Proteasome malfunction activates the PPP3/calcineurin-TFEB-SQSTM1/p62 pathway to induce macroautophagy in the heart

Proteasome inhibition (PSMI) is known to activate macroautophagy (autophagy hereafter), but the underlying mechanisms remain to be fully delineated. Here we discuss our recent work identifying an important PPP3/calcineurin-TFEB-SQSTM1/p62 pathway in mediating activation of autophagy by PSMI, a compensatory process for the heart with proteasome malfunction. Through increasing PPP3/calcineurin activity and inhibiting MTOR signaling, PSMI promotes the dephosphorylation and thereby nuclear translocation of TFEB, resulting in transactivation of genes in the autophagic-lysosomal pathway (ALP) such as Mcoln1 and Sqstm1. We have discovered that SQSTM1 is required for not only induction of autophagy but also cardiac activation of TFEB by PSMI, unveiling a novel feedforward role for SQSTM1 in TFEB activation.