Long-Term Efficacy and Safety of Cyclosporine in a Cohort of Steroid-Refractory Acute Severe Ulcerative Colitis Patients from the ENEIDA Registry (1989-2013): A Nationwide Multicenter Study.

OBJECTIVES: To determine the efficacy and safety of cyclosporine (CyA) in a large national registry-based population of patients with steroid-refractory (SR) acute severe ulcerative colitis (ASUC) and to establish predictors of efficacy and adverse events. METHODS: Multicenter study of SR-ASUC treated with CyA, based on data from the ENEIDA registry. SR-ASUC patients treated with infliximab (IFX) or sequential rescue therapy (CyA-IFX or IFX-CyA) were used as comparators. RESULTS: Of 740 SR-ASUC patients, 377 received CyA, 131 IFX and 63 sequential rescue therapy. The cumulative colectomy rate was higher in the CyA (24.1%) and sequential therapy (32.7%) than in the IFX group (14.5%; P=0.01) at 3 months and 5 years. There were no differences in early and late colectomy between CyA and IFX in patients treated after 2005. 62% of patients receiving CyA remained colectomy-free in the long term (median 71 months). There were no differences in mortality between CyA (2.4%), IFX (1.5%) and sequential therapy (0%; P=0.771). The proportion of patients with serious adverse events (SAEs) was lower in CyA (15.4%) than in IFX treated patients (26.5%) or sequential therapy (33.4%; P<0.001). This difference in favor of CyA was maintained when only patients treated after 2005 were analyzed. CONCLUSIONS: Treatment with CyA showed a lower rate of SAE and a similar efficacy to that of IFX thereby supporting the use of either CyA or IFX in SR-ASUC. In addition, the risk-benefit of sequential CyA-IFX for CyA non-responders is acceptable.

Disease severity in familial cases of IBD.

BACKGROUND: Phenotypic traits of familial IBD relative to sporadic cases are controversial, probably related to limited statistical power of published evidence. AIM: To know if there are phenotype differences between familial and sporadic IBD, evaluating the prospective Spanish registry (ENEIDA) with 11,983 cases. METHODS: 5783 patients (48.3%) had ulcerative colitis (UC) and 6200 (51.7%) Crohn's disease (CD). Cases with one or more 1st, 2nd or 3rd degree relatives affected by UC/CD were defined as familial case. RESULTS: In UC and CD, familial cases compared with sporadic cases had an earlier disease onset (UC: 33 years [IQR 25-44] vs 37 years [IQR 27-49]; p<0.0001); (CD: 27 years [IQR 21-35] vs 29 years [IQR 22-40]; p<0.0001), higher prevalence of extraintestinal immune-related manifestations (EIMs) (UC: 17.2% vs 14%; p=0.04); (CD: 30.1% vs 23.6%; p<0.0001). Familial CD had higher percentage of ileocolic location (42.7% vs 51.8%; p=0.0001), penetrating behavior (21% vs 17.6%; p=0.01) and perianal disease (32% vs 27.1%; p=0.003). Differences are not influenced by degree of consanguinity. CONCLUSION: When a sufficiently powered cohort is evaluated, familial aggregation in IBD is associated to an earlier disease onset, more EIMs and more severe phenotype in CD. This feature should be taken into account at establishing predictors of disease course.

Comparison of the long-term outcome of two therapeutic strategies for the management of abdominal abscess complicating Crohn's disease: percutaneous drainage or immediate surgical treatment.

