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Background The usefulness of particle therapy for skull base chordoma has not been established. The aim of this retrospective study was to analyse the treatment outcomes of proton therapy (PT) and carbon ion therapy (CIT) in patients with skull base chordoma at a single institution. Methods All patients who underwent PT or CIT with curative intent between 2003 and 2014 at Hyogo Ion Beam Medical Center were included in this study. Twenty-four patients were enrolled. Eleven (46%) received PT and 13 (54%) received CIT. Overall survival (OS), progression-free survival (PFS) and local control (LC) were calculated using the Kaplan–Meier method. Late toxicities were evaluated according to the Common Terminology Criteria for Adverse Events version 4.0. Results The median follow-up was 71.5 months (range, 14–175 months). The five-year LC, PFS and OS rates were 85, 81, and 86%, respectively. The LC (P = 0.048), PFS (P = 0.028) and OS (P = 0.012) were significantly improved in patients who had undergone surgery before particle therapy. No significant differences were observed in the LC rate and the incidence of grade 2 or higher late toxicities between patients who received PT and CIT. Conclusions Both PT and CIT appear to be effective and safe treatments and show potential to become the standard treatments for skull base chordoma. To increase the local control, surgery before particle therapy is preferable.

Purpose This retrospective study aimed to determine the clinical outcomes following particle monotherapy (ie, proton therapy [PT] or carbon ion therapy [CIT]) in patients with sinonasal squamous cell carcinoma at a single institution. Methods and Materials Between August 2001 and March 2012, 59 patients were treated with definitive PT or CIT; none underwent chemotherapy or surgery. Of the patients, 22 (37%) had unresectable disease. PT was used in 38 patients (64%); CIT, 21 patients (36%). Almost half of the patients (n = 29, 47%) received 65.0 Gy (relative biological effectiveness) in 26 fractions. Results The median follow-up period was 30 months (range, 8-127 months) for all patients and 65 months (range, 9-127 months) for the survivors. The 3- and 5-year overall survival rates were 56.2% and 41.6%, respectively; progression-free survival rates, 42.9% and 34.7%, respectively; and local control rates, 54.0% and 50.4%, respectively. Late toxicities of grade ≥3 occurred in 13 patients (22%). Conclusions To our knowledge, this is the largest retrospective study of sinonasal squamous cell carcinoma treated with particle therapy alone. The efficacy of PT and CIT indicated that particle therapy can serve an important role in treating this disease.

Purpose To evaluate the efficacy and safety of definitive proton beam therapy (PBT) for primary sacral chordoma. Methods and Materials We conducted a retrospective analysis of the clinical outcomes of eligible patients with primary sacral chordoma who had undergone definitive PBT with 70.4 Gy (relative biological effectiveness) in 32 fractions at our institution from September 2009 to October 2015. Local progression-free survival, distant metastasis-free survival, disease-free survival, cause-specific survival, and overall survival were evaluated. To explore the factors that influenced local progression, the following parameters were analyzed: sex, the presence of a spacer (Gore-Tex sheets), gross tumor volume, and extent of cranial tumor extension. Adverse events were evaluated using the Common Terminology Criteria for Adverse Events, version 4.0. To assess the impact of PBT on pain relief, the change in pain grades was investigated between the initiation of PBT and the last follow-up visit. Results Thirty-three eligible patients were analyzed. The median follow-up period was 37 months. The 3-year estimated local progression-free survival, distant metastasis-free survival, disease-free survival, cause-specific survival, and overall survival rates were 89.6%, 88.2%, 81.9%, 95.7%, and 92.7%, respectively. No significant association was between the patients’ clinicopathologic characteristics and local progression-free survival. Four patients developed grade 3 adverse events, including acute dermatitis (n = 1), ileus (n = 1), and pain due to sacral insufficiency fractures (n = 2). The pain grades had improved, were unchanged, or had deteriorated in 15, 7, and 11 patients, respectively. Conclusions Definitive PBT with 70.4 Gy (relative biological effectiveness) in 32 fractions is an effective treatment with acceptable toxicity for primary sacral chordoma and has the potential to reduce pain.

