Identification of protein modulation by the synthetic retinoid CD437 in lung carcinoma cells using high throughput immunoblotting

The novel synthetic retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) induces growth arrest and apoptosis in various tumor cell lines including non-small cell lung cancer (NSCLC) cells. CD437 binds retinoic acid receptor γ (RARγ) selectively, and can enhance receptor-dependent transcriptional activation of various genes. However, some of the effects of this retinoid on cell growth inhibition and apoptosis appear to be receptor-independent. To gain a better understanding of the mechanism by which CD437 exerts its effects, we employed a high throughput western blotting method (PowerBlot™) using 760 monoclonal antibodies to compare the levels of their target cellular signaling proteins in untreated and CD437-treated NSCLC H460 cells. CD437 (1 µM, 24 h) increased the levels of 70 proteins and decreased the levels of 28 proteins. These proteins play a role in fundamental cellular processes including: DNA synthesis and repair, transcription and DNA-binding, cell cycle, apoptosis, cytoskeleton assembly, cell adhesion, endocytosis, growth and signal transduction. Some proteins identified by this approach have been implicated previously in the effect of CD437 (e.g., p53, Bax, cyclin B, CDK2). Additionally we identified proteins that are novel candidates for mediating the cellular responses to CD437 (e.g., FAF1, Bid, caspase 8, cdk1, KAP, NDR, RBBP, 53BP2, Grb2, PLCγ1, p70s6k, PP2Cδ, PKBα/AKT, PDK1, and several DNA repair enzymes).