Functional activation of Jak1 and Jak3 by selective association with IL-2 receptor subunits

The interleukin-2 receptor (IL-2R) consists of three subunits: the IL-2R alpha, IL-2R beta, and IL-2R gamma chains, the last of which is also used in the receptors for IL-4, IL-7, and IL-9. Stimulation with IL-2 induces the tyrosine phosphorylation and activation of the Janus kinases Jak1 and Jak3. Jak1 and Jak3 were found to be selectively associated with the "serine-rich" region of IL-2R beta and the carboxyl-terminal region of IL-2R gamma, respectively. Both regions were necessary for IL-2 signaling. Furthermore, Jak3-negative fibroblasts expressing reconstituted IL-2R became responsive to IL-2 after the additional expression of Jak3 complementary DNA. Thus, activation of Jak1 and Jak3 may be a key event in IL-2 signaling.

CHIP is a chaperone-dependent E3 ligase that ubiquitylates unfolded protein

The ubiquitin-proteasome system catalyses the immediate destruction of misfolded or impaired proteins generated in cells, but how this proteolytic machinery recognizes abnormality of cellular proteins for selective elimination remains elusive. Here, we report that the C-terminus of Hsc70-interacting protein (CHIP) with a U-box domain is an E3 ubiquitin-ligase collaborating with molecular chaperones Hsp90 and Hsc70. Thermally denatured firefly luciferase was multiubiquitylated by CHIP in the presence of E1 and E2 (Ubc4 or UbcH5c) in vitro, only when the unfolded substrate was captured by Hsp90 or Hsc70 and Hsp40. No ubiquitylating activity was detected in CHIP lacking the U-box region. CHIP efficiently ubiquitylated denatured luciferase trapped by the C-terminal region of Hsp90, which contains a CHIP binding site. CHIP also showed self-ubiquitylating activity independent of target ubiquitylation. Our results indicate that CHIP can be regarded as 'a quality-control E3' that selectively ubiquitylates unfolded protein(s) by collaborating with molecular chaperones.

The IL-2 receptor complex: its structure, function, and target genes

Proliferation of T lymphocytes is triggered by the interaction of IL-2 with its specific receptor following T lymphocyte activation. The receptor for IL-2 consists of at least three distinct subunits, the alpha chain (IL-2R alpha), the beta chain (IL-2R beta), and the gamma chain (IL-2R gamma). Although the role of IL-2R gamma in IL-2 signalling remains unclear, IL-2R beta is the subunit critical for receptor-mediated signalling. Because IL-2R beta lacks any apparent catalytic motifs, IL-2R beta may be physically or functionally coupled to other signalling molecules. Structure-function studies of IL-2R beta have revealed that at least two distinct cytoplasmic regions of IL-2R beta are involved in IL-2-induced cellular signalling. The "serine-rich" region of IL-2R beta was identified as a region critical for IL-2-induced mitotic signalling from experiments in which IL-2R beta mutant cDNAs lacking a particular cytoplasmic region or regions were expressed in an IL-3-dependent mouse pro-B cell line (BAF-B03). Meanwhile, another cytoplasmic region of IL-2R beta, the "acidic" region, is responsible for its physical association with an src-family protein tyrosine kinase (PTK), p56lck and is critical for activating the p56lck PTK following IL-2 stimulation. It is now evident that IL-2R beta is linked to at least two intracellular signalling pathways that mediate nuclear proto-oncogene induction. One pathway is linked to tyrosine phosphorylation events, mediated by a src-family protein tyrosine kinase (PTK), and that pathway leads to the induction of the c-fos, c-jun, and other genes of this family. Another pathway leads to c-myc gene induction by an as yet unknown mechanism. We discuss the complex signalling machinery that links the cell surface receptor to the nuclear events.

Hip, a novel cochaperone involved in the eukaryotic Hsc70/Hsp40 reaction cycle

The Hsc70-interacting protein Hip, a tetratricopeptide repeat protein, participates in the regulation of the eukaryotic 70 kDa heat shock cognate Hsc70. One Hip oligomer binds the ATPase domains of at least two Hsc70 molecules dependent on activation of the Hsc70 ATPase by Hsp40. While hydrolysis remains the rate-limiting step in the ATPase cycle, Hip stabilizes the ADP state of Hsc70 that has a high affinity for substrate protein. Through its own chaperone activity, Hip may contribute to the interaction of Hsc70 with various target proteins. We propose a mechanism for the regulation of eukaryotic Hsc70 that is distinct from that of bacterial Hsp70. The Hsc70/Hsp40/Hip system is apparently independent of a GrpE-like nucleotide exchange factor.

