American Association for Cancer Research
15357163mct130714-sup-fig1-4.pdf (438.89 kB)

Supplementary Figures 1 - 4 from Dinaciclib (SCH727965) Inhibits the Unfolded Protein Response through a CDK1- and 5-Dependent Mechanism

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journal contribution
posted on 2023-04-03, 14:01 authored by Tri K. Nguyen, Steven Grant

PDF file - 438K, Supplementary Figure 1: SCH727965 blocks induction of XBP-1s and Grp78; Supplementary Figure 2: Knockdown CDK1 or CDK5 reduced nuclear XBP-1s expression; Supplementary Figure 3: Knockdown CDK2 or CDK9 exhibits very modestly or no changes in XBP-1s or Grp78 following Tg exposure; Supplementary Figure 4: Knockdown CDK1 or CDK5 increases sensitivity to ER stress inducers.



Evidence implicating dysregulation of the IRE1/XBP-1s arm of the unfolded protein response (UPR) in cancer pathogenesis (e.g., multiple myeloma) has prompted the development of IRE1 RNase inhibitors. Here, effects of cyclin-dependent kinase (CDK) inhibitor SCH727965 (dinaciclib) on the IRE1 arm of the UPR were examined in human leukemia and myeloma cells. Exposure of cells to extremely low (e.g., nmol/L) concentrations of SCH727965, a potent inhibitor of CDKs 1/2/5/9, diminished XBP-1s and Grp78 induction by the endoplasmic reticulum (ER) stress-inducers thapsigargin and tunicamycin, while sharply inducing cell death. SCH727965, in contrast to IRE1 RNase inhibitors, inhibited the UPR in association with attenuation of XBP-1s nuclear localization and accumulation rather than transcription, translation, or XBP-1 splicing. Notably, in human leukemia cells, CDK1 and 5 short hairpin RNA (shRNA) knockdown diminished Grp78 and XBP-1s upregulation while increasing thapsigargin lethality, arguing for a functional role for CDK1/5 in activation of the cytoprotective IRE1/XBP-1s arm of the UPR. In contrast, CDK9 or 2 inhibitors or shRNA knockdown failed to downregulate XBP-1s or Grp78. Furthermore, IRE1, XBP-1, or Grp78 knockdown significantly increased thapsigargin lethality, as observed with CDK1/5 inhibition/knockdown. Finally, SCH727965 diminished myeloma cell growth in vivo in association with XBP-1s downregulation. Together, these findings demonstrate that SCH727965 acts at extremely low concentrations to attenuate XBP-1s nuclear accumulation and Grp78 upregulation in response to ER stress inducers. They also highlight a link between specific components of the cell-cycle regulatory apparatus (e.g., CDK1/5) and the cytoprotective IRE1/XBP-1s/Grp78 arm of the UPR that may be exploited therapeutically in UPR-driven malignancies. Mol Cancer Ther; 13(3); 662–74. ©2013 AACR.