ACAP3 regulates neurite outgrowth through its GAP activity specific to Arf6 in mouse hippocampal neurons

2016 ◽  
Vol 473 (17) ◽  
pp. 2591-2602 ◽  
Author(s):  
Yuki Miura ◽  
Tsunaki Hongu ◽  
Yohei Yamauchi ◽  
Yuji Funakoshi ◽  
Naohiro Katagiri ◽  
...  
Keyword(s):  
Neurite Outgrowth ◽  
Hippocampal Neurons ◽  
Coiled Coil ◽  
Small Gtpase ◽  
Nucleotide Exchange ◽  
Wild Type ◽  
Guanine Nucleotide Exchange ◽  
Gtpase Activating Proteins ◽  
Nucleotide Exchange Factor ◽  
Adp Ribosylation Factor

ACAP3 (ArfGAP with coiled-coil, ankyrin repeat and pleckstrin homology domains 3) belongs to the ACAP family of GAPs (GTPase-activating proteins) for the small GTPase Arf (ADP-ribosylation factor). However, its specificity to Arf isoforms and physiological functions remain unclear. In the present study, we demonstrate that ACAP3 plays an important role in neurite outgrowth of mouse hippocampal neurons through its GAP activity specific to Arf6. In primary cultured mouse hippocampal neurons, knockdown of ACAP3 abrogated neurite outgrowth, which was rescued by ectopically expressed wild-type ACAP3, but not by its GAP activity-deficient mutant. Ectopically expressed ACAP3 in HEK (human embryonic kidney)-293T cells showed the GAP activity specific to Arf6. In support of this observation, the level of GTP-bound Arf6 was significantly increased by knockdown of ACAP3 in hippocampal neurons. In addition, knockdown and knockout of Arf6 in mouse hippocampal neurons suppressed neurite outgrowth. These results demonstrate that ACAP3 positively regulates neurite outgrowth through its GAP activity specific to Arf6. Furthermore, neurite outgrowth suppressed by ACAP3 knockdown was rescued by expression of a fast cycle mutant of Arf6 that spontaneously exchanges guanine nucleotides on Arf6, but not by that of wild-type, GTP- or GDP-locked mutant Arf6. Thus cycling between active and inactive forms of Arf6, which is precisely regulated by ACAP3 in concert with a guanine-nucleotide-exchange factor(s), seems to be required for neurite outgrowth of hippocampal neurons.

scholarly journals Rab7a and Mitophagosome Formation

Cells ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 224 ◽  
Author(s):  
Esther Tan ◽  
Bor Tang
Keyword(s):  
Retrograde Transport ◽  
Small Gtpase ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Autophagosome Formation ◽  
Guanine Nucleotide Exchange ◽  
Gtpase Activating Proteins ◽  
Retromer Complex ◽  
Nucleotide Exchange Factor

The small GTPase, Rab7a, and the regulators of its GDP/GTP-binding status were shown to have roles in both endocytic membrane traffic and autophagy. Classically known to regulate endosomal retrograde transport and late endosome-lysosome fusion, earlier work has indicated a role for Rab7a in autophagosome-lysosome fusion as well as autolysosome maturation. However, as suggested by recent findings on PTEN-induced kinase 1 (PINK1)-Parkin-mediated mitophagy, Rab7a and its regulators are critical for the correct targeting of Atg9a-bearing vesicles to effect autophagosome formation around damaged mitochondria. This mitophagosome formation role for Rab7a is dependent on an intact Rab cycling process mediated by the Rab7a-specific guanine nucleotide exchange factor (GEF) and GTPase activating proteins (GAPs). Rab7a activity in this regard is also dependent on the retromer complex, as well as phosphorylation by the TRAF family-associated NF-κB activator binding kinase 1 (TBK1). Here, we discuss these recent findings and broadened perspectives on the role of the Rab7a network in PINK1-Parkin mediated mitophagy.

scholarly journals Unfolded protein response regulates yeast small GTPase Arl1p activation at late Golgi via phosphorylation of Arf GEF Syt1p

2016 ◽  
Vol 113 (12) ◽  
pp. E1683-E1690 ◽  
Author(s):  
Jia-Wei Hsu ◽  
Pei-Hua Tang ◽  
I-Hao Wang ◽  
Chia-Lun Liu ◽  
Wen-Hui Chen ◽  
...  
Keyword(s):  
Unfolded Protein Response ◽  
Small Gtpase ◽  
Nucleotide Exchange ◽  
Unfolded Protein ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Active Transcription ◽  
Arf Gtpases ◽  
Protein Response ◽  
Adp Ribosylation Factor