Three distinct IL-2 signaling pathways mediated by bcl-2, c-myc, and lck cooperate in hematopoietic cell proliferation

Two interleukin-2 receptor-dependent signaling pathways have thus far been identified: the c-fos/c-jun induction pathway mediated by src family protein-tyrosine kinases and the c-myc induction pathway. Here, we provide evidence for the existence of a third, rapamycin-sensitive pathway, which results in the induction of another proto-oncogene, bcl-2. In the hematopoietic cell line BAF-B03, the expression of any two of lckF505 (an active form of p56lck), Bcl-2, or c-Myc is sufficient to promote transit of the cell cycle, regardless of the activation state of the third pathway. We also provide evidence that epidermal growth factor receptor signaling may act through the same pathway that involves p56lck. These studies demonstrate a novel approach to dissecting signaling pathways regulating cellular proliferation.

Hybrid proteasomes. Induction by interferon-gamma and contribution to ATP-dependent proteolysis

Eukaryotic cells contain various types of proteasomes. Core 20 S proteasomes (abbreviated 20 S below) have two binding sites for the regulatory particles, PA700 and PA28. PA700-20 S-PA700 complexes are known as 26 S proteasomes and are ATP-dependent machines that degrade cell proteins. PA28 is found both in previously described complexes of the type PA28-20 S-PA28 and in complexes that also contain PA700, as PA700-20 S-PA28. We refer to the latter as "hybrid proteasomes." The relative amounts of the various types of proteasomes in HeLa extracts were determined by a combination of immunoprecipitation and immunoblotting. Hybrid proteasomes accounted for about a fourth of all proteasomes in the extracts. Association of PA28 and proteasomes proved to be ATP-dependent. Hybrid proteasomes catalyzed ATP-dependent degradation of ornithine decarboxylase (ODC) without ubiquitinylation, as do 26 S proteasomes. In contrast, the homo-PA28 complex (PA28-20 S-PA28) was incapable of degrading ODC. Intriguingly, a major immunomodulatory cytokine, interferon-gamma, appreciably enhanced the ODC degradation in HeLa and SW620 cells through induction of the hybrid proteasome, which may also be responsible for the immunological processing of intracellular antigens. Taken together, we report here for the first time the existence of two types of ATP-dependent proteases, the 26 S proteasome and the hybrid proteasome, which appear to share the ATP-dependent proteolytic pathway in mammalian cells.

Asciminib in Chronic Myeloid Leukemia after ABL Kinase Inhibitor Failure

BACKGROUND

Asciminib is an allosteric inhibitor that binds a myristoyl site of the BCR-ABL1 protein, locking BCR-ABL1 into an inactive conformation through a mechanism distinct from those for all other ABL kinase inhibitors. Asciminib targets both native and mutated BCR-ABL1, including the gatekeeper T315I mutant. The safety and antileukemic activity of asciminib in patients with Philadelphia chromosome-positive leukemia are unknown.

METHODS

In this phase 1, dose-escalation study, we enrolled 141 patients with chronic-phase and 9 with accelerated-phase chronic myeloid leukemia (CML) who had resistance to or unacceptable side effects from at least two previous ATP-competitive tyrosine kinase inhibitors (TKIs). The primary objective was to determine the maximum tolerated dose or the recommended dose (or both) of asciminib. Asciminib was administered once or twice daily (at doses of 10 to 200 mg). The median follow-up was 14 months.

RESULTS

Patients were heavily pretreated; 70% (105 of 150 patients) had received at least three TKIs. The maximum tolerated dose of asciminib was not reached. Among patients with chronic-phase CML, 34 (92%) with a hematologic relapse had a complete hematologic response; 31 (54%) without a complete cytogenetic response at baseline had a complete cytogenetic response. A major molecular response was achieved or maintained by 12 months in 48% of patients who could be evaluated, including 8 of 14 (57%) deemed to have resistance to or unacceptable side effects from ponatinib. A major molecular response was achieved or maintained by 12 months in 5 patients (28%) with a T315I mutation at baseline. Clinical responses were durable; a major molecular response was maintained in 40 of 44 patients. Dose-limiting toxic effects included asymptomatic elevations in the lipase level and clinical pancreatitis. Common adverse events included fatigue, headache, arthralgia, hypertension, and thrombocytopenia.

