Stand-up test could be a helpful adjunct for screening elbow disorders in Little League baseball players.

BACKGROUND: The purpose of this study is to justify the result of the modified Stand-Up test (MSUT) in Little League baseball players and to clarify the association with sports related disorders in the elbow. METHODS: A total of 245 (240 boys and 5 girls) Little League baseball players aged 9 to 12 underwent physical examination, elbow ultrasonography and questionnaires during a routine medical checkup. In addition, the MSUT, based on the Japanese Orthopaedic Association (JOA)'s original Stand-Up test to evaluate the risk of Locomotive syndrome, was performed. RESULTS: Seventeen osteochondritis dissecans (OCD) of capitellum and 4 medial epicondylar fragmentation (MEF) cases were diagnosed with ultrasonography in 242 players. Based on the MSUT, five boys could not stand up from 40 cm platform with the single leg stance, two of whom complained of current elbow pain, three of whom diagnosed with a positive finding with ultrasonography. Odds ratio (95% confidence limits) of risk factors for failing to the 40 cm-MSUT with the single leg stance were: incidence of current elbow pain 5.7 (0.9-35.5); OCD (Grade 1b and 2) 8.2 (0.8-83); and MEF 19.5 (1.7-230). CONCLUSION: Two percent of Little League baseball players were unable to stand up from a 40 cm high platform/stool with the single leg stance by the MSUT and it was associated with an increase in MEF or OCD diagnosis by ultrasonography and presence of elbow pain. These results suggest that players who failed to the 40 cm-MSUT with the single leg stance are at risk of elbow disorders. Also, these results are consistent with previous research on throwing injuries that have associated poor control in the legs or trunk with pain and injury involving the upper extremities. MSUT, a relatively simple procedure, may be a helpful adjunct for screening to estimate readiness for resuming general physical activity in Little League baseball players.

Risk factors for remnant gastric cancer after distal gastrectomy for gastric cancer: a retrospective database review.

Background: The number of patients with remnant gastric cancer (RGC) following gastrectomy for gastric cancer (GC) is increasing due to the increasing number of patients undergoing function-preserving gastrectomy and improved outcomes for patients with GC. A few studies involving a small number of cases reported male sex, old age, differentiated type, tumor depth and synchronous multiple GC were associated with RGC development. However, the risk factors for RGC development had not been fully understood. This study aimed to examine the clinicopathological features, followed up patients with GC after they underwent distal gastrectomy (DG), and evaluated the potential risk factors for RGC development. Methods: A retrospective database review of 438 patients who underwent DG for GC at a single institution, from 2006 to 2017, was conducted. We investigated the relationship of clinicopathological features, operative findings, and postoperative course with RGC development was estimated using Cox proportional hazard analysis. The cumulative incidences of RGC were calculated using the Kaplan-Meier method. Results: We retrospectively analyzed 405 cases. The median patient age was 69 years, and the patient cohort consisted of 263 men and 142 women. The Billroth-I reconstruction method was used in 204 cases, Billroth-II method was used in 3 cases, and Roux-en Y method was used in 198 cases. RGC was diagnosed in 11 of the 405 patients. The median follow-up period was 5 years. The cumulative incidences of RGC calculated by the Kaplan-Meier method were 3.0%, 4.1%, and 10.5% at 5, 10, and 15 years after DG, respectively. During the initial surgery, differentiated type was significantly associated with RGC development [hazard ratio (HR): 4.71, 95% confidence interval (CI): 1.02-21.80, P=0.05]. Male sex (HR: 2.97, 95% CI: 0.64-13.75, P=0.16), old age (≥70 years) (HR: 2.72, 95% CI: 0.78-9.47, P=0.11), and synchronous multiple GC (HR: 1.31, 95% CI: 0.28-6.08, P=0.73) were not associated with RGC development. Conclusions: Patients who have undergone DG for differentiated type GC were statistically significantly associated with developing RGC. Intensive endoscopic surveillance would be needed for the patients who underwent DG for differentiated type GC.

