Detection and clinical impact of human leukocyte antigen antibodies in lung transplantation: A systematic review and meta-analysis.

There is significant variability in lung transplant centers' approach to HLA antibodies, creating heterogeneity regarding their clinical significance. Some institutions use beads coated with multiple HLA to screen candidate sera and then use single antigen bead (SAB) to determine antibody identity if the pre-screen is positive. Other centers do not pre-screen, using SAB alone, which may detect low-level antibodies of unknown significance. The primary objective of this study was to review the current literature to identify sources of heterogeneity in the identification of pre- and post-lung transplant HLA antibodies, particularly regarding antibody-detection methods. A random effects model meta-analysis was used to evaluate the relationship between pre-transplant HLA antibodies and the development of de novo donor-specific antibodies (dnDSA) and dnDSA and chronic lung allograft dysfunction (CLAD). Each outcome was stratified by the method of antibody detection (pre-screen followed by SAB vs SAB alone). We identified 13 cohort studies with a total of 3039 patients. The use of pre-screening followed by SAB testing and the use of induction immunosuppression were associated with lower prevalence of dnDSA. Patients with pre-transplant HLA antibodies were more likely to develop dnDSA (hazard ratio [HR] = 1.49, 95% confidence interval [CI]: 1.19-1.86, P < .001). dnDSA was associated with CLAD (HR = 2.02, 95% CI = 1.37-2.97, P < .001). When considering studies using SAB alone, however, pre-transplant antibody status was no longer associated with dnDSA and dnDSA was no longer associated with CLAD. Based on the current literature, SAB-alone testing may detect less clinically relevant antibodies than pre-screening followed by SAB.

Lung disease severity in idiopathic pulmonary fibrosis is more strongly associated with impedance measures of bolus reflux than pH parameters of acid reflux alone.

BACKGROUND: Gastroesophageal reflux (GER) has been associated with idiopathic pulmonary fibrosis (IPF). Pathogenesis may be related to chronic micro-aspiration. We aimed to assess objective measures of GER on multichannel intraluminal impedance and pH study (MII-pH) and their relationship with pulmonary function testing (PFT) results, and to compare the performance of pH/acid reflux parameters vs corresponding MII/bolus parameters in predicting pulmonary dysfunction in IPF. METHODS: This was a retrospective cohort study of IPF patients undergoing prelung transplant evaluation with MII-pH off acid suppression, and having received PFT within 3 months. Patients with prior fundoplication were excluded. Severe pulmonary dysfunction was defined using diffusion capacity of the lung for carbon monoxide (DLCO) ≤40%. Six pH/acid reflux parameters with corresponding MII/bolus reflux measures were specified a priori. Multivariate analyses were applied using forward stepwise logistic regression. Predictive value of each parameter for severe pulmonary dysfunction was calculated by area-under-the-receiver-operating-characteristic-curve or c-statistic. KEY RESULTS: Forty-five subjects (67% M, age 59, 15 mild-moderate vs 30 severe) met criteria for inclusion. Patient demographics and clinical characteristics were similar between pulmonary dysfunction groups. Abnormal total reflux episodes and prolonged bolus clearance time were significantly associated with pulmonary dysfunction severity on univariate and multivariate analyses. No pH parameters were significant. The c-statistic of each pH parameter was lower than its MII counterpart in predicting pulmonary dysfunction. CONCLUSIONS & INFERENCES: MII/bolus reflux, but not pH/acid reflux, was associated with pulmonary dysfunction in prelung transplant patients with IPF. MII-pH may be more valuable than pH testing alone in characterizing GER in IPF.

Increased proximal acid reflux is associated with early readmission following lung transplantation.

