Inhibition of retinoblastoma tumor suppressor activity by RNA interference in lung cancer lines.

Background: Inactivation of retinoblastoma (RB) tumor suppressor function occurs frequently in lung cancer. Short-hairpin RNA can be constructed to target specific sequences and efficiently knock down protein expression. We developed a short-hairpin RNA approach to specifically target Rb in lung cancer cells to determine the influence of RB knockdown on proliferation.
Methods: NCI-H520 human lung cancer cells (wild-type Rb) were transfected with pMSCVpuro-Rb3C, a plasmid containing a short-hairpin sequence targeted to human Rb. Transfectants harboring the construct were selected with puromycin. Loss of RB expression in selected cell populations was determined by immunoblotting. Proliferating cells were counted to establish growth rates. Retinoblastoma-proficient and RB-deficient tumor growth was monitored in nude mice.
Results: Transfection with pMSCVpuro-Rb3C dramatically diminished RB expression and led to aberrant expression of RB-regulated genes. Cells harboring pMSCVpuro-Rb3C grew at an increased rate compared with control cells: 480.6 +/- 37.7 versus 159.4 +/- 36.2 (relative cell count at 12 days). Tumor growth in nude mice also increased with RB knockdown compared with control mice: 135.2 +/- 73.6 mm3 versus 40.0 +/- 17.0 mm3 (tumor volume at 10 days).
Conclusions: Inhibition of RB expression is efficiently achieved in lung cancer cells with short-hairpin RNA. Genetic targets of RB are deregulated with RB knockdown. Retinoblastoma depletion increases growth in vitro and in murine xenografts. These studies indicate that even in the context of an established tumor cell line, RB limits tumorigenic proliferation. Additionally, this model will serve as an ideal system to evaluate the role of RB activity on therapeutic response.