Protein kinase inhibitor H7 blocks the induction of immediate-early genes zif268 and c-fos by a mechanism unrelated to inhibition of protein kinase C but possibly related to inhibition of phosphorylation of RNA polymerase II

An Overview on the Potential Antimycobacterial Agents Targeting Serine/Threonine Protein Kinases from Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), still remains an urgent global health issue, mainly due to the emergence of multi-drug resistant strains. Therefore, there is a pressing need to develop novel and more efficient drugs to control the disease. In this context, targeting the pathogen virulence factors, and particularly signal mechanisms, seems to be a promising approach. An important transmembrane signaling system in Mtb is represented by receptor-type Serine/ Threonine protein kinases (STPKs). Mtb has 11 different STPKs, two of them, PknA and PknB, are essential. By contrast PknG and PknH are involved in Mtb virulence and adaptation, and are fundamental for the pathogen growth in infection models. Therefore, STPKs represent a very interesting group of pharmacological targets in M. tuberculosis. In this work, the principal inhibitors of the mycobacterial STPKs will be presented and discussed. In particular, medicinal chemistry efforts have been focused on discovering new antimycobacterial compounds, targeting three of these kinases, namely PknA, PknB and PknG. Generally, the inhibitory effect on these enzymes do not correlate with a significant antimycobacterial action in whole-cell assays. However, compounds with activity in the low micromolar range have been obtained, demonstrating that targeting Mtb STPKs could be a new promising strategy for the development of drugs to treat TB infections.

The basal transcription machinery as a target for cancer therapy

General transcription is required for the growth and survival of all living cells. However, tumor cells require extraordinary levels of transcription, including the transcription of ribosomal RNA genes by RNA polymerase I (RNPI) and mRNA by RNA polymerase II (RNPII). In fact, cancer cells have mutations that directly enhance transcription and are frequently required for cancer transformation. For example, the recent discovery that MYC enhances the transcription of the majority genes in the genome correlates with the fact that several transcription interfering drugs preferentially kill cancer cells. In recent years, advances in the mechanistic studies of the basal transcription machinery and the discovery of drugs that interfere with multiple components of transcription are being used to combat cancer. For example, drugs such as triptolide that targets the general transcription factors TFIIH and JQ1 to inhibit BRD4 are administered to target the high proliferative rate of cancer cells. Given the importance of finding new strategies to preferentially sensitize tumor cells, this review primarily focuses on several transcription inhibitory drugs to demonstrate that the basal transcription machinery constitutes a potential target for the design of novel cancer drugs. We highlight the drugs’ mechanisms for interfering with tumor cell survival, their importance in cancer treatment and the challenges of clinical application.

Transcriptional regulation of mitochondrial glycerophosphate acyltransferase is mediated by distal promoter via ChREBP and SREBP-1

We have recently identified two promoters, distal and proximal for rat mitochondrial glycerophosphate acyltransferase (mtGPAT). Here we are reporting further characterization of the promoters. Insulin and epidermal growth factor (EGF) stimulated while leptin and glucagon inhibited the luciferase activity of the distal promoter and the amounts of the distal transcript. Conversely, luciferase activity of the proximal promoter and proximal transcript remained unchanged due to these treatments. Only the distal promoter has binding sites for carbohydrate response element binding protein (ChREBP) and sterol regulatory element binding protein-1 (SREBP-1). Electromobility shift assays and chromatin immunoprecipitation assays demonstrated that ChREBP and SREBP-1 bind to the mtGPAT distal promoter. Insulin and EGF increased while glucagon and leptin decreased the binding of SREBP-1 and ChREBP to the distal promoter. Thus, the distal promoter is the regulatory promoter while the proximal promoter acts constitutively for rat mtGPAT gene under the influence of hormones and growth factor.

Involvement of protein phosphorylation in water stress-induced antioxidant defense in maize leaves

Using pharmacological and biochemical approaches, the role of protein phosphorylation and the interrelationship between water stress-enhanced kinase activity, antioxidant enzyme activity, hydrogen peroxide (H2O2) accumulation and endogenous abscisic acid in maize (Zea mays L.) leaves were investigated. Water-stress upregulated the activities of total protein phosphorylation and Ca2+-dependent protein kinase, and the upregulation was blocked in abscisic acid-deficient vp5 mutant. Furthermore, pretreatments with a nicotinamide adenine dinucleotide phosphate oxidase inhibitor and a scavenger of H2O2 significantly reduced the increased activities of total protein kinase and Ca2+-dependent protein kinase in maize leaves exposed to water stress. Pretreatments with different protein kinase inhibitors also reduced the water stress-induced H2O2 production and the water stress-enhanced activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase. The data suggest that protein phosphorylation and H2O2 generation are required for water stress-induced antioxidant defense in maize leaves and that crosstalk between protein phosphorylation and H2O2 generation may occur.

