Intermolecular and intramolecular interactions regulate catalytic activity of myotonic dystrophy kinase-related Cdc42-binding kinase alpha

Myotonic dystrophy kinase-related Cdc42-binding kinase (MRCK) is a Cdc42-binding serine/threonine kinase with multiple functional domains. We had previously shown MRCKalpha to be implicated in Cdc42-mediated peripheral actin formation and neurite outgrowth in HeLa and PC12 cells, respectively. Here we demonstrate that native MRCK exists in high-molecular-weight complexes. We further show that the three independent coiled-coil (CC) domains and the N-terminal region preceding the kinase domain are responsible for intermolecular interactions leading to MRCKalpha multimerization. N terminus-mediated dimerization and consequent transautophosphorylation are critical processes regulating MRCKalpha catalytic activities. A region containing the two distal CC domains (CC2 and CC3; residues 658 to 930) was found to interact intramolecularly with the kinase domain and negatively regulates its activity. Its deletion also resulted in an active kinase, confirming a negative autoregulatory role. We provide evidence that the N terminus-mediated dimerization and activation of MRCK and the negative autoregulatory kinase-distal CC interaction are two mutually exclusive events that tightly regulate the catalytic state of the kinase. Disruption of this interaction by a mutant kinase domain resulted in increased kinase activity. MRCK kinase activity was also elevated when cells were treated with phorbol ester, which can interact directly with a cysteine-rich domain next to the distal CC domain. We therefore suggest that binding of phorbol ester to MRCK releases its autoinhibition, allowing N-terminal dimerization and subsequent kinase activation.

A case series of acanthamoeba keratitis in Singapore

Acanthamoeba keratitis has become an important cause of severe ocular inflammation and visual loss in the past two decades. Its prevalence has been linked to the increasing use of contact lens. Early diagnosis, effective treatment regimes and education on proper contact lens wear are important in the management and prevention of visual loss from this debilitating disease. We described a series of two cases of culture positive acanthamoeba keratitis and their subsequent management.

Cell-based screen for antimitotic agents and identification of analogues of rhizoxin, eleutherobin, and paclitaxel in natural extracts

We describe a cell-based assay for antimitotic compounds that is suitable for drug discovery and for quantitative determination of antimitotic activity. In the assay, cells arrested in mitosis as a result of exposure to antimitotic agents in pure form or in crude natural extracts are detected by ELISA using the monoclonal antibody TG-3. The assay was used to screen >24,000 extracts of marine microorganisms and invertebrates and terrestrial plants and to guide the purification of active compounds from 5 of 119 positive extracts. A new rhizoxin analogue was found in a Pseudomonas species, six new eleutherobin analogues were identified from the octocoral Erythropodium caribaeorum, and two paclitaxel analogues were found in the stem bark of the tree Ilex macrophylla. The assay was also used for quantitative comparison of the antimitotic activity of different analogues. It revealed the importance of the C-11 to C-13 segment of the diterpene core of eleutherobin for its antimitotic activity. The identification of antimitotic compounds in very low abundance and their high (0.5%) occurrence in natural extracts indicates that drug discovery efforts using this cell-based assay may lead to the identification of structurally novel antimitotic agents.

Coupling of PAK-interacting exchange factor PIX to GIT1 promotes focal complex disassembly

The p21-activated kinase PAK is targeted to focal complexes (FCs) through interactions with the SH3 domains of the PAK-interacting exchange factor PIX and Nck. PIX is a Rac GTP exchange factor that also binds the G-protein-coupled receptor kinase-interacting protein known as GIT1. Overexpression of GIT1 in fibroblasts or epithelial cells causes a loss of paxillin from FCs and stimulates cell motility. This is due to the direct interaction of a C-terminal 125-residue domain of GIT1 with paxillin, under the regulation of PIX. In its activated state, GIT1 can promote FC disassembly independent of actin-myosin contractile events. Additionally, GIT directly couples to a key component of FCs, focal adhesion kinase (FAK), via a conserved Spa2 homology domain. We propose that GIT1 and FAK cooperate to promote motility both by directly regulating focal complex dynamics and by the activation of Rac.

