In prostate cancer, HSPA9 maintains the protein stability of sine oculis homeobox 1 (SIX1), a developmental transcriptional regulator frequently overexpressed in human cancers, by inhibiting its polyubiquitination and degradation through recruiting the deubiquitinating enzyme ubiquitin-specific protease 1 (USP1). This evidence concerns the gene USP1 and Familial prostate cancer.