NF-E2-related factor 2 (NRF2) transcription factor has a fundamental role in cell
homeostasis maintenance as one of the master regulators of oxidative and electrophilic
stress responses. Previous studies have shown that a regulatory connection exists
between NRF2 and autophagy during reactive oxygen species-generated oxidative stress.
The aim of the present study was to investigate how autophagy is turned off during
prolonged oxidative stress, to avoid overeating and destruction of essential cellular
components. AMPK is a key cellular energy sensor highly conserved in eukaryotic organisms,
and it has an essential role in autophagy activation at various stress events. Here
the role of human AMPK and its Caenorhabditis elegans counterpart AAK-2 was explored
upon oxidative stress. We investigated the regulatory connection between NRF2 and
AMPK during oxidative stress induced by tert-butyl hydroperoxide (TBHP) in HEK293T
cells and C. elegans. Putative conserved NRF2/protein skinhead-1 binding sites were
found in AMPK/aak-2 genes by in silico analysis and were later confirmed experimentally
by using EMSA. After addition of TBHP, NRF2 and AMPK showed a quick activation; AMPK
was later down-regulated, however, while NRF2 level remained high. Autophagosome formation
and Unc-51-like autophagy activating kinase 1 phosphorylation were initially stimulated,
but they returned to basal values after 4 h of TBHP treatment. The silencing of NRF2
resulted in a constant activation of AMPK leading to hyperactivation of autophagy
during oxidative stress. We observed the same effects in C. elegans demonstrating
the conservation of this self-defense mechanism to save cells from hyperactivated
autophagy upon prolonged oxidative stress. We conclude that NRF2 negatively regulates
autophagy through delayed down-regulation of the expression of AMPK upon prolonged
oxidative stress. This regulatory connection between NRF2 and AMPK may have an important
role in understanding how autophagy is regulated in chronic human morbidities characterized
by oxidative stress, such as neurodegenerative diseases, certain cancer types, and
in metabolic diseases.-Kosztelnik, M., Kurucz, A., Papp, D., Jones, E., Sigmond, T.,
Barna, J., Traka, M. H., Lorincz, T., Szarka, A., Banhegyi, G., Vellai, T., Korcsmaros,
T., Kapuy, O. Suppression of AMPK/aak-2 by NRF2/SKN-1 down-regulates autophagy during
prolonged oxidative stress.
