Stress- and ubiquitylation-dependent phase separation of the proteasome.

The proteasome is a major proteolytic machine that regulates cellular proteostasis through selective degradation of ubiquitylated proteins1,2. A number of ubiquitin-related molecules have recently been found to be involved in the regulation of biomolecular condensates or membraneless organelles, which arise by liquid-liquid phase separation of specific biomolecules, including stress granules, nuclear speckles and autophagosomes3-8, but it remains unclear whether the proteasome also participates in such regulation. Here we reveal that proteasome-containing nuclear foci form under acute hyperosmotic stress. These foci are transient structures that contain ubiquitylated proteins, p97 (also known as valosin-containing protein (VCP)) and multiple proteasome-interacting proteins, which collectively constitute a proteolytic centre. The major substrates for degradation by these foci were ribosomal proteins that failed to properly assemble. Notably, the proteasome foci exhibited properties of liquid droplets. RAD23B, a substrate-shuttling factor for the proteasome, and ubiquitylated proteins were necessary for formation of proteasome foci. In mechanistic terms, a liquid-liquid phase separation was triggered by multivalent interactions of two ubiquitin-associated domains of RAD23B and ubiquitin chains consisting of four or more ubiquitin molecules. Collectively, our results suggest that ubiquitin-chain-dependent phase separation induces the formation of a nuclear proteolytic compartment that promotes proteasomal degradation.

Enzalutamide versus flutamide for castration-resistant prostate cancer after combined androgen blockade therapy with bicalutamide: the OCUU-CRPC study.

BACKGROUND: Before the androgen target therapy era, flutamide was widely used for castration-resistant prostate cancer in Japan. Enzalutamide is currently the recommended treatment; however, the efficacy and safety of enzalutamide and flutamide after combined androgen blockade therapy with bicalutamide, has not been compared. METHODS: Patients with castration-resistant prostate cancer who received combined androgen blockade therapy with bicalutamide were randomly assigned to receive either enzalutamide or flutamide. The primary endpoint for efficacy was the 3-month prostate-specific antigen response rate. This trial is registered with ClinicalTrials.gov (NCT02346578) and the University hospital Medical Information Network (UMIN000016301). RESULTS: Overall, 103 patients were enrolled. The 3- (80.8% vs. 35.3%; p < 0.001) and 6-month (73.1% vs. 31.4%; p < 0.001) prostate-specific antigen response rates were higher in the enzalutamide than in the flutamide group. The 3-month disease progression rates (radiographic or prostate-specific antigen progression) were 6.4% and 38.8% in the enzalutamide and flutamide groups, respectively [hazard ratio (HR): 0.16; 95% confidence interval (CI): 0.05-0.47; p < 0.001]; the 6-month rates were 11.4% and 51.1%, respectively (HR 0.22; 95% CI 0.09-0.50; p < 0.001). Enzalutamide provided superior prostate-specific antigen progression-free survival compared with flutamide (HR 0.29; 95% CI 0.15-0.54; p < 0.001). Median time to prostate-specific antigen progression-free survival was not reached and was 6.6 months in the enzalutamide and flutamide groups, respectively. CONCLUSIONS: As an alternative anti-androgen therapy in patients with castration-resistant prostate cancer who fail bicalutamide-combined androgen blockade therapy, enzalutamide provides superior clinical outcomes compared with flutamide. Enzalutamide should be preferred over flutamide in these patients.

Enzalutamide versus flutamide for castration-resistant prostate cancer after combined androgen blockade therapy with bicalutamide: study protocol for a multicenter randomized phase II trial (the OCUU-CRPC study).