CONCLUSIONS

Asciminib was active in heavily pretreated patients with CML who had resistance to or unacceptable side effects from TKIs, including patients in whom ponatinib had failed and those with a T315I mutation. (Funded by Novartis Pharmaceuticals; ClinicalTrials.gov number, NCT02081378.).

Regulation of the heat-shock protein 70 reaction cycle by the mammalian DnaJ homolog, Hsp40

The effects of the human DnaJ homolog, Hsp40, on the ATPase and chaperone functions of the constitutively expressed Hsp70 homolog, Hsc70, were analyzed. Hsp40 stimulates the hydrolysis of ATP by Hsc70, causing a approximately 7-fold increase in its steady-state ATPase activity. In contrast to the prokaryotic Hsp70 system, ATP-hydrolysis and not the release of bound ADP is the rate-limiting step in the overall ATPase cycle of mammalian Hsc70. The ability to activate the Hsc70 ATPase is partially preserved in a deletion mutant containing the J-domain and the G/F region of Hsp40 but not in a deletion mutant that contains the J-domain alone. As a result of its ATPase stimulating activity, addition of Hsp40 allows Hsc70 to bind peptide in the presence of ATP, whereas in the absence of Hsp40, peptide is efficiently released upon ATP binding to Hsc70. The functional cooperation of Hsp40 with Hsc70 is essential to ensure the ATP hydrolysis-dependent binding of aggregation-sensitive denatured polypeptides, such as thermally denatured firefly luciferase and chemically denatured rhodanese. Binding of these proteins results in the formation of ternary complexes of Hsc70, Hsp40, and substrates. Hsc70 and Hsp40 cooperate with further factors in protein renaturation, as demonstrated by the finding that luciferase, thermally denatured in the presence of Hsc70, Hsp40, and ATP, refolds upon addition of rabbit reticulocyte cytosol. Our results indicate that Hsp40 has a critical regulatory function in the Hsc70 ATPase cycle that is required for the efficient loading of peptide substrate onto Hsc70.

Calcium-activated neutral protease and its endogenous inhibitor. Activation at the cell membrane and biological function

The structures of calcium-activated neutral protease (CANP) and its endogenous inhibitor elucidated recently have revealed novel features with respect to their structure-function relationship and enzyme activity regulation. The protease is regarded as a proenzyme which can be activated at the cell membrane in the presence of Ca2+ and phospholipid, and presumably regulates the functions of proteins, especially membrane-associated proteins, by limited proteolysis. Protein kinase C is hydrolysed and activated by CANP at the cell membrane to a cofactor-independent form. These results are reviewed and the possible involvement of CANP in signal transduction is discussed.

Tyrosine phosphorylation in T cells is regulated by phosphatase activity: studies with phenylarsine oxide

Activation of T cells induces rapid tyrosine phosphorylation on the T-cell receptor zeta chain and other substrates. These phosphorylations can be regulated by a number of protein-tyrosine kinases (ATP: protein-tyrosine O-phosphotransferase, EC 2.7.1.112) and protein-tyrosine-phosphatases (protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48). In this study, we demonstrate that phenylarsine oxide can inhibit tyrosine phosphatases while leaving tyrosine kinase function intact. We use this reagent to investigate the effect of tyrosine phosphatase inhibition in a murine T-cell hybridoma. Increasing concentrations of phenylarsine oxide result in an increase in tyrosine phosphate on a number of intracellular substrates in unstimulated T cells, suggesting that a protein-tyrosine kinase is constitutively active in these cells. The effect of phenylarsine oxide on T cells stimulated with an anti-Thy 1 monoclonal antibody is more complex. At low concentrations of drug, there is a synergistic increase in the level of tyrosine phosphate on certain cellular substrates. At higher concentrations, anti-Thy 1-stimulated tyrosine phosphorylation is inhibited. These results indicate that tyrosine phosphorylation in T cells is tightly regulated by tyrosine phosphatases. Partial inhibition of these enzymes results in enhanced substrate phosphorylation. Inhibition of all stimulated tyrosine phosphorylation by high doses of phenylarsine oxide suggests that tyrosine kinase activity is regulated by tyrosine phosphatases.

