Anti-neoplastic agent thymoquinone induces degradation of α and β tubulin proteins in human cancer cells without affecting their level in normal human fibroblasts

The microtubule-targeting agents derived from natural products, such as vinca-alkaloids and taxanes are an important family of efficient anti-cancer drugs with therapeutic benefits in both haematological and solid tumors. These drugs interfere with the assembly of microtubules of alpha/beta tubulin heterodimers without altering their expression level. The aim of the present study was to investigate the effect of thymoquinone (TQ), a natural product present in black cumin seed oil known to exhibit putative anti-cancer activities, on alpha/beta tubulin expression in human astrocytoma cells (cell line U87, solid tumor model) and in Jurkat cells (T lymphoblastic leukaemia cells). TQ induced a concentration- and time-dependent degradation of alpha/beta tubulin in both cancer cell types. This degradation was associated with the up-regulation of the tumor suppressor p73 with subsequent induction of apoptosis. Interestingly, TQ had no effect on alpha/beta tubulin protein expression in normal human fibroblast cells, which were used as a non-cancerous cell model. These data indicate that TQ exerts a selective effect towards alpha/beta tubulin in cancer cells. In conclusion, the present findings indicate that TQ is a novel anti-microtubule drug which targets the level of alpha/beta tubulin proteins in cancer cells. Furthermore, they highlight the interest of developing anti-cancer therapies that target directly tubulin rather than microtubules dynamics.