BACKGROUND: Enzalutamide is an oral androgen receptor targeted agent that has been shown to improve survival in PREVAIL trials and has been approved for patients with chemo-naïve metastatic castration-resistant prostate cancer (CRPC). Meanwhile, flutamide is a non-steroidal oral anti-androgen that was commonly used before the approval of bicalutamide. The objective of the OCUU-CRPC study is to compare the efficacy and safety between second-line hormonal therapy of enzalutamide and flutamide as alternative anti-androgen therapy (AAT) after combined androgen blockade (CAB) therapy that included bicalutamide in patients with CRPC. METHODS: A total of 100 patients with CRPC with or without distant metastases after disease progression who received CAB therapy with bicalutamide were randomly assigned at a 1:1 ratio according to distant metastases to the enzalutamide (160 mg/day, 4 × 40 mg capsules once daily) and flutamide (375 mg/day; 3 × 125 mg tablets thrice daily) groups. The primary endpoint for the drug efficacy is the response rate of prostate-specific antigen (PSA) (i.e., the ratio of patients whose PSA declined by ≥50% from baseline) at 3 months. Meanwhile, the secondary endpoints are PSA progression rate at 3 and 6 months, PSA response rate at 6 months, change in quality of life, PSA progression-free survival, and safety. The patient registration started in January 2015 and will end in March 2018, and the follow-up period is 6 months after the last patient registration. The main result will be reported in March 2019. DISCUSSION: In the OCUU-CRPC study, we compare the efficacy and safety of enzalutamide or alternative AAT with flutamide in participants with CRPC who were previously treated with a CAB therapy with bicalutamide. The expected results of this study will be that enzalutamide is superior to flutamide in terms of PSA response. A longer time to disease progression with enzalutamide over flutamide may translate to better overall survival. However, flutamide may be more accessible for patients owing to its lower cost than enzalutamide. TRIAL REGISTRATION: The OCUU-CRPC study was prospectively registered at clinicaltrials.gov ( NCT02346578 , January 2015) and University Hospital Medical Information Network ( UMIN000016301 , January 2015).

Enzalutamide versus flutamide for castration-resistant prostate cancer after combined androgen blockade therapy with bicalutamide: a retrospective study.

BACKGROUND: Alternative anti-androgen therapy (AAT) with flutamide after combined androgen blockade (CAB) therapy with bicalutamide for metastatic prostate cancer is common. However, no studies have compared enzalutamide without AAT with enzalutamide after AAT with flutamide as treatment for castration-resistant prostate cancer (CRPC). We aimed to compare the efficacies of flutamide and enzalutamide for CRPC. METHODS: In our hospital, 55 patients were diagnosed with CRPC after CAB therapy and administered flutamide or enzalutamide between May 2014 and December 2017. Patients with flutamide failure were administered enzalutamide. We evaluated the (1) prostate-specific antigen (PSA) best response with initial therapy, (2) PSA progression-free survival with initial therapy (PSA-PFS), (3) PSA best response with enzalutamide therapy, (4) PSA-PFS of enzalutamide therapy, and (5) overall survival (OS). RESULTS: As first-line therapy, patients were administered enzalutamide (n = 29) or flutamide (n = 26). In the flutamide group, 18 patients showed disease progression and were administered enzalutamide. PSA best response was statistically higher in the enzalutamide group. PSA-PFS was significantly longer in the enzalutamide group [hazard ratio (HR) 0.42, 95% confidence interval (CI) 0.19-0.92, p = 0.024]. However, there was no significant difference in PSA best response with enzalutamide therapy and PSA-PFS between the first- and second-line enzalutamide therapies (HR 0.80, 95% CI 0.33-1.94, p = 0.62). There was no significant difference in OS between enzalutamide and flutamide groups (HR 1.85, 95% CI 0.53-6.42, p = 0.33). CONCLUSIONS: AAT with subsequent flutamide after CAB therapy with bicalutamide may be suitable for some CRPC patients.

A change from gonadotropin releasing hormone antagonist to gonadotropin releasing hormone agonist therapy does not affect the oncological outcomes in hormone sensitive prostate cancer.

