Lysine acetyltransferase 5 in EGFR mutated non-small cell lung cancer
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Histone modifications are crucial in activities such as transcriptional activation, gene silencing, and epigenetic cellular memory. In particular, lysine acetylation via lysine (K) acetyltransferases (KATs) has been implicated in cancer development. Interestingly, KAT5, also known as Tip60 (tat-interactive protein-60kDa), has been reported to possess both tumor promoting and tumor suppressing properties depending on the context of malignancy. Herein we report that KAT5 contributes to tumorigenesis in epidermal growth factor receptor (EGFR) mutated lung cancer, and Kat5-knockout mice models demonstrate significantly reduced lung tumor burden. To probe the aberrant modification of KAT5, we demonstrated that KAT5 binds to and is phosphorylated by oncogenic EGFR in co-immunoprecipitation experiments. Next, to investigate whether KAT5 is involved in cell proliferation and survival, H1975 cells harboring L858R-T790M double-activating mutations were transfected with doxycycline inducible short helical RNA (shRNA) targeting KAT5 (shKAT5). Following treatment, shKAT5 cells were observed to have suppressed proliferation rates. Pharmacological inhibition using TH1834, a known KAT5 inhibitor, also suppressed proliferation rates in shKAT5 cells; in contrast BEAS2B cells, an immortalized normal human bronchial cell line, surprisingly exhibited increased viability compared to transformed human lung H1975 cells. This finding supports KAT5’s context-dependent role in in normal and abnormal cell homeostasis. To further investigate KAT5 in lung tumorigenesis in vivo, we generated EGFR-mutant conditional Kat5 knockout mice using a tetracycline-induced Cre/loxP system. Following doxycycline treatment for 10 weeks, isolated mice lungs for EGFRTL/CCSP-rtTA/Cre/Kat5F/F possessed significantly lower tumor volume compared to EGFRTL/CCSP-rtTA/Cre/Kat5wt/F and EGFRTL/CCSP-rtTA/Cre/Kat5wt/wt mice lungs. Hemotoxylin and eosin staining showed no evident hyperproliferation in lungs isolated from EGFRTL/CCSP-rtTA/Cre/Kat5F/F mice whereas lungs isolated from EGFRTL/CCSP-rtTA/Cre/Kat5wt/wt and EGFRTL/CCSP-rtTA/Cre/Kat5wt/F did, signifying that KAT5 has a potential regulatory role in cellular proliferation. RNA-Seq analysis of shKAT5 H1975 cells identified downstream targets involved in tumorigenic pathways. Subsequent quantitative polymerase chain reaction (PCR) of shKAT5 cells served to validate the reported targets. Taken together, these data offer insight into a KAT5 mediated oncogenic pathway that can provide novel therapeutic approaches in treating lung cancer.
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