The optimal treatment for isolated local recurrence (ILR) of pancreatic adenocarcinoma (PDAC) after surgical resection remains unclear. This study aimed to evaluate the safety and efficacy of proton radiotherapy (PRT) for ILR of PDAC after surgery. The medical records of patients with ILR of PDAC after surgery who underwent proton beam therapy between 2011 and 2015 at Hyogo Ion Beam Medical Center were retrospectively studied. The study analyzed 30 patients (14 women and 16 men) with a median age of 65 years (range 38–81 years) who had initially undergone pancreatoduodenectomy (n = 23) or distal pancreatectomy (n = 7) for their primary tumors. Upon ILR, PRT was administered with a median total cumulative dose of 67.5 gray equivalent (GyE) (range 50–67.5 GyE) using 19 to 25 fractions. For 25 patients, concurrent chemotherapy was administered using gemcitabine (n = 18) or S-1 (n = 7). Four patients (13.3%) experienced acute grade ≥ 3 gastrointestinal toxicities. After a median follow-up period of 17.6 months (range 2.1–50.4 months), 23 patients had experienced tumor progression and 10 had died. Nine patients (30%) experienced local tumor progression. The median overall, progression-free, and local progression-free survival rates were 26.1, 12.3, and 41.2 months, respectively. Pre-PRT serum levels of cancer antigen 19-9 higher than 100 U/mL and duke pancreatic monoclonal antigen type 2 higher than 150 U/mL were significantly associated with shorter progression-free survival rates. Proton radiotherapy for ILR of PDAC after surgery is well tolerated and produces good locoregional control and should be considered for eligible patients.

Carbon ion therapy is a type of radiotherapy that can deliver high-dose radiation to a tumor while minimizing the dose delivered to organs at risk. Moreover, carbon ions are classified as high linear energy transfer radiation and are expected to be effective for even photon-resistant tumors. A 73-year-old man with glottic squamous cell carcinoma, T3N0M0, refused laryngectomy and received carbon ion therapy of 70 Gy (relative biological effectiveness) in 35 fractions. Three months after the therapy, the patient had an upper airway inflammation, and then laryngeal edema and pain occurred. Five months after the therapy, the airway stenosis was severe and computed tomography showed lack of the left arytenoid cartilage and exacerbation of laryngeal necrosis. Despite the treatment, 5 and a half months after the therapy, the laryngeal edema and necrosis had become even worse and the surrounding mucosa was edematous and pale. Six months after the therapy, pharyngolaryngoesophagectomy and reconstruction with free jejunal autograft were performed. The surgical specimen pathologically showed massive necrosis and no residual tumor. Three years after the carbon ion therapy, he is alive without recurrence. The first reported laryngeal squamous cell carcinoma case treated with carbon ion therapy resulted in an unexpected radiation laryngeal necrosis. Tissue damage caused by carbon ion therapy may be difficult to repair even for radioresistant cartilage; therefore, hollow organs reinforced by cartilage, such as the larynx, may be vulnerable to carbon ion therapy. Caution should be exercised when treating tumors in or adjacent to such organs with carbon ion therapy.

The purpose of this study is to determine the incidence, clinical characteristics and risk factors of postradiation pelvic insufficiency fracture (PIF) in women with uterine cervical cancer. We reviewed the medical records of 126 patients who received definitive radiotherapy (RT) for uterine cervical cancer between 2003 and 2009 at our institution. Among them, 99 patients who underwent at least one computed tomography (CT) or magnetic resonance imaging of the pelvis during their follow-up at more than 6 months were included in this analysis. The relationship between the incidence of PIF and several patient- and treatment-related factors was analyzed. The median follow-up period was 21 months. Of the 126 patients, 33 (with a total of 50 lesions) were diagnosed with PIF. The 2-year cumulative incidence was 32%. Univariate analysis showed that age ≥70 years (P= 0.0010), postmenopausal state (P = 0.0013), and lower CT density of bone and bone marrow (P= 0.020) significantly related to PIF. In a multivariate analysis, of the 59 patients whose CT densities were evaluable, lower CT density was the only significant factor associated with PIF (P = 0.0026). In conclusion, postradiation PIFs were detected in a considerable number of patients after definitive RT for cervical cancer. Predisposing factors were older age, postmenopausal state, and decreased density of bone and bone marrow on CT.

