Clinical and biochemical characteristics of prolidase deficiency in siblings

Recurrent Skin Ulcers with Facial Dysmorphism and Sinopulmonary Infections: Thinking Beyond Hyper-IgE Syndrome

Prolidase deficiency (PD) is a rare inborn error of metabolism causing ulcers and other skin disorders, splenomegaly, developmental delay, and recurrent infections. Most of the literature is constituted of isolated case reports. It occurs due to the mutations in the prolidase gene ( PEPD ) that result in loss of prolidase activity. We reported here a child who had presented with features compatible with hyper-immunoglobulin E syndrome (HIES) like recurrent skin ulcers, recurrent infections, facial dysmorphism, retained primary teeth, and elevated levels of immunoglobulin E levels but with normal flow cytometric assays, which was later diagnosed as PD.

Poliosis, hair pigment dilution, and premature graying of the hair: A diagnostic approach in pediatric patients and review of the literature

Poliosis is defined as the absence of melanin in hair, and hair graying typically occurs with hair melanin reduction. Poliosis can occur at any age but presents in childhood in certain genetic and acquired conditions, with many families seeking evaluation from a pediatric dermatologist. Poliosis presents as white hair typically restricted to a certain location of the scalp. Children may also present with a reduction of expected hair pigmentation, referred to as pigment dilution, or the development of hair graying. This review aims to provide a streamlined diagnostic approach for pediatric dermatologists when presented with these hair findings. Poliosis should be recognized as a potential diagnostic feature or initial sign in many syndromes and thus can guide clinicians in diagnosing and managing conditions earlier in a patient's care. Since many of the genetic and acquired conditions that present with poliosis or hair pigment dilution have extracutaneous manifestations, early diagnosis is vital in establishing multidisciplinary care.

Recombinant Human Prolidase (rhPEPD) Induces Wound Healing in Experimental Model of Inflammation through Activation of EGFR Signalling in Fibroblasts

The potential of recombinant human prolidase (rhPEPD) to induce wound healing in an experimental model of IL-1β-induced inflammation in human fibroblasts was studied. It was found that rhPEPD significantly increased cell proliferation and viability, as well as the expression of the epidermal growth factor receptor (EGFR) and downstream signaling proteins, such as phosphorylated PI3K, AKT, and mTOR, in the studied model. Moreover, rhPEPD upregulated the expression of the β1 integrin receptor and its downstream signaling proteins, such as p-FAK, Grb2 and p-ERK 1/2. The inhibition of EGFR signaling by gefitinib abolished rhPEPD-dependent functions in an experimental model of inflammation. Subsequent studies showed that rhPEPD augmented collagen biosynthesis in IL-1β-treated fibroblasts as well as in a wound healing model (wound closure/scratch test). Although IL-1β treatment of fibroblasts increased cell migration, rhPEPD significantly enhanced this process. This effect was accompanied by an increase in the activity of MMP-2 and MMP-9, suggesting extracellular matrix (ECM) remodeling during the inflammatory process. The data suggest that rhPEPD may play an important role in EGFR-dependent cell growth in an experimental model of inflammation in human fibroblasts, and this knowledge may be useful for further approaches to the treatment of abnormalities of wound healing and other skin diseases.

Recombinant Prolidase Activates EGFR-Dependent Cell Growth in an Experimental Model of Inflammation in HaCaT Keratinocytes. Implication for Wound Healing

This study was conducted to investigate the proliferative capacity of recombinant human prolidase (rhPEPD) in a human model of inflammation induced by IL-1β in HaCaT keratinocytes. In this report, we provide evidence that IL-1β stimulates keratinocyte proliferation, and rhPEPD significantly augmented this process through activation of epidermal growth factor receptor (EGFR) and downstream signaling proteins as phosphorylated Akt, ERK1/2, and STAT3, which are implicated in keratinocyte migration, proliferation, and epithelialization during the wound healing process. Inhibition of PEPD-dependent EGFR signaling by gefitinib supported the finding. Moreover, during activation of EGFR in the presence of IL-1β the epithelial-to-mesenchymal transition (EMT) occurred via downregulation of E-cadherin and upregulation of N-cadherin. The phenomenon was accompanied by an increase in the activity of matrix metalloproteinase-9 (MMP-9), suggesting extracellular matrix (ECM) remodeling during the inflammatory process. MMP-9 activation may result from nuclear translocation of NF-κB through IKK-mediated IκBα degradation. Interestingly, some mutated variants of PEPD (rhPEPD-G448R, rhPEPD-231delY, and rhPEPD-E412K) evoked the ability to induce EGFR-dependent HaCaT cell proliferation. To the best of our knowledge, this is the first report on the cross-talk between PEPD and IL-1β in the process of keratinocyte proliferation. The data suggest that both enzymatically active and inactive rhPEPD may activate EGFR-dependent cell growth in an experimental model of inflammation in HaCaT keratinocytes and the knowledge may be useful for further approaches for therapy of wound healing disorders.