Phosphorylation and subcellular localization of human phospholipase A1, DDHD1/PA-PLA1.

Protein phosphorylation is the most common post-translational modification of proteins and functions as a molecular switch for their regulation. This modification is reversibly regulated by protein kinases and phosphatases. In most cases, the phosphorylation of enzymes positively or negatively regulates enzyme activity. However, we found that the phosphorylation of DDHD1 phospholipase A1 (PLA1) did not affect PLA1 activity. Integrated analyses, including phospho-proteomics, Phos-tag SDS-PAGE, PLA1 enzyme assays, and immunofluorescent microscopy, revealed the subcellular localization of DDHD1 without greatly affecting its PLA1 activity. Our findings may contribute to understanding rare clinical cases that concern the implications of protein phosphorylation.

The complex formation of MASP-3 with pattern recognition molecules of the lectin complement pathway retains MASP-3 in the circulation.

The complement system plays an important role in host defense and is activated via three different activation pathways. We have previously reported that mannose-binding lectin-associated serine protease (MASP)-3, unlike its splicing variant MASP-1, circulates in an active form and is essential for the activation of the alternative pathway (AP) via the activation of complement factor D (FD). On the other hand, like MASP-1 and MASP-2 of the lectin pathway (LP), MASP-3 forms a complex with the pattern recognition molecules (PRMs) of the LP (LP-PRMs). Both MASP-1 and MASP-2 can be activated efficiently when the LP-PRMs complexed with them bind to their ligands. On the other hand, it remains unclear how MASP-3 is activated, or whether complex formation of MASP-3 with LP-PRMs is involved in activation of MASP-3 or its efficiency in the circulation. To address these issues, we generated wild-type (WT) and four mutant recombinant mouse MASP-3 proteins fused with PA (human podoplanin dodecapeptide)-tag (rmMASP-3-PAs), the latter of which have single amino acid substitution for alanine in the CUB1 or CUB2 domain responsible for binding to LP-PRMs. The mutant rmMASP-3-PAs showed significantly reduced in-vivo complex formation with LP-PRMs when compared with WT rmMASP-3-PA. In the in-vivo kinetic analysis of MASP-3 activation, both WT and mutant rmMASP-3-PAs were cleaved into the active forms as early as 30 minutes in the circulation of mice, and no significant difference in the efficiency of MASP-3 cleavage was observed throughout an observation period of 48 hours after intravenous administration. All sera collected 3 hours after administration of each rmMASP-3-PA showed full restoration of the active FD and AP activity in MASP-3-deficient mouse sera at the same levels as WT mouse sera. Unexpectedly, all mutant rmMASP-3-PAs showed faster clearance from the circulation than the WT rmMASP-3-PA. To our knowledge, the current study is the first to show in-vivo kinetics of MASP-3 demonstrating rapid activation and clearance in the circulation. In conclusion, our results demonstrated that the complex formation of MASP-3 with LP-PRMs is not required for in-vivo activation of MASP-3 or its efficiency, but may contribute to the long-term retention of MASP-3 in the circulation.

Selection of RNA-based evaluation methods for tumor microenvironment by comparing with histochemical and flow cytometric analyses in gastric cancer.

Understanding the tumor microenvironment (TME) and anti-tumor immune responses in gastric cancer are required for precision immune-oncology. Taking advantage of next-generation sequencing technology, the feasibility and reliability of transcriptome-based TME analysis were investigated. TME of 30 surgically resected gastric cancer tissues was analyzed by RNA-Seq, immunohistochemistry (IHC) and flow cytometry (FCM). RNA-Seq of bulk gastric cancer tissues was computationally analyzed to evaluate TME. Computationally analyzed immune cell composition was validated by comparison with cell densities established by IHC and FCM from the same tumor tissue. Immune cell infiltration and cellular function were also validated with IHC and FCM. Cell proliferation and cell death in the tumor as assessed by RNA-Seq and IHC were compared. Computational tools and gene set analysis for quantifying CD8+ T cells, regulatory T cells and B cells, T cell infiltration and functional status, and cell proliferation and cell death status yielded an excellent correlation with IHC and FCM data. Using these validated transcriptome-based analyses, the immunological status of gastric cancer could be classified into immune-rich and immune-poor subtypes. Transcriptome-based TME analysis is feasible and is valuable for further understanding the immunological status of gastric cancer.

