Identification of BXDC2 as a Key Downstream Effector of the Androgen Receptor in Modulating Cisplatin Sensitivity in Bladder Cancer

Abstract

Underlying mechanisms for resistance to cisplatin-based chemotherapy in bladder cancer patients are largely unknown, although androgen receptor (AR) activity, as well as extracellular signal-regulated kinase (ERK) signaling, has been indicated to correlate with chemosensitivity. We also previously showed ERK activation by androgen treatment in AR-positive bladder cancer cells. Because our DNA microarray analysis in control vs. AR-knockdown bladder cancer lines identified BXDC2 as a potential downstream target of AR, we herein assessed its functional role in cisplatin sensitivity, using bladder cancer lines and surgical specimens. BXDC2 protein expression was considerably downregulated in AR-positive or cisplatin-resistant cells. BXDC2-knockdown sublines were significantly more resistant to cisplatin, compared with respective controls. Without cisplatin treatment, BXDC2-knockdown resulted in significant increases/decreases in cell proliferation/apoptosis, respectively. An ERK activator was also found to reduce BXDC2 expression. Immunohistochemistry showed downregulation of BXDC2 expression in tumor (vs. non-neoplastic urothelium), higher grade/stage tumor (vs. lower grade/stage), and AR-positive tumor (vs. AR-negative). Patients with BXDC2-positive/AR-negative muscle-invasive bladder cancer had a significantly lower risk of disease-specific mortality, compared to those with a BXDC2-negative/AR-positive tumor. Additionally, in those undergoing cisplatin-based chemotherapy, BXDC2 positivity alone (p = 0.083) or together with AR negativity (p = 0.047) was associated with favorable response. We identified BXDC2 as a key molecule in enhancing cisplatin sensitivity. AR-ERK activation may thus be associated with chemoresistance via downregulating BXDC2 expression in bladder cancer.

Androgen Receptor Signaling Induces Cisplatin Resistance via Down-Regulating GULP1 Expression in Bladder Cancer

“…Although resistance to CDDP-based chemotherapy is not uncommonly seen in patients with urothelial cancer, its underlying mechanisms are not fully understood. Meanwhile, AR activation in bladder cancer cells has been implicated to be associated with chemoresistance [ 12 , 13 , 14 , 15 , 21 , 22 , 23 , 24 ]. In the present study, we further investigated the role of GULP1, as a downstream target of AR, in CDDP resistance, using bladder cancer cell lines as well as surgical specimens.…”

“…In particular, it has been documented that GULP1 activates SMAD3 [ 27 ] or inactivates AKT/PDK1 and MAPK [ 28 ] in ovarian cancer cells, while it inhibits the nuclear translocation of NRF2 and subsequently reduces the expression of HMOX1 in bladder cancer cells [ 29 ]. Interestingly, all of these potentially downstream of GULP1 have been linked to CDDP resistance [ 10 , 24 , 32 , 33 , 34 , 35 ]. Further studies are required for elucidating the molecular mechanisms responsible for AR/GULP1-mediated chemoresistance.…”

“…Immunohistochemical staining was performed on the 5 µm sections using a primary antibody to GULP1 (dilution 1:50), as we described previously [ 9 , 13 , 24 ]. All stains were manually quantified by a single pathologist (H.M.) who was blinded to sample identity.…”

Sex Hormone Receptor Signaling in Bladder Cancer: A Potential Target for Enhancing the Efficacy of Conventional Non-Surgical Therapy

“…Immunohistochemistry in surgical specimens form patients subsequently undergoing cisplatin-based neoadjuvant chemotherapy, phospho-ELK1 positivity was significantly ( p = 0.039) higher in those from non-responders (71%) than in those from responders (38%) [ 68 ]. We recently demonstrated that androgen/AR could down-regulate the expression of BXDC2, also named BRIX1, which involves ribosome biogenesis, in bladder cancer cells, and loss of BXDC2 in cell lines and surgical specimens was associated with cisplatin resistance [ 79 ]. Furthermore, an ERK activator reduced BXDC2 expression in bladder cancer cells, while BXDC2 knockdown failed to affect phospho-ERK expression [ 79 ], suggesting cisplatin resistance via the AR → ERK → BXDC2 signaling pathway.…”

Gender Differences in Urothelial Bladder Cancer. Effects of Natural Killer Lymphocyte Immunity

“…In a complementary fashion, AR blocking drugs increased cisplatin sensitivity [76,77]. Among the mechanisms responsible, Miamoto's group [78] found that androgens reduced expression of an RNA-and ribosome-processing protein, BRIX1 (BXDC2) in UBC cell lines. Furthermore, AR and BRIX1 showed complementary expression patterns in UBC tissue sections [78].…”