Osteoarticular Manifestations of Prolidase Deficiency and Disability: Case Reports of Two Moroccan Sisters

Prolidase deficiency (PD) is a rare autosomal recessive disorder that has symptoms such as chronic skin ulcers, dysmorphic facies, cognitive retardation, hematological anomalies, splenomegaly, and chronic infections. Bone and joint abnormalities were referred occasionally and included the signs and symptoms of prolidase deficiency, but were not deeply investigated in PD patients. We report a case of two PD Moroccan sisters with osteoarticular deformities, some of them were never described before: toes deformities and equinovalgus with fusion and dislocation of a tarsal bone in radiography x-rays.

Quantitative analysis of the natural history of prolidase deficiency: description of 17 families and systematic review of published cases

PURPOSE

Prolidase deficiency is a rare inborn error of metabolism causing ulcers and other skin disorders, splenomegaly, developmental delay, and recurrent infections. Most of the literature is constituted of isolated case reports. We aim to provide a quantitative description of the natural history of the condition by describing 19 affected individuals and reviewing the literature.

METHODS

Nineteen patients were phenotyped per local institutional procedures. A systematic review following PRISMA criteria identified 132 articles describing 161 patients. Main outcome analyses were performed for manifestation frequency, diagnostic delay, overall survival, symptom-free survival, and ulcer-free survival.

RESULTS

Our cohort presented a wide variability of severity. Autoimmune disorders were found in 6/19, including Crohn disease, systemic lupus erythematosus, and arthritis. Another immune finding was hemophagocytic lymphohistiocytosis (HLH). Half of published patients were symptomatic by age 4 and had a delayed diagnosis (mean delay 11.6 years). Ulcers were present initially in only 30% of cases, with a median age of onset at 12 years old.

CONCLUSION

Prolidase deficiency has a broad range of manifestations. Symptoms at onset may be nonspecific, likely contributing to the diagnostic delay. Testing for this disorder should be considered in any child with unexplained autoimmunity, lower extremity ulcers, splenomegaly, or HLH.

Extracellular Prolidase (PEPD) Induces Anabolic Processes through EGFR, β1-integrin, and IGF-1R Signaling Pathways in an Experimental Model of Wounded Fibroblasts

The role of prolidase (PEPD) as a ligand of the epidermal growth factor receptor (EGFR) was studied in an experimental model of wound healing in cultured fibroblasts. The cells were treated with PEPD (1-100 nM) and analysis of cell viability, proliferation, migration, collagen biosynthesis, PEPD activity, and the expressions of EGFR, insulin-like growth factor 1 (IGF-1), and β₁-integrin receptor including downstream signaling proteins were performed. It has been found that PEPD stimulated proliferation and migration of fibroblasts via activation of the EGFR-downstream PI3K/Akt/mTOR signaling pathway. Simultaneously, PEPD stimulated the expression of β₁-integrin and IGF-1 receptors and proteins downstream to these receptors such as FAK, Grb2, and ERK1/2. Collagen biosynthesis was increased in control and "wounded" fibroblasts under PEPD treatment. The data suggest that PEPD-induced EGFR signaling may serve as a new attempt to therapy wound healing.