BACKGROUND: Gastroesophageal reflux disease has been associated with poor outcomes following lung transplantation. However, the association between pretransplant reflux and post-transplant readmission, an indicator of early clinical outcome, has not been previously assessed. METHODS: This was a retrospective cohort study of lung transplant recipients undergoing pretransplant multichannel intraluminal impedance and pH (MII-pH) study off acid suppression at a tertiary care center since 2007. Subjects with pretransplant fundoplication were excluded. Time to readmission was defined as duration from post-transplant discharge to next hospital admission for any reason. Subgroup analysis was performed to exclude elective readmissions. Time-to-event analysis was performed using Cox proportional hazards model, with appropriate censoring. KEY RESULTS: Forty-three subjects (60% men, mean age: 57, median follow-up: 1.7 years) met inclusion criteria for the study. Patient demographics and pretransplant cardiopulmonary function were similar between readmission cohorts. Time to all-cause readmission was associated with increased distal acid episodes (HR: 3.15, p = 0.04) and proximal acid episodes (HR: 3.61, p = 0.008) on impedance, increased acid exposure on pH (HR: 2.22, p = 0.04), and elevated Demeester score (HR: 2.26, p = 0.03). When elective readmissions were excluded, early readmission remained significantly associated with increased proximal acid reflux episodes (HR: 2.49, p = 0.04). All findings were confirmed on Kaplan-Meier analysis. CONCLUSIONS & INFERENCES: Elevated proximal acid reflux on pretransplant MII-pH testing was associated with early readmission following lung transplantation, even after excluding elective readmissions. Exposure to severe acid reflux has measurable effects on early postoperative outcomes such as readmission, and aggressive early antireflux therapy should be considered.

Idiopathic pulmonary fibrosis is associated with increased impedance measures of reflux compared to non-fibrotic disease among pre-lung transplant patients.

BACKGROUND: Gastroesophageal reflux (GER) has been associated with idiopathic pulmonary fibrosis (IPF), although the mechanism remains unclear. Gastroesophageal reflux/microaspiration may lead to lung fibrosis, while increased pulmonary workload may also worsen GER. Comparing the GER profile of IPF patients to chronic obstructive pulmonary disease (COPD) patients with similar lung function may help delineate the role of GER in IPF pathogenesis. METHODS: This was a retrospective cohort study of IPF and COPD patients undergoing pre-lung transplant multichannel intraluminal impedance and pH study (MII-pH) off acid suppression at a tertiary center in 2008-2014. Patients with prior fundoplication were excluded. Baseline demographics, pulmonary function test, and MII-pH results were recorded. Univariate analyses were performed using Fisher's exact (binary variables) and Student's t (continuous variables) tests. Logistic regression was performed to adjust for potential confounders. KEY RESULTS: A total of 90 subjects (54 IPF, 36 COPD) met inclusion criteria. Compared to COPD, IPF patients had increased total reflux episodes (65.9 vs 46.1, p = 0.02), proximal reflux episodes (30.3 vs 20.3, p = 0.04), and prevalence of abnormal total reflux episodes (38.9% vs 16.7%, p = 0.02). On multivariate analyses, abnormal total reflux episodes (OR: 4.9, p = 0.05) and bolus reflux exposure time (OR: 4, p = 0.04) remained significantly associated with IPF. CONCLUSIONS & INFERENCES: Abnormal reflux was significantly more prevalent among IPF patients after controlling for lung disease severity. Gastroesophageal reflux/microaspiration likely plays a role in fibrosis in IPF. A significant portion of IPF patients had increased non-acid reflux. Therapies aiming to prevent reflux of gastric contents may be more beneficial than antisecretory medications alone in these patients.

Cytomegalovirus disease in lung transplantation: impact of recipient seropositivity and duration of antiviral prophylaxis.

