Histone deacetylase inhibitor induced pVHL-independent degradation of HIF-1α and hierarchical quality control of pVHL via chaperone system.

The mortality rate of ovarian cancer is increasing and the role of hypoxia inducible factor-1α (HIF-1α) in tumor progression has been confirmed. von Hippel-Lindau tumor suppressor protein (pVHL) binds HIF-1α and mediates proteasome degradation of HIF-1α. Besides, histone deacetylase inhibitor (HDACi) mitigates tumor growth via targeting HIF-1α, whereas underlying mechanism still requires investigation. In this research, we exposed ovarian cancer cell lines OV-90 and SKOV-3 to escalating concentrations of HDACi LBH589. As a result, cell viability was significantly suppressed and expression of HIF-1α was remarkably reduced along with decreased levels of signal molecules, including phosphoinositide 3-kinase (PI3K) and glycogen synthase kinase 3ß (GSK3ß) (P = 0.000). Interestingly, pVHL was expressed in a notably declining tendency (P = 0.000). Chaperone heat shock protein-70 (HSP70) was expressed in an ascending manner, whereas expression of chaperonin TCP-1α was reduced clearly (P = 0.000). Besides, co-inhibition of pVHL plus HDAC did not contribute to a remarkable difference in HIF-1α expression as compared with single HDAC inhibition. Furthermore, both cell lines were transfected with plasmids of VHL plus VHL binding protein-1 (VBP-1). Consequently, the expression of HIF-1α as well as lactate dehydrogenase-A (LDHA) was remarkably decreased (P = 0.000). These findings indicate HDACi may repress expression of HIF-1α via inhibiting PI3K and GSK3ß and promote degradation of HIF-1α via HSP70, independent of pVHL. Additionally, a sophisticated network of HDAC and chaperones may involve in pVHL quality control.

Landscape of PD-1/PD-L1 Regulation and Targeted Immunotherapy.

Programmed cell death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) is a significant immune checkpoint, and the dysfunction of this axis contributes to tumor metastasis and immune escape. PI3K/Akt/mTOR and MAPK signal network induces PD-1/PD-L1 expression and facilitates tumor progression. Transcriptional factors such as hypoxia induced factors, PTEN, p53, CDK5, BRD4, STAT modulate PD-1/PD-L1 expression. PD-1/PD-L1 level is also regulated via epigenetic and post-translational manner. The underlying mechanisms mentioned above may provide potential targets for tumor treatment. At present, the combination therapy of PD-1/PD-L1 monoclonal antibodies plus small molecular inhibitors has achieved good outcomes in tumor treatment.