Phosphatidylinositol 3-kinase is required for CD28 but not CD3 regulation of the TEC family tyrosine kinase EMT/ITK/TSK: functional and physical interaction of EMT with phosphatidylinositol 3-kinase

Ligation of the TCR or CD28 induces activation of phosphatidylinositol 3-kinase (PI3K), the TEC family protein tyrosine kinase, EMT/ITK/TSK (EMT), and the SRC family tyrosine kinase, LCK. LCK is required for the activation and phosphorylation of EMT induced by ligation of the TCR or CD28 placing LCK upstream of EMT in T cell signaling cascades. We report herein that inhibition of PI3K activity with the specific inhibitors LY294002 and wortmannin markedly decreased EMT activation induced by CD28 cross-linking but not by CD3 cross-linking. Further, inhibition of PI3K markedly decreased EMT in vitro autokinase activity induced by activated LCK. In contrast, PI3K inhibitors did not alter CD28 or CD3 cross-linking or LCK-induced EMT phosphorylation. Consistent with the requirement of PI3K activity for CD28 but not CD3-induced stimulation of the EMT in vitro autokinase activity, a small but significant portion of cellular EMT associates with PI3K following CD28 cross-linking but not following CD3 cross-linking. CD28-induced association of EMT with PI3K also requires functional expression of LCK. Fusion proteins containing the SRC homology 2 domain of EMT interact with PI3K or a PI3K-associated molecule in a tyrosine phosphorylation-dependent manner. Taken together, the data suggest that EMT is differentially regulated and recruited to different signaling complexes following ligation of CD28 or the TCR complex, perhaps contributing to the disparate roles that EMT appears to play downstream of CD28 and the TCR.

Anti-apoptotic versus pro-apoptotic signal transduction: checkpoints and stop signs along the road to death

The activation of caspases is a final commitment step for apoptosis. It is now evident that signal transduction pathways involving specific protein kinases modulate the apoptotic response. Both pro-apoptotic and anti-apoptotic pathways integrate environmental cues that control the decision to undergo apoptosis. Pro- and anti-apoptotic signal pathways regulate the activation of the caspases. In this review we describe our current understanding of apoptotic signal transduction.

Spontaneous bacterial peritonitis caused by infection with Listeria monocytogenes: a case report and review of the literature

Spontaneous bacterial peritonitis is a frequent and often serious complication of long-standing ascites in the presence of advanced liver disease. Coliform bacteria account for the infection in most cases and are thought to be related to translocation of bacteria from the bowel into the peritoneal cavity. The empiric use of cefotaxime is well established as most of the causative organisms are sensitive to this antibiotic. However, we report on a case of spontaneous bacterial peritonitis in a patient with hepatitis C related cirrhosis who was awaiting liver transplantation caused by infection with Listeria monocytogenes, in which the patient did not improve with empiric antibiotic therapy. This case adds to the 23 others reported in the literature since 1966. Our case raises some concerns about the universal empiric usage of cefotaxime for spontaneous bacterial peritonitis because it does not offer adequate coverage against organisms such as Listeria, enterococci, Pasturella, and anaerobes.

Procorticotrophin-releasing hormone: endoproteolytic processing and differential release of its derived peptides within AtT20 cells

Procorticotrophin-releasing hormone (proCRH) is expressed mainly in the hypothalamus and in the placenta, where it undergoes tissue-specific endoproteolysis. Our results show that within stably transfected AtT20/D16V cells proCRH is cleaved to generate two fragments of approximately 8 and 3 kDa which could account for proCRH(125-194) and proCRH(125-151), respectively, and a 4.5 kDa product which could account for mature IR-CRH(1-41). The immunofluorescence staining patterns for IR-CRH and IR-ACTH and their response of secretagogues indicate targeting of proCRH and POMC to the secretory pathway in transfected AtT20 cells. In this work, we have used a unique set of specific RIAs and IRMAs to the full length POMC and proCRH molecules and several products of endoproteolytic processing to assess if they could be released differentially in response to stimulation. Although the release of both IR-ACTH and IR-CRH peptides from transfected AtT20 cells is stimulated in response to exposure to high potassium stimulation (51 mM KCl/SmM CaCl2), the sorting index (SI) suggests that mature ACTH is sorted to the regulated secretory pathway 2.1-fold more efficiently than mature CRH(1-41). Mature ACTH is also sorted to the regulated secretory pathway 9-fold more efficiently than IR-proCRH(125-151). Also, mature CRH(1-41) is sorted to the regulated secretory pathway 3-fold more efficiently than IR-proCRH(125-151). These results therefore indicate that the intracellular mechanisms for the storage and release of POMC, proCRH and their endoproteolytic products differ and would sustain the hypothesis that within mammalian peptidergic cells, different biologically active peptides originating from the same or different precursor molecules, could be differentially released in response to specific stimuli. This would give these cells the capacity to finely regulate neurotransmitter release in response to environmental and physiological demands.