Prolidase Stimulates Proliferation and Migration through Activation of the PI3K/Akt/mTOR Signaling Pathway in Human Keratinocytes

Recent reports have indicated prolidase (PEPD) as a ligand of the epidermal growth factor receptor (EGFR). Since this receptor is involved in the promotion of cell proliferation, growth, and migration, we aimed to investigate whether prolidase may participate in wound healing in vitro. All experiments were performed in prolidase-treated human keratinocytes assessing cell vitality, proliferation, and migration. The expression of downstream signaling proteins induced by EGFR, insulin-like growth factor 1 (IGF-1), transforming growth factor β₁ (TGF-β₁), and β₁-integrin receptors were evaluated by Western immunoblotting and immunocytochemical staining. To determine collagen biosynthesis and prolidase activity radiometric and colorimetric methods were used, respectively. Proline content was determined by applying the liquid chromatography coupled with mass spectrometry. We found that prolidase promoted the proliferation and migration of keratinocytes through stimulation of EGFR-downstream signaling pathways in which the PI3K/Akt/mTOR axis was involved. Moreover, PEPD upregulated the expression of β₁-integrin and IGF-1 receptors and their downstream proteins. Proline concentration and collagen biosynthesis were increased in HaCaT cells under prolidase treatment. Since extracellular prolidase as a ligand of EGFR induced cell growth, migration, and collagen biosynthesis in keratinocytes, it may represent a potential therapeutic approach for the treatment of skin wounds.

Proline-dependent regulation of collagen metabolism

This review is focused on recent data on the role of proline (Pro) in collagen biosynthesis and cellular metabolism. It seems obvious that one of the main substrates for collagen biosynthesis Pro is required to form collagen molecule. The question raised in this review is whether the Pro for collagen biosynthesis is synthesized "de novo", comes directly from degraded proteins or it is converted from other amino acids. Recent data provided evidence that extracellular Pro (added to culture medium) had significant, but relatively little impact on collagen biosynthesis in fibroblasts (the main collagen synthesized cells) cultured in the presence of glutamine (Gln). However, extracellular Pro drastically increased collagen biosynthesis in the cells cultured in Gln-free medium. It suggests that Pro availability determines the rate of collagen biosynthesis and demand for Pro in fibroblasts is predominantly met by conversion from Gln. The potential mechanism of this process as well as possible implication of this knowledge in pharmacotherapy of connective tissue diseases is discussed in this review.

Topical tacrolimus therapy in the management of lower extremity ulcers due to prolidase deficiency

Prolidase deficiency is a rare autosomal recessive disorder characterized by cutaneous ulcers, facial dysmorphism, recurrent infections, and intellectual disability. We report a unique case of a 6-year-old boy with prolidase deficiency and Crohn's disease who presented with lower extremity ulcers. Cutaneous ulcers due to prolidase deficiency are historically resistant to treatment, and we report success with the novel use of topical tacrolimus.

Enalapril stimulates collagen biosynthesis through prolidase-dependent mechanism in cultured fibroblasts

The mechanism of a lower incidence of dermatological manifestations in patients treated with enalapril compared to patients treated with other ACE-inhibitors, e.g., captopril, is not known. The finding that prolidase plays an important role in collagen biosynthesis and that some angiotensin-converting enzyme inhibitors affect prolidase activity led us to evaluate its effect on collagen biosynthesis in cultured human skin fibroblasts. Since insulin-like growth factor (IGF-I) and transforming growth factor beta 1 (TGF-β1) are the most potent stimulators of both collagen biosynthesis and prolidase activity, and prolidase is regulated by β₁ integrin signaling, the effect of enalapril and enalaprilat on IGF-IR, TGF-β1, and β₁ integrin receptor expressions was evaluated. Cells were treated with milimolar concentrations (0.3 and 0.5 mM) of enalapril and enalaprilat for 24 h. The activity of prolidase was determined by colorimetic assay. Collagen biosynthesis was evaluated by radiometric assay. Expression of signaling proteins was evaluated using Western blot. It was found that enalapril- and enalaprilat-dependent increase in prolidase activity and expression was accompanied by parallel increase in collagen biosynthesis. The exposure of the cells to 0.5 mM enalapril and enalaprilat contributed to increase in IGF-IR and α₂β₁ integrin receptor as well as TGF-β1 and NF-κB p65 expressions. Enalapril- and enalaprilat-dependent increase of collagen biosynthesis in fibroblasts results from increase of prolidase activity and expression, which may undergo through activation of α₂β₁ integrin and IGF-IR signaling as well as upregulation of TGF-β1 and NF-κB p65, the inhibitor of collagen gene expression.

