Search

Previous studies indicated that compounds termed Disulfide bond Disrupting Agents (DDAs) exhibit anti-cancer activity that is associated with downregulation of EGFR/HER1, HER2, and HER3, and activation of Death Receptors 4 and 5 (DR4/5). DDA-induced HER1-3 downregulation is preceded by disulfide-mediated oligomerization. In contrast, DDA-mediated DR4/5 oligomerization results in DR5 upregulation, and activation of DR4/5 pro-apoptotic signaling through Caspases 8 and 3. However, the precise mechanisms by which altered disulfide bonding stabilizes and activates DR5 are unknown. A recent report indicated that the extracellular domain of DR5 acts in an auto-inhibitory manner to prevent DR5 oligomerization and pro-apoptotic signaling in the absence of its ligand, TRAIL. A subsequent paper showed that the DR5 auto-inhibitory domain is a positive patch consisting of three basic residues. Importantly, the structure of the auto-inhibitory loop is formed by two disulfide bonds. We hypothesize that DDAs disrupt the disulfide bonds that make up the auto-inhibitory loop, resulting in DR5 oligomerization, and activation of Caspase 8/3-driven apoptosis in a TRAIL-independent manner. Due to their novel mechanisms of action, DDAs may overcome the pharmacological liabilities that have limited the efficacy of TRAIL analogs and DR5 agonist antibodies. Another unanswered question is how precisely DDAs alter DR5 and EGFR disulfide bonding. The direct targets of DDA action were revealed through affinity purification studies with biotinylated-DDA analogs. These studies identified the protein disulfide isomerases AGR2, ERp44, and PDIA1 as DDA target proteins, explaining how DDAs alter DR5 and EGFR disulfide bonding patterns. Consistent with this interpretation, knockdown of AGR2 or ERp44, or expression of catalytically null AGR2 or ERp44 mutants, mimicked DDAs in inducing disulfide-mediated DR5 oligomerization and Caspase 8 activation. Together, these results demonstrate a fundamentally novel, ligand-independent mechanism for activation of DR5 through DDA-mediated inhibition of the PDIs AGR2, ERp44, and PDIA1. Significantly, DDAs are the first identified active site inhibitors of AGR2 and ERp44. Citation Format: Brian K. Law, Mary E. Law, Elham Yaaghubi, Amanda Ghilardi, Brad J. Davis, Renan Ferreira, Samantha Eggleston, Jade Nguyen, Grace Alexandrow, Jin Koh, Sixue Chen, Chi-Wu Chiang, Coy Heldermon, Peter Norgaard, Ronald K. Castallano, Zaafir M. Dulloo. Disulfide isomerases AGR2, ERp44, and PDIA1 maintain death receptor 5 in an auto-inhibited, monomeric form. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6148.

Oral cancer is a subtype of head and neck cancer, the eighth common cancer type in the world. MicroRNAs (miRNAs) are small non-coding RNAs that mediate gene expression at the post-transcriptional level by degrading target messenger RNA or repressing their translation. The deregulation of certain microRNAs has been associated with the progression and metastasis of various cancer types. A total of 133 miRs were dysregulated in oral cancer cells when compared with normal oral keratinocytes by using microRNA microarray hybridization. Among them, miR-22, often silenced in breast cancer, colon cancer, and multiple myeloma, is downregulated and least known in oral carcinogenesis. In this study, we confirmed the down-regulation of miR-22 in the majority of oral cell lines and 70 % of the tested clinical specimens, as measured by real-time PCR. Both gain-of-function and loss-of-function experiments showed that increased miR-22 expression significantly reduced oral cancer cell migration and invasion, whereas decreased miR-22 expression dramatically enhanced cell migration and invasion. Snail, a transcription factor that promotes cell invasion and tumor metastasis, was predicted to be a target of miR-22. The prediction was validated by the inverse correlation of miR-22 and snail protein, and the luciferase reporter assay bearing 3’- translated region derived from snail. Silencing snail expression by using shRNA recapitulated the anti-metastatic function of miR-22, whereas restored snail expression attenuated the function of miR-22 in oral cancer cells. Together, these results suggest that miR-22 may act as a tumor suppressor through decreasing snail expression in oral cancer and thus be used as a therapeutic target to block oral cancer metastasis. Citation Format: Yi-Zih Kuo, Yun-Chu Huang, Yuh-Ling Chen, Hung-I Lo, Sen-Tien Tsai, Chi-Wu Chiang, Li-Wha Wu. Identification of dysregulated miRs and its target genes in head and neck cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4195. doi:10.1158/1538-7445.AM2013-4195