaglandin E2 (PGE2)-mediated elevation of intracellular cyclic AMP (cAMP). When BAC1.2F5 cells were growth arrested in early G1 by CSF-1 starvation and stimulated to synchronously enter the cell cycle by readdition of growth factor, PGE2 inhibited [3H]thymidine incorporation when added before mid-G1, but its addition at later times did not block the onset of S phase. Reversible cell cycle arrest mediated by a cAMP analog required the presence of CSF-1 for cells to initiate DNA synthesis, whereas cells released from an aphidicolin block at the G1/S boundary entered S phase in the absence of CSF-1. PGE2 or cAMP analogs did not block the initial induction of c-myc mRNA by CSF-1 but abolished the CSF-1-dependent expression of c-myc mRNA in the mid-G1 stage of the cell cycle. The cAMP-mediated reduction in c-myc RNA levels was due to decreased c-myc transcription. However, CSF-1-dependent BAC1.2F5 clones infected with a c-myc retrovirus were growth arrested by cAMP analogs despite constitutive c-myc expression. Therefore, the reduction of endogenous c-myc expression by cAMP is neither necessary nor sufficient for growth inhibition.

Transformation of renal tubule epithelial cells by simian virus-40 is associated with emergence of Ca(2+)-insensitive K+ channels and altered mitogenic sensitivity to K+ channel blockers

We compared the pattern of K+ channels and the mitogenic sensitivity to K+ channel blocking agents in primary cultures of rabbit proximal tubule cells (PC.RC) (Ronco et al., 1990) and two derived SV-40-transformed cell lines exhibiting specific functions of proximal (RC.SV1) and more distal (RC.SV2) tubule cells (Vandewalle et al., 1989). First, K+ channel equipment surveyed by the patch-clamp technique was modified after SV-40 transformation in both cell lines; although a high conductance Ca(2+)-activated K+ channel [K+200 (Ca2+)] remained the most frequently recorded K+ channel, the transformed state was characterized by emergence of three Ca(2+)-insensitive K+ channels (150, 50, and 30 pS), virtually absent from primary culture, contrasting with reduced frequency of two Ca(2+)-sensitive K+ channels (80 and 40 pS). Second, quinine (Q), tetraethylammonium ion (TEA) and charybdotoxin (CTX), at concentrations not affecting cell viability, all decreased 3H-TdR incorporation and cell growth in PC.RC cultures, but only TEA had similar effects in transformed cells. The latter were further characterized by paradoxical effects of Q that induced a marked increase in thymidine incorporation. Q also exerted contrasting effects on channel activity: it inhibited the [K+200 (Ca2+)] when the channel was highly active, with a Ki (0.2 mM) similar to that measured for 3H-TdR incorporation in PC.RC cells (0.3 mM), but increased the mean current through poorly active channels. TEA blocked all K+ channels with conductance greater than or equal to 50 pS, including the [K+200 (Ca2+)], in a range of concentrations that substantially affected cell proliferation. The unique effect of TEA on SV-40-transformed cells might be related to broad inhibition of K+ channels.

Macrophage growth arrest by cyclic AMP defines a distinct checkpoint in the mid-G1 stage of the cell cycle and overrides constitutive c-myc expression

Proliferation of a murine macrophage cell line (BAC1.2F5) in response to colony-stimulating factor 1 (CSF-1) is inhibited by prostaglandin E2 (PGE2)-mediated elevation of intracellular cyclic AMP (cAMP). When BAC1.2F5 cells were growth arrested in early G1 by CSF-1 starvation and stimulated to synchronously enter the cell cycle by readdition of growth factor, PGE2 inhibited [3H]thymidine incorporation when added before mid-G1, but its addition at later times did not block the onset of S phase. Reversible cell cycle arrest mediated by a cAMP analog required the presence of CSF-1 for cells to initiate DNA synthesis, whereas cells released from an aphidicolin block at the G1/S boundary entered S phase in the absence of CSF-1. PGE2 or cAMP analogs did not block the initial induction of c-myc mRNA by CSF-1 but abolished the CSF-1-dependent expression of c-myc mRNA in the mid-G1 stage of the cell cycle. The cAMP-mediated reduction in c-myc RNA levels was due to decreased c-myc transcription. However, CSF-1-dependent BAC1.2F5 clones infected with a c-myc retrovirus were growth arrested by cAMP analogs despite constitutive c-myc expression. Therefore, the reduction of endogenous c-myc expression by cAMP is neither necessary nor sufficient for growth inhibition.