BACKGROUND: The aim of our retrospective study was to evaluate the 5-year survival and time to castration resistant prostate cancer in patients with hormone sensitive prostate cancer treated with the gonadotropin releasing hormone antagonist, degarelix. Another aim was to evaluate the effects of changing the treatment from degarelix to a gonadotropin releasing hormone agonist after achieving stable disease control, on the clinical and oncological outcomes. RESULTS: Our analysis was based on the data of 108 patients with prostate cancer who were treated with degarelix. Of these, the treatment was changed from degarelix to a gonadotropin releasing hormone agonist in 57 patients (changed group), and the treatment with degarelix was continued in the other 51 (continued group). The overall 5-year survival was statistically superior in the changed (96.6%) group than that in the continued (74.1%) group (p = 0.006). The 5-year cancer-specific survival was also superior in the changed (100%) group than that in the continued (84.6%) group (p = 0.027). The average time to castration resistant prostate cancer was comparable in both the changed (43.3 months) and continued (35.2 months) groups (p = 0.117). Lower serum levels of prostate specific antigen and alkaline phosphatase were maintained after changing the therapy from degarelix to a gonadotropin releasing hormone agonist. CONCLUSIONS: Degarelix is effective in the treatment of prostate cancer. Degarelix therapy can also be safely changed to a gonadotropin releasing hormone agonist without any adverse clinical or oncological effects.

CONTEXTE: L'objectif de notre étude rétrospective était d'évaluer la survie à 5 ans et le délai de transition du cancer de la prostate hormono-sensible au cancer de la prostate résistant à la castration chez des patients porteurs d'un cancer de la prostate hormono-sensible qui étaient traités par un antagoniste de la gonadolibérine, le dégarélix. Un autre objectif était d'évaluer les effets sur les résultats cliniques et oncologiques du remplacement du dégarélix par un agoniste de la gonadolibérine après obtention d'un état stable et contrôlé. RÉSULTATS: Notre analyse repose sur les données de 108 patients atteints d'un cancer de la prostate traités par dégarélix. Parmi ceux-ci, le traitement par dégarélix a été remplacé par un agoniste de la gonadolibérine chez 57 (groupe modifié), et le traitement par dégarélix a été poursuivi chez les autres patients (groupe inchangé). La survie globale à 5 ans était statistiquement plus élevée pour le groupe modifié (96.6%) que pour le groupe inchangé (74,1%; p = 0.006). Les chances de survie cancer-spécifiques à 5 ans était également plus élevées pour le groupe modifié (100%) que pour le groupe inchangé (84,6%; p = 0.027). Le délai moyen de transition du cancer de la prostate hormono-sensible au cancer de la prostate résistant à la castration était comparable dans le groupe modifié (43,3 mois) et dans le groupe inchangé (35,2 mois). Des taux sériques plus bas d'antigène spécifique de la prostate et de phosphatase alcaline ont été maintenus après le remplacement du dégarélix par un agoniste de la gonadolibérine. CONCLUSIONS: Le dégarélix est. efficace dans le traitement du cancer de la prostate. Le traitement par dégarélix peut aussi être remplacé en toute sécurité par un agoniste de la gonadolibérine sans aucun effet clinique ou oncologique indésirable. MOTS-CLÉS: Antagonistes et inhibiteurs de la gonadolibérine, Agoniste de la gonadolibérine, Cancer de la prostate, Dégarélix, Résistant à la castration.

The difference in the survival rate of patients with metastatic renal cell carcinoma in the intermediate-risk group of the Memorial Sloan Kettering Cancer Center criteria.