Purpose To retrospectively analyze the treatment outcomes of particle therapy using protons or carbon ions for unresectable or incompletely resected bone and soft tissue sarcomas (BSTSs) of the pelvis. Methods and Materials From May 2005 to December 2014, 91 patients with nonmetastatic histologically proven unresectable or incompletely resected pelvic BSTSs underwent particle therapy with curative intent. The particle therapy used protons (52 patients) or carbon ions (39 patients). All patients received a dose of 70.4 Gy (relative biologic effectiveness) in 32 fractions (55 patients) or 16 fractions (36 patients). Results The median patient age was 67 years (range 18-87). The median planning target volume (PTV) was 455 cm 3 (range 108-1984). The histologic type was chordoma in 53 patients, chondrosarcoma in 14, osteosarcoma in 10, malignant fibrous histiocytoma/undifferentiated pleomorphic sarcoma in 5, and other in 9 patients. Of the 91 patients, 82 had a primary tumor and 9 a recurrent tumor. The median follow-up period was 32 months (range 3-112). The 3-year rate of overall survival (OS), progression-free survival (PFS), and local control was 83%, 72%, and 92%, respectively. A Cox proportional hazards model revealed that chordoma histologic features and a PTV of ≤500 cm 3 were significantly associated with better OS, and a primary tumor and PTV of ≤500 cm 3 were significantly associated with better PFS. Ion type and number of fractions were not significantly associated with OS, PFS, or local control. Late grade ≥3 toxicities were observed in 23 patients. Compared with the 32-fraction protocol, the 16-fraction protocol was associated with significantly more frequent late grade ≥3 toxicities (18 of 36 vs 5 of 55; P Conclusions Particle therapy using protons or carbon ions was effective for unresectable or incompletely resected pelvic BSTS, and the 32-fraction protocol was effective and relatively less toxic. Nevertheless, a longer follow-up period is needed to confirm these results.

The Rab6 GTPase regulates a retrograde transport route connecting endosomes and the endoplasmic reticulum (ER) via the Golgi apparatus. Recently it was shown that active (GTP-loaded) Rab6A regulates intracellular processing of the amyloid precursor protein (APP). To characterize the role of Rab6A in APP trafficking and to identify effector proteins of the active Rab6A protein, we screened a human placenta cDNA library using the yeast two-hybrid system. We isolated an interacting cDNA clone encoding part of the adaptor protein mint3. The interaction between Rab6A and mint3 is GTP-dependent and requires the complete phosphotyrosine-binding (PTB) domain of the mint protein, which also mediates the association with APP. By confocal microscopy we show that Rab6A, mint3 and APP co-localize at Golgi membranes in HeLa cells. Density gradient centrifugation of cytosolic extracts confirms a common distribution of these three proteins. Our data suggest that mint3 links Rab6A to APP traffic.

Background: Rab3A, a member of the Rab3 small G protein family, regulates Ca2+-dependent exocytosis of neurotransmitter. The cyclical activation and inactivation of Rab3A are essential for the Rab3A action in exocytosis. GDP-Rab3A is activated to GTP-Rab3A by Rab3 GDP/GTP exchange protein (Rab3 GEP) and GTP-Rab3A is inactivated to GDP-Rab3A by Rab3 GTPase-activating protein (Rab3 GAP). We have recently found a novel protein, named rabconnectin-3, which is co-immunoprecipitated with Rab3 GEP or GAP from the extract of the crude synaptic vesicle (CSV) fraction of rat brain. Rabconnectin-3 is abundantly expressed in the brain where it is associated with synaptic vesicles. We have found that two more proteins are co-immunoprecipitated with Rab3 GEP from the CSV fraction of rat brain. We attempted here to isolate and characterize one of them. Results: We determined its partial amino acid sequence, cloned its cDNA from a human cDNA library, and determined its primary structure. The protein consisted of 1490 amino acids (aa) and showed a calculated molecular weight of 163 808. The protein had 7 WD domains. The protein was abundantly expressed in the brain where it co-localized with rabconnectin-3 on synaptic vesicles. The protein formed a stable complex with rabconnectin-3. We named this protein rabconnectin-3β and renamed rabconnectin-3 rabconnectin-3α. Rabconnectin-3β, but not rabconnectin-3α, directly bound Rab3 GEP. Neither rabconnectin-3α nor -3β directly bound Rab3 GAP. Conclusion: These results indicate that rabconnectin-3 consists of the α and β subunits and binds directly Rab3 GEP through the β subunit and indirectly Rab3 GAP through an unidentified molecule(s).

