Poly ADP-ribose polymerase (PARP) which is closely related to Poly ADP-ribose glycohydrolase (PARG) has already been thoroughly investigated in both experimental and clinical cancer trials compared to the latter. Nevertheless, in this experiment the importance of PARG expression was highlighted; whereby it is being silenced via lentivirus vector-mediated short hairpin RNA (shRNA). MTT assay showed that there was an inhibition in human Lovo colon cancer cell growth and flow cytometry demonstrated an increase in the population of cells in G(0)/G(1) phase with a decrease in the S phase in transfected Lovo cells. Furthermore, our results suggested that the effect of silencing PARG leads to the inhibition of PARP expression; related to a decrease in the expression of Nuclear Factor Kappa-B (NFκ-B) with an increase in Akt(473) phosphorylation; suggesting that the Phosphoinositol 3-kinase (PI3K)/Akt/NFκ-B pathway is important for cellular growth and proliferation. Hence, this study emphasizes and converges on the relevance of silencing PARG which inhibits growth of human colonic cancer cells via PI3K/Akt/NFκ-B pathway; as colon carcinoma remains to be amongst one of the commonest cancers throughout the world with high morbidity and mortality rates.

Aims: To investigate the role and mechanism of PARG inhibition of metastatic behavior in colonic carcinoma cells. Methods: We examined the effects of PARG protein knockdown by RNA interference on invasion, migration and matrix adhesion of colon carcinoma cell lines in vitro and using a murine in vivo model of liver metastasis. Metastasis related genes were detected using mRNA and protein levels. Moreover, LY294002, an Akt phosphorylation inhibitor, was used to determine whether the suppression of metastatic behavior of colon carcinoma cells was mediated by Akt phosphorylation that was confirmed by EMSA. Pyrrolidine dithiocarbamate (PDTC) was used as a selective NFĸ-B inhibitor to clarify the relationship between PARG, PARP and NF-ĸB. Results: PARG protein was undetectable following specific shRNA transfection; mRNA and protein levels of PARP were significantly decreased. PARG-shRNA cells showed high levels of phosphorylated Akt with decreased expression of NF-ĸB (both total & nuclear), MMP2 and MMP9. However, no additional changes were noted following inhibition of PI3K/Akt pathway by LY294002 in the PARG-shRNA cells; these cells displayed reduced number of liver metastases when characterized in the murine in vivo model. Conclusion: PARG knockdown, concomitant with inhibition of PARP, suppressed the metastatic potency of colon carcinoma cells by activation of PI3K/Akt signaling pathway.

Objective: To investigate the significance of Poly (ADP-ribose) glycolhydrolase (PARG) and membrane type 1 matrix metalloproteinase (MT1-MMP) expressions in human colorectal carcinoma.Methods: Immunohistochemical staining for PARG and MT1-MMP was carried out on colorectal adenoma-carcinoma tissue microarrays containing normal colorectal mucosae, adenoma, adenoma with malignant transformation and adenocarcinoma (total 130 specimens). The expressions of PARG and MT1-MMP in the GLTN [Gallotannin]-treated and GLTN-untreated lovo cells were detected by Western Blot.Results: PARG expression in adenocarcinoma (83.1%) and adenoma with malignant transformation (66.7%) was significantly higher than that in normal colorectal mucosa (10%) and adenoma (10.5%). Expression of MT1-MMp in normal colorectal mucosa and adenoma was negative, while the expression in adenocarcinoma (80.3%) and adenoma with malignant transformation (72.2%) was high. The expressions of PARG and MT1-MMP in adenocarcinoma with metastasis and in late tumor stages were significantly higher than those in adenocarcinoma with no metastasis and in early tumor stages. Thus, PARG expression shows a positive correlation with the expression of MT1-MMP. The expressions of PARG and MT1-MMP in GLTN-treated lovo cells were weaker than that in GLTN-untreated lovo cells.Conclusion: The expression of PARG was probably related to the development of colorectal carcinoma. PARG may play an important role for the regulation of MT1-MMP expression in colorectal carcinoma.