NIH Research Festival
Caenorhabditis elegans and parasitic helminths are unable to synthesize heme de novo, but instead acquire heme from exogenous sources for growth and development. Dietary heme transport is mediated by HRG-1-related importers and ABCC5/MRP-5 exporter in C. elegans. Loss of mrp-5 results in embryonic lethality which can be suppressed by heme supplementation, raising the possibility that alternative pathways exist for the regulated transport of heme. Here, we conducted a forward genetic screen to identify suppressors of mrp-5(ok2067) lethality. Screening of 160,000 haploid genomes yielded thirty-two mrp-5(ok2067) suppressors. Deep-sequencing variant analysis revealed three of the suppressors contain mutations in subunits of adapter protein complex 3 (AP-3). Subsequent studies confirmed that RNAi knockdown of either AP-2 or AP-3 subunits constitutes bypass embryonic lethality due to mrp-5 deficiency. Further, loss of AP-3 subunits abrogated zinc mesoporphyrin IX (ZnMP) accumulation in the intestinal lysosome-related organelles, restored susceptibility to gallium protoporphyrin IX (GaPP) toxicity, and elevated global heme availability in the mrp-5(ok2067) strain. Together, we revealed that loss of the heme exporter MRP-5 can be suppressed by reducing AP-3 function, suggesting intra- and intercellular heme trafficking is regulated through multiple routes.
Scientific Focus Area: Cell Biology
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