Background. The purpose of the present study was to present the treatment outcomes of particle therapy for indeterminate pulmonary nodules (IPNs) diagnosed as stage I non-small cell lung cancer, including a comparative analysis involving pathologically proven lung cancer (PPLC).Material and methods. A total of 54 patients (57 lesions) who underwent particle therapy for IPNs were enrolled in this study. Median patient age was 76 (range 52–87) years. T-classification was: T1a, 30; T1b, 16; and T2a, 11. Particle therapy using protons or carbon ions was delivered at total doses of 52.8–80 Gy equivalent in 4–26 fractions. The PPLC cohort included 111 patients.Results. The median follow-up time was 41 (range 7–90) months. For all IPN patients, the three-year overall survival, progression-free survival, local control and distant progression-free survival rates were 90%, 72%, 94% and 79%, respectively. Grade 2 toxicities were radiation pneumonitis (19%), dermatitis (9%), rib fracture (2%), chest wall pain (2%) and neuropathy (2%). No ≥ grade 3 toxicities were observed. In univariate analysis, the IPN group showed significantly better survival relative to the PPLC group. However, after adjustment for baseline imbalances between these two groups in multivariate analysis, pathological confirmation did not correlate with survival.Conclusions. Particle therapy for IPNs provided favorable outcomes with minimal toxicities, which may be comparable to those for PPLC patients. Further studies are needed to clarify the optimal management of IPN patients.

Rab3A, a member of the Rab3 small G protein family, regulates Ca(2+)-dependent exocytosis of neurotransmitter. The cyclical activation and inactivation of Rab3A are essential for the Rab3A action in exocytosis. GDP-Rab3A is activated to GTP-Rab3A by Rab3 GDP/GTP exchange protein (Rab3 GEP), and GTP-Rab3A is inactivated to GDP-Rab3A by Rab3 GTPase-activating protein (Rab3 GAP). It remains unknown how or in which step of the multiple exocytosis steps these regulators are activated and inactivated. We isolated here a novel protein that was co-immunoprecipitated with Rab3 GEP and GAP by their respective antibodies from the crude synaptic vesicle fraction of rat brain. The protein, named rabconnectin-3, bound both Rab3 GEP and GAP. The cDNA of rabconnectin-3 was cloned from a human cDNA library and its primary structure was determined. Human rabconnectin-3 consisted of 3,036 amino acids and showed a calculated M(r) of 339,753. It had 12 WD domains. Tissue and subcellular distribution analyses in rat indicated that rabconnectin-3 was abundantly expressed in the brain where it was enriched in the synaptic vesicle fraction. Immunofluorescence and immunoelectron microscopy revealed that rabconnectin-3 was concentrated on synaptic vesicles at synapses. These results indicate that rabconnectin-3 serves as a scaffold molecule for both Rab3 GEP and GAP on synaptic vesicles.

Doc2 has one Munc13-interacting domain at the N-terminal region and two C2-like domains interacting with Ca2+ and phospholipid at the C-terminal region. Doc2 consists of two isoforms, Doc2α and -β. Doc2α is specifically expressed in neuronal cells and implicated in Ca2+-dependent neurotransmitter release, whereas Doc2β is ubiquitously expressed and its function is unknown. We show here that both Doc2α and -β interact with rat tctex-1, a light chain of cytoplasmic dynein, in both cell-free and intact cell systems. Overexpression of the N-terminal fragment of Doc2 containing the tctex-1-interacting domain induces changes in the intracellular localization of cation-independent mannose 6-phosphate receptor and its ligand, cathepsin D, which are transported from trans-Golgi network to late endosomes. Overexpression of the C-terminal fragment containing two C2-like domains shows the similar effect, but to a lesser extent, whereas overexpression of full-length Doc2 or the C-terminal fragment of rabphilin3 containing two C2-like domains does not show this effect. Because dynein is a minus-end-directed microtubule-based motor protein, these results suggest that Doc2, especially Doc2β, plays a role in dynein-dependent intracellular vesicle transport.

