Background: It has been reported that ubiquitin specific peptidase 4
(USP4) was functional in several tumors, but its function and mechanism in
gastric cancer were still unknown. Methods: Bioinformatic tools were
used to predict the prognosis of gastric cancer patients and the expression
levels of USP4 in gastric cancer. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunoblotting were carried out to
detect the messenger RNA (mRNA) and protein levels. Cell viability of gastric cancer was
evaluated by Cell Counting Kit-8 (CCK-8) assay. Cell line-derived xenograft models were established to
evaluate the tumor growth of gastric cancer. Luciferase assay and immunoblotting
were used to determine the activation of nuclear factor kappa B (NF-B) signaling.
Results: The public database Kaplan-Meier Plotter showed that gastric
cancer patients with high USP4 expression had a shorter overall survival or
post-progression survival than the patients with decreased USP4. Further studies
indicated that USP4 was elevated in gastric cancer tumor tissues. In contrast,
knockdown of USP4 markedly inhibited gastric cancer cell growth, and suppressed
the tumor growth of gastric cancer. Further studies revealed that USP4 knockdown
significantly suppressed NF-B-driven luciferase activity, and inhibited
the phosphorylation of NF-B p65 in gastric cancer cells. Additionally,
qRT-PCR analysis showed that USP4 knockdown significantly downregulated the
expressions of cyclin D2 (CCND2) and B cell leukemia/lymphoma 2 (BCL2). We also found that USP4 knockdown decreased the
expressions of phosphatase of regenerating liver-3 (PRL-3), in contrast, overexpression of PRL-3 attenuated the
inhibitory effects of USP4 knockdown on NF-B signaling and cell
viability in gastric cancer cells. Finally, PR-619, which has been proven to
inhibit the activities of USP4 and other deubiquitinases, could inhibit cell
viability and NF-B signaling in gastric cancer cells.
Conclusions: This study indicated that elevated USP4 predicted a poor
index for gastric cancer patients, and mediated gastric cancer cell growth by
regulating PRL-3/NF-B signaling, which suggested USP4 may be a novel
therapeutic target for gastric cancer.