ABSTRACT
To relieve endoplasmic reticulum (ER) stress, IRE1 splices XBP1 messenger RNA (mRNA) or engages regulated IRE1-dependent decay (RIDD) of other mRNAs. Upon XBP1 deficiency, IRE1 switches to perform RIDD. We examined IRE1 in XBP1-deficient B cells and discovered that IRE1 undergoes phosphorylation at S729. We generated an anti-phospho-S729 antibody to investigate such phosphorylation. Compared with pharmacological ER stress inducers or Toll-like receptor ligands, the bacterial subtilase cytotoxin has an unusual capability in causing rapid and strong phosphorylation at S729 and triggering B cells to express spliced XBP1. To assess the function of S729 in IRE1, we generated S729A knock-in mice and found S729 is critically important for lipopolysaccharide-stimulated plasmablasts to respond to additional ER stress and for antibody production in response to immunization. We further crossed mice carrying an S729A mutation or ΔIRE1 (missing the kinase domain) with B cell-specific XBP1-deficient mice to trigger RIDD and discovered a critical role for S729 in regulating RIDD in B cells.
Subject(s)
Antibody Formation , B-Lymphocytes/metabolism , Immunization , Membrane Proteins/metabolism , Phosphoserine/metabolism , Protein Serine-Threonine Kinases/metabolism , RNA Stability , Amino Acid Sequence , Animals , Dithiothreitol/pharmacology , Endoplasmic Reticulum Stress/drug effects , Immunoglobulin G/blood , Immunoglobulin M/blood , Lipopolysaccharides , Membrane Proteins/chemistry , Mice, Inbred C57BL , Models, Animal , Models, Biological , Phosphorylation , Protein Serine-Threonine Kinases/chemistry , T-Lymphocytes/metabolism , Up-Regulation/drug effects , X-Box Binding Protein 1/metabolismABSTRACT
A new lucentamycin analogue, lucentamycin E (5), was isolated from the culture broth of the marine-derived actinomycete Nocardiopsis lucentensis, strain CNR-712. The absolute stereostructure of 5 was assigned by comprehensive analyses of NMR data and by application of the advanced Marfey's method. The planar structure of 5 was analogous to lucentamycins A-D, whereas the olefin geometry of the 3-methyl-4-ethylideneproline moiety was found to be E, opposite of that previously reported. Consequently, a reinvestigation of the olefin geometries of the 3-methyl-4-ethylideneproline residues of lucentamycins A-D showed that the olefin geometries of the substituted proline functionalities must be revised to (2S,3R,E)-3-methyl-4-ethylideneproline.