Let-7g suppresses tumor initiation in an autochthonous NSCLC model. (A) Diagram of the Puro.Cre lentiviral vector for coexpression of let-7g/let-7g sm with Cre recombinase. (B) Small RNA Northern blot analysis was performed against let-7g (both wild type and seed mutant), miR-17 and Glutamine tRNA in HEK293 cells infected with Puro.Cre (empty), Puro.let7gsm.Cre (let-7g sm), and Puro.let7g.Cre (let-7g). (C–E) KrasLSL-G12D;Trp-53flox/flox mice were intratracheally infected with the Puro.Cre lentiviral vectors described above. Twelve weeks after infection, animals were killed, and tumor number (C), tumor and lung area (D), and tumor size (E) were quantified with Bioquant software. Values are mean ± SEM (n = 9 for empty, n = 11 for let-7g, and n = 11 for let-7g sm). *, P < 0.0005, #, P < 0.01; ###, P < 0.1. (F) Small RNA Northern blotting was performed against let-7g (both wild type and seed mutant), and Glutamine tRNA on lung tumors was generated from KrasLSL-G12D;Trp-53flox/flox mice infected with Puro.Cre (empty), Puro.let7g.Cre (let-7g), and Puro.let7gsm.Cre (let-7g sm). (G) Western blot analysis was performed on lung tumors generated from KrasLSL-G12D;Trp-53flox/flox mice infected with Puro.Cre (empty), Puro.let7g.Cre (let-7g), and Puro.let7gsm.Cre (let-7g sm). All samples were probed on the same blot.