Modulation of macrophage colony stimulating factor in cultured human retinal pigment epithelial cells

Steady-state mRNA expression and protein production of macrophage colony stimulating factor were measured in visually confluent monolayers of unstimulated cultured human retinal pigment epithelial cells and after cells were stimulated with recombinant cytokines. Using reverse transcription polymerase chain reaction, macrophage colony stimulating factor mRNA expression was detected in unstimulated cells obtained from each of four separate donors. In these cells, mRNA expression was accompanied by secretion of macrophage colony stimulating factor protein into cell-conditioned medium; 48 hr after cells were switched to fresh medium, the mean (+/- S.D.) quantity of macrophage colony stimulating factor, measured by enzyme-linked immunoassay, was 5.1 +/- 2.3 ng 10(-6) cells. There was a dose- and time-dependent induction of macrophage colony stimulating factor mRNA after cells were exposed to recombinant human interleukin-1 and tumor necrosis factor alpha. Maximal mRNA induction was observed in cells exposed for 4 hr to interleukin-1 beta (5 U ml-1) or for 4-8 hr to tumor necrosis factor alpha; under these conditions, macrophage colony stimulating factor mRNA was induced up to 23- and 46-fold after exposure to interleukin-1 beta and tumor necrosis factor alpha, respectively. Similarly, macrophage colony stimulating factor protein production was enhanced after cells were exposed to recombinant cytokines. Protein secretion increased 1.3-2.5-fold (P less than 0.001) after exposure to interleukin-1 beta (5 U ml-1), and 1.2-1.6-fold after exposure to tumor necrosis factor alpha (P less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Signalling through CSF receptors

The finely regulated process of blood cell formation is under the control of a family of glycoprotein hormones, known as colony-stimulating factors (CSFs), and their receptors. The complexity of the intracellular mechanisms involved in the action of such factors has been appreciated only recently. In this review, Gino Vairo and John Hamilton discuss the biochemistry of CSF action and its relevance to growth control, and examine the possibility that different CSFs may use common control pathways within the one cell type.

GM-CSF and IL-3 stimulate diacylglycerol generation in murine bone marrow-derived macrophages

In murine bone marrow-derived macrophages, prelabeled with either [3H]myristic acid or [3H]arachidonic acid, the mitogenic colony stimulating factors GM-CSF and IL-3 stimulated a transient increase in [3H]diacylglycerol generation. Maximum [3H]diacylglycerol levels were detected at 10-15 min. The stimulation of [3H]diacylglycerol generation was dependent on the concentration of CSF and correlated with their ability to activate a variety of processes in the macrophage, including DNA synthesis. This is the first report to demonstrate that GM-CSF elevates diacylglycerol levels in macrophages and also to show that diacylglycerol generation may be an important signaling mechanism for IL-3 action. In conjunction with our recent demonstration that the mitogenic agents CSF-1, 12-0-tetradecanoylphorbol-13-acetate and exogenous phospholipase C also stimulate diacylglycerol generation in the macrophage (Veis and Hamilton, J.Cell.Physiol., 147, 298-305, 1991), our findings suggest that an increase in diacylglycerol levels is necessary but not sufficient for macrophage proliferation.

Hematopoietic growth factor receptors

The molecular cloning for most of the hematopoietic growth factor receptors has been achieved over the past few years and revealed that they can by assigned to two discrete receptor families, namely the hematopoietic growth factor superfamily (HRS) and the receptor tyrosine kinase family (RTK). The members of the HRS, including granulocyte-macrophage colony-stimulating factor receptor (GM-CSF-R), interleukin 3 receptor (IL-3-R), granulocyte CSF receptor (G-CSF-R) and erythropoietin receptor (Epo-R), share a common binding domain and the absence of a tyrosine kinase domain in their cytoplasmic portion. In some cases (e.g., GM-CSF-R), the high-affinity receptor structure is obtained through the association of the low-affinity binding chain (alpha chain) with an accessory protein (beta chain). It is conceivable that this protein might also represent the common subunit shared by GM-CSF-R and by IL-3-R when they are co-expressed to form the putative GM-CSF-R/IL-3-R complex. Although tyrosine phosphorylation following ligand receptor activation seems to be a common event in the HRS, its role in the signal transduction mechanisms is unknown. Due to the structural analogies among the members of this family any new insight into one particular receptor member, such as its subunit structure and its signal transduction pathways, will be generalizable to the other family members. The subclass III of the RTK family, including the CSF-1-R and c-kit, is characterized by an additional insert into the kinase domain that recognizes and binds protein substrates. Ligand induced activation of the kinase domain and its signaling potential are mediated by receptor oligomerization which stabilizes interactions between adjacent cytoplasmic domains and leads to activation of kinase function by molecular interaction. Interestingly, the receptors included in this subclass are the products of well known cellular proto-oncogenes. A large variety of structural alteration found in receptor-derived oncogene products may lead to constitutive activation of receptor signals that, consequently, result in the subversion of the mechanisms controlling the cell growth.