OBJECTIVES: To investigate the necessity of stratifying patients in the intermediate-risk group of the Memorial Sloan Kettering Cancer Center (MSKCC) criteria in a real-world population of patients with metastatic renal cell carcinoma. PATIENTS AND METHODS: We retrospectively analyzed 234 consecutively treated patients who had received molecular targeted drugs. We examined the difference between progression-free survival and overall survival among patients in the intermediate-risk group of MSKCC criteria. We divided the intermediate group into two subgroups as follows: patients positive for only one risk factor (Int-1) and those positive for two risk factors (Int-2) including performance status, serum hemoglobin level, time from diagnosis to treatment, and corrected calcium and lactate dehydrogenase levels. Next, we evaluated the association between the number of metastatic organs, the presence of pancreatic metastasis, Int-1 or Int-2 grouping, and overall survival. RESULTS: The median overall survival was 41.2 months. The median overall survival of the favorable-, intermediate-, and poor-risk groups of the MSKCC criteria were 91.0, 33.6, and 15.2 months, respectively. Patient characteristics were similar between the Int-1 and Int-2 groups. Increased positivity for risk factors of MSKCC classification between the two groups was for performance status and serum hemoglobin level. Progression-free survival and overall survival of the Int-1 group were significantly higher than those of the Int-2 group. In Cox proportional stepwise multivariate analysis, the Int-1 and Int-2 classification was an independent risk factor for overall survival. CONCLUSION: Patients in the intermediate-risk group had different prognoses depending on the number of positive risk factors.

Kamikihito improves cancer-related fatigue by restoring balance between the sympathetic and parasympathetic nervous systems.

BACKGROUND: Cancer-related fatigue is one of the most prevalent symptoms that patients with cancer experience, but the mechanisms underlying it are unknown. We aimed to quantify and mechanistically evaluate the improvement in fatigue related to administration of the Kampo medicine, Kamikihito. MATERIALS AND METHODS: Initially, we recruited outpatients with urological diseases and compared fatigue levels of 37 patients with cancer with a control group of 23 volunteers who had recovered completely from cancer or who were being treated for dysuria. Fatigue level was estimated using an autonomic function analyzer. Then, Kamikihito was administered to another 35 patients treated with hormone or antitumor therapy for prostate cancer and metastatic renal cell cancer. Subjective fatigue and other problems of the patients were assessed using the Chalder fatigue scale, the Center for Epidemiologic Studies Depression scale, and the Epworth sleepiness scale. Serum levels of derivatives of reactive oxygen species and biological antioxidant potential were also measured. RESULTS: Patients in the cancer treatment group experienced more fatigue compared with the control patients when evaluated using an autonomic function analyzer. The group of 35 patients who were administered Kamikihito showed improved scores for fatigue, depression, and sleepiness. Autonomic nervous system balance was also improved with Kamikihito administration. The Kamikihito group also had significantly lower reactive oxygen species metabolite levels and significantly higher antioxidant potential. CONCLUSIONS: Fatigue was more serious in patients with cancer than in control patients. Kamikihito rescued this fatigue and improved anxiety and sleepiness. It restored autonomic nervous system balance and antioxidant function.

Oncological outcomes classified according to metastatic lesions in the era of molecular targeted drugs for metastatic renal cancer.

Since the introduction of molecular targeted agents for the treatment of metastatic renal cell cancer (mRCC), several treatment outcomes, including those from our facilities, have been reported. However, the outcome of these drugs, classified by the metastatic organs, is not well known. The present study reported the treatment results of molecular-targeted agents as classified by the metastatic organ at Osaka City University Graduate School of Medicine. A total of 180 consecutively treated patients who had received molecular targeted agents for metastatic renal cancer for 3 or more months were retrospectively analyzed. The overall survival was calculated and compared according to the Memorial Sloan-Kettering Cancer Center (MSKCC) criteria, the number of metastatic organs, and metastatic lesions. The median overall survival of patients with mRCC treated by molecular targeted agents was 34 months. A significant difference in survival rate between groups was found according to the MSKCC criteria. Patients with single metastatic organ lived significantly longer compared with those with metastases in multiple organs. Patients with pancreatic metastasis had a good response to molecular targeted drugs. Pancreatic metastasis, the number of metastatic organs, and MSKCC criteria were independent risk factors for overall survival. Treatment of mRCC by molecularly targeted agents did not show any difference by metastatic organs except for the pancreas, although its efficacy depends on the number of metastatic organs and the MSKCC classification.