Prolidase is required for early trafficking events during influenza A virus entry

Influenza A virus (IAV) entry is a multistep process that requires the interaction of the virus with numerous host factors. In this study, we demonstrate that prolidase (PEPD) is a cellular factor required by IAV for successful entry into target cells. PEPD was selected as a candidate during an entry screen performed on nonvalidated primary hits from previously published genome-wide small interfering RNA (siRNA) screens. siRNA-mediated depletion of PEPD resulted in the decreased growth of IAV during mono- and multicycle growth. This growth defect was independent of cell type or virus strain. Furthermore, IAV restriction was apparent as early as 3 h postinfection, and experiments in the absence of protein biosynthesis revealed that the nuclear import of viral ribonucleoprotein complexes (vRNPs) was already blocked in the absence of PEPD. These results led us to investigate which step during entry was affected. Receptor expression, IAV attachment, or IAV internalization was not dependent on the presence of PEPD. However, when looking at the distribution of incoming IAV particles in PEPD-knockdown cells, we found a localization pattern that differed from that in control cells: IAV mostly localized to the cell periphery, and consequently, viral particles displayed reduced colocalization with early and late endosome markers and fusion between viral and endosomal membranes was strongly reduced. Finally, experiments using a competitive inhibitor of PEPD catalytic activity suggested that the enzymatic function of the dipeptidase is required for its proviral effect on IAV entry. In sum, this study establishes PEPD as a novel entry factor required for early endosomal trafficking of IAV.

IMPORTANCE

Influenza A virus (IAV) continues to be a constant threat to public health. As IAV relies on its host cell for replication, the identification of host factors required by the virus is of importance. First, such studies often reveal novel functions of cellular factors and can extend our knowledge of cellular processes. Second, we can further our understanding of processes that are required for the entry of IAV into target cells. Third, the identification of host factors that contribute to IAV entry will increase the number of potential targets for the development of novel antiviral drugs that are of urgent need. Our study identifies prolidase (PEPD) to be a novel entry factor required by IAV for correct routing within the endosomal compartment following virus internalization. Thereby, we link PEPD, which has been shown to play a role during collagen recycling and growth factor signaling, to early events of viral infection.

Prolidase deficiency breaks tolerance to lupus-associated antigens

AIM

Prolidase deficiency is a rare autosomal recessive disease in which one of the last steps of collagen metabolism, cleavage of proline-containing dipeptides, is impaired. Only about 93 patients have been reported with about 10% also having systemic lupus erythematosus (SLE).

METHODS

We studied a large extended Amish pedigree with four prolidase deficiency patients and three heterozygous individuals for lupus-associated autoimmunity. Eight unaffected Amish children served as normal controls. Prolidase genetics and enzyme activity were confirmed. Antinuclear antibodies (ANA) were determined using indirect immunofluorescence and antibodies against extractable nuclear antigens were determined by various methods, including double immunodiffusion, immunoprecipitation and multiplex bead assay. Serum C1q levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Two of the four homozygous prolidase deficiency subjects had a positive ANA. One had anti-double-stranded DNA, while another had precipitating anti-Ro. By the simultaneous microbead assay, three of the four had anti-Sm and anti-chromatin. One of the three heterozygous subjects had a positive ANA and immunoprecipitation of a 75 000 molecular weight protein. The unaffected controls had normal prolidase activity and were negative for autoantibodies.

CONCLUSIONS

Prolidase deficiency may be associated with the loss of immune tolerance to lupus-associated autoantigens even without clinical SLE.

Prolidase-dependent regulation of collagen biosynthesis

Prolidase [EC.3.4.13.9] is a cytosolic imidodipeptidase, which specifically splits imidodipeptides with C-terminal proline or hydroxyproline. The enzyme plays an important role in the recycling of proline from imidodipeptides (mostly derived from degradation products of collagen) for resynthesis of collagen and other proline-containing proteins. The enzyme activity is up-regulated by beta(1)-integrin receptor stimulation. The increase in the enzyme activity is due to its phosphorylation on serine/threonine residues. Collagen is not only structural component of extracellular matrix. It has been recognized as a ligand for integrin receptors, which play an important role in signaling that regulate ion transport, lipid metabolism, kinase activation and gene expression. Therefore, changes in the quantity, structure and distribution of collagens in tissues may affect cell signaling, metabolism and function. Several line of evidence suggests that prolidase activity may be a step-limiting factor in the regulation of collagen biosynthesis. It has been shown in different physiologic and pathologic conditions. It is of great importance during wound healing, inflammation, aging, tissue fibrosis and possibly skeletal abnormalities seen in Osteogenesis Imperfecta. The mechanism of prolidase-dependent regulation of collagen biosynthesis was found at both transcriptional and post-transcriptional levels. In this study, we provide evidence for prolidase-dependent transcriptional regulation of collagen biosynthesis. The mechanism was found at the level of NF-kB, known inhibitor of type I collagen gene expression. Modulation of integrin-dependent signaling by stimulatory (i.e. thrombin) or inhibitory (i.e. echistatin) beta(1)-integrin ligands or by nitric oxide donors (i.e. DETA/NO) affect prolidase at post-transcriptional level. All those factors may represent novel approach to pharmacotherapy of connective tissue disorders.

