Anti-Ki/anti-PA28γ autoantibodies contribute to the HEp-2 indirect immunofluorescence nuclear speckled pattern.

OBJECTIVES: Antinuclear antibodies (ANAs) are associated with several autoimmune diseases. Indirect immunofluorescence (IIF) on human epithelial type 2 (HEp-2) cells is the golden standard for ANA detection in the clinic. In case of a positive HEp-2 IIF test result, follow-up tests are done to determine autoantibody specificity. For a fraction of the HEp-2 IIF-positive samples, the nature of the autoantigens remains uncharacterized. Our objective was to characterize autoantigens in such samples. METHODS: To characterize autoantigens in an unbiased way, we combined protein immunoprecipitation with liquid chromatography (LC) tandem mass spectrometry (MS/MS) sequencing. RESULTS: Using such approach we detected the Ki antigen, also referred to as PA28γ, in the immunoprecipitate of serum samples of three individuals with an autoimmune disease. The HEp-2 nuclear speckled IIF fluorescent signal of all three serum samples was abolished after pre-absorption of the serum with recombinant Ki antigen, confirming that autoantibodies against Ki underlie the HEp-2 IIF signal. CONCLUSIONS: Our data suggest that anti-Ki autoantibodies can underlie a nuclear speckled HEp-2 IIF pattern.

Protease propeptide structures, mechanisms of activation, and functions.

Proteases are a diverse group of hydrolytic enzymes, ranging from single-domain catalytic molecules to sophisticated multi-functional macromolecules. Human proteases are divided into five mechanistic classes: aspartate, cysteine, metallo, serine and threonine proteases, based on the catalytic mechanism of hydrolysis. As a protective mechanism against uncontrolled proteolysis, proteases are often produced and secreted as inactive precursors, called zymogens, containing inhibitory N-terminal propeptides. Protease propeptide structures vary considerably in length, ranging from dipeptides and propeptides of about 10 amino acids to complex multifunctional prodomains with hundreds of residues. Interestingly, sequence analysis of the different protease domains has demonstrated that propeptide sequences present higher heterogeneity compared with their catalytic domains. Therefore, we suggest that protease inhibition targeting propeptides might be more specific and have less off-target effects than classical inhibitors. The roles of propeptides, besides keeping protease latency, include correct folding of proteases, compartmentalization, liganding, and functional modulation. Changes in the propeptide sequence, thus, have a tremendous impact on the cognate enzymes. Small modifications of the propeptide sequences modulate the activity of the enzymes, which may be useful as a therapeutic strategy. This review provides an overview of known human proteases, with a focus on the role of their propeptides. We review propeptide functions, activation mechanisms, and possible therapeutic applications.

EDTA/gelatin zymography method to identify C1s versus activated MMP-9 in plasma and immune complexes of patients with systemic lupus erythematosus.

Gelatin zymography analysis is a sensitive method and commonly used to characterize and quantify the presence of the gelatinases (MMP-2 and MMP-9) in biological samples. In human plasma samples from healthy controls and systemic lupus erythematosus (SLE) patients, we observed a gelatinolytic molecule at 80 kDa, suggestive for activated human MMP-9. However, by developing and using the EDTA/gelatin zymography method and after purification of the 80 kDa entity, we proved that this molecule was the C1s subunit of the complement system. The zymolytic capacity of C1s was validated and found to be enhanced, in the absence of calcium and in the presence of EDTA. Our findings indicate that for correct identification of gelatinolytic proteins in complex biological samples the use of EDTA/gelatin zymography for enzyme development is advised. In addition, by quantification of EDTA/gelatin zymography analysis and ELISA, we observed that the levels of C1s were higher in plasma and immune complexes of SLE patients than of healthy individuals. Therefore, our data imply that C1s may become a marker for the diagnosis of SLE.

Endotoxemia shifts neutrophils with TIMP-free gelatinase B/MMP-9 from bone marrow to the periphery and induces systematic upregulation of TIMP-1.