Endoplasmic reticulum-to-Golgi trafficking of procollagen III via conventional vesicular and tubular carriers.

Collagen is the major protein component of the extracellular matrix. Synthesis of procollagens starts in the endoplasmic reticulum (ER), and three α chains form a rigid triple helix 300-400 nm in length. It remains unclear how such a large cargo is transported from the ER to the Golgi apparatus. In this study, to elucidate the intracellular transport of fibril-forming collagens, we fused cysteine-free GFP to the N-telopeptide region of procollagen III (GFP-COL3A1) and analyzed transport by live-cell imaging. We found that the maturation dynamics of procollagen III was largely different from that of network-forming procollagen IV. Proline hydroxylation of procollagen III uniquely triggered the formation of intralumenal droplet-like structures, similarly to events caused by liquid-liquid phase separation, and ER exit sites surrounded large droplets containing chaperones. Procollagen III was transported to the Golgi apparatus via vesicular and tubular carriers containing ERGIC53 and RAB1B; this process required TANGO1 and CUL3, which we previously reported to be dispensable for procollagen IV. GFP-COL3A1 and mCherry-α1AT were cotransported in the same vesicle. Based on these findings, we propose that shortly after ER exit, enlarged carriers containing procollagen III fuse to ERGIC for transport to the Golgi apparatus by conventional cargo carriers.

A three-component model of the spinal nerve ramification: Bringing together the human gross anatomy and modern Embryology.

Due to its long history, the study of human gross anatomy has not adequately incorporated modern embryological findings; consequently, the current understanding has often been incompatible with recent discoveries from molecular studies. Notably, the traditional epaxial and hypaxial muscle distinction, and their corresponding innervation by the dorsal and ventral rami of the spinal nerve, do not correspond to the primaxial and abaxial muscle distinction, defined by the mesodermal lineages of target tissues. To resolve the disagreement between adult anatomy and embryology, we here propose a novel hypothetical model of spinal nerve ramification. Our model is based on the previously unknown developmental process of the intercostal nerves. Observations of these nerves in the mouse embryos revealed that the intercostal nerves initially had superficial and deep ventral branches, which is contrary to the general perception of a single ventral branch. The initial dual innervation pattern later changes into an adult-like single branch pattern following the retraction of the superficial branch. The modified intercostal nerves consist of the canonical ventral branches and novel branches that run on the muscular surface of the thorax, which sprout from the lateral cutaneous branches. We formulated the embryonic branching pattern into the hypothetical ramification model of the human spinal nerve so that the branching pattern is compatible with the developmental context of the target muscles. In our model, every spinal nerve consists of three components: (1) segmental branches that innervate the primaxial muscles, including the dorsal rami, and short branches and long superficial anterior branches from the ventral rami; (2) plexus-forming intramural branches, the serial homolog of the canonical intercostal nerves, which innervate the abaxial portion of the body wall; and (3) plexus-forming extramural branches, the series of novel branches located outside of the body wall, which innervate the girdle and limb muscles. The selective elaboration or deletion of each component successfully explains the reasoning for the standard morphology and variability of the spinal nerve. Therefore, our model brings a novel understanding of spinal nerve development and valuable information for basic and clinical sciences regarding the diverse branching patterns of the spinal nerve.

Two distinct phenotypes of immunologically hot gastric cancer subtypes.

