Proteolytic cleavage of LEDA-1/PIANP by furin-like proprotein convertases precedes its plasma membrane localization

Targeting furin, a cellular proprotein convertase, for COVID-19 prevention and therapeutics

SARS-CoV-2 has triggered an international outbreak of the highly contagious acute respiratory disease known as COVID-19. Identifying key targets in the virus infection lifecycle is crucial for developing effective prevention and therapeutic strategies against it. Furin is a serine endoprotease that belongs to the family of proprotein convertases and plays a critical role in the entry of host cells by SARS-CoV-2. Furin can cleave a specific S1/S2 site, PRRAR, on the spike protein of SARS-CoV-2, which promotes viral transmission by facilitating membrane fusion. Hence, targeting furin could hold clinical implications for the prevention and treatment of COVID-19. This review offers an overview of furin's structure, substrates, function, and inhibitors, with a focus on its potential role in SARS-CoV-2 infection.

A perspective on the applications of furin inhibitors for the treatment of SARS-CoV-2

Currently, the world is facing a pandemic of the new coronavirus SARS-CoV-2 that causes COVID-19. Identifying key targets in the viral infection lifecycle is urgently needed for designing therapeutic strategies to combat the virus. Furin is a subtilisin-like proprotein convertase with diverse cellular functions. Emerging evidence suggests that furin plays a critical role in the activation and/or infectivity of SARS-CoV-2. In this perspective, we discuss the potential role of furin in the entry SARS-CoV-2 into host cells. Furthermore, we evaluate available peptide and non-peptide furin inhibitors and potential outcomes, including immune responses.

Pianp deficiency links GABAB receptor signaling and hippocampal and cerebellar neuronal cell composition to autism-like behavior

Pianp (also known as Leda-1) is a type I transmembrane protein with preferential expression in the mammalian CNS. Its processing is characterized by proteolytic cleavage by a range of proteases including Adam10, Adam17, MMPs, and the γ-secretase complex. Pianp can interact with Pilrα and the GB1a subunit of the GABA_B receptor (GBR) complex. A recent case description of a boy with global developmental delay and homozygous nonsense variant in PIANP supports the hypothesis that PIANP is involved in the control of behavioral traits in mammals. To investigate the physiological functions of Pianp, constitutive, global knockout mice were generated and comprehensively analyzed. Broad assessment did not indicate malformation or malfunction of internal organs. In the brain, however, decreased sizes and altered cellular compositions of the dentate gyrus as well as the cerebellum, including a lower number of cerebellar Purkinje cells, were identified. Functionally, loss of Pianp led to impaired presynaptic GBR-mediated inhibition of glutamate release and altered gene expression in the cortex, hippocampus, amygdala, and hypothalamus including downregulation of Erdr1, a gene linked to autism-like behavior. Behavioral phenotyping revealed that Pianp deficiency leads to context-dependent enhanced anxiety and spatial learning deficits, an altered stress response, severely impaired social interaction, and enhanced repetitive behavior, which all represent characteristic features of an autism spectrum disorder-like phenotype. Altogether, Pianp represents a novel candidate gene involved in autism-like behavior, cerebellar and hippocampal pathology, and GBR signaling.

Leda-1/Pianp is targeted to the basolateral plasma membrane by a distinct intracellular juxtamembrane region and modulates barrier properties and E-Cadherin processing

Leda-1/Pianp is a type-I transmembrane protein which is sorted to the basolateral membrane domain of polarized epithelial cells. Here, we investigated trafficking mechanisms and functions of Leda-1/Pianp in MDCK and MCF-7 cells. Basolateral sorting and posttranslational modifications depended on the intracellular juxtamembrane region. Functionally, Leda-1/Pianp increased the transepithelial electrical resistance generated by a polarized cell sheet. Furthermore, resistance to junctional destabilization by tumor cells was enhanced by Leda-1/Pianp indicating increased stability and tightness of intercellular junctions. While Claudin 1 and 4 expression and activities of small GTPases were not affected, γ-Secretase-mediated cleavage of E-Cadherin was attenuated by Leda-1/Pianp. Regulation of proteolytic processing is thus a molecular mechanism by which Leda-1/Pianp can affect junctional integrity and function.

Counter-regulation of the ligand-receptor pair Leda-1/Pianp and Pilrα during the LPS-mediated immune response of murine macrophages

Liver endothelial differentiation-associated protein-1 (Leda-1/Pianp) is a type-I-transmembrane protein that is able to bind and activate immune inhibitory receptor Pilrα. Here we show that Leda-1/Pianp is strain-specifically expressed in lymphoid organs and macrophages of Th2-prone BALB/c mice but not of Th1-prone C57BL/6J mice. LPS stimulation of BALB/c bone marrow-derived macrophages (BMM) and macrophage-like Raw 264.7 cells conversely regulated Leda-1/Pianp and Pilrα expression. Pilrα induction was caused by LPS-mediated transcriptional modulation and increased mRNA expression. On the other hand, the LPS-mediated decline of Leda-1/Pianp expression was the result of proteolytic degradation by matrix metalloproteinases. In summary, these findings demonstrate that counter-regulation of the ligand-receptor pair Leda-1/Pianp and Pilrα is part of the complex innate immune response of macrophages and its genetically determined strain-specific modulation.