Regulated Ire1-dependent decay of messenger RNAs in mammalian cells

Hollien, Julie; Lin, Jonathan H.; Li, Han; Stevens, Nicole; Walter, Peter; Weissman, Jonathan S.

Consistent with the RIDD pathway functioning in these cells, we observed that several RNAs were down-regulated in response to ER stress in the hIre1 R but not the Ire1 / cells ( Fig. 1 genome encode membrane or ECM proteins, as do 6 of the 7 confirmed targets that displayed increased decay rates. The seventh confirmed target, Blos1, encodes a protein that does not appear to contain a membrane-spanning domain itself but is part of a complex detected in both cytosolic and peripheral membrane fractions (Starcevic and Dell'Angelica, 2004) . We consistently observed partial splicing of XBP-1 in our hIre1 R cells in the absence of ER stress, which is likely caused by overexpression of hIre1 in these cells. To confirm that the mRNA decay we observed was not an artificial product of additional stress or Ire1 activity caused by overexpression, we measured the mRNA decay rates of two confirmed RIDD targets in NIH-3T3 cells (Fig. 2) . As in our reconstituted cells, NIH-3T3 cells displayed increased decay rates and lower abundance for RIDD targets in the presence of DTT. Collectively, our data indicate that RIDD is a general, conserved pathway associated with folding stress in the ER.