Coupled and uncoupled induction of fos and jun transcription by different second messengers in cells of hematopoietic origin

The early signaling pathway of live yeast cell derivative in THP-1 monocytes

Live yeast cell derivative (LYCD) is a medicinal yeast extract that has been used in the treatment of burns, wounds and hemorrhoids for over 70 years. It has been shown to enhance the closure of skin wounds in diabetic mice by increasing inflammation, angiogenesis, formation of granulation tissue and epithelial migration. An active fraction of LYCD has been identified as a mixture of peptides ranging in size from 5 kDA to 17 kDA. Despite its widespread use over many years, understanding of the mechanism by which LYCD acts to effect tissue repair responses is very limited. In this study, we have used a human monocyte-derived cell line, THP-1, as a representative of the inflammatory component of the wound healing process. We have identified two of the earliest responses to LYCD as an increase in cytoplasmic free calcium ([Ca2+]i) and the transcripts for c-fos. We have found that the increase in [Ca2+]i is both necessary and sufficient to account for the LYCD-induced elevation of c-fos. Furthermore, we have shown that the signaling pathway by which LYCD elevates [Ca2+]i involves both mobilization of Ca2+ from intracellular stores and influx of Ca2+ from the extracellular medium. Mobilization of store Ca2+ occurs first via activation of phospholipase C and this is followed by influx through activation of store operated calcium channels. These results constitute the first delineation of the early steps of the LYCD signaling pathway.

miR-21 Gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism

miR-21 has been reported to be highly expressed in various cancers and to be inducible in a human promyelocytic cell line, HL-60, after phorbol 12-myristate 13-acetate (PMA) treatment. To examine molecular mechanisms involved in miR-21 expression, we analyzed the structure of the miR-21 gene by determining its promoter and primary transcripts. We show that activation protein 1 (AP-1) activates the miR-21 transcription in conjugation with the SWI/SNF complex, after PMA stimulation, through the conserved AP-1 and PU.1 binding sites in the promoter identified here. The previous findings of enhanced miR-21 expression in several cancers may therefore reflect the elevated AP-1 activity in these carcinomas. A single precursor RNA containing miR-21 was transcribed just downstream from the TATA box in this promoter, which is located in an intron of a coding gene, TMEM49. More important, expression of this overlapping gene is completely PMA-independent and all its transcripts are polyadenylated before reaching the miR-21 hairpin embedding region, indicating that miRNAs could have their own promoter even if overlapped with other genes. By available algorithms that predict miRNA target using a conservation of sequence complementary to the miRNA seed sequence, we next predicted and confirmed that the NFIB mRNA is a target of miR-21. NFIB protein usually binds the miR-21 promoter in HL-60 cells as a negative regulator and is swept off from the miR-21 promoter during PMA-induced macrophage differentiation of HL-60. The translational repression of NFIB mRNA by miR-21 accelerates clearance of NFIB in parallel with the simultaneous miR-21-independent transcriptional repression of NFIB after PMA stimulation. Since exogenous miR-21 expression moderately induced endogenous miR-21, an evolutionarily conserved double-negative feedback regulation would be operating as a mechanism to sustain miR-21 expression.

Purification and characterization of C-terminal truncated forms of histone H2A in monocytic THP-1 cells

Histones are key components of chromatin. We investigated histone H2A-immunoreactive proteins in acute monocytic leukemia THP-1 cells using three polyclonal antibodies raised against peptides corresponding to distinct regions of H2A. Two unknown immunoreactive proteins (9- and 12-kDa proteins), H2A (14kDa) and ubiquitinated H2A (23kDa) were found in the cell lysates prepared by immediate direct addition of SDS-PAGE sample buffer to the cells as well as in the nuclear and chromatin fractions. However, they were not found in the cytoplasmic fraction. The unknown proteins were successfully purified by immunoaffinity chromatography from the cell nucleus extract and identified as 9-kDa H2A(1-87) and 12-kDa H2A(1-114), suggesting that both were produced by limited proteolysis of intact H2A(1-129). The truncated forms of H2A probably persisted as chromatin constituents, since the stability of H2A(1-87) in the chromatin fraction was sensitive to treatment with micrococcal nuclease, and H2A(1-114) was solubilized with lower ionic strength from the chromatin fraction obtained by micrococcal nuclease treatment. Truncated H2A proteins in THP-1 cells were transiently increased in amount by short-term treatment with phorbol 12-myristate 13-acetate or all-trans-retinoic acid, both of which induce macrophage-like differentiation. Furthermore, these increases were suppressed by preceding treatment with carbobenzoxy-l-leucyl-l-leucyl-l-leucinal (MG132) but not with carbobenzoxy-l-isoleucyl-gamma-t-butyl-l-glutamyl-l-alanyl-l-leucinal (PSI), both of which are generally known as proteasome inhibitors. Our results suggest that histone H2A is cleaved at least at two sites by protease(s) that remain obscure, and might affect chromatins in the early stage of THP-1 cell differentiation.

An efficient strategy to identify early TPA-responsive genes during differentiation of HL-60 cells

We have adopted a special experimental strategy to identify early responsive genes during 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced macrophage-like differentiation of human myeloid leukemia cells (HL-60). This was performed in cells that were synchronized by nocodazole and treated with TPA in the presence of a protein synthesis inhibitor, cycloheximide, to prevent activation of secondary targets and therefore increase the probability of early transcripts in total RNA pool. The expression alteration was analyzed by microarray and the selection criteria of candidate genes were adjusted by real-time PCR validation to increase its reliability. Finally, 56 genes were identified as early TPA-responsive genes in this multiscreening step approach. Furthermore, upregulation of three candidate genes (NFIL3, SKIL, and JMJD3) was shown to be dosage and time dependent with TPA treatment and was found to be directly regulated by TPA through PKC-dependent signaling. These results revealed that our screenings provide a useful and efficient approach to identify early TPA-responsive genes and these genes might involve the regulation of TPA-induced differentiation program of HL-60 cells as primary

Arachidonic acid induces mobilization of calcium stores and c-jun gene expression: evidence that intracellular calcium release is associated with c-jun activation

Arachidonic acid (AA) plays a signaling role in the induction of several genes. We previously demonstrated that AA induces c-jun gene expression in the stromal cell line +/+.1 LDA 11 by a signaling pathway involving activation of the c-jun amino-terminal kinase (JNK). This study investigated the role of calcium in AA signaling of c-jun activation in +/+.1 LDA 11 cells. AA (10-50 microM) caused a rapid dose-dependent rise in cytosolic calcium. AA-induced calcium mobilization involved both influx of extracellular calcium and the release of intracellular calcium. The importance of calcium was investigated by variation of the extracellular calcium concentration, chelation of intracellular calcium and by calcium ionophore-induced influx of extracellular calcium. AA-induced c-jun gene expression and increased luciferase activity of a construct containing the high affinity AP-1 binding site was decreased in cells preincubated with the intracellular calcium chelator 1,2-bis(o-aminophenoxy)-eThane-N,N,N',N',-tetraacetic acid tetra(aceToxymethyl-esTer) (BAPTA-AM, 10 microM) prior to stimulation with AA. Similarly, chelation of intracellular calcium decreased AA-induced JNK activation. On the contrary, changes in the extracellular calcium concentration had no effect. Also, ionophore A23187 failed to induce c-jun and JNK activation either alone than in combination with AA. These results suggested that calcium was required for AA-dependent activation of c-jun, but that calcium alone was insufficient to induce activation of c-jun. Thus, release of calcium from intracellular stores is implicated in the signaling pathway of AA-induced c-jun activation in stromal cells.