Volumetric object modeling for surgical simulation

Surgical simulation has many applications in medical education, surgical training, surgical planning and intra-operative assistance. However, extending current surface-based computer graphics methods to model phenomena such as the deformation, cutting, tearing or repairing of soft tissues poses significant challenges for real-time interactions. This paper discusses the use of volumetric methods for modeling complex anatomy and tissue interactions. New techniques are introduced that use volumetric methods for modeling soft-tissue deformation and tissue cutting at interactive rates. An initial prototype for simulating arthroscopic knee surgery is described which uses volumetric models of the knee derived from 3-D magnetic resonance imaging, visual feedback via real-time volume and polygon rendering, and haptic feedback provided by a force-feedback device.

Caspase-dependent cleavage of signaling proteins during apoptosis. A turn-off mechanism for anti-apoptotic signals

Caspases are activated during apoptosis and cleave specific proteins, resulting in the irreversible commitment to cell death. The signal transduction proteins MEKK1, p21-activated kinase 2, and focal adhesion kinase are caspase substrates that contribute to the cell death response when cleaved. Thirty additional signaling proteins were screened for their ability to be cleaved during apoptosis. Twenty-two of these proteins were not affected in Jurkat cells stimulated to undergo apoptosis by Fas ligation, exposure to ultraviolet-C or incubation with etoposide. Ras GTPase-activating protein was found to be a caspase substrate whose cleavage followed the same time course as that for activation of caspase activity and the cleavage of MEKK1 and focal adhesion kinase. Four additional proteins, Cbl, Cbl-b, Raf-1, and Akt-1, were cleaved later in the apoptotic response. These signaling proteins were similarly cleaved in U937 cells undergoing apoptosis. Cleavage of the proteins was blocked by caspase inhibitors in Jurkat cells or in U937 cells expressing BclxL, demonstrating that the cleavage was dependent on caspase activation. Cleavage of Raf-1 and Akt correlated with the loss of extracellular signal-regulated kinase and Akt activities in apoptotic cells. Neither c-Jun N-terminal kinase nor p38 mitogen-activated protein kinase was cleaved in cells undergoing apoptosis, and the activation of the c-Jun N-terminal kinase and p38 mitogen-activated protein kinase pathways was not compromised in apoptotic cells. These results indicate that caspase-dependent cleavage of specific proteins induces the turn off of survival pathways, such as the extracellular signal-regulated kinase and phosphatidylinositol-3 kinase/Akt pathways, that could otherwise interfere with the apoptotic response.

Efficient CD28 signalling leads to increases in the kinase activities of the TEC family tyrosine kinase EMT/ITK/TSK and the SRC family tyrosine kinase LCK

Optimal T cell activation requires crosslinking of the T cell receptor (TCR) concurrently with an accessory receptor, most efficiently CD28. Crosslinking of CD28 leads to increased interleukin 2 (IL2) production, inhibition of anergy and prevention of programmed cell death. Crosslinking of CD28 leads to rapid increases in tyrosine phosphorylation of specific intracellular substrates including CD28 itself. Since CD28 does not encode an intrinsic tyrosine kinase domain, CD28 must activate an intracellular tyrosine kinase(s). Indeed, crosslinking of CD28 increases the activity of the intracellular tyrosine kinases EMT/ITK and LCK. The phosphatidylinositol 3-kinase (PI3K) and GRB2 binding site in CD28 is dispensable for optimal IL2 production in Jurkat T cells. We demonstrate herein that murine Y170 (equivalent to human Y173) in CD28 is also dispensable for activation of the SRC family tyrosine kinase LCK and the TEC family tyrosine kinase EMT/ITK. In contrast, the distal three tyrosines in CD28 are required for optimal IL2 production as well as for optimal activation of the LCK and EMT/ITK tyrosine kinases. The distal three tyrosines of CD28, however, are not required for recruitment of PI3K to CD28. Furthermore, PI3K is recruited to CD28 in JCaM1 cells which lack LCK and in which EMT/ITK is not activated by ligation of CD28. Thus optimal activation of LCK or EMT/ITK is not obligatory for recruitment of PI3K to CD28 and thus is also not required for tyrosine phosphorylation of the YMNM motif in CD28. Taken together the data indicate that the distal three tyrosines in CD28 are integral to the activation of LCK and EMT/ITK and for subsequent IL2 production.

