Mortality following surgery for trauma in an Indian trauma cohort

Background

India accounts for 20 per cent of worldwide trauma mortality. Little is known about the quality of trauma surgery in an Indian setting. The aim of this study was to estimate the overall perioperative mortality rate, and to assess the association between type of acute surgical intervention and perioperative mortality among adult patients treated for trauma in an urban Indian setting.

Methods

Data were obtained from injured adult patients enrolled in four urban Indian hospitals during 2013–2015. Those who had surgery within 24 h of arrival at hospital were included in the analysis. Patients with missing data were excluded. The perioperative mortality rate was measured at 48 h and 30 days after arrival at hospital. Generalized linear mixed models were used for risk adjustment of procedure-specific mortality.

Results

Among 2986 patients who underwent trauma surgery, the overall 48-h mortality rate was 6·0 per cent, and the 30-day mortality rate was 23·1 per cent. The highest adjusted odds ratios (ORs) for 48-h mortality were found for patients who underwent surgery on the peripheral vasculature (OR 4·71, 95 per cent c.i. 1·18 to 16·59; P = 0·030) and the digestive system and spleen (OR 3·77, 1·33 to 9·01; P = 0·010) compared with those who had nervous system surgery.

Conclusion

In this study of surgery in an Indian trauma cohort, there was an excess of late perioperative deaths. Mortality differed significantly according to the type of surgery being undertaken.

The impact of T-cell depletion techniques on the outcome after haploidentical hematopoietic SCT

Several T-cell depletion (TCD) techniques are used for haploidentical hematopoietic SCT (HSCT), but direct comparisons are rare. We therefore studied the effect of in vitro TCD with graft engineering (CD34 selection or CD3/CD19 depletion, 74%) or in vivo TCD using alemtuzumab (26%) on outcome, immune reconstitution and infections after haploidentical HSCT. We performed a retrospective multicenter analysis of 72 haploidentical HSCT in Switzerland. Sixty-seven patients (93%) had neutrophil engraftment. The 1-year OS, TRM and relapse incidence were 48 (36-60)%, 20 (11-33)% and 42 (31-57)%, respectively, without differences among the TCD groups. In vivo TCD caused more profound lymphocyte suppression early after HSCT, whereas immune recovery beyond the second month was comparable between the two groups. Despite anti-infective prophylaxis, most patients experienced post-transplant infectious complications (94%). Patients with in vivo TCD had a higher incidence of CMV reactivations (54% vs 28%, P=0.015), but this did not result in a higher TRM. In conclusion, TCD by graft engineering or alemtuzumab are equally effective for haploidentical HSCT.

Signed outside: a surface marker system for transgenic cytoplasmic proteins

Chronic granulomatous disease is a primary immunodeficiency, comprising five molecular defects, characterized by an impaired respiratory burst activity of myeloid cells. We are currently developing a gene therapy vector for the p47phox-deficient form of chronic granulomatous disease. Classic intracellular immunostaining of the cytoplasmic p47phox transgene product, however, interferes with respiratory burst activity. In this study we report a new system for measuring p47phox expression: A single open reading frame encoding the surface marker protein ΔLNGFR (truncated low-affinity nerve growth factor receptor) linked to the p47phox transgene by the 2A oligopeptide coexpression technology. Translation generates two discrete products: p47phox localizing to the cytoplasm and 'ΔLNGFR-2A' localizing to the cell surface. Six weeks after transplantation of transduced autologous hematopoietic stem cells into p47-/- mice, the intracellular p47phox fluorescence-activated cell sorting (FACS) signal intensities corresponded to surface ΔLNGFR staining in monocytes, B cells, T cells and Sca I+ bone marrow cells in vivo. The p47phox cleavage product restored nicotinamide adenine dinucleotide phosphate-oxidase activity in granulocytes differentiated from transduced p47phox-/- murine hematopoietic stem cells ex vivo, in murine granulocytes/monocytes in vivo, and in transduced human monocyte derived macrophages from p47phox-deficient chronic granulomatous disease patients. In conclusion, this new marker system allows highly efficient, indirect detection of cytoplasmic transgene products by FACS surface staining.

Persistent low thymic activity and non-cardiac mortality in children with chromosome 22q11.2 microdeletion and partial DiGeorge syndrome

A subgroup of patients with 22q11.2 microdeletion and partial DiGeorge syndrome (pDGS) appears to be susceptible to non-cardiac mortality (NCM) despite sufficient overall CD4(+) T cells. To detect these patients, 20 newborns with 22q11.2 microdeletion and congenital heart disease were followed prospectively for 6 years. Besides detailed clinical assessment, longitudinal monitoring of naive CD4(+) and cytotoxic CD3(+)CD8(+) T cells (CTL) was performed. To monitor thymic activity, we analysed naive platelet endothelial cell adhesion molecule-1 (CD31(+)) expressing CD45RA(+)RO(-)CD4(+) cells containing high numbers of T cell receptor excision circle (T(REC))-bearing lymphocytes and compared them with normal values of healthy children (n = 75). Comparing two age periods, low overall CD4(+) and naive CD4(+) T cell numbers were observed in 65%/75%, respectively, of patients in period A (< 1 year) declining to 22%/50%, respectively, of patients in period B (> 1/< 7 years). The percentage of patients with low CTLs (< P10) remained robust until school age (period A: 60%; period B: 50%). Low numbers of CTLs were associated with abnormally low naive CD45RA(+)RO(-)CD4(+) T cells. A high-risk (HR) group (n = 11) and a standard-risk (SR) (n = 9) group were identified. HR patients were characterized by low numbers of both naive CD4(+) and CTLs and were prone to lethal infectious and lymphoproliferative complications (NCM: four of 11; cardiac mortality: one of 11) while SR patients were not (NCM: none of nine; cardiac mortality: two of nine). Naive CD31(+)CD45RA(+)RO(-)CD4(+), naive CD45RA(+)RO(-)CD4(+) T cells as well as T(RECs)/10(6) mononuclear cells were abnormally low in HR and normal in SR patients. Longitudinal monitoring of naive CD4(+) and cytotoxic T cells may help to discriminate pDGS patients at increased risk for NCM.

Immunological detection of phosphorylation

Incorporation of phosphates into serine, threonine, and tyrosine acceptors in proteins is a common mechanism for regulating protein function. This unit presents protocols that use specific anti-phosphoamino acid (PAA) and anti-phosphoprotein antibodies to detect protein phosphorylation and protein kinase activity. Immunoblotting to detect protein phosphorylation using either anti-PAA or anti-phosphoprotein antibodies. This is a convenient method that usually yields impressive results. Phosphorylation can also be detected by immunoprecipitation followed by immunoblot analysis or by immunofluorescent staining; these methods are typically more complicated and time consuming. All three methods have been successfully used to detect protein phosphorylation with a wide variety of antibodies and most phosphorylated proteins.