Mouse Ror2 receptor tyrosine kinase is required for the heart development and limb formation

BACKGROUND

A mouse receptor tyrosine kinase (RTK), mRor2, which belongs to the Ror-family of RTKs consisting of at least two structurally related members, is primarily expressed in the heart and nervous system during mouse development. To elucidate the function of mRor2, we generated mice with a mutated mRor2 locus.

RESULTS

Mice with a homozygous mutation in mRor2 died just after birth, exhibiting dwarfism, severe cyanosis, and short limbs and tails. Whole-mount in situ hybridization analysis showed that mRor2 was expressed in the branchial arches, heart and limb/tailbuds, in addition to the developing nervous system. The mutants had cardiac septal defects, mainly a ventricular septal defect. In addition, an examination of the skeletal systems revealed that the mutants had shorter limbs, vertebrae and facial structure, with a particular defect in their distal portions, and that almost no calcification was observed in their distal limbs. Histological examination showed abnormalities in the chondrocytes.

CONCLUSIONS

Our findings suggest that mRor2 plays essential roles in the development of the heart and in limb/tail formation, in particular cardiac septal formation and ossification of distal portions of limbs and tails.

Building a multichain receptor: synthesis, degradation, and assembly of the T-cell antigen receptor

The murine T-cell antigen receptor consists of at least seven chains and six different proteins. The two clonotypic chains alpha and beta are glycoproteins of 40-45 kDa present as a disulfide-linked heterodimer. Four clonally invariant chains include delta (a 26-kDa glycoprotein), gamma (a 21-kDa glycoprotein), epsilon (a 25-kDa protein), and zeta (a 16-kDa protein). zeta is found in the complex as a disulfide-linked homodimer. The clonotypic chains and the invariant chains form a noncovalent complex on the cell surface. We have developed antibodies against each of the chains and used them to examine the assembly of the mature complex in the murine antigen-specific T-cell hybridoma 2B4. Pulse-chase studies of metabolically labeled cells demonstrate that many of the chains are synthesized in great excess over the amount assembled into the mature complex. These excess chains, either as free components or as partially assembled complexes, are rapidly degraded. This degradation most likely takes place in the lysosomes. The complete complex is quite stable with a long half-life. A specific hierarchy of partially assembled complexes can be discerned.

Regulation of the antioncogenic Chk2 kinase by the oncogenic Wip1 phosphatase

The antioncogenic Chk2 kinase plays a crucial role in DNA damage-induced cell-cycle checkpoint regulation. Here we show that Chk2 associates with the oncogenic protein Wip1 (wild-type p53-inducible phosphatase 1) (PPM1D), a p53-inducible protein phosphatase. Phosphorylation of Chk2 at threonine68 (Thr68), a critical event for Chk2 activation, which is normally induced by DNA damage or overexpression of Chk2, is inhibited by expression of wild-type (WT), but not a phosphatase-deficient mutant (D314A) of Wip1 in cultured cells. Furthermore, an in vitro phosphatase assay revealed that Wip1 (WT), but not Wip1 (D314A), dephosphorylates Thr68 on phosphorylated Chk2 in vitro, resulting in the inhibition of Chk2 kinase activity toward glutathione S-transferase-Cdc25C. Moreover, inhibition of Wip1 expression by RNA interference results in abnormally sustained Thr68 phosphorylation of Chk2 and increased susceptibility of cells in response to DNA damage, indicating that Wip1 acts as a negative regulator of Chk2 in response to DNA damage.

Activation of Stat5 by interleukin 2 requires a carboxyl-terminal region of the interleukin 2 receptor beta chain but is not essential for the proliferative signal transmission

The high-affinity interleukin 2 (IL-2) receptor (IL-2R) consists of three subunits: the IL-2R alpha, IL-2R beta c, and IL-2R gamma c chains. Two members of the Janus kinase family, Jak1 and Jak3, are associated with IL-2R beta c and IL-2R gamma c, respectively, and they are activated upon IL-2 stimulation. The cytokine-mediated Jak kinase activation usually results in the activation of a family of latent transcription factors termed Stat (signal transducer and activator of transcription) proteins. Recently, the IL-2-induced Stat protein was purified from human lymphocytes and found to be the homologue of sheep Stat5/mammary gland factor. We demonstrate that the human Stat5 is activated by IL-2 and that Jak3 is required for the efficient activation. The cytoplasmic region of the IL-2R beta c chain required for activation of Stat5 is mapped within the carboxyl-terminal 147 amino acids. On the other hand, this region is not essential for IL-2-induced cell proliferation.

