Tumorigenesis and Augmented Chemosensitivity Caused by Aberrant Expression of the Components in the Mammalian TREX-2 Complex

DNA is frequently damaged by genotoxic stresses such as ionizing radiation, reactive oxygen species, and nitrogen species. DNA damage is a key contributor to cancer initiation and progression, and thus the precise and timely repair of these harmful lesions is required. Recent studies revealed transcription as a source of genome instability, and transcription-coupled DNA damage has been a focus in cancer research. Impaired mRNA export is closely related to DNA damage through R-loop formation. The molecular machineries of transcription-coupled DNA damage have been extensively analyzed in Saccharomyces cerevisiae. However, the molecular basis of these phenomena in higher eukaryotes remains elusive. In this review, we focus on the relationship between deregulated mRNA export, especially through the transcription-export-2 (TREX-2) complex, and cancer development. The expression of GANP, a key molecule in the TREX-2 complex, is highly associated with tumorigenesis in mouse and human. Additionally, we describe recent evidence for medical application that downregulation of the other components may be a good candidate for chemotherapeutic target in terms of reducing the side effects, although the involvement of R-loop is still ambiguous.