[Improvement of tissue fibrosis in TAFRO syndrome by prednisolone monotherapy].

We report the case of a 48-year-old man who presented with fatigue and weight loss. A local physician observed elevated alkaline phosphatase levels, anemia, thrombocytopenia, and renal dysfunction. Fever also appeared, and the patient was admitted to our hospital. Computed tomography revealed hepatosplenomegaly, pleural and ascitic fluid, and left axillary lymphadenopathy. Bone marrow biopsy indicated hyperplasia with increased megakaryocytes and reticulin fibrosis. Axillary lymph node biopsy showed Castleman's disease-like features. Liver biopsy revealed proliferation of reticulin fibrosis. Therefore, TAFRO syndrome was diagnosed and treatment with 1 mg/kg prednisolone was started. Anemia and thrombocytopenia improved, and after 24 weeks of treatment, serum hyaluronic acid and type IV collagen decreased to the normal range. Bone marrow biopsy after 18 weeks of treatment showed decreased reticular fibers. In TAFRO syndrome, improvement of liver and bone marrow fibrosis can be expected with adequate intervention, and serum hyaluronic acid and type IV collagen are useful for evaluating fibrosis.

Chronic stress alters lipid mediator profiles associated with immune-related gene expressions and cell compositions in mouse bone marrow and spleen.

Despite the importance of lipid mediators in stress and depression and their link to inflammation, the influence of stress on these mediators and their role in inflammation is not fully understood. This study used RNA-seq, LC-MS/MS, and flow cytometry analyses in a mouse model subjected to chronic social defeat stress to explore the effects of acute and chronic stress on lipid mediators, gene expression, and cell population in the bone marrow and spleen. In the bone marrow, chronic stress induced a sustained transition from lymphoid to myeloid cells, accompanied by corresponding changes in gene expression. This change was associated with decreased levels of 15-deoxy-d12,14-prostaglandin J2, a lipid mediator that inhibits inflammation. In the spleen, chronic stress also induced a lymphoid-to-myeloid transition, albeit transiently, alongside gene expression changes indicative of extramedullary hematopoiesis. These changes were linked to lower levels of 12-HEPE and resolvins, both critical for inhibiting and resolving inflammation. Our findings highlight the significant role of anti-inflammatory and pro-resolving lipid mediators in the immune responses induced by chronic stress in the bone marrow and spleen. This study paves the way for understanding how these lipid mediators contribute to the immune mechanisms of stress and depression.

Amyloid deposition through endocytosis in vascular endothelial cells.

No mechanistic lead is known for establishing AL amyloid deposits in organs. We here report an electron microscopic (EM) analysis in a case of intestinal AL amyloidosis before initiating treatment for amyloidosis. The dense deposits of amyloid fibrils are concentrated around the small blood vessels in the submucosal area of intestinal tissue. Surprisingly, we observed endothelial cells (ECs) of blood vessels containing plenty of endocytotic (pinocytotic) and transcytotic vesicles at the luminal side and above the basement membrane, indicating the one-way active trafficking of either the immunoglobulin (Ig) light chain or preassembled amyloid fibrils from the luminal side of ECs to the extraluminal area of ECs. Immunoelectron microscopy displayed that the immuno-gold signals were observed in the vascular cavity and the subendothelial area of amyloid deposits. However, there is no sign of an Ig light chain in pinocytotic vesicles. Therefore, the intestinal ECs may actively pump out mainly the preassembled amyloid fibrils (not light chains) from the blood stream into the subendothelial area as a physiologic function.

Tfl deletion induces extraordinary Cxcl13 secretion and cachexia in VavP-Bcl2 transgenic mice.