An in-depth understanding of the tumor microenvironment (TME) is required for the development of improved combination immunotherapies for gastric cancer. Recently, we classified these cancers into four main types defined by their immunological attributes, namely Hot 1, Hot 2, Intermediate and Cold. Of these, the T cell-inflamed "Hot" tumors were further divided into Hot 1 and Hot 2 with different clinical outcomes. Thus, overall survival and progression-free survival of patients with Hot 1 tumors were shorter than with Hot 2. In the present study, we re-evaluated RNA-Seq data of 6 Hot 1 and 6 Hot 2 gastric cancers to elucidate the underlying reason for the poor prognosis and T cell dysfunction in the former. In addition, 56 Hot 1 and 27 Hot 2 tumors in The Cancer Genome Atlas (TCGA) were analyzed. We report that single sample Gene Set Enrichment Analysis (ssGSEA) and differential gene expression analysis identified differences between Hot 1 and Hot 2 tumors involved in metabolism and cell adhesion pathways. Therefore, it is suggested that strategies to modulate active metabolism in Hot 1 tumors should be integrated into the treatment of these gastric cancers.

IZUMO family member 3, IZUMO3, is involved in male fertility through the acrosome formation.

Many factors are involved in acrosome biogenesis in order for appropriate acrosome formation to occur. Here, we demonstrate that IZUMO family member 3, IZUMO3, plays an important role in acrosome biogenesis, as proven by gene disruption experiments. A loss of IZUMO3 in round spermatids affects acrosomal granule positioning due to lack of acrosomal granule contact with the inner acrosomal membrane, leading to the formation of grossly malformed spermatozoa associated with male subfertility. Thus, we suggest that mammalian spermiogenesis needs an elaborate acrosome biogenesis through IZUMO3 involvement.

Phosphorylation of human phospholipase A1 DDHD1 at newly identified phosphosites affects its subcellular localization.

Phospholipase A1 (PLA1) hydrolyzes the fatty acids of glycerophospholipids, which are structural components of the cellular membrane. Genetic mutations in DDHD1, an intracellular PLA1, result in hereditary spastic paraplegia (HSP) in humans. However, the regulation of DDHD1 activity has not yet been elucidated in detail. In the present study, we examined the phosphorylation of DDHD1 and identified the responsible protein kinases. We performed MALDI-TOF MS/MS analysis and Phos-tag SDS-PAGE in alanine-substitution mutants in HEK293 cells and revealed multiple phosphorylation sites in human DDHD1, primarily Ser8, Ser11, Ser723, and Ser727. The treatment of cells with a protein phosphatase inhibitor induced the hyperphosphorylation of DDHD1, suggesting that multisite phosphorylation occurred not only at these major, but also at minor sites. Site-specific kinase-substrate prediction algorithms and in vitro kinase analyses indicated that cyclin-dependent kinase CDK1/cyclin A2 phosphorylated Ser8, Ser11, and Ser727 in DDHD1 with a preference for Ser11 and that CDK5/p35 also phosphorylated Ser11 and Ser727 with a preference for Ser11. In addition, casein kinase CK2α1 was found to phosphorylate Ser104, although this was not a major phosphorylation site in cultivated HEK293 cells. The evaluation of the effects of phosphorylation revealed that the phosphorylation mimic mutants S11/727E exhibit only 20% reduction in PLA1 activity. However, the phosphorylation mimics were mainly localized to focal adhesions, whereas the phosphorylation-resistant mutants S11/727A were not. This suggested that phosphorylation alters the subcellular localization of DDHD1 without greatly affecting its PLA1 activity.

Evolutionarily conserved sperm factors, DCST1 and DCST2, are required for gamete fusion.

