Bcl-xL blocks activation of related adhesion focal tyrosine kinase/proline-rich tyrosine kinase 2 and stress-activated protein kinase/c-Jun N-terminal protein kinase in the cellular response to methylmethane sulfonate

Focal Adhesion Genes Refine the Intermediate-Risk Cytogenetic Classification of Acute Myeloid Leukemia

In recent years, several attempts have been made to identify novel prognostic markers in patients with intermediate-risk acute myeloid leukemia (IR-AML), to implement risk-adapted strategies. The non-receptor tyrosine kinases are proteins involved in regulation of cell growth, adhesion, migration and apoptosis. They associate with metastatic dissemination in solid tumors and poor prognosis. However, their role in haematological malignancies has been scarcely studied. We hypothesized that PTK2/FAK, PTK2B/PYK2, LYN or SRC could be new prognostic markers in IR-AML. We assessed PTK2, PTK2B, LYN and SRC gene expression in a cohort of 324 patients, adults up to the age of 70, classified in the IR-AML cytogenetic group. Univariate and multivariate analyses showed that PTK2B, LYN and PTK2 gene expression are independent prognostic factors in IR-AML patients. PTK2B and LYN identify a patient subgroup with good prognosis within the cohort with non-favorable FLT3/NPM1 combined mutations. In contrast, PTK2 identifies a patient subgroup with poor prognosis within the worst prognosis cohort who display non-favorable FLT3/NPM1 combined mutations and underexpression of PTK2B or LYN. The combined use of these markers can refine the highly heterogeneous intermediate-risk subgroup of AML patients, and allow the development of risk-adapted post-remission chemotherapy protocols to improve their response to treatment.

Angiotensin II induces mitochondrial dysfunction and promotes apoptosis via JNK signalling pathway in primary mouse calvaria osteoblast

OBJECTIVES

This present study was designed to investigate the effects of Angiotensin II on mitochondrial functions, ROS generation and c-jun N-terminal kinases (JNK) signalling pathway-mediated cell apoptosis in mouse calvaria osteoblasts.

METHODS

Calvaria osteoblast were isolated and cultured. The cells were separated into two groups-control and treated groups-where the latter was stimulated with angiotensin II (Ang II). Mitochondrial reactive oxygen species (ROS) and superoxide production were measured. Intracellular ATP levels were also detected. The cell proliferation rate was determined for the two groups. Protein production such as Anti-Bax, Bcl-2, COX IV and activation of c-jun N-terminal kinases signal (JNK) pathway was measured by enzyme-linked immunosorbent assay (ELISA) methods and Western blotting in this study.

RESULTS

Ang II treated cells showed significantly higher levels of superoxide production compared to the control group (p<0.05). Conversely, Ang II induced inhibitory effects on mitochondrial respiratory enzyme complexes, cause membrane potential dissipation, ATP loss and promote ROS generation, cell apoptosis in cultured osteoblasts. In addition, JNK phosphorylations were involved in activating the mitochondria-dependent apoptotic pathway following Ang II stimulation, as pre-treatment of JNK-specific inhibitor SP600125 could rescue osteoblast cells from apoptosis by enhancing the anti-apoptotic protein Bcl-2 expressions, suppressing the translocation of Bax from cytosol into mitochondria, blocking cytochrome C release and caspase-3 activation.

CONCLUSIONS

Ang II stimulates osteoblast apoptosis via suppression of the mitochondrial respiratory enzymes, membrane potential and cellular ATP productions. Clinical application with Ang II-stimulated osteoblast could be used for modelling or bone resorption in the oral region.

AT-101, a small molecule inhibitor of anti-apoptotic Bcl-2 family members, activates the SAPK/JNK pathway and enhances radiation-induced apoptosis

Background

Gossypol, a naturally occurring polyphenolic compound has been identified as a small molecule inhibitor of anti-apoptotic Bcl-2 family proteins. It induces apoptosis in a wide range of tumor cell lines and enhances chemotherapy- and radiation-induced cytotoxicity both in vitro and in vivo. Bcl-2 and related proteins are important inhibitors of apoptosis and frequently overexpressed in human tumors. Increased levels of these proteins confer radio- and chemoresistance and may be associated with poor prognosis. Consequently, inhibition of the anti-apoptotic functions of Bcl-2 family members represents a promising strategy to overcome resistance to anticancer therapies.

