Fig. 7: SPOP-ELK3 axis regulates docetaxel-induced cell death.

a Inverse correlation of ELK3 and phospho-CHK1/2 protein levels under docetaxel treatment. The cell lysates of 22Rv1 cells treated with docetaxel (300 nM) for an indicated time were used to evaluate the indicated protein levels by WB. b Rescue of docetaxel-mediated decreased ELK3 protein level by MG132 treatment. The 22Rv1 cell lysates treated with docetaxel (300 nM) in the presence or absence of MG132 (10 μM) were used to evaluate ELK3 protein levels by WB. c Docetaxel-mediated decreased ELK3 protein is rescued by SPOP knockdown. The cell lysates of 22Rv1 cells stably expressing sh-SPOP and treated with docetaxel (300 nM) were used to evaluate ELK3 protein level by WB. d Docetaxel induces SPOP and ELK3 interaction. The cell lysates of HEK293T cells transfected with indicated plasmids and treated with docetaxel (300 nM) were used to evaluate the SPOP and ELK3 interaction by IP and WB. e Docetaxel induces ELK3 ubiquitination. The cell lysates of HEK293T cells transfected with indicated plasmids and treated with docetaxel (300 nM) were used to evaluate ELK3 ubiquitination by IP and WB. f Diminished interaction between SPOP and ELK3 increases PCa cell survivability. 22Rv1 cells stably expressing SPOP-WT or each of SPOP mutants treated with docetaxel (1 μM) for 48 h were used to cell survivability by CCK-8 assay. g SPOP and ELK3 double knockdown inhibits cell survivability by docetaxel in SPOP knockdown cells. 22Rv1 cells stably expressing sh-SPOP and/or sh-ELK3 treated with docetaxel (1 μM) for 48 h were used to evaluate cell survivability by CCK-8 assay. h SPOP and ELK3 double knockdown enhances apoptosis signaling by docetaxel. The cell lysates of 22Rv1 cells stably expressing sh-SPOP and/or sh-ELK3 treated with docetaxel (300 nM) were used to evaluate the protein levels of apoptosis-related signaling molecules by WB. i, j The SPOP-ELK3 axis plays a critical role in docetaxel-induced cell death. The cell lysates of 22Rv1 cells stably expressing sh-SPOP and/or SPOP were used to evaluate the protein levels of ELK3 and SPOP by WB (i), and to assess cell viability using the CCK-8 assay (j). k Increased ELK3 protein levels in PCa cancer tissues. IHC images of ELK3 in prostate cancer tissues (n = 117) stained by DAB staining were analyzed by TissueFAXS system. Data, DAB intensity in normal vs. cancer tissues; Significance was obtained by Anova t test. l Increased ELK3 protein levels in PCa patient harboring SPOP-F133V mutation. Representative IHC image of ELK3 protein levels by DAB staining in prostate cancer tissues harboring SPOP-WT or SPOP-F133V. f, g Data, three independent experiments; Significance, *p < 0.05 obtained by Student t test.