To trigger gamete fusion, spermatozoa need to activate the molecular machinery in which sperm IZUMO1 and oocyte JUNO (IZUMO1R) interaction plays a critical role in mammals. Although a set of factors involved in this process has recently been identified, no common factor that can function in both vertebrates and invertebrates has yet been reported. Here, we first demonstrate that the evolutionarily conserved factors dendrocyte expressed seven transmembrane protein domain-containing 1 (DCST1) and dendrocyte expressed seven transmembrane protein domain-containing 2 (DCST2) are essential for sperm-egg fusion in mice, as proven by gene disruption and complementation experiments. We also found that the protein stability of another gamete fusion-related sperm factor, SPACA6, is differently regulated by DCST1/2 and IZUMO1. Thus, we suggest that spermatozoa ensure proper fertilization in mammals by integrating various molecular pathways, including an evolutionarily conserved system that has developed as a result of nearly one billion years of evolution.

SEL1L degradation intermediates stimulate cytosolic aggregation of polyglutamine-expanded protein.

Misfolded proteins in the endoplasmic reticulum (ER) are degraded by ER-associated degradation (ERAD). In mammalian cells, the HRD1-SEL1L membrane ubiquitin ligase complex plays a central role in this process. However, SEL1L is inherently unstable, and excess SEL1L is also degraded by ERAD. Accordingly, when proteasome activity is inhibited, multiple degradation intermediates of SEL1L appear in the cytosol. In this study, we searched for factors that inhibit SEL1L degradation and identified OS-9 and XTP3-B, two ER lectins that regulate glycoprotein ERAD. SEL1L degradation was characterized by a ladder of degradation products, and the C-terminal Pro-rich region of SEL1L was responsible for generation of this pattern. In the cytosol, these degradation intermediates stimulated aggregation of polyglutamine-expanded Huntingtin protein (Htt-polyQ-GFP) by interacting with aggregation-prone proteins, including Htt-polyQ-GFP. Collectively, our findings indicate that peptide fragments of ER proteins generated during ERAD may affect protein aggregation in the cytosol, revealing the interconnection of protein homeostasis across subcellular compartments.

Integrative immunogenomic analysis of gastric cancer dictates novel immunological classification and the functional status of tumor-infiltrating cells.

OBJECTIVES: A better understanding of antitumor immunity will help predict the prognosis of gastric cancer patients and tailor the appropriate therapies in each patient. Therefore, we propose a novel immunological classification of gastric cancer. METHODS: We performed whole-exome sequencing (WES), RNA-Seq and flow cytometry in 29 gastric cancer patients who received surgery. The TCGA data set of 323 gastric cancer patients and RNA-Seq data of 45 patients who received pembrolizumab (Kim et al. Nat Med 2018; 24: 1449-1458) were also analysed. RESULTS: Immunogram analysis of cancer-immunity interaction of gastric cancer revealed immune signatures of four main types, designated Hot1, Hot2, Intermediate and Cold. Immunologically hot tumors displayed a dysfunctional T-cell signature, while cold tumors had an exclusion signature. Ex vivo tumor-infiltrating lymphocyte analysis documented T-cell dysfunction with the expression of checkpoint molecules and impaired cytokine production. The T-cell function was more profoundly damaged in Hot1 than Hot2 tumors. Patients in Hot2 subtypes had better survival in our cohort and TCGA cohort. Although these immunological subtypes overlapped to some degree with the molecular subtypes in the TCGA, intratumoral immune responses cannot be predicted solely based on histological or molecular subtyping of gastric cancer. Molecular and immunological classifications complement each other to predict the responses to anti-PD-1 therapy and have the potential to be a biomarker for the treatment of gastric cancer. CONCLUSION: The immunological classification of gastric cancer resulted in four subtypes. Hot tumors were further divided into two subtypes, between which the functional status of T cells was different.

Unveiling a novel function of CD9 in surface compartmentalization of oocytes.