Methods

We tested the effect of (-)-gossypol, also denominated as AT-101, radiation and the combination of both on apoptosis induction in human leukemic cells, Jurkat T and U937. Because activation of the SAPK/JNK pathway is important for apoptosis induction by many different stress stimuli, and Bcl-X_L is known to inhibit activation of SAPK/JNK, we also investigated the role of this signaling cascade in AT-101-induced apoptosis using a pharmacologic and genetic approach.

Results

AT-101 induced apoptosis in a time- and dose-dependent fashion, with ED₅₀ values of 1.9 and 2.4 μM in Jurkat T and U937 cells, respectively. Isobolographic analysis revealed a synergistic interaction between AT-101 and radiation, which also appeared to be sequence-dependent. Like radiation, AT-101 activated SAPK/JNK which was blocked by the kinase inhibitor SP600125. In cells overexpressing a dominant-negative mutant of c-Jun, AT-101-induced apoptosis was significantly reduced.

Conclusion

Our data show that AT-101 strongly enhances radiation-induced apoptosis in human leukemic cells and indicate a requirement for the SAPK/JNK pathway in AT-101-induced apoptosis. This type of apoptosis modulation may overcome treatment resistance and lead to the development of new effective combination therapies.

Prostate cancer antigen-1 contributes to cell survival and invasion though discoidin receptor 1 in human prostate cancer

A novel gene, prostate cancer antigen (PCA)-1, was recently reported to be expressed in the prostate; however, its biological roles remain unclear. Knockdown of the PCA-1 gene by small interfering RNA transfection induced apoptosis through reducing the expression of the anti-apoptotic molecule Bcl-xl and cytoplasmic release of cytochrome c in the androgen-independent prostate cancer cell line PC3. Moreover, in vitro matrigel and in vivo chorioallantoic membrane assays showed that silencing of PCA-1 significantly downregulated discoidin receptor (DDR)-1 expression, resulting in suppression of cancer-cell invasion. Transfection with PCA-1 increased the levels of both Bcl-xl and DDR1, which made the cells more invasive through the upregulation of matrix metalloproteinase 9 in DU145. Interestingly, long-term culture using androgen-free medium increased the level of PCA-1 and the related expression of Bcl-xl and DDR-1 in the androgen-sensitive cancer cell line LNCaP, suggesting that PCA-1 signaling is associated with androgen independence. Immunohistochemical analysis in a series of 169 prostate carcinomas showed that PCA-1 and DDR1 were strongly expressed in prostate cancer cells, including preneoplastic lesions, but there was little or no expression in normal epithelium. Moreover, the expression of PCA-1 and DDR-1 was associated with a hormone-independent state of prostate cancer. Taken together, we propose that PCA-1-DDR-1 signaling is a new important axis involved in malignant potential prostate cancer associated with hormone-refractory status.

Survival response-linked Pyk2 activation during potassium depletion-induced apoptosis of cerebellar granule neurons

Numerous extracellular stimuli trigger trans-autophosphorylation at Tyr402 of Pyk2, inducing its activation. Pyk2 is a key mediator of several signaling pathways and has been implicated in apoptosis induced by specific stress signals. We investigated whether Pyk2 participates in cerebellar granule neuron (CGN) apoptosis induced by the suppression of membrane depolarization. We demonstrate that shifting CGN cultures from 25 mM to 5 mM KCl-containing medium induces an early, transient 70% increase in phosphorylated Tyr402 and Tyr580 Pyk2 levels that is triggered by Ca(2+) released from intracellular stores and mediated by calmodulin (CaM). Overexpression of Pyk2 increases CGN survival after 24 h by 70% compared to the control, thus suggesting that Pyk2 is involved in an anti-apoptotic response to K+ lowering. Furthermore, we show that CGN grown in K25 medium exhibit detectable CaM-dependent Pyk2 activity. When silencing Pyk2 activity by expressing a dominant-negative form, only 40% of the transfected neurons were alive 24 h after transfection when compared to the control. Overall, the present findings demonstrate for the first time that Pyk2 is a critical mediator of CGN survival.