Modulation of Na+/K+ exchange potentiates lipopolysaccharide-induced gene expression in murine peritoneal macrophages

The role of Na+/K+ exchange in regulating lipopolysaccharide (LPS)-mediated induction of cytokine gene expression has been examined in murine peritoneal macrophages. Depletion of K+ from the culture medium resulted in a three- to five-fold potentiation of tumor necrosis factor-alpha (TNF alpha), KC (gro), and IP-10 mRNA expression in LPS-treated macrophages. The potentiating effect was apparently the result of inhibition of Na+/K+ exchange through the Na+/K(+)-adenosine triphosphatase (ATPase) because ouabain-mediated inhibition of Na+/K(+)-ATPase was also able to potentiate cytokine mRNA expression as much or more than did K+ depletion. The effects of K+ depletion or ouabain treatment were not caused by depolarization of the macrophage membrane because depolarization mediated by elevating extracellular K+ levels was inhibitory to cytokine mRNA expression. Depletion of Na+ by substitution with choline in the culture medium also markedly potentiated LPS-induced gene expression. The Na+/H+ antiporter was not, however, involved in potentiating cytokine expression because treatment of macrophages with amiloride either had no effect on or was inhibitory to the LPS-induced changes in mRNA levels. The potentiation of gene expression was selective and was at least partially the result of increased transcriptional activity of each gene. Whereas Na+ depletion and ouabain both inhibited 86Rb+ uptake by macrophages, treatment with LPS had no effect either on Rb+ uptake or on efflux. Thus altered Na+/K+ exchange is not a component of the primary signalling pathway(s) mediating response to LPS. Nevertheless, modulation of macrophage Na+/K+ exchange by agents encountered during an inflammatory response may be an important determinant of the magnitude and quality of specific gene expression.

Colony stimulating factor-1 stimulates diacylglycerol generation in murine bone marrow-derived macrophages, but not in resident peritoneal macrophages

Colony stimulating factor-1 (CSF-1) stimulates DNA synthesis in murine bone marrow-derived macrophages (BMM); however, unlike BMM, murine resident peritoneal macrophages (RPM) undergo a poor proliferative response. It has previously been shown that phosphatidylinositol-4,5-bisphosphate hydrolysis is not associated with CSF-1 action in BMM. In this report we demonstrate that, despite a lack of inositol trisphosphate generation, CSF-1 transiently elevated both [3H]myristoyl- and [3H]arachidonyl-diacylglycerol (DAG) in BMM in a dose-dependent fashion. CSF-1 failed, however, to stimulate an increase in either species of DAG in RPM. Thus, DAG could be a second messenger for the proliferative action of CSF-1 in macrophages. Other mitogenic agents, 12-0-tetradecanoyl phorbol 13-acetate (TPA) and exogenous phospholipase C, also increased BMM levels of [3H]myristoyl- and [3H]arachidonyl-DAG. The nonmitogenic agents, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) and zymosan, had different effects on the generation of either species of DAG in BMM. LPS failed to elevate either form, TNF-alpha increased only [3H]arachidonyl-DAG, while zymosan stimulated levels of both species of DAG. It therefore appears that increased diacylglycerol generation may be necessary, but perhaps not sufficient, for macrophage proliferation.

Ethylisopropylamiloride-sensitive pH control mechanisms modulate vascular smooth muscle cell growth

