The number of glutamines in the N-terminal of the canine androgen receptor affects signalling intensities

Most male dogs are castrated at young ages, making them easy to rear following androgen deprivation. Although the incidence of canine prostate cancer is low, several patients have resistance to androgen therapy and poor clinical prognosis. These outcomes are similar to those of end-stage human androgen-independent prostate cancer. The androgen receptor (AR) of canines has two polyglutamine (polyQ) sequences (Q × 10 and Q × 23) at its N-terminal. The length of polyQ may be a risk factor for the development of prostate cancer in dogs; however, there is no evidence to support this. Hence, we artificially created polyQ deletion mutants of canine AR and evaluated their effects on AR signalling. The deletions of Q × 10 and Q × 23 were associated with significant reductions in AR signalling intensities. The Q × 10 mutants, which increase or decrease Q sequentially, also altered AR signalling. Furthermore, the Q × 10 deletion mutant, compared with the Q × 10 control, altered the intensities of the binding of polyQ to the C-terminal of AR, which contains a ligand-binding domain; this was not observed with the Q × 9, 11, and 12 variants. The number of glutamines in the N-terminals of canine ARs may influence AR signalling intensities and contribute to the risk of prostate cancer in dogs.