Muscarinic acetylcholine receptors stimulate Ca2+ influx in PC12D cells predominantly via activation of Ca2+ store-operated channels

Activation of muscarinic acetylcholine receptors (mAChRs) causes the rapid release of Ca2+ from intracellular stores and a sustained influx of external Ca2+ in PC12D cells, a subline of the widely studied cell line PC12. Release of Ca2+ from intracellular stores and a sustained influx of Ca2+ are also observed following exposure to thapsigargin, a sesquiterpene lactone that depletes intracellular Ca2+ pools by irreversibly inhibiting the Ca2+ pump of the endoplasmic reticulum. In this study, we show that carbachol and thapsigargin empty the same intracellular Ca2+ stores, and that these stores are a subset of intracellular stores depleted by the Ca2+ ionophore ionomycin. Intracellular Ca2+ stores remain depleted during continuous stimulation of mAChR with carbachol in medium containing 2 mM extracellular Ca2+, but rapidly refill following inhibition of mAChRs with atropine. Addition of atropine to carbachol-stimulated cells causes intracellular Ca2+ levels to return to baseline levels in two steps: a rapid decrease that correlates with the reuptake of Ca2+ into internal stores and a delayed decrease that correlates with the inhibition of a Mn2+-permeable Ca2+ channel. Several lines of evidence suggest that carbachol and thapsigargin stimulate Ca2+ influx by a common mechanism: (i) pretreatment with thapsigargin occludes atropine-mediated inhibition of Ca2+ influx, (ii) carbachol and thapsigargin applied individually or together are equally efficient at stimulating the influx of Mn2+, and (iii) identical rates of Ca2+ influx are observed when Ca2+ is added to cells pretreated with carbachol, thapsigargin, or both agents in the absence of extracellular Ca2+. Taken together, these data suggest that the sustained influx of extracellular Ca2+ observed following activation of mAChRs in PC12D cells is mediated primarily by activation of a Mn2+-permeable, Ca2+ store-operated Ca2+ channel.

Interpretation of BMP signaling in early Xenopus development

Very little is known about how the extracellular binding of a morphogen is transduced to the nucleus of a cell in a concentration-related way, enabling cells to interpret their position in a concentration gradient. Here, we have analyzed when and how Xenopus embryo cells perceive and interpret a BMP signal. Dissociated embryo cells are exposed for short times to different concentrations of BMP4. We find that cells are already competent to receive a BMP4 signal at the blastula stage. They phosphorylate Smad1 very rapidly and express downstream genes less than half an hour after exposure to BMP. However, Smad1 is present in the nucleus even in the absence of BMP. To quantitate intracellular signaling after BMP exposure, we have constructed a chimeric type I receptor that registers BMP signaling as the intranuclear migration of Smad2, and as the transcription of Smad2 downstream genes. The combination of the chimeric receptor and GFP-Smad2 makes it possible to follow the transduction of BMP signaling to the nucleus. From our results, we conclude that an extracellular BMP concentration is interpreted by the steady state nuclear concentration of phosphorylated Smad1.

Nuclear export of influenza A virus mRNAs requires ongoing RNA polymerase II activity

Influenza A virus transcribes its segmented negative sense RNA genome in the nuclei of infected cells in a process long known to require host RNA polymerase II (RNAP-II). RNA polymerase II synthesizes pre-mRNAs whose 5'-cap structures are scavenged by the viral RNA-dependent RNA polymerase during synthesis of viral mRNAs. Drugs that inhibit RNAP-II therefore block viral replication, but not necessarily solely by denying the viral polymerase a source of cap-donor molecules. We show here that 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB), a compound that prevents processive transcription by RNAP-II, inhibits expression of the viral HA, M1 and NS1 genes at the post-transcriptional level. Abundant quantities of functionally and structurally intact viral mRNAs are made in the presence of DRB but with the exception of NP and NS2 mRNAs, are not efficiently translated. Taking M1 and NP mRNAs as representatives of DRB-sensitive and insensitive mRNAs, respectively, we found that the block to translation operates at the level of nuclear export. Furthermore, removal of DRB reversed this block unless a variety of chemically and mechanistically distinct RNAP-II inhibitors were added instead. We conclude that influenza A virus replication requires RNAP-II activity not just to provide capped mRNA substrates but also to facilitate nuclear export of selected viral mRNAs.

