RKIP inhibits the malignant phenotypes of gastric cancer cells

Abstract

Raf kinase inhibitor protein (RKIP) is first identified as an interacting partner of Raf-1. RKIP expression is low or absent in several established cell lines derived from metastatic breast cancer, prostate cancer and melanoma cells. However, the functional role of RKIP in gastric cancer remains unclear. In this study, we employed human gastric cancer cell line SGC7901 as a model to reconstitute RKIP expression in gastric cancer cells. The growth curve and soft agar assay showed that RKIP inhibited the growth and clonogenicity of SGC7901 cells. Flow cytometry analysis showed that RKIP inhibited the cell cycle progression and induced the apoptosis of SGC7901 cells. Wound healing and transwell invasion assay showed that RKIP inhibited the migration and invasion of SGC7901 cells. Furthermore, we observed that RKIP inhibited the growth of SMGC7901 cells in xenografts in nude mice. Taken together, our in vitro and in vivo data demonstrate that RKIP modulates the proliferation, apoptosis, migration, invasion and tumorigenicity of SGC7901 cells. These results reveal the tumor suppressor role of RKIP in gastric cancer and suggest that RKIP may be new therapeutic target for gastric cancer. Key words: gastric cancer, RKIP, Raf, tumor suppressor, SGC7901, apoptosisIn the last decade, great progress has been made in the treatment of patients with gastric cancer, one of the most prevalent malignancies in Asia [1]. However, a significant percentage of gastric cancer patients fail to achieve complete remission, leading to the relapse or poor prognosis [2]. Metastasis has been regarded as an important mechanism underlying tumor relapse after successful surgical resections [3][4][5]. Metastasis is the advanced stage of solid tumor progression and is a multistep process that involves invasion, intravasation, extravasation to distant organs and final growth of the secondary tumor. A group of genes, termed metastasis suppressor genes (MSGs), encode for proteins that inhibit various steps of the metastatic cascade [6].Raf kinase inhibitor protein (RKIP) is one of the MSGs that suppress metastasis. RKIP is first identified as an interacting partner of Raf-1 and as a negative regulator of mitogen-activated protein kinase (MAPK) pathway downstream of Raf-1 [7]. RKIP expression is low or absent in several established cell lines derived from metastatic breast cancer, prostate cancer and melanoma cells. Moreover, loss of RKIP has been shown to promote tumor development by conferring radioresistance and chemoresistance [8]. However, the functional role of RKIP in gastric cancer remains unclear.Our preliminary study showed that RKIP expression was low in gastric cancer tissues compared to adjacent normal gastric tissues [9]. Therefore, in this study we used gastric cancer cell line SGC7901 cells as a model to investigate whether and how the loss of RKIP contributes to gastric cancer development. Our results demonstrated that reconstitution of RKIP inhibited the proliferation, clonogenicity, migration and invasion of SGC7901 cells in vitro, ...

Reduced RKIP expression levels are associated with frequent non-small cell lung cancer metastasis and STAT3 phosphorylation and activation

“…A previous study indicated using immunohistochemistry that RKIP expression levels were detectable in all non-cancerous prostate tissues and were decreased to low or undetectable levels in all prostate cancer metastases (25). Similar results have been demonstrated in malignant melanoma, colorectal, breast, thyroid and liver cancer (26–28). Concordant with the results from previous studies, the current study also revealed that RKIP may be associated with the Raf/MEK/ERK/STAT3 pathway, and clinical data from 100 patients with NSCLC also supported the hypothesis that RKIP expression levels are associated with NSCLC metastasis.…”

Dihydroartemisinin induces apoptosis of cervical cancer cells via upregulation of RKIP and downregulation of bcl-2

“…13,17 RKIP, an inhibitor of the RAF/MEK/ERK pathway, has been reported to play an important role in modulating a number of signaling pathways which regulate proliferation, motility, and epithelial-mesenchymal transition (EMT). [29][30][31] Downregulation of RKIP was shown to be associated with increased viability and proliferation, increased migration, and increased vascularization. 24 We previously reported that downregulation of RKIP was associated with metastasis of cervical cancer and speculated that the tumor suppressor function of RKIP could potentially be mediated via inhibition of tumor cell migration.…”

RKIP: Much more than Raf Kinase inhibitory protein

“…The role of RKIP has been assessed in hepatocellular carcinoma (HCC), in which its expression was significantly reduced, likely accounting for the hyper‐activation of ERK cascade in human HCC (Schuierer et al, 2006; Xu et al, 2010; Notarbartolo et al, 2011; Walker et al, 2011; Wu et al, 2011). RKIP expression was also diminished in pancreatic cancer (Kim et al, 2010; Song et al, 2012), cancer of the ampulla of Vater (Kim et al, 2012a), non‐melanocytic skin cancers (Libra and Torrisi, 2009; Zaravinos et al, 2009), esophageal cancer (Birner et al, 2012; Gao et al, 2012; Guo et al, 2012a; Kim et al, 2012b), gastrointestinal stromal tumors (Martinho et al, 2009) and its response to Imatinib (Valadao et al, 2012), gastric cancers (Fujimori et al, 2012; Jia et al, 2012; Guo et al, 2012a; Zhang et al, 2013), renal cell carcinoma (Moon et al, 2012), endometrial cancer (Martinho et al, 2012a), and brain tumors (Gimenez et al, 2010; Maresch et al, 2011; Martinho et al, 2012b). In breast cancer, lymph node metastases displayed significantly reduced levels of RKIP (Hagan et al, 2005; Minn et al, 2012).…”