STATEMENT OF SIGNIFICANCE: Loss of TFL, found in several types of lymphoma, induces excessive CXCL13 secretion through RNA dysregulation contributing to body weight loss and early death in lymphoma model mice. Follicular lymphoma (FL) is associated with overexpressed BCL-2 and other genetic aberrations, including 6q-. We identified a novel gene on 6q25, "Transformed follicular lymphoma (TFL)," from a transformed FL. TFL regulates several cytokines via mRNA degradation, which has been suggested to underlie resolving inflammation. Fluorescence in situ hybridization revealed a deletion of TFL occurred in 13.6% of various B-cell lymphoma samples. We developed VavP-bcl2 transgenic, TFL deficit mice (Bcl2-Tg/Tfl -/-) to seek how TFL affects disease progression in this lymphoma model. While Bcl2-Tg mice developed lymphadenopathy and died around 50 weeks, Bcl2-Tg/Tfl -/- mice lost body weight around 30 weeks and died about 20 weeks earlier than Bcl2-Tg mice. Furthermore, we found a unique B220-IgM+ cell population in the bone marrow of Bcl2-Tg mice. cDNA array in this population revealed that Cxcl13 mRNA in Bcl2-Tg/Tfl -/- mice expressed significantly higher than Bcl2-Tg mice. In addition, bone marrow extracellular fluid and serum showed an extremely high Cxcl13 concentration in Bcl2-Tg/Tfl -/- mice. Among bone marrow cells, the B220-IgM+ fraction was the main producer of Cxcl13 in culture. A reporter assay demonstrated TFL regulates CXCL-13 via induction of 3'UTR mRNA degradation in B lineage cells. These data suggest Tfl regulates Cxcl13 in B220-IgM+ cells in the bone marrow, and a very high concentration of serum Cxcl13 arising from these cells may contribute to early death in lymphoma-bearing mice. Since several reports have suggested the association of CXCL13 expression with lymphoma, these findings provide new insights into cytokine regulation via TFL in lymphoma.

Regulation of granulocyte colony-stimulating factor-induced hematopoietic stem cell mobilization by the sympathetic nervous system.

PURPOSE OF REVIEW: Granulocyte colony-stimulating factor (G-CSF) is now a standard agent to mobilize hematopoietic stem cells (HSCs) from the bone marrow to circulation. This review introduced mechanistic insights from the aspect of the sympathetic nervous system (SNS). RECENT FINDINGS: Mobilization efficiency is determined by the balance between promotion and suppression pathways critically regulated by the SNS. G-CSF-induced high catecholaminergic tone promotes mobilization by (1) the strong suppression of osteolineage cells as a hematopoietic microenvironment and (2) fibroblast growth factor 23 production from erythroblasts, which inhibits CXCR4 function in HSCs. Simultaneously, SNS signals inhibit mobilization by (1) prostaglandin E2 production from mature neutrophils to induce osteopontin in osteoblasts to anchor HSCs and (2) angiopoietin-like protein 4 production from immature neutrophils via peroxisome proliferator-activated receptor δ to inhibit BM vascular permeability. SUMMARY: We now know not only the regulatory mechanisms of G-CSF-induced mobilization but also the leads about unfavorable clinical phenomena, such as low-grade fever, bone pain, and poor mobilizers. Recent understanding of the mechanism will assist clinicians in the treatment for mobilization and researchers in the studies of the hidden potential of BM.

Transvaginal mesh surgery for pelvic organ prolapse without blind maneuver.

AIM: To present the techniques of transvaginal mesh surgery for pelvic organ prolapse without the blind maneuver and elucidate its safety and efficacy. METHODS: This retrospective study included 45 women with a mean age of 77.9 years old. We investigated surgical outcomes including complications, anatomical recurrence rates, and changes in both subjective symptoms and quality of life. RESULTS: The surgery required 111 ± 18 min and blood loss was 40 ± 24 g. Minor injuries of the bladder and rectum occurred in two and one patient, respectively. The urethral catheter was removed on postoperative day 1.1 and patients were discharged on postoperative day 4.4. No one experienced voiding dysfunction requiring catheterization. Wound infections occurred in two patients but they subsided with only antibiotics administered. Five patients had anatomical recurrence during a median follow-up of 17 months. Of these, two underwent reoperation and the remaining three were solely followed-up because there were no or few associated problems. Chronic pain, mesh erosion, and exposure were absent in all cases. Subjective symptoms and quality of life significantly improved after surgery at 12 months postoperatively. CONCLUSION: It is considered that transvaginal mesh surgery without the blind maneuver is a safe and effective way to treat women with pelvic organ prolapse.

Impact of Histological Variants on Clinical Responses to Pembrolizumab in Patients With Metastatic Urothelial Cancer.