Progress and prospects: gene therapy clinical trials (part 1)

Over the last two decades gene therapy has moved from preclinical to clinical studies for many diseases ranging from single gene disorders such as cystic fibrosis and Duchenne muscular dystrophy, to more complex diseases such as cancer and cardiovascular disorders. Gene therapy for severe combined immunodeficiency (SCID) is the most significant success story to date, but progress in many other areas has been significant. We asked 20 leaders in the field succinctly to summarize and comment on clinical gene therapy research in their respective areas of expertise and these are published in two parts in the Progress and Prospect series.

Growth factor-stimulated phosphorylation cascades: activation of growth factor-stimulated MAP kinase

Protein phosphorylation is an important mechanism in the response of cells to growth factors by which signals can be conveyed from cell surface receptors to intracellular targets. In addition to stimulation of protein tyrosine phosphorylation, activation of growth factor receptors having protein tyrosine kinase activity leads to dramatic alterations in the levels of protein serine/threonine phosphorylation. Several growth factor-stimulated serine/threonine-specific kinases have been identified as potential mediators of such signalling. MAP (microtubule-associated protein) kinase has emerged as a very interesting member of this group, because it activates a separate kinase, pp90rsk, which is also growth factor-stimulated. MAP kinase itself appears to be regulated by protein phosphorylation, because it can be inactivated by protein phosphatases. We have identified two 60 kDa proteins that promote the phosphorylation and full activation of MAP kinase in a manner paralleling its activation by growth factors in intact cells. These 'MAP kinase activators' are themselves stimulated by growth factors, suggesting that they function as intermediates between the MAP kinase and cell surface receptors in a growth factor-stimulated kinase cascade. Identification of the components of this protein kinase cascade reveals a mechanism by which at least some of the effects of receptor tyrosine kinases can be mediated through serine/threonine phosphorylation.

The probability of identifying a 10/10 HLA allele-matched unrelated donor is highly predictable

Identification of an unrelated HLA allele-matched hematopoietic stem cell (HSC) donor is a costly and time-consuming procedure. To improve search logistics, we have limited the search period to 6 months and have introduced a probability estimate of the chances of identifying a 10/10 HLA allele-matched donor. Probabilities were classified as high (>95%), intermediate (50%) and low (<5% chance) based on allele and haplotype frequencies. By analyzing 350 consecutive searches between 2002 and 2005 (1719 donors tested), the probability estimates turned out to be correct for 96% (high), 88% (low) and 56% (intermediate) patients. For searches with a high probability of success, at least one of the 10 most frequent haplotypes in Caucasoids was found in 69% of the patients, but in only 11% of the patients with a low-probability estimate (P<0.00001). Survival probability at 3 years was significantly higher for HSCT patients classified with a high-probability estimate when compared to patients in the intermediate/low-probability groups (74 vs 51 and 54% respectively, P=0.01). The same difference in survival probabilities was observed when only 10/10 matched unrelated HSCT patients were analyzed. In the intermediate-/low-probability groups, patients with alternative (haploidentical, autologous) or mismatched unrelated donors had similar survival estimates. Probability prediction is therefore feasible in the search process for unrelated donors and can guide the therapeutic strategy.

Activation of the AMPK regulated metabolic stress response by a small molecule HER2/EGFR tyrosine kinase inhibitor protects cardiac myocytes from apoptotic stimuli

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Background: The HER2 receptor tyrosine kinase is a survival factor for human cardiomyocytes, providing a potential explanation for the increased incidence of cardiomyopathy associated with anti-HER2 monoclonal antibody trastuzumab. Here we show that GW2974, a HER2/EGFR TKI, but not trastuzumab activates AMP kinase (AMPK), initiating a metabolic stress response in human cardiomyocytes that protects against TNFa induced cell death. GW2974 stimulates calcium dependent fatty acid oxidation in vitro resulting in upregulation of ATP and in myocardium of GW2974 treated rodents. Methods: Western blot: p-Akt, p-Erk1/2, p-AMPKa and p- eEF2 (Cell Signaling); ERRa, ERR? (R&D Systems); PGC-1 (Chemicon); MCAD (Cayman Chemicals); Heregulin, NF?B, and Actin (Sigma). ATP was performed utilizing a bioluminescence assay kit H52 (Roche). Lipid staining was done with Oil Red O (Sigma). Cells: Au565 breast cancer and primary human cardiomyocytes (HMC) were grown in RPMI supplemented with 15% BFS treatments. BAPTA/AM and Compound C (Calbiochem); GW2974 and TNFa (Sigma); trastuzumab (Genentech). Results: Our results show that treatment with GW2974 activates catabolic pathways by activation of AMPK. AMPK is a key regulator in mitochondrial energy producing pathways in human cardiac cells. Phosphorylation of AMPK resulted in phosphorylation of eEF2, upregulation of ERRa and PGC-1 and upregulation of ATP levels. AMPK activation depends on Ca++ as the calcium chelation abolished it. Trastuzumab and Gleevec failed to activate AMPK survival pathways. In addition, GW2974 protected cardiac cells from TNFa killing, whereas treatment with TNFa and trastuzumab resulted in pervasive cellular death. Inhibition of AMPK by Compound C or siRNA resulted in cardiomyocyte killing. Conclusion: Activation of AMPK and its effects on metabolic pathways and energy production in HMC may explain the apparent reduced risk of cardiotoxicity associated with HER2 TKI compared with trastuzumab in treating patients with HER2 overexpressing breast cancers. Although activation of AMPK protected normal cardiac myocytes, this effect appears to be lethal to sensitive HER2 overexpressing breast cancer cells, which are “addicted” to glycolysis.

No significant financial relationships to disclose.

Posaconazole for treatment of refractory invasive fungal disease

Invasive fungal infections are usually associated with immunocompromised states About 40-60% of these patients are refractory to standard antifungal therapy We describe the effect of posaconazole in the treatment of a 12 years-old girl with uncontrolled diabetes mellitus with life-threatening cerebral mucor mycosis and a 4 year old girl boy with chronic granulomatous disease presenting with invasive Aspergillus nidulans infection.

