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PLoS One. 2014 Aug 28;9(8):e105372. doi: 10.1371/journal.pone.0105372. eCollection 2014.

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

Author information

1
Department of Pathology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.
2
Department of Ophthalmology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.
3
Department of Ophthalmology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America; Department of Oncology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.
4
Department of Neurological Surgery, School of Medicine, Case Western Reserve University, Cleveland, Ohio, United States of America.
5
Department of Pathology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America; Department of Ophthalmology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America; Department of Oncology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.

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 1α (HIF-1α) 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-1α protein accumulation in normoxia was inhibited by rapamycin. As expected, hypoxia (1% pO2) further induced HIF-1α 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-1α mutant into Mel285 cells with low HIF-1α baseline levels. In contrast, HIF-1α knockdown using shRNA significantly decreased growth in hypoxia, and reduced by more than 50% tumor invasion in four lines with high HIF-1α baseline levels. Pharmacologic blockade of HIF-1α 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-1α signaling in promoting the invasive capacity of uveal melanoma cells in both hypoxia and normoxia, and suggest that pharmacologically targeting HIF-1α pathway directly or through blockade of Notch or Erk1-2 pathways can slow tumor spread.

PMID:
25166211
PMCID:
PMC4148307
DOI:
10.1371/journal.pone.0105372
[Indexed for MEDLINE]
Free PMC Article

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