Calcium-dependent immediate-early gene induction in lymphocytes is negatively regulated by p21Ha-ras

Targeting an alternate Wilms' tumor antigen 1 peptide bypasses immunoproteasome dependency

Designing effective antileukemic immunotherapy will require understanding mechanisms underlying tumor control or resistance. Here, we report a mechanism of escape from immunologic targeting in an acute myeloid leukemia (AML) patient, who relapsed 1 year after immunotherapy with engineered T cells expressing a human leukocyte antigen A*02 (HLA-A2)-restricted T cell receptor (TCR) specific for a Wilms' tumor antigen 1 epitope, WT1_126-134 (T_TCR-C4). Resistance occurred despite persistence of functional therapeutic T cells and continuous expression of WT1 and HLA-A2 by the patient's AML cells. Analysis of the recurrent AML revealed expression of the standard proteasome, but limited expression of the immunoproteasome, specifically the beta subunit 1i (β1i), which is required for presentation of WT1_126-134. An analysis of a second patient treated with T_TCR-C4 demonstrated specific loss of AML cells coexpressing β1i and WT1. To determine whether the WT1 protein continued to be processed and presented in the absence of immunoproteasome processing, we identified and tested a TCR targeting an alternative, HLA-A2-restricted WT1_37-45 epitope that was generated by immunoproteasome-deficient cells, including WT1-expressing solid tumor lines. T cells expressing this TCR (T_TCR37-45) killed the first patients' relapsed AML resistant to WT1_126-134 targeting, as well as other primary AML, in vitro. T_TCR37-45 controlled solid tumor lines lacking immunoproteasome subunits both in vitro and in an NSG mouse model. As proteasome composition can vary in AML, defining and preferentially targeting these proteasome-independent epitopes may maximize therapeutic efficacy and potentially circumvent AML immune evasion by proteasome-related immunoediting.

Knockout of stim2a Increases Calcium Oscillations in Neurons and Induces Hyperactive-Like Phenotype in Zebrafish Larvae

Stromal interaction molecule (STIM) proteins play a crucial role in store-operated calcium entry (SOCE) as endoplasmic reticulum Ca²⁺ sensors. In neurons, STIM2 was shown to have distinct functions from STIM1. However, its role in brain activity and behavior was not fully elucidated. The present study analyzed behavior in zebrafish (Danio rerio) that lacked stim2a. The mutant animals had no morphological abnormalities and were fertile. RNA-sequencing revealed alterations of the expression of transcription factor genes and several members of the calcium toolkit. Neuronal Ca²⁺ activity was measured in vivo in neurons that expressed the GCaMP5G sensor. Optic tectum neurons in stim2a^-/- fish had more frequent Ca²⁺ signal oscillations compared with neurons in wildtype (WT) fish. We detected an increase in activity during the visual-motor response test, an increase in thigmotaxis in the open field test, and the disruption of phototaxis in the dark/light preference test in stim2a^-/- mutants compared with WT. Both groups of animals reacted to glutamate and pentylenetetrazol with an increase in activity during the visual-motor response test, with no major differences between groups. Altogether, our results suggest that the hyperactive-like phenotype of stim2a^-/- mutant zebrafish is caused by the dysregulation of Ca²⁺ homeostasis and signaling.

RNAP II CTD phosphorylated on threonine-4 is required for histone mRNA 3' end processing

The RNA polymerase II (RNAP II) largest subunit contains a C-terminal domain (CTD) with up to 52 Tyr(1)-Ser(2)-Pro(3)-Thr(4)-Ser(5)-Pro(6)-Ser(7) consensus repeats. Serines 2, 5, and 7 are known to be phosphorylated, and these modifications help to orchestrate the interplay between transcription and processing of messenger RNA (mRNA) precursors. Here, we provide evidence that phosphorylation of CTD Thr(4) residues is required specifically for histone mRNA 3' end processing, functioning to facilitate recruitment of 3' processing factors to histone genes. Like Ser(2), Thr(4) phosphorylation requires the CTD kinase CDK9 and is evolutionarily conserved from yeast to human. Our data thus illustrate how a CTD modification can play a highly specific role in facilitating efficient gene expression.