PGE2 up-regulates EGF-like growth factor biosynthesis in human granulosa cells: new insights into the coordination between PGE2 and LH in ovulation

LH and prostaglandin E(2) (PGE(2)) share many similar effects on the pre-ovulatory follicle. They can induce independently cumulus expansion, the resumption of meiosis and progesterone production. However, cyclooxygenase-2 (COX-2) inhibitors were found to hinder most of the LH-induced effects. Recently, EGF-like growth factors amphiregulin (Ar) and epiregulin (Ep) were found to be produced in response to LH stimulation and to induce cumulus expansion and oocyte maturation. We aimed at evaluating whether PGE(2) induces Ar and Ep syntheses in human granulosa cells and whether the inhibition of PGE(2) production by selective COX-2 inhibitor, nimesulide, affects LH-induced Ar and Ep biosynthesis. Ar and Ep mRNA levels increased following PGE(2) stimulation, in a dose- and time-dependent manner, which resembled those of LH. The blockade of protein kinase A (PKA) (by H89) and mitogen-activated protein kinase (MAPK) (by UO126) reduced the expression of PGE(2)-induced Ar and Ep biosynthesis. Although the stimulation of the cells with LH in the presence of nimesulide did not change the progesterone levels, it resulted in a significant reduction of Ar and Ep biosynthesis. In conclusion, PGE(2) may mimic LH action, at least in part, by the induction of Ar and Ep biosynthesis, which involves cAMP/PKA and MAPK pathways. The negative effect of nimesulide on the ovulatory process may be due to the reduction of Ar and Ep biosynthesis, which implies a possible collaborative role between PGE(2) and LH on their induction.

Impact of high-resolution matching in allogeneic unrelated donor stem cell transplantation in Switzerland

It is currently unknown what degree of human leukocyte antigen (HLA)-mismatching is acceptable in unrelated donor hematopoietic stem cell transplantation (UD-HSCT). Mismatches at some loci may be more permissive than others. We have analyzed the effect of high-resolution HLA-matching on outcome of all 214 consecutive recipients of UD-HSCT carried out in Switzerland. All typing was by the Swiss reference laboratory. Donor-recipient pairs were HLA-10/10 matched (n=130) or mismatched for either HLA-A/-B/-DRB1/multiple loci (n=33; (HLA-A/-B=10); (-DRB1=8); (multiple=15)); HLA-C (n=29) or HLA-DQ/-DRB3 (n=22; (DQ=16); (-DRB1=6)). The median follow-up was 32 months. Survival probabilities (+/-95% confidence interval) at 3 years were 57 (+/-10)% for recipients of HLA 10/10-matched transplants, 53 (+/-22)% for recipients of HLA-DQ/-DRB3-mismatched transplants, 44 (+/-20)% for recipients of HLA-C-mismatched transplants and 0% for recipients of transplants mismatched at HLA-A/-B/-DRB1/multiple loci (P<0.0001). In multivariate analyses, HLA compatibility was the variable most significantly associated with survival and treatment-related mortality. We found important differences in survival in recipients of UD-HSCT with best results for transplants from 10/10 matched donors. Single mismatches at HLA-DQ/-DRB3 were well tolerated, mismatches at HLA-C had intermediate results and mismatches at HLA-A/-B/-DRB1/multiple loci resulted in poor survival.

Infectious inflammation of the CNS involves activation of mitogen-activated protein kinase and AKT proteins in CSF in humans

The mitogen-activated protein kinases (MAPKs) and the AKT are interacting proteins that serve as transmitters of numerous extracellular signals to their intracellular targets, thereby regulating many cellular processes, such as proliferation, differentiation, development or stress responses. Whereas a large amount of information about the MAPKs/AKT participation in biological processes is available, less is known about their role in human diseases. We postulated that the MAPKs/AKT could be involved in inflammatory processes of the central nervous system (CNS) in humans and we investigated the CSF of 12 patients with viral infection of the CNS for the presence of the distinct components of these cascades. The cerebrospinal fluid (CSF) of 18 individuals who underwent a lumbar puncture for diagnostic purposes served as controls. Six patients with inflammatory disease of the CNS revealed the presence of activated ERK. In five patients p38MAPK was detected, in three in its activated form. The activity of AKT could be demonstrated in four patients. JNK was not found. None of the control patients showed the presence of MAPK enzymes. The mean CSF cellularity was higher in MAPK-positive than in MAPKnegative patients. There was no difference in mean age or gender between the patients and controls, or between the MAPK- and AKT-positive or -negative patients. Our work demonstrates that the MAPK and AKT cascades might participate in inflammatory processes of the CNS. As selective inhibitors of the MAPKs are available, their application in the future might reduce an inappropriate inflammatory response and thus limit brain damage in severe cases of meningoencephalitis.

The PI3K inhibitor LY294002 prevents p53 induction by DNA damage and attenuates chemotherapy-induced apoptosis

The p53 tumor suppressor plays a key role in the natural protection against cancer. Activation of p53 by DNA-damaging agents can contribute to successful elimination of cancer cells via chemotherapy-induced apoptosis. The phosphatidylinositol-3 kinase (PI3K) pathway, triggered in normal cells upon exposure to growth factors, regulates a cascade of proliferation and survival signals. The PI3K pathway is abnormally active in many cancers, thus making it an attractive target for inactivation in an attempt to achieve better cancer therapy. We report here that exposure to LY294002, a potent PI3K inhibitor, aborts the activation of p53 by several drugs commonly used in cancer chemotherapy. Concomitantly, LY294002 attenuates p53-dependent, chemotherapy-induced apoptosis of cancer cells. These findings invoke an unexpected positive role for PI3K in p53 activation by anticancer agents, and suggest that the efficacy of PI3K inhibitors in cancer therapy may be greatly affected by the tumor p53 status.

Analysis of signal transduction stimulated by gonadotropins in granulosa cells

Gonadotropins exert their effect on ovarian follicular cells through the activation of the hormone sensitive adenylate cyclase and consequent elevation of intracellular cyclic AMP (cAMP). Desensitization to the hormone in cultured primary granulosa cells can occur within a short period and internalization of the hormone-receptor complex has been observed both in vivo and in vitro. It was recently documented that the gonadotropins as well as cAMP activate MAP kinase (MAPK) in granulosa cells. Moreover we discovered that specific inhibitors of extracellular signal-regulated kinase phosphorylation, 1 and 2, augment steroidogenesis in granulosa cells up-regulating steroidogenic acute regulatory (StAR) protein expression, and that this modulation is blocked by specific inhibitors of protein kinase A. It is therefore suggested that gonadotropins may activate both stimulatory and inhibitory pathways which regulate steroidogenesis. Moreover the ratio between the activity of these two pathways may determine the rate of steroidogenesis, and rapid activation of MAPK may account as part of the mechanism of desensitization to the hormonal action. Steroidogenic factor-1 and DAX-1 may be involved in the regulation of the MAPK-dependent attenuation of steroidogenesis, since they exhibit sites that could be potentially phosphorylated by the MAPK cascade.