Evaluation of a primary care counselling service in Dorset

BACKGROUND

Research into the effectiveness of counselling in primary care is rare. This study attempts to provide a thorough evaluation of the effects of a new counselling service introduced throughout Dorset.

AIM

To evaluate the impact of counselling on client symptomatology, self-esteem, and quality of life. The effect of counselling on drug prescribing, referrals to other mental health professionals, and client and general practitioner (GP) satisfaction were also assessed.

METHOD

All new clients referred for counselling were asked to complete and return questionnaires before and after counselling. A total of 385 clients took part in the study. The first and second assessments were compared statistically. Clients were ascribed a psychiatric diagnosis using a simplified version of DSM-IIIR (Diagnostic and Statistical Manual of the American Psychiatric Association). GPs' views of the service were determined using a specially designed questionnaire. Drug data were obtained from the Prescription Pricing Authority and referral statistics from Dorset HealthCare National Health Service (NHS) Trust.

RESULTS

The number of psychiatric symptoms and their severity were significantly reduced by counselling. There were no significant differences in the prescription of anxiolytic/hypnotic and anti-depressant medication between matched practices with and without counsellors. The presence of a counsellor did not affect the rate of referral to other mental health professionals. Clients and GPs valued the service highly.

CONCLUSIONS

The Psychology Managed Counselling Service is an effective method of running a counselling service and is well received by both clients and GPs. Counselled clients improved significantly on several measures.

European Multicentre Association Study of Schizophrenia: a study of the DRD2 Ser311Cys and DRD3 Ser9Gly polymorphisms

As part of the European Multicentre Association Study of Schizophrenia (EMASS), we studied polymorphisms in the dopamine DRD2 and DRD3 receptor genes. The EMASS collaboration was established to create a large, statistically powerful sample of schizophrenic patients and controls from different European centres. Previous studies have suggested associations between schizophrenia and the Ser311Cys polymorphism in exon 7 of the dopamine DRD2 receptor gene [Arinami et al., (1994): Lancet 343:703-704] and a polymorphism Ser9gly in exon 1 of the dopamine DRD3 receptor gene [Crocq et al. (1992): J Med Genet 29:858-860]. We tested for these associations in samples of 373 and 413, and 311 and 306 patients and controls, respectively. We found no evidence for allelic association between schizophrenia and the Cys311 variant of the DRD2 receptor gene and no homozygotes for this variant were observed by any group. However, an excess of homozygotes for both alleles of the DRD3 polymorphism was observed in schizophrenic patients (chi2 = 8.54, P = 0.003, odds ratio = 1.64, 95% CI = 1.18-2.29). We also observed a significant excess of the 1-1 (Ser9Ser) genotype (chi2 = 8.13, P = 0.004, odds ratio = 1.7, 95% CI = 1.18-2.4). No evidence of heterogeneity between samples was detected and there was no evidence of an allelic association. These findings suggest that the rare Cys311 variant in exon 7 of the DRD2 receptor gene does not play a role in the pathogenesis of schizophrenia in European populations. Currently, our results do support the previous findings of an association between increased homozygosity of the Ser/Gly variant of the Dopamine D3 receptor gene and schizophrenia.

Infected cardiac pacemaker wires demonstrated by Tc-99m labeled white blood cell scintigraphy

Multiple cardiac pacing wires present a potential source of thrombosis and infection within veins and cardiac chambers. A case is presented where persistent infection involved thrombus on cardiac pacing wires in and around the right subclavian and brachiocephalic veins, which proved difficult to localize and treat. Early Ga-67 and Tc-99m labeled white blood cell imaging were negative but, when the latter test was repeated after 5 weeks, the septic focus was identified. Treatment with antibiotic therapy combined with surgical removal of the infected thrombus and both pacing wires was effective in eradicating infection. Failure to demonstrate an infection focus early in the course of the illness may have related to the size of the infection focus; however, in a later phase of the illness, Tc-99m labeled white blood cell imaging proved helpful in localizing focal infection associated with pacemaker wires.