BACKGROUND: The efficacy of anti-programmed celldeath protein 1 treatment in patients with urothelial carcinoma (UC) with molecular subtypes of histological variants has not been investigated. This study aimed to examine the impact of histological variants classified according to molecular subtypes on clinical outcomes in patients with platinum-resistant metastatic UC treated with pembrolizumab. PATIENTS AND METHODS: Data of 168 patients with metastatic UC who received intravenous pembrolizumab after platinum-based chemotherapy between December 2017 and November 2020 were retrospectively reviewed. Relationships between histological variant type (basal or luminal molecular subtypes) and survival outcome and response to immunotherapy were examined. Clinicopathological factors were analyzed using the Cox proportional hazards model. RESULTS: UC with histological variants was identified in 19 (11.3%) cases (basal subtype in 12; luminal subtype in 7). The median age of the patients was 72.5 years (range=40-89 years). The performance status was 0-1 in 151 (89.9%) patients. Liver metastasis was detected in 44 (26.2%) patients. The median progression-free survival was 3.5 months (range=0.5-34.3 months). Treatment with immune checkpoint inhibitors resulted in an overall mean survival (from the start of treatment) of 8.1 months (range=1.2-34.3 months). Patients with basal-type UC had significantly shorter progression-free survival and cancer-specific survival than those with pure UC (p=0.010 and p=0.035, respectively). A complete response was observed in eight patients (seven with pure UC, one with basal type). CONCLUSION: The basal histological variant might be a potential prognostic indicator in patients with platinum-resistant metastatic UC treated with pembrolizumab.

Mobilization efficiency is critically regulated by fat via marrow PPARδ.

The mobilization efficiency of hematopoietic stem/progenitor cells from bone marrow (BM) to circulation by granulocyte colony-stimulating factor (G-CSF) is dramatically dispersed in humans and mice with no mechanistic lead for poor mobilizers. The regulatory mechanism for mobilization efficiency by dietary fat was assessed in mice. Fat-free diet (FFD) for 2 weeks greatly increased mobilization compared to normal diet (ND). The BM mRNA level of peroxisome proliferator-activated receptor δ (PPARδ), a receptor for lipid mediators, was markedly up-regulated by G-CSF in mice fed with ND and displayed strong positive correlation with widely scattered mobilization efficiency. It was hypothesized that BM fat ligand for PPARδ might inhibit mobilization. The PPARδ agonist inhibited mobilization in mice fed with ND and enhanced mobilization by FFD. Treatment with the PPARδ antagonist and chimeric mice with PPARδ+/- BM showed enhanced mobilization. Immunohistochemical staining and flow cytometry revealed that BM PPARδ expression was enhanced by G-CSF mainly in mature/immature neutrophils. BM lipid mediator analysis revealed that G-CSF treatment and FFD resulted in the exhaustion of ω3-polyunsaturated fatty acids such as eicosapentaenoic acid (EPA). EPA induced the up-regulation of genes downstream of PPARδ, such as carnitine palmitoyltransferase-1α and angiopoietin-like protein 4 (Angptl4), in mature/immature neutrophils in vitro and inhibited enhanced mobilization in mice fed with FFD in vivo. Treatment of wild-type mice with the anti-Angptl4 antibody enhanced mobilization together with BM vascular permeability. Collectively, PPARδ signaling in BM mature/immature neutrophils induced by dietary fatty acids negatively regulates mobilization, at least partially, via Angptl4 production.

FGF-23 from erythroblasts promotes hematopoietic progenitor mobilization.

Fibroblast growth factor 23 (FGF-23) hormone is produced by bone-embedded osteocytes and regulates phosphate homeostasis in kidneys. We found that administration of granulocyte colony-stimulating factor (G-CSF) to mice induced a rapid, substantial increase in FGF-23 messenger RNA in bone marrow (BM) cells. This increase originated mainly from CD45-Ter119+CD71+ erythroblasts. FGF-23 protein in BM extracellular fluid was markedly increased during G-CSF-induced hematopoietic progenitor cell (HPC) mobilization, but remained stable in the blood, with no change in the phosphate level. Consistent with the BM hypoxia induced by G-CSF, low oxygen concentration induced FGF-23 release from human erythroblast HUDEP-2 cells in vitro. The efficient mobilization induced by G-CSF decreased drastically in both FGF-23-/- and chimeric mice with FGF-23 deficiency, only in hematopoietic cells, but increased in osteocyte-specific FGF-23-/- mice. This finding suggests that erythroblast-derived, but not bone-derived, FGF-23 is needed to release HPCs from BM into the circulation. Mechanistically, FGF-23 did not influence CXCL-12 binding to CXCR-4 on progenitors but interfered with their transwell migration toward CXCL-12, which was canceled by FGF receptor inhibitors. These results suggest that BM erythroblasts facilitate G-CSF-induced HPC mobilization via FGF-23 production as an intrinsic suppressor of chemoattraction.

