A cascade for zinc mediated transcriptional activation by the zinc-sensing nuclear receptor HIZR-1 on the regulator of lysosome biogenesis HLH-30 to achieve homeostasis

Zinc is an essential element for animals and stored in de novo synthesized lysosome related organelles called bilobed granules in Caenorhabditis elegans. Defining how zinc regulated transcription drives the observed lysosome remodeling is key to understand zinc homeostasis processes. Here we describe a positively regulated zinc network controlled by HIZR-1 and HLH-30, the zinc sensor and the master regulator of the autophagy-lysosomal pathway in Caenorhabditis elegans, respectively; essential for connecting zinc homeostasis to lysosome biogenesis. Our studies indicate that either hizr-1 and hlh-30 are necessary and sufficient to activate transcription of lysosome-genes under high dietary zinc conditions. Consistent with the hizr-1 and hlh-30 dependency for high zinc response, we found DNA enhancer elements corresponding to the high zinc activation element consistently adjacent to E-boxes in the promoter regions of lysosome-genes. We defined a regulatory network based on the contribution of each transcription factor. Since zinc cannot be degraded, the autophagy-lysosomal pathway could play a key role in removing zinc excess Two Caenorhabditis elegans strains, wild type and a hizr-1 loss-of-function mutant were independtly exposed to high dietary zinc conditions and compared to a non-supplemented zinc condition. Two biological samples each strain and each condition were used.