Bortezomib alone and in combination with other anticancer agents are extensively used for chemotherapeutic treatment of multiple myeloma (MM) patients and are being developed for treating other cancers. Bortezomib acts through multiple pathways, and in this study with ANBL-6 and RPMI 8226 MM cells we show that bortezomib inhibited growth and induced apoptosis and that this was accompanied by downregulation of specificity protein (Sp) 1, Sp3, and Sp4 transcription factors that are overexpressed in these cells. Similar results were observed in pancreatic and colon cancer cells. The functional importance of this pathway was confirmed by showing that individual knockdown of Sp1, Sp3, and Sp4 in MM cells inhibited cell growth and induced apoptosis, and that this correlates with the results of previous studies in pancreatic, colon, and other cancer cell lines. The mechanism of bortezomib-mediated downregulation of Sp transcription factors in MM was due to the induction of caspase-8 and upstream factors, including Fas-associated death domain. These results demonstrate that an important underlying mechanism of action of bortezomib was due to the activation of caspase-8-dependent downregulation of Sp1, Sp3, Sp4, and pro-oncogenic Sp-regulated genes.

Background: Pancreatic cancer is lethal and the fourth leading cause of cancer deaths in the United States with a 5-year overall survival rate of 6.7%. The orphan nuclear receptor 4A2 (NR4A2, Nurr1) has been implicated in various cellular processes, including inflammation, vascular remodeling, and cancer as a transcriptional facilitator of tumorigenesis, through its regulation of various proliferation, invasion, and metastasis-associated genes. In the pancreatic cancer context, very little is known about NURR1. Here, we explored the expression, prognostic value, and function of NURR1 in human PDA growth and metastasis. We also investigated the role of NURR1 in regulating pancreatic cancer metabolism. Methods: We analyzed The Cancer Genome Atlas (TCGA) database for PDA and microarray expression data from GEO and examined NURR1 expression in normal pancreatic tissue, primary pancreatic tumors and metastatic tumors by using the R statistical computing environment. Kaplan-Meier analysis were performed to investigate the prognostic significance of NURR1 for PDA. NURR1 levels were depleted with siRNA oligos, and also overexpressed with NURR1 cDNA. Following characterization of NURR1 expression, we performed a cell proliferation (XTT) assay and assessed anchorage-independence over a 3-week period by soft agar colony formation assay under normal condition and metabolic stress. Metastatic potential was measured by Matrigel invasion and transwell migration assays. Experiments were performed in MIA PaCa-2, Panc-1 and L3.6pl cell lines. Results: Analysis of messenger RNA (mRNA) expression data from 177 PDA samples from TCGA showed that NURR1 was overexpressed in PDA tissues compared with the pancreatic normal samples (P< 0.001). Kaplan-Meier analysis revealed that 5-year median overall survival (OS) and progression free survival (PFS) were significantly poorer in the NURR1-overexpression group (P= 0.002). Moreover, knockdown of NURR1 significantly reduced PDA cell proliferation, migration, and invasion, whereas NURR1 overexpression resulted in a significant increase in proliferation and migration. In addition, mRNA expression of NURR1 was increased after 12 hours of glucose deprivation in 2 cell lines (vs. 25mM glucose). However, NURR1 depletion impaired survival in low glucose media (5mM) and overexpression of NURR1 had a protective effect under glucose deprivation in Panc-1 cells. Conclusion: NURR1 exhibits a tumor-promoting effect on PDA and NURR1 expression is critical for pancreatic cancer cell survival under glucose deprivation. Our work demonstrates that manipulation of NURR1 expression affects key characteristics of pancreatic tumorigenesis (i.e. proliferation, invasion, and migration). Improved understanding of how NURR1 regulates metabolism in response to stress should uncover novel therapeutic strategies against pancreatic cancer. Note: This abstract was not presented at the meeting. Citation Format: Sneha Harishchandra, Xi Li, Stephen Safe, Mahsa Zarei. Nuclear receptor Nurr1 facilitates pancreatic ductal adenocarcinoma cell survival under metabolic stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1714.

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