The Disruption of the ER Stress Response Pathway by R-CHOP and Proteasome Inhibition in DLBCL Converges in GRP78/Bip and GADD153/Chop
A Mozos, G Roue, O Balague, A Lopez-Guillermo, D Colomer, E Campo, A Martinez. Hospital Clinic, IDIBAPS, U. Barcelona, Barcelona, Spain; Netherlands Cancer Institute, Amsterdam, Netherlands
Background: The ER stress response controls the homeostasis of the ER. This pathway involves Ire1-Xbp1, Perk-Chop and Atf6. The chaperone Bip and the transcription factor Xbp1 are key players in this response. We have shown that Xbp1 activation in DLBCL is associated with aggressive disease. Proteasome inhibition (PI) disrupts the ER stress response in myeloma but the role of this response in DLBCL treated with R-CHOP or PI is unknown.
Design: We analyze the expression of Bip, Chop, Xbp-1, Ire-1 and Noxa by western blot and rtPCR in 9 lymphoma cell lines. DLBCL cell lines were treated either with R-CHOP or PI. Cell viability was analyzed by annexin V and MTT assays. We also analyze Bip and Chop expression in 138 DLBCL by immunohistochemistry.
Results: All cell lines expressed Bip, Ire1 and active Xbp1 and 6 also expressed Chop. All DLBCL cell lines were sensitive to R-CHOP and MG-132 but resistant to Bortezomib. After treatment, Bip expression was altered in all cell lines studied, induced by PI and reduced by R-CHOP. SUDHL16 was the most sensitive to PI (30% vs 50% viability) and showed high Bip expression unaltered by treatment but lacked Chop that was highly induced by treatment. Both Ire1 and Xbp1 were reduced by MG-132. The proapototic molecules Chop and Noxa were induced only in SUDHL16. R-CHOP reduced Bip expression more than 60% without altering Ire1 and Xbp-1. Only in SUDHL-16 cells Chop was induced, although at lower levels than PI treatment. We studied Bip and Chop expression in reactive tissues and in 138 DLBCL. Bip was expressed in the light zone of the germinal centers (GC) in association with the plasma cell transcription factors. Chop was upregulated in GC. Bip was expressed in 96 out of 138 (69.5%) and Chop in 59 out of 101 (58.4%) DLBCL. Neither Bip or Chop had impact on complete response rate, disease-free or overall-survival.
Conclusions: In summary R-CHOP and MG-132 treatments disrupt ER stress response in DLBCL and target Bip expression. In cell lines, high Bip expression and lack of Chop was correlated with an impaired response to R-CHOP but a better response to PI. Although Bip expression alone had not clinical impact in DLBCL patients, the combination of Bip and Chop expression may help to identify patients that may respond to PI.
Monday, March 9, 2009 9:30 AM
Poster Session I Stowell-Orbison/Autopsy Award # 188, Monday Morning