Time to progression to castration-resistant prostate cancer after commencing combined androgen blockade for advanced hormone-sensitive prostate cancer.

PURPOSE: The aim of our retrospective study was to determine the time to progression to castration-resistant prostate cancer (CRPC) in prostate cancer patients who undergo combined androgen blockade (CAB), as well as their prognoses. MATERIALS AND METHODS: We examined the overall survival (OS) and disease-specific survival rates, as well as the time to CRPC development, in 387 patients who were treated with CAB for prostate cancer. The disease-specific survival rate and time to CRPC were stratified by prostate-specific antigen (PSA) levels, Gleason score (GS), and presence of metastasis at diagnosis. We designated high-risk patients as those satisfying at least two of the following three criteria: extent of disease of bone metastasis grade ≥2, presence of metastasis at diagnosis, and a GS ≥8. RESULTS: The 10- and 15-year OS rates were 74.0% and 50.4%, respectively, while the corresponding disease-specific survival rates were both 86.8%. Metastasis at diagnosis was an independent prognostic factor for disease-specific survival. The median time to CRPC development was 140.7 months. A PSA level ≥20 ng/mL, a GS ≥8, and the presence of metastasis at diagnosis were independent predictors of a shorter time to CRPC development. The 10-year disease-specific survival rate in the high-risk group was significantly lower than that in the low-risk group (approximately 74% vs. 98%), and the time to CRPC development was significantly shorter (median: 20.5 months vs. not reached). CONCLUSIONS: The time to CRPC development was shorter in high-risk prostate cancer patients with metastases. Such patients require alternative novel treatment modalities.

Second-line treatment after sunitinib therapy in patients with renal cell carcinoma: a comparison of axitinib and mammalian target of rapamycin inhibitors.

This retrospective study compared the outcomes of sequential therapy using sunitinib followed by axitinib or the mammalian target of rapamycin (mTOR) inhibitors (everolimus or temsirolimus). Among 234 patients treated with molecular-targeted drugs for metastatic renal cell carcinoma, we selected 137 patients treated with sunitinib as the first-line therapy. We then compared patients treated with axitinib (n = 52) or mTOR inhibitors (n = 31), as the second-line treatment, and investigated the progression-free survival (PFS) and overall survival (OS). The PFS of axitinib-treated patients (median 8.7 months) was superior to that of mTOR inhibitors-treated patients (median 3.4 months; P = 0.001). Additionally, the OS from baseline of axitinib-treated patients (median 69 months) was superior to that of mTOR inhibitors-treated patients (median 33.4 months; P = 0.034). A multivariate analysis was performed with the following factors: the drugs used for the second-line treatment, the Memorial Sloan Kettering Cancer Center risk classification during the initial treatment, whether the discontinuation of the first-line treatment was due to adverse events, and whether the duration of response of the first-line treatment was less than 6 or 12 months. Importantly, the drugs used for the second-line treatment and Memorial Sloan Kettering Cancer Center risk classification were independent factors. Our findings suggest that axitinib works better than mTOR inhibitors after the first-line treatment with sunitinib.

Ubiquitination of exposed glycoproteins by SCFFBXO27 directs damaged lysosomes for autophagy.