The reported effects of alterations in Na-H exchange activity on mitogenesis are variable and appear dependent on the cell type examined. We examined the effects of reductions in ethylisopropylamiloride (EIPA)-sensitive pH-regulating mechanisms including Na-H exchange and alterations in intracellular pH (pHi) on the growth characteristics of rat aortic smooth muscle cells (RASM) cultured in serum-containing bicarbonate-buffered medium. Exposure of RASM replicating in bicarbonate-containing medium to the Na-H exchange inhibitors EIPA, dimethylamiloride (DMA), or amiloride (A) attenuated their replication rate. The order of potency of the inhibitors (EIPA greater than DMA much greater than A) was similar to their documented effects on Na-H exchange activity and to their order of potency for inhibiting recovery from CO2-induced acidosis in these cells. Reductions in pHi induced by lowering extracellular pH also attenuated the incorporation of [3H]-thymidine into DNA, while increases in pHi were associated with an acceleration in the rate of incorporation of [3H]thymidine into DNA. The effects of the Na-H exchange inhibitors on RASM replication were due to a reduction in the ability of the smooth muscle cells to enter the S phase of the mitotic cell cycle. This appeared predominantly the consequence of effects late within the G1 phase of the cell cycle. Concentrations of EIPA that markedly reduced the ability of RASM to enter S phase and to replicate also attenuated the increase in protein synthesis occurring 6-8 h after exposure to serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotactic peptides but not macrophage colony stimulating factor effect the synthesis of inositol lipids in macrophages

Normal bone marrow derived macrophages display a wide variety of biological responses to a number of distinct agonists, for example, Macrophage Colony Stimulating Factor (M-CSF) and chemotactic peptides (such as FMLP). FMLP stimulates reactive oxygen intermediate production in these cells, whilst M-CSF stimulates DNA synthesis. We have compared the effects of these two agents on the production of novel inositol lipids in macrophages. Evidence is presented that FMLP, but not M-CSF elevate the levels of a lipid putatively identified as phosphatidylinositol-3,4-bisphosphate. The implications of this observation on proposed role of novel inositol lipids in macrophage proliferation are discussed.

Hematopoietic colony-stimulating factors

In summary, hematopoietic growth factors have been discovered, biochemically characterized, cloned, produced by recombinant DNA technology, and put into clinical use in a period of 25 years. We are approaching a greater understanding of the cellular anatomy and molecular mechanisms that regulate production of the CSFs, the ways in which the CSFs interact with their cell surface receptors and trigger their biological effects, the nature of these receptors themselves and their mechanisms of signal transduction, and the effects of the CSFs in vitro and in vivo on hematopoietic progenitor cells and mature leukocytes. However, many questions remain. What is the mechanism that couples growth-factor binding to the triggering of cellular proliferation? How do multi-CSF and GM-CSF cross-compete at the level of the cell-surface receptor, and yet show no primary amino acid sequence homology? What are the mechanisms that regulate the tissue expression profile of multi-CSF compared to the genetically similar growth factor GM-CSF? And, what are the optimal dosages, schedules of administration, and combinations of CSFs optimal for each of several conditions of marrow failure? These are but a few of the questions that continue to occupy much current research interest.

Membrane depolarization was required to induce DNA synthesis in murine macrophage cell line PU5-1.8

The role of membrane potential (Em) on the initiation of DNA synthesis in murine macrophage cell line PU5-1.8 was investigated with fluorescent probes bis-oxonol and diS-C3-(5). Incubation of PU5-1.8 cells in high K(+)-HEPES buffer or with gramicidin at 37 degrees C for 1h that depolarized the membrane induced [3H]-thymidine incorporation and expression of early response gene such as c-myc and c-fos. When PU5-1.8 cells were treated with a number of agents including fetal calf serum (FCS), lipopolysaccharide (LPS), epidermal growth factor (EGF), N-formyl-methionyl-leucyl-phenylalanine (FMLP) and bradykinin (BK), only FCS caused DNA synthesis and membrane depolarization. Other agents had no effect on these events. The FCS-mediated DNA synthesis in PU5-1.8 cells was inhibited by clamping the membrane potential with valinomycin. Moreover, intracellular alkalinization induced by nigericin at pH 7.9, which is believed to be a permissive signal for mitogenesis, caused membrane depolarization. On the other hand, challenge of cells with phorbol 12-myristate 13 acetate (PMA) suppressed the K(+)-mediated DNA synthesis. However, the treatment of cells with PMA did not change the membrane potential but suppressed the gramicidin-mediated membrane depolarization. These observations suggest that there is a correlation between membrane depolarization and initiation of DNA synthesis in PU5-1.8 cells. PKC may be acting as a modulator in this transducing pathway.