A nonsense mutation of PEPD in four Amish children with prolidase deficiency

Encoded by the peptidase D (PEPD) gene located at 19q12-q13.11, prolidase is a ubiquitous cytosolic enzyme that catalyzes hydrolysis of oligopeptides with a C-terminal proline or hydroxyproline. We describe here four Amish children with a severe phenotype of prolidase deficiency in the Geauga settlements of Ohio as the first report of prolidase deficiency in the Amish population as well as in the United States. The patients presented with infection, hepatosplenomegaly, or thrombocytopenia, in contrast to most cases previously reported in the literature, presenting with skin ulcers. All four patients had typical facial features, classic skin ulcers, and multisystem involvement. Recurrent infections, asthma-like chronic reactive airway disease, hyperimmunoglobulins, hepatosplenomegaly with mildly elevated aspartate transaminase (AST), anemia, and thrombocytopenia were common and massive imidodipeptiduria was universal. Prolidase activity in our patients is nearly undetectable. Direct sequencing of PCR-amplified genomic DNA for all of the exons from the four patients revealed the same homozygous single nucleotide mutation c.793 T > C in exon 11, resulting in a premature stop-codon at amino acid residue 265 (p.R265X). It is speculated that the severe phenotype in these patients might be associated with the type of the PEPD gene mutation.

Prolidase deficiency diagnosed by 1H NMR spectroscopy of urine

Three urine samples from two prolidase-deficient patients were analysed using 1H NMR spectroscopy. One-dimensional 1H NMR spectra showed a characteristic pattern of overlapping resonances of the proline and hydroxyproline protons of the imidodipeptides. The model compounds Ala-Pro, Gly-Pro, Phe-Pro, Leu-Pro, Val-Pro, Gly-Hyp and Pro-Hyp were measured as well. The non-proline resonances of Val-Pro, Ala-Pro and Gly-Pro could be assigned in the urine spectra. These resonances could then be used for quantification of the corresponding imidodipeptids. The presence of Leu-Pro in the patients' urine was demonstrated by the results of COSY experiments. However, this imidodipeptide could not be quantified owing to overlap of the resonaces in the one-dimensional 1H NMR spectrum of the patients' urine. Phe-Pro, Pro-Hyp and Gly-Hyp could not be assigned in the spectrum of the patient's urine. The characteristic resonances in the urine from a prolidase-deficient patient, i.e. Ala-Pro, Val-Pro, Gly-Pro, and resonances of the (hydroxy)proline part of the imidodipeptides can be used to diagnose this disease.

Defects of type I procollagen metabolism correlated with decrease of prolidase activity in a case of lethal osteogenesis imperfecta

We have studied the structure and metabolism of type I procollagen in a case of perinatal lethal osteogenesis imperfecta (OI) type II. Cultured skin fibroblasts from the proband synthesized both normal and abnormal forms of type I procollagen. Some abnormal, overmodified molecules were secreted by OI cells, although less efficiently than normal molecules from control cells. The OI fibroblasts accumulated large amounts of abnormal proalpha1(I) and proalpha2(I) chains intracellularly. The extracellular collagenolytic activity was decreased compared to control cells. Furthermore, OI cells produced less type I procollagen and demonstrated lower capacity to synthesize DNA than control cells. We have found that in contrast to prolinase activity, the activity of prolidase (an enzyme essential for collagen synthesis and cell growth) is also significantly reduced in OI cells. No differences were found in the amount of the enzyme protein recovered from both the OI and control cells. However, we found that expressions of beta1 integrin and insulin-like growth factor-I receptor (receptors known to play an important role in up regulation of prolidase activity) were decreased in OI cells compared to control cells. The decrease in prolidase activity may provide an important mechanism of altered cell growth and collagen metabolism involved in producing the perinatal lethal form of the OI phenotype.