AIM: The management of abdominal abscesses complicating Crohn's disease is complex and involves a difficult choice between medical, radiological and surgical procedures. The long-term outcome was compared for two strategies for the management of abdominal abscess: percutaneous drainage (PD) followed by rescue surgery in the case of failure vs direct immediate surgery (IS). We also compared the results of IS with surgery performed after PD failure. METHODS: We retrospectively identified 44 patients with Crohn's disease with an abdominal abscess from January 2000 to December 2009. Therapeutic success was defined as abscess resolution and no reappearance within 1 year of follow-up. RESULTS: The first therapeutic approach was PD in 22 cases and IS in the other 22 cases. IS had a higher therapeutic success rate than PD (95.5% vs 27.2% respectively; P < 0.001). PD was the only independent variable related to treatment failure in the multivariate analysis after adjustment for possible confounders such as abscess size, multilocularity, presence of fistula and corticosteroid use (OR 88.26, 95% CI 7.38-1055.36; P < 0.001). Surgery after failure of PD (n = 16) was associated with longer total hospitalization (56.12 ± 35.89 vs 27.52 ± 15.11 days; P = 0.017) and longer postoperative stay (44.0 ± 83.7 vs 14.3 ± 30 days; P = 0.179) and needed a second operation more often (5/16, 31% vs 1/22, 4.5%; P = 0.065) than IS. CONCLUSIONS: Percutaneous drainage provided durable abscess resolution in only one-third of the patients compared with more than 90% of those treated with IS. In addition, surgery performed after PD failure results in a poorer outcome than IS.

Smoking does influence disease behaviour and impacts the need for therapy in Crohn's disease in the biologic era.

BACKGROUND: Recently, the notion that smoking may adversely affect Crohn's disease (CD) outcomes has been challenged by the suggestion that the widespread use of immunosuppressants and anti-TNF drugs might offset the adverse effects of tobacco. AIM: To reassess the influence of tobacco smoking on disease phenotype and complications on a time-dependent analysis, taking into account the different therapeutic interventions. METHODS: We designed a retrospective cohort study of 3224 patients with Crohn's disease. The data were collected from the Spanish national inflammatory bowel disease registry (ENEIDA), including information regarding demographics, clinical characteristics, disease complications, therapeutic interventions and smoking status. Patients were classified as nonsmokers, smokers and former smokers, according to their present and past smoking habits. RESULTS: In the univariate analysis, smokers had more strictures (22.6% vs. 19.3%, P < 0.05) and less colonic involvement (7.2% vs. 10.9%, P < 0.05), and were more frequently under treatment with steroids (91.6% vs. 85.8%, P < 0.05), immunosuppressants (73.5% vs. 63.6% P < 0.05) or anti-TNF drugs (31.4% vs. 25.1%, P < 0.05) than nonsmokers. In the time-dependent multivariate analysis, smokers were found to have a significantly decreased survival free of stricturing disease (HR: 1.5, CI 95% 1.18-1.90) or perianal complications (HR: 1.50, CI 95% 1.01-1.46), and had a higher risk for requiring thiopurine therapy (HR: 1.20, CI 95% 1.05-1.30). CONCLUSION: These results suggest that, despite the widespread use of immunosuppressants and anti-TNF drugs, smokers with Crohn's disease still have a more severe disease course, with increased therapeutic requirements when compared with nonsmokers.

Long-term durability of response to adalimumab in Crohn's disease.

BACKGROUND: Adalimumab is an effective treatment for Crohn's disease (CD), but may also be associated with loss of response. Few reports provide insight into the durability of treatment of CD with adalimumab for periods longer than 12 months in clinical practice. AIMS: To evaluate the long-term durability of adalimumab maintenance treatment and to identify predictive factors associated with loss of response. METHODS: CD patients who initially responded to adalimumab were evaluated in a historical cohort study. Maintenance of long-term response was estimated using Kaplan-Meier analysis. Cox regression analysis was performed to identify potential predictive factors for loss of efficacy. RESULTS: In all, 380 CD patients were included (mean age, 38 years; 52% female). Of these, 43% had ileocolic CD, 50% inflammatory CD, and 41% perianal CD. Median follow-up with adalimumab was 8 months (range, 4-75 months). The annual risk of loss of response to adalimumab was 18% per patient-year of follow-up. Twenty-eight percent of patients were anti-TNF-naïve and 72% anti-TNF-experienced. The loss of efficacy was 8% per patient-year of follow-up in the anti-TNF-naïve patients and 22% in the anti-TNF-experienced group (P < 0.01). In the multivariate analysis, the presence of extraintestinal manifestations (hazard ratio [HR] = 1.7; 95% confidence interval [CI] = 1.02-2.9) and previous experience with other anti-TNF agents (HR = 2.5,95% CI = 1.2-5.3) were associated with higher risk of loss of efficacy. CONCLUSIONS: A relevant proportion of CD patients on long-term adalimumab lost response. The risk of loss of response was higher (more than 2-fold) in anti-TNF-experienced than in anti-TNF-naïve patients (22% vs. 8% per patient-year of treatment). Having extraintestinal manifestations seems to increase the risk of loss of efficacy.

