Hypoxia promotes uveal melanoma invasion through enhanced Notch and MAPK activation.

ABSTRACT: The transcriptional response promoted by hypoxia-inducible factors has been associated with metastatic spread of uveal melanoma. We found expression of hypoxia-inducible factor 1? (HIF-1?) protein in well-vascularized tumor regions as well as in four cell lines grown in normoxia, thus this pathway may be important even in well-oxygenated uveal melanoma cells. HIF-1? protein accumulation in normoxia was inhibited by rapamycin. As expected, hypoxia (1% pO2) further induced HIF-1? protein levels along with its target genes VEGF and LOX. Growth in hypoxia significantly increased cellular invasion of all 5 uveal melanoma lines tested, as did the introduction of an oxygen-insensitive HIF-1? mutant into Mel285 cells with low HIF-1? baseline levels. In contrast, HIF-1? knockdown using shRNA significantly decreased growth in hypoxia, and reduced by more than 50% tumor invasion in four lines with high HIF-1? baseline levels. Pharmacologic blockade of HIF-1? protein expression using digoxin dramatically suppressed cellular invasion both in normoxia and in hypoxia. We found that Notch pathway components, including Jag1-2 ligands, Hes1-Hey1 targets and the intracellular domain of Notch1, were increased in hypoxia, as well as the phosphorylation levels of Erk1-2 and Akt. Pharmacologic and genetic inhibition of Notch largely blocked the hypoxic induction of invasion as did the pharmacologic suppression of Erk1-2 activity. In addition, the increase in Erk1-2 and Akt phosphorylation by hypoxia was partially reduced by inhibiting Notch signaling. Our findings support the functional importance of HIF-1? signaling in promoting the invasive capacity of uveal melanoma cells in both hypoxia and normoxia, and suggest that pharmacologically targeting HIF-1? pathway directly or through blockade of Notch or Erk1-2 pathways can slow tumor spread.

SUBMITTER: Asnaghi L 

PROVIDER: S-EPMC4148307 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature