CMTM3 Inhibits Human Testicular Cancer Cell Growth through Inducing Cell-Cycle Arrest and Apoptosis

Zesong Li,Xiaojuan Sun,Aifa Tang,Wenjie Li,Feng Wang,Xianxin Li,Zhiping Wang,Liping Nie,Jianting Wu,Yaoting Gui,Ren Liu,Zhiming Cai,Hongbing Mei,Jun Xie,Thomas G Hofmann

doi:10.1371/journal.pone.0088965

Abstract

Human CMTM3 has been proposed as a putative tumor suppressor gene. The loss of CMTM3 has been found in several carcinomas. However, the regulation of CMTM3 expression and its function in tumor progression remain largely unknown. Here, we investigated the regulation of CMTM3 expression, function and molecular mechanism in human testicular cancer cells. CMTM3 was frequently downregulated or silenced in testicular cancer cell lines and tumor tissues but highly expressed in normal testis tissues. The re-expression of CMTM3 significantly suppressed the colony formation, proliferation, and migration capacity of testicular cancer cells by inducing a G2 cell cycle arrest and apoptosis. Moreover, the re-expression of CMTM3 activated the transcription of p53, induced p53 accumulation, up-regulated the expression of p21, and increased the cleavage of caspase 9, 8, 3, and PARP. The downregulation of CMTM3 in clinical tumor tissues was associated with the methylation of a single CpG site located within the Sp1/Sp3-responsive region of the core promoter. These results indicate that CMTM3 can function as tumor suppressor through the induction of a G2 cell cycle arrest and apoptosis. CMTM3 is thus involved in testicular cancer pathogenesis, and it is frequently at least partially silenced by the methylation of a single, specific CpG site in tumor tissues.

Highlights

Testicular germ cell tumors (TGCTs) are common in men aged 15 to 35 years and account for 1% of all malignant neoplasms in males [1]
We found that CMTM3 was frequently downregulated or silenced in testicular cancer cell lines and primary tumors (Figure 1, Table 1).We further performed functional studies in NCCIT cells to unveil the biological function of CMTM3
We found that the re-expression of CMTM3 strongly impaired NCCIT cell motility and suppressed colony formation (Figure 2), which was consistent with previous reports in other cancers [8,13]

Summary

Introduction

Testicular germ cell tumors (TGCTs) are common in men aged 15 to 35 years and account for 1% of all malignant neoplasms in males [1]. The incidence of TGCTs has increased dramatically over the last century [2]. TGCTs originate from transformed gonocytes or undifferentiated spermatogonia, which are derived from fetal germ cells and adult germ stem cells, respectively. TGCTs are classified as seminomas or non-seminomatous germ cell tumors according to their histologic characteristics [1]. Seminomas are the most frequent (50–70%) testicular germ cell tumors. Non-seminomatous germ cell tumors include embryonal cell carcinoma, yolk sac tumors, choriocarcinoma, and teratomas [1]. TGCTs have become one of the most curable solid neoplasms, due to advances in diagnostic and therapeutic methods [3]. The molecular mechanisms operating in TGCTs are not fully understood

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