Phosphorylation of ERM proteins at filopodia induced by Cdc42

BACKGROUND

ERM (ezrin, radixin, and moesin) proteins function as membrane-cytoskeletal linkers, and are known to be localized at filopodia and microvilli-like structures. We have shown that Rho-associated kinase (Rho-kinase)/ROKalpha/ROCK II phosphorylates moesin at Thr-558 at the lower stream of Rho, and the phosphorylation is crucial to the formation of microvilli-like structures (Oshiro, N., Fukata, Y. & Kaibuchi, K. (1998) Phosphorylation of moesin by Rho-associated kinase (Rho-kinase) plays a crucial role in the formation of microvilli-like structures. J. Biol. Chem. 273, 34663- 34666). However, the role of ERM proteins in the formation of filopodia is less well characterized.

RESULTS

Here we examined the phosphorylation state of ERM during filopodia formation induced by Cdc42 using the antibody recognizing ERM proteins phosphorylated at COOH (C)-terminal threonine. When NIH 3T3 cells were transfected with constitutively active Cdc42 (Cdc42V12), filopodia formation was induced and phosphorylation of ERM at C-terminal threonine was observed at the tip of filopodia, while the phosphorylation levels of ERM were lower and phosphorylated ERM was distributed throughout the cytoplasm in the control cells. We also showed that Myotonic dystrophy kinase-related Cdc42-binding kinase (MRCK) which has been identified as an effector of Cdc42, phosphorylated moesin at C-terminal threonine in a cell-free system. Coexpression of the dominant negative form of MRCK inhibited both the formation of filopodia and accumulation of C-terminal threonine-phosphorylated ERM proteins at filopodia induced by Cdc42V12.

CONCLUSION

The formation of filopodia induced by Cdc42 is accompanied by phosphorylation of ERM proteins, and MRCK is a candidate for the kinase that phosphorylates ERM proteins at filopodia.

p21-activated kinase PAK phosphorylates desmin at sites different from those for Rho-associated kinase

p21-activated kinase (PAK) and Rho-associated kinase (Rho-kinase) have been shown to induce Ca(2+)-independent contraction of smooth muscle. PAK-induced contraction of Triton-skinned smooth muscle correlates with increased phosphorylation of caldesmon and desmin, although the role of desmin phosphorylation has remained obscure. Here we report that desmin serves as an excellent substrate for PAK in vitro. PAK phosphorylated desmin in a GTP. Cdc42/Rac-dependent manner. Phosphorylation of desmin by PAK dramatically inhibited its filament-forming ability. PAK phosphorylated mainly serine residues of the head domain of desmin, and the major phosphorylation sites differed from those for Rho-kinase. These results suggest that different site-specific phosphorylation of desmin via two divergent protein kinases downstream of Rho family GTPases would seem to increase the regulatory potential for organization of desmin filaments.

Interaction between PAK and nck: a template for Nck targets and role of PAK autophosphorylation

The kinase PAK binds tightly to the SH3 domain of its partner PIX via a central proline-rich sequence. A different N-terminal sequence allows alphaPAK to bind an SH3 domain of the adaptor Nck. The Nck SH3[2] domain interacts equally with an 18-mer PAK-derived peptide and full-length alphaPAK. Detailed analysis of this binding by saturation substitution allows related Nck targets to be accurately identified from sequence characteristics alone. All Nck SH3[2] binding proteins, including PAK, NIK, synaptojanin, PRK2, and WIP, possess the motif PXXPXRXXS; in the case of PAK, serine phosphorylation at this site negatively regulates binding. We show that kinase autophosphorylation blocks binding by both Nck and PIX to alphaPAK, thus providing a mechanism to regulate PAK interactions with its SH3-containing partners. One cellular consequence of the regulatable binding of PAK is facilitation of its cycling between cytosolic and focal complex sites.

Penetrating keratoplasty for keratoconus: visual outcome and success

OBJECTIVE

To determine the long-term effect on vision of penetrating keratoplasty performed for keratoconus.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

All patients with keratoconus who received a corneal graft and who remained in our center for follow-up and visual rehabilitation during the study period.