The SH3 domain of Itk/Emt binds to proline-rich sequences in the cytoplasmic domain of the T cell costimulatory receptor CD28

Engagement of the transmembrane receptor CD28 potentiates T cell survival, proliferation, and activation. The biochemical basis by which CD28 controls these outcomes is unclear, although early events following cross-linking of the receptor are characterized by tyrosine phosphorylation of CD28 and other cellular substrates. We demonstrate that following CD28 ligation, a CD28-associated tyrosine kinase activity is increased in parallel to activation of the T cell-specific tyrosine kinase Itk (Itk/Emt), while Lck and Fyn kinase activities are not increased. We show that Itk forms an inducible complex with CD28, mediated by the SH3 domain of Itk and the diproline motifs of CD28. Site-directed mutagenesis of the N-terminal diproline motif of CD28 abrogates the association of CD28 with the SH3 domain of Itk, while mutations within the C-terminal diproline motif have little effect. Peptides corresponding to the N-terminal diproline motif were more efficient at abrogating the interaction between CD28 and the SH3 domain of Itk, than peptides corresponding to the C-terminal diproline motif. In addition, peptides corresponding to the N-terminal diproline motif of CD28 activated the tyrosine kinase activity of Itk to levels similar to those observed following Ab-mediated cross-linking of CD28. Together, our data show that the SH3 domain of Itk binds to a proline-rich motif within the cytoplasmic tail of CD28, and define a mechanism by which CD28 couples to and activates a downstream tyrosine kinase.

The SH3 domain of Itk/Emt binds to proline-rich sequences in the cytoplasmic domain of the T cell costimulatory receptor CD28

Engagement of the transmembrane receptor CD28 potentiates T cell survival, proliferation, and activation. The biochemical basis by which CD28 controls these outcomes is unclear, although early events following cross-linking of the receptor are characterized by tyrosine phosphorylation of CD28 and other cellular substrates. We demonstrate that following CD28 ligation, a CD28-associated tyrosine kinase activity is increased in parallel to activation of the T cell-specific tyrosine kinase Itk (Itk/Emt), while Lck and Fyn kinase activities are not increased. We show that Itk forms an inducible complex with CD28, mediated by the SH3 domain of Itk and the diproline motifs of CD28. Site-directed mutagenesis of the N-terminal diproline motif of CD28 abrogates the association of CD28 with the SH3 domain of Itk, while mutations within the C-terminal diproline motif have little effect. Peptides corresponding to the N-terminal diproline motif were more efficient at abrogating the interaction between CD28 and the SH3 domain of Itk, than peptides corresponding to the C-terminal diproline motif. In addition, peptides corresponding to the N-terminal diproline motif of CD28 activated the tyrosine kinase activity of Itk to levels similar to those observed following Ab-mediated cross-linking of CD28. Together, our data show that the SH3 domain of Itk binds to a proline-rich motif within the cytoplasmic tail of CD28, and define a mechanism by which CD28 couples to and activates a downstream tyrosine kinase.

Nuclear accumulation of Saccharomyces cerevisiae Mcm3 is dependent on its nuclear localization sequence

BACKGROUND

The proteins of the Mcm2-7 family are required for the initiation of DNA replication. In Saccharomyces cerevisiae the nuclear envelope does not break down during the mitotic phase of the cell cycle. Large nuclear proteins, such as the Mcm proteins, which accumulate in the nucleus during specific portions of the cell cycle, must have regulated mechanisms to direct their entry into the nucleus.

RESULTS

We have identified a nuclear localization sequence (NLS) in Mcm3, and demonstrated that it is necessary for the translocation of Mcm3 into the nucleus and sufficient for directing Escherichia coli beta-galactosidase to the nucleus. Immediately adjacent to the nuclear localization sequence are four potential sites for phosphorylation by Cdc28. Mutagenesis of all four sites has no immediate phenotypic effect on cell growth or viability, nor does it affect nuclear accumulation of Mcm3, although two-dimensional protein gel analysis has shown that at least some of these sites are normally phosphorylated in vivo. Substitution of the Mcm3 NLS by the SV40 large T-antigen NLS also directs the nuclear accumulation of the Mcm3-T-antigen protein, although cell growth is compromised. Replication activity in cells bearing either the Mcm3-Cdc28 phosphorylation site mutations or the Mcm3 T-antigen NLS substitution, as measured by plasmid stability assays, is comparable to activity in wild-type cells.

CONCLUSIONS

The Mcm3 protein is imported into the nucleus by a specific NLS. The cell cycle specific nuclear accumulation of Mcm3 appears to be a result of nuclear retention or nuclear targeting, rather than nuclear import regulated through the NLS.