Phosphorylation of prolidase increases the enzyme activity

Prolidase [EC 3.4.13.9] is a ubiquitously distributed imidodipeptidase that catalyzes the hydrolysis of C-terminal proline-containing dipeptides. The enzyme plays an important role in the recycling of proline for collagen synthesis and cell growth. Although, the increase in the enzyme activity is correlated with increased rate of collagen turnover, the mechanism by which prolidase is regulated remain largely unknown. In the present study we found that phosphorylation of fibroblast's prolidase may be an underlying mechanism for up regulation of the enzyme activity. Supporting evidence comes from the following observations: (1) immunoprecipitated prolidase was detected as a phosphotyrosine protein as shown by western immunoblot analysis, (2) tyrosine kinase inhibitor-erbstatin induced (in a dose dependent manner) a decrease in prolidase activity in cultured human skin fibroblasts, (3) anti-phosphotyrosine antibody reduced and phosphotyrosine phosphatase 1B antibody (anti-PTP 1B) increased (in a dose dependent manner) the prolidase activity in extract of fibroblast's homogenate, (4) decrease in prolidase activity from collagenase treated or serum starved fibroblasts can be partially prevented by incubating fibroblast's homogenate extract with anti-PTP 1B antibody. These results provide evidence that prolidase is phosphotyrosine enzyme and suggest that the activity of prolidase may be up regulated by the enzyme phosphorylation.

Transient beneficial effect of GH replacement therapy and topical GH application on skin ulcers in a boy with prolidase deficiency

A diagnostic examination for short stature in a boy with chronic ulcers of the feet due to prolidase deficiency, a rare disorder associated with intractable ulcers of the skin, led to the diagnosis of growth hormone (GH) deficiency. Replacement treatment with r-hGH associated with the topical application of a GH-containing ointment when the boy was 13 years old resulted in complete but transitory healing of the ulcers, which can probably be attributed to the growth-promoting effects of GH on dermal connective tissue.

Prolidase in human breast cancer MCF-7 cells

Prolidase (EC 3.4.13.9) is an ubiquitously distributed imidodipeptidase that catalyzes the hydrolysis of dipeptides containing C-terminal proline or hydroxyproline. The enzyme plays an important role in the recycling of proline for collagen synthesis and cell growth. We have shown previously that prolidase activity in normal human skin fibroblasts is regulated by the interaction of type I collagen with beta1 integrin receptor. In the present study, we investigate prolidase activity in MCF-7 cells and find it is only one-third of that in normal human skin fibroblasts. The relative difference in prolidase activity is corroborated by enzyme protein with Western immunoblot analysis. We propose that the decrease in prolidase activity is due to derangement of regulation by the collagen-beta1 integrin receptor axis. Supporting evidence comes from the following observations: (1) relative collagen content elaborated by MCF-7 cells as compared to fibroblasts is lower by 30% in sparse cells and by 80% at confluence; (2) collagenase treatment of both cell types results in decreased enzyme activity; (3) in contrast to fibroblasts, prolidase activity in MCF-7 cells is not stimulated by the addition of type I collagen or beta1 integrin antibodies (agonist for beta1 integrin receptor); and (4) in contrast to fibroblasts, MCF-7 cells express only trace amounts of beta1 integrin receptor as shown by Western immunoblot analysis. Thus, we conclude that depressed prolidase activity in MCF-7 cells may be a result of disturbances in signaling mediated by beta1 integrin-collagen interaction.

Proline specific peptidases

Proline is unique among the 20 amino acids due to its cyclic structure. This specific conformation imposes many restrictions on the structural aspects of peptides and proteins and confers particular biological properties upon a wide range of physiologically important biomolecules. In order to adequately deal with such peptides, nature has developed a group of enzymes that recognise this residue specifically. These peptidases cover practically all situations where a proline residue might occur in a potential substrate. In this paper we endeavour to discuss these enzymes, particularly those responsible for peptide or protein hydrolysis at proline sites. We have detailed their discovery, biochemical attributes and substrate specificities and have provided information as to the methodology used to detect and manipulate their activities. We have also described the roles, or potential roles that these enzymes may play physiologically and the consequences of their dysfunction in varied disease states.