A unifying model of the cell proliferation emphasizing plasma membrane fluxes

The regulation of cellular growth and proliferation is perhaps the most investigated and elusive problem in cell biology and seems to be possible to solve from almost any angle of study chosen. Among the non-systemic factors that have been discussed are genetic damage, genomic control, regulation by stimulatory and inhibitory peptide factors such as EGF, chalones, and fibronectin, protein kinase activation with tyrosine phosphorylation, adenylylcyclase and cAMP, cGMP, membrane perturbations and specifically in tumours the failure of the Pasteur effect in control of glycolysis, excessive membrane ATPase activity, and excessive hydrolytic and proteolytic activities at the cell surface. This article focuses on the central role of fluxes within the plasma membrane and re-examines the possibility that changes of flux of metabolites, ions, and reducing equivalents may be the common denominator regulating cellular proliferation.

Colony stimulating factor-1 is a negative regulator of the macrophage respiratory burst

Several cytokines have previously been shown to prime macrophages for enhanced release of oxygen radicals in response to subsequent stimulation. We now demonstrate that the presence of the macrophage-specific colony stimulating factor-1 (CSF-1) inhibits the priming of murine macrophages by a variety of agents including tumor necrosis factor alpha, granulocyte/macrophage colony stimulating factor, interferon-gamma, and bacterial lipopolysaccharide. CSF-1 is also able to reduce the respiratory burst in the absence of priming. Our results indicate that CSF-1 is a potent negative regulator of the macrophage respiratory burst which acts to oppose the priming (enhancing) action of macrophage activating agents. We propose that CSF-1 may have a potentially important and previously unrecognized, role as a physiological regulator which restricts or terminates the activation of macrophages in order to prevent an uncontrolled inflammatory reaction.

Macrophage-colony-stimulating factor (CSF-1) modulates a differentiation-specific inward-rectifying potassium current in human leukemic (HL-60) cells

A voltage-activated inward-rectifying K+ conductance (lKi) appears in human promyelocytic leukemia (HL-60) cells during phorbol ester-induced differentiation into macrophages. This conductance was detected in the cells 24 hours after exposure to phorbol-12-myristate-13-acetate (PMA), as the cells began to express the macrophage phenotype, and continued to increase for 4 days after PMA exposure. The magnitude of inward current was a function of external K+; current was blocked by extracellular or intracellular Cs+ and by extracellular Ba++. Hyperpolarization produced activation at membrane potentials more negative than -80 mV, and a slower, partial inactivation also occurred at potentials more negative than -100 mV. This conductance was not detected in proliferating cells nor in granulocytes derived from HL-60 cells which were induced to differentiate with retinoic acid (RA). Exposure of differentiated macrophages to recombinant human CSF-1 produced inhibition of the lKi beginning within 1 minute after exposure. CSF-1 inhibition of lKi channels in cell-attached patches indicated that channel modulation was via intracellular mediators. The rapid inhibition of the inward rectifier by the macrophage-specific CSF-1 appears to be one of the earliest cellular responses to this factor.

Granulocyte-macrophage colony-stimulating factor can stimulate macrophage proliferation via persistent activation of Na+/H+ antiport. Evidence for two distinct roles for Na+/H+ antiport activation

Macrophages respond to a variety of extracellular stimuli which can modulate the proliferation, development, activation and functional activity of these cells. The effects of two such agents, granulocytemacrophage colony-stimulating factor (GM-CSF, which stimulates proliferation) and platelet-activating factor (PAF, which stimulates chemotaxis and bactericidal activity), on cellular signal transduction mechanisms were compared. PAF can stimulate inositol lipid hydrolysis leading to Ca2+ mobilization. GM-CSF on the other hand has no effect on these events. Both agonists do, however, share an ability to activate an amiloride-sensitive Na+/H+ antiport and, furthermore, amiloride analogues are shown to inhibit the proliferative effects of GM-CSF on these cells. Long-term incubations with either PAF or GM-CSF demonstrate that it is only those cells pretreated with the latter which show a persistent activation of the antiport together with a sustained increase in intracellular pH. PAF-treated cells exhibit only a transitory increase in antiport activity, their intracellular pH levels returning to resting levels in spite of the continuous presence of the agonist in the medium. These effects of GM-CSF and PAF on Na+/H+ exchange are observed in both bicarbonate-free and bicarbonate-containing medium. These results lead us to suggest that the Na+/H+ antiport has a role in macrophage proliferation and in the regulation of intracellular pH during the oxidative burst stimulated by PAF and other agonists, and that differential mechanisms whereby this antiport is regulated exist in macrophages.