Lipopolysaccharides or endotoxins elicit an excessive host inflammatory response and lead to life-threatening conditions such as endotoxemia and septic shock. Lipopolysaccharides trigger mobilization and stimulation of leukocytes and exaggerated production of pro-inflammatory molecules including cytokines and proteolytic enzymes. Matrix metalloproteinase-9 (MMP-9) or gelatinase B, a protease stored in the tertiary granules of polymorphonuclear leukocytes, has been implicated in such inflammatory reactions. Moreover, several studies even pinpointed MMP-9 as a potential target molecule to counter excessive inflammation in endotoxemia. Whereas the early effect of lipopolysaccharide-induced inflammation in vivo on the expression of MMP-9 in various peripheral organs has been described, the effects on the bone marrow and during late stage endotoxemia remain elusive. We demonstrate that TIMP-free MMP-9 is a major factor in bone marrow physiology and pathology. By using a mouse model for late-stage endotoxemia, we show that lipopolysaccharides elicited a depletion of neutrophil MMP-9 in the bone marrow and a shift of MMP-9 and MMP-9-containing cells towards peripheral organs, a pattern which was primarily associated with a relocation of CD11bhighGr-1high cells. In contrast, analysis of the tissue inhibitors of metalloproteinases was in line with a natural, systematic upregulation of TIMP-1, the main tissue inhibitor of TIMP-free MMP-9, and a general shift toward control of matrix metalloproteinase activity by tissue inhibitors of metalloproteinases.

Glycosylation of matrix metalloproteases and tissue inhibitors: present state, challenges and opportunities.

Matrix metalloproteases (MMPs) are crucial components of a complex and dynamic network of proteases. With a wide range of potential substrates, their production and activity are tightly controlled by a combination of signalling events, zymogen activation, post-translational modifications and extracellular inhibition. Slight imbalances may result in the initiation or progression of specific disease states, such as cancer and pathological inflammation. As glycosylation modifies the structures and functions of glycoproteins and many MMPs contain N- or O-linked oligosaccharides, we examine, compare and evaluate the evidence for whether glycosylation affects MMP catalytic activity and other functions. It is interesting that the catalytic sites of MMPs do not contain O-linked glycans, but instead possess a conserved N-linked glycosylation site. Both N- and O-linked oligosaccharides, attached to specific protein domains, endow these domains with novel functions such as the binding to lectins, cell-surface receptors and tissue inhibitors of metalloproteases (TIMPs). Validated glycobiological data on N- and O-linked oligosaccharides of gelatinase B/MMP-9 and on O-linked structures of membrane-type 1 MMP/MMP-14 indicate that in-depth research of other MMPs may yield important insights, e.g. about subcellular localizations and functions within macromolecular complexes.

Antinuclear antibodies in individuals with COVID-19 reflect underlying disease: Identification of new autoantibodies in systemic sclerosis (CDK9) and malignancy (RNF20, RCC1, TRIP13).

A high prevalence of antinuclear antibodies (ANA) in COVID-19 has been insinuated, but the nature of the target antigens is poorly understood. We studied ANA by indirect immunofluorescence in 229 individuals with COVID-19. The target antigens of high titer ANA (≥1:320) were determined by immunoprecipitation (IP) combined with liquid-chromatography-mass spectrometry (MS). High titer ANA (≥1:320) were found in 14 (6%) of the individuals with COVID-19. Of the 14 COVID-19 cases with high titer ANA, 6 had an underlying autoimmune disease and 5 a malignancy. IP-MS revealed known target antigens associated with autoimmune disease as well as novel autoantigens, including CDK9 (in systemic sclerosis) and RNF20, RCC1 and TRIP13 (in malignancy). The novel autoantigens were confirmed by IP-Western blotting. In conclusion, in depth analysis of the targets of high titer ANA revealed novel autoantigens in systemic sclerosis and in malignant disease.

Complementarity determining regions in SARS-CoV-2 hybrid immunity.

Pre-vaccination SARS-CoV-2 infection can boost protection elicited by COVID-19 vaccination and post-vaccination breakthrough SARS-CoV-2 infection can boost existing immunity conferred by COVID-19 vaccination. Such 'hybrid immunity' is effective against SARS-CoV-2 variants. In order to understand 'hybrid immunity' at the molecular level we studied the complementarity determining regions (CDR) of anti-RBD (receptor binding domain) antibodies isolated from individuals with 'hybrid immunity' as well as from 'naive' (not SARS-CoV-2 infected) vaccinated individuals. CDR analysis was done by liquid chromatography/mass spectrometry-mass spectrometry. Principal component analysis and partial least square differential analysis showed that COVID-19 vaccinated people share CDR profiles and that pre-vaccination SARS-CoV-2 infection or breakthrough infection further shape the CDR profile, with a CDR profile in hybrid immunity that clustered away from the CDR profile in vaccinated people without infection. Thus, our results show a CDR profile in hybrid immunity that is distinct from the vaccination-induced CDR profile.