Prolidase activity in fibroblasts is regulated by interaction of extracellular matrix with cell surface integrin receptors

Prolidase (EC 3.4.13.9) is a ubiquitously distributed imidodipeptidase that catalyzes the hydrolysis of C-terminal proline or hydroxyproline containing dipeptides. The enzyme plays an important role in the recycling of proline for collagen synthesis and cell growth. An increase in enzyme activity is correlated with increased rates of collagen turnover indicative of extracellular matrix (ECM) remodeling, but the mechanism linking prolidase activity and ECM is poorly understood. Thus, the effect of ECM-cell interaction on intracellular prolidase activity is of special interest. In cultured human skin fibroblasts, the interaction with ECM and, more specifically, type I collagen mediated by the beta 1 integrin receptor regulates cellular prolidase activity. Supporting evidence comes from the following observations: 1) in sparse cells with a low amount of ECM collagen or in confluent cells in which ECM collagen was removed by collagenase (but not by trypsin or elastase) treatment, prolidase activity was decreased; 2) this effect was reversed by the addition of type I collagen or beta 1 integrin antibody (agonist for beta 1 integrin receptor); 3) sparse cells (with typically low prolidase activity) showed increased prolidase activity when grown on plates coated with type I collagen or on type IV collagen and laminin, constituents of basement membrane; 4) the relative differences in prolidase activity due to collagenase treatment and subsequent recovery of the activity by beta 1 integrin antibody or type I collagen treatment were accompanied by parallel differences in the amount of the enzyme protein recovered from these cells, as shown by Western immunoblot analysis. Thus, we conclude that prolidase activity responded to ECM metabolism (tissue remodeling) through signals mediated by the integrin receptor.

Use of capillary zone electrophoresis for analysis of imidodipeptides in urine of prolidase-deficient patients

Prolidase deficiency (PD) is characterized by massive urinary excretion of imidodipeptides X-Pro and X-Hyp. We report the applicability of capillary zone electrophoresis to urinary imidodipeptide determination. The protocol is fast, simple, reliable, only small amounts of sample are required and there is minimal sample preparation. Electropherograms of urine samples from control subjects and four patients with prolidase deficiency were compared. The presence of imidodipeptides normally absent in urine was evident in patients' urine. Further analysis of urine samples enabled identification of excreted imidodipeptides and the pattern of excretion appeared to be heterogeneous for different patients. This method appears to be useful for identification of imidodipeptides in biological samples, as an efficient aid in diagnosis of PD, and as a method for providing more information about this disease.

Prolidase deficiency: a multisystemic hereditary disorder

Prolidase deficiency is a rare hereditary disorder with a wide spectrum of clinical manifestations including skin ulcers, eczematous eruptions, characteristic facies, mental retardation, splenomegaly, and susceptibility to infections. We report two new cases of prolidase deficiency. Our patients had the typical manifestations of prolidase deficiency. One also had lupus erythematosus. Prolidase activity was either normal or half-normal in all family members. The skin disease in our patients did not respond to topical glycine/proline ointment or to oral vitamin C.

Normal production, nature, and extent of intracellular degradation of newly synthesized collagen in fibroblasts from a patient with prolidase deficiency

We have examined the extent of intracellular degradation of newly synthesized collagen occurring in fibroblasts from a patient with prolidase deficiency, a rare, autosomal recessively inherited disorder, in which a lack of prolidase, which normally cleaves imidodipeptides with a C-terminal Pro or Hyp residue, results in hyperimidodipeptiduria. The main clinical feature of the condition is chronic, intractable ulceration of the skin, and the suggestion has been made that it represents a specific disorder of collagen metabolism. Although most of the hydroxy-[14]proline derived from the intracellular degradation of newly synthesized collagen in prolidase-deficient fibroblasts occurred in imidodipeptides, with a similar chromatographic profile to those occurring in the patient's urine, the proportion of collagen undergoing such degradation was as in control cells. No abnormality was found in other parameters of collagen metabolism studied, and the results confirm that, although the pathogenesis of its clinical manifestations remains unclear, the disorder is one of protein degradation in general.

Blood transfusions in the therapy of a case of prolidase deficiency

A case is reported of a 15-year-old boy with prolidase deficiency and marked urinary excretion of the iminodipeptide gly-pro. Prolidase activity of erythrocytes against substrate glycyl-proline was deficient, but after blood transfusions this was increased to 15.7% of donor activity and declined to 12% and 3.4% of normal activity after 8 and 45 days, respectively. Urinary iminodipeptide levels following transfusion remained unaltered.