Expression of a mutant p193/CUL7 molecule confers resistance to MG132- and etoposide-induced apoptosis independent of p53 or Parc binding

p193/CUL7 is an E3 ubiquitin ligase initially identified as an SV40 Large T Antigen binding protein. Expression of a dominant interfering variant of mouse p193/CUL7 (designated 1152stop) conferred resistance to MG132- and etoposide-induced apoptosis in U2OS cells. Immune precipitation/Western analyses revealed that endogenous p193/CUL7 formed a complex with Parc (a recently identified parkin-like ubiquitin ligase) and p53. Apoptosis resistance did not result from 1152stop-mediated disruption of the endogenous p193/CUL7 binding partners. Moreover, 1152stop molecule did not directly bind to endogenous p193/CUL7, Parc or p53. These data suggested a role for p193/CUL7 in the regulation of apoptosis independently of p53 and Parc activity.

Reactive oxygen species mediate crosstalk between NF-κB and JNK

The activation of NF-kappaB inhibits apoptosis via a mechanism involving upregulation of various antiapoptotic genes, such as cellular FLICE-inhibitory protein (c-FLIP), Bcl-xL, A1/Bfl-1, and X chromosome-liked inhibitor of apoptosis (XIAP). In contrast, the activation of c-Jun N-terminal kinase (JNK) promotes apoptosis in a manner that is dependent on the cell type and the context of the stimulus. Recent studies have indicated that one of the antiapoptotic functions of NF-kappaB is to downregulate JNK activation. Further studies have also revealed that NF-kappaB inhibits JNK activation by suppressing accumulation of reactive oxygen species (ROS). In this review, we will focus on the signaling crosstalk between the NF-kappaB and JNK cascades via ROS.

Expression of focal adhesion kinase in acute myeloid leukemia is associated with enhanced blast migration, increased cellularity, and poor prognosis

Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase playing an important role in cell motility and survival. However, very little is known about FAK in normal and leukemic myeloid cells. In this study, FAK protein expression and mRNA were detected in 25 of 60 cases (42%) of acute myeloid leukemia (AML). Whereas FAK was expressed in 46% of CD34+ AML cells, it was not detected in normal purified CD34+ cells. Conversely, the FAK homologue proline-rich tyrosine kinase 2 (PYK2) was found to be expressed both in normal and leukemic myeloid cells. When expressed, FAK displayed phosphorylation on Tyr-397, an important step for its activation. Moreover, FAK expression was correlated with the phosphorylation of PYK2 on Tyr-881, a critical site for the PYK2 function in cell migration. FAK+ AML cells displayed significantly higher migration capacities and resistance to daunorubicin, compared with FAK- cells. The implication of FAK in both cell motility and drug resistance was demonstrated by small interfering RNA experiments with the FAK-positive KG1 cell line. However, adhesion on fibronectin efficiently protected FAK- AML cells from daunorubicin-mediated killing, suggesting that cellular adhesion mediated-drug resistance is not mediated by FAK. Finally, in a retrospective cohort of 60 AML patients, FAK expression was significantly correlated with high blast cell count, early death, and shorter survival rate. Altogether, this study shows that FAK is aberrantly expressed and activated in about half of the cases of AML and suggests that FAK may contribute to the regulation of AML cell transit from the marrow to blood compartment and that it may influence clinical outcome.

