Proteasome Inhibition Activates Autophagy-Lysosome Pathway Associated With TFEB Dephosphorylation and Nuclear Translocation

Abstract

Ubiquitin-proteasome pathway (UPS) and autophagy-lysosome pathway (ALP) are the two major protein degradation pathways, which are critical for proteostasis. Growing evidence indicates that proteasome inhibition-induced ALP activation is an adaptive response. Transcription Factor EB (TFEB) is a master regulator of ALP. However, the characteristics of TFEB and its role in proteasome inhibition-induced ALP activation are not fully investigated. Here we reported that the half-life of TFEB is around 13.5 h in neuronal-like cells, and TFEB is degraded through proteasome pathway in both neuronal-like and non-neuronal cells. Moreover, proteasome impairment not only promotes TFEB accumulation but also facilitates its dephosphorylation and nuclear translocation. In addition, proteasome inhibition-induced TFEB accumulation, dephosphorylation and nuclear translocation significantly increases the expression of a number of TFEB downstream genes involved in ALP activation, including microtubule-associated protein 1B light chain-3 (LC3), particularly LC3-II, cathepsin D and lysosomal-associated membrane protein 1 (LAMP1). Furthermore, we demonstrated that proteasome inhibition increases autophagosome biogenesis but not impairs autophagic flux. Our study advances the understanding of features of TFEB and indicates that TFEB might be a key mediator of proteasome impairment-induced ALP activation.

Promiscuous Roles of Autophagy and Proteasome in Neurodegenerative Proteinopathies

“…This is in line with studies indicating a reciprocal regulation between the two cell-clearing systems, with UPS behaving as a sentinel in sensing and regulating autophagy, and vice versa [68,[108][109][110][111][112][113]. In detail, UPS regulates the duration and amplitude of the autophagy response by controlling the stability of Unc-51 like autophagy activating kinase (ULK1)/Atg1 complex as well as mTOR and transcription factor EB (TFEB) kinases [108][109][110]. ULK1 acts at multiple steps of autophagy initiation and response, in part by phosphorylating autophagy proteins such as Atg13, Beclin 1, and Atg9 [114].…”

“…On the one hand, UPS inhibition promotes TFEB accumulation, de-phosphorylation and nuclear translocation, leading to an increased expression of downstream autophagy-related genes including LC3-II, cathepsin D, and LAMP1. Remarkably, despite increasing autophagosome biogenesis, UPS inhibition does not affect autophagy flux [110]. This fits with recent evidence showing that UPS activity, rather than inhibition, promotes autophagy both by fostering the nuclear translocation of TFEB, and remarkably, by degrading mTOR itself, leading to its downregulation and detachment from the lysosomes [111].…”

“…UPS may control autophagy dynamics also through regulating TFEB turnover, which upon de-phosphorylation and cytoplasm-to-nucleus shuttling, induces the expression of a variety of autophagy-related genes [110,111]. On the one hand, UPS inhibition promotes TFEB accumulation, de-phosphorylation and nuclear translocation, leading to an increased expression of downstream autophagy-related genes including LC3-II, cathepsin D, and LAMP1.…”

RCAN1 Inhibits BACE2 Turnover by Attenuating Proteasome-Mediated BACE2 Degradation

“…After treatment, the cells were harvested at 0, 2, 4, 8, and 12 h time points, respectively. The lysosomal inhibitor NH 4 Cl was applied to determine the involvement of the lysosome pathway in BACE2 degradation, while the proteasomal inhibitor N-carbobenzoxy-L-leucinyl-L-leucinyl-L-leucinal (MG-132) was applied to determine the involvement of proteasome pathway in BACE2 degradation, respectively [16,23,[28][29][30]. MG-132 and NH 4 Cl were purchased from Sigma.…”

Tissue-Specific Impact of Autophagy Genes on the Ubiquitin–Proteasome System in C. elegans

“…The UPS and ALP were previously believed to have exceedingly distinct substrates, and they were regarded as independent proteolytic systems, but accumulating evidence has established extensive crosstalk between the two, reviewed in [ 17 ]. Several studies using human cell lines and mice have reported that pharmacological and genetic inhibition of the UPS leads to the activation of autophagy [ 18 , 19 , 20 , 21 ]. However, the blocking of autophagy has reportedly more complex and contrasting results, both inhibiting and activating UPS [ 22 , 23 , 24 , 25 ].…”