Background and purpose: miR-122 is abnormally expressed in various tumors and involved in tumor cell proliferation and apoptosis

while cAMP response element-binding protein 1 (CREB1) is involved in esophageal cancer development. This study aimed to investigate the effect of miR-122-5p on proliferation of esophageal cancer cells and xenografts by targeting CREB1 and its mechanism. Methods: Forty-three specimens of esophageal cancer and corresponding adjacent normal tissues (3-5 cm from the edge of cancer) were collected after tumor resection in Quanzhou First Hospital Affiliated to Fujian Medical University from November 2017 to November 2019. The expressions of miR-122-5p mRNA and CREB1 mRNA in esophageal cancer tissues and cells were detected by real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR). Cells were divided into control group

miR-NC group

pc-NC group

miR-122-5p mimic group

pc-CREB1 group and miR-122-5p mimic+pc-CREB1 group. The miR-NC

pc-NC

miR-122-5p mimic and pc-CREB1 plasmids were transfected into EC109 cells separately or jointly using Lipofectamine

TM

2000. The targeting relationship was verified by the dual-luciferase reporter assay. The cell proliferation was detected by MTT assay. Cell growth ability was tested by cloning formation experiment. The rate of apoptosis was detected by flow cytometry. The Ki-67 labelling index

proliferating cell nuclear antigen (PCNA)

activated caspase-3

Bax

Bcl-2 and CREB1 were detected by Western blot. All nude mice were divided into four groups: control group

miR-122-5p mimic group

pc-CREB1 group

miR-122-5p mimic+pc-CREB1 group. Transfected EC109 cells were injected subcutaneously in the left armpit of nude mice. After 30 days

the nude mice were sacrificed

the subcutaneous tumors were completely removed

and the volume and weight of the transplanted tumors were measured. The Ki-67 labelling index and caspase-3 were detected by immunohistochemistry. Results: miR-122-5p was expressed at a low level in esophageal cancer tissues and cells

while CREB1 was highly expressed in esophageal cancer tissues and cells (both P0.01). miR-122-5p targeted down-regulation of CREB1 was observed. Compared with the control group

the number of esophageal cancer cell clones in the miR-122-5p group decreased

PCNA and Ki-67 labelling index were down- regulated

the apoptotic rate increased

activated caspase-3 and Bax protein expressions were up-regulated

Bcl-2 protein expression was down-regulated

the volume and weight of esophageal cancer EC109 transplanted tumor decreased

the ratio of Ki-67 positive cells increased

and the ratio of caspase-3 positive cells decreased (all P0.01). Overexpression of CREB1 reversed the effects of miR-122-5p on proliferation and apoptosis of esophageal cancer cells and transplanted tumors. Conclusion: miR-122-5p can inhibit the proliferation of esophageal cancer cells and induce apoptosis by targeted down-regulation of CREB1

thereby inhibiting the growth of esophageal cancer cells and transplanted tumors.