Lung cancer is one of the most threatening malignant
tumors to human health.
Epidermal growth factor receptor (EGFR)-targeted
therapy is a common and essential means for the clinical treatment of
lung cancer. However, drug resistance has always affected the
therapeutic effect and survival rate in
non-small cell lung cancer (NSCLC).
Tumor heterogeneity is a significant reason, yielding various drug resistance mechanisms, such as EGFR-dependent or -independent
extracellular signal-regulated kinase 1 and/or 2 (ERK1/2) activation in NSCLC. To examine whether this aberrant activation of ERK1/2 is related to the loss of function of its specific
phosphatase, a series of in vitro and in vivo assays were performed. We found that F-box/SPRY domain-containing
protein 1 (Fbxo45) induces ubiquitination of NP-STEP46 , an active form of striatal-enriched
protein tyrosine phosphatase, with a K6-linked poly-
ubiquitin chain. This ubiquitination led to
proteasome degradation in the nucleus, which then sustains the aberrant level of phosphorylated-ERK (pERK) and promotes
tumor growth of NSCLC. Fbxo45 silencing can significantly inhibit cell proliferation and
tumor growth. Moreover, NSCLC cells with silenced Fbxo45 showed great sensitivity to the EGFR
tyrosine kinase inhibitor (TKI)
afatinib. Here, we first report this critical pERK maintenance mechanism, which might be independent of the upstream
kinase activity in NSCLC. We propose that inhibiting Fbxo45 may combat the issue of drug resistance in NSCLC patients, especially combining with EGFR-TKI
therapy.