Citrullination as a novel posttranslational modification of matrix metalloproteinases.

Matrix metalloproteinases (MMPs) are enzymes with critical roles in biology and pathology. Glycosylation, nitrosylation and proteolysis are known posttranslational modifications (PTMs) regulating intrinsically the activities of MMPs. We discovered MMP citrullination by peptidyl arginine deiminases (PADs) as a new PTM. Upon hypercitrullination, MMP-9 acquired a higher affinity for gelatin than control MMP-9. Furthermore, hypercitrullinated proMMP-9 was more efficiently activated by MMP-3 compared to control MMP-9. JNJ0966, a specific therapeutic inhibitor of MMP-9 activation, inhibited the activation of hypercitrullinated proMMP-9 by MMP-3 significantly less in comparison with control proMMP-9. The presence of citrullinated/homocitrullinated MMP-9 was detected in vivo in neutrophil-rich sputum samples of cystic fibrosis patients. In addition to citrullination of MMP-9, we report efficient citrullination of MMP-1 and lower citrullination levels of MMP-3 and MMP-13 by PAD2 in vitro. In conclusion, citrullination of MMPs is a new PTM worthy of additional biochemical and biological studies.

Proteoform Analysis of Matrix Metalloproteinase-9/Gelatinase B and Discovery of Its Citrullination in Rheumatoid Arthritis Synovial Fluids.

Objectives: To explore posttranslational modifications (PTMs), including proteolytic activation, multimerization, complex formation and citrullination of gelatinases, in particular of gelatinase B/MMP-9, and to detect in gelatin-Sepharose affinity-purified synovial fluids, the presence of specific MMP proteoforms in relation to arthritis. Methods: Latent, activated, complexed and truncated gelatinase-A/MMP-2 and gelatinase B/MMP-9 proteoforms were detected with the use of zymography analysis to compare specific levels, with substrate conversion assays, to test net proteolytic activities and by Western blot analysis to decipher truncation variants. Citrullination was detected with enhanced sensitivity, by the use of a new monoclonal antibody against modified citrullines. Results: All MMP-9 and MMP-2 proteoforms were identified in archival synovial fluids with the use of zymography analysis and the levels of MMP-9 versus MMP-2 were studied in various arthritic diseases, including rheumatoid arthritis (RA). Secondly, we resolved misinterpretations of MMP-9 levels versus proteolytic activities. Thirdly, a citrullinated, truncated proteoform of MMP-9 was discovered in archival RA synovial fluid samples and its presence was corroborated as citrullinated hemopexin-less MMP-9 in a small prospective RA sample cohort. Conclusion: Synovial fluids from rheumatoid arthritis contain high levels of MMP-9, including its truncated and citrullinated proteoform. The combination of MMP-9 as analyte and its PTM by citrullination could be of clinical interest, especially in the field of arthritic diseases.

Recombinant Protein-Based Nanoparticles: Elucidating their Inflammatory Effects In Vivo and their Potential as a New Therapeutic Format.

Bacterial inclusion bodies (IBs) are protein-based nanoparticles of a few hundred nanometers formed during recombinant protein production processes in different bacterial hosts. IBs contain active protein in a mechanically stable nanostructured format that has been broadly characterized, showing promising potential in different fields such as tissue engineering, protein replacement therapies, cancer, and biotechnology. For immunomodulatory purposes, however, the interference of the format immunogenic properties-intrinsic to IBs-with the specific effects of the therapeutic protein is still an uncovered gap. For that, active and inactive forms of the catalytic domain of a matrix metalloproteinase-9 (MMP-9 and mutMMP-9, respectively) have been produced as IBs and compared with the soluble form for dermal inflammatory effects in mmp9 knock-out mice. After protein injections in air-pouches in the mouse model, MMP-9 IBs induce local neutrophil recruitment and increase pro-inflammatory chemokine levels, lasting for at least two days, whereas the effects triggered by the soluble MMP-9 format fade out after 3 h. Interestingly, the IB intrinsic effects (mutMMP-9 IBs) do not last more than 24 h. Therefore, it may be concluded that IBs could be used for the delivery of therapeutic proteins, such as immunomodulating proteins while preserving their stability in the specific tissue and without triggering important unspecific inflammatory responses due to the protein format.

The Biological Potential Hidden in Inclusion Bodies.