Gene expression after short periods of coronary occlusion

Brief periods of coronary occlusion render the affected myocardium more tolerant to the otherwise devastating effects of long coronary occlusion. Besides this phenomena, called ischemic preconditioning, short periods of ischemia cause a regional dysfunction, namely myocardial stunning. The molecular mechanisms of both syndromes are not very well understood. We therefore investigated the expression of genes which may be involved in cardioprotection or repair processes. Using our porcine model of ischemia and reperfusion we were able to show an induction of genes coding for transcription factors (proto-oncogenes), for proteins involved in repair processes (heat shock genes), for proteins implicated in the calcium homeostasis (calcium-handling genes) and for growth factors. We could show that the increased mRNA levels are due to an enhanced transcriptional activity and not to a prolonged half-life of the transcripts. The angiogenic growth factor vascular endothelial growth factor (VEGF) represents an exception. It exhibits--in addition to a HIF-motif (Hypoxia Inducible Factor) in its promoter/enhancer--a protein binding region in its 3' UTR which when occupied renders the mRNA more stable. However to what extent the expression of the distinct genes contributes to the cardioprotective effect of ischemic preconditioning or myocardial stunning can only be presumed. Increased mRNA stability can be confered via adenosine which is produced during ischemia by ATP-breakdown. The demasking of unknown genes--via differential display reverse transcription polymerase chain reaction (DDRT-PCR)--should provide a more comprehensive view of the mechanisms underlying both processes.

Comparison of the expression of c-fos, nur77 and egr1 mRNAs in rat hypothalamic magnocellular neurons and their putative afferent projection neurons: cell- and stimulus-specific induction

Hypothalamic magnocellular neurons and their afferent inputs provide a model system in which to study the regulation of inducible transcription factors in the brain in vivo. Osmotic stimulation of rats produced by graded infusions of saline at different tonicities was found to lead to the induction of c-fos, nur77 and egr1 mRNAs in magnocellular neurons, as well as in putative afferent neurons, including those in structures of the forebrain (subfornical organ, median preoptic nucleus and organum vasculosum of the lamina terminalis). The results presented suggest that stronger levels of osmotic stimulation recruit additional afferents from the forebrain and brainstem that can act on magnocellular neurons via alternative receptors. A single systemic injection of the peptide cholecystokinin produced robust induction of c-fos and nur77 mRNAs in afferent neurons of the brainstem nucleus tractus solitarii and in magnocellular neurons. Despite the fact that these two neuronal populations are clearly electrically active, egr1 was not induced by this stimulus, providing examples of cell- and stimulus-specificity of its expression. This study re-emphasizes that the induction of transcription factors is largely dependent on the nature of the afferent input and does not correlate necessarily to the electrical activity of the neuron.

Stimulation of DNA synthesis by natural ceramide 1-phosphate

We found that natural (long-chain) ceramide 1-phosphate can be dispersed into aqueous solution when dissolved in an appropriate mixture of methanol/dodecane (49:1, v/v). This solvent mixture facilitates the interaction of this phosphosphingolipid with cells. Under these conditions, incubation of EGFR T17 fibroblasts with natural ceramide 1-phosphate caused a potent stimulation of DNA synthesis. This effect was accompanied by an increase in the levels of proliferating-cell nuclear antigen. Concentrations of natural ceramide 1-phosphate that stimulated the synthesis of DNA did not inhibit adenylate cyclase activity, nor did they stimulate phospholipase D. Natural ceramide 1-phosphate did not alter the cellular phosphorylation state of tyrosine residues or of mitogen-activated protein kinase. Furthermore, natural ceramide 1-phosphate failed to induce the expression of the proto-oncogenes c-myc and c-fos. Both the stimulation of DNA synthesis and the induction of proliferating-cell nuclear antigen by natural ceramide 1-phosphate were inhibited by natural ceramides. This work suggests that the use of methanol and dodecane to deliver natural ceramide 1-phosphate to cells may be useful for elucidation of the biological function(s) and mechanism(s) of action of ceramide 1-phosphate.

Lovastatin inhibits gene expression of type-I scavenger receptor in THP-1 human macrophages

Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, inhibits the synthesis of mevalonic acid and is widely used as an anti-atherosclerotic drug. The macrophage scavenger receptor (SCR), a trimeric membrane glycoprotein, is postulated to play a key role in atheroma macrophage foam cell formation. HMG-CoA reductase is involved in the control of the synthesis of glycoproteins and farnesylated proteins, including ras proteins, which are involved in the transcriptional regulation of SCR gene expression. Accordingly, we examined whether lovastatin alters the gene expression of SCRs in THP-1 cell derived human macrophages. Lovastatin (5-15 microM) caused a significant dose-related reduction in steady state levels of type-I SCR mRNA in phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells. The addition of exogenous mevalonate (1 mM) completely restored the lovastatin-induced decrease of type-I SCR mRNA levels. While the addition of the isoprenoid end-product, isopentenyl adenine (50 microM), had little effect on the type-I SCR mRNA levels in lovastatin treated cells, the addition of isoprenoid farnesol (5 microM) largely restored the lovastatin-induced decrease of type-I SCR mRNA levels. Actinomycin D treatment showed that degradation rates of type-I SCR mRNA did not differ between the THP-1 derived cells with and without lovastatin treatment. Nuclear run-on assays showed that lovastatin markedly decreased the transcription of SCR gene in the cells. These results suggest that lovastatin inhibits the transcription of type-I SCR gene by affecting mevalonate metabolism, possibly through the farnesyl-pyrophosphate related end-product(s) in the THP-1-derived macrophages.

Domain-specific gene activation by parathyroid hormone in osteoblastic ROS17/2.8 cells

Parathyroid hormone (PTH)-mediated gene activation was assessed in the osteoblast-like rat cell line ROS17/2.8 with two PTH fragments harboring distinct activating domains: PTH-(1-34) and PTH-(28-48). The PTH response of genes expressed immediate early in the cell cycle or in the osteoblast developmental sequence was investigated. In addition, subtractive cloning was used to identify genes in ROS17/2.8 cells that are activated by the two PTH domains. PTH-(1-34) immediately increased the transcript levels of c-fos and c-jun at a considerably higher rate than PTH-(28-48). A significant immediate PTH effect on osteoblastic marker genes could not be detected, with the exception of elevated ornithine decarboxylase transcript levels. However, continuous application of PTH-(1-34) increased transcript levels of the osteoblast-specific osteocalcin gene and reduced those of other osteoblastic marker genes including alkaline phosphatase and the PTH/PTH-related peptide receptor. By subtractive cloning, nine cDNAs were isolated corresponding to mRNAs directly up-regulated by PTH-(1-34) or PTH-(28-48). Among these were a cyclic phosphodiesterase, a (cytosine 5)-methyltransferase, an 80-kDa protein kinase C substrate, junB, and a novel GC-binding protein. Three cDNAs are unknown at present. Interestingly, in all cases, the efficiency of gene activation by PTH-(28-48) was substantially lower in comparison with PTH-(1-34). PTH-mediated protein kinase C signaling in ROS17/2.8 cells may therefore constitute a minor pathway in comparison with the dominant cAMP/protein kinase A cascade.