Implantes en pacientes VIH-positivo. A propósito de tres casos / Dental implants in HIV-positive patients. A presentation of three cases

El aumento de la calidad y la esperanza de vida de los pacientes VIH-positivo, ha hecho que la solicitud de tratamiento estético dental se haya incrementado significativamente en estos pacientes, considerándose actualmente las prótesis implanto soportadas como una opción terapéutica válida. Se presentan 3 pacientes varones, VIH-positivo que acudieron a nuestro Servicio de Implantología Bucofacial, para valorar una posible rehabilitación implanto soportada. La evolución clínica de los pacientes había sido estable durante un periodo mínimo de 4 años. Se colocaron un total de 12 implantes (caso1: 4 implantes Defcon®, 2 en maxilar superior y 2 en mandíbula; caso 2: 2 implantes ITI® en mandíbula; caso 3: 6 implantes Brånemark System® en maxilar superior), todos ellos bajo anestesia lo corregional y siguiendo la técnica habitual. No se llevó a cabo ningún tipo de técnica de regeneración ósea guiada. No se presentaron complicaciones intra y/o postoperatorias. Tampoco se produjo ninguna alteración de los parámetros biológicos de control de la enfermedad de base tras la intervención quirúrgica. Los implantes han sido considerados como una opción de tratamiento en este tipo de pacientes pese a que su fiabilidad, no ha sido todavía establecida a largo plazo. A excepción de dos artículos (implante unitario inmediato y una rehabilitación bucal completa), ningún otro estudio ha sido publicado referente a la rehabilitación con implantes en pacientes VIH-positivo. En ambos artículos se corrobora la hipótesis que la cirugía bucal menor no aumenta el riesgo de infección loc orregional en los pacientes VIH-positivo correctamente controlados, como evidenciamos en nuestros 3 casos. En el postoperatorio inmediato, no se observó ninguna disminución significativa del marcador CD4 ni de ningún otro parámetro biológico, tal como se describe en la literatura, obteniéndose una excelente curación de los tejidos blandos y duros (AU)

The improvement in survival and quality of life of HIV-positive patients has led to a significant rise in demand for esthetic dental treatment among these patients. In this context, implant-supported prostheses are currently considered a valid treatment option. We present three HIV-positive males seen in our Service of Oral Implantology for the evaluation of possible implant-supported rehabilitation. The clinical course of the patients had remained stable for a minimum of four years. A total of 12 implants were positioned (case 1: 4 Defcon® implants, 2 in the upper maxilla and 2 in the mandible; case 2: 2 ITI® implants in the mandible; and case 3: 6 Brånemark System® implants in the upper maxilla;), all under locoregional anesthesia and applying the usual technique. No guided bone regeneration procedures were applied. There were no intra and/or postoperative complications, and no alterations in the biological parameters of background disease control following the surgical intervention. Implants have been considered a treatment option in patients of this kind, despite the fact that their long-term reliability has not been established. With the exception of two articles (respectively involving immediate singe implant placement and complete oral rehabilitation), no other study has been published on rehabilitation with implants in HIV-positive patients. Both of these articles corroborate the hypothesis that minor oral surgery does not increase the risk of locoregional infection in correctly controlled HIV-positive patients, as reflected in our three cases. In the immediate postoperative period, there were no significant variations in CD4+ cell count or in any other biological parameter, as described in the literature, with excellent soft and hard tissue healing (AU)

Anti-inflammatory effects of pancreatitis associated protein in inflammatory bowel disease.