The production of nitric oxide in EL4 lymphoma cells overexpressing growth hormone

Growth hormone (GH) is produced by immunocompetent cells and has been implicated in the regulation of a multiplicity of functions in the immune system involved in growth and activation. However, the actions of endogenous or lymphocyte GH and its contribution to immune reactivity when compared with those of serum or exogenous GH are still unclear. In the present study, we overexpressed lymphocyte GH in EL4 lymphoma cells, which lack the GH receptor (GHR), to determine the role of endogenous GH in nitric oxide (NO) production and response to genotoxic stress. Western blot analysis demonstrated that the levels of GH increased approximately 40% in cells overexpressing GH (GHo) when compared with cells with vector alone. The results also show a substantial increase in NO production in cells overexpressing GH that could be blocked by N(G)-monomethyl-L-arginine (L-NMMA), an L-arginine analogue that competitively inhibits all three isoforms of nitric oxide synthase (NOS). No evidence was obtained to support an increase in peroxynitrite in cells overexpressing GH. Overexpression of GH increased NOS activity, inducible nitric oxide synthase (iNOS) promoter activity, and iNOS protein expression, whereas endothelial nitric oxide synthase and neuronal nitric oxide synthase protein levels were essentially unchanged. In addition, cells overexpressing GH showed increased arginine transport ability and intracellular arginase activity when compared with control cells. GH overexpression appeared to protect cells from the toxic effects of the DNA alkylating agent methyl methanesulfonate. This possibility was suggested by maintenance of the mitochondrial transmembrane potential in cells overexpressing GH when compared with control cells that could be blocked by L-NMMA. Taken together, the data support the notion that lymphocyte GH, independently of the GH receptor, may play a key role in the survival of lymphocytes exposed to stressful stimuli via the production of NO.

The role of Aktand RAFTK in beta1 integrin mediated survival of precursor B-acute lymphoblastic leukemia cells

In this study, we report that the related adhesion focal tyrosine kinase RAFTK, is an upstream kinase in beta1 integrin mediated activation of Akt. Stimulation through beta1 integrins by fibronectin reversed apoptosis induced by adriamycin. Inhibitors of phosphatidylinositol 3-kinase (PI3 kinase)/Akt (LY 294002), tyrosine kinases (Herbimycin-A) and the cytotoxic agent adriamycin induced apoptosis of REH cells. beta1 integrin ligation induced activation of Akt, and tyrosine phosphorylation of RAFTK and FAK, but not SYK in REH cells. This suggested that RAFTK and FAK activation might be linked to Akt activation. Evidence that RAFTK is a modulator of Akt came from phorbol myristic acetate (PMA) stimulation. RAFTK and Akt were activated but FAK was not. Using fibroblasts from FAK -/- mice, which express high levels of RAFTK, fibronectin plating enhanced Akt activation. Pretreatment of REH cells with a P13 kinase/Akt inhibitor LY 294002 did not inhibit RAFTK tyrosine phosphorylation showing that RAFTK is upstream of P13k/Akt. Further evidence for a link between RAFTK tyrosine phosphorylation and Akt activation was the observation that the p85 subunit of P13 kinase associated with RAFTK following integrin ligation in REH cells. These results suggest that RAFTK plays an anti-apoptotic role through the activation of Akt.

Protein-tyrosine kinase Pyk2 mediates endothelin-induced p38 MAPK activation in glomerular mesangial cells

Endothelin-1 (ET-1), a member of a family of 21 amino acid peptides possessing vasoconstrictor properties, is known to stimulate mesangial cell proliferation. In this study, ET-1 (100 nm) induced a rapid activation of p21(ras) in human glomerular mesangial cells (HMC). Inhibition of Src family tyrosine kinase activation with [4-Amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] or chelation of intracellular free calcium with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester significantly decreased ET-1dependent p21(ras) activation and suggested the involvement of the cytoplasmic proline-rich tyrosine kinase Pyk2. We have observed that Pyk2 was expressed in HMC and was tyrosine-phosphorylated within 5 min of ET-1 treatment. ET-1-induced activation of Pyk2 was further confirmed using phospho-specific anti-Pyk2 antibodies. Surprisingly, Src kinase activity was required upstream of ET-1-induced autophosphorylation of Pyk2. To determine whether Pyk2 autophosphorylation mediated ET-1-dependent p21(ras) activation, adenovirus-mediated transfer was employed to express a dominant-negative form of Pyk2 (CRNK). CRNK expression inhibited ET-1-induced endogenous Pyk2 autophosphorylation, but did not abolish ET-1-mediated increases in GTP-bound p21(ras) levels. ET-1-induced activation of the p38 MAPK (but not ERK) pathway was inhibited in HMC and in rat glomerular mesangial cells expressing the dominant-negative form of Pyk2. These findings suggest that the engagement of Pyk2 is important for ET-1-mediated p38 MAPK activation and hence the biological effect of this peptide in mesangial cells.

