Expression of the tumor suppressor ARHI inhibits the growth of pancreatic cancer cells by inducing G1 cell cycle arrest

Abstract

Abstract.A Ras homologue member I (ARHI) is an imprinted tumor suppressor gene whose expression is frequently lost in pancreatic cancers. This small GTP-binding protein is a member of the Ras superfamily with significant homology to Ras. In contrast to the Ras oncogene, ARHI has been shown to have anti-proliferative effects, but the mechanisms by which it inhibits pancreatic cancer cell proliferation and induces cell cycle arrest remain unclear. By generating stable transfectants, ARHI was reexpressed in pancreatic cancer cells that had lost its expression. Flow cytometry analysis indicated that ARHI blocked cell cycle progression at the G 1 phase in pancreatic cancer cells. In ARHI transfectants, phosphorylated AKT protein expression decreased compared to that of vector transfectants. Reexpression of ARHI increased the expression of the cyclin-dependent kinase (CDK) inhibitor (CKI) p21 WAF1 , through the accumulation of p53 protein by the inhibition of PI-3K/AKT signaling. In addition, ARHI enhances expression of CKI p27 kip1 through the inhibition of PI-3K/AKT signaling. The expression of cyclins A and D1 decreased, while cyclin E was not affected under the same conditions. The activities of cyclin-dependent kinases 2 (CDK2) and 4 (CDK4) were reduced in ARHI transfectants. These results suggest that the PI-3K/AKT pathway plays a pivotal role in the pathogenesis of pancreatic cancer and ARHI exerts its growth-inhibitory effects through modulation of several key G 1 regulatory proteins, such as p21 WAF1 , p27 kip1 , CDK2, CDK4 and cyclins A and D1. ARHI represents a modulator of cancer cell proliferation and may play an important role in the development of pancreatic cancer. IntroductionPancreatic cancer is one of the most lethal cancers in the industrialized world and the sixth leading cause of cancerrelated death in China (1). The incidence of pancreatic cancer almost equals that of pancreatic cancer-related mortality, with fewer than 20% of patients surviving the first year and with only 3% surviving 5 years after the diagnosis (2-4). This poor outcome motivates ongoing molecular research to understand tumor biology. A variety of regulatory mechanisms contribute to the development and growth of pancreatic cancer. The up-regulation of numerous oncogenic genes and the downregulation of tumor suppressor genes are responsible, in part, for the uncontrolled growth, survival and metastasis of pancreatic cancer cells during the development of this disease. The genetic abnormalities found in pancreatic cancer affect the mechanisms controlling G 1 to S cell cycle progression and cellular proliferation.A Ras homologue member I (ARHI) is a maternally imprinted human tumor suppressor gene that encodes a 26-kDa small G protein with 50-60% amino acid homology to Rap and Ras. In ovarian and breast cancers, reexpression of ARHI inhibits cancer cell growth in vitro and in vivo, induces p21 WAF1 and down-regulates cyclin D1 promoter activity (5). Recent studies showed that ARHI regulates autophagy and tumor dormancy in ovarian...

The mechanisms of DIRAS family members in role of tumor suppressor

“…DIRAS3 was also downregulated or lost in pancreatic cancers compared with its wide expression in ductal and acinar cells of normal pancreatic tissue (Y. Q. Hu et al, 2013;Lu et al, 2009;Yang et al, 2010). Similar result was found in pancreatic endocrine tumors, that DIRAS3 expression showed a statistically significant difference between either normal pancreas or well-differentiated endocrine tumors and poorly differentiated endocrine carcinomas (Dalai et al, 2007).…”

“…Moreover, Lu et al (2009) proved increase of p21 (WAF1/CIP1) and p27 kip1 , decrease of cyclins A and D1, along with activity reductions of cyclin-dependent kinases 2 (CDK2) and CDK4 in DIRAS3 transfected cells. However, Rosen et al (2004) revealed that DIRAS3 expression is only correlated with the expression of p21 (WAF1/CIP1) but not with cyclin D1 in clinical epithelial ovarian cancers.…”

“…It was first reported that DIRAS3 suppresses growth in ovarian and breast cancer cells (Yu et al, ), then the cell growth inhibition capacity of DIRAS3 is discovered in various cancers including hepatocellular carcinoma (HCC; Huang, et al, a), pancreatic cancers (Lu et al, ), prostate cancer (Y. Chen et al, ), gastric cancer (Tang et al, ), lung cancer (Wu et al, ), glioma (J. Chen, Shi, Yang, & Chen, ), and osteosarcoma (Ye et al, ). Mechanically, DIRAS family members exert its growth‐inhibitory effects through arrest in cell cycle, decrease in angiogenesis, and changes in signaling pathways.…”

“…Regarding the signaling pathways implicated in the regulation of cell growth, DIRAS3 has been proved to inhibit cell proliferation through blocking PI-3K/AKT, mTOR, NF-κB, and ERK1/2 and STAT3 protein kinases related proliferation signaling pathways (Figure 3; Y. Q. Hu et al, 2013;Lu et al, 2009;Ye et al, 2015;Zhao et al, 2010;Q. Zhu et al, 2014).…”

The Importance of Targeted Drug Delivery Systems on Pancreatic Cancer

“…The recent studies have been found that BRCA2, BRCA1, PALB2, STK11/LKB1, SOX15 genes and TGFBR1, TGFBR2, or ACVR1B receptors [60][61][62][63][64][65][66][67][68] are inactivated in a small subset of PC. In addition, ARH1 and KLF4 genes may be candidate in pancreatic tumorigenesis [69][70][71][72].…”