BACKGROUND AND AIMS: Increased pancreatitis associated protein (PAP) mRNA has been reported in active inflammatory bowel disease (IBD). The aims of the current study were to characterise PAP production in IBD and the effects of PAP on inflammation. PATIENTS AND METHODS: Serum PAP levels were determined in healthy controls (n = 29), inflammatory controls (n = 14), and IBD patients (n = 171). Ex vivo PAP secretion in intestinal tissue was measured in 56 IBD patients and 13 healthy controls. Cellular origin of PAP was determined by immunohistochemistry. The effects of exogenous PAP on nuclear factor kappaB (NFkappaB) activation, proinflammatory cytokine production, and endothelial adhesion molecule expression were also analysed ex vivo. RESULTS: Patients with active IBD had increased serum PAP levels compared with controls, and these levels correlated with clinical and endoscopic disease severity. Ex vivo intestinal PAP synthesis was increased in active IBD and correlated with endoscopic and histological severity of inflammatory lesions. PAP localised to colonic Paneth cells. Incubation of mucosa from active Crohn's disease with PAP dose dependently reduced proinflammatory cytokines secretion. PAP prevented TNF-alpha induced NFkappaB activation in monocytic, epithelial, and endothelial cells and reduced proinflammatory cytokine mRNA levels and adhesion molecule expression. CONCLUSIONS: PAP is synthesised by Paneth cells and is overexpressed in colonic tissue of active IBD. PAP inhibits NFkappaB activation and downregulates cytokine production and adhesion molecule expression in inflamed tissue. It may represent an anti-inflammatory mechanism and new therapeutic strategy in IBD.

Functional analysis of MCCA and MCCB mutations causing methylcrotonylglycinuria.

Methylcrotonylglycinuria (MCG; MIM 210200) is an autosomal recessive inherited human disorder caused by the deficiency of 3-methylcrotonyl-CoA carboxylase (MCC, E.C.6.4.1.4), involved in leucine catabolism. This mitochondrial enzyme is one of the four biotin-dependent carboxylases known in humans. MCC is composed of two different types of subunits, alpha and beta, encoded by the nuclear genes MCCA and MCCB, respectively, recently cloned and characterized. Several mutations have been identified, in both genes, the majority are missense mutations along with splicing mutations and small insertions/deletions. We have expressed four missense mutations, two MCCA and two MCCB mapping to highly evolutionarily conserved residues, by transient transfection of SV40-transformed deficient fibroblasts in order to confirm their pathogenic effect. All the missense mutations expressed resulted in null or severely diminished MCC activity providing direct evidence that they are disease-causing ones. The MCCA mutations have been analysed in the context of three-dimensional structural information modelling the changes in the crystallized biotin carboxylase subunit of the Escherichia coli acetyl-CoA carboxylase. The apparent severity of all the MCC mutations contrasts with the variety of the clinical phenotypes suggesting that there are other cellular and metabolic unknown factors that affect the resulting phenotype.

Nuevas dianas terapéuticas en la enfermedad inflamatoria intestinal: moléculas de adhesión / New therapeutic targets in Inflammatory Bowel Disease (IBD): cell adhesion molecules

El reclutamiento de leucocitos hacia las áreas de inflamación es un proceso finamente regulado que tiene importantes implicaciones en la patogenia, diagnóstico y tratamiento de la enfermedad inflamatoria intestinal. La expresión de moléculas de adhesión, incluyendo selectinas y miembros de la superfamilia de las inmunoglobulinas, se halla aumentada en la microcirculación de los pacientes con enfermedad inflamatoria intestinal activa. La detección de este aumento en la expresión de moléculas de adhesión endoteliales puede utilizarse para localizar áreas que presentan inflamación activa mediante técnicas de imaten. Los fármacos que modulan la expresión o función de las moléculas de adhesión implicadas en el reclutamiento de leucocitos hacia el intestino inflamado son eficaces para el tratamiento de la enfermedad inflamatoria intestinal. Estudios experimentales han demostrado que la inmunoneutralización de VLA-4, VCAM-1 o P-selectina produce una mejoría de las lesiones inflamatorias en diversos modelos de colitis. La inmunoneutralización de VLA-4 resulta muy eficaz en el tratamiento de la enfermedad de Crohn humana, logrando unas tasas de respuesta y remisión similares a las obtenidas con la utilización de anticuerpos anti-factor de necrosis tumoral alfa (AU)

