Carcinoma-associated eIF3i overexpression facilitates mTOR-dependent growth transformation.

Molecular processes controlling mRNA translation are complex, multilayered, and their deregulation can lead to cancer pathogenesis. Eukaryotic initiation factor 3 (eIF3) is involved in the initiation process of protein translation and overexpression of its subunit eukaryotic translation initiation factor i (eIF3i) has been observed in carcinomas. Nevertheless, the potential role of eIF3i in carcinogenesis is poorly understood. Here, we show that in vitro overexpression of human eIF3i resulted in cell size increase, proliferation enhancement, cell-cycle progression, and anchorage-independent growth. Without external stimuli, eIF3i overexpressing cells arrested in G1/G0 phase, demonstrating the requirement of additional growth signals. Inhibition of the kinase mTOR, a key player in the integration of nutrition and growth signals into protein synthesis, with rapamycin reduced serine phosphorylation of eIF3i and resulted in a loss of anchorage-independent growth. Thus, eIF3i overexpression fosters the integration of growth signals by mTOR into the mRNA translation process, promoting protein synthesis and tumor growth.