scholarly journals Dual function of cTAGE5 in collagen export from the endoplasmic reticulum

2016 ◽  
Vol 27 (13) ◽  
pp. 2008-2013 ◽  
Author(s):  
Tomoya Tanabe ◽  
Miharu Maeda ◽  
Kota Saito ◽  
Toshiaki Katada
Keyword(s):  
Endoplasmic Reticulum ◽  
Dual Function ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Collagen Secretion ◽  
Nucleotide Exchange Factor ◽  
Independent Functions ◽  
Er Exit Sites ◽  
Gtpase Cycle ◽  
Collagen Vii

Two independent functions of cTAGE5 have been reported in collagen VII export from the endoplasmic reticulum (ER). cTAGE5 not only forms a cargo receptor complex with TANGO1, but it also acts as a scaffold to recruit Sec12, a guanine-nucleotide exchange factor for Sar1 GTPase, to ER exit sites. However, the relationship between the two functions remains unclear. Here we isolated point mutants of cTAGE5 that lost Sec12-binding ability but retained binding to TANGO1. Although expression of the mutant alone could not rescue the defects in collagen VII secretion mediated by cTAGE5 knockdown, coexpression with Sar1, but not with the GTPase-deficient mutant, recovered secretion. The expression of Sar1 alone failed to rescue collagen secretion in cTAGE5-depleted cells. Taken together, these results suggest that two functionally irreplaceable and molecularly separable modules in cTAGE5 are both required for collagen VII export from the ER. The recruitment of Sec12 by cTAGE5 contributes to efficient activation of Sar1 in the vicinity of ER exit sites. In addition, the GTPase cycle of Sar1 appears to be responsible for collagen VII exit from the ER.

scholarly journals cTAGE5 acts as a Sar1 GTPase regulator for collagen export

2018 ◽  
Author(s):  
Norito Sasaki ◽  
Masano Shiraiwa ◽  
Miharu Maeda ◽  
Tomohiro Yorimitsu ◽  
Ken Sato ◽  
...  
Keyword(s):  
Small Gtpase ◽  
Coated Vesicles ◽  
Secretory Proteins ◽  
Efficient Production ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Guanine Nucleotide Exchange ◽  
Collagen Secretion ◽  
Nucleotide Exchange Factor ◽  
Er Exit Sites

AbstractSecretory proteins synthesized within the endoplasmic reticulum (ER) are exported via coat protein complex II (COPII)-coated vesicles. The formation of the COPII-coated vesicles is initiated by activation of the small GTPase, Sar1. cTAGE5 directly interacts with a guanine-nucleotide exchange factor (GEF), Sec12, and a GTPase-activating protein (GAP) of Sar1, Sec23. We have previously shown that cTAGE5 recruits Sec12 to the ER exit sites for efficient production of activated Sar1 for collagen secretion. However, the functional significance of the interaction between cTAGE5 and Sec23 has not been fully elucidated. In this study, we showed that cTAGE5 enhances the GAP activity of Sec23 toward Sar1. In addition, the interaction of cTAGE5 with Sec23 is necessary for collagen exit from the ER. Our data suggests that cTAGE5 acts as a Sar1 GTPase regulator for collagen secretion.

scholarly journals Concentration of Sec12 at ER exit sites via interaction with cTAGE5 is required for collagen export

2014 ◽  
Vol 206 (6) ◽  
pp. 751-762 ◽  
Author(s):  
Kota Saito ◽  
Koh Yamashiro ◽  
Noriko Shimazu ◽  
Tomoya Tanabe ◽  
Kenji Kontani ◽  
...  
Keyword(s):  
Direct Interaction ◽  
Secretory Proteins ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Transport Vesicles ◽  
Nucleotide Exchange Factor ◽  
Receptor Component ◽  
Er Exit Sites ◽  
Guanosine Triphosphatase ◽  
Trimeric Structure

Mechanisms for exporting variably sized cargo from the endoplasmic reticulum (ER) using the same machinery remain poorly understood. COPII-coated vesicles, which transport secretory proteins from the ER to the Golgi apparatus, are typically 60–90 nm in diameter. However, collagen, which forms a trimeric structure that is too large to be accommodated by conventional transport vesicles, is also known to be secreted via a COPII-dependent process. In this paper, we show that Sec12, a guanine-nucleotide exchange factor for Sar1 guanosine triphosphatase, is concentrated at ER exit sites and that this concentration of Sec12 is specifically required for the secretion of collagen VII but not other proteins. Furthermore, Sec12 recruitment to ER exit sites is organized by its direct interaction with cTAGE5, a previously characterized collagen cargo receptor component, which functions together with TANGO1 at ER exit sites. These findings suggest that the export of large cargo requires high levels of guanosine triphosphate–bound Sar1 generated by Sec12 localized at ER exit sites.

scholarly journals Identification of a Rab GTPase-activating protein cascade that controls recycling of the Rab5 GTPase Vps21 from the vacuole