Protein kinase Cδ inactivation inhibits cellular proliferation and decreases survival in human neuroendocrine tumors

The concept of targeting cancer therapeutics toward specific mutations or abnormalities in tumor cells, which are not found in normal tissues, has the potential advantages of high selectivity for the tumor and correspondingly low secondary toxicities. Many human malignancies display activating mutations in the Ras family of signal-transducing genes or over-activity of p21(Ras)-signaling pathways. Carcinoid and other neuroendocrine tumors have been similarly demonstrated to have activation of Ras signaling directly by mutations in Ras, indirectly by loss of Ras-regulatory proteins, or via constitutive activation of upstream or downstream effector pathways of Ras, such as growth factor receptors or PI(3)-kinase and Raf/mitogen-activated protein kinases. We previously reported that aberrant activation of Ras signaling sensitizes cells to apoptosis when the activity of the PKCδ isozyme is suppressed and that PKCδ suppression is not toxic to cells with normal levels of p21(Ras) signaling. We demonstrate here that inhibition of PKCδ by a number of independent means, including genetic mechanisms (shRNA) or small-molecule inhibitors, is able to efficiently and selectively repress the growth of human neuroendocrine cell lines derived from bronchopulmonary, foregut, or hindgut tumors. PKCδ inhibition in these tumors also efficiently induced apoptosis. Exposure to small-molecule inhibitors of PKCδ over a period of 24  h is sufficient to significantly suppress cell growth and clonogenic capacity of these tumor cell lines. Neuroendocrine tumors are typically refractory to conventional therapeutic approaches. This Ras-targeted therapeutic approach, mediated through PKCδ suppression, which selectively takes advantage of the very oncogenic mutations that contribute to the malignancy of the tumor, may hold potential as a novel therapeutic modality.

Small G proteins exhibit pattern sensitivity in MAPK activation during the induction of memory and synaptic facilitation in Aplysia

Memory formation is highly sensitive to specific patterns of training, but the cellular and molecular mechanisms underlying pattern sensitivity are not well understood. We explored this general question by using Aplysia californica as a model system. We examined the regulation of MAPK (ERK1/2) activation by small G proteins in the CNS by using different patterns of analog stimuli that mimic different patterns of behavioral training for memory induction. We first cloned and characterized the Aplysia homologs of the small G proteins, Ras and Rap1 (ApRas and ApRap, respectively). We next examined changes in ApRas and ApRap activity that accompany MAPK activation. Last, by delivering recombinant ApRas and ApRap into the CNS, we directly manipulated their activity and examined the resultant MAPK activation. We found that MAPK activation induced by analog training depends on the combined activity of ApRas and ApRap, rather than the individual activity of either one alone. Also, ApRas and ApRap have a complex role in MAPK activation: they can act as activators or inhibitors, depending on the specific pattern of the training. The pattern-sensitive regulation of MAPK by interactive ApRas and ApRap activity that we have identified could contribute to the molecular routing of different downstream effects of spatially localized MAPK required for the induction of specific pattern-sensitive forms of synaptic facilitation and memory.

Divergent behavioral roles of angiotensin receptor intracellular signaling cascades

Central injections of angiotensin II (AngII) increase both water and NaCl intake. These effects of AngII occur largely through stimulation of the AngII type 1 (AT(1)) receptor. Stimulation of the AT(1) receptor leads to a number of intracellular events, including phospholipase C (PLC) activation and the subsequent formation of diacylglycerol and inositol trisphosphate (IP(3)), which then activate protein kinase C (PKC) and increase intracellular calcium, respectively. In addition, AT(1) receptor stimulation leads to the activation of MAPK family members. Recent experiments using mutated AT(1) receptor constructs or the AngII analog Sar(1),Ile(4),Ile(8)-AngII (SII) revealed that MAPK activation can occur independent of PLC/PKC/IP(3) activation. The present experiments used in vitro and in vivo approaches to clarify the cellular and behavioral responses to SII. Specifically, SII mimicked AngII stimulation of MAPK in AT(1) receptor-transfected COS-1 cells and rat brain but blocked the effects of AngII in two distinct settings: in vitro stimulation of IP(3) and in vivo increases in water intake. Moreover, SII increased intake of 1.5% NaCl, despite the SII blockade of IP(3) formation and water intake. Examination of brain tissue showed increases in Fos expression in several AngII-sensitive brain areas after injection of AngII, but not SII. The lack of SII-induced IP(3) production, water intake, and Fos expression strongly suggest that the PLC/PKC/IP(3) pathway is required for water intake, but not NaCl consumption stimulated by AngII. Collectively, these results support the hypothesis that divergent intracellular signals from a single receptor type can give rise to separable behavioral phenomena.

