BCR and B-cell chronic lymphocytic leukemia: ER stress response and IRE1/XBP1 pathway are aberrantly activated in human CLL and in TCL1-tg mice.22 TCL1 is directly involved in ER response by physical interaction with XBP1 and alteration of its transcriptional activity, resulting in constitutive activation of BCR signaling and influencing cross talk with other factors such as IRF4, BLIMP1 and AID.