Cell membrane-associated
epidermal growth factor receptor (EGFR) translocates into a perinuclear/nuclear location upon stimulation, where it complexes with mRNAs. Treatment with radiation and
cisplatin decreases the amounts of mRNAs present within this complex. Gene array analyses of mRNAs in complex with immunoprecipitated nEGFR revealed significant enrichment of different
mRNA species compared to the control immunoprecipitation. Functional annotation with help of DAVID Gene Ontology Analysis identified under other terms the HIF-1A/
VEGF signaling pathway as one of the top scoring KEGG pathways. RT-PCR and western blots revealed the radiation-induced expression of mRNAs and
proteins involved in HIF-1A/
VEGF signaling. Simultaneously, the levels of the corresponding validated
miRNAs within the complex containing nEGFR and mRNAs were decreased. This finding argues that an
mRNA/
miRNA/nEGFR complex regulates
protein expression. Indeed, we detected the GW182, AGO2, PABPC1 and cNOT1
proteins, which belong to the deadenylase complex, in a complex with nuclear EGFR.
Erlotinib-mediated inhibition of EGFR
kinase reduced the radiation-induced increase in
mRNA expression. In this context,
erlotinib reduced AGO2 phosphorylation by the EGFR
kinase at residue Y393, which was associated with increased cNOT1 deadenylase activity and reduced mRNA stability. To prove the roles of
miRNAs in this context, we transfected cells with an inhibitor of Hsa-mir-1180p5, which targets the NFATC4
mRNA, an
mRNA associated with
VEGF signaling, or pretreated cells with
erlotinib. Indeed, Hsa-mir-1180p5 knockdown increased and the
erlotinib treatment decreased the expression of the
NFATC4 protein. The expression of the
NFATC4 protein controlled the cloning efficiency and radiosensitivity of A549 and FaDu
tumor cells. Thus, this study is the first to show that a membrane-located
tyrosine kinase receptor, such as EGFR, is internalized to a nuclear/perinuclear location upon exposure to stress and modulates the stability and translation of
miRNA-selected mRNAs. This mechanism enables cells to directly express
proteins in response to EGFR activation and may contribute to treatment resistance in EGFR-overexpressing
tumors.