Proteasome α6 Subunit Negatively Regulates the JAK/STAT Pathway and Blood Cell Activation in Drosophila melanogaster.

Mirva Järvelä-Stölting,Matthew K Maasdorp,Laura Vesala,Joanna Ciantar,Susanna Valanne,Mika Rämet

doi:10.3389/fimmu.2021.729631

Mirva Järvelä-Stölting, Matthew K Maasdorp + Show 4 more

Open Access

https://doi.org/10.3389/fimmu.2021.729631

Copy DOI

Abstract

JAK/STAT signaling regulates central biological functions such as development, cell differentiation and immune responses. In Drosophila, misregulated JAK/STAT signaling in blood cells (hemocytes) induces their aberrant activation. Using mass spectrometry to analyze proteins associated with a negative regulator of the JAK/STAT pathway, and by performing a genome-wide RNAi screen, we identified several components of the proteasome complex as negative regulators of JAK/STAT signaling in Drosophila. A selected proteasome component, Prosα6, was studied further. In S2 cells, Prosα6 silencing decreased the amount of the known negative regulator of the pathway, ET, leading to enhanced expression of a JAK/STAT pathway reporter gene. Silencing of Prosα6 in vivo resulted in activation of the JAK/STAT pathway, leading to the formation of lamellocytes, a specific hemocyte type indicative of hemocyte activation. This hemocyte phenotype could be partially rescued by simultaneous knockdown of either the Drosophila STAT transcription factor, or MAPKK in the JNK-pathway. Our results suggest a role for the proteasome complex components in the JAK/STAT pathway in Drosophila blood cells both in vitro and in vivo.

Highlights

Regulation of blood cell differentiation and function is a central aspect in immune responses in animals
We show that silencing Proteasome a6 subunit in vivo in Drosophila hemocytes induces Janus kinase (JAK)/Signal Transducer Activator of Transcription (STAT) activation in them, leading to typical JAK/STAT induced hemocyte phenotypes, the appearance of melanotic nodules and the formation of different types of hemocytes usually present after an immune challenge
After proteins that were found in the negative controls were excluded, we identified in total 173 Drosophila melanogaster proteins in complex with Eye Transformer (ET) under the conditions where the JAK/STAT pathway was inactive (ET-V5 alone) and 175 proteins when the ligand Upd1 was present (ET-V5 + Upd1myc)

Summary

Introduction

Regulation of blood cell differentiation and function is a central aspect in immune responses in animals. Prosa in Drosophila Hemocyte Activation of transcription (JAK/STAT) signaling is involved in controlling and regulating biological functions including cell differentiation, developmental processes and immune responses [3]. The Drosophila larval blood cell system consists of three main types of hemocytes: plasmatocytes, lamellocytes and crystal cells [9, 10]. Lamellocytes are a specialized hemocyte type, produced as a response to infection by parasitoid wasps and other pathogens that cannot be phagocytosed [16]. They encapsulate the intruder and produce melanin to seal the capsule [17]. The activation of several signaling pathways, including the JAK/STAT, Toll, Ras-MAPK and the c-Jun N-terminal kinase (JNK) signaling pathways, is known to induce lamellocyte formation [6, 20]

Methods

Results

Conclusion