Coexpression of Mutant p53 and p193 Renders Embryonic Stem Cell–Derived Cardiomyocytes Responsive to the Growth-Promoting Activities of Adenoviral E1A

Abstract —Expression of adenoviral E1A in cardiomyocytes results in the activation of DNA synthesis followed by apoptosis. In contrast, expression of simian virus 40 large T antigen induces sustained cardiomyocyte proliferation. Previous studies have shown that T antigen binds to 2 proapoptotic proteins in cardiomyocytes, namely the p53 tumor suppressor and p193 (a new member of the BH3-only proapoptosis subfamily). Structure-function analyses identified a p193 C-terminal truncation mutant that encodes prosurvival activity. This mutant was used to test the role of p193 in E1A-induced cardiomyocyte apoptosis. E1A induced apoptosis in cardiomyocytes derived from differentiating embryonic stem cells. Expression of the prosurvival p193 mutant alone or a mutant p53 alone did not block E1A-induced apoptosis. In contrast, combinatorial expression of mutant p193 and mutant p53 blocked E1A-induced apoptosis, resulting in a proliferative response indistinguishable from that seen with T antigen. These results confirm the hypothesis that there are 2 proapoptotic pathways, encoded by p53 and p193, respectively, which restrict cardiomyocyte cell cycle activity in differentiating embryonic stem cell cultures. Furthermore, these results explain in molecular terms the phenotypic differences of E1A versus T-antigen gene transfer in cardiomyocytes.

Insulin-like growth factor-I and Bcl-X(L) inhibit c-jun N-terminal kinase activation and rescue Schwann cells from apoptosis

We previously reported that Schwann cells undergo apoptosis after serum withdrawal. Insulin-like growth factor-I, via phosphatidylinositol-3 kinase, inhibits caspase activation and rescues Schwann cells from serum withdrawal-induced apoptosis. In this study, we examined the role of c-jun N-terminal protein kinase (JNK) in Schwann cell apoptosis induced by serum withdrawal. Activation of both JNK1 and JNK2 was detected 1 h after serum withdrawal with the maximal level detected at 2 h. A dominant negative JNK mutant, JNK (APF), blocked JNK activation induced by serum withdrawal and Schwann cell apoptosis, suggesting JNK activation participates in Schwann cell apoptosis. Serum withdrawal-induced JNK activity was caspase dependent and inhibited by a caspase 3 inhibitor, Ac-DEVD-CHO. Because insulin-like growth factor-I and Bcl-X(L) are both Schwann cell survival factors, we tested their effects on JNK activation during apoptosis. Insulin-like growth factor-I treatment decreased both JNK1 and JNK2 activity induced by serum withdrawal. LY294002, a phosphatidylinositol-3 kinase inhibitor, blocked insulin-like growth factor-I inhibition on JNK activation, suggesting that phosphatidylinositol-3 kinase mediates the effects of insulin-like growth factor-I. Overexpression of Bcl-X(L) also resulted in less Schwann cell death and inhibition of JNK activation after serum withdrawal. Collectively, these results suggest JNK activation is involved in Schwann cell apoptosis induced by serum withdrawal. Insulin-like growth factor-I and Bcl family proteins rescue Schwann cells, at least in part, by inhibition of JNK activity.

