Overexpression of MutSα Complex Proteins Predicts Poor Prognosis in Oral Squamous Cell Carcinoma

Abstract

The DNA mismatch repair (MMR) system is responsible for the detection and correction of errors created during DNA replication, thereby avoiding the incorporation of mutations in dividing cells. The prognostic value of alterations in MMR system has not previously been analyzed in oral squamous cell carcinoma (OSCC).The study comprised 115 cases of OSCC diagnosed between 1996 and 2010. The specimens collected were constructed into tissue microarray blocks. Immunohistochemical staining for MutSα complex proteins hMSH2 and hMSH6 was performed. The slides were subsequently scanned into high-resolution images, and nuclear staining of hMSH2 and hMSH6 was analyzed using the Nuclear V9 algorithm. Univariable and multivariable Cox proportional hazard regression models were performed to evaluate the prognostic value of hMSH2 and hMSH6 in OSCC.All cases in the present cohort were positive for hMSH2 and hMSH6 and a direct correlation was found between the expression of the proteins (P < 0.05). The mean number of positive cells for hMSH2 and hMSH6 was 64.44 ± 15.21 and 31.46 ± 22.38, respectively. These values were used as cutoff points to determine high protein expression. Cases with high expression of both proteins simultaneously were classified as having high MutSα complex expression. In the multivariable analysis, high expression of the MutSα complex was an independent prognostic factor for poor overall survival (hazard ratio: 2.75, P = 0.02).This study provides a first insight of the prognostic value of alterations in MMR system in OSCC. We found that MutSα complex may constitute a molecular marker for the poor prognosis of OSCC.

FIGURE 1

MutSα complex expression in OSCC. A, Representative examples of hMSH2 and hMSH6 expression in OSCC. hMSH2 and hMSH6 presented nuclear staining in tumor cells. Note that in low expression cases, staining was restricted in the periphery of tumor islands (^∗), whereas in high expression cases, staining was homogenously distributed throughout the tumor. Box plots of (B) hMSH2 and (C) hMSH6 demonstrating the distributing of proteins expression in the present OSCC cohort. For each protein, the main value (horizontal line) was used as a cutoff point to determine cases of low and high expression. OSCC = oral squamous cell carcinoma.

FIGURE 2

Box plots of hMSH2 and hMSH6 according to the main clinical-pathological aspects. Note very homogenous distribution in the expression of both proteins with regard to tobacco habits, nodal metastasis, clinical stage, recurrence, and histopathological grade. In relation to tumor size, patients with higher T status (T3/T4) had lower hMHS2 expression (P = 0.03, Mann-Whitney test).

FIGURE 3

Direct correlation between hMSH2 and hMSH6 (scatter plot). Note that an increase in hMSH2 was correlated with an increase in hMSH6 (Spearman correlation coefficient: 0.38; P < 0.05).

FIGURE 4

Kaplan-Meier analysis of (A) OSCC patient overall survival and (B) according to MutSα expression. Patients with higher expression of MutSα presented more pronounced decline in the survival curve compared with patients with lower MutSα expression in the first year after diagnosis (12-months) and also in a later period (after 50-months) (Log rank test, P = 0.03). OSCC = oral squamous cell carcinoma.