Ubiquitination functions as a signal to recruit autophagic machinery to damaged organelles and induce their clearance. Here, we report the characterization of FBXO27, a glycoprotein-specific F-box protein that is part of the SCF (SKP1/CUL1/F-box protein) ubiquitin ligase complex, and demonstrate that SCFFBXO27 ubiquitinates glycoproteins in damaged lysosomes to regulate autophagic machinery recruitment. Unlike F-box proteins in other SCF complexes, FBXO27 is subject to N-myristoylation, which localizes it to membranes, allowing it to accumulate rapidly around damaged lysosomes. We also screened for proteins that are ubiquitinated upon lysosomal damage, and identified two SNARE proteins, VAMP3 and VAMP7, and five lysosomal proteins, LAMP1, LAMP2, GNS, PSAP, and TMEM192. Ubiquitination of all glycoproteins identified in this screen increased upon FBXO27 overexpression. We found that the lysosomal protein LAMP2, which is ubiquitinated preferentially on lysosomal damage, enhances autophagic machinery recruitment to damaged lysosomes. Thus, we propose that SCFFBXO27 ubiquitinates glycoproteins exposed upon lysosomal damage to induce lysophagy.

In Vivo Ubiquitin Linkage-type Analysis Reveals that the Cdc48-Rad23/Dsk2 Axis Contributes to K48-Linked Chain Specificity of the Proteasome.

Ubiquitin-binding domain (UBD) proteins regulate numerous cellular processes, but their specificities toward ubiquitin chain types in cells remain obscure. Here, we perform a quantitative proteomic analysis of ubiquitin linkage-type selectivity of 14 UBD proteins and the proteasome in yeast. We find that K48-linked chains are directed to proteasomal degradation through selectivity of the Cdc48 cofactor Npl4. Mutating Cdc48 results in decreased selectivity, and lacking Rad23/Dsk2 abolishes interactions between ubiquitylated substrates and the proteasome. Among them, only Npl4 has K48 chain specificity in vitro. Thus, the Cdc48 complex functions as a K48 linkage-specifying factor upstream of Rad23/Dsk2 for proteasomal degradation. On the other hand, K63 chains are utilized in endocytic pathways, whereas both K48 and K63 chains are found in the MVB and autophagic pathways. Collectively, our results provide an overall picture of the ubiquitin network via UBD proteins and identify the Cdc48-Rad23/Dsk2 axis as a major route to the proteasome.

Mon1-Ccz1 activates Rab7 only on late endosomes and dissociates from the lysosome in mammalian cells.

Rab GTPases act as molecular switches regulating various aspects of membrane trafficking. Among them, Rab5 and Rab7 play central roles in the endolysosomal network. Although many effectors downstream of Rab7 have been elucidated, our present understanding of the mechanism regulating Rab7 activity is extremely limited. It has only recently been accepted that the Mon1-Ccz1 complex is a Rab7 guanine nucleotide exchange factor, but it still remains unclear what the location where Mon1-Ccz1 works with Rab7 is. To address what kind of change or switch exists in the regulatory mechanism upstream of Rab7 during its transition from the late endosome to lysosome, we examined Rab7 activity in steady-state cells and during EGF-induced macropinocytosis using a newly developed FRET sensor. A combination of a Rab7 sensor and confocal FRET imaging techniques revealed that the activation of Rab7 on late endosomes depends on Mon1-Ccz1 and is implicated in late-endosome-lysosome fusion. In contrast, Rab7 activity on lysosomes was independent of Mon1-Ccz1 and active Rab7 played a role in perinuclear clustering of lysosomes.

GTP hydrolysis of TC10 promotes neurite outgrowth through exocytic fusion of Rab11- and L1-containing vesicles by releasing exocyst component Exo70.