Induction of members of the Fos/Jun family of immediate-early genes in identified hypothalamic neurons: in vivo evidence for differential regulation

In situ hybridization was used to measure the expression of members of the Fos/Jun family of immediate-early genes in hypothalamic neurons in vivo following defined stimuli that utilize different afferent pathways. Only c-jun messenger RNA was expressed in the hypothalamic supraoptic and paraventricular nuclei of control animals. Intravenous infusions of sodium chloride solutions of different tonicity produced a range of plasma osmolalities within physiological limits. While the induction of c-fos and jun B messenger RNAs followed the stimulus intensity, the expression of c-jun was repressed at low levels of stimulation. A higher level of osmotic stimulation was able to co-induce c-jun with the c-fos, jun B and fos B genes, suggesting that other signalling pathways may then be activated. Parturition or systemic administration of cholecystokinin, that activate supraoptic and paraventricular neurons via ascending afferent pathways from the brainstem, both induced c-fos, but not the other genes, in the magnocellular nuclei. Use of double in situ hybridization confirmed that, unlike with osmotic stimulation, induction of c-fos only occurred in oxytocin neurons. These two stimuli did not cause a concomitant repression of c-jun messenger RNA expression in magnocellular oxytocin neurons. These patterns of induction provide evidence for the differential regulation of members of this family of genes in a physiological context.

Differential regulation of AP-1 and novel TRE-specific DNA-binding complexes during differentiation of oligodendrocyte-type-2-astrocyte (O-2A) progenitor cells

AP-1 is an ubiquitous transcription factor which is composed of the Jun and Fos proto-oncogene proteins and is thought to play a role in both cell proliferation and differentiation. We have used an immortal, bipotential oligodendrocyte-type-2 astrocyte progenitor cell line (O-2A/c-myc) which can differentiate into oligodendrocytes or type-2 astrocytes in vitro, to investigate whether AP-1 DNA-binding activity fluctuates during glial cell differentiation. Unexpectedly, DNA-mobility shift assays using a TRE-containing oligonucleotide derived from the promoter of the glial-specific gene, glial fibrillary acidic protein (GFAP/AP-1), revealed that O-2A/c-myc progenitor cells were devoid of conventional AP-1 DNA-binding complexes. O-2A/c-myc cells did however contain several novel GFAP/AP-1-specific DNA-binding complexes, which we have termed APprog. APprog complexes recognise the TRE consensus motif present in the GFAP/AP-1 oligonucleotide together with adjacent 3′ sequences but do not contain c-Jun or any other known Jun-related proteins. When O-2A/c-myc cells underwent terminal differentiation APprog complexes were lost and conventional AP-1 DNA-binding activity became evident, particularly in astrocytes. These changes appear to be closely linked to the differentiation process since they did not occur in a derivative of the O-2A/c-myc cell line that contains an activated v-ras oncogene and which fails to differentiate under appropriate culture conditions. The inverse regulation of conventional AP-1 and APprog complexes within the O-2A lineage suggests that these factors may play a role in the regulation of glial cell differentiation or glial cell-specific gene expression.

The regulation of protein transport to the nucleus by phosphorylation

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Towards understanding the molecular basis of thyroid cancer

Cancer is a multistep phenomenon and multiple genetic lesions are involved in the emergence of the cancerous lesion. This has best been demonstrated in colonic cancer. The authors review their work and that of others highlighting what is known about thyroid cancer. They implicate ras mutations predominantly in follicular carcinoma, rearrangement of the ret proto-oncogene in papillary carcinoma and the tumor suppressor genes p53 and retinoblastoma gene product in all stages of thyroid carcinoma. They find a low rate of ret proto-oncogene rearrangement in the Saudi population (>5%) as compared to elsewhere in the world (20%). They find TSH receptor message abundance to be predictive of prognosis in thyroid cancer patients. Lastly, they examine whether the abundance of the anti-metastatic gene nm23 message abundance negatively correlated with the tendency of thyroid tumors to metastasize and find that not to be the case in thyroid carcinoma. The study of oncogenes and tumor suppressor genes in the pathogenesis of thyroid cancer is in its infancy; however, rapid progress is being made in identifying genes participating in malignant thyroid cell transformation.

Small Maf proteins heterodimerize with Fos and may act as competitive repressors of the NF-E2 transcription factor

The maf oncogene encodes a bZip nuclear protein which recognizes sequences related to an AP-1 site either as a homodimer or as heterodimers with Fos and Jun. We describe here a novel maf-related gene, mafG, which shows extensive homology with two other maf-related genes, mafK and mafF. These three maf-related genes encode small basic-leucine zipper proteins lacking the trans-activator domain of v-Maf. Bacterially expressed small Maf proteins bind to DNA as homodimers with a sequence recognition profile that is virtually identical to that of v-Maf. As we have previously described, the three small Maf proteins also dimerize with the large subunit of NF-E2 (p45) to form an erythroid cell-specific transcription factor, NF-E2, which has distinct DNA-binding specificity. This study shows that the small Maf proteins can also dimerize among themselves and with Fos and a newly identified p45-related molecule (Ech) but not with v-Maf or Jun. Although the small Maf proteins preferentially recognize the consensus NF-E2 sequence as heterodimers with either NF-E2 p45, Ech, or Fos, these heterodimers seemed to be different in their transactivation potentials. Coexpression of Fos and small Mafs could not activate a promoter with tandem repeats of the NF-E2 site. These results raise the possibility that tissue-specific gene expression and differentiation of erythroid cells are regulated by competition among Fos, NF-E2 p45, and Ech for small Maf proteins and for binding sites.

Transcriptional regulation of the vacuolar H(+)-ATPase B2 subunit gene in differentiating THP-1 cells

Monocyte-macrophage differentiation was used as a model system for studying gene regulation of the human vacuolar H(+)-ATPase (V-ATPase). We examined mRNA levels of various V-ATPase subunits during differentiation of both native monocytes and the cell line THP-1, and found that transcriptional and post-transcriptional mechanisms could account for increases in cell V-ATPase content. From nuclear runoff experiments, we found that one subunit in particular, the B2 isoform (Mr = 56,000), was amplified primarily by transcriptional means. We have begun to examine the structure of the B2 subunit promoter region. Isolation and sequencing of the first exon and 5'-flanking region of this gene reveal a TATA-less promoter with a high G + C content. Primer extension and ribonuclease protection analyses indicate a single major transcriptional start site. We transfected promoter-luciferase reporter plasmids into THP-1 cells to define sequences that mediate transcriptional control during monocyte differentiation. We found that sequences downstream from the transcriptional start site were sufficient to confer increased expression during THP-1 differentiation. DNase I footprinting and sequence analysis revealed the existence of multiple AP2 and Sp1 binding sites in the 5'-untranslated and proximal coding regions.