Effects of kinase inhibitors on TGF-beta induced upregulation of Kv1.3 K+ channels in brain macrophages

Deactivation of brain macrophages (microglia) by transforming growth factor-beta (TGF-beta) is characterized by enhanced Kv1.3 K+ channel expression. The intracellular mechanisms by which TGF-beta causes K+ channel upregulation in microglia have remained unclear. We show here that the protein kinase inhibitor H7 abolishes TGF-beta-induced increases in delayed rectifier K+ current density. However, this effect cannot be related to inhibition of protein kinase C (PKC) or protein kinase A (PKA) activity, because specific PKC and PKA inhibitors did not exhibit effects identical to H7. TGF-beta-induced Kv1.3 channel expression was also unaffected by inhibitors of tyrosine kinase, Ca2+/calmodulin kinase II and mitogen-activated protein (MAP) kinase ERK. In contrast, delayed rectifier K+ current density was larger in TGF-beta-stimulated cells pretreated with the p38 MAP kinase inhibitor SB203580 or the phosphatidylinositol 3-OH (PI3) kinase inhibitor wortmannin, suggesting that both p38 MAP kinase and PI3 kinase regulate negatively the upregulation of Kv1.3 K+ channels in TGF-beta-treated microglial cells.

Cannabinoids inhibit the activation of ERK MAPK in PMA/Io-stimulated mouse splenocytes

The mechanism of action of immune suppression by cannabinoids involves suppression of interleukin-2 (IL-2) production in phorbol ester plus calcium ionophore (PMA/Io)-stimulated lymphocytes. This decrease in IL-2 was due to inhibition of activator protein-1 (AP-1) and nuclear factor of activated T cells (NF-AT) transcription factors, both of which depend on proteins that are regulated by the extracellular signal-regulated kinase subgroup of the mitogen-activated protein kinases (ERK MAPK). Thus, the objective of the present study was to characterize the effects of cannabinoid compounds on ERK MAPK under conditions where IL-2 expression was suppressed. Using the MEK inhibitor PD098059 in order to assess the role of ERK MAPK in PMA/Io-stimulated splenocytes (SPLC), it was determined that IL-2 production and expression of c-fos and c-jun nuclear protein expression depended on activation of ERK MAPK. In response to PMA/Io, expression of nuclear phosphorylated ERK MAPK was rapidly induced, peaked at approximately 15 min, and was sustained for up to 240 min. Pretreatment with cannabinol (CBN) inhibited expression of phosphorylated ERK MAPK at several time points up to 240 min post cellular activation. Furthermore, WIN-55212-2, a synthetic cannabinoid, inhibited expression of phosphorylated ERK MAPK at 240 min post cellular activation. CBN did not induce activation of ERK MAPK in the absence of PMA/Io. Collectively, these studies suggest that cannabinoid-induced inhibition of IL-2 in PMA/Io-stimulated splenocytes might be due, in part, to inhibition of ERK MAPK activation.

A protein kinase inhibitor as an antimycobacterial agent

The protein kinase inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7) was found to inhibit the growth of two different mycobacterial strains, the slow-growing Mycobacterium bovis Bacille Calmette Guerin (BCG) and the fast-growing saprophyte Mycobacterium smegmatis mc2 155, in a dose-dependent manner. While screening for the effect of kinase inhibitors on mycobacterial growth, millimolar concentrations of H7 induced a 40% decrease in the growth of M. bovis BCG when measured as a function of oxidative phosphorylation. This H7-induced decrease in growth was shown to involve a 2-log fold decrease in the viable counts of M. smegmatis within a 48-h period and a 50% reduction in the number of BCG viable counts within a 10-day period. Micromolar concentrations of H7 compound induced a significant decrease in the activity of the Mycobacterium tuberculosis protein serine/threonine kinase (PSTK) PknB. The inhibition of mycobacterial growth as well as the inhibition of a representative M. tuberculosis protein serine/threonine kinase PknB suggests that conventional PSTK inhibitors can be used to study the role that the mycobacterial PSTK family plays in controlling bacterial growth.

