A conserved CCM complex promotes apoptosis non-autonomously by regulating zinc homeostasis

Eric M Chapman,Issam A Awad,Christopher Go,Romuald Girard,Deepika Dogra,Michael Schertzberg,W Brent Derry,Bin Yu,Yan Li,Salim Abdelilah-Seyfried,Yota Ohashi,Janne Koskimäki,Anne-Claude Gingras,Benjamin Lant,Andrew G Fraser

doi:10.1038/s41467-019-09829-z

Abstract

Apoptotic death of cells damaged by genotoxic stress requires regulatory input from surrounding tissues. The C. elegans scaffold protein KRI-1, ortholog of mammalian KRIT1/CCM1, permits DNA damage-induced apoptosis of cells in the germline by an unknown cell non-autonomous mechanism. We reveal that KRI-1 exists in a complex with CCM-2 in the intestine to negatively regulate the ERK-5/MAPK pathway. This allows the KLF-3 transcription factor to facilitate expression of the SLC39 zinc transporter gene zipt-2.3, which functions to sequester zinc in the intestine. Ablation of KRI-1 results in reduced zinc sequestration in the intestine, inhibition of IR-induced MPK-1/ERK1 activation, and apoptosis in the germline. Zinc localization is also perturbed in the vasculature of krit1−/− zebrafish, and SLC39 zinc transporters are mis-expressed in Cerebral Cavernous Malformations (CCM) patient tissues. This study provides new insights into the regulation of apoptosis by cross-tissue communication, and suggests a link between zinc localization and CCM disease.

Highlights

Apoptotic death of cells damaged by genotoxic stress requires regulatory input from surrounding tissues
Given that the ERK1 homologue MPK-1 is necessary in the pachytene region of the germline for ionizing radiation (IR)-induced apoptosis[9,10], we wondered if germline MPK-1 might be regulated by KRI-1
Since CCM2 and ICAP1 bind separate NPxY/F motifs of KRIT1/CCM1 in vertebrates[34] (Supplementary Fig. 4C), we propose that the C. elegans KRI-1 complex contains both Cerebral Cavernous Malformations (CCM)-2 and ICAP-1, and inhibits the ERK-5 pathway through MEKK-3, as observed in vertebrates[16,24]

Summary

Introduction

Apoptotic death of cells damaged by genotoxic stress requires regulatory input from surrounding tissues. We reveal that KRI-1 exists in a complex with CCM-2 in the intestine to negatively regulate the ERK-5/MAPK pathway This allows the KLF-3 transcription factor to facilitate expression of the SLC39 zinc transporter gene zipt-2.3, which functions to sequester zinc in the intestine. We define the apoptotic pathway downstream of KRI-1 by conducting a forward genetic mutagenesis screen to restore IR-induced apoptosis in kri-1 mutant worms This screen uncovers a conserved ERK-5/MAPK signaling pathway and the KLF-3 transcription factor[15,16]. Transcriptome analysis in kri-1 mutant worms reveals that the zinc transporter gene zipt-2.3 is regulated by KLF-3 and required for intestinal zinc storage This permits MPK-1 phosphorylation in the germline to promote apoptosis. By understanding the conserved KRTI1/CCM1 signaling network it will be possible to identify novel therapeutics for a condition that currently relies on invasive surgery for treatment[17]

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Results

Conclusion