An Arf/Rab cascade controls the growth and invasiveness of glioblastoma

Abstract

Glioblastoma is the most common and deadly malignant brain cancer. We now demonstrate that loss of function of the endosomal GTPase Rab35 in human brain tumor initiating cells (BTICs) increases glioblastoma growth and decreases animal survival following BTIC implantation in mouse brains. Mechanistically, we identify that the GTPase Arf5 interacts with the guanine nucleotide exchange factor (GEF) for Rab35, DENND1/connecdenn, and allosterically enhances its GEF activity toward Rab35. Knockdown of either Rab35 or Arf5 increases cell migration, invasiveness, and self-renewal in culture and enhances the growth and invasiveness of BTIC-initiated brain tumors in mice. RNAseq of the tumors reveals up-regulation of the tumor-promoting transcription factor SPOCD1, and disruption of the Arf5/Rab35 axis in glioblastoma cells leads to strong activation of the epidermal growth factor receptor, with resulting enhancement of SPOCD1 levels. These discoveries reveal an unexpected cascade between an Arf and a Rab and indicate a role for the cascade, and thus endosomal trafficking, in brain tumors.

The glycoprotein GP130 governs the surface presentation of the G protein–coupled receptor APLNR

“…This might ultimately detune ARFs, which are instrumental molecular switches of vesicular trafficking ( Donaldson and Jackson, 2011 ; Sztul et al, 2019 ). In line with previous reports pointing to the role of endovesicular trafficking in GBM cell vitality ( Shingu et al, 2017 ; Jacobs et al, 2020 ; Kulasekaran et al, 2021 ), our study reports on how modulating receptor dynamics might limit nononcogene signaling involved in tumor progression.…”

“…Thus, GP130 not only interacts with APLNR but also contributes to their copresentation at the plasma membrane by transcriptionally enabling ELMOD1 expression, which in turn involves a fine-tuned balance between endocytosis/recycling ARF-based activities ( Donaldson and Jackson, 2011 ; Sztul et al, 2019 ; Schweitzer et al, 2011 ). This could be attributed to the modulation of receptor membrane trafficking at the plasma membrane and/or coreceptor clustering, as previously reported for VEGFR2 and EGFR ( Zhu et al, 2017 ; Kulasekaran et al, 2021 ). Our data therefore suggest that this endocytic–recycling pathway may constitute an interesting process to target in cancer cells dependent on APLN supply.…”

“…Yet, how exactly ELMOD1 controls APLNR surface expression requires further investigation, as ELMOD1 might target ARF GTPases either by its GAP activity and/or binding, reminiscent of SAT (suppressors of Arf ts) identified in yeast ( Zhang et al, 1998 ). Overall, this suggests a complex modulation in endovesicular dynamics, which recently emerged as a potent checkpoint for tumor cell expansion in GBM cells ( Shingu et al, 2017 ; Jacobs et al, 2020 ; Kulasekaran et al, 2021 ).…”

Who’s in control? Principles of Rab GTPase activation in endolysosomal membrane trafficking and beyond

“…Recently, another example of Arf-mediated Rab activation was reported ( Kulasekaran et al, 2021 ). Rab35, an endocytic Rab found at the plasma membrane and REs ( Sato et al, 2008 ; Kouranti et al, 2006 ), is involved in cell adhesion and cell migration by controlling the trafficking of β1-integrin and the EGF receptor ( Klinkert and Echard, 2016 ; Allaire et al, 2013 ).…”

“…Rab35, an endocytic Rab found at the plasma membrane and REs ( Sato et al, 2008 ; Kouranti et al, 2006 ), is involved in cell adhesion and cell migration by controlling the trafficking of β1-integrin and the EGF receptor ( Klinkert and Echard, 2016 ; Allaire et al, 2013 ). Arf5 binds the Rab35 GEF DENND1 and stimulates its GEF activity, with dysregulation of this cascade linked to glioblastoma growth ( Kulasekaran et al, 2021 ). DENND1 GEF activity is initially autoinhibited and relieved by phosphorylation via the central Akt kinase ( Fig.…”