BACKGROUND: A recent randomized trial demonstrated that 1 year of antiviral prophylaxis for cytomegalovirus (CMV) after lung transplantation is superior to 3 months of treatment for prevention of CMV disease. However, it is uncertain if a shorter duration of prophylaxis might result in a similar rate of CMV disease among select lung transplant (LT) recipients who are at lower risk for CMV disease, based on baseline donor (D) and recipient (R) CMV serologies. METHODS: We retrospectively assessed incidence, cumulative probability, and predictors of CMV disease and viremia in LT recipients transplanted between July 2004 and December 2009 at our center, where antiviral CMV prophylaxis for 6-12 months is standard. RESULTS: Of 129 LT recipients, 94 were at risk for CMV infection based on donor CMV seropositivity (D+) or recipient seropositivity (R+); 14 developed CMV disease (14.9%): 11 with CMV syndrome, 2 with pneumonitis, and 1 with gastrointestinal disease by the end of follow-up (October 2010); 17 developed asymptomatic CMV viremia (18.1%). The cumulative probability of CMV disease was 17.4% 18 months after transplantation. CMV D+/R- recipients who routinely received 1 year of prophylaxis were more likely to develop CMV disease compared with D+/R+ or D-/R+ recipients, who routinely received 6 months of prophylaxis (12/45 vs. 2/25 vs. 0/24, P = 0.005). Recipients who stopped CMV prophylaxis before 12 months (in D+/R- recipients) and 6 months (in R+ recipients) tended to develop CMV disease more than those who did not (9/39 vs. 3/41, P = 0.06). CONCLUSIONS: On a 6-month CMV prophylaxis protocol, few R+ recipients developed CMV disease in this cohort. In contrast, despite a 12-month prophylaxis protocol, D+/R- LT recipients remained at highest risk for CMV disease.

Non-tuberculous mycobacterial infection among lung transplant recipients: a 15-year cohort study.

BACKGROUND: The incidence of infection with non-tuberculous mycobacteria (NTM) after lung transplant is insufficiently defined. Data on the impact of NTM infection on lung transplant survival are conflicting. METHODS: To quantify the incidence and outcomes of colonization and disease with NTM in patients after lung transplantation, the medical records, chest imaging, and microbiology data of 237 consecutive lung transplant recipients between 1990 and 2005 were reviewed. American Thoracic Society (ATS)/Infectious Diseases Society of America and Centers for Disease Control criteria were used to define pulmonary NTM disease and NTM surgical-site infections (SSI), respectively. Incidence rates for NTM colonization and disease were calculated. Comparisons of median survival were done using the log-rank test. RESULTS: NTM were isolated from 53 of 237 patients (22.4%) after lung transplantation over a median of 25.2 months of follow-up. The incidence rate of NTM isolation was 9.0/100 person-years (95% confidence interval [CI), 6.8-11.8), and the incidence rate of NTM disease was 1.1/100 person-years (95% CI 0.49-2.2). The most common NTM isolated was Mycobacterium avium complex (69.8%), followed by Mycobacterium abscessus (9.4%), and Mycobacterium gordonae (7.5%). Among these 53 patients, only 2 patients met ATS criteria for pulmonary disease and received treatment for M. avium. One patient had recurrent colonization after treatment, the other one was cured. Four of the 53 patients developed SSI, 3 caused by M. abscessus and 1 caused by Mycobacterium chelonae. Three of these patients had persistent infection requiring chronic suppressive therapy and one died from progressive disseminated disease. A total of 47 (89%) patients who met microbiologic but not radiographic criteria for pulmonary infection were not treated and were found to have only transient colonization. Median survival after transplantation was not different between patients with transient colonization who did not receive treatment and those who never had NTM isolated. CONCLUSION: Episodic isolation of NTM from lung transplant recipients is common. Most isolates occur among asymptomatic patients and are transient. Rapidly growing NTM can cause significant SSI, which may be difficult to cure. NTM disease rate is higher among lung transplant recipients than in the general population. In this cohort, NTM isolation was not associated with increased post-transplantation mortality.

Mesangial cell NADPH oxidase upregulation in high glucose is protein kinase C dependent and required for collagen IV expression.

