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  • Title: Collaboration Between RSK-EphA2 and Gas6-Axl RTK Signaling in Arginine Starvation Response That Confers Resistance to EGFR Inhibitors.
    Author: Kuo MT, Long Y, Tsai WB, Li YY, Chen HHW, Feun LG, Savaraj N.
    Journal: Transl Oncol; 2020 Feb; 13(2):355-364. PubMed ID: 31887630.
    Abstract:
    Many human malignancies require extracellular arginine (Arg) for survival because the key enzyme for de novo Arg biosynthesis, argininosuccinate synthetase 1 (ASS1), is silenced. Recombinant arginine deiminase (ADI-PEG20), which digests extracellular Arg, has been in clinical trials for treating ASS1-negative tumors. Reactivation of ASS1 is responsible for the treatment failure. We previously demonstrated that ASS1 reactivation is transcriptionally regulated by c-Myc via the upstream Gas6-Axl tyrosine kinase (RTK) signal. Here, we report that another RTK EphA2 is coactivated via PI3K-ERK/RSK1 pathway in a ligand-independent mechanism. EphA2 is also regulated by c-Myc. Moreover, we found that knockdown Axl upregulates EphA2 expression, demonstrating cross-talk between these RTKs. ADIR cell lines exhibits enhanced sensitivities to nutrient deprivation such as charcoal-stripped FBS and multiple RTK inhibitor foretinib but resistance to EGFR inhibitors. Knockdown EphA2, and to lesser extent, Axl, overcomes EGFRi resistance. c-Myc inhibitor JQ1 can also sensitize ADIR cells to ADI-PEG20. This study elucidates molecular interactions of multiple RTKs in Arg-stress response and offers approaches for developing strategies of overcoming ADI-PEG20 resistance.
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