Published online Dec 15, 2022. doi: 10.4251/wjgo.v14.i12.2340
Peer-review started: August 11, 2022
First decision: October 5, 2022
Revised: October 17, 2022
Accepted: November 16, 2022
Article in press: November 16, 2022
Published online: December 15, 2022
Processing time: 123 Days and 2.8 Hours
Esophageal squamous cell carcinoma (ESCC), the predominant type of esophageal cancer, has a 5-year survival rate less than 20%. Although the cause of poor prognosis is the high incidence and mortality of ESCC, the high rate of metastasis after esophageal cancer surgery is the main cause of death after the surgery. Bromodomain-containing protein 4 (BRD4), an epigenetic reader of chromatin-acetylated histones in tumorigenesis and development, plays an essential role in regulating oncogene expression. BRD4 inhibition and BRD4 inhibition-based treatment can potentially suppress ESCC growth. However, the effects and mechanisms of action of BRD4 on ESCC cell migration remain unclear.
To explore the effect of BRD4 on cell migration of ESCC in vitro and its possible molecular mechanism.
Human ESCC cell lines KYSE-450 and KYSE-150 were used. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay was performed to examine cell proliferation, and the transwell migration assay was conducted to test ESCC cell migration. JQ1, a BRD4 inhibitor, was applied to cells, and BRD4 siRNA was transfected into ESCC cells to knockdown endogenous BRD4. GFP-RFP-LC3 adenovirus was infected into ESCC cells to evaluate the effect of JQ1 on autophagy. Western blotting was performed to determine the protein levels of BRD4, E-cadherin, vimentin, AMP-activated protein kinase (AMPK), and p-AMPK.
BRD4 was either downregulated by small interfering RNA or pretreated with JQ1 in ESCC cells, leading to increased tumor migration in ESCC cells in a dose- and time-dependent manner. Inhibition of BRD4 not only significantly suppressed cell proliferation but also strongly increased cell migration by inducing epithelial-mesenchymal transition (EMT). The protein expression of vimentin was increased and E-cadherin decreased in a dose-dependent manner, subsequently promoting autophagy in KYSE-450 and KYSE-150 cells. Pretreatment with JQ1, a BRD4 inhibitor, inhibited BRD4-induced LC3-II activation and upregulated AMPK phosphorylation in a dose-dependent manner. Additionally, an increased number of autophagosomes and autolysosomes were observed in JQ1-treated ESCC cells. The autophagy inhibitor 3-methyladenine (3-MA) reversed the effects of BRD4 knockdown on ESCC cell migration and blocked JQ1-induced cell migration. 3-MA also downregulated the expression of vimentin and upregulation E-cadherin.
BRD4 inhibition enhances cell migration by inducing EMT and autophagy in ESCC cells via the AMPK-modified pathway. Thus, the facilitating role on ESCC cell migration should be considered for BRD4 inhibitor clinical application to ESCC patients.
Core Tip: It has been demonstrated that bromodomain-containing protein 4 (BRD4) as a transcriptional regulator promotes tumor development. Thus, targeting of BRD4 has recently emerged as a promising anti-cancer therapeutic strategy. We present here that BRD4 inhibition suppresses esophageal squamous cell carcinoma (ESCC) cell proliferation, but promotes ESCC cell migration by induction of autophagy, which further facilities epithelial-mesenchymal transition process. Our study implies that the migration-promoting effect should be carefully considered when clinical targeting BRD4 as anti-cancer approach and combination with autophagy inhibitor might be a new therapeutic strategy to avoid the deleterious role of BRD4-targeted strategies.