Expression data from primary hepatocytes knocking down or overexpressing IRE1a

The ER-resident protein kinase/endoribonuclease IRE1 is activated through trans-autophosphorylation in response to protein folding overload in the ER lumen and maintains ER homeostasis by triggering a key branch of the unfolded protein response. Here we show that mammalian IRE1a in liver cells is also phosphorylated by a kinase other than itself in response to metabolic stimuli. Glucagon stimulated protein kinase PKA, which in turn phosphorylated IRE1a at Ser724, a highly conserved site within the kinase activation domain. Blocking Ser724 phosphorylation impaired the ability of IRE1a to augment the upregulation by glucagon signaling of the expression of gluconeogenic genes. Moreover, hepatic IRE1a was highly phosphorylated at Ser724 by PKA in mice with obesity, and silencing hepatic IRE1a markedly reduced hyperglycemia and glucose intolerance. Hence, these results suggest that IRE1a integrates signals from both the ER lumen and the cytoplasm in the liver and is coupled to the glucagon signaling in the regulation of glucose metabolism.

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Mao T, Shao M, Qiu Y, Huang J, Zhang Y, Song B, Wang Q, Jiang L, Liu Y, Han JD, Cao P, Li J, Gao X, Rui L, Qi L, Li W, Liu Y