A phase II trial of liposomal busulphan as an intravenous myeloablative agent prior to stem cell transplantation: 500 mg/m(2) as a optimal total dose for conditioning

We conducted a phase I/II trial, to evaluate the efficacy and safety of an intravenous liposomal formulation of busulphan (LBu) as a myeloablative agent for stem cell transplantation (SCT). The liposomal busulphan was administered as a 3 h infusion twice daily over 4 consecutive days. Six adults received 1.6-2 mg/kg/dose and 18 children received 1.8-3 mg/kg/dose. Pharmacokinetic parameters were studied after the first and the last dose of busulphan. No significant difference in clearance, AUC, elimination half-lives or distribution volume between the first and the last dose was found in either groups. A significantly (P < 0.005) higher clearance was observed in children after the first and the last dose (3.61 and 3.79 ml/min/kg, respectively) compared to adults (2.40 and 2.33 ml/min/kg, respectively). The elimination half-lives after the first and the last dose were significantly (P < 0.005) shorter in children (2.59 and 2.72 h, respectively) compared to adults (3.35 and 3.61 h, respectively). Clearance correlated significantly with age. However, no significant correlation with age was observed when clearance was adjusted to the body surface area. Two cases of VOD following a total dose of 24 mg/kg were observed. Six patients experienced mucositis. No other organ toxicity was observed. We conclude that intravenous liposomal busulphan pharmacokinetics is age dependent. A dosage schedule based on body surface area should be used especially in young children to reduce the age-dependent difference in kinetics. An intravenous liposomal dose of busulphan of 500 mg/m(2) is suggested to reach a similar systemic exposure and myeloablative effect in both children and adults. Moreover, the novel liposomal form of busulphan showed a favorable toxicity profile and seems safe as a part of the high-dose therapy prior to SCT.

Hyperglycemia reduces nitric oxide synthase and glycogen synthase activity in endothelial cells

Hyperglycemia is considered a primary cause of diabetic vascular complications. A hallmark of vascular disease is endothelial cell dysfunction characterized by diminished nitric-oxide (NO)-dependent phenomena such as vasodilation, angiogenesis, and vascular maintenance. This study was designed to investigate the effects of a high level of D-glucose on endothelial NO response, oxidative stress, and glucose metabolism. Bovine aortic endothelial cells (BAECs) were pretreated with a high concentration of glucose (HG) (22 mmol/L) for at least 2 weeks and compared with control cells exposed to 5 mmol/L glucose (NG). The effect of chronic hyperglycemia on endothelial NO-synthase (eNOS) activity and expression, glycogen synthase (GS) activity, extracellular-signal-regulated kinase (ERK 1,2), p38, Akt expression, and Cu/Zn superoxide-dismutse (SOD-1) activity and expression were determined. Western blot analysis showed that eNOS protein expression decreased in HG cells and was accompanied by diminished eNOS activity. The activity of GS was also significantly lower in the HG cells than in NG cells, 25.0+/-17.4 and 89+/-22.5 nmol UDP-glucose.mg protein(-1)x min(-1), respectively. Western blot analysis revealed a 40-60% decrease in ERK 1,2 and p38 protein levels, small modification of phosphorylated Akt expression, and a 30% increase in SOD-1 protein expression in HG cells. Although SOD expression was increased, no change was observed in SOD activity. These results support the findings that vascular dysfunction due to exposure to pathologically high D-glucose concentrations may be caused by impairment of the NO pathway and increased oxidative stress accompanied by altered glucose metabolism.

Non-regulated and stimulated mechanisms cooperate in the nuclear accumulation of MEK1

MEKs, which operate within the ERK cascade, shuttle into the nucleus, but are rapidly exported from this location, forming an apparent cytosolic distribution both before and after stimulation. Two different mechanisms have been proposed for the nuclear translocation of MEKs. One of them involves a constant and non-regulated shuttling of MEKs into the nucleus operating both before and after mitogenic stimulation. The other mechanism seems to require the activity of MEKs and is facilitated in response to mitogenic stimulation. Here we show that these two mechanisms may coexist in the same cells. We found that leptomycin B (LMB), a potent inhibitor of nuclear export, induces a nuclear accumulation of MEKs, and this was significantly facilitated by stimulation of LMB-treated cells with EGF, TPA and peroxovanadate. The EGF-stimulated, but not the LMB-induced translocation was attenuated by MEK inhibitors and by using inactive forms of MEK1. We also show that LMB slightly activates the ERK cascade, but this activity only partially induces the nuclear accumulation of MEKs in cells treated by LMB alone. Thus, MEKs translocate into the nucleus by a combination of non-regulated and stimulated processes that contribute to the nuclear translocation of MEKs either in resting cells or upon mitogenic stimulation.

Human Toll-like receptor 2 mediates induction of the antimicrobial peptide human beta-defensin 2 in response to bacterial lipoprotein

Recognition of pathogens by Drosophila Toll or human Toll-like receptors results in translocation of Dorsal or its human homologue NF-kappaB, respectively; in Drosophila, this is followed by the production of antimicrobial peptides serving as antimicrobial effector system of the innate immune response. We investigated whether human Toll-like receptors also mediate induction of the synthesis of antimicrobial peptides. We found that HEK293 cells transfected with Toll-like receptor 2, but not wild-type cells responded to stimulation with bacterial lipoprotein by production of human beta-defensin 2. Furthermore, the human lung epithelial cell line A549 was found to constitutively express Toll-like receptor 2 and to produce beta-defensin 2 in response to bacterial lipoprotein. This response was abrogated by blocking the signaling pathway activated through Toll-like receptors by transfecting the A549 cells with a dominant-negative form of IRAK-2. Thus, exposure of human cells to bacterial lipoprotein elicits production of the antimicrobial peptide beta-defensin 2 through Toll-like receptor 2.

Intracellular signaling pathways mediated by the gonadotropin-releasing hormone (GnRH) receptor

The hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator of the reproductive system, triggering the synthesis and release of LH and FSH in the pituitary. GnRH transmits its signal via two specific serpentine receptors that belong to the large group of G-protein coupled receptors (GPCRs). Here we review the intracellular signaling pathways mediated by the GnRH receptor (GnRHR). In pituitary-derived alpha T3-1 cells, a widely used model for GnRH action, GnRHR signaling includes activation of mitogen-activated protein kinase (MAPK) cascades, which provide an important link for the transmission of signals from the cell surface to the nucleus and play a role in the regulation of gonadotropin transcription. Activation of ERK--one of the MAPK cascades--by GnRH in these cells depends mainly on the phosphorylation of Raf1 by PKC, supported by a pathway involving c-Src, dynamin, and Ras. On the other hand, the activation of JNK, another MAPK cascade, involves PKC, c-Src, CDC42/Rac1, and probably MEKK1. The GnRHR is also expressed in non-pituitary cells and was found to be involved in the inhibition of cell proliferation in certain cells. Therefore, GnRHR represents a potential target for GnRH-analogs used for cancer treatment. Interestingly, the signaling mechanism of the GnRHR in other cell types significantly differs from that in pituitary cells. Studies conducted in GnRHR-expressing COS7 cells have shown that GnRHR transmits its signals mainly via Gi, EGF receptor, c-Src, and is not dependent on PKC. Understanding the signaling mechanisms elicited by GnRHR can shed light on the mechanism of action of GnRH in pituitary and extra-pituitary tissues.

