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bioRxiv2023

Real-time measurements of ATP dynamics via ATeams in Plasmodium falciparum reveal drug-class-specific response patterns

Malaria tropica, caused by the parasite Plasmodium falciparum (P. falciparum) remains one of the greatest public health burdens for humankind. Due to its pivotal role in parasite survival, the energy metabolism of P. falciparum is an interesting target for drug design. To this end, analysis of the central metabolite ATP is of great interest. So far, only cell disruptive or intensiometric ATP assays have been available in this system, with various drawbacks for mechanistic interpretation, and partly inconsistent results. To address this, we have established fluorescent probes, based on FRET and known as ATeam, for use in blood stage parasites. ATeams are capable of measuring MgATP2- levels in a ratiometric manner, thereby facilitating in cellulo measurements of ATP dynamics in real-time using fluorescence microscopy and plate reader detection, and overcoming many of the obstacles of established ATP analysis methods. Additionally, we established a superfolder variant of the ratiometric pH sensor pHluorin (sfpHluorin) in P. falciparum to monitor pH homeostasis and control for pH fluctuations, which may affect ATeam measurements. We characterized recombinant ATeam and sfpHluorin protein in vitro and stably integrated the sensors into the genome of the P. falciparum NF54attB cell line. Using these new tools, we found distinct sensor response patterns caused by several different drug classes. Arylamino alcohols increased and redox-cyclers decreased ATP, doxycycline caused first-cycle cytosol alkalization, and 4-aminoquinolines caused aberrant proteolysis. Our results open up a completely new perspective on drugs mode of action with possible implications for target identification and drug development.

microbiology↗

bioRxiv2023

RBM39 shapes innate immunity through transcriptional and splicing control of IRF3 and other key factors

RNA-binding motif protein 39 (RBM39) is an RNA-binding protein involved in tumorigenesis, cell metabolism, and development. Here, we performed a genome-wide CRISPR/Cas9 screen in two liver-derived cell lines and identified RBM39 as a regulator of cell intrinsic innate immune responses. The knockdown of RBM39 or the treatment with Indisulam, an aryl sulfonamide drug targeting RBM39 for proteasomal degradation, strongly reduced the induction of interferon-stimulated genes (ISGs) in response to double-stranded RNA (dsRNA) or viral infections upon sensing by toll-like receptor 3 (TLR3) or cytosolic RIG-I-like receptors. RNA sequencing (seq) and mass spectrometry identified that transcription and/or splicing of the key pathway components IRF3, RIG-I, and MDA5 were affected by RBM39 depletion. RBM39 knockdown further restrained type I and type III IFN pathways, by reducing expression of the type I IFN receptor subunit interferon alpha and beta receptor subunit 2 (IFNAR2), type III IFN receptor subunit interleukin 10 receptor subunit beta (IL-10RB) and transcription factor signal transducer and activator of transcription (STAT) 1 and 2. RBM39 overall orchestrates innate immunity by regulating basal expression of key factors of the interferon response via transcription and/or alternative splicing. SignificanceThe function of RBM39 in tumorigenesis has been investigated intensively in the last decade, but its immunological role is still largely unknown. In our study, we identified RBM39 as a regulatory factor of cell intrinsic signaling via a CRISPR/Cas9 screen. Depletion of RBM39 impairs TLR3, RIG-I/MDA5, and IFN pathways, and thus attenuates innate immune responses. Our omics analysis revealed that RBM39 governs the basal expression of several key factors within these pathways, such as RNA sensors RIG-I and MDA5, type I/III receptors, transcription factors IRF3, STAT1 and STAT2, via its transcriptional and splicing function. Therefore, RBM39 might be a therapeutic target to modulate innate immunity, e.g. in the context of autoimmune disorders.

immunology↗