A calcium-based theory of carcinogenesis

Most human cancers are initiated by chronic injuries that repeatedly kill cells and must, therefore, repeatedly raise cell calcium within nearby survivors. They may also raise calcium in distant cells via calcium waves. Here it is argued that these calcium increases initiate oncogenesis by breaking gap junctions and thus disorganizing tissues and by activating proto-oncogenes. It is also argued that these calcium increases become self-perpetuating in part through the development of an ability of cells to divide in reduced extracellular calcium, i.e., habituation to reduced extracellular calcium. I propose to test these calcium-based theories by using aequorinated mice.

Dopaminergic D1-like receptor-dependent inhibition of tyrosine hydroxylase mRNA expression and catecholamine production in human lymphocytes

Activation of human peripheral blood mononuclear cells (PBMC) triggers endogenous production of catecholamines (CA) through protein kinase (PK) C-dependent induction of tyrosine hydroxylase (TH; EC 1.14.16.2), the first and rate-limiting enzyme in the synthesis of CA. Since CA themselves are major mediators of the neural input to the immune system, we have examined their ability to affect PKC-induced TH mRNA expression and CA production in human isolated PBMC. In T- and B-lymphocytes (but not in monocytes) the PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA) (but not its inactive analogue 4alpha-phorbol-12,13-didecanoate) induced TH mRNA expression which was followed by an increase in the amount of intracellular CA. Coincubation of human PBMC with dopamine (DA) (but not with norepinephrine or epinephrine) inhibited TPA-induced TH mRNA expression. The effect of DA was concentration-dependent and was mimicked by the dopaminergic D1-like receptor agonist SKF-38393 but not by the D2-like receptor agonist bromocriptine. The D1-like antagonist SCH-23390 shifted to the right the concentration-response curves of both DA and SKF-38393, while neither the D2-like antagonist domperidone, nor the alpha1-adrenoceptor antagonist prazosin, the alpha2-adrenoceptor antagonist yohimbine, or the beta-adrenoceptor antagonist propranolol affected to any significant extent the inhibitory effect of DA. SKF-38393 also significantly reduced TPA-induced increase of intracellular CA, an effect which was antagonized by SCH-23390. It is thus suggested that in human T- and B-lymphocytes PKC activation leads to TH mRNA expression and subsequent increase of intracellular CA, which can be inhibited by D1-like receptor activation. Inhibition of intracellular CA production in human PBMC promotes cell survival through reduction of activation-induced apoptosis, and dopaminergic modulation of TH expression and intracellular CA content may thus represent a novel mechanism in the cross-talk between the nervous and the immune system as well as among immune system cells.

Characterization of p21Ras-mediated apoptosis induced by protein kinase C inhibition and application to human tumor cell lines