Altered regulation of ERK1b by MEK1 and PTP-SL and modified Elk1 phosphorylation by ERK1b are caused by abrogation of the regulatory C-terminal sequence of ERKs

ERK1b is an alternatively spliced form of ERK1, containing a 26-amino acid insertion between residues 340 and 341 of ERK1. Although under most circumstances the kinetics of ERK1b activation are similar to that of ERK1 and ERK2, we have previously found several conditions under which the activation of ERK1b by extracellular stimuli differs from that of other ERKs. We studied the molecular mechanisms that cause this differential regulation of ERK1b and found that ERK1b is altered in its ability to interact with MEK1 and this influenced its subcellular localization but not its kinetics of activation. ERK1b had a decreased ability to phosphorylate Elk1, but this did not change much the transcriptional activity of the latter. Importantly, the interaction of ERK1b with PTP-SL, which can act as a MAPK phosphatase, shortly after mitogenic stimulation, was significantly affected as well. Using mutants of ERK1b we found that the differential interaction of ERK1b with the three effectors is caused by the site of insertion that abrogates the cytosolic retention sequence/common docking motif of ERKs, and is not dependent on the actual sequence of the insert. Prolonged epidermal growth factor stimulation of Rat1 cells resulted in a differential inactivation and not activation of ERK1b as compared with ERK1 and ERK2. The reduced sensitivity to phosphatases without major differences in the kinetics of activation or activation of substrates, suggests that ERK1b plays a role in the transmission of extracellular signals under conditions of persistent stimulation, where ERK1b and MAPK phosphatases are induced, and the activity of ERK1 and ERK2 is suppressed.

Involvement of the activation loop of ERK in the detachment from cytosolic anchoring

The Extracellular signal-regulated kinases (ERKs) are translocated into the nucleus in response to mitogenic stimulation. The mechanism of translocation and the residues in ERKs that govern this process are not clear as yet. Here we studied the involvement of residues in the activation loop of ERK2 in determining its subcellular localization. Substitution of residues in the activation loop to alanines indicated that residues 173-181 do not play a significant role in the phosphorylation and activation of ERK2. However, residues 176-181 are responsible for the detachment of ERK2 from MEK1 upon mitogenic stimulation. This dissociation can be mimicked by substitution of residues 176-178 to alanines and is prevented by deletion of these residues or by substitution of residues 179-181 to alanines. On the other hand, residues 176-181, as well as residues essential for ERK2 dimerization, do not play a role in the shuttle of ERK2 through nuclear pores. Thus, phosphorylation-induced conformational rearrangement of residues in the activation loop of ERK2 plays a major role in the control of subcellular localization of this protein.

Mechanism of GnRH receptor signaling on gonadotropin release and gene expression in pituitary gonadotrophs

Gonadotropin releasing hormone (GnRH), the first key hormone of reproduction, is synthesized and secreted from the hypothalamus in a pulsatile manner and stimulates pituitary gonadotrophs (5-10% of the pituitary cells) to synthesize and release gonadotropin luteinizing hormone (LH) and follicle stimulating hormone (FSH). Gonadotrophs consist of 60% multihormonal cells (LH+FSH) and 18% LH- and 22% FSH-containing cells. LH and FSH, members of the glycoprotein hormone family, stimulate spermatogenesis, folliculogenesis, and ovulation. Although GnRH plays a pivotal role in gonadotropin synthesis and release, other factors such as gonadal steroids and gonadal peptides exert positive and negative feedback mechanisms, which affect GnRH actions. GnRH actions include activation of phosphoinositide turnover as well as phospholipase D and A2, mobilization and influx of Ca2+, activation of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK). A complex crosstalk between the above messenger molecules mediates the diverse actions of GnRH. Understanding the signaling mechanisms involved in GnRH actions is the basis for our understanding of basic reproductive functions in general and gonadotropin synthesis and release in particular.

In vitro phosphorylation of COOH termini of the epithelial Na+ channel and its effects on channel activity inXenopus oocytes

Recent findings have suggested the involvement of protein phosphorylation in the regulation of the epithelial Na+ channel (ENaC). This study reports the in vitro phosphorylation of the COOH termini of ENaC subunits expressed as glutathione S-transferase fusion proteins. Channel subunits were specifically phosphorylated by kinase-enriched cytosolic fractions derived from rat colon. The phosphorylation observed was not mediated by the serum- and glucocorticoid-regulated kinase sgk. For the γ-subunit, phosphorylation occurred on a single, well-conserved threonine residue located in the immediate vicinity of the PY motif (T630). The analogous residue on β(S620) was phosphorylated as well. The possible role of γT630 and βS620 in channel function was studied in Xenopus laevis oocytes. Mutating these residues to alanine had no effect on the basal channel-mediated current. They do, however, inhibit the sgk-induced increase in channel activity but only in oocytes that were preincubated in low Na+ and had a high basal Na+ current. Thus mutating γT630 or βS620 may limit the maximal channel activity achieved by a combination of sgk and low Na+.

The CK2 phosphorylation of vitronectin. Promotion of cell adhesion via the alpha(v)beta 3-phosphatidylinositol 3-kinase pathway

Phosphorylation of vitronectin (Vn) by casein kinase II was previously shown to occur at Thr50 and Thr57 and to augment a major physiological function of vitronectin-cell adhesion and spreading. Here we show that this phosphorylation increases cell adhesion via the alpha(v)beta3 (not via the alpha(v)beta5 integrin), suggesting that alpha(v)beta3 differs from alpha(v)beta5 in its biorecognition profile. Although both the phospho (CK2-PVn) and non-phospho (Vn) analogs of vitronectin (simulated by mutants Vn(T50E,T57E), and Vn(T50A,T57A), respectively) trigger the alpha(v)beta3 as well as the alpha(v)beta5 integrins, and equally activate the ERK pathway, these two forms are different in their activation of the focal adhesion kinase/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) pathway. Specifically, we show (i) that, upon exposure of cells to Vn/CK2-PVn, their PKB activation depends on the availability of the alpha(v)beta3 integrin on their surface; (ii) that upon adhesion of the beta3-transfected cells onto the CK2-PVn, the extent of PKB activation coincides with the enhanced adhesion of these cells, and (iii) that both the PKB activation and the elevation in the adhesion of these cells is PI3K-dependent. The occurrence of a cell surface receptor that specifically distinguishes between a phosphorylated and a non-phosphorylated analog of Vn, together with the fact that it preferentially activates a distinct intra-cellular signaling pathway, suggest that extra-cellular CK2 phosphorylation may play an important role in the regulation of cell adhesion and migration.