Molecular characterization of the in vivo alkylating agent resistant murine EMT-6 mammary carcinoma tumors

The expression of several early-response genes and genes associated with malignant disease was assessed in the EMT-6/parent tumor and the EMT-6/CTX and EMT-6/CDDP in vivo resistant tumor lines growing as tumors or as monolayers in culture. In the absence of treatment the levels of mRNA for the genes c-jun, c-fos, c-myc, Ha-ras and p53 were increased in the EMT-6/CTX and EMT-6/CDDP as compared with the EMT-6/parent tumor, whereas the expression of erb-2 was similar in all three tumors. Although the cells from each of the three tumors show increased expression of early response genes after exposure to cisplatin (CDDP; 100 microM, 2 h) or 4-Hydroxyperoxycyclophosphamide (4-HC; 100 microM, 2 h) in culture, in mRNA extracted from tumor tissue these changes are absent or very small. Both C-jun and erb-2 were detectable in liver. There was increased expression of both of these genes in the livers of tumor-bearing animals as compared with non-tumor-bearing animals. The highest expression of both c-jun and erb-2 occurred in the livers of animals bearing the EMT-6/CDDP tumor. Treatment of the animals with CDDP or cyclophosphamide, in general, resulted in increased expression of both genes at 6 h post treatment. The increased expression of these genes may impart metabolic changes in the tumors and/or hosts that contribute to the resistance of these tumors to specific antitumor alkylating agents.

Calcium regulation of immediate-early response genes

A rise in intracellular Ca2+ concentration induces the transcription of a number of eukaryotic genes through transcription factors interacting with calcium response elements. Immediate-early response genes encode proteins that couple extracellular signals to phenotypic alterations by modulating the transcription rates of target genes. Since the activation of early response genes occurs within minutes, this class of genes has served as a paradigm for the understanding of the molecular mechanisms by which external signals are conveyed to the nucleus to induce changes in genetic programs. In this review, we outline the recent information which has been gained specifically on how the Ca2+ messenger system modulates early response gene expression. We also discuss some lines of research with the intent of linking closer Ca2+ homeostasis and gene expression studies which in the past have followed their own separate routes.

The ether lipid 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine induces expression of fos and jun proto-oncogenes and activates AP-1 transcription factor in human leukaemic cells

The ether lipid analogue 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) has been recently shown to induce apoptosis in the human leukaemic HL-60 and U937 myeloid cell lines [Mollinedo, Martinez-Dalmau and Modolell (1993) Biochem. Biophys. Res. Commun. 192, 603-609]. We have found that ET-18-OCH3 is also able to promote apoptosis in the human leukaemic Jurkat T lymphoid cell line. This lymphoid cell line as well as the two myeloid HL-60 and U937 cell lines incorporated significant amounts of exogenously added radiolabelled ET-18-OCH3. Addition of ET-18-OCH3 to these human leukaemic cells induced an increase in the steady-state mRNA levels of fos and jun proto-oncogenes, components of the transcription factor AP-1. These increases in fos and jun mRNA levels were associated with the activation of the AP-1 transcription factor after addition of ET-18-OCH3 to human leukaemic cells, as assessed by an enhanced binding activity of transcription factor AP-1 to its cognate DNA sequence as well as by stimulation of transcription from an AP-1 enhancer element. These data demonstrate that the ether lipid ET-18-OCH3 can affect gene expression by inducing expression of fos and jun proto-oncogenes and by modulating the activity of transcription factor AP-1.

Monocyte deactivation by interleukin 10 via inhibition of tyrosine kinase activity and the Ras signaling pathway

Activation of monocytes by bacterial lipopolysaccharides (LPSs) is a central component in the pathogenesis of septic shock syndrome. Interleukin 10 (IL-10) is a potent monocyte-deactivating factor and transcriptionally inhibits LPS-induced expression of proinflammatory mediators. The intracellular signaling pathways of LPS have been only partially characterized and mechanisms of IL-10 signaling remain unknown. We show that LPS activates the protein tyrosine kinase (PTK) p56lyn and that this is associated with tyrosine phosphorylation of the protooncogene product Vav. These events are completely blocked by the tyrosine kinase inhibitor herbimycin A. LPS also increases Ras activation in monocytes. LPS-triggered phosphorylation of mitogen-activated protein kinase is a downstream activation event that is also reduced by herbimycin A. Analysis of the IL-10 effects shows that it completely inhibits the p56lyn tyrosine kinase activation and all other subsequent events in this pathway including Ras activation. The IL-10 effects are selective since it reduced PTK-dependent cytokine mRNA expression but not the PTK independent induction of c-jun and c-fos mRNA in LPS-activated monocytes. These results identify the Ras signaling pathway as a component of intracellular signaling in LPS-stimulated monocytes and define early events in this response as targets of monocyte deactivation by IL-10.

Signal transduction pathways mediating parathyroid hormone regulation of osteoblastic gene expression

Parathyroid hormone (PTH) plays a central role in regulation of calcium metabolism. For example, excessive or inappropriate production of PTH or the related hormone, parathyroid hormone related protein (PTHrP), accounts for the majority of the causes of hypercalcemia. Both hormones act through the same receptor on the osteoblast to elicit enhanced bone resorption by the osteoclast. Thus, the osteoblast mediates the effect of PTH in the resorption process. In this process, PTH causes a change in the function and phenotype of the osteoblast from a cell involved in bone formation to one directing the process of bone resorption. In response to PTH, the osteoblast decreases collagen, alkaline phosphatase, and osteopontin expression and increases production of osteocalcin, cytokines, and neutral proteases. Many of these changes have been shown to be due to effects on mRNA abundance through either transcriptional or post-transcriptional mechanisms. However, the signal transduction pathway for the hormone to cause these changes is not completely elucidated in any case. Binding of PTH and PTHrP to their common receptor has been shown to result in activation of protein kinases A and C and increases in intracellular calcium. The latter has not been implicated in any changes in mRNA of osteoblastic genes. On the other hand activation of PKA can mimic all the effects of PTH; protein kinase C may be involved in some responses. We will discuss possible mechanisms linking PKA and PKC activation to changes in gene expression, particularly at the nuclear level.

Evaluation of the role of Ap1-like proteins in the enhanced apolipoprotein E gene transcription accompanying phorbol ester induced macrophage differentiation

Differentiation of THP1 monocytes to a macrophage phenotype is accompanied by increased apolipoprotein E gene transcription. Using transfection analysis with 5' deletion mutations of the 5' control region of the apo E gene in THP1 cells, we show that the -651 to +86 chloramphenicol acetyltransferase (CAT) construct is efficiently expressed in the monocyte; as has been reported for other cell types. Further, we found that an 176 bp region between -623 to -447 was required for the induction of apolipoprotein E gene transcription during 12-O-tetradecanoylphorbol-13-acetate-induced differentiation of monocytes to macrophages. Gel-retardation patterns of the apolipoprotein E promoter region using nuclear extracts from differentiated or undifferentiated THP1 cells revealed altered binding of Ap1-like nuclear factor/s to the -620 to -583 bp region after macrophage differentiation. Mutation of an Ap1 element at position -602 abolished specific binding of Ap1-like proteins to the -620 to -583 bp fragment of the apo E gene and significantly reduced expression of a -623 to +86 apo E-CAT construct during differentiation. These data indicate that differentiation-related expression of the apolipoprotein E gene following phorbol ester stimulation is transduced by gene elements between -623 and -447. Furthermore, the data indicate that transcriptional activation of the apo E gene during macrophage differentiation is associated with induction of Ap1-like proteins which bind to the Ap1 response element present at -602 in the apolipoprotein E gene and importantly contribute to enhanced gene expression.