2015 ◽  
Vol 26 (13) ◽  
pp. 2535-2549 ◽  
Author(s):  
Meenakshi Rana ◽  
Jens Lachmann ◽  
Christian Ungermann
Keyword(s):  
Endoplasmic Reticulum ◽  
Endocytic Pathway ◽  
Rab Gtpase ◽  
Guanine Nucleotide ◽  
Membrane Recycling ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Guanine Nucleotide Exchange ◽  
Vacuole Fusion ◽  
Nucleotide Exchange Factor

Transport within the endocytic pathway depends on a consecutive function of the endosomal Rab5 and the late endosomal/lysosomal Rab7 GTPases to promote membrane recycling and fusion in the context of endosomal maturation. We previously identified the hexameric BLOC-1 complex as an effector of the yeast Rab5 Vps21, which also recruits the GTPase-activating protein (GAP) Msb3. This raises the question of when Vps21 is inactivated on endosomes. We provide evidence for a Rab cascade in which activation of the Rab7 homologue Ypt7 triggers inactivation of Vps21. We find that the guanine nucleotide exchange factor (GEF) of Ypt7 (the Mon1-Ccz1 complex) and BLOC-1 both localize to the same endosomes. Overexpression of Mon1-Ccz1, which generates additional Ypt7-GTP, or overexpression of activated Ypt7 promotes relocalization of Vps21 from endosomes to the endoplasmic reticulum (ER), which is indicative of Vps21 inactivation. This ER relocalization is prevented by loss of either BLOC-1 or Msb3, but it also occurs in mutants lacking endosome–vacuole fusion machinery such as the HOPS tethering complex, an effector of Ypt7. Importantly, BLOC-1 interacts with the HOPS on vacuoles, suggesting a direct Ypt7-dependent cross-talk. These data indicate that efficient Vps21 recycling requires both Ypt7 and endosome–vacuole fusion, thus suggesting extended control of a GAP cascade beyond Rab interactions.

scholarly journals Eng2, a new player involved in feedback loop regulation of Cdc42 activity in fission yeast

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Patricia García ◽  
Pedro M. Coll ◽  
Francisco del Rey ◽  
M. Isabel Geli ◽  
Pilar Pérez ◽  
...  
Keyword(s):  
Fission Yeast ◽  
Feedback Loop ◽  
Oscillatory Behavior ◽  
Small Gtpase ◽  
Dual Function ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Endocytic Machinery ◽  
Mutant Cells

AbstractCell polarity and morphogenesis are regulated by the small GTPase Cdc42. Even though major advances have been done in the field during the last years, the molecular details leading to its activation in particular cellular contexts are not completely understood. In fission yeast, the β(1,3)-glucanase Eng2 is a “moonlighting protein” with a dual function, acting as a hydrolase during spore dehiscence, and as component of the endocytic machinery in vegetative cells. Here, we report that Eng2 plays a role in Cdc42 activation during polarized growth through its interaction with the scaffold protein Scd2, which brings Cdc42 together with its guanine nucleotide exchange factor (GEF) Scd1. eng2Δ mutant cells have defects in activation of the bipolar growth (NETO), remaining monopolar during all the cell cycle. In the absence of Eng2 the accumulation of Scd1 and Scd2 at the poles is reduced, the levels of Cdc42 activation decrease, and the Cdc42 oscillatory behavior, associated with bipolar growth in wild type cells, is altered. Furthermore, overexpression of Eng2 partially rescues the growth and polarity defects of a cdc42-L160S mutant. Altogether, our work unveils a new factor regulating the activity of Cdc42, which could potentially link the polarity and endocytic machineries.

scholarly journals cTAGE5 mediates collagen secretion through interaction with TANGO1 at endoplasmic reticulum exit sites

2011 ◽  
Vol 22 (13) ◽  
pp. 2301-2308 ◽  
Author(s):  
Kota Saito ◽  
Koh Yamashiro ◽  
Yuki Ichikawa ◽  
Patrik Erlmann ◽  
Kenji Kontani ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Lymphoma ◽  
Coiled Coil ◽  
Integral Membrane Protein ◽  
Cutaneous T Cell Lymphoma ◽  
Rich Domain ◽  
Collagen Secretion ◽  
Er Exit Sites ◽  
Antigen 5 ◽  
Collagen Vii

Cutaneous T-cell lymphoma-–associated antigen 5 (cTAGE5), an originally identified tumor antigen, is overexpressed in various cancer cell lines. The cDNA encodes an integral membrane protein containing two coiled-coil motifs and a proline-rich domain. We show that cTAGE5 specifically localizes to the endoplasmic reticulum (ER) exit sites. In addition, cTAGE5 forms a complex with TANGO1 (MIA3), a previously characterized cargo receptor for collagen VII, by the interaction of their coiled-coil motifs. Of interest, cTAGE5, as well as TANGO1, is capable of interacting with the inner-layer coatomer of COPII Sec23/24 complex through their C-terminal proline-rich domains and required for collagen VII secretion. We propose that cTAGE5 acts as a coreceptor of TANGO1 for collagen VII export from the ER.

scholarly journals Warburg Micro syndrome is caused by RAB18 deficiency or dysregulation