Variations of proline-rich kinase Pyk2 expression correlate with prostate cancer progression

Proline-rich kinase 2 (Pyk2), also known as CAKbeta (cell adhesion kinase beta), is a cytoplasmic tyrosine kinase that is structurally related to focal adhesion kinase. Pyk2 is expressed in different cell types including brain cells, fibroblasts, platelets, and other hemopoietic cells. Pyk2 is rapidly tyrosine phosphorylated in response to diverse extracellular signals acting via different post receptor pathways. We have investigated whether this protein kinase is functionally expressed in normal and neoplastic prostate tissues. In this study, we demonstrate that Pyk2 is expressed only in normal epithelial prostate tissue and in benign prostatic hyperplasia, whereas its expression progressively declines with an increasing grade of malignancy of prostate cancer.

Inhibition of LPS-induced cytokines by Bcl-xL in a murine macrophage cell line

The antiapoptotic molecule Bcl-xL has been implicated in the differentiation and survival of activated macrophages in inflammatory conditions. In this report, the role of Bcl-xL in LPS-induced cytokine gene expression and secretion was studied. Bcl-xL-transfected RAW 264 macrophages were protected from gliotoxin-induced apoptosis, indicating the presence of functional Bcl-xL. Overexpression of Bcl-xL in this macrophage cell line was also associated with a marked inhibition of LPS-induced TNF-alpha, JE/monocyte chemoattractant protein 1, and macrophage inflammatory protein 2 secretion. Inhibition of LPS-induced cytokine secretion was paralleled by a decrease in levels of steady-state mRNA for the above cytokines and for IL-1beta. Decreased production of TNF-alpha in Bcl-xL transfectants was not due to increased mRNA degradation, as the mRNA half-lives were the same in Bcl-xL transfectants and control macrophages. Although the composition of NF-kappaB complexes detected by EMSA and supershift analysis in nuclear lysates derived from Bcl-xL transfectants and control cells was indistinguishable, LPS-induced inhibitory kappaBalpha degradation, as well as NF-kappaB binding and AP-1 activation, were slightly decreased by ectopic expression of Bcl-xL. More strikingly, LPS-induced phosphorylation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase was strongly repressed by Bcl-xL overexpression, offering a possible mechanism for the inhibition of LPS-induced cytokine production. These data provide the first evidence for a novel role for Bcl-xL as an anti-inflammatory mediator in macrophages.

Activation of MEK kinase 1 by the c-Abl protein tyrosine kinase in response to DNA damage

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents and regulates induction of the stress-activated c-Jun N-terminal protein kinase (SAPK). Here we show that nuclear c-Abl associates with MEK kinase 1 (MEKK-1), an upstream effector of the SEK1-->SAPK pathway, in the response of cells to genotoxic stress. The results demonstrate that the nuclear c-Abl binds to MEKK-1 and that c-Abl phosphorylates MEKK-1 in vitro and in vivo. Transient-transfection studies with wild-type and kinase-inactive c-Abl demonstrate c-Abl kinase-dependent activation of MEKK-1. Moreover, c-Abl activates MEKK-1 in vitro and in response to DNA damage. The results also demonstrate that c-Abl induces MEKK-1-mediated phosphorylation and activation of SEK1-SAPK in coupled kinase assays. These findings indicate that c-Abl functions upstream of MEKK-1-dependent activation of SAPK in the response to genotoxic stress.

