Poster Presentation ASDR Annual Scientific Meeting 2019

MITF regulates dynamic melanoma heterogeneity and structural integrity in melanoma (#45)

Loredana Spoerri 1 , Crystal A Tonnessen 1 , Kimberley A Beaumont 2 , David S Hill 2 , Russell J Jurek 3 , Aaron G Smith 4 , Ethan Scott 4 , Helmut Schaider 1 , Wolfgang Weninger 2 , Brian Gabrielli 4 , Nikolas K Haass 1
  1. University of Queensland, The University of Queensland Diamantina Institute, Translational Research Institute , Woolloongabba, Australia
  2. Centenary Institute, Newtown, NSW, Australia
  3. Astronomy & Space Sciences, CSIRO, Sydney, NSW, Australia
  4. University of Queensland, Woolloongabba, QLD, Australia

Differential tumor cell behavior caused by environmental conditions, termed dynamic heterogeneity, is a prime source for drug resistance. We utilize real-time cell cycle imaging (FUCCI) to study melanoma heterogeneity. As distinct proliferative and invasive capabilities reflect variable drug sensitivities, identifying these different responses is crucial to design effective therapies. Mouse xenograft tumors generated from cell lines with high microphthalmia-associated transcription factor (MITF) level displayed a homogeneous distribution of cycling cells throughout. In contrast, tumors generated from cell lines with low MITF levels were composed of clusters of cycling cells and clusters of G1-arrested cells. The proliferating areas were in close proximity to blood vessels, presumably characterized by oxygen/nutrient availability. Melanoma spheroids recapitulated the in vivo cycling behavior, considering that here oxygen and nutrients are supplied by diffusion. MITF was undetectable within the hypoxic G1-arrested spheroid core, indicating hypoxia-induced MITF downregulation. Furthermore, modulation of MITF expression impacted spheroid morphology, with overexpression giving rise to flatter structures whereas knock down to smaller aggregates with unaffected sphericity. The loss of morphological integrity caused by increased MITF expression did not reduce spheroids’ inner hypoxic level, dismissing the hypothesis that these compromised structured could be be more permeable to oxygen resulting in decreased hypoxia induced G1-arrest. Proteomic analysis revealed that modulation of MITF level induced differences in cell-cell and cell-ECM adhesion. In addition, inhibition of the Rho/ROCK signalling pathway, known to control cell contractility, partially mimicked the morphology and cell cycle effects of MITF overexpression. We conclude that MITF protects from cell cycle arrest induced by oxygen deprivation. We hypothesise that high MITF levels prevent cell cycle arrest by reducing the cell-intrinsic propensity to arrest in response to low oxygen via a mechanism involving cell-cell/ECM crosstalk.

  • Are you an ECR (within 4 years of conferring of PhD)?: No