e13552 Background: Identification of cancer-specific oncoproteins is an effective approach to develop new diagnostics and therapeutics. Methods: We have established a strategy as follows to identify new oncoproteins, which can be applied as biomarkers and drug development; i) To identify genes overexpressed in 120 clinical lung cancers using the cDNA microarray representing 27,648 genes, ii) To verify the genes for their low expression in 23 normal tissues by northern-blotting, iii) To validate the clinicopathological significance of their protein expression by tissue microarray covering 262 cases of non-small cell lung cancers (NSCLCs), iv) To verify whether they are essential for the growth of cancer cells by siRNAs, v) To do immunoprecipitation assays and mass-spectrometric analysis to identify their interacting proteins in cancer cells, and screening of cell-permeable peptides that could inhibit the protein-protein interaction that is essential for carcinogenesis. Results: We identified 35 oncoproteins to be upregulated in the majority of lung cancers, and further selected CDCA5 (cell division cycle associated 5) as a good candidate. Tumor tissue microarray analysis of 262 NSCLC patients revealed that CDCA5 positivity was an independent prognostic factor. Suppression of CDCA5 expression with siRNAs inhibited the growth of lung cancer cells; concordantly, induction of exogenous expression of CDCA5 conferred growth-promoting activity in mammalian cells. We also found that extracellular signal-regulated kinase (ERK) kinase interacted with and phosphorylated CDCA5 at Serine 209 in vivo. Functional inhibition of the interaction between CDCA5 and ERK kinase by a cell-permeable peptide corresponding to a 20-amino-acid sequence part of CDCA5, which included the Serine 209 phosphorylation site by ERK, significantly reduced phosphorylation of CDCA5 and resulted in growth suppression of lung cancer cells. Conclusions: CDCA5 positivity should be useful as a novel prognostic biomarker in the clinic. Selective suppression of the ERK-CDCA5 pathway by cell-permeable peptide or small molecule-based drugs could be a promising strategy for cancer therapy.
A High-Throughput Small Molecule Screen Identifies Ouabain as Synergistic with miR-34a in Killing Lung Cancer Cells