RAFTK/PYK2-dependent and -independent apoptosis in multiple myeloma cells

Related Adhesion Focal Tyrosine Kinase (RAFTK; also known as Pyk2), is a member of the Focal Adhesion Kinase (FAK) subfamily and is activated by TNF alpha, UV light and increases in intracellular calcium levels. However, the function of RAFTK remains largely unknown. Our previous studies demonstrated that treatment with dexamethasone (Dex), ionizing radiation (IR), and anti-Fas mAb induces apoptosis in multiple myeloma (MM) cells. In the present study, we examined the potential role of RAFTK during induction of apoptosis in human MM cells triggered by these three stimuli. Dex-induced apoptosis, in contrast to apoptosis triggered by anti-Fas mAb or IR, is associated with activation of RAFTK. Transient overexpression of RAFTK wild type (RAFTK WT) induces apoptosis, whereas transient overexpression of Kinase inactive RAFTK (RAFTK K-M) blocks Dex-induced apoptosis. In contrast, transient overexpression of RAFTK K-M has no effect on apoptosis triggered by IR or Fas. In Dex-resistant cells, Dex does not trigger either RAFTK activation or apoptosis. Finally, interleukin-6 (IL-6), a known survival factor for MM cells, inhibits both activation of RAFTK and apoptosis of MM.1S cells triggered by Dex. Our studies therefore demonstrate Dex-induced RAFTK-dependent, and IR or Fas induced RAFTK-independent apoptotic signaling cascades in MM cells.

Negative regulation of PYK2/related adhesion focal tyrosine kinase signal transduction by hematopoietic tyrosine phosphatase SHPTP1

Related adhesion focal tyrosine kinase (RAFTK) (also known as PYK2) is a cytoplasmic tyrosine kinase related to the focal adhesion kinase (FAK) p125(FAK). RAFTK is rapidly phosphorylated on tyrosine residues in response to various stimuli, such as tumor necrosis factor-alpha, changes in osmolarity, elevation in intracellular calcium concentration, lysophosphatidic acid, and bradykinin. Overexpression of RAFTK induces activation of c-Jun amino-terminal kinase (also known as stress-activated protein kinase), mitogen-activated protein kinase (MAPK), and p38 MAPK. The present studies demonstrate that RAFTK binds constitutively to the protein tyrosine phosphatase SHPTP1. In contrast to PTP1B, overexpression of wild-type SHPTP1 blocks tyrosine phosphorylation of RAFTK. The results further demonstrate that RAFTK is a direct substrate of SHPTP1 in vitro. Moreover, treatment of PC12 cells with bradykinin is associated with inhibition in tyrosine phosphorylation of RAFTK in the presence of SHPTP1. Furthermore, in contrast to the phosphatase-dead SHPTP1 C453S mutant, overexpression of wild-type SHPTP1 blocks interaction of RAFTK with the SH2-domain of c-Src and inhibits RAFTK-mediated MAPK activation. Significantly, cotransfection of RAFTK with SHPTP1 did not inhibit RAFTK-mediated c-Jun amino-terminal kinase activation. Taken together, these findings suggest that SHPTP1 plays a negative role in PYK2/RAFTK signaling by dephosphorylating RAFTK.

Effect of ethanol on tumor necrosis factor signaling during liver regeneration

OBJECTIVES

The liver has tremendous regenerative capacity but can be damaged by toxins, such as ethanol (EtOH). It has long been known that EtOH inhibits liver regeneration. Recent work demonstrates that the proinflammatory cytokine, tumor necrosis factor ( (TNF), is required for normal liver regeneration, as well as for EtOH-related liver damage. Therefore, it is conceivable that EtOH promotes liver damage by altering TNF signal transduction in such a way that proliferative signals are aborted and death signals predominate.

DESIGN AND METHODS

Anti-TNF antibodies were used to characterize the TNF signals that are induced in the regenerating liver after two-thirds (partial) hepatectomy (PH) in normal mice and rats. Then, these TNF-regulated processes were evaluated in animals that had been fed nutritionally replete, EtOH-containing diets for several weeks before PH.

RESULTS

During normal liver regeneration, TNF induces potentially dangerous responses, such as increased mitochondrial ROS production, but also promotes the activation of several factors, including NF kappa B, Jun N-terminal Kinase (JNK), and various mitochondrial membrane proteins, which are likely to permit hepatocytes to survive apoptotic and oxidant stress. Previous EtOH exposure inhibits the normal regenerative induction of NF kappa B and JNK.

CONCLUSIONS

These finding are consistent with the possibility that potential hepatotoxins compromise the balanced induction of toxic and trophic signals by TNF.