Repeated social defeat stress induces neutrophil mobilization in mice: maintenance after cessation of stress and strain-dependent difference in response.

BACKGROUND AND PURPOSE: Inflammation has been associated with stress-related mental disturbances. Rodent studies have reported that blood-borne cytokines are crucial for stress-induced changes in emotional behaviours. However, the roles and regulation of leukocytes in chronic stress remain unclear. EXPERIMENTAL APPROACH: Adult male C57BL/6N mice were subjected to repeated social defeat stress (R-SDS) with two protocols which differed in stress durations, stress cycles, and housing conditions, followed by the social interaction test. The numbers of leukocyte subsets in the bone marrow, spleen, and blood were determined by flow cytometry shortly after or several days after R-SDS. These leukocyte changes were studied in two strains of mice with different stress susceptibility, C57BL/6N and BALB/c mice. KEY RESULTS: R-SDS with both protocols similarly induced social avoidance in C57BL/6N mice. In the bone marrow, neutrophils and monocytes were increased, and T cells, B cells, NK cells, and dendritic cells were decreased with both protocols. In the blood, neutrophils and monocytes were increased with both protocols, whereas T cells, B cells, NK cells, and dendritic cells were decreased with one of these. Neutrophils and monocytes were also increased in the spleen. Changes in the bone marrow and increased levels of circulating neutrophils were maintained for 6 days after R-SDS. BALB/c mice showed greater social avoidance and increase in circulating neutrophils than C57BL/6N mice. CONCLUSION AND IMPLICATIONS: In two strains of mice, chronic stress induced neutrophil mobilization and its maintenance. These effects were strain-related and may contribute to the pathology of mental illness. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.4/issuetoc.

Vitamin D receptor-mediated skewed differentiation of macrophages initiates myelofibrosis and subsequent osteosclerosis.

Myelofibrosis in myeloproliferative neoplasms (MPNs) with mutations such as JAK2V617F is an unfavorable sign for uncontrollable disease progression in the clinic and is complicated with osteosclerosis whose pathogenesis is largely unknown. Because several studies have revealed that macrophages are an indispensable supporter for bone-forming osteoblasts, we speculated that macrophages might play a significant role in the proliferation of collagen-producing myofibroblasts in marrow fibrotic tissues. Here, we show that myelofibrosis critically depends on macrophages whose differentiation is skewed by vitamin D receptor (VDR) signaling. In our novel myelofibrosis model established by transplantation of VDR+/+ hematopoietic stem/progenitor cells into VDR-/- mice, donor-derived F4/80+ macrophages proliferated together with recipient-derived α-smooth muscle actin-positive myofibroblasts, both of which comprised fibrotic tissues with an indistinguishable spindle-shaped morphology. Interfering VDR signals, such as low vitamin D diet and VDR deficiency in donor cells as well as macrophage depletion prevented myelofibrosis in this model. These interventions also ameliorated myelofibrosis in JAK2V617F-driven murine MPNs likely in a transforming growth factor-ß1- or megakaryocyte-independent manner. These results suggest that VDR and macrophages may be novel therapeutic targets for MPNs with myelofibrosis.

Circulating osteocyte-derived exosomes contain miRNAs which are enriched in exosomes from MLO-Y4 cells.

Signaling molecules produced by osteocytes have been proposed to serve as soluble factors that contribute to bone remodeling, as well as to homeostasis of other organs. However, to the best of our knowledge, there are currently no studies investigating the role of osteocyte-secreted exosomes. In the present study, ablation of osteocytes in mice [osteocyte-less (OL)] was used to examine the microRNA (miRNA) levels of plasma-circulating exosomes. In order to investigate the function of osteocyte-secreted exosomes, exosomes derived from MLO-Y4 cells were extracted and their miRNA expression levels were examined using miRNA array analysis and deep sequencing. Comparison of miRNA expression levels between plasma exosomes from OL mouse plasma and MLO-Y4-derived exosomes revealed that decreases in the number of miRNAs from exosomes circulating in the OL mouse plasma may be caused by a decrease in secretion of exosomes from osteocytes. These results suggest that osteocytes secrete exosomes containing characterized miRNAs and then circulate in the blood, and may thus transfer their components, including miRNAs, to recipient cells where they function as signaling molecules in other organs and/or tissues to regulate biological responses.