Suppression of PKC activity can selectively induce apoptosis in cells expressing a constitutively activated p21Ras protein. We demonstrate that continued expression of p21Ras activity is required in PKC-mediated apoptosis because farnesyltransferase inhibitors abrogated the loss of viability in p21Ras-transformed cells occurring following PKC inhibition. Studies utilizing gene transfer or viral vectors demonstrate that transient expression of oncogenic p21Ras activity is sufficient for induction of apoptosis by PKC inhibition, whereas physiologic activation of p21Ras by growth factor is not sufficient to induce apoptosis. Mechanistically, the p21Ras-mediated apoptosis induced by PKC inhibition is dependent upon mitochondrial dysregulation, with a concurrent loss of mitochondrial membrane potential (psim). Cyclosporine A, which prevented the loss of psim, also inhibited HMG-induced DNA fragmentation in cells expressing an activated p21Ras. Induction of apoptosis by PKC inhibition in human tumors with oncogenic p21Ras mutations was demonstrated. Inhibition of PKC caused increased apoptosis in MIA-PaCa-2, a human pancreatic tumor line containing a mutated Ki-ras allele, when compared to HS766T, a human pancreatic tumor line with normal Ki-ras alleles. Furthermore, PKC inhibition induced apoptosis in HCT116, a human colorectal tumor line containing an oncogenic Ki-ras allele but not in a subline (Hke3) in which the mutated Ki-ras allele had been disrupted. The PKC inhibitor 1-O-hexadecyl-2-O-methyl-rac-glycerol (HMG), significantly reduced p21Ras-mediated tumor growth in vivo in a nude mouse MIA-PaCa-2 xenograft model. Collectively these studies suggest the therapeutic feasibility of targeting PKC activity in tumors expressing an activated p21Ras oncoprotein.

Negative regulatory role of overexpression of PLC gamma 1 in the expression of early growth response 1 gene in rat 3Y1 fibroblasts

The early growth response 1 (Egr-1) gene product is a transcription factor that functions as an oikis factor. Loss of Egr-1 expression is closely associated with tumor formation. Phospholipase Cgamma1 (PLCgamma1) is overexpressed in some tumors, and its overexpression causes anchorage-independent growth. Here we report that overexpression of PLCgamma1 and SH2-SH3 domain of PLCgamma1 decreased induction of Egr-1 and the Egr-1-regulated genes TSP-1 and PAI-1. Results from the nuclear run-on assay and transfection experiment with the proximal 455 base pair region of the Egr-1 promoter (-454 to +1) showed that Egr-1 transcriptional activity was suppressed in PLCgamma1-3Y1 cells whereas decay of Egr-1 mRNA was similar in both cell lines. Serum response element- and ternary complex factor Elk-1-mediated transcriptional activation of the reporter gene in response to EGF were also inhibited in PLCgamma1-3Y1 cells. Pretreatment with the protein synthesis inhibitor cycloheximide (CHX) partially abrogated the serum-induced suppression of Egr-1 transcription in PLCgamma1-3Y1 cells, suggesting that a CHX-sensitive factor(s) is involved in the suppression of Egr-1 transcription in PLCgamma1-3Y1 cells. Our results demonstrated that overexpression of PLCgamma1 functions as a negative modulator of the tumor suppressor Egr-1 gene expression, possibly through inhibition of Elk-1-dependent transcriptional activity.

Induction of early growth response-1 gene expression by calmodulin antagonist trifluoperazine through the activation of Elk-1 in human fibrosarcoma HT1080 cells

The early growth response gene-1 (Egr-1) is a transcription factor that plays an important role in cell growth and differentiation. It has been known that Egr-1 expression is down-regulated in many types of tumor tissues, including human fibrosarcoma HT1080 cells, and introduction of the Egr-1 gene into HT1080 cells inhibits cell growth and tumorigenic potential. Trifluoperazine (TFP), a phenothiazine class calmodulin antagonist, is known to inhibit DNA synthesis and cell proliferation and potentially important in antitumor activities. To understand the regulatory mechanism of Egr-1, we investigated the effect of TFP on expression of Egr-1 in HT1080 cells. Herein, we report that Egr-1 expression was increased by TFP in synergy with serum at the transcriptional level. Both the Ca(2+)/calmodulin-dependent protein kinase II inhibitor KN62 and the calcineurin inhibitor cyclosporin A enhanced TFP-dependent increase of Egr-1, suggesting that the Ca(2+)/calmodulindependent pathway plays a role in regulation of Egr-1 expression in HT1080 cells. The TFP-stimulated increase of the Egr-1 protein was preferentially inhibited by the MEK-specific inhibitor PD98059. In addition, activation of human Egr-1 promoter and the transcriptional activation of the ternary complex factor Elk-1 induced by TFP were inhibited both by pretreatment of PD98059 and by expression of the dominant-negative RasN17. These results indicate that the Ras/MEK/Erk/Elk-1 pathway is necessary for TFP-induced Egr-1 expression. We propose that the calmodulin antagonist TFP stimulates Egr-1 gene expression by modulating Ras/MEK/Erk and activation of the Elk-1 pathway in human fibrosarcoma HT1080 cells.