ADP ribosylation factor (Arf) GTPases are key regulators of membrane traffic at the Golgi complex. In yeast, Arf guanine nucleotide-exchange factor (GEF) Syt1p activates Arf-like protein Arl1p, which was accompanied by accumulation of golgin Imh1p at late Golgi, but whether and how this function of Syt1p is regulated remains unclear. Here, we report that the inositol-requiring kinase 1 (Ire1p)-mediated unfolded protein response (UPR) modulated Arl1p activation at late Golgi. Arl1p activation was dependent on both kinase and endo-RNase activities of Ire1p. Moreover, constitutively active transcription factor Hac1p restored the Golgi localization of Arl1p and Imh1p inIRE1-deleted cells. Elucidating the mechanism of Ire1p–Hac1p axis actions, we found that it regulated phosphorylation of Syt1p, which enhances Arl1p activation, recruitment of Imh1p to the Golgi, and Syt1p interaction with Arl1p. Consistent with these findings, the induction of UPR by tunicamycin treatment increases phosphorylation of Syt1p, resulting in Arl1p activation. Thus, these findings clarify how the UPR influences the roles of Syt1p, Arl1p, and Imh1p in Golgi transport.

scholarly journals Activation of Cdc42 GTPase upon CRY2-Induced Cortical Recruitment Is Antagonized by GAPs in Fission Yeast

Cells ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 2089 ◽  
Author(s):  
Iker Lamas ◽  
Nathalie Weber ◽  
Sophie G. Martin
Keyword(s):  
Fission Yeast ◽  
Positive Feedback ◽  
Antagonistic Activity ◽  
Cell Polarization ◽  
Small Gtpase ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Cell Architecture

The small GTPase Cdc42 is critical for cell polarization in eukaryotic cells. In rod-shaped fission yeast Schizosaccharomyces pombe cells, active GTP-bound Cdc42 promotes polarized growth at cell poles, while inactive Cdc42-GDP localizes ubiquitously also along cell sides. Zones of Cdc42 activity are maintained by positive feedback amplification involving the formation of a complex between Cdc42-GTP, the scaffold Scd2, and the guanine nucleotide exchange factor (GEF) Scd1, which promotes the activation of more Cdc42. Here, we use the CRY2-CIB1 optogenetic system to recruit and cluster a cytosolic Cdc42 variant at the plasma membrane and show that this leads to its moderate activation also on cell sides. Surprisingly, Scd2, which binds Cdc42-GTP, is still recruited to CRY2-Cdc42 clusters at cell sides in individual deletion of the GEFs Scd1 or Gef1. We show that activated Cdc42 clusters at cell sides are able to recruit Scd1, dependent on the scaffold Scd2. However, Cdc42 activity is not amplified by positive feedback and does not lead to morphogenetic changes, due to antagonistic activity of the GTPase activating protein Rga4. Thus, the cell architecture is robust to moderate activation of Cdc42 at cell sides.

scholarly journals Myoblast Migration and Directional Persistence Affected by Syndecan-4-Mediated Tiam-1 Expression and Distribution

2020 ◽  
Vol 21 (3) ◽  
pp. 823 ◽  
Author(s):  
Daniel Becsky ◽  
Szuzina Gyulai-Nagy ◽  
Arpad Balind ◽  
Peter Horvath ◽  
Laszlo Dux ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Underlying Mechanism ◽  
Small Gtpase ◽  
Asymmetric Distribution ◽  
Nucleotide Exchange ◽  
Muscle Stem Cells ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
T Lymphoma ◽  
Migration Capacity

Skeletal muscle is constantly renewed in response to injury, exercise, or muscle diseases. Muscle stem cells, also known as satellite cells, are stimulated by local damage to proliferate extensively and form myoblasts that then migrate, differentiate, and fuse to form muscle fibers. The transmembrane heparan sulfate proteoglycan syndecan-4 plays multiple roles in signal transduction processes, such as regulating the activity of the small GTPase Rac1 (Ras-related C3 botulinum toxin substrate 1) by binding and inhibiting the activity of Tiam1 (T-lymphoma invasion and metastasis-1), a guanine nucleotide exchange factor for Rac1. The Rac1-mediated actin remodeling is required for cell migration. Syndecan-4 knockout mice cannot regenerate injured muscle; however, the detailed underlying mechanism is unknown. Here, we demonstrate that shRNA-mediated knockdown of syndecan-4 decreases the random migration of mouse myoblasts during live-cell microscopy. Treatment with the Rac1 inhibitor NSC23766 did not restore the migration capacity of syndecan-4 silenced cells; in fact, it was further reduced. Syndecan-4 knockdown decreased the directional persistence of migration, abrogated the polarized, asymmetric distribution of Tiam1, and reduced the total Tiam1 level of the cells. Syndecan-4 affects myoblast migration via its role in expression and localization of Tiam1; this finding may facilitate greater understanding of the essential role of syndecan-4 in the development and regeneration of skeletal muscle.

Sign in / Sign up

Export Citation Format

Share Document