Lysophosphatidylcholine stimulates activator protein 1 and the c-Jun N-terminal kinase activity

Lysophosphatidylcholine (lyso-PC), a natural lipid generated through the action of phospholipase A2 on membrane phosphatidylcholine, has been implicated in atherogenesis and the inflammatory process. In vitro studies have established a role for lyso-PC in modulation of gene expression and other cellular responses including differentiation and proliferation. There is also evidence that lyso-PC may act as an intracellular second messenger transducing signals elicited from membrane-associated receptors. The mechanisms behind the diverse activities of lyso-PC are poorly understood. We report, in this study, that treatment of cultured cells with exogenous lyso-PC, at nontoxic concentrations, potently induced activator protein-1 (AP-1) DNA binding and transcriptional activity independent of well known AP-1 activators, protein kinase C or mitogen-activated protein kinases ERK1 and ERK2. Lyso-PC also activated the c-Jun N-terminal kinase (JNK/SAPK), a recently characterized member of the mitogen-activated protein kinase family, known to activate AP-1. The stimulated JNK and AP-1 activities probably mediate or contribute to some bioactive effects of lyso-PC.

Principal components describing biological activities and molecular diversity of heterocyclic aromatic ring fragments

Ten physicochemical variables have been calculated for each of 100 different aromatic rings. These variables were selected because of their potential involvement in the molecular recognition of drug-receptor binding interactions, and they include size, lipophilicity, dipole magnitude and orientation, HOMO and LUMO energies, and electronic point charges. A total of 59 different aromatic ring systems were studied including monocyclics and [5.5]-, [6.5]- and [6.6]-fused bicyclics. A principal components analysis of b1ese results generated four principal components which account for 84% of the total variance in the data. These principal components provide a quantitative measure of molecular diversity, and their relevance for structure-activity relationships is discussed. The principal components correlate with the in vitro biological activity of heterocyclic aromatic fragments within a series of previously reported HIV-1 reverse transcriptase inhibitors.

The EMT/ITK/TSK (EMT) tyrosine kinase is activated during TCR signaling: LCK is required for optimal activation of EMT

Functional T lymphocyte activation requires concurrent stimulation of the TCR complex and an accessory molecule, most frequently CD28. We have previously demonstrated that the TEC family tyrosine kinase EMT/ITK/TSK (EMT) is activated following cross-linking of CD28. We demonstrate herein that cross-linking of the CD3 component of the TCR complex also leads to EMT activation as indicated by a rapid and transient increase in EMT tyrosine phosphorylation and kinase activity in anti-EMT immunoprecipitates. However, although concurrent cross-linking of the TCR and CD28 results in a marked increase in production of the T cell growth factor IL-2, it does not result in a significant alteration in the magnitude or duration of EMT activation. Somatic cell mutants of the Jurkat T cell line, which lack the SRC family kinase LCK (JCaM1.6), fail to produce IL-2 when stimulated through the TCR complex. EMT activation, as evidenced by increased EMT tyrosine phosphorylation and EMT-associated kinase activity, was also greatly reduced following stimulation of the TCR in the JCaM1.6 Jurkat T cell mutants that lack LCK. In support of a role for LCK in EMT activation, reconstitution of the LCK-negative Jurkat T cell line by enforced expression of LCK restored TCR-mediated EMT activation. Taken together, the data indicate that the EMT tyrosine kinase is activated following cross-linking of the TCR, a process in which LCK likely plays an important role.

The EMT/ITK/TSK (EMT) tyrosine kinase is activated during TCR signaling: LCK is required for optimal activation of EMT

Functional T lymphocyte activation requires concurrent stimulation of the TCR complex and an accessory molecule, most frequently CD28. We have previously demonstrated that the TEC family tyrosine kinase EMT/ITK/TSK (EMT) is activated following cross-linking of CD28. We demonstrate herein that cross-linking of the CD3 component of the TCR complex also leads to EMT activation as indicated by a rapid and transient increase in EMT tyrosine phosphorylation and kinase activity in anti-EMT immunoprecipitates. However, although concurrent cross-linking of the TCR and CD28 results in a marked increase in production of the T cell growth factor IL-2, it does not result in a significant alteration in the magnitude or duration of EMT activation. Somatic cell mutants of the Jurkat T cell line, which lack the SRC family kinase LCK (JCaM1.6), fail to produce IL-2 when stimulated through the TCR complex. EMT activation, as evidenced by increased EMT tyrosine phosphorylation and EMT-associated kinase activity, was also greatly reduced following stimulation of the TCR in the JCaM1.6 Jurkat T cell mutants that lack LCK. In support of a role for LCK in EMT activation, reconstitution of the LCK-negative Jurkat T cell line by enforced expression of LCK restored TCR-mediated EMT activation. Taken together, the data indicate that the EMT tyrosine kinase is activated following cross-linking of the TCR, a process in which LCK likely plays an important role.