Rottlerin stimulates metallothionein gene expression but inhibits metal transport in Chinese hamster ovary cells

Metallothionein (MT) can be induced by various metals. We have shown previously that H7, a protein kinase C (PKC) inhibitor, inactivates metal-induced MT gene expression. To investigate whether a specific PKC isoform is involved in the induction process, inhibitors for various PKC isoforms were administered to cadmium-resistant Chinese hamster ovary (Cd(R)) cells. None of the inhibitors used can reduce metal-induced MT gene expression. However, a PKCdelta inhibitor, rottlerin, induced MT mRNA expression in Cd(R) cells in the presence or absence of Cd. Notably, the induction occurs through the activation of the MT transcriptional factor (MTF-1) and is not related to an increase of metal influx. Furthermore, metal accumulation is reduced in the presence of rottlerin. Pulse-labeling analysis indicated that MT protein synthesis increased in Cd(R) cells upon rottlerin treatment. These results suggest that rottlerin blocks metal transport but stimulates MT synthesis in Cd(R) cells. Since rottlerin is capable of reducing the cellular accumulation of Cd, it was expected that the cytotoxic effect of Cd would decrease in the presence of rottlerin. Treating the parental cell of Cd(R) with Cd and rottlerin together indeed showed a decline of cytotoxicity compared to cells treated with Cd alone. We further examined how MTF-1 was activated by rottlerin. Rottlerin-induced MTF-1 activity was not affected in Cd(R) cells by the addition of EDTA. It was, however, diminished by administering an intracellular Zn chelator, TPEN. The result implies a mobilization of intracellular Zn ions after rottlerin treatment in Cd(R) cells. To investigate whether the described results occur in all types of cells, another cell line (GH(3)) was used to study the effect of rottlerin on MT gene expression. The result revealed that rottlerin did not increase the amount of MT mRNA in GH(3) cells. This differential effect between cell lines may be useful for investigating the regulatory mechanism of MT gene expression.

Phosphorylation is involved in the activation of metal-regulatory transcription factor 1 in response to metal ions

We have studied the role of phosphorylation in the activation of metal-regulatory transcription factor-1 (MTF-1) and metallothionein (MT) gene expression. We showed that MTF-1 is phosphorylated in vivo and that zinc stimulates MTF-1 phosphorylation 2-4-fold. Several kinase inhibitors were used to examine the possible involvement of kinase cascades in the activation of MTF-1. Metal-induced MT gene expression was abrogated by protein kinase C (PKC), c-Jun N-terminal kinase (JNK), phosphoinositide 3-kinase, and tyrosine-specific protein kinases inhibitors, as assayed by Northern analysis and by cotransfection experiments using a metal regulatory element-luciferase reporter plasmid. The extracellular signal-activated protein kinase and the p38 kinase cascades did not appear to be essential for the activation of MT gene transcription by metals. By using dominant-negative mutants of PKC, JNK, mitogen-activated kinase kinase 4 (MKK4), and MKK7, we provide further evidence supporting a role for PKC and JNK in the activation of MTF-1 in response to metals. Notably, increased MTF-1 DNA binding in response to zinc and MTF-1 nuclear localization was not inhibited in cells preincubated with the different kinase inhibitors despite strong inhibition of MTF-1-mediated gene expression. This suggests that phosphorylation is essential for MTF-1 transactivation function. We hypothesize that metal-induced phosphorylation of MTF-1 is one of the primary events leading to increased MTF-1 activity. Thus, metal ions such as cadmium could activate MTF-1 and induce MT gene expression by stimulating one or several kinases in the MTF-1 signal transduction pathway.

Endoplasmic reticulum stress prolongs GH-induced Janus kinase (JAK2)/signal transducer and activator of transcription (STAT5) signaling pathway

