The KU70 gene is composed of 13 exons.

2156 bp mRNA.

The Ku70 protein is 609 amino acid long and its molecular weight is 69.8 kDa. It is composed of 3 domains: an amino (N) amino-terminal alpha/beta domain, a central beta-barrel domain and a helical C-terminal arm (Rivera-Calzada et al., 2007). The C-terminal region consists of a 5 kDa SAP domain (Ku70-SAP) which involved in DNA binding during NHEJ reaction.

Ku70 is ubiquitously expressed. Changes in Ku70 expression correlated to a pathological state.

Ku was originally reported to be a nuclear protein, consistent with its functions as a subunit of DNA-PK involved in DNA double strand breaks repair. However, several studies have revealed the cytoplasmic or cell surface localization of Ku proteins in various cell types (Prabhakar et al., 1990). Recently, it has been demonstrated that the shift from the nucleus to the cytoplasm of the Ku70/Ku80 proteins in tumor cells could represents a mechanism to inhibit cell death through the Ku70-Bax-sCLU interactions, giving rise to a new chemoresistant clone with a more aggressive phenotype.

Ku is a heterodimeric protein composed of two subunits with molecular weight of 70 and 86 kDa. Ku forms a complex with the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) to form the full DNA-dependent protein kinase, DNA-PK, consisting of 470 kDa and required for the non-homologous end joining (NHEJ) pathway of DNA repair. The Ku heterodimer binds the ends of various types of DNA discontinuity, and is involved in the repair of DNA breaks caused by an incorrect DNA replication, V(D)J recombination, physiological oxidations, ionizing irradiation, and some chemotherapeutic drug effects (Featherstone and Jackson, 1999). The principal role of Ku proteins is to take care of the homeostasis of the genome being involved in telomere maintenance, specific gene transcription, DNA replication, cell-cycle regulation and regulation of apoptosis induction. Ku70 has been shown to bind to the pro-apoptotic protein BAX in the cytoplasm in normal, undamaged cell. After DNA damage inducing DNA double-strand breaks repair (UV treatment, ionizing radiation, etc.) Ku70 allows the translocation of Bax to the mitochondria leading to the release of death-promoting factors, such as cytochrome c, in the cytoplasmic compartment. In normal cells, after an irreversible cell damage, nCLU cooperates with Ku70 to induce apoptotic death, activating the translocation of Bax to mitochondria whereas the sCLU protein stabilizes the Ku70-Bax interaction in the cytoplasm acting as cytoprotectant. The Ku70-Bax-sCLU interaction in the cytoplasm seems to play an important role in cell survival pathways and in cell death escape, that in pathological condition could lead to the survival of the aberrant cell clone. Overall, the dynamic interactions among CLU, Ku70, and Bax seems to have an important role in both tumor insurgence and its progression (Pucci et al., 2009a; Pucci et al., 2009b).