Excess collagen IV expression by mesangial cells contributes to diabetic glomerulosclerosis. We hypothesized that in high glucose reactive oxygen species (ROS) generation by NADPH oxidase is PKC dependent and required for collagen IV expression by mesangial cells. In rat mesangial cells cultured in 5 mM (NG) or 25 mM d-glucose (HG), RT-PCR and Western immunoblotting detected p22(phox) and p47(phox) mRNA and protein, respectively. Quantitative real-time RT-PCR analyzed collagen IV mRNA. With the use of confocal microscopy, ROS were detected with dichlorofluorescein and intracellular collagen IV by immunofluorescence. In HG, ROS were generated within 1 h, sustained up to 48 h, and prevented by a NADPH oxidase inhibitor, diphenylenechloride iodonium (DPI), or a conventional PKC isozyme inhibitor, Gö6976. In NG, phorbol myristate acetate stimulated ROS generation that was inhibited with DPI. In HG, expression of p22(phox) and p47(phox) was increased within 3 to 6 h and inhibited by Gö6976. In HG, Gö6976 or transfection with antisense against p22(phox) reversed the 1.8-fold increase in collagen IV mRNA. In HG, the antioxidants Tempol or Tiron, or transfection with antisense against p22(phox) or p47(phox), prevented ROS generation and the 2.3-fold increase in collagen IV protein. Increased mitochondrial redox potential in HG was unaffected by transfection with antisense against p22(phox). We conclude that in HG, mesangial cell ROS generation by upregulated NADPH oxidase is dependent on conventional PKC isozymes and also required for collagen IV expression.

High glucose-enhanced mesangial cell extracellular signal-regulated protein kinase activation and alpha1(IV) collagen expression in response to endothelin-1: role of specific protein kinase C isozymes.

High glucose (HG) stimulates glomerular mesangial cell (MC) expression of extracellular matrix, a process involving protein kinase C (PKC) isozymes and enhanced signaling by autocrine peptides such as endothelin-1 (ET-1). The purpose of this study was to identify the specific PKC isozymes mediating the effects of HG on MC extracellular signal-regulated protein kinase (ERK1/2) signaling and alpha1(IV) collagen expression in response to ET-1. HG (30 mmol/l for 72 h) enhanced ET-1-stimulated alpha1(IV) collagen mRNA expression from 1.2 +/- 0.1-fold to 1.9 +/- 0.2-fold (P < 0.05 vs. normal glucose [NG] + ET-1), and the effect was significantly reduced by Calphostin C or the MEK (mitogen-activated protein kinase kinase) inhibitor PD98059. In transiently transfected MCs, dominant-negative (DN)-PKC-delta, -epsilon, or -zeta inhibited ET-1 activation of ERK1/2. Likewise, downstream of ERK1/2, ET-1 stimulated Elk-1-driven GAL4 luciferase activity to 11 +/- 1-fold (P < 0.002 vs. NG + ET-1) in HG, and DN-PKC-delta, -epsilon, or -zeta attenuated this response to NG levels. HG enhanced ET-1-stimulated intracellular alpha1(IV) collagen protein expression, assessed by confocal immunofluorescence imaging, showed that individual DN-PKC-delta, -epsilon, -zeta, as well as DN-PKC-alpha and -beta, attenuated the response. Thus, HG-enhanced ET-1 stimulation of alpha1(IV) collagen expression requires PKC-delta, -epsilon, and -zeta to act through an ERK1/2-dependent pathway and via PKC-alpha and -beta, which are independent of ERK1/2.

Extracellular signal-regulated kinase and the small GTP-binding protein p21Rac1 are involved in the regulation of gene transcription by angiotensin II.

To study the role of extracellular-signal-regulated kinase (ERK) cascade and the small GTP-ase proteins in the activation of the c-fos promoter by angiotensin II (AII), transient transfection experiments were performed in CHO cells stably expressing the rat AT(1A) receptor. In this system AII activated ERK in 1 min and also increased the transcriptional activity of the c-fos promoter-luciferase reporter gene construct. The activation of the promoter proved to be dependent on the Ras-Raf-ERK cascade as cotransfection of expression vectors known to specifically inhibit this cascade blocked the effect of AII. Dominant-negative p21Rac1 mutant partially blocked the activation of the c-fos promoter by AII. However, activation of the c-fos promoter was independent of protein kinase C (PKC) as bisindolylmaleimide I, a specific PKC inhibitor did not block the effect of AII. These results suggest that AII activates the transcription of the c-fos through the Ras-Raf-ERK cascade. Furthermore, p21Rac1 is involved in the modulation of the c-fos promoter by AII.