The desensitization of the GH-induced Janus kinase 2 (JAK2) and signal transducer and activator of transcription 5 (STAT5) signaling pathway plays a crucial role in GH regulation of hepatic genes. Previous studies have demonstrated that the inactivation of the GH-induced JAK2/STAT5 pathway is regulated by protein translation and suppressors of cytokine signaling (SOCS). In this study we sought to explore the relationships between endoplasmic reticulum stress, GH-induced JAK2/STAT5 activity and SOCS expression. 1,2-bis(o-Aminophenoxy)ethane-N,N,N,N-tetraacetic acid (acetoxymethyl)ester (BAPTA-AM), used to provoke endoplasmic reticulum stress, caused a drastic inhibition of protein translation that correlated with the phosphorylation of the eukaryotic translation initiation factor 2alpha. Both GH and BAPTA-AM caused a rapid induction of the transcription factor C/EBP homology protein (CHOP) and an additive effect was observed with combined treatment, which suggests a regulatory role of GH on endoplasmic reticulum stress. Endoplasmic reticulum stress did not interfere with the rapid GH activation of STAT5 DNA binding activity. However, BAPTA-AM prolonged the DNA binding activity of STAT5 without affecting STAT5 or JAK2 protein levels. GH-induced phosphorylation of JAK2 and STAT5 DNA binding activity were prolonged in the presence of BAPTA-AM, suggesting that endoplasmic reticulum stress prevents the inactivation of STAT5 DNA binding activity by modulating the rate of JAK2/STAT5 dephosphorylation. Like BAPTA-AM, the endoplasmic reticulum stressors dithiothreitol and A23187 also prolonged the GH-induced STAT5 DNA binding activity. We were not able to correlate BAPTA-AM effects to the GH-dependent expression of SOCS proteins or SOCS mRNA, suggesting that endoplasmic reticulum stress modulates the rate of JAK2/STAT5 dephosphorylation through mechanisms other than inhibition of SOCS expression. This study indicates that cellular stress may modulate transcription through the JAK/STAT pathway.

Astrocyte-released cytokines induce ramification and outward K+ channel expression in microglia via distinct signalling pathways

Differentiation of microglial cells is characterized by transformation from ameboid into ramified cell shape and up-regulation of K+ channels. The processes of microglial differentiation are controlled by astrocytic factors. The mechanisms by which astrocytes cause developmental changes in morphological and electrophysiological properties of microglia have remained unclear. We show here that the cytokines transforming growth factor-beta (TGF-beta), macrophage colony-stimulating factor (M-CSF) and granulocyte/macrophage colony-stimulating factor (GM-CSF) are released by astrocytes at concentrations sufficient to induce ramification and up-regulation of delayed rectifier (DR) K+ channels in microglia. Transformation from ameboid into ramified morphology induced in microglia by exposure to astrocyte-conditioned medium (ACM) was inhibited by neutralizing antibodies against TGF-beta, M-CSF or GM-CSF, whilst ACM-induced DR channel expression was exclusively inhibited by antibodies against TGF-beta. Although both ramification and DR channel up-regulation occurred simultaneously, DR channel blockade by charybdotoxin failed to inhibit microglial ramification. The ACM-induced ramification of microglia was inhibited by the tyrosine kinase inhibitor genistein, whereas DR channel up-regulation did not occur in the presence of the serine/threonine kinase inhibitor H7. Our data suggest that astrocytes modulate processes of microglial differentiation in parallel but via distinct signalling pathways.

A CalDAG-GEFI/Rap1/B-Raf cassette couples M(1) muscarinic acetylcholine receptors to the activation of ERK1/2

In this study we examine signaling pathways linking the M(1) subtype of muscarinic acetylcholine receptor (M(1) mAChR) to activation of extracellular signal-regulated kinases (ERK) 1 and 2 in neuronal PC12D cells. We first show that activation of ERK1/2 by the M(1) mAChR agonist carbachol takes place primarily via a Ras-independent pathway that depends largely upon Rap1, another small GTP-binding protein in the Ras family. Rap1 in turn activates B-Raf, an upstream activator of ERK1/2. Consistent with these results, carbachol was found to activate Rap1 more potently than Ras. Similar to other small GTP-binding proteins, activation of Rap1 requires a guanine nucleotide exchange factor (GEF) to promote its conversion from the GDP- to GTP-bound form. Using specific antibodies, we show that a recently identified Rap1 GEF, calcium- and diacylglycerol-regulated guanine nucleotide exchange factor I (CalDAG-GEFI), is expressed in PC12D cells and that carbachol stimulates the formation of a complex containing CalDAG-GEFI, Rap1, and activated B-Raf. Finally, we show that expression of CalDAG-GEFI antisense RNA largely blocks carbachol-stimulated activation of hemagglutinin (HA)1-tagged B-Raf and formation of the CalDAG-GEFI/Rap1/HA1-tagged B-Raf complex. Together, these data define a novel signaling pathway for M(1) mAChR, where increases in Ca(2+) and diacylglycerol stimulate the sequential activation of CalDAG-GEFI, Rap1, and B-Raf, resulting in the activation of MEK and ERK1/2.