We recently purified and characterized from rat brain a GTPase-activating protein (GAP) specific for the Rab3 small G protein subfamily implicated in Ca2+-dependent exocytosis. Rab3 GAP showed two bands with M r of about 130,000 (p130) and 150,000 (p150) on SDS-polyacrylamide gel electrophoresis. p130, but not p150, showed the catalytic activity. Because p150 was likely the subunit of Rab3 GAP, here we cloned the cDNA of p150, determined its primary structure, and characterized it. The tissue and subcellular distribution patterns of p150 and p130 were similar, and both the proteins were enriched in the synaptic soluble fraction. p150 was co-immunoprecipitated with p130 from this fraction. Recombinant p150 formed a heterodimer with recombinant p130 as estimated by sucrose density gradient ultracentrifugation. Recombinant p150 neither showed the Rab3A GAP activity nor affected the activity of recombinant p130. When p150 and p130 were co-expressed in the cells, the subcellular localization of each protein did not change. These results indicate that p150 is the noncatalytic subunit of Rab3 GAP.

We purified a novel actin filament (F-actin)-binding protein from the soluble fraction of Saccharomyces cerevisiae by successive column chromatographies by use of the 125I-labeled F-actin blot overlay method. The purified protein showed a minimum Mr of about 140 kDa on SDS-polyacrylamide gel electrophoresis and we named it ABP140. A search with the partial amino acid sequences of ABP140 against the Saccharomyces Genome Database revealed that the open reading frame of the ABP140 gene (ABP140) corresponded to YOR239W fused with YOR240W by the +1 translational frame shift. The encoded protein consisted of 628 amino acids with a calculated Mr of 71,484. The recombinant protein interacted with F-actin and showed the activity to crosslink F-actin into a bundle. Indirect immunofluorescence study demonstrated that ABP140 was colocalized with both cortical actin patches and cytoplasmic actin cables in intact cells. However, elimination of ABP140 by gene disruption did not show a deleterious effect on cell growth or affect the organization of F-actin. These results indicate that ABP140 is not required for cell growth but may be involved in the reorganization of F-actin in the budding yeast.

International audience; Oculocerebrorenal Lowe syndrome is a rare X-linked disorder characterized by bilateral cataract, mental retardation and renal Fanconi syndrome. The Lowe syndrome protein Ocrl1 is a PIP2 5-phosphatase, primarily localized to the trans-Golgi network (TGN), which 'loss of function' mutations result in PIP2 accumulation in patient's cells. Although PIP2 is involved in many cell functions including signalling, vesicle trafficking and actin polymerization, it has been difficult so far to decipher molecular/cellular mechanisms responsible for Lowe syndrome phenotype. We have recently shown that, through its C-terminal RhoGAP domain, Ocrl1 forms a stable complex with Rac GTPase within the cell. In line with this finding, we report here that upon epidermal growth factor induced Rac activation in COS-7 cells, a fraction of Ocrl1 translocates from TGN to plasma membrane and concentrates in membrane ruffles. In order to investigate the functionality of Ocrl1 in plasma membrane, we have analysed PIP2 distribution in human dermal fibroblasts (HDFs) from Lowe patients versus control HDFs. As revealed by both immunodetection and green fluorescent protein-PH binding, PIP2 was found strikingly to accumulate in PDGF induced ruffles in Lowe HDFs when compared with control. This suggests that Ocrl1 is active as a PIP2 5-phosphatase in Rac induced membrane ruffles. Cellular properties such as cell migration and establishment of cell-cell contacts, which depend on ruffling and lamellipodia formation, should be further investigated to understand the pathophysiology of Lowe syndrome.

Rab3A, a member of the Rab3 small G protein family, regulates Ca2+-dependent exocytosis of neurotransmitter. The cyclical activation and inactivation of Rab3A are essential for the Rab3A action in exocytosis. GDP-Rab3A is activated to GTP-Rab3A by Rab3 GDP/GTP exchange protein (Rab3 GEP) and GTP-Rab3A is inactivated to GDP-Rab3A by Rab3 GTPase-activating protein (Rab3 GAP). We have recently found a novel protein, named rabconnectin-3, which is co-immunoprecipitated with Rab3 GEP or GAP from the extract of the crude synaptic vesicle (CSV) fraction of rat brain. Rabconnectin-3 is abundantly expressed in the brain where it is associated with synaptic vesicles. We have found that two more proteins are co-immunoprecipitated with Rab3 GEP from the CSV fraction of rat brain. We attempted here to isolate and characterize one of them.We determined its partial amino acid sequence, cloned its cDNA from a human cDNA library, and determined its primary structure. The protein consisted of 1490 amino acids (aa) and showed a calculated molecular weight of 163808. The protein had 7 WD domains. The protein was abundantly expressed in the brain where it co-localized with rabconnectin-3 on synaptic vesicles. The protein formed a stable complex with rabconnectin-3. We named this protein rabconnectin-3beta and renamed rabconnectin-3 rabconnectin-3alpha. Rabconnectin-3beta, but not rabconnectin-3alpha, directly bound Rab3 GEP. Neither rabconnectin-3alpha nor -3beta directly bound Rab3 GAP.These results indicate that rabconnectin-3 consists of the alpha and beta subunits and binds directly Rab3 GEP through the beta subunit and indirectly Rab3 GAP through an unidentified molecule(s).

