Poster Presentation 2nd Australian Cancer and Metabolism Meeting 2017

Annexin A6 recruits TBC1D15 to regulate Rab7-dependent delivery of late endosomal cholesterol for cancer cell migration (#37)

Thomas Grewal 1 , Elsa Elsa Meneses-Salas 2 , Ana Garcia-Melero 2 , Monira Hoque 1 , Mohamed Wahba 1 , Syeed S Beevi 1 , Carles Rentero 2 , Carlos Enrich 2
  1. University of Sydney, Sydney, NEW SOUTH WALES, Australia
  2. Dep de Biomedicina, Unitat de Biologia Cellular, CELLEX, IDIBAPS, Facultat de Medicina, Universitat de Barcelona, Barcelona, Catalunia, Spain

LDL-cholesterol is considered to promote cancer cell migration. However, the underlying mechanisms and cholesterol transport routes remain unclear. We have previously demonstrated that the Niemann Pick Type C1 (NPC1) mutation, which is characterized by an inhibition of LDL-cholesterol export from late endosomes (LE), interfered with syntaxin-6 (Stx6)-dependent recycling of integrins to the cell surface (Cell Rep 7, 883-97, 2014). Consequently, blocked distribution of LDL-cholesterol in NPC mutants inhibited cell migration and invasion in 2- and 3D environments and reduced lung metastasis in vivo. Similarly, upregulation of a member of the annexin family, Annexin A6 (AnxA6), which induces an NPC1-mutant like phenotype, was associated with Stx6 and integrin accumulation in recycling endosomes, leading to reduced cell motility in 2D and 3D-migration/invasion assays (J Biol Chem 291, 1320-35, 2016). Mechanistically, we found that AnxA6 recruits TBC1D15, a Rab7-GTPase activating protein (Rab7-GAP) to LE, downregulating Rab7 GTPase activity and its ability to regulate LE-cholesterol transport. Vice versa, AnxA6 depletion elevated Rab7-GTP levels and rescued LE-cholesterol export in NPC1 mutant cells. This coincided with increased interaction of Rab7 with ORP1L, a cholesterol-sensor, to promote formation of membrane contact sites (MCS) between LE and the Endoplasmic Reticulum (ER), enabling LDL-cholesterol transfer to the ER. This is followed by ACAT-dependent cholesterol esterification (CE) and deposition in lipid droplets. Recent reports have identified CE accumulation in lipid droplets to promote prostate cancer aggressiveness. Moreover, loss of AnxA6 and increased Rab7 levels in metastatic prostate cancers indicate that LE-cholesterol transport, AnxA6-dependent Rab7 activity and the resulting CE accumulation in lipid droplets could critically contribute to prostate cancer aggressiveness.