Different mechanisms of regulation of the human stromelysin and collagenase genes. Analysis by a reverse-transcription-coupled-PCR assay

Tissue-remodeling processes are largely controlled by matrix metalloproteinases that degrade the extracellular components of connective tissues. In this study, gene regulation of two human matrix metalloproteinases, stromelysin and collagenase, was investigated by a reverse-transcription-coupled (RT)-PCR assay. Here, signals from both the heterogenous nuclear RNA (hnRNA) and mRNA are amplified, allowing the regulation of gene expression to be divided between transcriptional and/or post-transcriptional control. In confluent human lung fibroblast cultures, tumor-necrosis factor-alpha and 12-O-tetradecanoyl-phorbol 13-acetate induce stromelysin and collagenase genes transcriptionally. Interleukin-1 beta (IL-1 beta) induces stromelysin gene transcription but has little, if any, effect on the collagenase gene transcription in cells cultured in the presence of 10% serum. By a competitive RT-PCR assay, the IL-1 beta-reated cultures contain an average of 60 molecules of stromelysin mRNA/cell and the untreated cultures about 1.9 molecules/cell. In serum-starved cells, both IL-1 beta and serum induce transcription of the collagenase gene. Also, in serum-starved cells type II collagen can induce collagenase mRNA but not stromelysin mRNA. Inhibition of protein synthesis with cycloheximide induces stromelysin gene transcription but has no effect on the collagenase gene. These data indicate different mechanisms of regulation of the human stromelysin and collagenase genes in cultured cells.

Double immunofluorescence staining of Fos and Jun in the hypothalamus of the rat

The nuclear factor Fos participates in the transcriptional regulation of genes that contain a functional AP-1 binding site. Hyperosmotic stress induces Fos-like immunoreactivity in neurons of the hypothalamus. Fos appears to depend on the co-expression of the nuclear factor Jun, with which it dimerizes, to complete its regulatory role. The immunocytochemical co-localization of both peptides, however, has not been reported. The present study was designed to analyze the distribution of Fos and Jun by double immunofluorescence staining in Long-Evans rats that were osmotically challenged by a single intraperitoneal injection of 1.5 M NaCl. Non-injected and isotonic saline-injected animals were used as controls. Hypertonic saline injection induced Jun immunoreactivity in cell nuclei in the supraoptic nucleus, paraventricular nucleus, and median preoptic nucleus. The immunofluorescence for Jun was strong in the supraoptic and paraventricular nuclei, but weak in the median preoptic nucleus. The immunofluorescence for Fos in all 3 nuclei followed a similar pattern to that for Jun. Double immunofluorescence staining revealed co-localization of Jun with Fos in 87.4% of the cells of the supraoptic nucleus. Neither Jun nor Fos immunofluorescence was detected in control animals. The data support a role for Jun in transcriptional regulation of genes in hypothalamic neurons during acute hyperosmotic stress. Moreover, the findings are compatible with the suggestion that Fos and Jun act cooperatively in the regulation of gene transcription in neuroendocrine systems involved in the control of water balance during acute hyperosmotic stimulation.

Differential induction of the two early genes c-jun and c-fos in weakly and strongly metastatic murine lymphoma cell lines

Induction of the 2 early-response genes c-jun and c-fos was investigated in the weakly metastatic T-lymphoma Eb line and the related strongly metastatic lymphomacrophage ESb line to find possible correlations with their different in vitro and in vivo phenotypes. The response of c-jun was elicited by the protein kinase-C activators TPA and A23187 in ESb but not in Eb cells. A much lower response of c-fos was also found in Eb than in ESb cells, in this case by means of serum and the cAMP elevator forskolin. However, both TPA and the calcium ionophore A23187 were similarly effective in inducing fos-mRNA in both cell lines. The uncoupling of c-jun and c-fos induction in Eb, but not in ESb cells, as well as the uncoupling of c-fos response to different stimulators, point to a differential activation of these 2 early-response genes by the main signal transduction pathways in the 2 cell types. The coordinate/uncoordinate availability of the fos/jun heterodimer may confer distinct regulatory patterns on different target genes in ESb/Eb cells. Activation of these genes may underlie the distinct differentiation phenotypes and in vivo behavior of Eb/ESb cells.

The effects of glucocorticoids on phorbol ester and cytokine stimulated transcription factor activation in human lung

Glucocorticoids have a wide variety of effects which result in the dampening of inflammatory and immune responses and other challenges to homeostasis. An important site of steroid action may be on the control of transcription factor binding to DNA. The interaction of the transcription factors, activator protein 1 (AP-1) and nuclear factor kappa from B cells (NF kappa B) with DNA and glucocorticoid receptors was analysed by gel mobility shift assays following stimulation by tumour necrosis factor alpha (TNF alpha) and a phorbol ester (PMA) that activates protein kinase C. PMA and TNF alpha both caused significant (180-340%) increases in AP-1 and NF kappa B DNA binding which peaked at 15 minutes and decreased to a constant elevated level at between 1-3 hrs and was sustained for 24hrs. Dexamethasone (1 microM) caused a rapid and long lasting 40-50% decrease in both AP-1 and NF kappa B DNA binding lasting over 24hrs. Combined treatment with dexamethasone and PMA or TNF alpha prevented the increase in both AP-1 and NF kappa B binding due to PMA and TNF alpha returning levels to those seen in control untreated samples. This suggests that in human lung, the glucocorticoid receptor functionally interacts within the nucleus with other transcription factors that are induced by inflammatory mediators such as cytokines. This may be an important molecular site of steroid action in chronic inflammatory lung diseases such as asthma.

Activator protein-1 (AP-1) is stimulated by microbial superantigens in human monocytic cells

Microbial superantigens bind to major histocompatibility complex (MHC) class II molecules and activate gene transcription in monocytes. In search of transcription factors that potentially mediate the effects of superantigens at the nuclear level, we examined the capacity of staphylococcal superantigens to stimulate the activity of the transcriptional promoter factor activator protein-1 (AP-1). Electrophoretic mobility shift assays showed an increase in nuclear proteins that bound to the consensus AP-1 motif within 5 min following the stimulation of the monocytic cell line THP-1 with toxic shock syndrome toxin-1 (TSST-1) or staphylococcal endotoxin A. We show that mRNA levels for the subunits that compose AP-1, the protooncogenes c-fos and c-jun, are upregulated by stimulation of THP-1 cells with TSST-1. The activated AP-1 complexes were functional, as evidenced by the capacity of TSST-1 to stimulate the expression of an AP-1-driven reporter gene construct transfected into THP-1 cells. These results establish that the engagement of MHC class II molecules by superantigens increases the activity of functional AP-1 complexes and that this may proceed in part by transcriptional activation of c-fos and c-jun protooncogenes.

A Fos-Jun element in the first intron of an alpha 2u-globulin gene

The hepatic expression of the alpha-2u-globulin gene family is controlled by a variety of hormones including steroids, growth hormone and insulin. The mechanisms by which these hormones affect alpha 2u-globulin expression are only partially understood. Recently we isolated and characterized clone RAP 01, an alpha 2u-globulin gene expressed in the liver. In preliminary experiments we noted that partial hepatectomy, a procedure which results in a sharp rise in the level of the oncoproteins c-Fos and c-Jun, also causes a transient induction of the messenger RNA corresponding to clone RAP 01. Using the DNAseI footprinting technique we were able to show that this clone contains a TPA (phorbol 12-myristate 13-acetate)-responsive element (TRE) in its first intron. This element (denoted as element X) is identical to the consensus AP-1 binding site (TGACTCAG) and is protected by rat liver nuclear extracts as well as by purified c-Jun. Gel retardation experiments show that an oligonucleotide containing the TRE consensus sequence competes for binding of liver nuclear proteins to element X and that antibodies directed against the M2 peptide of the mouse Fos protein or the PEP-2 peptide of Jun prevent the formation of specific complexes with the same element. Moreover, element X functions as a TRE in transfected BWTG3 hepatoma cells treated with TPA. Co-transfection with fos and jun expression vectors mimics the effects of TPA suggesting that AP-1 is in fact the mediator of the observed response. It is concluded that the first intron of RAP 01 contains a functional Fos-Jun element.