INTERVENTION

Penetrating keratoplasty was performed in 93 eyes of 78 patients.

MAIN OUTCOME MEASURES

Graft survival, visual acuity, and astigmatism.

RESULTS

One (1.08%) graft failure was encountered over a mean follow-up of 46 months. Mean preoperative (best corrected) and postoperative visual acuity is (best-tolerated correction) were 0.9 (20/160) and 0.24 (20/80) logMAR, respectively. Visual acuity in 86% of eyes was 0.3 logMAR (20/40) or better at the latest follow-up, with 67% of eyes being corrected with spectacles. Mean preoperative corneal power by keratometry was more than 52 diopters (D) in 83% of eyes; mean postoperative corneal power was 45 +/- 2 D. No significant predictors of postgraft astigmatism were found. Mean preoperative and postoperative best-eye acuities of the better eye were 0.32 (20/40-1) and 0.18 (20/32+1) logMAR, respectively (P < 0.001).

CONCLUSIONS

Graft survival was excellent. A corrected visual acuity of 20/40 or better was obtained in 86% of eyes. Astigmatism could not be predicted from preoperative factors. Visual acuity measured in the better eye improved by 0.14 logMAR (1.4 lines), implying an overall functional gain for the patient.

Reverse geometry contact lens wear after photorefractive keratectomy, radial keratotomy, or penetrating keratoplasty

PURPOSE

To determine if a super diffusion coefficient of lens/lens thickness (Dk/L) reverse geometry gas permeable (steep peripheral and flatter central curve) contact lenses can be successfully worn after excimer photorefractive keratectomy (PRK), radial keratotomy (RK), or penetrating keratoplasty (PK).

METHODS

Patients with residual ametropia after PRK, RK, or PK were fitted with reverse geometry lenses (Plateau lens in SF-P material; Menicon USA, Inc, Clovis, CA, U.S.A.). Contact lens fit characteristics and comfort were assessed. Lens centration, visual quality, and ocular surface status were graded and visual acuity charted.

RESULTS

Thirteen eyes of 11 patients were fitted; eight eyes with PRK, one eye with RK, and four eyes with PK previously performed. The mean follow up of the patients was six months. The visual acuity prior to lenses ranged from 6/12 to counting fingers, and the acuity with lenses ranged from 6/6 to 6/30. Eight of the 11 patients wore the lenses the whole day without problems; 3 patients discontinued lens wear due to discomfort or unsatisfactory vision.

CONCLUSIONS

The combination of super Dk/L and reverse geometry lenses facilitate lens wear and is associated with good visual acuity.

Antimicrobial susceptibility of 19 Australian corneal isolates of Acanthamoeba

PURPOSE

To determine the in vitro drug susceptibility of Australian corneal isolates of Acanthamoeba and to correlate the results with patient treatment and visual outcome.

METHODS

Acanthomoeba isolates were obtained from a reference laboratory Cyst suspensions were prepared from 19 strains and exposed to 10 antimicrobial agents for 7 days. The minimum drug concentrations required to inhibit excystation were determined. Inhibited cells were then plated out to determine minimum cysticidal concentrations.

RESULTS

Overall, propamidine proved to be the most active anti-Acanthamoeba agent tested. The disinfectant polyhexamethylene biguanide, either pure or in Baquacil, was also effective. Pentamidine, hexamidine, chlorhexidine and chloroxylenol had intermediate activity, while neomycin, amphotericin B and povidone-iodine had poor activity. There was no clear relationship between in vitro susceptibility and visual outcome.

CONCLUSIONS

Propamidine and polyhexamethylene biguanide drops are recommended as initial choices for the treatment of Acanthamoeba keratitis. The variability in the susceptibility to any one agent suggests that individual testing of isolates is necessary to identify the most appropriate treatment. A number of factors influence visual outcome in these cases; further studies are required to resolve the importance or otherwise of in vitro susceptibility.