A fungal perspective on human inborn errors of metabolism: alkaptonuria and beyond.

Crucial for the establishment and development of biochemical genetics as a self-standing discipline was Beadle and Tatum's choice of Neurospora crassa as experimental organism some 60 years ago. Although Garrod's insights on biochemical genetics and his astonishingly modern concepts of biochemical individuality and susceptibility to disease had been ignored by their contemporaries, Beadle acknowledged on several occasions how close Garrod had come to the "one-gene-one-enzyme" hypothesis. In an unexpected turn of events, several genes involved in human inborn errors of metabolism, including the gene for Garrod's favorite disease, alkaptonuria, have been characterized by exploitation of the experimental advantages of another mold, Aspergillus nidulans, which shares with N. crassa the experimental advantages that prompted pioneers of biochemical genetics to use them: rapid growth, facile genetic manipulation, and an environment (the composition of the growth medium) that can be manipulated à la carte.

Reduced function of a phenylacetate-oxidizing cytochrome p450 caused strong genetic improvement in early phylogeny of penicillin-producing strains.

The single-copy pahA gene from Penicillium chrysogenum encodes a phenylacetate 2-hydroxylase that catalyzes the first step of phenylacetate catabolism, an oxidative route that decreases the precursor availability for penicillin G biosynthesis. PahA protein is homologous to cytochrome P450 monooxygenases involved in the detoxification of xenobiotic compounds, with 84% identity to the Aspergillus nidulans homologue PhacA. Expression level of pahA displays an inverse correlation with the penicillin productivity of the strain and is subject to induction by phenylacetic acid. Gene expression studies have revealed a reduced oxidative activity of the protein encoded by pahA genes from penicillin-overproducing strains of P. chrysogenum compared to the activity conferred by phacA of A. nidulans. Sequencing and expression of wild-type pahA from P. chrysogenum NRRL 1951 revealed that an L181F mutation was responsible for the reduced function in present industrial strains. The mutation has been tracked down to Wisconsin 49-133, a mutant obtained at the Department of Botany of the University of Wisconsin in 1949, at the beginning of the development of the Wisconsin family of strains.

The molecular basis of 3-methylcrotonylglycinuria, a disorder of leucine catabolism.

3-Methylcrotonylglycinuria is an inborn error of leucine catabolism and has a recessive pattern of inheritance that results from the deficiency of 3-methylcrotonyl-CoA carboxylase (MCC). The introduction of tandem mass spectrometry in newborn screening has revealed an unexpectedly high incidence of this disorder, which, in certain areas, appears to be the most frequent organic aciduria. MCC, an heteromeric enzyme consisting of alpha (biotin-containing) and beta subunits, is the only one of the four biotin-dependent carboxylases known in humans that has genes that have not yet been characterized, precluding molecular studies of this disease. Here we report the characterization, at the genomic level and at the cDNA level, of both the MCCA gene and the MCCB gene, encoding the MCC alpha and MCC beta subunits, respectively. The 19-exon MCCA gene maps to 3q25-27 and encodes a 725-residue protein with a biotin attachment site; the 17-exon MCCB gene maps to 5q12-q13 and encodes a 563-residue polypeptide. We show that disease-causing mutations can be classified into two complementation groups, denoted "CGA" and "CGB." We detected two MCCA missense mutations in CGA patients, one of which leads to absence of biotinylated MCC alpha. Two MCCB missense mutations and one splicing defect mutation leading to early MCC beta truncation were found in CGB patients. A fourth MCCB mutation also leading to early MCC beta truncation was found in two nonclassified patients. A fungal model carrying an mccA null allele has been constructed and was used to demonstrate, in vivo, the involvement of MCC in leucine catabolism. These results establish that 3-methylcrotonylglycinuria results from loss-of-function mutations in the genes encoding the alpha and beta subunits of MCC and complete the genetic characterization of the four human biotin-dependent carboxylases.

