CBX4 contributes to radioresistance by regulating autophagic activity in esophageal squamous cell carcinoma

Background: The function of Chromobox 4 (CBX4) function has attracted attention in many cancer types due to its unique biological role; however, its mechanism in esophageal squamous cell carcinoma (ESCC) under radiotherapeutic treatment has not yet been investigated.

Methods: Silencing of CBX4 was carried out in TE-13 and KYSE-150 cell lines. Cell proliferation, radiosensitivity, DNA damage, apoptosis, and cell cycle distribution were determined by Cell Counting Kit-8 (CCK-8), colony formation assay, immunofluorescence, flow cytometry, and immunoblot in vitro. In vivo xenograft models were also used to assess tumor cell growth and radioresistance. The underpinning mechanisms were explored based on pathway analysis and confirmed by rescue experiments, detecting cellular autophagy.

Results: Knockdown of CBX4 resulted in reduced tumor growth and enhanced radio-response in vivo and in vitro. Down-regulating CBX4 increased DNA damage, apoptotic rate, and G2/M arrest induced by radiation in ESCC cell lines. Gene Set Enrichment Analysis (GSEA) revealed that CBX4 was associated with cellular autophagy regulation. Enhanced radiosensitivity in ESCC cells silenced for CBX4 was partially blocked by autophagy inhibition (P<0.05). Beclin 1 was upregulated at the gene and protein levels in ESCC cells with CBX4 knockdown after irradiation, and overexpressing Beclin 1 reversed the radiosensitivity of ESCC cells with CBX4 knockdown (P<0.05).

Conclusions: By regulating autophagic activity, CBX4 contributes to radioresistance. Targeting CBX4 might constitute an efficient approach for increasing radiosensitivity in ESCC.