Inclusion bodies (IBs) are protein nanoclusters obtained during recombinant protein production processes, and several studies have demonstrated their potential as biomaterials for therapeutic protein delivery. Nevertheless, IBs have been, so far, exclusively sifted by their biological activity in vitro to be considered in further protein-based treatments in vivo. Matrix metalloproteinase-9 (MMP-9) protein, which has an important role facilitating the migration of immune cells, was used as model protein. The MMP-9 IBs were compared with their soluble counterpart and with MMP-9 encapsulated in polymeric-based micelles (PM) through ionic and covalent binding. The soluble MMP-9 and the MMP-9-ionic PM showed the highest activity values in vitro. IBs showed the lowest activity values in vitro, but the specific activity evolution in 50% bovine serum at room temperature proved that they were the most stable format. The data obtained with the use of an air-pouch mouse model showed that MMP-9 IBs presented the highest in vivo activity compared to the soluble MMP-9, which was associated only to a low and a transitory peak of activity. These results demonstrated that the in vivo performance is the addition of many parameters that did not always correlate with the in vitro behavior of the protein of interest, becoming especially relevant at evaluating the potential of IBs as a protein-based nanomaterial for therapeutic purposes.

MMP-9/Gelatinase B Degrades Immune Complexes in Systemic Lupus Erythematosus.

Systemic Lupus Erythematosus (SLE) is a common and devastating autoimmune disease, characterized by a dysregulated adaptive immune response against intracellular antigens, which involves both autoreactive T and B cells. In SLE, mainly intracellular autoantigens generate autoantibodies and these assemble into immune complexes and activate the classical pathway of the complement system enhancing inflammation. Matrix metalloproteinase-9 (MMP-9) levels have been investigated in the serum of SLE patients and in control subjects. On the basis of specific studies, it has been suggested to treat SLE patients with MMP inhibitors. However, some of these inhibitors induce SLE. Analysis of LPR-/-MMP-9-/- double knockout mice suggested that MMP-9 plays a protective role in autoantigen clearance in SLE, but the effects of MMP-9 on immune complexes remained elusive. Therefore, we studied the role of MMP-9 in the clearance of autoantigens, autoantibodies and immune complexes and demonstrated that the lack of MMP-9 increased the levels of immune complexes in plasma and local complement activation in spleen and kidney in the LPR-/- mouse model of SLE. In addition, we showed that MMP-9 dissolved immune complexes from plasma of lupus-prone LPR-/-/MMP-9-/- mice and from blood samples of SLE patients. Surprisingly, autoantigens incorporated into immune complexes, but not immunoglobulin heavy or light chains, were cleaved by MMP-9. We discovered Apolipoprotein-B 100 as a new substrate of MMP-9 by analyzing the degradation of immune complexes from human plasma samples. These data are relevant to understand lupus immunopathology and side-effects observed with the use of known drugs. Moreover, we caution against the use of MMP inhibitors for the treatment of SLE.

Propeptide glycosylation and galectin-3 binding decrease proteolytic activation of human proMMP-9/progelatinase B.

Matrix metalloproteinases (MMPs) are secreted as proenzymes, containing propeptides that interact with the catalytic zinc, thereby controlling MMP activation. The MMP-9 propeptide is unique in the MMP family because of its post-translational modification with an N-linked oligosaccharide. ProMMP-9 activation by MMP-3 occurs stepwise by cleavage of the propeptide in an aminoterminal (pro-AT) and carboxyterminal (pro-CT) peptide. We chemically synthesized aglycosyl pro-AT and pro-CT and purified recombinant glycosylated pro-ATSf-9 . First, we report new cleavage sites in the MMP-9 propeptide by MMP-3 and neutrophil elastase. Additionally, we demonstrated with the use of western blot analysis a higher resistance of glycosylated versus aglycosyl pro-AT against proteolysis by MMP-3, MMP-9, meprin α, neutrophil elastase and by protease-rich synovial fluids from rheumatoid arthritis patients. Moreover, we investigated the effect of glycosylation on proteolytic activation of human proMMP-9 with the use of zymography and dye-quenched gelatin cleavage analysis. Compared to recombinant Sf-9 proMMP-9 glycoforms, larger oligosaccharides of human neutrophil proMMP-9 increased resistance against proteolytic activation. Additionally, proMMP-9 from Congenital Disorder of Glycosylation patients, compared to healthy controls, showed a higher activation rate by MMP-3. Finally, we demonstrated that glycan-galectin-3 interactions reduced proMMP-9 activation. In conclusion, modification of MMP-9 propeptide glycosylation is a fine-tuning mechanism and co-determines the specific activity of MMP-9 in physiology and pathology. ENZYMES: MMP-9 EC 3.4.24.35, MMP-3 EC 3.4.24.17, meprin α EC 3.4.24.18, neutrophil elastase EC 3.4.21.37, trypsin EC 3.4.21.4 and PNGase F EC 3.5.1.52.

