The Function Of Calnexin In Aspergillus Nidulans In Regulating Intracellular Calcium Balance And Coping With Endoplasmic Reticulum Pressure

Calnexin,which is known as a membrane-bound molecular chaperone protein in ER,participates in the folding and quality control of newly synthesized glycoproteins.In mammalian,calnexin is originally described as one of the two major calcium-binding proteins in the ER membrane.In spite of the structure of calnexin contains calcium-binding region,the evidence for its roles on calcium homeostasis and/or cross-talk with calcium signaling is of scarcity.Here we characterized the biological functions of the calnexin in Aspergillus nidulans for response to endoplasmic reticulum stress(Dithiothreitol,namely DTT and thermal stress)through the methods of genetics and molecular biology.Calnexin showed a transient increased transcriptional expression level under DTT or heat shock.Disrupting calnexin gene(clxA)greatly reduced conidia production under DTT stress or thermal stress(42?).In comparison,there were no detectable differences between wild type and AclxA mutant at normal conditions.We also found that the defect phenotype can be rescued by the addition extra-cellular Ca2+,but the Ca2+ didn't reduce the level of UPR(unfolded protein response)in fungus under DTT stress.The experiment suggested that the calnexin play a role for keep balance of the cytoplasmic Ca2+.Furthermore,disequilibrate calcium homeostasis by deletion the main components of the calcium signaling pathway:CchA/MidA(Calcium channels in plasma),PmrA(Putative calcium-transporting ATPase in Golgi),aggravates the mutants' sensitivity to DTT stress and thermal stress.Collectively,our results suggested calnexin played a regulatory role on maintaining calcium homeostasis apart from its chaperone function.Calnexin in combination with calcium signaling pathway mediates a fundamental aspect on A.nidulans endoplasmic reticulum stress.