The role of calcineurin in lymphocyte activation

Lymphokine gene transcription involves numerous signal transduction molecules and second messengers. The serine/threonine phosphatase calcineurin has been demonstrated to play a central role in the immediate, early activation of numerous lymphokines (such as interleukin [IL]-2) and in the regulation of cell surface receptors such as CD40L, CD95, and recently CD25 alpha (the alpha chain of the IL-2 receptor). In addition to lymphocyte activation, calcineurin functions include control of neuronal signaling, muscle contraction, muscle hypertrophy and cellular death. Therefore, calcineurin not only plays a vital role in the regulation of T lymphocyte function, but also functions in cellular environments outside the immune system.

A novel functional interaction between Vav and PKCtheta is required for TCR-induced T cell activation

Vav and PKCtheta play an early and important role in the TCR/CD28-induced stimulation of MAP kinases and activation of the IL-2 gene. Vav is also essential for actin cytoskeleton reorganization and TCR capping. Here, we report that PKCtheta function was selectively required in a Vav signaling pathway that mediates the TCR/CD28-induced activation of JNK and the IL-2 gene and the upregulation of CD69 expression. Vav also promoted PKCtheta translocation from the cytosol to the membrane and cytoskeleton and induced its enzymatic activation in a CD3/CD28-initiated pathway that was dependent on Rac and on actin cytoskeleton reorganization. These findings reveal that the Vav/Rac pathway promotes the recruitment of PKCtheta to the T cell synapse and its activation, essential processes for T cell activation and IL-2 production.

Expression and activation of RAS and mitogen-activated protein kinases in macrophages treated in vitro with cisplatin: regulation by kinases, phosphatases and Ca2+/calmodulin

Cisplatin (cis-dichlorodiammineplatinum II), a potent antitumour compound, stimulates immune responses by activating monocytes/macrophages and other cells of the immune system. However, the exact mechanism by which cisplatin activates these cells is poorly characterized and attempts are being made to understand this mechanism. Previous studies from this laboratory have shown that Lyn, a protein tyrosine kinase of the src family, and nuclear factor (NF)-kappaB are involved in cisplatin-induced macrophage activation. Recent studies suggest that the RAS and mitogen-activated protein (MAP) kinases function as a connecting link between activated lyn and NF-kB, which raises the possibility of their involvement in cisplatin-induced macrophage activation. Therefore, this study was undertaken to investigate the effect of cisplatin treatment on the expression/activation of RAS (a low molecular weight GTP-binding protein) and MAP kinases in murine peritoneal macrophages. The underlying mechanism of expression/activation of RAS and MAP kinases in cisplatin-treated macrophages was also investigated. Immunoblotting and immune-complex kinase assays revealed that cisplatin treatment of macrophages leads to increased expression/activation of RAS and MAP kinases, with optimal expression/activation at 15 min of treatment. Using a battery of specific inhibitor/modulators of different signalling molecules, this study shows that expression and activation of MAP kinases are two unrelated processes. It was also observed that kinase (protein tyrosine and protein kinase C) inhibitor and Ca2+/calmodulin antagonist inhibit expression/activation of RAS/MAP kinases in macrophages, whereas phosphatases (protein tyrosine and serine/threonine) inhibitor up-regulate these kinases.

