The interaction between androgen receptor and semenogelin I: a synthetic LxxLL peptide antagonist inhibits the growth of prostate cancer cells

BACKGROUND: We previously demonstrated that a seminal plasma protein, semenogelin I (SgI), functioned as an androgen receptor (AR) coactivator. Meanwhile, several short sequence motifs in AR coregulators, such as LxxLL (L=leucine), have been shown to mediate specific interactions with AR. METHODS: We investigated the role of the LxxLL motif within SgI in the interactions with AR and cell growth in prostate cancer lines in vitro. RESULTS: A full-length SgI with mutations in the motif (i.e., LxxAA; A=alanine) failed to significantly increase cell proliferation/migration as well as androgen-mediated AR transcription. Co-immunoprecipitation showed no physical interactions between AR and the mutant SgI. In addition, transfection of an 18-amino acid peptide of SgI containing LxxLL, but not LxxAA, resulted in considerable reduction in cell growth and prostate-specific antigen expression in LNCaP and C4-2 lines. CONCLUSIONS: The LxxLL motif of SgI could be a novel therapeutic target for both androgen-sensitive and castration-resistant prostate cancers.