Mediator subunit MDT-15/MED15 and Nuclear Receptor HIZR-1/HNF4 cooperate to regulate toxic metal stress responses in Caenorhabditis elegans

Abstract

Zinc is essential for cellular functions as it is a catalytic and structural component of many proteins. In contrast, cadmium is not required in biological systems and is toxic. Zinc and cadmium levels are closely monitored and regulated as their excess causes cell stress. To maintain homeostasis, organisms induce metal detoxification gene programs through stress responsive transcriptional regulatory complexes. In Caenorhabditis elegans, the MDT-15 subunit of the evolutionarily conserved Mediator transcriptional coregulator is required to induce genes upon exposure to excess zinc and cadmium. However, the regulatory partners of MDT-15 in this response, its role in cellular and physiological stress adaptation, and the putative role for mammalian MED15 in the metal stress responses remain unknown. Here, we show that MDT-15 interacts physically and functionally with the Nuclear Hormone Receptor HIZR-1 to promote molecular, cellular, and organismal adaptation to cadmium and excess zinc. Using gain- and loss-of-function mutants and qRT-PCR and reporter analysis, we find that mdt-15 and hizr-1 cooperate to induce zinc and cadmium responsive genes. Moreover, the two proteins interact physically in yeast-two-hybrid assays and this interaction is enhanced by the addition of zinc or cadmium, the former a known ligand of HIZR-1. Functionally, mdt-15 and hizr-1 mutants show defective storage of excess zinc in the gut and are hypersensitive to zinc-induced reductions in egg-laying. Furthermore, mdt-15 but not hizr-1 mutants are hypersensitive to cadmium-induced reductions in egg-laying, suggesting potential divergence of regulatory pathways. Lastly, mammalian MDT-15 orthologs bind genomic regulatory regions of metallothionein and zinc transporter genes in a cadmium and zinc-stimulated fashion, and human MED15 is required to induce a metallothionein gene in lung adenocarcinoma cells exposed to cadmium. Collectively, our data show that mdt-15 and hizr-1 cooperate to regulate cadmium detoxification and zinc storage and that this mechanism is at least partially conserved in mammals.

Stress increases in exopher-mediated neuronal extrusion require lipid biosynthesis, FGF, and EGF RAS/MAPK signaling

“…MDT-15 has been shown to promote health and longevity by orchestrating many of the metabolic changes that occur in response to short-term fasting ( 32 ). MDT-15 encodes a subunit of the transcriptional coregulator Mediator complex that is required to express fatty acid metabolism genes and fasting-induced transcripts ( 32 – 35 ), heavy metal and xenobiotic detoxification genes ( 32 , 36 ), and oxidative stress genes ( 37 ). SBP-1, the homolog of the mammalian sterol regulatory element-binding protein (SREBF2) transcription activator that regulates fatty acid homeostasis, is a known partner of MDT-15, and together, MDT-15 and SBP-1 promote the expression of lipid synthesis genes ( 32 ).…”

Nuclear hormone receptors promote gut and glia detoxifying enzyme induction and protect C. elegans from the mold P. brevicompactum

“…There are numerous examples of NHRs involved in regulating immune or stress responses following microbe or toxin exposure. This includes nhr-49 and nhr-8 , which regulate immune responses to Staphylococcus aureus and P. aeruginosa , respectively ( Wani et al, 2021 ; Otarigho and Aballay, 2020 ), and nhr-176 and nhr-33 / hizr-1 , which regulate resistance to thiabendazole and cadmium, respectively ( Jones et al, 2013 ; Shomer et al, 2019 ). Our observation that natural variations in the nhr-156 gene in wild isolates result in differential transcriptional responses in AMsh glia to microbe exposure supports the idea that NHRs may act as sensors for environmental cues.…”

“…The NHR family in C. elegans has undergone massive expansion and sequence diversification ( Taubert et al, 2011 ). NHR genes promote responses to microbe exposure and environmental stress ( Jones et al, 2013 ; Mao et al, 2019 ; Otarigho and Aballay, 2020 ; Park et al, 2018 ; Peterson et al, 2019 ; Rajan et al, 2019 ; Shomer et al, 2019 ; Wani et al, 2021 ; Ward et al, 2014 ; Yuen and Ausubel, 2018 ). Induction of XMEs has also been observed in C. elegans in response to exposure to several model pathogens ( Engelmann et al, 2011 ).…”

Neuronal control of lipid metabolism by STR‐2 G protein‐coupled receptor promotes longevity in Caenorhabditis elegans

“…Brood size was measured at 25°C as reported (Shomer et al, 2019;Soukas et al, 2009). Single late L4 stage worms (10 worms per strain)…”