This chapter describes the assays for the Rab3 guanosine-5'-triphosphate (GTP)ase-activating proteins (GAP) activity, the procedures for the purification of native Rab3 GAP from rat brain synaptic soluble fraction, the procedures for the purification of recombinant hexahistidine (His6)-tagged Rab3 GAP from Escherichia coli, and the properties of Rab3 GAP. The Rab3 GAP activity to stimulate the intrinsic GTPase activity of Rab3A is assayed by three methods: (1) standard assay (filter assay), (2) overlay assay, and (3) thin-layer chromatography assay. The steps used in the purification of native Rab3 GAP are: (1) preparation of the synaptic soluble fraction from rat brain, (2) QSepharose FF column chromatography, (3) hydroxyapatite column chromatography, (4) heparin-Sepharose CL-6B column chromatography, and (5) Mono Q PC 1.6/5 column chromatography. All the purification procedures are performed at 0–4°C.

The Rab3 small G protein subfamily (Rab3) consists of four members, Rab3A, -B, -C, and -D. We have recently isolated and characterized the Rab3 regulators, GDP/GTP exchange protein (GEP) and GTPase activating protein (GAP), both of which are specific for the Rab3 subfamily. Rab3 GEP stimulates the conversion of the GDP-bound inactive form to the GTP-bound active form, whereas Rab3 GAP stimulates the reverse reaction. Of the four members of the Rab3 subfamily, evidence is accumulating that Rab3A is involved in Ca2+-dependent exocytosis, particularly in neurotransmitter release. We first analyzed the subcellular localization of Rab3 GEP and GAP in rat brain. Subcellular fractionation analysis showed that both Rab3 GEP and GAP were enriched in the synaptic soluble fraction. Immunocytochemical analysis in primary cultured rat hippocampal neurons showed that both Rab3 GEP and GAP were concentrated at the presynaptic nerve terminals. We then examined whether Rab3 GEP and GAP were involved in Ca2+-dependent exocytosis by use of human growth hormone (GH) co-expression assay system of cultured PC12 cells. Overexpression of the deletion mutant of Rab3 GEP possessing the catalytic activity reduced the high K+-induced GH release without affecting the basal GH release, whereas that of the deletion mutant lacking the catalytic activity showed no effect on the high K+-induced GH release. In contrast, overexpression of Rab3 GAP or its deletion mutant possessing the catalytic activity did not affect the high K+-induced GH release or the basal GH release. These results indicate that Rab3 GEP and GAP are colocalized with Rab3A at the synaptic release sites and suggest that they regulate the activity of Rab3A and are involved in Ca2+-dependent exocytosis.

The kinetic properties of MSS4 are studied in comparison with those of Rab3A GRF. MSS4 stimulates the dissociation of [3H]GDP from the lipid-modified and lipid-unmodified forms of Rab3A to the same extent, although Rab3A GRF is more effective on the lipid-modified form than on the lipid-unmodified form. Both MSS4 and Rab3A GRF are inactive on other Rab/Sec/Ypt family members including at least Rab2, Rab5, and Rab11. Rab GDI inhibits the MSS4 and Rab3A GRF effects on the lipid-modified form of Rab3A, but the doses of Rab GDI necessary for this inhibitory effect on Rab3A GRF are lower than those on MSS4. Moreover, Rab GDI slightly inhibits the Rab3A GRF effect on the lipid-unmodified form of Rab3A, but does not affect the MSS4 effect on the lipid-unmodified form of Rab3A. These results suggest that MSS4 and Rab3A GRF are different GDP/GTP exchange proteins for Rab3A.