Integrin-linked kinase (ILK) is a mediator of aggressive phenotype in pancreatic cancer. On the basis of our finding that knockdown of either KRAS or ILK has a reciprocal effect on the other’s expression, we hypothesized the presence of an ILK-KRAS regulatory loop that enables pancreatic cancer cells to regulate KRAS expression. This study aimed to elucidate the mechanism by which this regulatory circuitry is regulated and to investigate the translational potential of targeting ILK to suppress oncogenic KRAS signaling in pancreatic cancer. Interplay between KRAS and ILK and the roles of E2F1, c-Myc and heterogeneous nuclear ribonucleoprotein as intermediary effectors in this feedback loop was interrogated by genetic manipulations through small interfering RNA/short hairpin RNA knockdown and ectopic expression, western blotting, PCR, promoter-luciferase reporter assays, chromatin immunoprecipitation and pull-down analyses. In vivo efficacy of ILK inhibition was evaluated in two murine xenograft models. Our data show that KRAS regulated the expression of ILK through E2F1-mediated transcriptional activation, which, in turn, controlled KRAS gene expression via hnRNPA1-mediated destabilization of the G-quadruplex on the KRAS promoter. Moreover, ILK inhibition blocked KRAS-driven epithelial–mesenchymal transition and growth factor-stimulated KRAS expression. The knockdown or pharmacological inhibition of ILK suppressed pancreatic tumor growth, in part, by suppressing KRAS signaling. These studies suggest that this KRAS-E2F1-ILK-hnRNPA1 regulatory loop enables pancreatic cancer cells to promote oncogenic KRAS signaling and to interact with the tumor microenvironment to promote aggressive phenotypes. This regulatory loop provides a mechanistic rationale for targeting ILK to suppress oncogenic KRAS signaling, which might foster new therapeutic strategies for pancreatic cancer.
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This work was supported by the Lucius A Wing Endowed Chair Fund (CSC), Ministry of Science and Technology grant MOST 103-2320-B-001-017 (PCC), Bi-institutional Collaborative Pancreatic Cancer Research grants from National Cheng Kung University College of Medicine (CSC) and The Ohio State University Wexner Medical Center and Comprehensive Cancer Center (TBS) and National Institutes of Health grant P30 CA016058, which supports, in part, the Comparative Pathology and Mouse Phenotyping Shared Resource at The Ohio State University Comprehensive Cancer Center.
The authors declare no conflict of interest.
Supplementary Information accompanies this paper on the Oncogene website
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Chu, P., Yang, M., Kulp, S. et al. Regulation of oncogenic KRAS signaling via a novel KRAS-integrin-linked kinase-hnRNPA1 regulatory loop in human pancreatic cancer cells. Oncogene 35, 3897–3908 (2016). https://doi.org/10.1038/onc.2015.458
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