Gamete fusion is an indispensable process for bearing offspring. In mammals, sperm IZUMO1-oocyte JUNO recognition essentially carries out the primary step of this process. In oocytes, CD9 is also known to play a crucial role in gamete fusion. In particular, microvilli biogenesis through CD9 involvement appears to be a key event for successful gamete fusion, because CD9-disrupted oocytes produce short and sparse microvillous structures, resulting in almost no fusion ability with spermatozoa. In order to determine how CD9 and JUNO cooperate in gamete fusion, we analyzed the molecular profiles of each molecule in CD9- and JUNO-disrupted oocytes. Consequently, we found that CD9 is crucial for the exclusion of GPI-anchored proteins, such as JUNO and CD55, from the cortical actin cap region, suggesting strict molecular organization of the unique surface of this region. Through distinct surface compartmentalization due to CD9 governing, GPI-anchored proteins are confined to the appropriate fusion site of the oocyte.

Visualization of Procollagen IV Reveals ER-to-Golgi Transport by ERGIC-independent Carriers.

Collagen is the most abundant protein in animal tissues and is critical for their proper organization. Nascent procollagens in the endoplasmic reticulum (ER) are considered too large to be loaded into coat protein complex II (COPII) vesicles, which have a diameter of 60-80 nm, for exit from the ER and transport to the Golgi complex. To study the transport mechanism of procollagen IV, which generates basement membranes, we introduced a cysteine-free GFP tag at the N-terminus of the triple helical region of the α1(IV) chain (cfSGFP2-col4a1), and examined the dynamics of this protein in HT-1080 cells, which produce endogenous collagen IV. cfSGFP2-col4a1 was transported from the ER to the Golgi by vesicles, which were a similar size as small cargo carriers. However, mCherry-ERGIC53 was recruited to α1-antitrypsin-containing vesicles, but not to cfSGFP2-col4a1-containing vesicles. Knockdown analysis revealed that Sar1 and SLY1/SCFD1 were required for transport of cfSGFP2-col4a1. TANGO1, CUL3, and KLHL12 were not necessary for the ER-to-Golgi trafficking of procollagen IV. Our data suggest that procollagen IV is exported from the ER via an enlarged COPII coat carrier and is transported to the Golgi by unique transport vesicles without recruitment of ER-Golgi intermediate compartment membranes.Key words: collagen, procollagen IV, endoplasmic reticulum, ER-to-Golgi transport, ERGIC.

Evaluation of the Cytotoxicity of Various Hand Disinfectants and Ozonated Water to Human Keratinocytes in a Cultured Epidermal Model.

OBJECTIVE: To evaluate the cytotoxicity of various hand disinfectants and ozonated water to human keratinocytes using a cultured epidermal model. DESIGN: Using a test protocol from the Organization for Economic Co-operation and Development, investigators applied hand disinfectants containing either 83% ethanol, 0.2% benzalkonium chloride, 0.5% povidone-iodine, 1% chlorhexidine, 1% chlorhexidine ethanol, or ozonated water to a cultured human epidermal model. Surface morphology and histologic changes were evaluated by scanning electron microscopy and hematoxylin-eosin staining. MAIN OUTCOME MEASURES: Production of inflammatory cytokine interleukin 1α by keratinocytes and cell death rate. MAIN RESULTS: Electron microscopic analysis revealed the creation of small holes on the stratum corneum, and hematoxylin-eosin staining revealed perinuclear vacuolation of keratinocytes and cells with a condensed nucleus. Interleukin 1α was detected in the culture supernatants. More than 80% of keratinocytes did not survive after a 15-minute application of disinfectants. However, no significant damage was detected with ozonated water. CONCLUSIONS: Ozonated water did far less damage to keratinocytes than the tested disinfectants. Although the ability of ozonated water to disinfect hands of medical staff members requires further study, it might serve as an alternative with minimum cytotoxicity.

Radiographic analysis of subclinical appearances of the hip joint among patients with labral tears.

