J. Cancer Mol. 3: 49-54, 2007

[Research Paper]

In Vivo Effects of Cyclooxygenase-2 Deletion on Cellular Signaling in Hepatocellular Carcinoma Xenografts in Nude Mice

Wei Cui, Shirley X Hu, Zhen-Ya Tang, and Ke-Qin Hu¹

Division of Gastroenterology and Chao Family Comprehensive Cancer Center, University of California Irvine, Orange, CA, USA [W. Cui, K.-Q. Hu]; Earl Warren College, University of California San Diego, La Jolla, CA, USA [S. X. Hu]; Transplantation Laboratory, Ochsner Clinic Foundation, New Orleans, LA, USA [Z.-Y. Tang]

Abstract:

AIM: It is known that cyclooxygenase-2 (COX-2) overexpression is associated with growth of hepatocellular carcinoma (HCC) cells, but its in vivo mechanisms remain to be determined. 

METHODS: In the present study, the parental HuH7, a human HCC cell line, and COX-2 deleted HuH7 cells were inoculated to nude mice to assess the in vivo effects of COX-2 deletion (C2D) on cellular signaling in HCC xenografts. 

RESULTS: We found that C2D significantly inhibited Ki-67 and increased peroxisome proliferator-activated receptor-gamma (PPAR-gamma) expression, and reduced plasma prostaglandin E₂ and alpha-fetoprotein levels in association with reduced Rb phosphorylation and cyclin D1/CDK4 complex, and increased p21/CDK4 complex, indicating COX-2 overexpression promotes G₁-S transition of the cell cycle in human HCC xenografts via a series of complicated signaling.  C2D also resulted in significantly reduced phosphorylation of Akt, indicating a potential role of PTEN/PI3K/Akt pathway in COX-2-mediated alteration of HCC growth.  We also demonstrated that C2D significantly inhibited histone deacetylase-2 (HDAC-2) expression, but increased the acetylation levels of histone-3 and histone-4, indicating that altered histone acetylation by histone deacetylases may be involved in COX-2-mediated HCC cell proliferation.  In contrast to previous in vitro reports, we found that C2D did not significantly affect apoptosis and formation of activated caspase-3 and 9 in HCC xenografts.

CONCLUSION:  Our results revealed that C2D results in a series of in vivo alteration of cellular signaling in HCC xenografts that demonstrated important pathogenic mechanisms of COX-2 overexpression in HCC growth and provided valuable information on searching novel approaches to HCC chemoprevention.

Received 1/7/07; Revised 3/12/07; Accepted 3/13/07.

¹Correspondence: Dr. Ke-Qin Hu, Division of GI/Hepatology, University of California at Irvine, 101 The City Drive, Building 53, Room 113, Orange, CA 92868, USA.  Phone: 1-714-4566745. Fax: 1-714-4567753. E-mail: kqhu@uci.edu

²Abbreviations: HCC, hepatocellular carcinoma; COX-2, cyclooxygenase-2; C2D, COX-2 deletion; PPAR-gamma, peroxisome proliferator-activated receptor-gamma; PGE₂, prostaglandin E₂; AFP, alpha-fetoprotein; CD1, cyclin D1; HDAC-2, histone deacetylase-2; AC-H3 and AC-H4, acetylation of histone H3 and H4; PTEN, phosphatase and tensin homolog deleted on chromosome ten; MAPK, mitogen-activated protein kinase; p-ERK, phosphorylated extracellular-regulated kinase; IP, immunoprecipitation; IB, immunobloting. 

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