MiR-35 buffers apoptosis thresholds in the C. elegans germline by antagonizing both MAPK and core apoptosis pathways

Abstract

Apoptosis is a genetically programmed cell death process with profound roles in development and disease. MicroRNAs modulate the expression of many proteins and are often deregulated in human diseases, such as cancer. C. elegans germ cells undergo apoptosis in response to genotoxic stress by the combined activities of the core apoptosis and MAPK pathways, but how their signalling thresholds are buffered is an open question. Here we show mir-35-42 miRNA family play a dual role in antagonizing both NDK-1, a positive regulator of MAPK signalling, and the BH3-only pro-apoptotic protein EGL-1 to regulate the magnitude of DNA damage-induced apoptosis in the C. elegans germline. We show that while miR-35 represses EGL-1 by promoting transcript degradation, repression of NDK-1 may be through sequestration of the transcript to inhibit translation. Importantly, dramatic increase in NDK-1 expression was observed in cells about to die. In the absence of miR-35, increased NDK-1 activity enhanced MAPK signalling that lead to significant increases in germ cell death. Our findings demonstrate that NDK-1 acts upstream of (or in parallel to) EGL-1, and that miR-35 targets both egl-1 and ndk-1 to fine-tune cell killing in response to genotoxic stress.

The Function of NM23-H1/NME1 and Its Homologs in Major Processes Linked to Metastasis

“…In response to irradiation in the C. elegans germline (applying genotoxic stress), elevated NDK-1::GFP levels were experienced in germ cells destined to die; especially, if the mir-35 binding site was mutated in ndk-1's 3'-UTR, the refractile morphology of apoptotic germ cells suddenly occurred. The authors conclude that mir-35 acts as a buffer to maintain the threshold of apoptosis, by influencing MAPK activation through NDK-1 [114].…”

“…Both human and C. elegans studies suggest that NDPKs play a role in several cases in the apoptotic cell. A recent study in C. elegans showed that germ cell death in response to DNA damage is mediated by NDK-1 through activation of the MAPK cascade [114]. NDK-1 acts as an activator of the MAPK pathway in somatic tissues of the worm; and this function of NDK-1 was confirmed from a different aspect, during germ cell apoptosis [114].…”

“…A recent study in C. elegans showed that germ cell death in response to DNA damage is mediated by NDK-1 through activation of the MAPK cascade [114]. NDK-1 acts as an activator of the MAPK pathway in somatic tissues of the worm; and this function of NDK-1 was confirmed from a different aspect, during germ cell apoptosis [114]. DNA damage-induced apoptosis of C. elegans germ cells is mostly driven by the MAPK pathway [115,116].…”

Two microRNAs are sufficient for embryogenesis in C. elegans

“…Zebrafish miR-430 is expressed in the zygote, where it plays a role in maternal mRNA clearance (4). In contrast, miR-35 fam and -51 fam are present in the germline and, at least for miR-35 fam , there is strong evidence that it is already active in the maternal germline (31,32). Moreover, the expression levels of the predicted targets of the miR-35 fam and -51 fam tend to stay constant during embryogenesis or even increase ( Fig.…”

“…The miR-35 fam and -51 fam are broadly conserved, with miR-51 being a homolog of miR-100, the most ancient animal miRNA (12,27). Yet, the functions of these two miRNA families remain poorly understood and neither has been linked to mRNA targets that explain the penetrant embryonic lethality (12,(28)(29)(30)(31)(32). Zebrafish miR-430 is expressed in the zygote, where it plays a role in maternal mRNA clearance (4).…”