OBJECTIVE: Labral tears can be complicated by hip diseases, including osteoarthritis or femoral acetabular impingement. To accurately plan hip arthroscopy or subsequent conversion to total hip arthroplasty, the presence of bony abnormalities in the hip joint must be evaluated. This study aimed to elucidate the utility of multiplanar reconstruction computed tomography (mCT) for the detection of subclinical coincidence of osteoarthritis or femoral acetabular impingement with a labrum tear. MATERIALS AND METHODS: We retrospectively analysed 34 patients (36 hips) with labrum tears without apparent osteoarthritis or hip dysplasia from 2012 to 2015. The joint spaces were calculated using radiographs or mCT, and the detection rates of degenerative cyst and herniation pit were compared. RESULTS: Narrow joint spaces (< 2 mm) were more clearly detected in mCT (p < 0.05, chi-square analysis) than in radiographs. The detection rate of cysts in the acetabulum was 8.3% using radiographs and 36.1% using mCT (p < 0.001, chi-square analysis). Additionally, the detection of herniation pit was 8.3% and 25.0% using radiographs and mCT, respectively (p = 0.053, chi-square analysis). CONCLUSION: We performed the radiographic analysis of patients with labral tears using radiographs and mCT. The mCT allowed for fine detection of narrow joint spaces and subtle subclinical appearances. The results of this study may provide surgeons with more appropriate strategies for the treatment of labral tears.

Sperm IZUMO1-Dependent Gamete Fusion Influences Male Fertility in Mice.

Sperm-egg fusion is accomplished through the interaction of a specific set of membrane proteins in each gamete: sperm IZUMO1 and oocyte JUNO. Recently, we found that alternative splicing of the Izumo1 gene generates a novel IZUMO1 isoform (IZUMO1_v2). Here, we obtained four mouse lines, having graded different levels of IZUMO1 protein by combining an original IZUMO1 (IZUMO1_v1) knockout with IZUMO1-null (both IZUMO1_v1 and _v2 disrupted) genetic background, in order to determine how the quantity of IZUMO1 influences male fertility. Subsequently, we clarified that the signal intensity from two quantitative assays, western blot and immunostaining analyses with a monoclonal antibody against mouse IZUMO1, were strongly correlated with average litter size. These results suggest that evaluating IZUMO1 protein levels is useful for predicting fecundity, and is a suitable test for male fertility.

SDF2-like protein 1 (SDF2L1) regulates the endoplasmic reticulum localization and chaperone activity of ERdj3 protein.

Molecular chaperones facilitate protein folding by associating with nascent polypeptides, thereby preventing protein misfolding and aggregation. Endoplasmic reticulum (ER) chaperone BiP, the sole HSP70 chaperone in the ER, is regulated by HSP40 chaperones, including ER-resident protein ERdj3 (DNAJB11). ERdj3 lacks an ER retrieval signal, is secreted under ER stress conditions, and functions as a chaperone in the extracellular space, but how its secretion is regulated remains unclear. We recently showed that ERdj3 forms a complex with ER-resident stromal cell-derived factor 2 (SDF2) and SDF2L1 (SDF2-like protein 1) and thereby prevents protein aggregation during the BiP chaperone cycle. However, the contribution of the ERdj3-SDF2L1 complex to protein quality control is poorly understood. Here, we analyzed the intracellular localization and chaperone activity of ERdj3 in complex with SDF2L1. We found that ERdj3 was retained in the ER by associating with SDF2/SDF2L1. In vitro analyses revealed that the ERdj3 dimer incorporated two SDF2L1 molecules; otherwise, ERdj3 alone formed a homotetramer. The ERdj3-SDF2L1 complex suppressed ER protein aggregation, and this suppression did not require substrate transfer to BiP. The ERdj3-SDF2L1 complex inhibited aggregation of denatured GSH S-transferase (GST) in vitro and maintained GST in a soluble oligomeric state. Both in cellulo and in vitro, the chaperone activities of the ERdj3-SDF2L1 complex were higher than those of ERdj3 alone. These findings suggest that, under normal conditions, ERdj3 functions as an ER chaperone in complex with SDF2/SDF2L1 but is secreted into the extracellular space when it cannot form this complex.