Heat-induced chaperone activity of HSP90

The 90-kDa stress protein, HSP90, is a major cytosolic protein ubiquitously distributed in all species. Using two substrate proteins, dihydrofolate reductase (DHFR) and firefly luciferase, we demonstrate here that HSP90 newly acquires a chaperone activity when incubated at temperatures higher than 46 degrees C, which is coupled with self-oligomerization of HSP90. While chemically denatured DHFR refolds spontaneously upon dilution from denaturant, oligomerized HSP90 bound DHFR during the process of refolding and prevented it from renaturation. DHFR was released from the complex with HSP90 by incubating with GroEL/ES complexes in an ATP-dependent manner and refolded into the native form. alpha-Casein inhibited the binding of DHFR to HSP90 and also chased DHFR from the complex with HSP90. These results suggest that HSP90 binds substrates to maintain them in a folding-competent structure. Furthermore, we found that HSP90 prevents luciferase from irreversible thermal denaturation and enables it to refold when postincubated with reticulocyte lysates. This heat-induced chaperone activity of HSP90 associated with its oligomerization may have a pivotal role in protection of cells from thermal damages.

Effect of atorvastatin on microRNA 221 / 222 expression in endothelial progenitor cells obtained from patients with coronary artery disease

BACKGROUND

Endothelial progenitor cells (EPCs) play an important role in the maintenance of vascular integrity. Lipid lowering therapy (LLT) with statins may contribute to biologically relevant activities including the proliferation of endothelial cells. The physiological role of microRNA (miR)-221/222, a newly discovered class of small RNA, is closely linked to the proliferation of endothelial cells. We therefore investigated whether LLT with statins might affect miR-221/222 expression in EPCs obtained from patients with coronary artery disease (CAD).

MATERIALS AND METHODS

This study included 44 patients with stable CAD and 22 subjects without CAD (non-CAD). Patients with CAD were randomized to 12 months of LLT with atorvastatin (10 mg day(-1)) or pravastatin (10 mg day(-1)). EPCs were obtained from peripheral blood at baseline and after 12 months of statin therapy. Levels of miR-221/222 in EPCs were measured by real-time RT-PCR.

RESULTS

Levels of miR-221/222 were significantly higher in the CAD group than in the non-CAD group (P < 0.01). Levels of miR-221/222 were weakly negatively correlated with EPC number in the CAD group. After 12 months of therapy, changes in lipid profiles were greater in the atorvastatin group than in the pravastatin group. LLT with atorvastatin markedly increased EPC numbers and decreased miR-221/222 levels (all P < 0.05), whereas LLT with pravastatin did not change EPC numbers or miR-221/222 levels.

CONCLUSIONS

This study demonstrates that LLT with atorvastatin increases EPC numbers and decreases miR-221/222 levels in patients with CAD, possibly contributing to the beneficial effects of LLT with atorvastatin in this disorder.

Protein tyrosine kinase Syk is associated with and activated by the IL-2 receptor: possible link with the c-myc induction pathway

The IL-2 receptor (IL-2R) consists of three subunits, the IL-2R alpha, IL-2R beta, and IL-2R gamma chains. The IL-2-induced proliferative signals emanate from the cytoplasmic domains of IL-2R beta and IL-2R gamma, but the nature and function of the signaling molecules that transmit these signals are not fully understood. Here, we report that Syk protein tyrosine kinase (PTK) is physically associated with IL-2R in peripheral blood lymphocytes. cDNA expression studies further revealed that this association is critical for the IL-2-induced activation of Syk PTK, which occurs primarily via the serine-rich region of the IL-2R beta chain, which is essential for proliferative signal transmission. Furthermore, we provide evidence that in the hematopoietic cell line, BAF-B03, the activation of Syk PTK results in the induction of the c-myc gene, an event critical for the cell proliferation. Thus, Syk PTK may be a critical integral member of the signaling molecules engaged by the IL-2R.

