The
glial cell line-derived neurotrophic factor (
GDNF) has multiple functions that promote cell survival, proliferation and migration in different cell types. The experimental over-expression of
GDNF in mouse testis leads to
infertility and promotes seminomatous germ cell tumours in older animals, which suggests that deregulation of the
GDNF pathway may be implicated in germ cell
carcinogenesis.
GDNF activates downstream pathways upon binding to its specific co-receptor
GDNF family receptor-a 1 (GFRA1). This complex then interacts with Ret and other co-receptors to activate several intracellular signalling cascades. To explore the involvement of the
GDNF pathway in the onset and progression of testicular germ cell tumours, we analysed GFRA1 and Ret expression patterns in
seminoma samples. We demonstrated, via immunohistochemistry, that GFRA1, but not Ret, is over-expressed in in situ
carcinoma (CIS) and in intratubular and invasive
seminoma cells compared with normal human germ cells. Functional analysis of the
GDNF biological activity was performed on TCam-2
seminoma cell line. Reverse transcription-PCR (RT-PCR) and immunohistochemical analyses demonstrate that TCam-2 cells express both GFRA1 and Ret
mRNA, but only GFRA1 was detected at the
protein level. In TCam-2 cells, although
GDNF is not mitogenic, it is able to induce migration, as demonstrated by a Boyden chamber assay, possibly through the Src and
MEK pathways. Moreover,
GDNF promotes invasive behaviour, an effect dependent on pericellular
protease activity, possibly through the activity of
matrix metalloproteinases. GFRA1 over-expression in CIS and
seminoma cells, along with the functional analyses in TCam-2 cells, suggests an involvement of the
GDNF pathway in the progression of testicular
germ cell cancer.