High expression of TRPM8 predicts poor prognosis in patients with osteosarcoma

Abstract

The transient receptor potential melastatin member 8 (TRPM8) is a newly characterized oncoprotein involved in various malignant tumors. However, its expression pattern and biological function in osteosarcoma remain unclear. The present study aimed to explore the expression and prognostic significance of TRPM8 in osteosarcoma (OS). The results revealed that the expression of TRPM8 mRNA and protein in OS tissue was significantly higher than that in paired normal bone tissue (P<0.05). Additionally, the level of TRPM8 mRNA and protein in patients with a higher clinical stage and with distant metastasis was markedly higher than in those with a lower clinical stage and no metastasis (P<0.05). Furthermore, a high TRPM8 level was closely associated with clinical stage and distant metastasis (P=0.007 and 0.030), but not associated with the patient age (P=0.481), gender (P=0.905), tumor size (P=0.429), histological subtype (P=0.207) or anatomical location (P=0.369). In addition, OS patients with high TRPM8 expression had significantly shorter overall survival (P=0.008) and disease-free survival times (P=0.008) when compared with patients with low expression of TRPM8. In Cox multivariate analysis, TRPM8 overexpression was identified to be an independent and significant prognostic factor for overall survival (P=0.040), but not for disease-free survival (P=0.051). Collectively, the present data suggest that TRPM8 may play a crucial role in the development and progression of OS, and thus may be considered as a novel molecular target for therapy in patients with OS.

Keywords: TRPM8; disease-free survival; osteosarcoma; overall survival; prognosis.

Figure 1.

Receiver operating characteristic curves were created to determine the cutoff score for positive expression of transient receptor potential melastatin member 8 in osteosarcoma. The sensitivity and specificity for survival status was plotted and the areas under the curve are indicated.

Figure 2.

Relative mRNA expression of transient receptor potential melastatin member 8 (TRPM8) in osteosarcoma (OS) tissues compared with normal bone tissues. The gene expression of TRPM8 in OS tissues was much higher (3.34±0.23) than that in normal bone tissues (0.55±0.12; P<0.05). *P<0.05 OS tissues vs. normal bone tissues.

Figure 3.

Western blot analysis of transient receptor potential melastatin member 8 (TRPM8) protein expression in osteosarcoma tissues (OS) and normal bone tissues (N). The protein expression of TRPM8 in OS tissues was significantly higher than that in normal bone tissues (1.32±0.26 vs. 0.45±0.11; P<0.05). *P<0.05 OS tissues vs. normal bone tissues.

Figure 4.

Immunohistochemical analysis of transient receptor potential melastatin member 8 (TRPM8) expression in osteosarcoma patients. (A) Negative expression level of TRPM8. (B) Positive expression level of TRPM8. Original magnification ×400.

Figure 5.

High levels of transient receptor potential melastatin member 8 (TRPM8) predict stronger aggressiveness in osteosarcoma. TRPM8 mRNA and protein were investigated in tissues with various clinicopathological features including metastasis and clinical stage by quantitative polymerase chain reaction and western blot analysis. (A,C) TRPM8 mRNA and protein levels in patients with metastasis were significantly higher than those in non-metastatic patients (*P<0.05). (B,D) TRPM8 mRNA and protein levels in patients with a higher clinical stage (IIB/III) were significantly higher than in those with a lower stage (I/IIA; P<0.05).

Figure 6.

(A) Overall survival (OS) and (B) disease-free survival (DFS) rate in patients with osteosarcoma estimated according to the transient receptor potential melastatin member 8 (TRPM8) expression level (Kaplan-Meier method) with immunohistochemical staining. Patients with positive TRPM8 expression were inclined to have a significantly shorter OS and DFS than those with negative TRPM8 expression.