Gelatinase B/Matrix Metalloproteinase-9 as Innate Immune Effector Molecule in Achalasia.

OBJECTIVES: Achalasia is a primary esophageal motility disorder resulting from selective loss of inhibitory neurons in the esophageal myenteric plexus, likely due to an autoimmune response with involvement of the adaptive immune system. Innate immune processes of the host constitute the bridge between environmental etiological factors and the adaptive immune system. Although these remain poorly investigated, they might be of diagnostic and therapeutic relevance. In view of the role of extracellular proteolysis in organ-specific autoimmunity, we studied gelatinases of the matrix metalloproteinase (MMP) family in achalasia patients. METHODS: The presence of MMP-2 and MMP-9 proteoforms was analyzed in sera of two cohorts of achalasia patients. Additionally, with the use of immunohistopathological analysis, in situ MMP-2 and MMP-9 expression was investigated. Finally, we tested the paradigm of remnant epitopes generating autoimmunity (REGA) for achalasia-associated autoantigens by evaluating whether autoantigenic proteins are cleaved by MMP-9 into remnant epitopes. RESULTS: We showed significantly increased ratios of MMP-9/MMP-2 and activated MMP-9/proMMP-9 in sera of achalasia patients (n = 88) versus controls (n = 60). MMP-9-positive and MMP-2-positive cells were more abundant in achalasia (n = 49) versus control biopsies from transplant donors (n = 10). Furthermore, extensive damage within the plexus was found in the tissues with more MMP-9-positive cells. Additionally, we documented achalasia-associated autoantigens PNMA2, Ri, GAD65, and VIP as novel MMP-9 substrates. CONCLUSIONS: We provide new biomarkers and insights into innate immune mechanisms in the autoimmune pathology of achalasia. Our results imply that extracellular protease inhibition is worthwhile to test as therapeutic intervention in achalasia.

Neutrophils and Activated Macrophages Control Mucosal Immunity by Proteolytic Cleavage of Antileukoproteinase.

Antileukoproteinase or secretory leukocyte peptidase inhibitor is a small protein which protects the mucosal linings against excessive proteolysis, inflammation, and microbial infection. We discovered that gelatinase B or matrix metalloproteinase (MMP)-9, a secreted zinc-dependent endopeptidase typically found at sites of inflammation, destroys antileukoproteinase by cleavages within both of its two functional domains: the anti-microbial N-terminal and the anti-proteolytic C-terminal domains. Cleaved antileukoproteinase possessed a significantly lower ability to bind lipopolysaccharides (LPS) and a reduced capacity to inhibit neutrophil elastase (NE) activity. Whereas intact antileukoproteinase repressed proinflammatory transcript [prostaglandin-endoperoxide synthase 2 (PTGS2) and IL6] synthesis and protein secretion [e.g., of MMP-9] in human CD14+ blood monocytes stimulated with LPS, this effect was reduced or lost for cleaved antileukoproteinase. We demonstrated the in vivo presence of antileukoproteinase cleavage fragments in lower airway secretions of non-cystic fibrosis bronchiectasis patients with considerable levels of neutrophils and, hence, elastase and MMP-9 activity. As a comparison, other MMPs (MMP-2, MMP-7, and MMP-8) and serine proteases (NE, cathepsin G, and proteinase 3) were also able to cleave antileukoproteinase with similar or reduced efficiency. In conclusion, in specific mucosal pathologies, such as bronchiectasis, neutrophils, and macrophage subsets control local immune reactions by proteolytic regulation, here described as the balance between MMPs (in particular MMP-9), serine proteases and local tissue inhibitors.

Gelatinase B/matrix metalloproteinase-9 is a phase-specific effector molecule, independent from Fas, in experimental autoimmune encephalomyelitis.

