title: Protoporphyrins enhance oligomerization and enzymatic activity of HtrA1 serine protease.
abstract: High temperature requirement protein A1 (HtrA1), a secreted serine protease of the HtrA family, is associated with a multitude of human diseases. However, the exact functions of HtrA1 in these diseases remain poorly understood. We seek to unravel the mechanisms of HtrA1 by elucidating its interactions with chemical or biological modulators. To this end, we screened a small molecule library of 500 bioactive compounds to identify those that alter the formation of extracellular HtrA1 complexes in the cell culture medium. An initial characterization of two novel hits from this screen showed that protoporphyrin IX (PPP-IX), a precursor in the heme biosynthetic pathway, and its metalloporphyrin (MPP) derivatives fostered the oligomerization of HtrA1 by binding to the protease domain. As a result of the interaction with MPPs, the proteolytic activity of HtrA1 against Fibulin-5, a specific HtrA1 substrate in age-related macular degeneration (AMD), was increased. This physical interaction could be abolished by the missense mutations of HtrA1 found in patients with cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL). Furthermore, knockdown of HtrA1 attenuated apoptosis induced by PPP-IX. These results suggest that PPP-IX, or its derivatives, and HtrA1 may function as co-factors whereby porphyrins enhance oligomerization and the protease activity of HtrA1, while active HtrA1 elevates the pro-apoptotic actions of porphyrin derivatives. Further analysis of this interplay may shed insights into the pathogenesis of diseases such as AMD, CARASIL and protoporphyria, as well as effective therapeutic development.
authors.affiliation: Department of Environmental Health Science, Yale University School of Public Health, New Haven, Connecticut, United States of America; Department of Ophthalmology and Visual Sciences, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Hakryul
authors.initials: H
authors.lastname: Jo
authors.affiliation: Department of Environmental Health Science, Yale University School of Public Health, New Haven, Connecticut, United States of America; Department of Ophthalmology and Visual Sciences, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Victoria
authors.initials: V
authors.lastname: Patterson
authors.affiliation: Department of Environmental Health Science, Yale University School of Public Health, New Haven, Connecticut, United States of America; Department of Ophthalmology and Visual Sciences, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Sean
authors.initials: S
authors.lastname: Stoessel
authors.affiliation: Department of Pediatrics, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, Georgia, United States of America.
authors.forename: Chia-Yi
authors.initials: CY
authors.lastname: Kuan
authors.affiliation: Department of Environmental Health Science, Yale University School of Public Health, New Haven, Connecticut, United States of America; Department of Ophthalmology and Visual Sciences, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Josephine
authors.initials: J
authors.lastname: Hoh
mesh_terms: D017209:Apoptosis; D004353:Drug Evaluation, Preclinical; D000074289:High-Temperature Requirement A Serine Peptidase 1; D006801:Humans; D008665:Metalloporphyrins / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D011524:Protoporphyrins / Q000378:metabolism / Q000494:pharmacology*; D012697:Serine Endopeptidases / Q000187:drug effects* / Q000378:metabolism
chemical_list: D008665:Metalloporphyrins; D011524:Protoporphyrins; C028025:protoporphyrin IX; D000074289:High-Temperature Requirement A Serine Peptidase 1; C474012:HTRA1 protein, human; D012697:Serine Endopeptidases