A comparison of cell survival and heat shock protein expression after radiation in normal dermal fibroblasts, microvascular endothelial cells, and different head and neck squamous carcinoma cell lines

Head and neck squamous cell carcinoma (HNSCC) shows increased radioresistance due to the manipulation of homeostatic mechanisms like the heat shock response. This study intended to comparatively analyze effects of ionizing radiation on different HNSCC cell lines (PCI) and normal human dermal fibroblasts (NHFs) and human dermal microvascular endothelial cells (HDMECs) to uncover differences in radiation coping strategies. Proliferation (BrdU assay), apoptosis (caspase 3/7) and intracellular protein expression of heat shock protein (HSP)-70, and phosphorylated and total HSP27, determined by enzyme-linked immunosorbent assay (ELISA), were analyzed after exposure to increasing doses of ionizing radiation (2, 6, and 12 Gray, Gy). Cell count decreased dose-dependently, but PCI cell lines consistently showed higher numbers compared to NHF and HDMEC. Likewise, high doses reduced cell proliferation, but low-dose radiation (2 Gy) instead increased proliferation in PCI 9 and 52. Apoptosis was not detectable in PCI cell lines. Basic HSP70 expression was high in PCI cells with little additional increase by irradiation. PCI cells yielded high basic total HSP27 concentrations but irradiation dose-dependently increased HSP27 in HDMEC, NHF, and PCI cells. Phosphorylated HSP27 concentrations were highest in NHF. PCI cell lines showed higher resistance to dose-dependent reduction in cell number, proliferation, and protection from apoptosis compared to NHF and HDMEC. In parallel, we observed a high basic and radiation-induced expression of intracellular HSP70 leading to the assumption that the radioresistance of PCI cells is conferred by HSP70. HNSCC use HSP to escape radiation-induced apoptosis and certain subtypes might increase proliferation after low-dose irradiation.