Caffeine and theobromine levels in chocolate couverture and coating products

Thirty-two samples of chocolate products were analysed by HPLC for caffeine and theobromine contents. Defatted residues of samples were extracted with 80% aqueous acetone. After extraction into boiling water, the methylxanthines were identified and quantified with the use of μ-Bondapak column and mobile phase of methanol:water:acetic acid (20:79:1). Levels of caffein and theobromine in 32 samples of chocolate products averaged 0.62-1.14 mg/g and 0.026-0.153 mg/g respectively. Mean values for theobromine and caffeine content for chocolate coating were 0.82 and 0.07 mg/g respectively. The chocolate coating made from fat substitute had theobromine and caffeine levels ranging from 0.36-0.70 mg/g and 0.027-0.061 mg/g respectively, with mean values of 0.49 mg theobromine/g and 0.039 mg caffeine/g. In local chocolate, the mean theobromine and caffeine levels respectively were 0.72 mg/g and 0.04 mg/g in milk chocolate, and 0.85 mg/g and 0.06 mg/g in dark chocolate. Meanwhile, for imported chocolate, the mean theobromine and caffeine levels respectively were 1.05 mg/g and 0.12 mg/g in dark chocolate; 0.76 mg/g and 0.04 mg/g in milk chocolate; and 0.74 mg/g and 0.03 mg/g in white chocolate. Compared with the local chocolates, imported chocolates had higher levels of theobromine and caffeine at 1.141 mg/g and 0.1533mg/g. The average theobromine and caffeine concentrations in local chocolate were 0.082mg/g and 0.066mg/g. Theobromine concentration in chocolate samples is within the range of 0.62mg/g-1.141mg/g and the range of caffeine concentration is 0.026mg/g-0.153mg/g respectively. Bittersweet chocolates were found to have higher theobromine and caffeine concentrations than normal sweet chocolates and milk chocolates.

Phosphatidylinositol 3-kinase, Cdc42, and Rac1 act downstream of Ras in integrin-dependent neurite outgrowth in N1E-115 neuroblastoma cells

Ras and Rho family GTPases have been ascribed important roles in signalling pathways determining cellular morphology and growth. Here we investigated the roles of the GTPases Ras, Cdc42, Rac1, and Rho and that of phosphatidylinositol 3-kinase (PI 3-kinase) in the pathway leading from serum starvation to neurite outgrowth in N1E-115 neuroblastoma cells. Serum-starved cells grown on a laminin matrix exhibited integrin-dependent neurite outgrowth. Expression of dominant negative mutants of Ras, PI 3-kinase, Cdc42, or Rac1 all blocked this neurite outgrowth, while constitutively activated mutants of Ras, PI 3-kinase, or Cdc42 were each sufficient to promote outgrowth even in the presence of serum. A Ras(H40C;G12V) double mutant which binds preferentially to PI 3-kinase also promoted neurite formation. Activated Ras(G12V)-induced outgrowth required PI 3-kinase activity, but activated PI 3-kinase-induced outgrowth did not require Ras activity. Although activated Rac1 by itself did not induce neurites, neurite outgrowth induced by activated Cdc42(G12V) was Rac1 dependent. Cdc42(G12V)-induced neurites appeared to lose their normal polarization, almost doubling the average number of neurites produced by a single cell. Outgrowth induced by activated Ras or PI 3-kinase required both Cdc42 and Rac1 activity, but Cdc42(G12V)-induced outgrowth did not need Ras or PI 3-kinase activity. Active Rho(G14V) reduced outgrowth promoted by Ras(G12V). Finally, expression of dominant negative Jun N-terminal kinase or extracellular signal-regulated kinase did not inhibit outgrowth, suggesting these pathways are not essential for this process. Our results suggest a hierarchy of signalling where Ras signals through PI 3-kinase to Cdc42 and Rac1 activation (and Rho inactivation), culminating in neurite outgrowth. Thus, in the absence of serum factors, Ras may initiate cell cycle arrest and terminal differentiation in N1E-115 neuroblastoma cells.

