Somatostatin specifically binds p86 subunit of the autoantigen Ku

The heterodimer Ku, first described as a nuclear autoantigen, is a regulatory factor of DNA replication and transcription. We have expressed the p86 subunit of Ku in Escherichia coli as a fusion protein with glutathione-S-transferase, using the vector pGEX-2T. After splitting up by thrombin, p86 was isolated by Sephacryl S200 gel filtration. The recombinant protein was found to have the same electrophoretic migration and to react with the same monoclonal antibody as the somatostatin-binding protein we recently isolated from the human gastric tumor cell HGT1 [7]. Furthermore, using the analog [125I]Tyr-11 somatostatin-14 as a tracer, we found that, like the HGT1 cell-purified protein, recombinant p86 specifically bound somatostatin with high affinity (KD = 2.3 +/- 0.3 nM) and large capacity (10,300 +/- 1,700 pmol/mg protein). These findings suggest that p86 subunit of Ku stands for the protein we previously isolated from the HGT1 cell. It could represent a new somatostatin receptor subtype perhaps involved in the antimitogenic effect of this peptide.