Developmental extinction of liver lipoprotein lipase mRNA expression might be regulated by an NF-1-like site

The molecular mechanism underlying the extinction of lipoprotein lipase (LPL) expression in rat liver during development was investigated. A mouse (BWTG3) and a rat (7777) hepatoma, both of which exhibit characteristics of fetal hepatocytes, were found to contain LPL mRNA, whereas the more differentiated human (Hep G2 and Hep 3B) or rat (Fa32) hepatoma cell lines did not. Somatic cell hybrids between LPL-producing hepatoma cells and non-LPL-producing cells, such as adult rat hepatocytes or fibroblasts, exhibited extinction of LPL gene expression. Assay of expression of nested deletions in the 5' regulatory sequences of the LPL gene in the Hep G2 cell line and in BWTG3 cells localized sequences involved in the suppression of LPL production to a region between -591 and -288 relative to the transcription initiation site. A site with sequence homology to a glucocorticoid responsive element (GRE) was shown not to play an important role in the extinction process. A novel transcription factor, termed RF-1-LPL, was shown to bind to an NF-1-like site in this region. In contrast to neonatal animals, in adult animals an additional protein complex (RF-2-LPL), was formed on the NF-1-like site, suggesting that this sequence might recruit a trans-acting factor involved in the extinction of LPL gene expression in adult rat liver.

Differences in expression of transcription factor AP-1 in human promyelocytic HL-60 cells during differentiation towards macrophages versus granulocytes

Commitment of HL-60 cells to macrophage or granulocytic differentiation was achieved by incubation with 4 beta-phorbol 12-myristate 13-acetate (PMA) for 30-60 min or with dimethyl sulphoxide (DMSO) for 24 h respectively. The commitment stage towards PMA-induced macrophage differentiation was associated with increases in jun B and c-fos mRNA levels, as well as with an increase in the binding activity of transcription factor AP-1. Nevertheless, gel retardation analysis indicated that the AP-1 activity detected in untreated cells was drastically reduced during the commitment stage of DMSO-induced HL-60 differentiation towards granulocytes. When HL-60 cells were treated with sodium butyrate, which induced monocytic differentiation, a remarkable increase in AP-1 binding activity was detected. Treatment of HL-60 cells with 1 alpha,25-dihydroxyvitamin D3, another monocytic differentiation agent, induced a weak, but appreciable, increase in AP-1 activity. Furthermore, addition of sodium butyrate or 1 alpha,25-dihydroxyvitamin D3 to HL-60 cells induced the expression of c-fos, c-jun, jun B and jun D proto-oncogenes. In contrast, when HL-60 cells were treated with retinoic acid, a granulocytic differentiation inducer, no enhanced AP-1 binding activity was observed, and only a weak increase in jun D mRNA level was detected. These data indicate that formation of AP-1 is not required for the induction of HL-60 differentiation towards granulocytes, whereas induction of monocytic differentiation is correlated with an increase in AP-1 activity. The differential expression of AP-1 activity may be critical in the differentiation of HL-60 cells towards monocytic or granulocytic lineages.

Resolution of multiple AP-1 complexes in HL-60 cells induced to differentiate by 1,25-dihydroxyvitamin D3

Activator protein-1 (AP-1) complex plays a central role in the regulation of both growth and differentiation in many cell types. Monocytic differentiation of HL-60 cells by TPA (12-0-tetradecanoyl phorbol-13-acetate) has been reported to be paralleled by increased AP-1 binding to DNA and by elevated c-jun expression, suggesting transcriptional level of control. We show that two forms of AP-1 complex, designated AP-1/1 and AP-1/2, can be demonstrated in logarithmically growing HL-60 cells, that the exposure of these cells to 10(-8) M 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) results in increased binding of these complexes to the AP-1 DNA element, and that the AP-1 complex can be resolved into at least three forms in differentiated cells. Binding to, or competition with, a mutated form of the AP-1 binding site shows that the most slowly migrating complex (AP-1/3) binds to DNA with greater specificity than do complexes AP-1/1 and AP-1/2, while antibody inhibition and binding studies performed at 37 degrees C indicate that jun proteins predominate in AP-1/2 complexes. Exposure of extracts from differentiated, but not untreated, HL-60 cells to 2 mM ATP increases the prominence of AP-1/3 complexes, and reduces the DNA binding of AP-1/1 complexes. Treatment of the extracts with phosphatases abolishes the binding of AP-1/2 and AP-1/3 to DNA, and increases the binding intensity of AP-1/1. When extracts from differentiated cells are mixed with extracts from undifferentiated cells the AP-1/3 complexes become less prominent, suggesting than an inhibitory activity in undifferentiated cells prevents the formation of AP-1/3 complexes. These studies show the association of multiple forms of AP-1 complex with the mature monocytic phenotype, and suggest several levels of control of monocytic differentiation.

Synergism between protein-kinase C and cAMP-dependent pathways in the expression of the interleukin-1 beta gene is mediated via the activator-protein-1 (AP-1) enhancer activity

In many different cell types treatment with phorbol esters (e.g. 4 beta-phorbol 12-myristate 13-acetate, PMA) leads to the activation of protein-kinase C (PKC) and subsequently to the activation of the activator-protein-1(AP-1)-responsive gene expression. We have previously reported that a structural analog of cAMP (dibutyryl cAMP, Bt2cAMP) or agents elevating the endogenous cAMP levels strongly enhanced the PMA-induced interleukin-1 beta(IL-1 beta)-gene expression in human myeloid leukemia cells (THP-1, HL-60). We have now examined the role of AP-1 in the regulation of the IL-1 beta gene expression by PKC and cAMP in THP-1 cells. AP-1 is a complex composed of products of the jun and fos gene families. Our studies show that Bt2cAMP enhances the PMA-induced c-fos and jun-B expression, but inhibits c-jun expression. Electrophoretic mobility-shift assay revealed that Bt2cAMP also increased the PMA-induced AP-1 DNA-binding activity. The functional role of the increased AP-1 DNA-binding activity was studied by transfecting THP-1 cells with reporter constructs containing AP-1 sites [Col-TREx5/TK-CAT and IL-1 beta-X-CAT, which contains the putative 12-O-tetradecanoyl-phorbol-13-acetate(TPA)-responsive element of the IL-1 beta gene]. Transient transfection assay demonstrated that Bt2cAMP similarly increased the PMA-induced transcription from both of these reporter constructs. Taken together, these results suggest that cAMP increases the PMA-induced AP-1 activity which then leads to increased IL-1 beta expression.