The ERK signaling cascade inhibits gonadotropin-stimulated steroidogenesis

The response of granulosa cells to luteinizing hormone (LH) and follicle-stimulating hormone (FSH) is mediated mainly by cAMP/protein kinase A (PKA) signaling. Notably, the activity of the extracellular signal-regulated kinase (ERK) signaling cascade is elevated in response to these stimuli as well. We studied the involvement of the ERK cascade in LH- and FSH-induced steroidogenesis in two granulosa-derived cell lines, rLHR-4 and rFSHR-17, respectively. We found that stimulation of these cells with the appropriate gonadotropin induced ERK activation as well as progesterone production downstream of PKA. Inhibition of ERK activity enhanced gonadotropin-stimulated progesterone production, which was correlated with increased expression of the steroidogenic acute regulatory protein (StAR), a key regulator of progesterone synthesis. Therefore, it is likely that gonadotropin-stimulated progesterone formation is regulated by a pathway that includes PKA and StAR, and this process is down-regulated by ERK, due to attenuation of StAR expression. Our results suggest that activation of PKA signaling by gonadotropins not only induces steroidogenesis but also activates down-regulation machinery involving the ERK cascade. The activation of ERK by gonadotropins as well as by other agents may be a key mechanism for the modulation of gonadotropin-induced steroidogenesis.

Involvement of the ERK mitogen-activated protein kinase in cell resistance to complement-mediated lysis

Sublytic doses of complement desensitize cells and make them resistant to lytic complement doses. This process, named complement-induced protection, requires calcium ion influx, protein kinase C activation and protein synthesis. The involvement of the extracellular signal-regulated kinase, ERK, in cell desensitization by sublytic complement was examined in erythroleukaemia K562 cells and in COS-7 cells. As shown here, ERK is activated in K562 and COS-7 cells within 10 min of sublytic immune attack and then shows a decline and a second peak of activation at 20 min. C7- and C8-deficient human sera have a small effect on ERK activity. However, a significant increase in ERK activation is observed when C7 or C8, respectively, is added back to these sera. Complement-induced ERK activation was blocked in cells treated with GF109203X or Go6976, two selective PKC inhibitors, as well as by treatment with PD098059, an inhibitor of MEK1, the ERK kinase. PD098059 treatment also sensitized K562 cells to complement-mediated lysis and prevented complement-induced protection. COS-7 cells transfected with a dominant-negative MEK plasmid were incapable of undergoing the process of complement-induced protection. In conclusion, cell desensitization by sublytic doses of the complement membrane attack complex involves a signalling cascade that includes PKC-mediated ERK activation.

Role of dynamin, Src, and Ras in the protein kinase C-mediated activation of ERK by gonadotropin-releasing hormone

G-protein-coupled receptors are a large group of integral membranal receptors, which in response to ligand binding initiate diverse downstream signaling. Here we studied the gonadotropin-releasing hormone (GnRH) receptor, which uses Gq for its downstream signaling. We show that extracellular signal-regulated kinase (ERK) activation is fully dependent on protein kinase C (PKC), but only partially dependent on Src, dynamin, and Ras. Receptor tyrosine kinases, FAK, Gbetagamma, and beta-arrestin, which were implicated in some G-protein-coupled receptor signaling to MAPK cascades, do not play a role in the GnRH to ERK pathway. Our results suggest that the activation of ERK by GnRH involves two distinct signaling pathways, which converge at the level of Raf-1. The main pathway involves a direct activation of Raf-1 by PKC, and this step is partially dependent on a second pathway consisting of Ras activation, which occurs in a dynamin-dependent manner, downstream of Src.

Lipid constituents in oligodendroglial cells alter susceptibility to H2O2-induced apoptotic cell death via ERK activation

The present work examines the effect of membrane lipid composition on activation of extracellular signal-regulated protein kinases (ERK) and cell death following oxidative stress. When subjected to 50 microM docosahexaenoic acid (DHA, 22 : 6 n-3), cellular phospholipids of OLN 93 cells, a clonal line of oligodendroglia origin low in DHA, were enriched with this polyunsaturated fatty acid. In the presence of 1 mM N,N-dimethylethanolamine (dEa) a new phospholipid species analog was formed in lieu of phosphatidylcholine. Exposure of DHA-enriched cells to 0.5 mM H2O2, caused sustained activation of ERK up to 24 h. At this time massive apoptotic cell death was demonstrated by ladder and TUNEL techniques. H2O2-induced stress applied to dEa or DHA/dEa co-supplemented cells showed only a transient ERK activation and no cell death after 24 h. Moreover, while ERK was rapidly translocated into the nucleus in DHA-enriched cells, dEa supplements completely blocked ERK nuclear translocation. This study suggests that H2O2-induced apoptotic cell death is associated with prolonged ERK activation and nuclear translocation in DHA-enriched OLN 93 cells, while both phenomena are prevented by dEa supplements. Thus, the membrane lipid composition ultimately modulates ERK activation and translocation and therefore can promote or prevent apoptotic cell death.

Taxol-induced apoptosis depends on MAP kinase pathways (ERK and p38) and is independent of p53

The anti-cancer agent paclitaxel (Taxol) stabilizes microtubules leading to G2/M cell cycle arrest and apoptotic cell death. In order to analyse the molecular mechanisms of Taxol-induced cytotoxicity, we studied the involvement of mitogen-activated protein kinases (MAPK) ERK and p38 as well as the p53 pathways in Taxol-induced apoptosis. The human breast carcinoma cell line MCF7 and its derivatives, MCF7/HER-2 and MDD2, were used in the study. We found that Taxol treatment strongly activated ERK, p38 MAP kinase and p53 in MAP kinase MCF7 cells prior to apoptosis. PD98059 or SB203580, specific inhibitors of ERK and p38 kinase activities, significantly decreased apoptosis, leaving the surviving cells arrested in G2/M. These inhibitors did not significantly affect Taxol-induced alterations in the cell cycle regulatory proteins Rb, p53, p21/Waf1 and Cdk-2. In addition, inactivation of p53 did not affect cellular sensitivity to Taxol killing. However, cells with inactivated p53, unlike cells harboring wild type p53, failed to arrest in G2/M after treatment with Taxol and continued to divide or go into apoptosis. Our data show that both ERK and p38 MAP kinase cascades are essential for apoptotic response to Taxol-induced cellular killing and are independent of p53 activity. However, p53 may serve as a survival factor in breast carcinoma cells treated with Taxol by blocking cells in G2/M phase of the cell cycle.

