GULP1 as a Downstream Effector of the Estrogen Receptor-β Modulates Cisplatin Sensitivity in Bladder Cancer

Precise molecular mechanisms underlying resistance to cisplatin-based chemotherapy remain unclear, while the activity of estrogen receptor-β (ERβ) has been suggested to be associated with chemosensitivity in urothelial cancer. We aimed to determine if GULP1, an adapter protein known to facilitate phagocytosis, could represent a downstream effector of ERβ and thereby modulate cisplatin sensitivity in bladder cancer.

GULP1 expression and cisplatin cytotoxicity were compared in bladder cancer lines. Immunohistochemistry was used to determine the expression of GULP1 and ERβ in two sets of tissue microarray (TMA) consisting of transurethral resection specimens.

The levels of GULP1 expression were considerably higher in ERβ-knockdown sublines than in the respective control ERβ-positive sublines. Estradiol treatment reduced GULP1 expression in ERα-negative/ERβ-positive lines, which was restored by the anti-estrogen tamoxifen. Chromatin immunoprecipitation assay revealed the binding of ERβ to the GULP1 promoter in bladder cancer cells. Moreover, GULP1 knockdown sublines were significantly more resistant to cisplatin treatment, but not to other chemotherapeutic agents, including gemcitabine, methotrexate, vinblastine, and doxorubicin. In the first set of TMA (n=129), the expression of ERβ and GULP1 was inversely correlated (p=0.023), and ERβ(-)/GULP1(+) in 51 muscle-invasive tumors was associated with significantly lower risk of disease progression and cancer-specific mortality. Similarly, in the second set (n=43), patients with ERβ(-)/GULP1(+) muscle-invasive disease were significantly (p=0.021) more likely to be responders to cisplatin-based neoadjuvant chemotherapy before radical cystectomy.

ERβ activation was found to reduce the expression of GULP1 as a direct downstream target in bladder cancer cells, resulting in the induction of cisplatin resistance.