Differential intracellular mechanisms mediate the co-ordinate induction of c-fos and jun-B in the rat pineal gland

In the rat pineal gland the immediate early genes c-fos and jun-B are co-ordinately induced in vivo following the onset of darkness, and in vitro following treatment with adrenergic drugs. An extensive in vitro analysis of the mechanisms which regulate the induction of these two genes has revealed that, although there are common pathways of control, c-fos and jun-B exhibit differential regulation by adrenoceptor types, second messenger pathways and protein kinase C. The presence of differential intracellular mechanisms of regulation provides precise control over the expression pattern of immediate early genes, a pattern which is crucial for cellular response since the combinatorial actions of the products of these genes are a determinant of target gene activation. The pineal gland is a unique experimental model in which the molecular pharmacology of immediate early gene regulation can be investigated.

Proto-oncogene expression in porcine myocardium subjected to ischemia and reperfusion

The molecular basis of myocardial adaptation to ischemia and reperfusion is poorly understood. It is thought that nuclear proto-oncogenes act as third messengers, converting cytoplasmic signal transduction into long-term changes of gene expression. We studied the expression of six nuclear proto-oncogenes (Egr-1, c-fos, fosB, c-jun, junB, and c-myc) in myocardium subjected to ischemia and reperfusion in anesthetized pigs. Stunning was achieved by two 10-minute left anterior descending coronary artery occlusions separated by 30 minutes of reperfusion. Hearts were excised after the first occlusion, after the first reperfusion, and at 30, 120, 150, and 210 minutes of reperfusion after the second occlusion. Total RNA was prepared from stunned as well as normally perfused myocardial tissue and subjected to Northern blotting. The response of the six nuclear proto-oncogenes varied.fosB gene expression was never detected. The c-myc gene was expressed, but its level was unchanged by ischemia. c-jun expression was slightly increased by ischemia (3.1 +/- 0.6-fold). The c-fos, Egr-1, and junB genes were highly induced, being fivefold to sevenfold higher in experimental than in control tissue. In three animals pretreated with the beta 1-antagonist metoprolol and then subjected to the above experimental protocol, the induction of proto-oncogenes was similar to that in nonblocked controls. Our results show that the myocardial adaptive response to ischemic stress includes the induction of at least four transcription factors that may be further operative in repair processes and angiogenesis.

Neurotransmitter-stimulated immediate-early gene responses are organized through differential post-synaptic receptor mechanisms

The products of the cellular immediate-early genes (IEGs) are thought to act as messengers in the coupling of trans-synaptic stimuli with altered neuronal gene expression. However, the manner in which neurotransmission specifies particular responses through the IEGs is undefined. In this report, mRNA and transcription analysis of a precisely-timed, physiological IEG response illustrates how an IEG signal may be organized through differential neurotransmitter receptor activation. The nocturnal pattern of IEG expression in the rat pineal gland has been shown to be differentially regulated through post-synaptic adrenergic receptors. Induction of the c-fos gene is primarily mediated through alpha 1-receptors, whereas the coordinately regulated jun-B gene exhibits dual regulation through alpha 1- and beta-receptors. A simultaneous repression of c-jun expression is partly mediated through a beta-receptor mechanism. In vitro analysis of IEGs in cultured pineal glands has confirmed the receptor-specific link between adrenergic neurotransmission and IEG induction. The pineal is a unique neuroendocrine model in which the characteristics and function of the IEG third messenger system may be defined.

Involvement of FOS and JUN in the activation of visna virus gene expression in macrophages through an AP-1 site in the viral LTR

Gene expression of visna virus is highly restricted in monocytes, but is induced when monocytes differentiate into macrophages. A previous study on differential regulation of visna virus gene expression revealed that a specific AP-1 site in the long terminal repeat of the viral DNA is required for phorbol-ester-induced gene expression in macrophages (Gabuzda, Hess, Small, and Clements, Mol. Cell. Biol., 9, 2728-2733). In the present investigation, we examined the association of two DNA binding proteins, the proto-oncogene proteins FOS and JUN, with this AP-1 site in the visna virus LTR. We demonstrated that the concentrations of these two proteins and their mRNAs increased in U937 cells after phorbol ester induction. Furthermore, the binding of cellular proteins from the U937 nuclear extracts to this AP-1 site was significantly decreased in the presence of antibodies to JUN and FOS. In vitro-translated JUN protein also binds to this AP-1 sequence, and this binding is enhanced by the FOS protein. These results indicate that JUN and FOS are directly involved in the differential regulation of visna virus gene expression.

Alteration of a cyclic AMP-dependent protein kinase phosphorylation site in the c-Fos protein augments its transforming potential

We have studied the phosphorylation of the nuclear oncoprotein Fos by cyclic AMP-dependent protein kinase (PKA). We demonstrate that the human c-Fos protein, phosphorylated either in vitro with purified PKA or in vivo in JEG3 cells following treatment with forskolin, has similar phosphotryptic peptide maps. Serine 362, which constitutes part of a canonical PKA phosphorylation site (RKGSSS), is phosphorylated both in vivo and in vitro. A mutant of Fos protein in which serine residues 362 to 364 have been altered to alanine residues is not efficiently phosphorylated in vitro. Furthermore, Fos protein in which serines 362 to 364 have been altered to alanine shows increased transforming potential. We propose that phosphorylation of Fos by PKA is an important regulatory step in controlling its activity in normal cell growth and differentiation.

Alteration of a cyclic AMP-dependent protein kinase phosphorylation site in the c-Fos protein augments its transforming potential

We have studied the phosphorylation of the nuclear oncoprotein Fos by cyclic AMP-dependent protein kinase (PKA). We demonstrate that the human c-Fos protein, phosphorylated either in vitro with purified PKA or in vivo in JEG3 cells following treatment with forskolin, has similar phosphotryptic peptide maps. Serine 362, which constitutes part of a canonical PKA phosphorylation site (RKGSSS), is phosphorylated both in vivo and in vitro. A mutant of Fos protein in which serine residues 362 to 364 have been altered to alanine residues is not efficiently phosphorylated in vitro. Furthermore, Fos protein in which serines 362 to 364 have been altered to alanine shows increased transforming potential. We propose that phosphorylation of Fos by PKA is an important regulatory step in controlling its activity in normal cell growth and differentiation.

Changes in IgG Fc receptor expression induced by phorbol 12-myristate 13-acetate treatment of THP-1 monocytic leukemia cells

We studied changes in the three types of Fc gamma receptor (FcR) on the THP-1 human monocytic leukemia cells, after incubation with the phorbol ester, PMA, which has been shown to alter the expression of several genes in these cells. THP-1 cells constitutively express FcRI and FcRII, and PMA down-regulated the expression of both FcRI and FcRII. The FcRIII expression was not detected on either untreated or PMA-treated cells. Addition of PMA to THP-1 cells also resulted in a dose-dependent decrease of CD4 expression, as well as in an increased expression of activation-associated antigens. PMA treatment was followed by a progressive decrease in the steady state level of FcRI mRNA, while FcRII mRNA levels did not change, pointing to different regulatory mechanisms at the pre- and post-transcriptional level respectively. The FcRIII mRNA was undetectable. In order to further delineate the mechanism by which PMA induces alterations in FcR expression, we treated cells with stimulators of protein kinase C, of Ca2+ calmodulin-dependent kinase, and of protein kinase A. Since stimulation of none of these second messenger systems induced similar alterations in FcR expression as PMA we next tested the effects of PMA on differentiation and arrest of proliferation. The changes in FcR only occurred at PMA concentrations capable of inducing cell adherence and an arrest of proliferation, and showed a relatively slow time pattern. This suggested that the alterations in FcR expression may be linked to partial differentiation into a more macrophage-like cell. The changes in FcR expression could furthermore be reproduced by 1,25(OH)2 vitamin D3, another agent capable of differenting monocytes. In conclusion, PMA treatment of THP-1 cells decreases FcRI gene transcription and membrane expression and reduces membrane expression of FcRII. Both changes might be linked with an arrest of cell growth and induction of differentiation.

