Rab27a promotes melanoma proliferation, invasion and survival via regulation of the secretory pathway

GY Lui1,2, D Guo1,2, DM Sharp1,1, JL Stow3, MJ Rogers4, W Weninger1,5,6, NK Haass1,5,7 and KA Beaumont1,2

  1. Centenary Institute, Newtown, NSW, Australia
  2. Sydney Medical School, University of Sydney, NSW, Australia
  3. Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia
  4. Garvan Institute of Medical Research and St Vincent's Clinical School, UNSW Australia, Sydney, New South Wales, Australia
  5. Discipline of Dermatology, University of Sydney, NSW, Australia
  6. Department of Dermatology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia
  7. The University of Queensland Diamantina Institute, Translational Research Institute, Woolloongabba, QLD, Australia

The Rab GTPase family of trafficking proteins is increasingly being implicated in cancer cell biology. Genetic screens in early passage melanoma cell lines have identified Rab27a as a tumour dependency. While the role of Rab27a in melanosome trafficking in melanocytes is well known, its precise function in melanoma cells and melanoma progression remains poorly understood. In the present study, we found that Rab27a expression was significantly increased in human melanoma samples compared to benign nevi, and high Rab27a expression was associated with a poorer clinical outcome. Knockdown of Rab27a gene expression in melanoma cell lines inhibited proliferation, colony formation, 3D spheroid invasion and reduced cell motility in a collagen matrix. 2D migration was not impaired, indicating that interaction with the extracellular matrix is involved in the invasion phenotype. We also show that secreted factors from control cell conditioned media are able to partially rescue the invasion defect in Rab27a knockdown cells. Notably, we show that a novel Rab prenylation inhibitor can reduce melanoma cell proliferation and invasion by disrupting Rab membrane targeting. These studies indicate that Rab GTPases, and Rab27a in particular, play a central role in mediating proliferation and invasion in melanoma cells, making Rabs a novel potential therapeutic target for inhibiting melanoma progression.