Molecular characterization of the Caenorhabditis elegans Rho GDP-dissociation inhibitor

GDP-dissociation inhibitors (GDIs) form one of the classes of regulatory proteins that modulate the cycling of the Ras superfamily of GTPases between active GTP-bound and inactive GDP-bound states. We report here the characterization of the Caenorhabditis elegans RhoGDI (CeRhoGDI) as part of our investigations into Rho-GTPase signalling pathways that are involved in nematode development. CeRhoGDI is a 23-kDa protein that is localized predominantly in the cytosol. CeRhoGDI interacts only with the lipid-modified forms of C. elegans Rho-GTPases, CeRhoA, CeRac1 and Cdc42Ce, in vitro and is able to solubilize the membrane-bound forms of these GTPases. CeRhoGDI recognizes the GTPases in both GTP- and GDP-bound forms; hence it inhibits both the guanine-nucleotide dissociation and GTP-hydrolysis activities. The inhibitory activity towards the GTP-bound GTPases is weak compared with that towards GDP-bound GTPases. CeRhoGDI is expressed throughout development and is highly expressed in marginal and vulval epithelial cells, in sperm cells and spicules. Taken together, our results suggest that CeRhoGDI may be involved in specific morphogenetic events mediated by the C. elegans Rho-GTPases.

Melanoma chondroitin sulphate proteoglycan regulates cell spreading through Cdc42, Ack-1 and p130cas

Melanoma chondroitin sulphate proteoglycan (MCSP) is a cell-surface antigen that has been implicated in the growth and invasion of melanoma tumours. Although this antigen is expressed early in melanoma progression, its biological function is unknown. MCSP can stimulate the integrin-alpha4 beta1-mediated adhesion and spreading of melanoma cells. Here we show that stimulated MCSP recruits tyrosine-phosphorylated p130 cas, an adaptor protein important in tumour cell motility and invasion. MCSP stimulation also results in a pronounced activation and recruitment of the Rho-family GTPase Cdc42. MCSP-induced spreading of melanoma cells is dependent upon active Cdc42, a Cdc42-associated tyrosine kinase (Ack-1) and tyrosine phosphorylation of p130cas. Furthermore, vectors inhibiting Ack-1 or Cdc42 expression and/or function abrogate MCSP-induced tyrosine phosphorylation and recruitment of p130cas. Our findings indicate that MCSP may modify tumour growth or invasion by a unique signal-transduction pathway that links Cdc42 activation to downstream tyrosine phosphorylation and subsequent cytoskeletal reorganization.

Symptoms during normal pregnancy: a prospective controlled study

Symptoms of normal pregnancy have received scant attention in the literature and what is reported is largely unsubstantiated. Yet this is an important aspect of antenatal counselling and care which deserves further investigation if symptoms are to be interpreted correctly. Accordingly, we conducted a prospective controlled study of symptoms during normal pregnancy in both primigravidas and multigravidas. A total of 38 symptoms occurred with a significantly different frequency (mainly increased) in the pregnant subjects in the third trimester compared with the controls. Of these a mean of 24.2 symptoms was experienced by each pregnant woman, double that (mean, 11.2) experienced by healthy nonpregnant controls. The 5 symptoms reported most frequently by the pregnant subjects were frequency of micturition, fatigue, pelvic pressure, insomnia and lower backache. However, a wide range of symptoms involving most body systems were reported. This study has established that symptoms of pregnancy are more numerous than mentioned in current obstetric texts and that they can be attributed to the effects of pregnancy. The third trimester is associated with the greatest number of symptoms and there is a marked decline in their number after delivery.

Contact lens wear after photorefractive keratectomy: comparison between rigid gas permeable and soft contact lenses

PURPOSE

To determine if rigid gas permeable (RGP) or soft contact lenses can be successfully worn after photorefractive keratectomy (PRK) to correct residual refractive errors.

METHODS

Patients with residual stable ametropia after PRK were fit with RGP or soft lenses. Manifest refraction, corneal topography, and keratometry were performed, and post-PRK corneal haze was graded during the study visits. Contact lens fit characteristics and comfort were assessed. Lens centration, visual quality, and ocular surface status were graded, and visual acuity with contact lenses was charted.