G-CSF-induced sympathetic tone provokes fever and primes antimobilizing functions of neutrophils via PGE2.

Granulocyte colony-stimulating factor (G-CSF) is widely used for peripheral blood stem/progenitor mobilization. G-CSF causes low-grade fever that is ameliorated by nonsteroidal anti-inflammatory drugs (NSAIDs), suggesting the activation of arachidonic acid (AA) cascade. How G-CSF regulated this reaction was assessed. G-CSF treatment in mice resulted in fever, which was canceled in prostaglandin E synthase (mPGES-1)-deficient mice. Mobilization efficiency was twice as high in chimeric mice lacking mPGES-1, specifically in hematopoietic cells, suggesting that prostaglandin E2 (PGE2) from hematopoietic cells modulated the bone marrow (BM) microenvironment. Neutrophils from steady-state BM constitutively expressed mPGES-1 and significantly enhanced PGE2 production in vitro by ß-adrenergic stimulation, but not by G-CSF, which was inhibited by an NSAID. Although neutrophils expressed all ß-adrenergic receptors, only ß3-agonist induced this phenomenon. Liquid chromatography-tandem mass spectrometry traced ß-agonist-induced PGE2 synthesis from exogenous deuterium-labeled AA. Spontaneous PGE2 production was highly efficient in Gr-1high neutrophils among BM cells from G-CSF-treated mice. In addition to these in vitro data, the in vivo depletion of Gr-1high neutrophils disrupted G-CSF-induced fever. Furthermore, sympathetic denervation eliminated both neutrophil priming for PGE2 production and fever during G-CSF treatment. Thus, sympathetic tone-primed BM neutrophils were identified as one of the major PGE2 producers. PGE2 upregulated osteopontin, specifically in preosteoblasts, to retain progenitors in the BM via EP4 receptor. Thus, the sympathetic nervous system regulated neutrophils as an indispensable PGE2 source to modulate BM microenvironment and body temperature. This study provided a novel mechanistic insight into the communication of the nervous system, BM niche components, and hematopoietic cells.

[Thrombopoietin receptor agonists administration for acute exacerbation of chronic idiopathic thrombocytopenic purpura and subsequent anticoagulant therapy for accompanying deep venous thrombosis of the lower limbs].

We report two patients (70- and 49-year-old Japanese men) with acute exacerbation of chronic idiopathic thrombocytopenic purpura (ITP) and deep venous thrombosis of the lower extremities. Both were successfully managed with thrombopoietin receptor agonist (TPO-RA) administration. Both had ITP refractory to steroid treatment. Their immature platelet fraction (absolute-IPF) counts were increased and paralleled the platelet recoveries after TPO-RA (eltrombopag and romiplostim, respectively) without progression of thrombosis. Although ITP has recently been evaluated as a thrombophilic disorder, reports on acute exacerbation of ITP with newly diagnosed thrombosis are limited, and the pathophysiology and association between ITP and thrombosis remain to be elucidated. Moreover, the influences of TPO-RA on thrombosis are still controversial. To our knowledge, this is the first case report describing patients with exacerbation of ITP who developed thrombosis and were treated with TPO-RA. The outcomes of our cases underscore the importance of monitoring thrombosis and not delaying the initiation of anticoagulation treatment during the use of TPO-RA.

Epithelioid glioblastoma changed to typical glioblastoma: the methylation status of MGMT promoter and 5-ALA fluorescence.

