Interruption of RNA processing machinery by a small compound, 1-[(4-chlorophenyl)methyl]-1 H-indole-3-carboxaldehyde (oncrasin-1)

Abstract

Protein kinase Cι (PKCι) is activated by oncogenic Ras proteins and is required for K-Ras-induced transformation and colonic carcinogenesis in vivo. However, the role of PKCι in signal transduction and oncogenesis is not clear.We recently identified a small molecule, designated 1-[(4-chlorophenyl)methyl]-1 H-indole-3-carboxaldehyde (oncrasin-1), that can selectively kill K-Ras mutant cancer cells and induce abnormal nuclear aggregation of PKCι in sensitive cells but not in resistant cells.To determine the causes and biological consequences of PKCι aggregates in the nucleus, we analyzed the effect of oncrasin-1 on proteins involved in DNA repair and RNA processing.Our results showed that oncrasin-1 treatment led to coaggregation of PKCι and splicing factors into megaspliceo-somes but had no obvious effects on the DNA repair molecule Rad51.Moreover, oncrasin-1 treatment suppressed the phosphorylation of the largest subunit of RNA polymerase II and the expression of intronless reporter genes in sensitive cells but not in resistant cells, suggesting that suppression of RNA transcription is a major effect of oncrasin-1 treatment.Studies with cultured cells or with recombinant proteins showed that oncrasin-1 can disrupt the interaction of PKCι and cyclin- dependent protein kinase 9/cyclin T1 complex, which is known to phosphorylate the largest subunit of RNA polymerase II and is required for RNA transcription. Together, our results suggest that oncrasin-1 suppresses the function of RNA processing machinery and that PKCι might be involved in the biological function of RNA processing complexes. Copyright © 2009 American Association for Cancer Research.