The amino terminus of JAK3 is necessary and sufficient for binding to the common gamma chain and confers the ability to transmit interleukin 2-mediated signals

JAK3 is a protein tyrosine kinase that specifically associates with the common gamma chain (gammac), a shared subunit of receptors for interleukin (IL) 2, 4, 7, 9, and 15. Patients deficient in either JAK3 or gammac presented with virtually identical forms of severe combined immunodeficiency (SCID), underscoring the importance of the JAK3-gammac interaction. Despite the key roles of JAK3 and gammac in lymphocytic development and function, the molecular basis of this interaction remains poorly understood. In this study, we have characterized the regions of JAK3 involved in gammac association. By developing a number of chimeric JAK3-JAK2 constructs, we show that the binding specificity to gammac can be conferred to JAK2 by transferring the N-terminal domains of JAK3. Moreover, those JAK3-JAK2 chimeras capable of binding gammac were also capable of reconstituting IL-2 signaling as measured by inducible phosphorylation of the chimeric JAK3-JAK2 protein, JAK1, the IL-2 receptor beta chain, and signal transducer and activator of transcription 5A. Subsequent deletion analyses of JAK3 have identified the N-terminal JH7-6 domains as a minimal region sufficient for gammac association. Furthermore, expression of the mutant containing only the JH7-6 domains effectively competed with full-length JAK3 for binding to gammac. We conclude that the JH7-6 domains of JAK3 are necessary and sufficient for gammac association. These studies offer clues toward a broader understanding of JAK-mediated cytokine signaling and may provide a target for the development of novel therapeutic modalities in immunologically mediated diseases.

Histochemical localization of nitric oxide synthase in rat enteric nervous system

The localization of nitric oxide synthase, the enzyme responsible for producing the short-acting messenger nitric oxide, has been determined in the digestive tract of the rat using histochemistry for reduced nicotinamide adenine dinucleotide phosphate-diaphorase activity, a specific marker for neuronal nitric oxide synthase. Positively stained neurons were found throughout the entire digestive tract from the esophagus to the rectum. Positive neuronal somata were very common in the myenteric ganglia. Dense positive fibers were distributed in internodal strands, the secondary plexus, the tertiary plexus, and were particularly abundant in the deep muscular plexus, while very few were observed in the submucosal ganglia. The density of these positive structures was higher in the small and large intestine than in the esophagus and stomach. The pattern of distribution suggested that some of these positive cells innervate gut muscles. Double-staining revealed that in these enteric neurons, nitric oxide synthase does not co-localize with acetylcholinesterase. Instead, vasoactive intestinal polypeptide almost always coexists with nitric oxide synthase in the myenteric plexus. Thus, nitric oxide and vasoactive intestinal polypeptide may be co-transmitters in a population of non-adrenergic, non-cholinergic neurons in the enteric nervous system.

