Re-analysis of the Xq27–Xq28 region suggests a weak association of an X-linked gene with sporadic testicular germ cell tumour without cryptorchidism

SPANXN2 functions a cell migration inhibitor in testicular germ cell tumor cells

Background

SPANX family members are thought to play an important role in cancer progression. The SPANXN2 is a gene expressed mainly in normal testis, but its role in testicular germ cell tumors (TGCTs) has yet to be investigated. TGCT is one of the most common solid tumors in young men and is associated with poor prognosis; however, effective prognostic indicators remain elusive. Therefore, we investigated the role of SPANXN2 in TGCT development.

Methods

SPANXN2 expression levels were validated by quantitative real-time polymerase chain reaction (qRT-PCR) analyses of 14 TGCT samples and five adjacent normal tissue samples. SPANXN2 was transiently overexpressed in TGCT cells to study the consequences for cell function. The effects of SPANXN2 on cell migration were evaluated in transwell and wound healing assays. The effects on cloning ability were evaluated in colony formation assays. MTT assays and cell cycle analysis were used to detect the effects of SPANXN2 on cell proliferation. The expression levels of EMT- and AKT-related proteins in cells overexpressing SPANXN2 were analyzed by Western blotting.

Results

Compared with adjacent normal tissues, the Gene Expression Profiling Interactive Analysis database showed SPANXN2 expression was downregulated in TGCTs which was consistent with the qRT-PCR analysis. SPANXN2 overexpression reduced cell migration and colony formation capability and downregulated expression of EMT- and AKT-related proteins, Vimentin, Snail, AKT, and p-AKT.

Conclusion

Our results suggest that SPANXN2 regulates TGCT cell migration via EMT- and AKT-related proteins although its role in the occurrence and development of TGCT remains to be fully elucidated.

Screening for germline DND1 mutations in testicular cancer patients

Although several observations suggest that a strong genetic predisposition to developing testicular germ cell tumors (TGCT) exists, no associated, highly penetrant germline mutations have been identified so far. In the 129/Sv mouse strain, a germline mutation in the DND1 gene has been shown to strongly increase the TGCT risk. We screened 272 men with TGCT (89% sporadic cases, 11% familial) for germline mutations in the human homologue of DND1. A single nucleotide substitution c.657C > G (p.Asp219Glu) was observed in a non-familial case of testicular embryonal carcinoma. The variant was also present in the patient’s asymptomatic father and two brothers, but not observed in 210 control chromosomes. The wild type DND1 allele was not lost in the patient’s tumor. In silico analysis of the variant predicts it to be non-pathogenic. We conclude that germline DND1 mutations are unlikely to contribute significantly to human testicular germ cell tumor susceptibility. The role of human DND1 in normal physiology and disease, however, is still virtually unknown and it therefore warrants further research.

Clinical and genetic aspects of testicular germ cell tumours

In this paper we review clinical and genetic aspects of testicular germ cell tumours (TGCTs). TGCT is the most common type of malignant disorder in men aged 1540 years. Its incidence has increased sharply in recent years. Fortunately, survival of patients with TGCT has improved enormously, which can chiefly be attributed to the cisplatin-based polychemotherapy that was introduced in the nineteen eighties to treat patients with metastasized TGCT. In addition, new strategies have been developed in the surgical approach to metastasized/non-metastasized TGCT and alterations have been made to the radiotherapy technique and radiation dose for seminoma. Family history of TGCT is among the strongest risk factors for this tumour type. Although this fact and others suggest the existence of genetic predisposition to develop TGCT, no germline mutations conferring high risk of developing TGCT have been identified so far. A small deletion, referred to as gr/gr, identified on the Y chromosome is probably associated with only a modest increase in TGCT risk, and linkage of familial TGCT to the Xq27 region has not been confirmed yet. Whether highly penetrant TGCT-predisposing mutations truly exist or familial clustering of TGCT can be explained by combinations of weak predispositions, shared in utero or postnatal risks factors and coincidental somatic mutations is an intriguing puzzle, still waiting to be solved.

Chromosome X modulates incidence of testicular germ cell tumors in Ter mice

Germ cell tumor development in humans has been proposed to be part of testicular dysgenesis syndrome (TDS), which manifests as undescended testes, sterility, hypospadias, and, in extreme cases, as germ cell tumors. Males of the Ter mouse strain show interesting parallels to TDS because they either lack germ cells and are sterile or develop testicular germ cell tumors. We found that these defects in Ter mice are due to mutational inactivation of the Dead-end (Dnd1) gene. Here we report that chromosome X modulates germ cell tumor development in Ter mice. We tested whether the X or the Y chromosome influences tumor incidence. We used chromosome substitution strains to generate two new mouse strains: 129-Ter/Ter that carry either a C57BL/6J (B6)-derived chromosome (Chr) X or Y. We found that Ter/Ter males with B6-Chr X, but not B6-Chr Y, showed a significant shift in propensity from testicular tumor development to sterile testes phenotype. Thus, our studies provide unambiguous evidence that genetic factors from Chr X modulate the incidence of germ cell tumors in mice with inactivated Dnd1.