title: Dose-dependent differential response of mammalian cells to cytoplasmic stress is mediated through the heme-regulated eIF2α kinase.
abstract: The heme-regulated inhibitor (HRI), a regulator of translation initiation, is known to be activated and upregulated, and it acts as either a cytoprotective player promoting cell survival or as an inducer of apoptosis during stress. However, the exact role of HRI in these two responses has not been elucidated. In the present investigation, using human cell lines, we attempted to unravel the molecular mechanism(s) of HRI-mediated differential response and the involved signaling pathways. While during low dose (5 μM) lead acetate treatment, cells did not show any diminished cell survival, significant level of apoptosis was observed at high dose (100 μM) lead acetate. Based on the results of an interactome analysis, we determined the interaction of HRI with PI-3-Kca, only at a low dose stress, which is followed by phosphorylation and activation of its downstream target, AKT. Interestingly, such an interaction and AKT activation was not observed at a high dose stress. On the other hand, an increased level of APAF-1 and activation of caspases were observed. These results indicate a critical role of HRI in cell survival during low dose stress, and in apoptosis at high dose stress. Furthermore, HRI knockdown cells are sensitized even to 5 μM lead treatment leading to caspase activation and apoptosis. Our results taken together thus elucidate for the first time the molecular mechanism and the involved signaling pathways for dose-dependent differential response of mammalian cells to lead exposure. These findings thus suggest the possibility of using HRI downregulation as a therapeutic strategy to sensitize cancer cells subjected to apoptogenic drugs.
authors.affiliation: Department of Biotechnology, University of Pune, Pune 411007, India; National Centre for Cell Science, University of Pune Campus, Pune 411007, India.
authors.forename: Smriti P K
authors.initials: SP
authors.lastname: Mittal
authors.affiliation: Department of Biotechnology, University of Pune, Pune 411007, India.
authors.forename: Abhijeet P
authors.initials: AP
authors.lastname: Kulkarni
authors.affiliation: National Centre for Cell Science, University of Pune Campus, Pune 411007, India.
authors.forename: Jinumary
authors.initials: J
authors.lastname: Mathai
authors.affiliation: National Centre for Cell Science, University of Pune Campus, Pune 411007, India.
authors.forename: Samit
authors.initials: S
authors.lastname: Chattopadhyay
authors.affiliation: Department of Biotechnology, University of Pune, Pune 411007, India. Electronic address: jkpal@unipune.ac.in.
authors.forename: Jayanta K
authors.initials: JK
authors.lastname: Pal
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D030562:Databases, Protein; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006801:Humans; D020014:K562 Cells; D009942:Organometallic Compounds / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D054730:Protein Interaction Domains and Motifs; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013312:Stress, Physiological; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D009942:Organometallic Compounds; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D019892:eIF-2 Kinase; C008261:lead acetate
keywords: Cell survival; HRI; K562 cells; Lead acetate stress; PI-3-K