Gelatinase B/matrix metalloproteinase-9 (MMP-9) triggers multiple sclerosis (MS) and the animal model of experimental autoimmune encephalomyelitis (EAE) by the breakdown of the blood-brain barrier. Interestingly, MMP-9 is beneficial in systemic autoimmunity caused by Fas-deficiency. Fas-deficient (faslpr) and Fas-ligand-deficient mice are protected against EAE. We here investigated the interaction between Fas and MMP-9 in the setting of induction of EAE and compared short- and long-term effects. We provoked EAE with myelin oligodendrocyte glycoprotein (MOG) peptide and compared EAE development in four genotypes (wild-type (WT), single knockout mmp-9-/-, faslpr, and mmp-9-/-/faslpr) and monitored leukocytes, cytokines and chemokines as immunological parameters. As expected, faslpr mice were resistant against EAE induction, whereas MMP-9 single knockout mice were not. In the double mmp-9-/-/ faslpr mice the effects on disease scores pointed to independent rather than interrelated disease mechanisms. On a short term, after EAE induction leukocytes infiltrated into the brain and cytokine and chemokine levels were significantly higher in all the four genotypes studied, even in the faslpr and mmp-9-/-/faslpr, which did not develop clinical disease. The levels of MMP-9 but not of MMP-2 were increased in the brain and in the peripheral organs after EAE induction. After 40 days all the animals recovered and did not show signs of EAE. However, the absence of MMP-9 in the remission phase suggested a protective role of MMP-9 in the late phase of the disease, because single mmp-9-/- mice presented a delayed remission in comparison with WT animals suggesting a phase-dependent role of MMP-9 in the disease. Nevertheless, the levels of some cytokines and chemokines remained higher than in control animals even 100 days after EAE induction, attesting to a prolonged state of immune activation. We thus yielded new insights and useful markers to monitor this activated immune status. Furthermore, MMP-9 but not MMP-2 levels remained increased in the brains and, to a higher extend, in the spleens of the WT mice even during the remission phase, which is in line with the role of MMP-9 as a useful marker and a protective factor for EAE in the remission phase.

Differential inhibition of activity, activation and gene expression of MMP-9 in THP-1 cells by azithromycin and minocycline versus bortezomib: A comparative study.

Gelatinase B or matrix metalloproteinase-9 (MMP-9) (EC 3.4.24.35) is increased in inflammatory processes and cancer, and is associated with disease progression. In part, this is due to MMP-9-mediated degradation of extracellular matrix, facilitating influx of leukocytes into inflamed tissues and invasion or metastasis of cancer cells. MMP-9 is produced as proMMP-9 and its propeptide is subsequently removed by other proteases to generate proteolytically active MMP-9. The significance of MMP-9 in pathologies triggered the development of specific inhibitors of this protease. However, clinical trials with synthetic inhibitors of MMPs in the fight against cancer were disappointing. Reports on active compounds which inhibit MMP-9 should be carefully examined in this regard. In a considerable set of recent publications, two antibiotics (minocycline and azythromycin) and the proteasome inhibitor bortezomib, used in cancers, were reported to inhibit MMP-9 at different stages of its expression, activation or activity. The current study was undertaken to compare and to verify the impact of these compounds on MMP-9. With exception of minocycline at high concentrations (>100 µM), the compounds did not affect processing of proMMP-9 into MMP-9, nor did they affect direct MMP-9 gelatinolytic activity. In contrast, azithromycin specifically reduced MMP-9 mRNA and protein levels without affecting NF-κB in endotoxin-challenged monocytic THP-1 cells. Bortezomib, although being highly toxic, had no MMP-9-specific effects but significantly upregulated cyclooxygenase-2 (COX-2) activity and PGE2 levels. Overall, our study clarified that azithromycin decreased the levels of MMP-9 by reduction of gene and protein expression while minocycline inhibits proteolytic activity at high concentrations.

PHD1 regulates p53-mediated colorectal cancer chemoresistance.

Overcoming resistance to chemotherapy is a major challenge in colorectal cancer (CRC) treatment, especially since the underlying molecular mechanisms remain unclear. We show that silencing of the prolyl hydroxylase domain protein PHD1, but not PHD2 or PHD3, prevents p53 activation upon chemotherapy in different CRC cell lines, thereby inhibiting DNA repair and favoring cell death. Mechanistically, PHD1 activity reinforces p53 binding to p38α kinase in a hydroxylation-dependent manner. Following p53-p38α interaction and chemotherapeutic damage, p53 can be phosphorylated at serine 15 and thus activated. Active p53 allows nucleotide excision repair by interacting with the DNA helicase XPB, thereby protecting from chemotherapy-induced apoptosis. In accord with this observation, PHD1 knockdown greatly sensitizes CRC to 5-FU in mice. We propose that PHD1 is part of the resistance machinery in CRC, supporting rational drug design of PHD1-specific inhibitors and their use in combination with chemotherapy.