The mitochondrial localization of RelB and NFATx in immature T cells.

In order to exert their activity, transcription factors must be transported to the nucleus. Certain transcription factors have also been found on mitochondria. Here, the localization of RelB and NFATx in the mitochondrial fractions of normal thymocytes and thymic lymphoma cells is shown for the first time. CREB was only found in the nucleus, while p50 (NFkappaB) was found in both the nucleus and the cytoplasm, but outside the mitochondria. The translocation of transcription factors to the mitochondria is differentially regulated. Unlike RelB, which is always present in the mitochondrial fraction, NFATx appeared on the mitochondria in cells treated with ionomycin together with an immunosuppressant and inhibitor of calcineurin (FK506). This data reveals that the mitochondrial localization of some transcription factors is precisely controlled by a calcium signal sensitive to FK506 in T cells.