A naturally occurring 22-amino acid fragment of human hemoglobin A inhibits autophagy and HIV-1.

Autophagy is an evolutionarily ancient catabolic pathway and has recently emerged as an integral part of the innate immune system. While the core machinery of autophagy is well defined, the physiological regulation of autophagy is less understood. Here, we identify a C-terminal fragment of human hemoglobin A (HBA1, amino acids 111-132) in human bone marrow as a fast-acting non-inflammatory inhibitor of autophagy initiation. It is proteolytically released from full-length HBA1 by cathepsin E, trypsin or pepsin. Biochemical characterization revealed that HBA1(111-132) has an in vitro stability of 52 min in human plasma and adopts a flexible monomeric conformation in solution. Structure-activity relationship studies revealed that the C-terminal 13 amino acids of HBA1(120-132) are sufficient to inhibit autophagy, two charged amino acids (D127, K128) mediate solubility, and two serines (S125, S132) are required for function. Successful viruses like human immunodeficiency virus 1 (HIV-1) evolved strategies to subvert autophagy for virion production. Our results show that HBA1(120-132) reduced virus yields of lab-adapted and primary HIV-1. Summarizing, our data identifies naturally occurring HBA1(111-132) as a physiological, non-inflammatory antagonist of autophagy. Optimized derivatives of HBA1(111-132) may offer perspectives to restrict autophagy-dependent viruses.

CSNK2 suppresses autophagy by activating FLN-NHL-containing TRIM proteins.

Macroautophagy/autophagy is a tightly regulated cellular process integral to homeostasis and innate immunity. As such, dysregulation of autophagy is associated with cancer, neurodegenerative disorders, and infectious diseases. While numerous factors that promote autophagy have been characterized, the key mechanisms that prevent excessive autophagy are less well understood. Here, we identify CSNK2/CK2 (casein kinase 2) as a negative regulator of autophagy. Pharmacological inhibition of CSNK2 activity or siRNA-mediated depletion of CSNK2 increased basal autophagic flux in cell lines and primary human lung cells. Vice versa, ectopic expression of CSNK2 reduced autophagic flux. Mechanistically, CSNK2 interacted with the FLN (filamin)-NHL domain-containing tripartite motif (TRIM) family members TRIM2, TRIM3 and TRIM71. Our data show that recruitment of CSNK2 to the C-terminal NHL domain of TRIM3 lead to its robust phosphorylation at serine 661 by CSNK2. A phosphorylation-defective mutant of TRIM3 was unable to reduce autophagosome numbers indicating that phosphorylation by CSNK2 is required for TRIM-mediated autophagy inhibition. All three TRIMs facilitated inactivation of the ULK1-BECN1 autophagy initiation complex by facilitating ULK1 serine 757 phosphorylation. Inhibition of CSNK2 promoted autophagy upon influenza A virus (IAV) and measles virus (MeV) infection. In line with this, targeting of CSNK2 or depletion of TRIM2, TRIM3 or TRIM71 enhanced autophagy-dependent restriction of IAV, MeV and human immunodeficiency virus 1 (HIV-1). Thus, our results identify the CSNK2-TRIM2, -TRIM3, -TRIM71 axis as a key regulatory pathway that limits autophagy. Targeting this axis may allow for therapeutic induction of autophagy against viral infections and in diseases associated with dysregulated autophagy.

Synaptic disruption and CREB-regulated transcription are restored by K+ channel blockers in ALS.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, which is still missing effective therapeutic strategies. Although manipulation of neuronal excitability has been tested in murine and human ALS models, it is still under debate whether neuronal activity might represent a valid target for efficient therapies. In this study, we exploited a combination of transcriptomics, proteomics, optogenetics and pharmacological approaches to investigate the activity-related pathological features of iPSC-derived C9orf72-mutant motoneurons (MN). We found that human ALSC9orf72 MN are characterized by accumulation of aberrant aggresomes, reduced expression of synaptic genes, loss of synaptic contacts and a dynamic "malactivation" of the transcription factor CREB. A similar phenotype was also found in TBK1-mutant MN and upon overexpression of poly(GA) aggregates in primary neurons, indicating a strong convergence of pathological phenotypes on synaptic dysregulation. Notably, these alterations, along with neuronal survival, could be rescued by treating ALS-related neurons with the K+ channel blockers Apamin and XE991, which, respectively, target the SK and the Kv7 channels. Thus, our study shows that restoring the activity-dependent transcriptional programme and synaptic composition exerts a neuroprotective effect on ALS disease progression.