Abstract 4849
Background
Endoplasmic reticulum (ER) stress-induced, unfolded protein response (UPR)-mediated apoptosis is a protective mechanism whose failure contributes to malignant tumor progression. XAF1 is a stress-inducible, pro-apoptotic tumor suppressor which is inactivated in many human tumor cells. The molecular signal mechanism explaining its function in controlling ER stress, however, remains largely unclear. In this study, we explored the role of XAF1 in UPR signaling and ER stress-induced apoptosis.
Methods
XAF1 and GRP78 expression were determined by RT-PCR and immunoblot assay. the interplay of XAF1 with GRP78 was defined using immunoprecipitation and in vitro pull-down assays. ER stress was induced using thapsigargin, tunicamycin and brefeldin A. Flow cytometry was used to assess cell cycle progression and apoptosis.
Results
XAF1 expression is upregulated at the transcriptional level in response to ER stress and this activation is abolished by suppression of PERK-Nrf2 but not of IRE1a or ATF6 signaling. This indicates that XAF1 is a target of Nrf2 in transcriptional level and activated by ER stress through the PERK pathway. This XAF1 induction greatly enhances the apoptotic response of tumor cells to ER stress while blockade of XAF1 induction reduces apoptotic sensitivity of tumor cells to ER stress. Intriguingly, XAF1 decreases the protein level of the ER stress sensor, GRP78, and consequently activates UPR signaling. Mechanistically, XAF1 binds directly to GRP78 and stimulates its proteasomal degradation in an E3 ligase ZNF313-dependent manner. XAF1 facilitates ZNF313 interaction with GRP78 and thereby promoting ZNF313-mediated K48 ubiquitination of GRP78. Unlikely wild-type XAF1, mutant XAF1 lacking GRP78- or ZNF313-binding domain shows no activity to promote ER stress-induced apoptosis.
Conclusions
Conclusion: XAF1 sensitizes cells to ER stress and drives apoptotic switch of UPR function away from cell cycle arrest by directly antagonizing GRP78 through the assembly of a ZNF313-mediated destruction complex. Our study identifies first a cell-fate decisions function of XAF1 under ER stress conditions.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Sung-Gil Chi.
Funding
BK.
Disclosure
All authors have declared no conflicts of interest.
Resources from the same session
1269 - One-year follow-up results of eribulin for soft-tissue sarcoma including rare subtypes in a real-world observational study in Japan
Presenter: Shunji Takahashi
Session: Poster Display session 1
Resources:
Abstract
2868 - Prevalence of chemotherapy use and its impact on overall survival in patients with bone- and soft tissue sarcomas -A population-based analysis of 3746 patients
Presenter: Herbert Loong
Session: Poster Display session 1
Resources:
Abstract
3042 - Clinical course and therapeutic management of classical and endemic Kaposi’s Sarcoma (C/E KS)
Presenter: Lina Benajiba
Session: Poster Display session 1
Resources:
Abstract
3141 - The final outcomes of study on combined therapy of adult patients with localized synovial sarcoma
Presenter: Katarzyna Kozak
Session: Poster Display session 1
Resources:
Abstract
5449 - Real-world Outcomes of Patients with Locally Advanced or Metastatic Epithelioid Sarcoma
Presenter: Mrinal Gounder
Session: Poster Display session 1
Resources:
Abstract
4465 - SAKK 57/16 Nab-Paclitaxel And Gemcitabine in soft tissue sarcoma (NAPAGE): results from the phase I part of a phase I/II trial
Presenter: Antonia Digklia
Session: Poster Display session 1
Resources:
Abstract
5013 - Outcome of 98 patients with epithelioid sarcoma treated in curative intent: a retrospective study from the French Sarcoma Group (GSF-GETO)
Presenter: Maud Pedrono
Session: Poster Display session 1
Resources:
Abstract
5614 - Comparison of filgrastim and pegfilgrastim prophylaxis in sarcoma patients receiving highly myelosuppressive chemotherapy.
Presenter: Paolo Tarantino
Session: Poster Display session 1
Resources:
Abstract
1033 - Access to clinical trials for soft tissue sarcoma patients in Western and Eastern Europe
Presenter: Vasilii Ostafiichuk
Session: Poster Display session 1
Resources:
Abstract
4094 - Treatment outcomes for adult patients with localized osteosarcoma treated with chemotherapy without methotrexate
Presenter: Marília Silva
Session: Poster Display session 1
Resources:
Abstract