Open Biology ◽  
2015 ◽  
Vol 5 (6) ◽  
pp. 150047 ◽  
Author(s):  
Mark T. Handley ◽  
Sarah M. Carpanini ◽  
Girish R. Mali ◽  
Duska J. Sidjanin ◽  
Irene A. Aligianis ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Lines ◽  
Autosomal Recessive ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Multisystem Disorder ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Warburg Micro Syndrome

RAB18 , RAB3GAP1 , RAB3GAP2 and TBC1D20 are each mutated in Warburg Micro syndrome, a rare autosomal recessive multisystem disorder. RAB3GAP1 and RAB3GAP2 form a binary ‘RAB3GAP’ complex that functions as a guanine-nucleotide exchange factor (GEF) for RAB18, whereas TBC1D20 shows modest RAB18 GTPase-activating (GAP) activity in vitro . Here, we show that in the absence of functional RAB3GAP or TBC1D20, the level, localization and dynamics of cellular RAB18 is altered. In cell lines where TBC1D20 is absent from the endoplasmic reticulum (ER), RAB18 becomes more stably ER-associated and less cytosolic than in control cells. These data suggest that RAB18 is a physiological substrate of TBC1D20 and contribute to a model in which a Rab-GAP can be essential for the activity of a target Rab. Together with previous reports, this indicates that Warburg Micro syndrome can be caused directly by loss of RAB18, or indirectly through loss of RAB18 regulators RAB3GAP or TBC1D20.

scholarly journals Rab1b Interacts with GBF1 and Modulates both ARF1 Dynamics and COPI Association

2007 ◽  
Vol 18 (7) ◽  
pp. 2400-2410 ◽  
Author(s):  
Pablo Monetta ◽  
Ileana Slavin ◽  
Nahuel Romero ◽  
Cecilia Alvarez
Keyword(s):  
Time Lapse ◽  
Limited Range ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Golgi Membranes ◽  
Golgi Transport ◽  
Nucleotide Exchange Factor ◽  
Er Exit Sites ◽  
Interfering Rna

Assembly of the cytosolic coat protein I (COPI) complex at the ER–Golgi interface is directed by the ADP ribosylation factor1 (Arf1) and its guanine nucleotide exchange factor (GBF1). Rab1b GTPase modulates COPI recruitment, but the molecular mechanism underlying this action remains unclear. Our data reveal that in vivo expression of the GTP-restricted Rab1b mutant (Rab1Q67L) increased the association of GBF1 and COPI to peripheral structures localized at the ER exit sites (ERES) interface. Active Rab1b also stabilized Arf1 on Golgi membranes. Furthermore, we characterized GBF1 as a new Rab1b effector, and showed that its N-terminal domain was involved in this interaction. Rab1b small interfering RNA oligonucleotide assays suggested that Rab1b was required for GBF1 membrane association. To further understand how Rab1b functions in ER-to-Golgi transport, we analyzed GFP-Rab1b dynamics in HeLa cells. Time-lapse microscopy indicated that the majority of the Rab1b-labeled punctuated structures are relatively short-lived with limited-range movements. FRAP of Golgi GFP-Rab1bwt showed rapid recovery (t1/2 120 s) with minimal dependence on microtubules. Our data support a model where Rab1b-GTP induces GBF1 recruitment at the ERES interface and at the Golgi complex where it is required for COPII/COPI exchange or COPI vesicle formation, respectively.

scholarly journals ADP-Ribosylation Factor/COPI-dependent Events at the Endoplasmic Reticulum-Golgi Interface Are Regulated by the Guanine Nucleotide Exchange Factor GBF1

2003 ◽  
Vol 14 (6) ◽  
pp. 2250-2261 ◽  
Author(s):  
Rafael García-Mata ◽  
Tomasz Szul ◽  
Cecilia Alvarez ◽  
Elizabeth Sztul
Keyword(s):  
Endoplasmic Reticulum ◽  
Brefeldin A ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Adp Ribosylation ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Nucleotide Exchange Factor ◽  
Two Stages ◽  
Adp Ribosylation Factor

ADP-ribosylation factor (ARF) mediated recruitment of COPI to membranes plays a central role in transport between the endoplasmic reticulum (ER) and the Golgi. The activation of ARFs is mediated by guanine nucleotide exchange factors (GEFs). Although several ARF-GEFs have been identified, the transport steps in which they function are still poorly understood. Here we report that GBF1, a member of the Sec7-domain family of GEFs, is responsible for the regulation of COPI-mediated events at the ER-Golgi interface. We show that GBF1 is essential for the formation, differentiation, and translocation of pre-Golgi intermediates and for the maintenance of Golgi integrity. We also show that the formation of transport-competent ER-to-Golgi intermediates proceeds in two stages: first, a COPI-independent event leads to the formation of an unstable compartment, which is rapidly reabsorbed in the absence of GBF1 activity. Second, the association of GBF1 with this compartment allows COPI recruitment and leads to its maturation into transport intermediates. The recruitment of GBF1 to this compartment is specifically inhibited by brefeldin A. Our findings imply that the continuous recruitment of GBF1 to spatially differentiated membrane domains is required for sustained membrane remodeling that underlies membrane traffic and Golgi biogenesis.

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