Fig. 8

Proposed dynamic regulatory network of TFEB. TFEB is under long-term (dark blue area) and short-term (light blue area) control, regulating the strength and time span of its activation, i.e., nuclear localization. The long-term control limits the duration of TFEB activation upon sustained mTOR inhibition, displaying prominent mTOR-independent negative regulation of TFEB. The short-term control acts as a rheostat, which is highly sensitive to inactivation by mTOR, but tightly controls TFEB activation by multiple mechanisms, directly or indirectly regulated by mTOR. Under conditions of sustained mTOR inhibition (Fig. 2d, f), starting at 3 hours, TFEB is gradually inactivated (Fig. 4f, region R2), evidencing the action of other inhibitors with slower kinetics than mTOR. In contrast to Torin1 mTOR inhibition, nutrient deprivation displays a fast reactivation kinetics (Fig. 5c, region R2) followed by a second activation wave (Fig. 5c, region R3), suggesting that TFEB rheostat is sensitive to autophagy feedback on mTOR activity via nutrient recycling. Proteasome inhibition by epoxomicin enhances TFEB activation (Fig. 7d), suggesting that the proteasome mediates the degradation of a “positive regulator” of TFEB, labeled here with a question mark. The effect of epoxomicin on TFEB activation is only detectable under conditions of mTOR inhibition (Fig. 7d), suggesting that the “positive regulator” is not degraded under conditions of high mTOR activity (i.e., mTOR activity inhibits the degradation of the “positive regulator”)