Attenuation of haptoglobin gene expression by TGFbeta requires the MAP kinase pathway

In addition to important roles in the regulation of cell growth and cell restitution, both pro- and anti-inflammatory effects have been ascribed to TGFbeta in intestinal epithelial cells. However, the mechanisms involved in TGFbeta-dependent anti-inflammatory activities remain to be determined. In the rat intestinal epithelial cell line IEC-6, TGFbeta attenuated the glucocorticoid-dependent increases in mRNA levels of the acute phase protein gene haptoglobin, and of C/EBP isoforms beta and delta. Supershift assays demonstrated a TGFbeta-mediated decrease in the binding of C/EBP isoforms beta and delta to the haptoA and haptoC C/EBP DNA-binding sites from the haptoglobin promoter. Mutations of both HaptoA and HaptoC sites abolished the glucocorticoid-dependent activation and the TGFbeta-mediated attenuation of the haptoglobin promoter, as assessed by transient transfection assays. TGFbeta induced p42/p44 MAP kinase activities. Treatment with the MEK 1/2 inhibitor PD 98059 abolished TGFbeta attenuation. These results suggest that C/EBP isoforms are involved both in the glucocorticoid-dependent induction and in the TGFbeta-mediated attenuation of haptoglobin expression. Furthermore, p42/p44 MAP kinases may function in a TGFbeta-dependent signaling pathway leading to attenuation of haptoglobin expression.

Negative regulation of glucocorticoid-dependent induction of c-fos by ras in intestinal epithelial cells

In order to investigate the regulatory mechanisms involved in the expression of fos and jun family members by glucocorticoids, and the effect of ras transformation in intestinal epithelial cells, we used the rat cell line IEC-6. Dexamethasone treatment induced transiently c-jun mRNAs, in contrast to the sustained expression of c-fos, whereas its effect on junB expression resulted in a later increase. Dexamethasone-dependent stimulation of c-fos and c-jun was modulated predominantly at the level of transcription. Sustained levels of induced c-fos and c-jun proteins were observed after dexamethasone treatment. AP-1 DNA-binding capacity of c-fos, and to a smaller extent c-jun, was increased by glucocorticoids later than after serum treatment. To analyse the effect of ras on the glucocorticoid response of AP-1 components, we studied several IEC-6 cell clones transformed by the Ha-ras oncogene. In comparison to normal cells, these transformants displayed increased AP-1 DNA-binding activity with higher levels of junB and variable levels of c-jun in the AP-1 complex. Ras transformation repressed the growth-inhibitory properties of glucocorticoids. Furthermore, ras inhibited the glucocorticoid-dependent induction of c-fos protein and mRNA, leading to changes in AP-1 composition as compared to normal cells. As assessed by transient transfection luciferase assays, glucocorticoids induced significantly a minimal promoter containing 3 copies of an AP-1 DNA-binding site as well as the murine c-fos -276 to +112 promoter in non-transformed cells. In contrast, glucocorticoid addition did not induce these constructs in two ras transformed cell lines. These results suggest that ras negatively modulates specific responses of intestinal epithelial cells to glucocorticoids.

Attenuated expression of the serum responsive T1 gene in ras transformed fibroblasts due to the inhibition of c-fos gene activity

The T1 gene encodes a protein, which shares homology with the IL-1 receptors. In fibroblasts, T1 is induced by growth factors and in response to the onset of oncogene expression. The c-fos gene is transiently activated in these situations and was shown to be the major mediator of T1 gene induction. In contrast, the sustained expression of a ras oncogene in NIH3T3 cells resulted in the downregulation of basal T1 gene activity and the attenuation of T1 gene induction in response to mitogenic signals. Likewise, the immediate early genes encoding c-Fos, FosB, and Fra-2 are repressed in these cells. T1 gene repression could be overcome by the forced expression of c-fos in ras transformed fibroblasts. Thus, the lack of c-fos gene expression is the likely cause for ras mediated T1 gene repression. Fra-1, in contrast to the other three members of the Fos family, is permanently synthesized in high amounts in ras transformed NIH3T3 fibroblasts. We show that AP-1, which is abundant in these cells throughout the whole cell cycle, consists predominantly of Fra-1/c-Jun and Fra1/JunD heterodimers. We provide evidence that Fra1/c-Jun heterodimers are responsible for the repression of c-fos gene induction following serum stimulation. The introduction of a dominant negative version of c-Jun into ras transformed fibroblasts was able to rescue c-fos gene induction in response to serum stimulation, further demonstrating that AP-1 is indeed involved in c-fos gene repression. We conclude that oncogenic ras mediates the activation of the fra-1 gene which results in elevated AP-1 activity throughout the cell cycle. Fra-1 containing AP-1 complexes repress the c-fos and possibly other immediate early genes thereby preventing the induction of certain delayed early genes such as the T1 gene in response to mitogenic stimulation.