V(D)J recombination defects in lymphocytes due to RAG mutations: severe immunodeficiency with a spectrum of clinical presentations

Severe combined immunodeficiency (SCID) comprises a heterogeneous group of primary immunodeficiencies, a proportion of which are due to mutations in either of the 2 recombination activating genes (RAG)-1 and -2, which mediate the process of V(D)J recombination leading to the assembly of antigen receptor genes. It is reported here that the clinical and immunologic phenotypes of patients bearing mutations in RAGs are more diverse than previously thought and that this variability is related, in part, to the specific type of RAG mutation. By analyzing 44 such patients from 41 families, the following conclusions were reached: (1) null mutations on both alleles lead to the T-B-SCID phenotype; (2) patients manifesting classic Omenn syndrome (OS) have missense mutations on at least one allele and maintain partial V(D)J recombination activity, which accounts for the generation of residual, oligoclonal T-lymphocytes; (3) in a third group of patients, findings were only partially compatible with OS, and these patients, who also carried at least one missense mutation, may be considered to have atypical SCID/OS; (4) patients with engraftment of maternal T cells as a complication of a transplacental transfusion represented a fourth group, and these patients, who often presented with a clinical phenotype mimicking OS, may be observed regardless of the type of RAG gene mutation. Analysis of the RAG genes by direct sequencing is an effective way to provide accurate diagnosis of RAG-deficient as opposed to RAG-independent V(D)J recombination defects, a distinction that cannot be made based on clinical and immunologic phenotype alone.

Expression of MHC class II molecules contributes to lipopolysaccharide responsiveness

Activation of phagocytes by lipopolysaccharide (LPS) causes synthesis and secretion of various mediators of inflammation. CD14, a glycosylphosphatidylinositol-anchored monocytic antigen serving as receptor for LPS, and members of the family of Toll-like receptors mediate cellular activation in response to LPS. Here we investigated whether expression of MHC class II molecules modified the response to LPS. Comparing LPS responsiveness of human and murine cells differing for expression of MHC class II molecules, we found that lack or a low level of expression of MHC class II molecules resulted in diminished secretion of pro-inflammatory cytokines following stimulation with LPS. Thus, expression of MHC class II molecules modifies LPS responsiveness, a finding suggesting that these molecules contribute to the pathogenesis not only of exotoxin-triggered toxic shock but also of endotoxin-triggered septic shock. Additionally to their role in antigen-specific immunity MHC class II molecules may influence the inflammatory response triggered by microbial constituents.

Fibroblast growth factor (FGF) signaling through PI 3-kinase and Akt/PKB is required for embryoid body differentiation

The role of FGF signaling in early epithelial differentiation was investigated in ES (embryonic stem) cell derived embryoid bodies. A dominant negative fibroblast growth factor receptor (FGFR) mutation was created by stably introducing into ES cells an Fgfr2 cDNA, truncated in its enzymatic domains. These cells failed to differentiate into cystic embryoid bodies. No epithelial differentiation and cavitation morphogenesis could be observed, in the mutant, although its rate of cell proliferation remained unchanged. This phenotype was associated with a significant decrease in the activation of Akt/PKB and PLCgamma-1, as compared to the wild type, while the activation of MAPK/Erk was less affected. Requirement for PI 3-kinase signaling in embryoid body differentiation was demonstrated by specific inhibitors. Akt/PKB activation was abrogated by wortmannin in short-term experiments. In long-term cultures Ly294002 inhibited the differentiation of ES cells into embryoid bodies. Our data demonstrate that for early epithelial differentiation FGF signaling is required through the PI 3-kinase-Akt/ PKB pathway.

Bone marrow transplantation with unrelated donors: what is the probability of identifying an HLA-A/B/Cw/DRB1/B3/B5/DQB1-matched donor?

Patients transplanted with marrow from an HLA-ABDR serologically matched unrelated donor suffer from more post-transplant complications than those who are transplanted with marrow from an HLA-identical sibling. This is most likely due to either HLA-ABDR incompatibilities not resolved by standard techniques and/or HLA polymorphisms not tested for by routine tissue typing (HLA-Cw,-DQ). By resolving these incompatibilities by molecular techniques combined with the in vitro cytotoxic T lymphocyte precursor frequency (CTLpf) test, we have shown that a high degree of HLA compatibility is associated with increased patient survival. However, higher requirements for HLA matching decrease the number of available donors. We have estimated the probability of finding an HLA-A/B/Cw/DRB1/DRB3/DRB5/DQB1 compatible donor based on 104 consecutive unrelated bone marrow donor searches initiated between January 1995 and December 1997, with December 1998 as the endpoint. For 96 patients (92.3%), one or more ABDR-identical donors were listed in the Bone Marrow Donor Worldwide Registry (BMDW). After contacting the registries, we obtained at least one (mean, 5.36; range, 1-20; total, 461) blood sample for 86 patients. A highly compatible donor was identified for 33/86 patients (38.4%), after testing an average number of 4.5 donors/patients (range, 1-13). However, by accepting an HLA-DRB3 or -DQB1 or -Cw incompatibility, this number would be as high as 68.6%. Approximately half of the patients (n = 40) for whom a search had been initiated have been transplanted: 22 patients with a perfectly matched donor, 15 patients with an HLA-DRB3 or -DQB1 or -Cw mismatch and three with other mismatches. The average time needed to identify the most compatible donor was 4 months. Extremely long searches seemed to be less useful, because after testing the first seven, a more compatible donor was seldom found. These results show that even when requirements for compatibility are high, the chances of finding a donor remain considerably low.

ERK1b, a 46-kDa ERK isoform that is differentially regulated by MEK

We identified a 46-kDa ERK, whose kinetics of activation was similar to that of ERK1 and ERK2 in most cell lines and conditions, but showed higher fold activation in response to osmotic shock and epidermal growth factor treatments of Ras-transformed cells. We purified and cloned this novel ERK (ERK1b), which is an alternatively spliced form of ERK1 with a 26-amino acid insertion between residues 340 and 341 of ERK1. When expressed in COS7 cells, ERK1b exhibited kinetics of activation and kinase activity similar to those of ERK1. Unlike the uniform pattern of expression of ERK1 and ERK2, ERK1b was detected only in some of the tissues examined and seems to be abundant in the rat and human heart. Interestingly, in Ras-transformed Rat1 cells, there was a 7-fold higher expression of ERK1b, which was also more responsive than ERK1 and ERK2 to various extracellular treatments. Unlike ERK1 and ERK2, ERK1b failed to interact with MEK1 as judged from its nuclear localization in resting cells overexpressing ERK1b together with MEK1 or by lack of coimmunoprecipitation of the two proteins. Thus, ERK1b is a novel 46-kDa ERK isoform, which seems to be the major ERK isoform that responds to exogenous stimulation in Ras-transformed cells probably due to its differential regulation by MEK.