Structural and functional analysis of mutations in alkaptonuria.

Alkaptonuria (AKU), the prototypic inborn error of metabolism, was the first human disease to be interpreted as a Mendelian trait by Garrod and Bateson at the beginning of last century. AKU results from impaired function of homogentisate dioxygenase (HGO), an enzyme required for the catabolism of phenylalanine and tyrosine. With the novel 7 AKU and 22 fungal mutations reported here, a total of 84 mutations impairing this enzyme have been found in the HGO gene from humans and model organisms. Forty-three of these mutations result in single amino acid substitutions. This mutational information is analysed here in the context of the HGO structure and function using kinetic assays performed using purified AKU mutant enzymes and the crystal structure of human HGO. HGO is a topologically complex structure which assembles as a functional hexamer arranged as a dimer of trimers. We show how the intricate pattern of intra- and inter-subunit interactions and the extensive surfaces required for subunit folding and association of this oligomeric enzyme can be inactivated at multiple levels by single-residue substitutions. This explains, in part, the predominance of missense mutations (67%) in AKU.

Crystal structure of human homogentisate dioxygenase.

Homogentisate dioxygenase (HGO) cleaves the aromatic ring during the metabolic degradation of Phe and Tyr. HGO deficiency causes alkaptonuria (AKU), the first human disease shown to be inherited as a recessive Mendelian trait. Crystal structures of apo-HGO and HGO containing an iron ion have been determined at 1.9 and 2.3 A resolution, respectively. The HGO protomer, which contains a 280-residue N-terminal domain and a 140-residue C-terminal domain, associates as a hexamer arranged as a dimer of trimers. The active site iron ion is coordinated near the interface between subunits in the HGO trimer by a Glu and two His side chains. HGO represents a new structural class of dioxygenases. The largest group of AKU associated missense mutations affect residues located in regions of contact between subunits.

On how a transcription factor can avoid its proteolytic activation in the absence of signal transduction.

In response to alkaline ambient pH, the Aspergillus nidulans PacC transcription factor mediating pH regulation of gene expression is activated by proteolytic removal of a negative-acting C-terminal domain. We demonstrate interactions involving the approximately 150 C-terminal PacC residues and two regions located immediately downstream of the DNA binding domain. Our data indicate two full-length PacC conformations whose relative amounts depend upon ambient pH: one 'open' and accessible for processing, the other 'closed' and inaccessible. The location of essential determinants for proteolytic processing within the two more upstream interacting regions probably explains why the interactions prevent processing, whereas the direct involvement of the C-terminal region in processing-preventing interactions explains why C-terminal truncating mutations result in alkalinity mimicry and pH-independent processing. A mutant PacC deficient in pH signal response and consequent processing behaves as though locked in the 'closed' form. Single-residue substitutions, obtained as mutations bypassing the need for pH signal transduction, identify crucial residues in each of the three interactive regions and overcome the processing deficiency in the 'permanently closed' mutant.

Ambient pH signal transduction in Aspergillus: completion of gene characterization.

