Dual Targeting of EGFR and IGF1R in the TNFAIP8 Knockdown Non-small Cell Lung Cancer Cells

Aberrant regulation of EGFR is common in non-small cell lung carcinomas (NSCLC), and tumor resistance to targeted therapies has been attributed to emergence of other co-occurring oncogenic events, parallel bypass receptor tyrosine kinase pathways including IGF1R, and TNF-α-driven adaptive response via NF--κB. TNFAIP8, TNF-α-inducible protein 8, is an NF-αB-activated pro-survival and oncogenic molecule. TNFAIP8 expression protects NF-κB null cells from TNF-α-induced cell death by inhibiting caspase-8 activity. Here we demonstrate that knockdown of TNFAIP8 inhibited EGF and IGF-1-stimulated migration in NSCLC cells. TNFAIP8 knockdown cells showed decreased level of EGFR and increased expression of sorting nexin 1 (SNX1), a key regulator of the EGFR trafficking through the endosomal compartments, and treatment with SNX1 siRNA partially restored EGFR expression in these cells. TNFAIP8 knockdown cells also exhibited downregulation of IGF-1-induced pIGF1R and pAKT, and increased expression of IGF-1-binding protein 3 (IGFBP3), a negative regulator of the IGF-1/IGF1R signaling. Consistently, treatment of TNFAIP8 knockdown cells with IGFBP3 siRNA restored pIGF1R and pAKT levels. TNFAIP8 knockdown cells had enhanced sensitivities to inhibitors of EGFR, PI3K and AKT. Furthermore, immunohistochemical expression of TNFAIP8 was associated with poor prognosis in NSCLC. These findings demonstrate TNFAIP8-mediated regulation of EGFR and IGF1R via SNX1 and IGFBP3, respectively. We posit that TNFAIP8 is a viable, multi-pronged target downstream of the TNF-α/NF-κB axis, and silencing TNFAIP8 may overcome adaptive response in NSCLC. Implications: TNFAIP8 and its effectors SNX1 and IGFBP3 may be exploited to improve the efficacy of molecular targeted therapies in NSCLC and other cancers.