[Induction of apoptosis in lymphocytes by glucocorticoids: between physiology and pharmacology]

Glucocorticoids are physiological molecules that are also extensively used in clinics as anti-inflammatory, immunosuppressive or anti-tumoral agents. Glucocorticoids can induce apoptosis on normal lymphoid cells and play a key role in the physiology of thymic selection. In clinics these molecules are also used for their potencies in inducing apoptosis of malignant lymphoid cells. Glucocorticoids are mediating their effects after binding to an intracellular receptor belonging to the steroid receptor superfamily: the glucocorticoid receptor (GR). Once activated, the GR, can mediate his effects through direct binding on the DNA or via protein/protein interactions with transcription factors. Depending on the type of lymphocytes, the mechanism of apoptosis induced by glucocorticoids fall roughly in two categories: induction of "death genes" by the activated GR (I kappa B, c-jun) or repression of survival factors (AP-1, c-Myc). In the case of thymic selection the mechanism is more subtle depending on the mutual repression of Nur77 and GR.