Abstract
HIF-1α upregulated in many tumour types appears to be critical for radio- and chemosensitivity in pre-clinical studies. As the regulation and function of HIF-1α is unknown in thyroid carcinomas, we evaluated basal expression and regulation of HIF-1α and target genes in primary thyroid carcinomas and in thyroid cancer cell lines (NPA, FTC-133, ARO).
We investigated HIF-1α and target genes (Glut-1, CA-IX) in snap-frozen tissue from primary thyroid carcinomas by IHC. Functional changes were studied for HIF-1α in all cell lines basally, under graded hypoxia (2%, 1%, anoxia, and the hypoxia mimetic CoCl2100 μM) with and without blockage of PI3K (Ly294002, 50 μM) and MAPK/ERK (PD 98059, 50 μM) signaling. IF, western blot for HIF-α and the target genes Glut-1, CA-IX as well as a HIF-specific reporter gene assay were used as read-outs. HIF specific effects on proliferation were studied using the HIF antagonist YC-1. HIF-1α and target genes are expressed in dedifferentiated primary thyroid carcinomas and in NPA, FTC-133 and ARO cells. They are clearly up-regulated by hypoxia or CoCl2 stimulation. Using the PI3K inhibitor Ly294002 (FTC-133 cells) revealed that HIF-1α is stimulated by the PI3K pathway. Similarly, blockage of the MAPK/ERK pathway by PD 98059 (NPA cells) had a strong inhibitory effect on HIF-1α expression and significantly reduced CA-IX protein levels. YC-1 (50 umol/l) significantlt decreased proliferation in ARO and NPA cells.
Our data suggest that HIF-1α is expressed in primary thyroid carcinomas and appears upregulated in dedifferentiated tumours. HIF-1α is under oxygen control but is additionally regulated by the PI3K and the MAPK/ERK pathway, central oncogenic pathways in the thyroid. These data may be of major clinical importance when considering the sensitizing role of HIF-1α inhibition in the modulation radiosensitivity in other epithelial type carcinomas