GATA-Dependent expression of the interleukin-1 receptor-related T1 gene in mast cells

The murine delayed-early serum-responsive gene T1 encodes glycoproteins of the interleukin-1 receptor family. Transcriptional initiation in fibroblasts is regulated by c-Fos and gives rise to a rare 5-kb mRNA and an abundant 2.7-kb mRNA. These transcripts are translated into a receptor-like membrane-anchored protein and a secreted protein consisting only of the ectodomain. In mast cells, T1 gene transcription is initiated 10.5 kb further upstream than in fibroblasts and gives rise predominantly to the 5-kb transcript under normal growth conditions. Here we demonstrate that calcium ionophore stimulation of mast cells resulted in an upregulation of T1 gene expression and a switch from the long to the short T1 transcript. This was paralleled by the disappearance of the receptor-type T1 protein on the mast cell surface and the secretion of large amounts of the truncated T1 protein. c-Fos and a T1 enhancer, which have previously been identified to be essential for T1 expression in fibroblasts, were not required for calcium ionophore-mediated T1 gene upregulation. Overexpression of the transcription factor GATA-1 in mast cells caused elevated T1 synthesis. Three GATA elements were identified in the minimal GATA-responsive mast cell promoter. Mutational analysis revealed that all three GATA elements are involved in T1 gene expression. Point mutations within the middle GATA element eliminated promoter activity completely, while mutations of the distal and proximal GATA binding sites reduced promoter strength by factors of 2 and 5, respectively. Exogenous expression of GATA-1 was not sufficient to activate the mast cell-specific promoter in NIH 3T3 fibroblasts.

Differential regulation of discrete apoptotic pathways by Ras

The products of the ras genes are known to regulate cell proliferation and differentiation; recently, they have been found to play a role in apoptosis. The expression of oncogenic p21(ras) in a number of cell types, including Jurkat (a human T lymphoblastoid cell line) and murine fibroblasts, makes the cells susceptible to apoptosis following suppression of protein kinase C (PKC) activity (PKC/Ras-mediated apoptosis). Engagement of Fas antigen, a potent effector of apoptosis, activates cellular p21(ras), which may be required for completion of the cell death program. To further investigate the role of p21(ras) in the regulation of apoptosis, the cellular mechanisms employed in these two apoptotic processes in which Ras activity is involved (PKC/Ras-related and Fas-triggered apoptosis), was explored. Increasing p21(ras) activity by expressing v-ras or by treatment with an antisense oligonucleotide to the GTPase-activating protein was found to accelerate the Fas-mediated apoptotic process in Jurkat and mouse LF cells. PKC/Ras-related apoptosis was associated with, and required, cell cycle progression, accompanied by the expression of the G1/S cyclins. In contrast, Fas engagement, although inducing a vigorous and PKC-independent activation of endogenous p21(ras), did not alter cell cycle progression, nor did it require such progression for apoptosis. Both the protein synthesis inhibitor cycloheximide and cyclin E antisense oligonucleotides partially abolished PKC/Ras-mediated apoptosis but had only a moderate effect on Fas-induced apoptosis. In contrast, the CED-3/interleukin-1beta-converting enzyme (ICE) protease inhibitor Z-VADfmk efficiently suppressed Fas-induced apoptosis and only marginally inhibited PKC/Ras-mediated apoptosis. Induction of both pathways resulted in activation of the Jun NH2-terminal kinase/JUN signaling system. These results suggest that different cell death programs, such as PKC/Ras-mediated and Fas-mediated apoptosis, may be interconnected via p21(ras) and perhaps Jun NH2-terminal kinase/JUN. In response to various death stimuli, p21(ras) may act as a common intermediate regulator in the transduction of apoptotic signals.