Glypican-3
(GPC3) belongs to a six-member family of membrane-bound heparan sulfate
proteoglycans with a gene that is localized to Xq26.2. GPC3 belongs to a
family of cell-surface heparan sulfate proteoglycans and is highly expressed
during embryogenesis and organ development. GPC3 has limited expression in
adult tissues, including lung, ovaries, mammary epithelium, and mesothelium.
Normally, the liver does not express detectable levels of GPC3, but it has
been observed to be highly upregulated in hepatocellular carcinomas and
hepatoblastomas. Glypican-3 has been shown to play a role in the control of
cell growth through the induction of apoptosis. Mutations in glypican-3
result in cell overgrowth. Among all mammalian glypicans, only mutation of
GPC3 is associated with a phenotype in humans. GPC3 spans more than 500 kb of
genomic DNA and contains 8 exons. Loss-of-function mutations in GPC3 result
in overgrowth of many organs (Simpson-Golabi-Behmel syndrome), including the
liver, which has been confirmed using GPC3-deficient mice. This observation
suggests that GPC3 plays a role in growth suppression and organ size control.
GPC3 is highly expressed in yolk sac tumors and choriocarcinomas, with a
cytoplasmic staining pattern. It is only variably expressed in teratomas and
is absent in germinomas and embryonic carcinomas.
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