Functional expression of the human receptor for colony-stimulating factor 1 (CSF-1) in hamster fibroblasts: CSF-1 stimulates Na+/H+ exchange and DNA-synthesis in the absence of phosphoinositide breakdown

The human CSF-1 receptor (c-fms protooncogene product) was introduced into CSF-1-unresponsive Chinese hamster lung fibroblasts (CCL39 cell line) in order to study its coupling to biochemical signal-transducing systems and to compare the growth-regulating properties of CSF-1 to those of other growth factors. Independent clones expressing different levels of CSF-1 receptors were isolated and characterized. CSF-1 increased [3H]thymidine incorporation in serum-starved cells and potentiated the mitogenic effects of FGF and thrombin. As already observed for other growth factors activating receptor tyrosine kinases (EGF, FGF, IGF-I), CSF-1 alone did not trigger inositol phosphate formation, but slightly enhanced the activity of phospholipase C agonists (thrombin, A1F4- complex). Activation of the CSF-1 receptor by its ligand was evidenced by the rapid activation of the Na+/H+ exchanger resulting in amiloride-sensitive cytoplasmic alkalinization (0.1-0.2 pH units) within minutes after stimulation. Whereas pertussis toxin does not affect the action of EGF, FGF, or IGF-I in CCL39 cells, it partially inhibited both DNA synthesis reinitiation and activation of Na+/H+ exchange by CSF-1, indicating that the CSF-1 receptor can communicate with a signal-transducing GTP binding protein. A point-mutated form of the c-fms gene product, in which Tyr 969, a residue negatively modulating signal transduction, had been replaced with Phe [fms (F969)], did not generate responses significantly different from those obtained with the wild-type c-fms gene product. In the absence of CSF-1, cells expressing either wild-type or fms (F969) showed a considerably higher basal level of thymidine incorporation and decreased anchorage dependence compared with parental CCL39 cells. Monoclonal antibodies that interfere with signal transduction by the human CSF-1 receptor inhibited both basal [3H]thymidine incorporation and soft agar colony formation, indicating that relaxation of growth control was dependent on CSF-1 receptor expression.

Regulation of mononuclear phagocyte proliferation by colony-stimulating factor-1

Colony-stimulating factor-1 (CSF-1 or M-CSF) regulates pleiotropic developmental and functional responses of macrophages and their committed bone marrow progenitors and supports the viability of cells of the mononuclear phagocyte lineage. Its actions are mediated through its binding to cell surface CSF-1 receptors (CSF-1R) that exhibit ligand-stimulated tyrosine kinase activity. CSF-1R-induced phosphorylation of intracellular protein substrates initiates a cascade of biochemical reactions that relay signals to the cell nucleus, elicit transcription of CSF-1-responsive genes and culminate in cell division. The actions of the CSF-1R kinase can be interrupted by binding of certain monoclonal antibodies to the extracellular domain of the receptor or by agents which activate protein kinase C and accelerate receptor turnover. CSF-1R is encoded by the c-fms proto-oncogene, and specific genetic alterations, which constitutively activate the receptor kinase, provide sustained signals for cell growth leading to cell transformation. Perturbations in the structure or expression of the c-fms proto-oncogene might therefore contribute to leukemia.

Activation and proliferation signals in murine macrophages: relationships among c-fos and c-myc expression, phosphoinositide hydrolysis, superoxide formation, and DNA synthesis

Murine bone marrow-derived macrophages (BMM) undergo DNA synthesis in response to growth factors such as colony stimulating factor-1 (CSF-1) and granulocyte-macrophage CSF (GM-CSF). These macrophages can also be "activated," but without subsequent DNA synthesis, by a number of other agents, including lipopolysaccharide (LPS), concanavalin A, zymosan, formyl-methionyl-leucyl-phenylalanine (FMLP), and the Ca2+ ionophore, A23187. When BMM are treated with a range of stimuli, there is some, although not perfect, correlation between transient elevations in both c-myc mRNA and c-fos mRNA levels and increases in DNA synthesis. However, enhanced DNA synthesis and oncogene expression are readily dissociated from rises in inositol phosphates and, by implication, phospholipase C-mediated hydrolysis of phosphatidyl inositol 4,5-bisphosphate. Superoxide formation in BMM can also be dissociated from the other responses and does not necessarily depend on protein kinase C activation.

The molecular control of cell division, differentiation commitment and maturation in haemopoietic cells

Several glycoproteins that control blood-cell production and function have been purified and sequenced. The four colony-stimulating factors interact in a complex way to regulate the differentiation and maturation of the granulocyte and macrophage lineages and have potential applications for the clinical manipulation of blood-cell production.