A 55-year-old man was admitted to our hospital complaining of left hemiparesis. Magnetic resonance imaging (MRI) showed a smooth ring-like enhanced cystic tumor in the right parietal lobe. He underwent gross total resection of the tumor under neuronavigation and 5-aminolevulinic acid (5-ALA) fluorescence guiding method. Histopathological examination of the tumor showed small cells formed epithelioid solid nests with some focus of duct-like structure. On the basis of the MRI and operative and histological findings, this tumor was diagnosed as a metastatic poorly differentiated carcinoma, although the primary cancer could not be detected by metastatic work-ups. Afterward, this tumor recurred repeatedly. Histopathological examination of specimen from the fourth surgery indicated that the tumor was a glioblastoma (GBM). In the review of the histology and immunohistochemistry of the first tumor, atypical fibrillary cells were seen between solid nests and positive for glial fibrillary acidic protein, therefore the tumor was retrospectively diagnosed as epithelioid GBM. We assessed whether the changes in histopathology were accompanied by changes in the methylation status of O6-methylguanine methyltransferase (MGMT) promoter and the status of 5-ALA fluorescence. The methylation status of the MGMT promoter was found to have changed from methylated to unmethylated and 5-ALA fluorescence became positive along with the histological change.

The correlation between promoter methylation status and the expression level of O6-methylguanine-DNA methyltransferase in recurrent glioma.

BACKGROUND: The DNA repair protein O(6)-methylguanine-DNA methyltransferase is a drug-resistant protein, which protects the tumors from chemotherapeutic alkylating agents, such as temozolomide. The methylation status of O(6)-methylguanine-DNA methyltransferase promoter has been shown to be a major predictive factor for clinical outcome in glioma patients when treated by alkylating agents. Thereby, there were many reports on O(6)-methylguanine-DNA methyltransferase promoter methylation and mRNA expression in primary glioma, in contrast, there were only a few studies in recurrent glioma. METHODS: We evaluated the O(6)-methylguanine-DNA methyltransferase mRNA expression and promoter methylation status in glioma patients before and after recurrence by quantitative real-time PCR and methylation-specific PCR assay. Thirteen paired primary and recurrent glioma patients were analyzed, including four patients in whom malignant transformation occurred from Grade II to Grade III. RESULTS: Methylation-specific PCR assay demonstrated that the status of O(6)-methylguanine-DNA methyltransferase promoter changed from methylated to unmethylated in 10 of 13 samples when the tumor relapsed. Moreover, intra-individual O(6)-methylguanine-DNA methyltransferase mRNA level increased in recurrent gliomas than in primary ones (P = 0.016). O(6)-methylguanine-DNA methyltransferase mRNA level was correlated with the methylation status (P = 0.012). CONCLUSIONS: Our results give the evidence that the increase of O(6)-methylguanine-DNA methyltransferase mRNA expression caused by methylation changes in recurrence may be associated with chemoresistance in the recurrent glioma.

Radiation-induced cerebellar high-grade glioma accompanied by meningioma and cavernoma 29 years after the treatment of medulloblastoma: a case report.

Here, we report the case of a patient with cerebellar high-grade glioma that developed after the patient underwent treatment for medulloblastoma. A 34-year-old man visited our hospital with complaints of dizziness and truncal ataxia. Magnetic resonance image showed a cerebellar tumor with multiple cavernomas and two lesions that were suspected to be meningiomas. The cerebellar tumor was surgically removed. According to pathological examination, the tumor was a high-grade glioma that was positive for methylated O-6-methylguanine-DNA methyltransferase promoter. In the past, he had received radiotherapy at the age of 5, after which he was operated for desmoplastic medulloblastoma in his right cerebellar hemisphere. Seven years after the initial therapy, cavernoma-induced intracerebral hemorrhage of the right temporal lobe was noted. To our knowledge, this is the first case of radiation-induced double intracranial tumors accompanied by symptomatic cavernoma.

Two regulatory steps of ER-stress sensor Ire1 involving its cluster formation and interaction with unfolded proteins.

Chaperone protein BiP binds to Ire1 and dissociates in response to endoplasmic reticulum (ER) stress. However, it remains unclear how the signal transducer Ire1 senses ER stress and is subsequently activated. The crystal structure of the core stress-sensing region (CSSR) of yeast Ire1 luminal domain led to the controversial suggestion that the molecule can bind to unfolded proteins. We demonstrate that, upon ER stress, Ire1 clusters and actually interacts with unfolded proteins. Ire1 mutations that affect these phenomena reveal that Ire1 is activated via two steps, both of which are ER stress regulated, albeit in different ways. In the first step, BiP dissociation from Ire1 leads to its cluster formation. In the second step, direct interaction of unfolded proteins with the CSSR orients the cytosolic effector domains of clustered Ire1 molecules.