RESULTS

Eighteen patients were recruited for RGP lens fitting. The mean refractive error post-PRK was +0.80 D +/- 2.03 (range: -3.50 to+3.00 D). The mean contact lens power was -3.90 D +/- 2.03 (range: 0 to -7.00 D), and the mean contact lens base curve was 7.88 mm +/-0.16. A significant positive tear film at the site of the central ablation was noted, contributing to excessive minus lens power in all cases. Despite mild to moderate lens instability and de-centration, 14 patients reported excellent visual quality with the lenses, and pre-PRK best-corrected acuity was achieved in all patients. Twenty-five percent (4 of 16) of the patients were able to wear the lenses all day. Eleven patients were recruited for soft contact lens fitting-five from the RGP trial. The mean refractive error post-PRK was -0.64 D +/- 2.01 (range: -3.50 to +1.75D). The mean contact lens power was -0.60 D +/- 2.07 (range: -3.75 to +2.5 D), and the mean contact lens base curve was 8.33 mm +/- 0.42. Eight patients were corrected with lenses to their pre-PRK best-corrected acuity, and nine patients reported excellent visual quality with the lenses. All the patients had excellent lens centration. Thirty-six percent (four of 11) of patients were wearing the lenses all day.

CONCLUSIONS

Fitting RGP lenses after PRK results in good visual acuity but may be associated with mild to moderate lens instability and decentration. Soft contact lens fitting also results in good visual acuity. Soft lenses were better tolerated by the subjects in our study because of improved lens centration and stability.

HNF-3/forkhead homologue-4 influences lung morphogenesis and respiratory epithelial cell differentiation in vivo

HNF-3/forkhead homologue 4 (HFH-4), a transcription factor of the winged helix/forkhead family, is expressed in various tissues including lung, brain, oviduct, testis, and embryonic kidney. In order to test whether the temporospatial expression of HFH-4 influences lung morphogenesis, HFH-4 was expressed in lungs of transgenic mice under control of the surfactant protein C (SP-C) promoter. The morphology of the lungs from SP-C/HFH-4 embryos (day 18 postconception) was distinctly abnormal, and the severity of the alterations correlated with the level of transgene expression as detected by in situ hybridization. At high levels of expression, HFH-4 altered epithelial cell differentiation and inhibited branching morphogenesis. Atypical cuboidal or columnar cells lined the lung periphery of SP-C/HFH-4 transgenic mice. The atypical epithelial cells seen in the SP-C/HFH-4 mice expressed thyroid transcription factor-1 and hepatocyte nuclear factor 3beta (HNF-3beta). However, surfactant proteins SP-B, SP-C, and Clara cell secretory protein, normally produced by nonciliated epithelial cells in lung parenchyma were lacking. beta-Tubulin IV, a marker of ciliated cells, stained the atypical columnar cells produced by expression of high levels of the SP-C/HFH-4 transgene. Ectopic expression of HFH-4 in developing mouse lung altered epithelial cell differentiation and morphology, restricting the expression of markers typical of nonciliated cells of the distal lung parenchyma.

Variation in in-patient stroke management in ten centres in different countries: the INCLEN multicentre stroke collaboration

BACKGROUND AND PURPOSE

Large within-country variations have been described in stroke management and there have been a few studies of between-country variation (in the USA and the UK). We designed a study to examine stroke management across a wide range of countries representing different stages of economic development. Large variations would suggest the need to explore methods of increasing the uptake of evidence-based stroke practice.

METHODS

Members of the International Clinical Epidemiology Network (INCLEN) from 14 centres in ten countries agreed to review the records of the last 50 patients admitted to hospital with a clinical diagnosis of stroke. Information on demographic variables, the clinical diagnosis of stroke type, investigations performed and treatments given and the discharge destination of the patient were recorded and sent to the coordinating centre in Australia for analysis.

RESULTS

There were statistically significant between-centre differences in the proportions of patients cared for by a neurologist, staying in hospital for at least ten days and having CT or MRI scans. Significant between-centre differences were also seen for treatment, for example, the use of aspirin in non-haemorrhagic stroke varied from 11 to 79%. The variation (for all interventions studied) was no longer statistically significant when examined within strata according to availability of facilities.

CONCLUSIONS

The large variation between centres in the management of stroke is largely 'explained' by the availability of resources, even for interventions that do not depend on resource availability. It will be important to develop management guidelines that reflect evidence-based practice of relevance across a range of economic settings.

