HLA-G modulates the radiosensitivity of human neoplastic cells

MICHELIN S.; GALLEGOS C. E.; BAFFA TRASCI S.; DUBNER D.; FAVIER B.; CAROSELLA E. D.

Congreso; 14th International Congress of Radiation Research; 2011

HLA-G molecule is characterized by low polymorphism and tissue-restricted expression. It can be induced in transplantation, inflammatory diseases, cancer, multiple sclerosis, and viral infections. The expression of HLA-G gene is regulated through epigenetic mechanisms, and occurs at the transcriptional and post transcriptional level. The HLA-G primary transcript yields the production of 7 isoforms: 4 membrane-bound (HLA-G1 to -G4), and 3 soluble (HLA-G5 to -G7). Functionally, HLA-G inhibits the cytolytic function of NK cells and T lymphocytes, the alloproliferative response of CD4+ T cells, the on-going proliferation of T cells and NK cells, the maturation of dendritic cells and induces regulatory T cells. HLA-G mediates this inhibitory action by binding to the inhibitory receptors ILT2, ILT4 and KIR2DL4. Clinically, the expression of HLA-G has been correlated with the tolerance of the fetus by its mother, the acceptance of solid organ transplants, and the immune escape of tumors and virus-infected cells. It has been determined that gamma radiation modulates HLA-G expression at the plasma membrane of human melanoma cells. However its role in tumoral radiosensitivity has not been demonstrated yet. The objective of this work was to determine if the radiosensitivity of human neoplastic cell lines cultured in vitro was mediated by HLA-G expression. For this, 5 Gy gamma irradiation was performed on HLA-G negative (M8 G-) and HLA-G positive (M8 G+) human melanoma cells and in HLA-G negative and HLA-G positive erythroleukemia cells (K562). The M8 G+ survival frequency, evaluated by clonogenic assay 20 days post irradiation was diminished by 40% respect to the M8 G- cell line. No significant differences were observed in the apoptosis level or cell cycle profile between both M8 G+ and M8 G- cell lines. HLA-G1 surface expression was decreased in irradiated M8 G+ cells (~ 20% diminution 24 h post irradiation) and was accompanied by the concomitant increase in sHLA-G1 levels in the culture medium. The survival of the K562 G+ cell line was diminished by 20% with respect to K562 G- cells, suggesting that this response is not exclusive of the melanoma cell line. In summary, our results indicate for the first time that HLA-G confers higher radiosensitivity to human neoplastic cells, and would be a useful contribution for the optimization of radiotherapy protocols.