Gene therapy of chronic granulomatous disease

Chronic granulomatous disease (CGD) is a primary immunodeficiency disorder which results from absence or malfunction of the respiratory burst oxidase normally expressed in neutrophils and other phagocytic leukocytes. Two-thirds of the patients are males hemizygous for mutations in the X-linked gene coding for gp91-phox. As a therapeutic approach towards the X-linked form of CGD bicistronic retroviral vectors containing the gp91-phox gene and a selectable marker gene were constructed. The ability of these vectors to restore NADPH oxidase activity was tested in a human myeloid leukemic cell line that is defective in superoxide production, as well as in primary CD34+ cells obtained from X-CGD patients. Under optimal conditions 80% of the CD34+ cells derived from bone marrow of one X-CGD patient were transduced. The level of superoxide production, in phagocytes derived from transduced cells was 68.9% of normal levels. Considering that low levels of superoxide generating activity are sufficient for normal host defense, the present experiments provide the basis for the development of a gene replacement therapy for the X-linked form of CGD.

Induction of intracellular signalling by cyclic glycerophosphates and their deoxy analogues

Cyclic glycerophosphates can be formed by enzymic degradation of phospholipids. They have only recently attracted attention, and their physiological function is still obscure. In this study, we have searched for signalling functions of the natural 1,3-cyclic and 1,2-cyclic glycerophosphates, their deoxy analogues, and the phenyl esters of the 1,3-cyclic phosphates. Linear sn-glycerol 3-phosphate and glycerol 2-phosphate served as the control compounds. Each of the six-membered ring cyclic phosphates tested induced rapid intracellular tyrosine phosphorylation in CHO and NIH-3T3 cells when applied extracellularly at a concentration of 0.5-4 microM. The phosphorylated intracellular proteins had molecular masses of approximately 35 kDa, approximately 45 kDa, 60-70 kDa and approximately 120 kDa. The five-membered ring cyclic phosphates had a similar effect, but at an external concentration of 2-10 microM, while sn-glycerol 3-phosphate and glycerol 2-phosphate had no effect. The six-membered cyclic phosphates also induced rapid threonine phosphorylation in CHO cells of approximately 18-kDa, approximately 35-kDa, and approximately 38-kDa proteins. Further experiments indicated that the cyclic phosphates partition rapidly into the cell cytosol where they activate kinases, including mitogen-activated protein kinase. When their intracellular level increases, dephosphorylation presumably takes place. This pattern may account for the signalling profile of cyclic phosphates and suggests that they may take part in processes associated with cell differentiation.

The requirement of both extracellular regulated kinase and p38 mitogen-activated protein kinase for stimulation of cytosolic phospholipase A(2) activity by either FcgammaRIIA or FcgammaRIIIB in human neutrophils. A possible role for Pyk2 but not for the Grb2-Sos-Shc complex

The signal transduction pathways initiated by opsonized zymosan (OZ) leading to activation of cytosolic phospholipase A(2) (cPLA(2)) in human neutrophils remain obscure. In a previous study, we showed that the activation of cPLA(2) by OZ is tyrosine kinase-dependent. The present study demonstrates that the signals initiated by OZ involve activation of tyrosine kinase Pyk2 but not the formation of the adhesion protein complex, Shc-Grb2-Sos. Stimulation of cPLA(2) activity by OZ is mediated by Fc gamma receptors (FcgammaRs) and not by complement receptors for the C3b protein. Cross-linking of FcgammaRIIA or FcgammaRIIIB induces p38 mitogen-activated protein (MAP) kinase and extracellular regulated kinase (ERK) phosphorylation. The kinetics of cPLA(2) activity stimulated by either of the FcgammaRs or by both is similar to that of p38 MAP kinase and was detected as early as 15 s after stimulation, maintained a plateau for 10 min, and decreased thereafter. ERK activation was detected also within 15 s but decreased significantly 5 min after stimulation. The MEK inhibitor, PD-098059, or the p38 MAP kinase inhibitor, SB-203580, caused a partial inhibition during the time course of cPLA(2) activity, whereas their combination caused a total inhibition. Thus, although ERK activation is significantly shorter than that of p38 MAP kinase, it is equally required for activation and maintenance of cPLA(2) activity by occupancy of a single receptor, FcgammaRIIA or FcgammaRIIIB.

Activation of MAPK cascades by G-protein-coupled receptors: the case of gonadotropin-releasing hormone receptor

G-protein-coupled receptors (GPCRs) are a large group of integral membrane receptors that transmit signals from a diverse array of external stimuli, including neurotransmitters, hormones, phospholipids, photons, odorants and taste ligands. In response to ligand binding, the GPCRs initiate diverse downstream signaling pathways through four groups of G proteins and other interacting proteins. Key components in GPCR-induced intracellular signaling are four groups of mitogen-activated protein kinase (MAPK) cascades: extracellular signal-related kinase (ERK), Jun N-terminal kinase (JNK), p38MAPK and big MAPK (BMK). The hallmark of MAPK signaling is the stimulation-dependent nuclear translocation of the involved kinases, which regulate gene expression and the cytoplasmic acute response to mitogenic, stress-related, apoptotic and survival stimuli. A special type of GPCR is the gonadotropin-releasing hormone (GnRH) receptor, which uses primarily the Gq protein for its downstream signaling. GnRH activates all four MAPK cascades by a PKC-dependent mechanism. Common signaling molecules, including the tyrosine kinase c-SRC and the small GTPases CDC42, RAC and RAS, are implicated in various aspects of the GnRH-MAPK pathways. Thus, the activation of MAPK cascades by GnRH opens a new vista in the understanding of the transcriptional regulation of genes encoding gonadotropins. However, additional studies on cell lines and whole animals are required to understand GnRH signaling in the context of other hormones during the reproductive cycle of mouse and human.

Detection of partially phosphorylated forms of ERK by monoclonal antibodies reveals spatial regulation of ERK activity by phosphatases

When cells are stimulated by mitogens, extracellular signal-regulated kinase (ERK) is activated by phosphorylation of its regulatory threonine (Thr) and tyrosine (Tyr) residues. The inactivation of ERK may occur by phosphatase-mediated removal of the phosphates from these Tyr, Thr or both residues together. In this study, antibodies that selectively recognize all combinations of phosphorylation of the regulatory Thr and Tyr residues of ERK were developed, and used to study the inactivation of ERK upon mitogenic stimulation. We found that inactivation of ERK in the early stages of mitogenic stimulation involves separate Thr and Tyr phosphatases which operate differently in the nucleus and in the cytoplasm. Thus, ERK is differentially regulated in various subcellular compartments to secure proper length and strength of activation, which eventually determine the physiological outcome of many external signals.