Functional LCK Is required for optimal CD28-mediated activation of the TEC family tyrosine kinase EMT/ITK

Activation of CD28 on T lymphocytes initiates a cascade of intracellular events, which in concert with activation of the T cell receptor, culminates in production of cytokines and a functional immune response. One of the earliest biochemical changes observed following stimulation of CD28 is tyrosine phosphorylation. We have demonstrated that both the LCK and the EMT/ITK/TSK (EMT) intracellular tyrosine kinases are activated following cross-linking of CD28. Utilizing somatic cell mutants lacking LCK, we demonstrate that functional LCK is required for CD28-induced activation of EMT as evidenced by increased tyrosine phosphorylation and kinase activity. In support of a role for LCK in EMT activation, reconstitution of a LCK-negative Jurkat T cell line by transfection with normal LCK recreates CD28-mediated EMT activation. Furthermore, co-transfection of LCK and EMT into COS-7 cells showed that EMT becomes phosphorylated in the presence of LCK. In addition, increases in EMT association with CD28 were eliminated in a LCK-negative Jurkat cell line, but were restored following transfection of wild type LCK. The data are most compatible with a model in which LCK, either directly or indirectly, initiates EMT activation and association with CD28 following ligation of CD28.

Synthesis and muscarinic activities of 3-(pyrazolyl)-1,2,5,6-tetrahydropyridine derivatives

A series of 3-(pyrazolyl)-1,2,5,6-tetrahydropyridine derivatives (B) was synthesized and tested for muscarinic activity in receptor binding assays using [3H]-oxotremorine-M (3H-OXO-M) and [3H]-pirenzepine (3H-PZ) as ligands. Potential muscarinic agonistic or antagonistic properties of the compounds were determined using binding studies measuring their potencies to inhibit the binding of 3H-OXO-M and 3H-PZ. Preferential inhibition of 3H-OXO-M binding was used as an indicator for potential muscarinic agonistic properties; this potential was confirmed in functional studies on isolated organs. All compounds with agonistic properties showed 3H-PZ/3H-OXO-M potency ratios in excess of 20. In contrast, for antagonists this ratio was found to be close to unity. Mono-halogenation resulted in compounds (4b and 4d) with M3 agonistic properties as shown by their atropine sensitive stimulant properties in the guinea pig ileum, but with very little or no M1 activity. Some minor in vivo effects were observed for both these compounds, with the iodinated compound 4d inducing salivation. Compound 4d also showed some positive mnemonic properties in rats where spatial short-term memory had been compromised by temporary cholinergic depletion. These data indicate that some M3 agonism may be desired in therapeutic agents aimed at the treatment of the cognitive deficits of Alzheimer's disease patients.

Impaired processing of proopiomelanocortin in corticotroph macroadenomas

The regulation and secretion of the ACTH precursors POMC and pro-ACTH were assessed directly using a 2-site immunoradiometric assay in six patients with pituitary macroadenomas (> or = 1.2 cm in diameter) and 27 patients with Cushing's disease due to a microadenoma. ACTH precursor levels were elevated in patients with macroadenomas (150-3690 pmol/L; normal range, < 5-40 pmol/L) and significantly higher than those in microadenoma patients (median, 29 pmol/L; range, 9-104 pmol/L; P < 0.001). Patients with macroadenomas also had increased ACTH precursor/ACTH ratios (15-181:1) compared with microadenoma patients (median, 5:1, range, 0.7-18.5:1; P < 0.001). ACTH precursors were unresponsive to high dose dexamethasone in patients with macroadenomas, whereas ACTH and cortisol responses varied. After CRH administration, ACTH precursors were unchanged, whereas cortisol increased significantly, suggesting the release of biologically active ACTH. This study clearly demonstrates reduced processing of POMC to ACTH in large pituitary tumors, a characteristic usually associated with tumors causing the ectopic ACTH syndrome, and provides evidence for differential regulation of ACTH precursors and ACTH by glucocorticoid and CRH. Variation in the clinical symptoms of patients with corticotroph macroadenomas may be attributable to differences in biological potency between the ACTH precursors and ACTH.