M1 muscarinic acetylcholine receptors activate zif268 gene expression via small G-protein Rho-dependent and lambda-independent pathways in PC12D cells

We have previously shown that stimulation of M1 muscarinic acetylcholine receptors (mAChRs) in neuronal PC12D cells rapidly induces the immediate-early gene zif 268 [Ebihara, T. & Saffen, D. (1997) J. Neurochem. 68, 1001-1010]. Here we show that stimulation of M1 mAChRs in these cells activates four distal serum response elements (SREs) in the zif 268 promoter, and that this activation is strongly inhibited by Clostridium botulinum C3 exoenzyme (C3), which specifically inactivates the small G-protein Rho. Even with high doses of C3, however, a portion of the activation remains intact, indicating that stimulation of M1 mAChRs activates zif 268 SREs via Rho-dependent and Rho-independent pathways. Moreover, the Rho-independent activation of zif 268 SREs is inhibited by the dominant-negative form of the small G-protein Ras, suggesting that Rho-independent activation of zif 268 SREs is mediated by Ras. To determine if muscarinic agonists activate RhoA, we also measured the translocation of RhoA from the cytosolic fraction to the particulate fraction. Translocation of RhoA to the particulate fraction was observed within 15 min following stimulation of M1 mAChRs, indicating that RhoA is activated with sufficient rapidity to participate in the induction of zif 268 mRNA. Together, these results suggest that RhoA is activated following stimulation of M1 mAChRs and functions in SRE-dependent induction of the zif 268 gene within a Ras-independent pathway.

Phorbol ester activation of the neuronal nicotinic acetylcholine receptor alpha7 subunit gene: involvement of transcription factor Egr-1

alpha-Bungarotoxin-sensitive neuronal nicotinic acetylcholine receptors from bovine adrenomedullary chromaffin cells are up-regulated by long-term exposure to phorbol esters. The rise in receptor density is paralleled by an increase in transcripts corresponding to the alpha7 subunit, which is a component of this receptor subtype. Transcriptional activation of the alpha7 subunit gene is evidenced in reporter gene transfection experiments, in which phorbol esters increase alpha7 promoter activity by up to 14-fold. About 80% of this activation is abolished when at least two of the three sites for the immediate-early transcription factor Egr-1, present in the proximal promoter region of the alpha7 subunit gene, are mutated simultaneously. In addition, phorbol esters elevate both Egr-1 mRNA and Egr-1 protein levels in chromaffin cells, whereas electrophoretic mobility shift assays show that the Egr-1 component of the complexes that originate at the alpha7 promoter increases in cells treated with phorbol esters. These results suggest that the transcription factor Egr-1 is involved in triggering expression of alpha-bungarotoxin-sensitive nicotinic receptors in response to external stimuli, such as the ones resulting from phorbol ester treatment, and support our previous hypothesis that the alpha7 subunit gene is one of the specific targets for Egr-1.

Interleukin-4-induced transcriptional activation by Stat6 involves multiple serine/threonine kinase pathways and serine phosphorylation of Stat6

Stat6 transcription factor is a critical mediator of IL-4-specific gene responses. Tyrosine phosphorylation is required for nuclear localization and DNA binding of Stat6. The authors investigated whether Stat6-dependent transcriptional responses are regulated through IL-4-induced serine/threonine phosphorylation. In Ramos B cells, the serine/threonine kinase inhibitor H7 inhibited IL-4-induced expression of CD23. Treatment with H7 did not affect IL-4R-mediated immediate signaling events such as tyrosine phosphorylation of Jak1, Jak3, insulin receptor substrate (IRS)-1 and IRS-2, or tyrosine phosphorylation and DNA binding of Stat6. To analyze whether the H7-sensitive pathway was regulating Stat6-activated transcription, we used reporter constructs containing different IL-4 responsive elements. H7 abrogated Stat6-, as well as Stat5-, mediated reporter gene activation and partially reduced C/EBP-dependent reporter activity. By contrast, IL-4-induced transcription was not affected by wortmannin, an inhibitor of the phosphatidyl-inositol 3′-kinase pathway. Phospho-amino acid analysis and tryptic phosphopeptide maps revealed that IL-4 induced phosphorylation of Stat6 on serine and tyrosine residues in Ramos cells and in 32D cells lacking endogenous IRS proteins. However, H7 treatment did not inhibit the phosphorylation of Stat6. Instead, H7 inhibited the IL-4-induced phosphorylation of RNA polymerase II. These results indicate that Stat6-induced transcription is dependent on phosphorylation events mediated by H7-sensitive kinase(s) but that it also involves serine phosphorylation of Stat6 by an H7-insensitive kinase independent of the IRS pathway.