An Unforseen Mechanism for Protection Against Genotoxic Formaldehyde

HERNAN REINGRUBER; MARCO ADRIÁN SCHEIDEGGER; CARLA UMANSKY; LUCAS PONTEL

CABA

Simposio; Frontiers in Bioscience 3; 2018

Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck (IBioBA-MPSP)

Formaldehyde (FA) is a genotoxic compound that can produce severe damage to the cells if it is not detoxified. In blood, the level of FA can reach more than 10 µM according to several reports and our own data. To prevent FA toxicity, cells have evolved a two-tier mechanism of protection that consists of a detoxification enzyme and a DNA repair system. ADH5 is the main enzyme involved in FA metabolism. This enzyme requires the antioxidant glutathione (GSH) as a cofactor. To uncover whether other factor(s) works in the protection of cancer cells against FA, we have generated cells lacking ADH5 by CRISPR/Cas9. These cells showed decreased viability upon FA exposure. However, there is still some cell viability at high FA concentrations. We therefore hypothesized that GSH might have an independent role from ADH5 in the protection against FA. Experiments performed in a human colon carcinoma cell line (HCT116) show that GSH can react with FA and protect cells from FA toxicity. It also exerts a protective function by itself, even when ADH5 is absent, thus confirming its independent role. One of the effects produced by FA in cells is to cause DNA damage, which can activate a DNA damage response (via P53 activation), leading to cell cycle arrest (by increasing the level of P21) or to apoptosis. Upon formaldehyde treatment, we observe the accumulation of P21 in both wild type and ADH5-deficient cells, although P53 activation was only observed in ADH5-/- cells. The depletion of GSH does not change the P53 activation upon FA treatment but leads to a further accumulation of P21. This result along with the increased sensitivity of P21-/- cells to FA suggests an independent and protective role of P21 in cancer cells and an unforeseen function of GSH in the control of P21 accumulation and the cellular tolerance of FA.