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Human β-defensin 1 Functions as a Tumor Suppressor via ER Stress-triggered JNK pathway in Hepatocellular Carcinoma.

PURPOSE
Human β-defensin 1 (DEFB1) belongs to defensins family that contribute to innate immune responses and was recently found to downregulate a variety of cancers, including renal, prostatic, and oral squamous cell carcinoma, and therefore is considered as a potential tumor suppressor. However, the role of DEFB1 in hepatocellular carcinoma (HCC) still needs to be elucidated.


METHODS
Quantitative PCR and Western blot were used to measure the expression levels of interested proteins. CCK-8 and colony formation assays were performed to determine the ability of cell proliferation. Tumor formation experiments in nude mice were used to examine the tumor growth.


RESULTS
The expression level of DEFB1 was dramatically downregulated in human HCC. Quantitative PCR and Western blot results also showed a pronounced decrease of DEFB1 expression in the liver cancer cell lines. Rescuing the expression of DEFB1 in Huh7 cells effectively suppressed cell proliferation and reduced the colony forming ability, probably by inducing cell apoptosis and cell cycle arrest. Moreover, tumor formation experiments in nude mice also showed inhibition of tumor growth by DEFB1 expression in vivo. Furthermore, induction of DEFB1 expression induced degraded protein increase and endoplasmic reticulum (ER) stress, which subsequently activated JNK pathway. Pharmacologic inhibition of ER stress by 4-phenylbutyrate, a compound to alleviate ER stress, effectively eliminated DEFB1-induction inhibition of cell proliferation and migration.


CONCLUSION
DEFB1 functions as a tumor suppressor in HCC through activating ER stress and JNK pathway, which may provide a potential strategy for HCC treatment.