Prolonged elevation of intracellular cyclic AMP activates interleukin-1 production in human peripheral blood monocytes

The capability of elevated intracellular cyclic AMP concentration to activate IL-1 gene expression and protein production was examined in human peripheral blood monocytes. In accordance with previous studies it was observed that the transiently elevated cyclic AMP (induced either with prostaglandin E2 or with the direct adenylate cyclase activator, forskolin) was not a sufficient signal to activate IL-1 production. However, if the degradation of cyclic AMP was inhibited with isobutyl-methyl-xanthine (IBMX), IL-1 production was strongly activated. This prostaglandin E2 plus IBMX effect could also be mimicked with high concentrations of the cell permeant structural cyclic AMP analogue, dibutyryl cyclic AMP. The cyclic AMP-induced IL-1 production differed in some aspects from the bacterial lipopolysaccharide-induced IL-1 production: (1) the kinetics of both IL-1 gene expression and protein production was much slower; (2) the IL-1 beta gene expression was superinducible by inhibiting the protein synthesis with cycloheximide. Thus these data suggest that prolonged elevation of cyclic AMP is alone a sufficient signal to activate IL-1 production.

A phorbol diester resistant monocytic leukemia cell line is PKC deficient

MIA C51 is a rat monocytic leukemia cell line which exhibits undifferentiated monocytic phenotype in culture. The proliferation of MIA C51 cells was not inhibited by the addition of 12-O-tetradecanoyl-phorbol-13-acetate (TPA, 1 microgram/ml) or phorbol 12, 13 dibutyrate (PDBu, 10 micrograms/ml). Comparison of MIA C51 cells to a phorbol diester-sensitive human monoblastoid U-937 cell line demonstrated that MIA C51 cells contained significantly lower number of PDBu receptors, protein kinase C (PKC) activity, and PKC protein level. Further experiments demonstrated that addition of TPA to MIA C51 cells did not induce the expression of c-fos proto-oncogene; whereas incubation of MIA C51 cells with N6, O2-dibutyryl cyclic adenosine 3',5' monophosphate (Bt2cAMP) resulted in a rapid increase of c-fos mRNA level. Thus, this cell line provides a new system for studying the signal transduction mechanisms in induced monocytic differentiation.

Uncoupled changes in the expression of the jun family members during myeloid cell differentiation

The differentiation into macrophages of the U937 and HL60 human cell lines induced by 4 beta-phorbol 12-myristate 13-acetate (PMA) was accompanied by induction of the expression of the proto-oncogenes c-jun, jun B and jun D. However, expression of the three jun genes was regulated differently during induction of cell differentiation in both U937 and HL60 cells, with the three jun family members being expressed distinctly at different stages of cell differentiation. Whereas jun B transcription was strongly stimulated following treatment with PMA for 30 min, jun D mRNA levels were only increased 6 h after PMA treatment and the content of c-jun mRNA was elevated maximally only 24 h after PMA treatment. The rapid induction of the jun B mRNA level suggests a putative role for this proto-oncogene in the early triggering step of U937 and HL60 cell differentiation induced by PMA. Interestingly, a weak induction of jun B and jun D mRNA levels, but no induction of the c-jun mRNA level, was detected during Me2SO-induced granulocytic HL60 differentiation. These data suggest a different role for each jun proto-oncogene in regulating gene activity and that different transcriptional complexes involving distinct jun proto-oncogenes can be formed during macrophage and granulocytic differentiation.

Role of protein kinase C and cyclic adenosine monophosphate in the regulation of tissue-type plasminogen activator, plasminogen activator inhibitor-1, and platelet-derived growth factor mRNA levels in human endothelial cells. Possible involvement of proto-oncogenes c-jun and c-fos

Activation of protein kinase C leads to a strong induction of tissue-type plasminogen activator (t-PA) expression in endothelial cells. Using endothelial cells from human umbilical vein (HUVECs) and human aorta (HAECs), we have studied this regulation of t-PA and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), at the mRNA level and have compared their induction with the expression of platelet-derived growth factors A and B (PDGF-A and PDGF-B) and the proto-oncogenes c-jun and c-fos. Treatment of HUVECs with exogenous bacterial phospholipase C or the synthetic diacylglycerol 1-oleoyl-2-acetylglycerol led to a threefold and a twofold increase, respectively, in t-PA concentrations in 24-hour-conditioned medium. Similarly, the more stable protein kinase C activator 4 beta-phorbol-12-myristate-13-acetate (PMA) caused about a 10-fold increase in t-PA antigen levels. This effect of PMA is maximal between 8 and 16 hours at a concentration of 10 nM and is fully accounted for by parallel increases in t-PA mRNA levels. An increase in intracellular cyclic adenosine monophosphate levels by forskolin (10 microM) slightly diminished t-PA expression but further enhanced the PMA-induced increases in t-PA synthesis and mRNA levels by at least twofold. PMA also enhanced the mRNA levels of two other important endothelium-expressed genes, PDGF-A and PDGF-B, with a time profile similar to that of t-PA, with peak values about fivefold higher than control values. Forskolin did not further stimulate this PMA-induced PDGF expression in HUVECs, which suggests a regulatory mechanism different from that of t-PA. Qualitatively very similar induction patterns of t-PA, PDGF-A, and PDGF-B were seen with HAECs. In contrast to t-PA and PDGF, PAI-1 mRNA and antigen levels increased only slightly after PMA treatment of HUVECs or HAECs; forskolin alone or in combination with PMA diminished the expression of PAI-1. The induction of t-PA mRNA by PMA was dependent on protein synthesis and was preceded by a strong transient increase in c-jun and c-fos mRNA levels; the induction of c-fos but not of c-jun was potentiated by forskolin. Because the products of these two proto-oncogenes form dimeric complexes for which specific binding sites are present in the t-PA promoter region, they may mediate the protein kinase C-dependent increase in t-PA gene expression, including the stimulating action of cyclic adenosine monophosphate.

IP-1: a dominant inhibitor of Fos/Jun whose activity is modulated by phosphorylation

Transcription factor AP-1 is inducible by phorbol esters and thus could be considered to be one final target of the protein kinase C signal transduction pathway. AP-1 consists of the products of the fos and jun oncogenes, which associate as dimers to bind TPA-responsive promoter elements (TRE) efficiently. We show that AP-1 activity is modulated by an inhibitory protein (IP-1), present both in the nucleus and cytoplasm of several cell types. IP-1 specifically blocks DNA binding of AP-1 from nuclear extracts and of in vitro synthesized Fos/Jun proteins. It is a labile protein of 30-40 kd, which exerts its activity only in the nonphosphorylated form. Block of IP-1 function is obtained by PKA-mediated phosphorylation, possibly suggesting a cross talk mechanism at transcriptional level. Competition experiments with synthetic peptides suggest that IP-1 could interact with Fos and/or Jun leucine zippers. We speculate that IP-1 might act as a transcriptional antioncogene.