Completing the molecular analysis of the six pal genes of the ambient pH signal transduction pathway in Aspergillus nidulans, we report the characterization of palC and palH. The derived translation product of palH contains 760 amino acids with prediction of seven transmembrane domains in its N-terminal moiety. Remarkably, a palH frameshift mutant lacking just over half the PalH protein, including almost all of the long hydrophilic region C-terminal to the transmembrane domains, retains some PalH function. The palC-derived translation product contains 507 amino acids, and the null phenotype of a frameshift mutation indicates that at least one of the C-terminal 142 residues is essential for function. Uniquely among the A. nidulans pH-signalling pal genes, palC appears to have no Saccharomyces cerevisiae homologue, although it does have a Neurospora crassa expressed sequence tag homologue. In agreement with findings for the palA, palB and palI genes of this signalling pathway, levels of the palC and palH mRNAs do not appear to be pH regulated.

Disruption of phacA, an Aspergillus nidulans gene encoding a novel cytochrome P450 monooxygenase catalyzing phenylacetate 2-hydroxylation, results in penicillin overproduction.

Aspergillus nidulans utilizes phenylacetate as a carbon source via homogentisate, which is degraded to fumarate and acetoacetate. Mutational evidence strongly suggested that phenylacetate is converted to homogentisate through two sequential hydroxylating reactions in positions 2 and 5 of the aromatic ring. Using cDNA substraction techniques, we have characterized a gene, denoted phacA, whose transcription is strongly induced by phenylacetate and which putatively encodes a cytochrome P450 protein. A disrupted phacA strain does not grow on phenylacetate but grows on 2-hydroxy- or 2, 5-dihydroxyphenylacetate. Microsomal extracts of the disrupted strain are deficient in the NADPH-dependent conversion of phenylacetate to 2-hydroxyphenylacetate. We conclude that PhacA catalyzes the ortho-hydroxylation of phenylacetate, the first step of A. nidulans phenylacetate catabolism. The involvement of a P450 enzyme in the ortho-hydroxylation of a monoaromatic compound has no precedent. In addition, PhacA shows substantial sequence divergence with known cytochromes P450 and defines a new family of these enzymes, suggesting that saprophytic fungi may represent a source of novel cytochromes P450. Phenylacetate is a precursor for benzylpenicillin production. phacA disruption increases penicillin production 3-5-fold, indicating that catabolism competes with antibiotic biosynthesis for phenylacetate and strongly suggesting strategies for Penicillium chrysogenum strain improvement by reverse genetics.

Specificity determinants of proteolytic processing of Aspergillus PacC transcription factor are remote from the processing site, and processing occurs in yeast if pH signalling is bypassed.

The Aspergillus nidulans transcription factor PacC, which mediates pH regulation, is proteolytically processed to a functional form in response to ambient alkaline pH. The full-length PacC form is unstable in the presence of an operational pH signal transduction pathway, due to processing to the relatively stable short functional form. We have characterized and used an extensive collection of pacC mutations, including a novel class of "neutrality-mimicking" pacC mutations having aspects of both acidity- and alkalinity-mimicking phenotypes, to investigate a number of important features of PacC processing. Analysis of mutant proteins lacking the major translation initiation residue or truncated at various distances from the C terminus showed that PacC processing does not remove N-terminal residues, indicated that processing yields slightly heterogeneous products, and delimited the most upstream processing site to residues approximately 252 to 254. Faithful processing of three mutant proteins having deletions of a region including the predicted processing site(s) and of a fourth having 55 frameshifted residues following residue 238 indicated that specificity determinants reside at sequences or structural features located upstream of residue 235. Thus, the PacC protease cuts a peptide bond(s) remote from these determinants, possibly thereby resembling type I endonucleases. Downstream of the cleavage site, residues 407 to 678 are not essential for processing, but truncation at or before residue 333 largely prevents it. Ambient pH apparently regulates the accessibility of PacC to proteolytic processing. Alkalinity-mimicking mutations L259R, L266F, and L340S favor the protease-accessible conformation, whereas a protein with residues 465 to 540 deleted retains a protease-inaccessible conformation, leading to acidity mimicry. Finally, not only does processing constitute a crucial form of modulation for PacC, but there is evidence for its conservation during fungal evolution. Transgenic expression of a truncated PacC protein, which was processed in a pH-independent manner, showed that appropriate processing can occur in Saccharomyces cerevisiae.