INCREASED EXPRESSION OF PROTEIN KINASE CK2 SUBUNIT IN HUMAN GASTRIC CARCINOMA

Kai-Yuan Lin1 and Yih-Huei Uen1,2,3

1Department of Medical Research, Chi-Mei Medical Center; 2Department of Surgery, Chi-Mei Medical Center; and 3Department of Biotechnology, Southern Taiwan University, Tainan, Taiwan, R.O.C.

Purposes: Gastric carcinoma is one of the most common malignancies in the world, and yet little is known about its molecular process of development and progression. The aims of this study were to correlate the expression of protein kinase CK2 subunit with clinicopathologic parameters and patients’ survival.Materials and methods: CK2 protein levels were analyzed in gastric tissues from surgical specimens of 104 patients with gastric carcinoma employing immunohistochemistry.Results: CK2 protein expression was significantly upregulated in a retrospective cohort of 104 gastric carcinomas (P < 0.001). Overexpression of CK2 was correlated with depth of invasion (P = 0.042). Patients with high CK2 protein expression had a significantly poorer overall survival compared with patients with low CK2 protein expression (P = 0.0006). The multi-variate Cox regression analysis showed that overexpression of CK2 (P =0.0036) and stage (P = 0.0005) were two independent prognostic markers for gastric carcinoma (P = 0.0294).Conclusion: This study indicates that selective inhibition of CK2 expression may exert a chemopreventive effect against gastric carcinogenesis.

Introduction

In Taiwan, gastric cancer ranks as the fifth most frequently diagnosed malignancy and causes more than 2000 deaths annually. In spite of the current surgical techniques and chemotherapy that have made significant improvements, the cure rate for advanced gastric cancer remains low and the morbidity remains high. Thus, advances in treatment of this disease are likely to come from a fuller understanding of its pathogenesis and biological features. Among the prognostic markers now available for gastric carcinoma, the most important one is the American Joint Committee on Cancer (AJCC) stage determined by the depth of invasion, the involvement of the lymph nodes, and distant metastasis. However, in fact, the prognosis varies among patients of the same stage. Therefore, there has been a constant search for specific biological markers to identify subgroups of patients with a more aggressive course of disease. Protein kinase CK2 (formerly known as casein kinase 2) is a highly conserved serine/threonine kinase with a tetrameric structure consisting of two catalytic subunits (, ’’ or ’) and two regulatory subunits. Several studies have indicated that CK2 is required for cell viability and its nuclear localization appeares as a hallmark of proliferating cells. Interruption or interference of CK2 may cause cell death. Gene amplification and protein overexpression of CK2 subunit have been observed in many human cancers, including colorectal cancer and endometrial carcinoma. To our knowledge, the expression and prognostic significance of CK2 in human gastric carcinoma is still unknown. The aims of this study were to correlate the CK2 expression with clinicopathologic parameters and to evaluate the significance of CK2 in gastric carcinoma prognosis.

Materials and Methods

One hundred and four gastric tissues, collected from March 1997 to December 2001, were provided by the Tumor and Serum Bank of Chi-Mei Medical Center. All the patients received radical gastrectomy with lymph node dissection. All tissues were frozen in liquid nitrogen within 20 minutes and kept at -80˚C until use. For CK2 immunostaining, the sections were incubated with an antibody against CK2 after retrieval, and a sensitive Dako EnVision kit was used to detect the immunoreactivity according to the manufacturer’s instructions. Immunoreactivity was scored as follows: 0, no staining; 1, weak staining; 2, moderate staining; 3, strong staining. Clinical data collection and immunohistochemical analysis were performed independently of each other, in an investigator-blinded study. Clinicopathologic parameters of gastric carcinomas were determined according to the AJCC classification. Difference in ΔC between tumor and non-tumor tissues in the same patient was analyzed using a paired t test. A paired t test was also performed to determine the significance of the difference between CK2 protein level and clinicopathologic parameters. The cumulative overall survival rates were calculated by the Kaplan-Meier method and the differences in survival rates were analyzed by a log-rank test. To determine the relative prognostic impact overexpression of CK2 compared with established prognostic markers, overall survival was analyzed according to Cox proportional hazards model.

Results

Expression of CK2 Was Upregulated and Associated with Depth of Invasion in Gastric CarcinomaExpression levels of CK2 in tumor tissues were higher than those in non-tumor tissues (P < 0.001). Overexpression of CK2 (score = 2 or 3) was observed in 45 of 104 (43.3%) patients (Fig. 1A and 1B). In addition, overexpression of CK2 had a statistically significant correlation with depth of invasion (P = 0.042).

Overexpression of CK2 As an Independent Prognostic Marker for Gastric CarcinomaThe patients were divided into low and high CK2 expression groups. The Kaplan-Meier survival curve in Fig. 1C illustrated the increased hazard rate of patients (51.2%) with high CK2 expression with an overall survival rate of 33.61% compared with patients with low CK2 expression with an overall survival rate of 71.48% (P = 0.0006). In multi-variate analysis, overexpression of CK2 was shown to be an independent prognostic marker for survival (P = 0.0036, Table 1).

Fig. 1. Panel A-B) Gastric carcinoma analyzed by immunohistochemistry with an antibody against CK2. Panel A shows a sample with high expression level of CK2; Panel B shows a sample with low expression level of CK2; Panel C) Overall survival analysis of 104 patients stratified by CK2 immunoreactivity.

Table 1. Multi-variate Cox regression analysis of prognostic markers in 104 patients with gastric carcinoma

Variables Relative risk 95% CI P*

CK2

No and low expression

(score = 0 or 1)

High expression

(score = 2 or 3)

 

1

2.649

 

 

1.373-5.111

 

 

0.0036

Stage

I

II + III + IV

 

1

12.928

 

 

3.047-54.853

 

 

0.0005

*Significance level: P < 0.05.

A

C

B