Abstract A71: Post-transcriptional regulation of the proto-oncogene PIM1 by the mRNA stability factor HuR: implications for pancreatic cancer therapeutic response and cell survival
Authors: Blanco Fernando F. , Meisner-Kober Nicole , Londin Eric , Rigoutsos Isidore , Winter Jordan , Yeo Charles , Brody Jonathan 
Published: October 2015

Pancreatic ductal adenocarcinoma (PDA) is an aggressive malignancy characterized by its insidious development and resistance to conventional and targeted therapies. As a result of selective pressures imposed by cytotoxic agents and the tumor microenvironment, PDA cells orchestrate a potent and elusive chemoresistant mechanism. Recently, the serine-threonine kinase PIM1 has emerged as a key regulator of PDA cell survival under cancer-associated stress (e.g: cytotoxic DNA-damaging agents, hypoxia). However, the molecular mechanism behind PIM1 overexpression in PDAs is unknown. Here, we demonstrate that cis-acting AU-rich elements (ARE) present in the PIM1 mRNA 3’UTR mediate a regulatory interaction with the mRNA-stability factor HuR under clinically relevant hypoxic and chemotherapeutic stress. Given the previously described role of HuR in PDA cell survival and therapeutic response, we sought to determine if HuR-mediated regulation of PIM1 is essential to promote cell survival and therapeutic resistance under tumor-associated stress (e.g.: hypoxia, chemotherapy). Accordingly, PDA cells subjected to hypoxia exhibit dramatic elevated expression of PIM1 mRNA and protein. Moreover, siRNA-mediated knockdown of HuR abrogates hypoxia-mediated induction of PIM1. HuR-mediated stabilization of PIM1 is associated with high HuR cytoplasmic expression. As revealed by immunofluorescence and western blot analyses of fractionated lysates, we demonstrate that HuR translocates to the cytoplasm when PDA cells are exposed to a hypoxic microenvironment. To further ascertain HuR’s regulation of PIM1, PDA cells treated with MS-444 (Novartis), a small molecule known to disrupt the HuR mRNA-stabilizing activity by inhibiting its nuclear export, results in attenuated PIM1 expression. From a translational standpoint, we demonstrate that disruption of the HuR:PIM1 axis by HuR knockdown results in PDA cell growth inhibition and restores sensitivity to cytotoxic chemotherapeutic agents (e.g.: oxaliplatin). Similarly, pharmacological inhibition of HuR by MS-444 enhances PDA cell sensitivity to oxaliplatin and 5-Fluorouracil, key components of the promising combinatory therapy FOLFIRINOX. Taken together, these results provide continuing evidence that HuR has pro-oncogenic properties in the context of pancreatic cancer by enabling cells with selective growth advantages in stressful tumor microenvironment niches. Lastly, our studies implicate HuR’s regulation of PIM1 as a novel and targetable hallmark of PDA progression.

Citation Format: Fernando F. Blanco, Nicole Meisner-Kober, Eric Londin, Isidore Rigoutsos, Jordan Winter, Charles Yeo, Jonathan Brody. Post-transcriptional regulation of the proto-oncogene PIM1 by the mRNA stability factor HuR: implications for pancreatic cancer therapeutic response and cell survival. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A71.