Stretch-induced mesangial cell ERK1/ERK2 activation is enhanced in high glucose by decreased dephosphorylation.

Glomerular hypertension and hyperglycemia are major determinants of diabetic nephropathy. We sought to identify the mechanisms whereby stretch-induced activation of mesangial cell extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) is enhanced in high glucose (HG). Mesangial cells cultured on fibronectin Flex I plates in normal glucose (NG; 5.6 mM) or HG (30 mM), were stretched by 15% elongation at 60 cycles/min for up to 60 min. In HG, a 5-min stretch increased ERK1/ERK2 phosphorylation by 6.4 +/- 0.4/4.3 +/- 0.3-fold (P < 0.05 vs. NG stretch). In contrast, p38 phosphorylation was increased identically by stretch in NG and HG. Unlike many effects of HG, augmentation of ERK activity by HG was not dependent on protein kinase C (PKC) as indicated by downregulation of PKC with 24-h phorbol ester or inhibition with bisindolylmaleimide IV. In both NG and HG, pretreatment with arginine-glycine-aspartic acid peptide (0.5 mg/ml) to inhibit integrin binding or with cytochalasin D (100 ng/ml) to disassemble filamentous (F) actin, significantly reduced phosphorylation of ERK1/ERK2 and p38. To determine whether the rate of mitogen-activated protein kinase dephosphorylation is affected by HG, cellular kinase activity was inhibited by depleting ATP. Post-ATP depletion, phosphorylation of ERK1/ERK2 was reduced to 36 +/- 9/51 +/- 14% vs. 9 +/- 5/7 +/- 6% in NG (P < 0.05, n = 5). Thus stretch-induced ERK1/ERK2 and p38 activation in both NG and HG is beta(1)-integrin and F-actin dependent. Stretch-induced ERK1/ERK2 is enhanced in high glucose by diminished dephosphorylation, suggesting reduced phosphatase activity in the diabetic milieu. Enhanced mesangial cell ERK1/ERK2 signaling in response to the combined effects of mechanical stretch and HG may contribute to the pathogenesis of diabetic nephropathy.

Glucosamine activates the plasminogen activator inhibitor 1 gene promoter through Sp1 DNA binding sites in glomerular mesangial cells.

Increased flux through the hexosamine biosynthetic pathway is associated with altered gene expression. To investigate the underlying mechanisms, we treated glomerular mesangial cells with glucosamine and studied the regulation of the plasminogen activator inhibitor (PAI)-1 gene. Incubating mesangial cells with 2 mmol/l glucosamine for 4 days resulted in a 3.1+/-0.4-fold increase in PAI-1 mRNA levels (P < 0.01) and a 33+/-9-fold increase in the activity of a transiently transfected PAI-1 promoter-luciferase reporter gene (P < 0.01). Cotransfection of an expression vector for a dominant-negative type II TGF-beta receptor with the PAI-1 promoter-reporter gene did not interfere with this effect of glucosamine. However, mutation of 2 putative Sp1 sites in the PAI-1 promoter, at -76 to -71 and -44 to -39, markedly reduced induction of PAI-1 luciferase activity by glucosamine, from 8.9+/-1.9-fold to 1.7+/-0.5-fold (P < 0.01). An electrophoretic mobility shift assay demonstrated that glucosamine increased Sp1 DNA binding by 31+/-11% (P < 0.05), implying that the effects of glucosamine were explained, in part, by changes in Sp1 DNA binding. High glucose (20 mmol/l) also activated the transiently transfected PAI-1 promoter (2.5+/-0.4-fold). This effect was diminished by mutation of both the PAI-1 promoter Sp1 sites (1.2+/-0.3-fold, P < 0.05). In addition, 6-diazo-5-oxo-L-norleucine, a glutamine:fructose-6-phosphate-amidotransferase inhibitor, blocked the induction by high glucose (4.7+/-0.8- to 0.9+/-0.1-fold, P < 0.01). These results indicate that stimulation of the PAI-1 promoter by both high glucose and glucosamine involves Sp1 and that the hexosamine pathway may be involved in the regulation of gene expression by high glucose in glomerular mesangial cells.

