D nuclear magnetic resonance (NMR) spectroscopy, we show that MANF is definitely an ATP binding protein and ATP blocks MANF interaction with GRP78. We suggest that the ATP-binding properties of MANF warrant further research as these might have possible implications to its CDK2 Species biological function. To our surprise, mutating the amino acid residues R133 and E153, shown to become vital for GRP78-binding (44), did not abolish the survival-promoting activity of MANF in tunicamycin (Tm)-treated SCG neurons. This indicates that MANF has an more mechanism, unrelated to its interaction with GRP78, for rescuing neurons from ER-stress triggered apoptosis. We as a result propose that while MANF acts as a cofactor of GRP78, it exerts its survival-promoting function by regulating UPR signaling.Results Activation of PERK and IRE1 mediate MANF neuroprotective impact against tunicamycin-induced ER strain in cultured sympathetic neuronsOverexpression of MANF by JNK1 review plasmid or protein microinjection into SCG neurons has been shown to market their survival against serum deprivation, topoisomerase II inhibitor etoposide, and protein kinase inhibitor staurosporine, whereas MANF added to the culture medium has no impact around the survival of SCG neurons (15, 47). Despite MANF getting an ERstress regulated protein, the impact of MANF against ER stressinduced death in SCG neurons has not been reported. Right here, we investigated the neuroprotective effects and mechanisms of MANF in SCG neurons in an ER stress-related apoptosis paradigm. Neurons were treated with Tm, which can be an2 J. Biol. Chem. (2021) 296MANF RP78 interaction not necessary to rescue neuronsinhibitor of N-linked glycosylation, causing accumulation of misfolded glycoproteins within the ER lumen and eventually apoptosis by way of activation of UPR (for a review see (48)). Initially, we tested the effect of MANF plasmid and after that protein microinjection to neuron survival without the need of Tm remedy. MANF microinjection didn’t have an effect on neuronal survival as compared with na e or vector injected neurons (Fig. 1, B and C). As expected, Tm-treatment decreased the survival of SCG neurons to 30 compared with untreated neurons. The survival of Tm-treated SCG neurons injected with MANF plasmid (Fig. 1, A and B) or MANF protein (Fig. 1C) was considerably improved as compared with neurons injected with pCR3.1 control plasmid or PBS, respectively. Hence, whilst MANF had no impact on the survival of na e neuronal cultures, it efficiently rescued Tm-treated neurons from apoptosis, regardless of irrespective of whether it was injected as a plasmid or as a recombinant protein (Fig. 1, B and C). MANF has been largely studied for its neuroprotective properties or as an UPR-regulated ER-resident protein, but the mechanistic link among those functions has remained elusive. We hypothesized that the neuroprotective effect of MANF may possibly arise from its capability to cross-talk with all the UPR machinery. Therefore, to investigate the mechanism of the survivalpromoting effect of MANF, we tested no matter whether it can be dependent on the activity of PERK- and IRE1-mediated UPR signaling pathways. For this, UPR signaling was dampened by adding either GSK2606414, an inhibitor of PERK signaling (49), or 48C, an inhibitor of IRE1 signaling (50). The protective impact of MANF against Tm was lost on addition of either in the inhibitors, indicating that the activity of each PERK and IRE1 pathways are essential for the survival-promoting activity of MANF in SCG neurons against ER anxiety (Fig. 1D). Similarly, inhib.