Cancer microenvironment is extremely hypoxic condition and the analysis of cell biology under hypoxia is significantly important. Previously we have shown that leukocyte common antigen related interacting protein (liprin)-α4 could be a new therapeutic target for pancreatic cancer. In the present study, the biological significance of liprin-α4 in small cell lung cancer (SCLC) which was one of the refractory cancers and less therapeutical options was investigated.
SCLC cell lines (SBC-3 and SBC-5) were used as target cells. Cells were cultured under normoxia (20%O2) and under hypoxia (1%O2). Gene inhibition was performed using small interfering RNA. Proliferation was performed by MTT assay. Invasion was estimated by matrigel invasion assay. Chemosensitivity was analyzed using CDDP and 5-FU. Mice xenograft experiments were performed using BALB/c nude mice. Twenty human SCLC specimens were used for immunofluorescent staining.
1) Expression of liprin-α4 increased under hypoxia compared to normoxia. 2) Liprin-α4 inhibition decreased proliferation in vitro under hypoxia. 3) Liprin-α4 suppression did not affect migration and invasion under hypoxia. 4) Tumor volume in mice injected with liprin-α4-inhibited SCLC cells was significantly lower than that in control mice. 5) Signaling from liprin-α4 was through MAPK signaling pathway. 6) Chemosensitivities of CDDP and 5-FU under hypoxia were significantly lower than those under normoxia. Liprin-α4 inhibition significantly enhanced chemosensitivity of CDDP under hypoxia. 7) HIF-1α regulated liprin-α4 expression in SCLC cells. 8) HIF-1α inhibition led to decreased proliferation under hypoxia. 9) HIF-1α inhibition significantly improved chemosensitivity of CDDP under hypoxia. 10) Liprin-α4 and HIF-1α expressions were observed in all patients examined in SCLC specimen.
These results suggest that liprin-α4 which is expressed more under hypoxia, plays a pivotal role for increased proliferation and decreased chemosensitivity under hypoxia for SCLC as a downstream mediator of HIF-1α. Inhibition of HIF-1α and Liprin-α4 could be a new therapeutic strategy for SCLC.
Clinical trial identification
Legal entity responsible for the study
Kyushu University Ethics Committee.
Has not received any funding.
All authors have declared no conflicts of interest.