"Deathgrip" esophagus: segmental aperistalsis following electrical injury.

We report a case of documented transient segmental aperistalsis of the distal esophagus following an accidental electrical injury. There are no other reports in the literature demonstrating this phenomenon. A review of gastrointestinal injury secondary to electrical injury is presented.

Dominant-negative SMAD-3 interferes with transcriptional activation by multiple agonists.

Smad proteins have recently been identified as mediators of transcriptional activation by members of the transforming growth factor-beta superfamily. To determine if Smads might also be involved in inducing gene transcription in response to other agonists, expression vectors for dominant-negative Smad proteins were constructed. These plasmids were transiently cotransfected with luciferase reporter genes and the effects of various agonists on reporter gene activity evaluated in NIH 3T3 cells. Dominant-negative Smad3, but not other dominant-negative Smads, reduced stimulation of the plasminogen activator inhibitor-1 (PAI-1) and other gene promoters by phorbol ester, cAMP, and platelet-derived growth factor. Activation of the PAI-1 promoter by TGF-beta or prostaglandin F2 alpha, and transactivation by c-Jun or JunB were not inhibited by dominant-negative Smad3, supporting the specificity of this mutant. These results suggest that Smad3, like CREB-binding protein (CBP), may participate in transcriptional activation by multiple agonists.

Extracellular signal-regulated kinase and the small GTP-binding protein, Rac, contribute to the effects of transforming growth factor-beta1 on gene expression.

The kinases and regulatory proteins that convey signals initiated by transforming growth factor-beta (TGF-beta) to the nucleus are poorly characterized. To study the role of the extracellular signal-regulated kinase (ERK) pathway in this process, we transiently transfected NIH 3T3 fibroblasts with TGF-beta-responsive luciferase reporter genes and expression vectors designed to interrupt this kinase cascade. Mitogen-activated protein (MAP) kinase phosphatase-1 and a dominant negative MAP/ERK kinase 1 mutant reduced stimulation of plasminogen activator inhibitor-1 (PAI-1) promoter activity by TGF-beta1 from 11.5- to 4-fold and 4.9-fold, respectively. Similar results were observed with the type I collagen promoters. TGF-beta1 increased ERK1 activity 4.5-fold at 5 min and 3. 1-fold at 3 h, while Jun kinase and p38 activity were not affected. Cotransfection of a dominant negative mutant of the small G protein, Rac, but not dominant negative Ras, Cdc42, or Rho mutants, reduced the effects of TGF-beta1 on the PAI-1 promoter by approximately half. In support of a role for Rac in signaling by TGF-beta, GTP binding to Rac was increased 3.7-fold following exposure of NIH 3T3 cells to TGF-beta1 for 3 min. These findings indicate that TGF-beta1 modulates gene expression partly through ERK and Rac in NIH 3T3 cells.

RAS is required for epidermal growth factor-stimulated arachidonic acid release in rat-1 fibroblasts.