The use of exocytosis for membrane expansion at nerve growth cones is critical for neurite outgrowth. TC10 is a Rho family GTPase that is essential for specific types of vesicular trafficking to the plasma membrane. Recent studies have shown that TC10 and its effector Exo70, a component of the exocyst tethering complex, contribute to neurite outgrowth. However, the molecular mechanisms of the neuritogenesis-promoting functions of TC10 remain to be established. Here, we propose that GTP hydrolysis of vesicular TC10 near the plasma membrane promotes neurite outgrowth by accelerating vesicle fusion by releasing Exo70. Using Förster resonance energy transfer (FRET)-based biosensors, we show that TC10 activity at the plasma membrane decreased at extending growth cones in hippocampal neurons and nerve growth factor (NGF)-treated PC12 cells. In neuronal cells, TC10 activity at vesicles was higher than its activity at the plasma membrane, and TC10-positive vesicles were found to fuse to the plasma membrane in NGF-treated PC12 cells. Therefore, activity of TC10 at vesicles is presumed to be inactivated near the plasma membrane during neuronal exocytosis. Our model is supported by functional evidence that constitutively active TC10 could not rescue decrease in NGF-induced neurite outgrowth induced by TC10 depletion. Furthermore, TC10 knockdown experiments and colocalization analyses confirmed the involvement of Exo70 in TC10-mediated trafficking in neuronal cells. TC10 frequently resided on vesicles containing Rab11, which is a key regulator of recycling pathways and implicated in neurite outgrowth. In growth cones, most of the vesicles containing the cell adhesion molecule L1 had TC10. Exocytosis of Rab11- and L1-positive vesicles may play a central role in TC10-mediated neurite outgrowth. The combination of this study and our previous work on the role of TC10 in EGF-induced exocytosis in HeLa cells suggests that the signaling machinery containing TC10 proposed here may be broadly used for exocytosis.

Longest neurite-specific activation of Rap1B in hippocampal neurons contributes to polarity formation through RalA and Nore1A in addition to PI3-kinase.

In a developing nervous system, axon-dendrite formation is instructed by extrinsic cues, and the mechanism whereby a developing neuron interprets these cues using intracellular signaling is particularly important. Studies using dissociated hippocampal neurons have identified many signaling pathways underlying neuronal polarization. Among the components of these pathways, Rap1B is essential for axon specification in hippocampal cultures. However, spatiotemporal regulation of Rap1B activity in polarizing neurons and how it affects neuronal polarization remain unclear. Herein, we investigated spatiotemporal activity-change of Rap1B and its target molecules in hippocampal neurons. FRET imaging showed that specific activation of Rap1B was observed at the tip of a future axon. To dissect downstream signaling, we used three effector mutants of Rap1B. Expression of Rap1B-G12V/E37G and G12V/Y40C mutants resulted in supernumerary axons. The targets of Rap1B-G12V/E37G were RalA and Nore1A, whereas Rap1B-G12V/Y40C activated PI3-kinase. RalA was activated in the tip of stage 3 axons, and RalA-S28N expression reduced the fraction of neurons with supernumerary axons induced by Rap1B-G12V/E37G. Furthermore, Nore1A depletion reduced the number of cells without axons. These results indicate that specific activation of Rap1B contributes to neuronal polarization via interaction with RalA and Nore1A in addition to PI3-kinase.

All members of the EPI64 subfamily of TBC/RabGAPs also have GAP activities towards Ras.

The importance of interconnective signalling networks between distinct GTPases and their regulators is being recognized. EPI64C/TBC1D10C/carabin, a haematopoietically enriched GTPase-activating protein (GAP) for Rab35, has been shown to exhibit RasGAP activity. Owing to the diverged Rab specificities among the EPI64 members (EPI64A-C) and the relatively weak sequence conservation between EPI64A/B and EPI64C in their catalytic TBC domains, it is difficult to predict whether EPI64A and B will also have RasGAP activities. Therefore, in this study, we examined the RasGAP activities of all three EPI64 subfamily members. We found that EPI64A-C exhibited in vivo GAP activities towards Ras using three independent methods, spectrofluorometry with Förster resonance energy transfer (FRET) sensors, the Bos' pull-down assay and time-lapse FRET imaging. EPI64A and B were predominantly localized at the periphery of COS-7 cells. In COS-7 cells, confocal FRET imaging showed that H-Ras activity was higher at the Golgi than at the plasma membrane. Thus, we propose that EPI64A and B, which are ubiquitously expressed members of the EPI64 subfamily, inactivate Ras and certain Rabs at the periphery of cells.