Expression Of Gadd45γ In HCC And The Related Signal Transduction Pathways In Gadd45γ-induced Growth Suppression Of Hepatoma Cells

Primary hepatoma is the most common and lethal cancer around theworld which is very harmful to human health. In china, it is the secondmost frequent cancer. Hepatocellular carcinoma (HCC) is the mostcommon histological type among primary hepatoma. The identification ofthe abnormal gene expression profile in HCC will help us to clarify themechanisms of tumorigenesis and development of HCC and develop newtargets for prevention, diagnosis and therapy.Recently it was documented that Gadd45γcould induce cell cycleG2-M arrest in hepatoma HepG2 cell lines. Nevertheless, up to now themolecular mechanisms of HCC is still unclear. In this study, we describedthe expression of Gadd45γin HCC and the related signal transductionpathways that mediated cell cycle G2-M arrest by Gadd45γin HepG2cells.PartⅠGadd45γexepression in HCC and influence of UV onGadd45γin hepatoma cells Objective: To detect the protein expression of Gadd45γin HCC tissuesand observe the response of Gadd45γafter exposuring to UVB in HepG2cells.Methods: 30 cases of HCC were detected by immunohistochemistry.Then the stress response of Gadd45γwas observed in HepG2 cells at 1h,2h and 4h post-exposure with UVB. The mRNA and protein levels ofGadd45γwere assayed by RT-PCR and Western blot. HepG2 cellswithout exposure with UVB were set as the control group.Results:(1)The level of Gadd45γprotein was significantly decreased in 30 casesof HCC tumour tissues when compared with that of surroundingnon-neoplastic liver tissues. Gadd45γprotein expression was absent in 17cases of HCC tumour tissues and the rate of absence was nearly 57%.(2)The levels of Gadd45γmRNA and protein from HepG2 cells post-exposure with UVB increased and reached peak levels at 1h(0.91±0.24and 0.55±0.14 respectively), then down-regulated. There was a dramaticdifference in Gadd45γmRNA level at 4h (compared with that of controlgroup).Conclusions: Gadd45γprotein expression in HCC tumour tissues wasobviously lower than that of non-neoplastic liver tissues and UVB couldrapidly induce the expression of Gadd45γin HepG2 cells.PartⅡRelated signal transduction pathways in Gadd45γ-inducedcell cycle G2-M arrest in hepatoma cells Objective: To explore the related signal transduction pathways inGadd45γ-induced cell cycle G2-M arrest in HepG2 cells and provide theprimary indications of growth inhibition in hepatoma.Methods: Firstly, HepG2 cells were transfected with pCMV-tag2B-Gadd45γand pCMV-tag2B respectively and the changes in protein levelsof Gadd45γ, P38, p-P38, JNK and p-JNK were detected by Western blot.Then, the inhibitors of SB203580 and SP600125 were employed inHepG2 cells to block up the phosphorylation of P38 and JNK. Finally, thecell cycles of HepG2 cells were assayed by flow cytometry.Results:(1)In HepG2 cells transfected with pCMV-tag2B-Gadd45γexpressionvector, Gadd45γprotein expression reached the peak level(0.48±0.04)at48h and the phosphorylation levels of P38 and JNK apparently increased.(2)The degree of G2-M arrest was obviously attenuated after applyingwith the inhibitors in HepG2 cells.Conclusion: Gadd45γ-P38 and Gadd45γ-JNK signal transductionpathways played a role in Gadd45γ-induced cell cycle G2-M arrest.