Objective      To analyze the expression of leucine zipper/EF-hand-containing transmembrane protein 1 (LETM1) in the human hepatocellular carcinoma (HCC) and to determine the effect of RNA interference targeted to silence LETM1 gene on the proliferation and apoptosis of HCC cell line SMMC-7721.    Methods      Immunohistochemical assay and Western blotting were used to analyze the expression level of LETM1 protein in HCC tissues and paraneoplastic tissues from 60 HCC patients who admitted in our department from September 2012 to April 2013. The relationship between LETM1 expression and clinical pathological parameters was studied. Western blotting was also used to analyze the expression of LETM1 protein in SMMC-7721

HepG2 and normal liver LO2 cells. RNA interference targeted to silence LETM gene was transfected into the SMMC-7721 cells with Lipofectamine 2000 (representing the control group si-NC and the experimental group si-LETM1 ). Quantitative realtime PCR (qRT-PCR) and Western blotting were used to detect the mRNA and protein levels of LETM1 in the silenced cells. The proliferation and apoptosis of the transfected cells were assessed by CCK-8 assay and flow cytometry.    Results        Immunohistochemical assay indicated that LETM1 protein was expressed in 73.33% HCC tissues(44/60)

significantly higher than that of paraneoplastic tissues (28.33%

17/60

P0.01). The results showed that the expression at protein level was also higher in the HCC tissues than the paraneoplastic tissues (2.335±0.220 vs 1.386±0.080

P0.01). The expression of LETM1 protein was correlated with tumor size and portal vein invasion (P0.05)

but not with gender

age

alpha fetoprotein

HBsAg

Edmondson grade and TNM stage (P0.05). The expression level of LETM1 protein was significantly higher in the SMMC-7721 (1.447±0.149) and HepG2 cells (1.190±0.113) than the LO2 cells (0.918±0.027

P0.05). Compared with si-NC group and blank group

the cell proliferation was inhibited significantly in si-LETM1 treated cells (P0.01)

especially at 72 and 96 h. The early apoptosis of si-LETM1 transfected cells had a significant increase when compared with siNC treated cells [(14.6±2.3)% vs (6.3±0.7)%

P=0.04].     Conclusion           The protein expression of LETM1 is significantly higher in HCC tissues than the paraneoplastic tissues. RNAi of LETM1 may inhibit cells proliferation and induce apoptosis in the SMMC-7721 cells.