Novel glycoprotein SBSPON suppressed bladder cancer through the AKT signal pathway by inhibiting HSPA5 membrane translocation.

Bladder cancer poses severe threats to human health due to its aggressive nature and resistance to drug treatment; however, the underlying mechanisms have not been fully investigated. In the present study, we identify SBSPON (Somatomedin B and Thrombospondin Type 1 Domain Containing) as a novel tumor suppressor. The expression of SBSPON was downregulated in bladder cancer and correlated with poor overall survival. SBSPON suppressed the proliferation and migration ability of bladder cancer cells in vitro, and inhibited tumor growth of bladder cancer cells in vivo. Genetic ablation of Sbspon in mice significantly accelerated the progression of N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) induced bladder cancer. Mechanistically, SBSPON is a novel HSPA5 binding glycoprotein. SBSPON functioned through binding to HSPA5 and inhibiting its membrane translocation, resulting in an inactivated AKT signaling pathway. More importantly, SBSPON inhibited the cisplatin resistance of bladder cancer cells by reducing the inhibitory effect of HSPA5 on apoptosis. In summary, the novel glycoprotein SBSPON functions as a tumor suppressor and inhibits resistance to cisplatin in bladder cancer. This may provide novel therapeutic strategies for bladder cancer treatment.