Panagiotopoulou E, Panagoulias I, Pandini CE, Panduro Vazquez JG, Pani P, Panitkin S, Pantea D, Paolozzi L, Papadopoulou TD, Papageorgiou K, Paramonov A, Paredes Hernandez D, Parker AJ, Parker MA, Parker KA, Parodi F, Parsons JA, Parzefall U, Pascuzzi VR, Pasqualucci E, Passaggio S, Pastore F, Pásztor G, Pataraia S, Pater JR, Pauly T, Pearce J, Pearson B, Pedersen LE, Pedersen M, Pedraza Lopez S, Pedro R, Peleganchuk SV, Penc O, Peng C, Peng H, Penwell J, Peralva BS, Perego MM, Perepelitsa DV, Perez Codina E, Perini L, Pernegger H, Perrella S, Peschke R, Peshekhonov VD, Peters K, Peters RFY, Petersen BA, Petersen TC, Petit E, Petridis A, Petridou C, Petroff P, Petrolo E, Petrov M, Petrucci F, Pettersson NE, Peyaud A, Pezoa R, Phillips PW, Piacquadio G, Pianori E, Picazio A, Piccaro E, Piccinini M, Pickering MA, Piegaia R, Pilcher JE, Pilkington AD, Pin AWJ, Pinamonti M, Pinfold JL, Pingel A, Pires S, Pirumov H, Pitt M, Plazak L, Pleier MA, Pleskot V, Plotnikova E, Pluth D, Poettgen R, Poggioli L, Pohl D, Polesello G, Poley A, Policicchio A, Polifka R, Polini A, Pollard CS, Polychronakos V, Pommès K, Pontecorvo L, Pope BG, Popeneciu GA, Poppleton A, Pospisil S, Potamianos K, Potrap IN, Potter CJ, Potter CT, Poulard G, Poveda J, Pozdnyakov V, Pozo Astigarraga ME, Pralavorio P, Pranko A, Prell S, Price D, Price LE, Primavera M, Prince S, Prokofiev K, Prokoshin F, Protopopescu S, Proudfoot J, Przybycien M, Puddu D, Purohit M, Puzo P, Qian J, Qin G, Qin Y, Quadt A, Quayle WB, Queitsch-Maitland M, Quilty D, Raddum S, Radeka V, Radescu V, Radhakrishnan SK, Radloff P, Rados P, Ragusa F, Rahal G, Raine JA, Rajagopalan S, Rammensee M, Rangel-Smith C, Ratti MG, Rauch DM, Rauscher F, Rave S, Ravenscroft T, Ravinovich I, Raymond M, Read AL, Readioff NP, Reale M, Rebuzzi DM, Redelbach A, Redlinger G, Reece R, Reed RG, Reeves K, Rehnisch L, Reichert J, Reiss A, Rembser C, Ren H, Rescigno M, Resconi S, Rezanova OL, Reznicek P, Rezvani R, Richter R, Richter S, Richter-Was E, Ricken O, Ridel M, Rieck P, Riegel CJ, Rieger J, Rifki O, Rijssenbeek M, Rimoldi A, Rimoldi M, Rinaldi L, Ristić B, Ritsch E, Riu I, Rizatdinova F, Rizvi E, Rizzi C, Robertson SH, Robichaud-Veronneau A, Robinson D, Robinson JEM, Robson A, Roda C, Rodina Y, Rodriguez Perez A, Rodriguez Rodriguez D, Roe S, Rogan CS, Røhne O, Roloff J, Romaniouk A, Romano M, Romano Saez SM, Romero Adam E, Rompotis N, Ronzani M, Roos L, Ros E, Rosati S, Rosbach K, Rose P, Rosien NA, Rossetti V, Rossi E, Rossi LP, Rosten JHN, Rosten R, Rotaru M, Roth I, Rothberg J, Rousseau D, Rozanov A, Rozen Y, Ruan X, Rubbo F, Rudolph MS, Rühr F, Ruiz-Martinez A, Rurikova Z, Rusakovich NA, Ruschke A, Russell HL, Rutherfoord JP, Ruthmann N, Ryabov YF, Rybar M, Rybkin G, Ryu S, Ryzhov A, Rzehorz GF, Saavedra AF, Sabato G, Sacerdoti S, Sadrozinski HFW, Sadykov R, Safai Tehrani F, Saha P, Sahinsoy M, Saimpert M, Saito T, Sakamoto H, Sakurai Y, Salamanna G, Salamon A, Salazar Loyola JE, Salek D, Sales De Bruin PH, Salihagic D, Salnikov A, Salt J, Salvatore D, Salvatore F, Salvucci A, Salzburger A, Sammel D, Sampsonidis D, Sánchez J, Sanchez Martinez V, Sanchez Pineda A, Sandaker H, Sandbach RL, Sandhoff M, Sandoval C, Sankey DPC, Sannino M, Sansoni A, Santoni C, Santonico R, Santos H, Santoyo Castillo I, Sapp K, Sapronov A, Saraiva JG, Sarrazin B, Sasaki O, Sato K, Sauvan E, Savage G, Savard P, Savic N, Sawyer C, Sawyer L, Saxon J, Sbarra C, Sbrizzi A, Scanlon T, Scannicchio DA, Scarcella M, Scarfone V, Schaarschmidt J, Schacht P, Schachtner BM, Schaefer D, Schaefer L, Schaefer R, Schaeffer J, Schaepe S, Schaetzel S, Schäfer U, Schaffer AC, Schaile D, Schamberger RD, Scharf V, Schegelsky VA, Scheirich D, Schernau M, Schiavi C, Schier S, Schillo C, Schioppa M, Schlenker S, Schmidt-Sommerfeld KR, Schmieden K, Schmitt C, Schmitt S, Schmitz S, Schneider B, Schnoor U, Schoeffel L, Schoening A, Schoenrock BD, Schopf E, Schott M, Schouwenberg JFP, Schovancova J, Schramm S, Schreyer M, Schuh N, Schulte A, Schultens 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Performance of the ATLAS trigger system in 2015

During 2015 the ATLAS experiment recorded [Formula: see text] of proton-proton collision data at a centre-of-mass energy of [Formula: see text]. The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton-proton collision data.