{"doi":"10.1101/2021.06.06.447256","title":"Heme oxygenase-2 (HO-2) binds and buffers labile heme, which is largely oxidized, in human embryonic kidney cells","abstract":"Abstract Heme oxygenases (HO) detoxify heme by oxidatively degrading it into carbon monoxide, iron, and biliverdin, which is reduced to bilirubin and excreted. Humans express two isoforms: inducible HO-1, which is up-regulated in response to various stressors, including excess heme, and constitutive HO-2. While much is known about the regulation and physiological function of HO-1, comparatively little is known about the role of HO-2 in regulating heme homeostasis. The biochemical necessity for expressing constitutive HO-2 is largely dependent on whether heme is sufficiently abundant and accessible as a substrate under conditions in which HO-1 is not induced. By measuring labile heme, total heme, and bilirubin in human embryonic kidney HEK293 cells with silenced or over-expressed HO-2, and various HO-2 mutant alleles, we found that endogenous heme is too limiting to support HO-2 catalyzed heme degradation. Rather, we discovered that a novel role for HO-2 is to bind and buffer labile heme. Taken together, in the absence of excess heme, we propose that HO-2 regulates heme homeostasis by acting as a heme buffering factor in control of heme bioavailability. When heme is in excess, HO-1 is induced and both HO-2 and HO-1 can provide protection from heme toxicity by enzymatically degrading it. Our results explain why catalytically inactive mutants of HO-2 are cytoprotective against oxidative stress. Moreover, the change in bioavailable heme due to HO-2 overexpression, which selectively binds ferric over ferrous heme, is consistent with the labile heme pool being oxidized, thereby providing new insights into heme trafficking and signaling.","journal":"bioRxiv (Cold Spring Harbor Laboratory)","year":2021,"id":224544,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9505,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2021-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":259687,"name":"Courtney M. Moore","orcid":"0000-0001-8303-7164","position":1,"is_corresponding":false},{"id":792177,"name":"Liu Liu","orcid":"0000-0001-8905-1039","position":2,"is_corresponding":false},{"id":826589,"name":"Xiaojing Yuan","orcid":"0000-0002-0969-5748","position":3,"is_corresponding":false},{"id":393163,"name":"Angela S. Fleischhacker","orcid":"0000-0003-0818-3203","position":4,"is_corresponding":false},{"id":307344,"name":"Iqbal Hamza","orcid":"0000-0003-0045-0610","position":5,"is_corresponding":false},{"id":328499,"name":"Stephen W. Ragsdale","orcid":"0000-0003-3938-8906","position":6,"is_corresponding":false},{"id":259689,"name":"Amit R. Reddi","orcid":"0000-0003-3952-404X","position":7,"is_corresponding":false},{"id":688959,"name":"David A. Hanna","orcid":"0000-0003-0726-8707","position":0,"is_corresponding":true}],"reference_count":104,"raw_metadata":null,"created_at":"2026-07-18T23:54:18.470602Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}