Inhibiting the role of Skp2 suppresses cell proliferation and tumorigenesis of human gastric cancer cells via the upregulation of p27kip1

Abstract

Gastric cancer is a malignant disease of the digestive system with high rates of incidence and mortality. S‑phase kinase‑associated protein 2 (Skp2) is a novel oncogene, which has been identified to be important in tumor progression and metastasis. In order to clarify the role of Skp2 in human gastric cancer, the present study detected the expression of Skp2 in human gastric cancer tissues, and investigated the molecular mechanism of Skp2 in the progression of gastric carcinoma. The results of the initial bioinformatics analysis showed that Skp2 was significantly upregulated in 31 specimens of primary gastric cancer from a UK patient cohort, and in 10 gastric cancer lines of a side population, compared with normal gastric tissues (P<0.01). Specimens from 47 patients with gastric cancer and 19 normal gastric tissue specimens were obtained and analyzed using western blot analysis. The positive rate of expression of Skp2 was 87.2%, indicating that the expression of Skp2 was observed in 41 specimens of the detected gastric cancer samples, whereas the positive rate of the expression of Skp2 was 5.6% in the normal gastric samples (P<0.01). In the human gastric cancer cell lines, the defective regulation of Skp2 or presence of an Skp2 inhibitor inhibited the proliferation of BGC‑823 and MKN‑45 cells. In addition, the Skp2 inhibitor suppressed the proliferation of gastric cancer cells in a time‑ and dose‑dependent manner. Furthermore, transfection with Skp2 short hairpin (sh)RNA or treatment with SKP inhibitor C1 for 48 and 72 h led to the accumulation of p27kip1 in Hela cells. Tumorigenicity experiments involving nude mice showed that interference of the expression of Skp2 inhibited the growth of the human gastric tumor cells in the nude mice, and the tumor weights and volumes in the Skp2 shRNA group were significantly lower, compared with those in the negative control shRNA group (P<0.01) and untreated group (P<0.01). Taken together, these data suggested that Skp2 acted as an oncogene in human gastric cancer, and that Skp2‑mediated p27kip1 degradation contributed to the progression of gastric cancer. Abrogating the effects of Skp2 may effectively inhibit the growth of gastric cancer cells, which may be useful as a novel target in the clinical treatment of gastric cancer.

Role of p27Kip1 as a transcriptional regulator

“…The phosphorylation of T187 by Cyclin-Cdk2 complexes also induces its degradation in the nucleus. Specifically, this phosphorylation is recognized by the F-box protein Skp2, a subunit of the SCF E3 ubiquitin ligase that triggers its ubiquitylation and subsequent degradation via proteasome (Figure 1B ) [ 21 ]. Interestingly, phosphorylation of specific tyrosine residues in the D2 subdomain (Y74 and Y88 in p27), by different tyrosine kinases, including the Src family, allows the partial activation of the Cdk in the trimeric complexes formed by cyclin, Cdk and p27 due to a conformational change of this p27 domain (Figure 2B ) [ 22 – 26 ].…”

Emerging Roles of SKP2 in Cancer Drug Resistance

“…Skp2 is involved in cell proliferation, apoptosis, migration, invasion, angiogenesis, and metastasis of many malignant human tumors [ 16 , 17 ], and is over-expressed in many types of human cancers, including breast cancer, non-small cell lung cancer [ 19 , 20 ], prostate cancer [ 21 , 22 ], pancreatic cancer [ 23 ], multiple myeloma [ 24 ], gastric cancer [ 25 , 26 ], melanoma [ 27 , 28 , 29 ], lymphoma [ 30 , 31 , 32 ], nasopharyngeal carcinoma [ 33 , 34 ], and osteosarcoma [ 35 , 36 ]. Over-expression of Skp2 is often associated with higher grades and a greater malignancy of tumors as well as a poor prognosis of cancers, such as breast cancer [ 37 , 38 ], nasopharyngeal carcinoma [ 33 ], rectal cancer treated with chemoradiotherapy [ 39 ], oral squamous cell carcinomas [ 40 ], and non-small-cell lung cancer [ 41 ], which suggests that Skp2 engages in tumorigenic activity and is a promising target for cancer therapy.…”

Antisense oligonucleotide p45Skp-2 suppresses migratory chemotactic and metastasis of oral malignant Burkitt’s lymphoma cell through down-regulation of MTA-1 and induction of E-cadherin mechanism

“…p27 Kip1 level have been observed in lymphomas 8 , oral squamous cell carcinomas 3,16 , lung cancer 2 and gastric carcinoma. 9 In the present study, the phosphorotioate oligonucleotide AS and S strategy was delivered to investigate the activity of Skp-2 on migratory chemotactic and metastasis suppresion in an oral malignant Burkitt's lymphoma cell line (Raji cells) through the down-regulation of MTA-1 and induction of E-cadherin expression. Transfection with Skp-2 AS into Raji cells increased the migratory chemotactic suppression effect (Figure 1 and 2).…”

“…Up-regulation of Skp-2 has been observed in various types of human cancer. Overexpression of Skp-2 indicates a poor prognosis and aggressive disease among patients with colorectal, 7 hypupharingeal 8 , gastric, 9 and pancreatic cancers 2 Skp2 knock-out (-/-) mice show smaller organs and slower growth, and their cells exhibit induced apoptosis. 4 Despite these findings, however, little is known about the mechanism of Skp-2 overexpression in cancer cells or the nature of the contribution of this protein to the malignant phenotype.…”