The myotonic dystrophy kinase-related Cdc42-binding kinase is involved in the regulation of neurite outgrowth in PC12 cells

The myotonic dystrophy kinase-related Cdc42-binding kinase (MRCKalpha) has been implicated in the morphological activities of Cdc42 in nonneural cells. Both MRCKalpha and the kinase-related Rho-binding kinase (ROKalpha) are involved in nonmuscle myosin light-chain phosphorylation and associated actin cytoskeleton reorganization. We now show that in PC12 cells, overexpression of the kinase domain of MRCKalpha and ROKalpha resulted in retraction of neurites formed on nerve growth factor (NGF) treatment, as observed with RhoA. However, introduction of kinase-dead MRCKalpha did not result in NGF-independent neurite outgrowth as observed with dominant negative kinase-dead ROKalpha or the Rho inhibitor C3. Neurite outgrowth induced by NGF or kinase-dead ROKalpha was inhibited by dominant negative Cdc42(N17), Rac1(N17), and the Src homology 3 domain of c-Crk, indicating the participation of common downstream components. Neurite outgrowth induced by either agent was blocked by kinase-dead MRCKalpha lacking the p21-binding domain or by a minimal C-terminal regulatory region consisting of the cysteine-rich domain/pleckstrin homology domain plus a region with homology to citron. The latter region alone was an effective blocker of NGF-induced outgrowth. These results suggest that although ROKalpha is involved in neurite retraction promoted by RhoA, the related MRCKalpha is conversely involved in neurite outgrowth promoted by Cdc42 and Rac.

Influence of granulocyte-macrophage colony-stimulating factor (GM-CSF) on whole blood endotoxin responsiveness following trauma, cardiopulmonary bypass, and severe sepsis

Major surgery, multiple injury, and severe sepsis lead to an impaired immune response. The suppressed status of the immune system is reflected by a reduced TNFalpha production of whole blood after stimulation with endotoxin in vitro and by a decreased HLA-DR expression on monocytes. In the present study, the effect of the immunostimulating hematopoetic growth factor GM-CSF on whole blood cultures of multiple injury, cardiac surgery, and severe sepsis patients was investigated. Endotoxin-induced TNFalpha production and HLA-DR expression was reduced in blood cultures of these patients compared to healthy donors. Preincubation with GM-CSF in vitro increased cytokine production in volunteers' and all patients' blood specimens in a dose-dependent manner. The elevation of cytokine response in cardiopulmonary bypass patients' blood, caused by in vitro preincubation with GM-CSF, equaled that of normal patients, whereas GM-CSF caused a lower rise of TNFalpha-producing capacity in blood of multiple-injury and sepsis patients. Further, GM-CSF treatment in vitro increased the down-regulated HLA-DR expression on monocytes prepared after cardiac surgery to a degree comparable to preoperative levels. Finally, GM-CSF incubation in vitro elevated TNFalpha synthesis in normal monocytes and in cells treated with a combination of the anti-inflammatory mediators IL-10, TGFbeta, and PGE2. These experiments show that hyporesponsiveness of whole blood induced by trauma, sepsis, or cardiac surgery is not irreversible but can be, at least in vitro, overridden by the immunostimulating compound GM-CSF.

Pak functions downstream of Dock to regulate photoreceptor axon guidance in Drosophila

The SH2/SH3 adaptor protein Dock has been proposed to transduce signals from guidance receptors to the actin cytoskeleton in Drosophila photoreceptor (R cell) growth cones. Here, we demonstrate that Drosophila p21-activated kinase (Pak) is required in a Dock pathway regulating R cell axon guidance and targeting. Dock and Pak colocalize to R cell axons and growth cones, physically interact, and their loss-of-function phenotypes are indistinguishable. Normal patterns of R cell connectivity require Pak's kinase activity and binding sites for both Dock and Cdc42/Rac. A membrane-tethered form of Pak (Pak(myr) acts as a dominant gain-of-function protein. Retinal expression of Pak(myr) rescues the R cell connectivity phenotype in dock mutants. These data establish Pak as a critical regulator of axon guidance and a downstream effector of Dock in vivo.