Up-regulated CKS2 promotes tumor progression and predicts a poor prognosis in human colorectal cancer

Abstract

Cyclin-dependent kinases regulatory subunit 2 (CKS2) is a cyclin-dependent kinase-interacting protein, which is essential for cell cycle regulation. Elevated expression of CKS2 has been demonstrated in multiple types of human malignancies. However, the clinical significance, oncogenic functions and related mechanisms of CKS2 in colorectal cancer (CRC) remain largely unexplored. In this study, data from Oncomine database revealed that CKS2 is significantly up-regulated in CRC tissues compared with their normal counterparts. Immunohistochemical analysis of a CRC tissue microarray demonstrated that elevated CKS2 expression is closely associated with enhanced TNM stage, larger tumor size and a poor prognosis in patients with CRC. Multivariate Cox regression analysis revealed that CKS2 and TNM stage are two independent prognostic factors for CRC. Suppression of CKS2 expression resulted in decreased cell viability, increased cell apoptosis, cell cycle arrest and reduced expression of cyclins in Caco-2 and SW620 cells. Furthermore, gain and loss of function studies demonstrated that CKS2 promotes cell invasion in CRC cells through regulating claudin1. Taken together, our study reveal that CKS2 is promising prognostic indicator and contributes to tumor progression in CRC, and support that CKS2-related signaling may represent a novel target for CRC therapy.

Keywords: CKS2; claudin1; colorectal cancer; growth; invasion; prognosis.

Figure 1

CKS2 expression is elevated in CRC cells in Oncomine database. A. Gene expression analysis of CKS2 in a series of cancer cell lines demonstrated an increase in expression in CRC versus 15 other cancer cell types. B. CKS2 expression is significantly elevated in CRC cells compared with 7 other cancer cell types as demonstrated by analysis of Su multi-cancer dataset.

Figure 2

CKS2 expression is elevated in CRC tissues in Oncomine database. Oncomine heat map demonstrated a statistically significant increase in CKS2 expression in CRC tissues compared with the normal control tissues.

Figure 3

Elevated CKS2 predicts a poor prognosis in CRC patients. A. Representative images of CKS2 immunoreactivity in CRC tissues. Scale bar: 50 μm. B. Kaplan-Meier curves for patients grouped based on CKS2 expression.

Figure 4

Suppression of CKS2 inhibits cell proliferation and promotes cell apoptosis. (A) The mRNA expression of CKS2 in CRC cell lines and the normal control cells. (B) Western blotting analysis of the interfere efficiency of CKS2 in Caco-2 and SW620 cells. Effects of CKS2 knockdown on cell viability (C), cell apoptosis (D) and cell cycle (E) of Caco-2 and SW620 cells were analyzed by CCK8, caspase-3/7 activity and PI staining, respectively. (F). The implications of silencing of CKS2 on cyclins expression. (C-F). si-Ctrl versus si-CKS2-1 or si-CKS2-2, *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 5

Effects of CKS2 on cell invasion. A. The effect of silencing of CKS2 on cell invasion was analyzed by Transwell model (si-Ctrl versus si-CKS2-1 or si-CKS2-2, *P < 0.05, **P < 0.01). B. The over-expression efficiency of CKS2 was measured by Western blotting. C. The effect of over-expression of CKS2 on cell invasion (pcDNA3.1-Vector versus pcDNA3.1-CKS2, *P < 0.05, **P < 0.01).

Figure 6

Inhibition of CKS2 inhibits cell invasion via down-regulating claudin1 expression. A. Alternation of tight junction protein expression was measured upon silencing of CKS2 (si-Ctrl versus si-CKS2-1 or si-CKS2-2, *P < 0.05, **P < 0.01). B. The implication of silencing of CKS2 on the invasive potential of Caco-2 and SW620 cells was detected in the presence of si-claudin1 treatment (*P < 0.05, **P < 0.01). C. The effect of silencing of CKS2 on the invasive potential of Caco-2 and SW620 cells was detected in the presence of reintroduction of Claudin1 (**P < 0.01).