Elucidating the Mechanism by which KRI-1/CCM1 Regulates Apoptosis Cell Non-Autonomously in Caenorhabditis elegans

Programmed cell death initiated by genotoxic stress requires signalling from surrounding tissues, yet such mechanisms are poorly understood. The C. elegans germline is a powerful model to study cell non-autonomous regulation of apoptosis, since germ cells die in response to DNA damage, and because this death requires regulatory input from the soma. The scaffold protein KRI-1, a homologue of mammalian KRIT1/CCM1, was identified to promote DNA damage-induced germ cell apoptosis from the somatic tissue by an unknown mechanism. I reveal that KRI-1 is required for proper activation of MPK-1/ERK1 in the germline, and genetically up-regulating MPK-1/ERK1 restores germ cell apoptosis in the absence of KRI-1. To determine how KRI-1 signals cell non-autonomously to communicate with MPK-1/ERK1, I conducted a forward genetic screen and identified an ERK5/MAPK pathway and the KLF-3 transcription factor that function downstream of this scaffold. I have shown that like kri-1, mpk-2/erk-5 is expressed in the intestine, as is klf-3, and that over-activation of MPK-2/ERK-5 in this tissue is anti-apoptotic. Furthermore, I found that KRI-1 interacts with K07A9.3/CCM2 and Y45F10D.10/ICAP1, which are required to regulate germ cell apoptosis. RNA sequencing of wild type, kri-1, and kri-1; mpk-2/erk5 mutants, followed by an RNAi screen, identified that the zinc transporter, zipt-2.3/scl39, has a role in regulating germ cell apoptosis. ZIPT-2.3 is expressed in the intestine, and reduced zipt-2.3 expression in the absence of KRI-1 prevents proper zinc storage. This results in suppressed activation of MPK-1/ERK1 and germ cell apoptosis. Therefore, the KRI-1 scaffold protein ensures proper activation of MPK-1/ERK1 and germ cell apoptosis by regulating zinc storage.Ph.D.2019-11-16 00:00:0