Previous studies have provided suggestive evidence for an interaction between ras activation and signalling pathways involved in agonist-stimulated arachidonic acid release in a variety of cell systems. In order to clarify this interaction, we have measured epidermal growth factor (EGF)-stimulated arachidonic acid release in rat-1 fibroblasts transfected with the N-17 dominant negative mutation of ras. Cells transfected with the N-17 ras mutant, display a markedly attenuated arachidonic acid-release response to EGF, compared to sham-transfected and non-transfected cells. In contrast, the response to phorbol myristate acetate (PMA) was not attenuated in the N-17-mutant expressing cells. No differences were detected between sham-transfected and N-17 mutant expressing cells in levels of immunodetectable EGF receptor, cytosolic phospholipase A2 or mitogen-activated protein (MAP) kinase. Attenuation of EGF-stimulated arachidonic acid release in the N-17 mutant expressing cells, was accompanied by a marked diminution in EGF-stimulated tyrosine phosphorylation of MAP kinase. We conclude that the signalling pathway involved in epidermal growth factor-stimulated arachidonic acid release is similar to the signalling pathway for mitogenic responses to epidermal growth factor and requires ras activation, likely followed by a downstream cascade of kinases eventuating in MAP kinase activation.

Epidermal growth factor and phorbol myristate acetate increase expression of the mRNA for cytosolic phospholipase A2 in glomerular mesangial cells.

We have previously shown that phospholipase A2 (PLA2) activity is rapidly activated by epidermal growth factor (EGF) and phorbol 12-myristate 13-acetate (PMA) in renal mesangial cells and other cell systems in a manner that suggests a covalent modification of the PLA2 enzyme(s). This PLA2 activity is cytosolic (cPLA2) and is distinct from secretory forms of PLA2, which are also stimulated in mesangial cells in response to cytokines and other agonists. However, longer-term regulation of cPLA2 in renal cells may also occur at the level of gene expression. Cultured rat mesangial cells were used as a model system to test the effects of EGF and PMA on the regulation of cPLA2 gene expression. EGF and PMA both produced sustained increases in cPLA2 mRNA levels, with a parallel increase in enzyme activity over time. Inhibition of protein synthesis by cycloheximide increased basal cPLA2 mRNA accumulation in serum-starved mesangial cells, and the combination of EGF and cycloheximide resulted in super-induction of cPLA2 gene expression compared with EGF alone. Actinomycin D treatment entirely abrogated the effect of EGF on cPLA2 mRNA accumulation. These findings suggest that regulation of cPLA2 is achieved by factors controlling gene transcription and possibly mRNA stability, in addition to previously characterized posttranslational modifications.

The tyrosine kinase activity of the epidermal-growth-factor receptor is necessary for phospholipase A2 activation.

We have previously reported that epidermal growth factor (EGF) activates phospholipase A2 (PLA2) independently of phospholipase C (PLC) in renal mesangial cells. In this study we use NIH 3T3 cell lines transfected with the normal EGF receptor (HER14 cells) or with EGF receptor defective in tyrosine kinase activity (K721A cells), to determine whether the intrinsic tyrosine kinase activity of the EGF receptor is required for the PLC-independent activation of PLA2. Intact cells were preincubated with EGF or other ligands, and then PLA2 activity was assayed in cell-free extracts with 1-stearoyl-2-[14C]arachidonyl phosphatidylcholine as the substrate. In HER14 cells, EGF increased PLA2 activity by 226 +/- 30%, and the tumour promoter phorbol myristate acetate (PMA) increased activity by 223 +/- 30%. The effect of EGF was not mediated through protein kinase C (PKC), whose activation by EGF requires tyrosine kinase activity, since raising intracellular Ca2+ alone with the Ca2+ ionophore A23187 did not mimic its effect, and the effect of EGF persisted in PKC-down-regulated cells. In K721A cells EGF was ineffective, whereas PMA was still active. Furthermore, in intact HER14 cells prelabelled with [14C]arachidonate, EGF-stimulated release of [14C]arachidonic acid was synergistic with A23187, but was unaccompanied by a rise in [14C]diacylglycerol. EGF had no effect on [14C]arachidonic acid release in intact K721A cells. We conclude that the tyrosine kinase activity of the EGF receptor is necessary for the PLC-independent stimulation of PLA2 by EGF.