Combined De-Repression of Chemoresistance Associated Mitogen-Activated Protein Kinase 14 and Activating Transcription Factor 2 by Loss of microRNA-622 in Hepatocellular Carcinoma.

Valerie Fritz,Lara Malek,Anne Gaza,Markus F Neurath,Majken Appel,Peter Dietrich,Laura Wormser,Jürgen Siebler,Andreas E Kremer,Wolfgang E Thasler,Anja K Bosserhoff,Claus Hellerbrand

doi:10.3390/cancers13051183

Abstract

Simple SummaryNovel approaches to target RAS-signaling have led to the so called “RAS renaissance”. In HCC, it was demonstrated that wild-type RAS-RAF-ERK-signaling strongly contributes to HCC progression and drug resistance. In this context, microRNA-622 has emerged as one of the most promising tumorsuppressive microRNAs, targeting RAS-signaling in HCC. However, the majority of microRNA-622 target genes remained elusive. Moreover, limited chemoresponse of HCC was demonstrated by activation of MAPK14-ATF2-signaling which represents a RAS-collateral-pathway, but the expression and regulation of both MAPK14 and ATF2 remained to be clarified. In this study, we demonstrated co-overexpression of MAPK14 and ATF2 in HCC in vitro and in vivo. Moreover, in contrast to “one-microRNA-one-target” interactions, we identified common binding sites for microRNA-622 in both synergistic drug resistance-associated genes–MAPK14 and ATF2. Our data revealed that microRNA-622 functions as a superior pathway regulator inducing de-repression of the MAPK14-ATF2-axis in HCC.Chemoresistance is a major hallmark driving the progression and poor prognosis of hepatocellular carcinoma (HCC). Limited chemoresponse of HCC was demonstrated to be mediated by mitogen-activated protein kinase 14 (MAPK14) and activating transcription factor 2 (ATF2). Recently, we have demonstrated loss of control of RAS-RAF-ERK-signaling as a consequence of miR-622 downregulation in HCC. However, the majority of target genes of this potent tumorsuppressive microRNA had remained elusive. The MAPK14-ATF2-axis represents a collateral pathway ensuring persisting ERK-activation in the presence of sorafenib-mediated RAF-inhibition. In contrast to the function of the MAPK14-ATF2-axis, both the expression and regulation of MAPK14 and ATF2 in human HCC remained to be clarified. We found combined overexpression of MAPK14 and ATF2 in human HCC cells, tissues and in sorafenib resistant cell lines. High expression of MAPK14 and ATF2 was associated with reduced overall survival in HCC patients. Deciphering the molecular mechanism promoting combined upregulation of MAPK14 and ATF2 in HCC, we revealed that miR-622 directly targets both genes, resulting in combined de-repression of the MAPK14-ATF2-axis. Together, miR-622 represents a superior regulator of both RAS-RAF-ERK as well as MAPK14-ATF2-signaling pathways in liver cancer.

Highlights

Hepatocellular carcinoma (HCC) is considered as one of the deadliest cancer types worldwide [1,2,3]
Statistical significance was determined by 2-tailed, unpaired t-test (D–G). * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. It has been demonstrated by our group and others that microRNAs represent powerful small RNA molecules that modulate drug resistance related features in hepatocellular carcinoma (HCC) [10,24]
Applying comprehensive in silico prediction-database screening, we identified common miR-622 binding sites in both mitogen-activated protein kinase 14 (MAPK14) and activating transcription factor 2 (ATF2) 30 untranslated regions (UTR)

Summary

Introduction

Hepatocellular carcinoma (HCC) is considered as one of the deadliest cancer types worldwide [1,2,3]. Limited response of liver cancer cells to first-line systemic therapeutic options such as receptor-tyrosine-kinase inhibitors (i.e., lenvatinib and sorafenib) was demonstrated by our group to be mediated by RAS-activated collateral pathways ensuring persisting. In vivo RNAi screening had identified activation of the mitogen-activated protein kinase 14 (MAPK14)-activating transcription factor 2 (ATF2)-axis as a novel mechanism driving sorafenib resistance in HCC [11]. Upon phosphorylation by MAPK14, ATF2 can function as a tumor promotor [11,12]. MAPK14 ensures persisting ERK-activation in the presence of sorafenib-mediated RAF-inhibition [11]. Apart from these functional analyses, the expression and regulation of the MAPK14-ATF2axis remained unclear in HCC

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Conclusion