Expression of glypican 3 (GPC3) in embryonal tumors

Embryonal tumors, such as neuroblastoma, medulloblastoma and Wilms' tumor, have their peak incidence in the first 4 years of life. These neoplasias exhibit genetic and clinical heterogeneity, but little is known about their molecular pathogenesis. Application of the differential-display PCR approach led to the identification of a gene, glypican 3 (GPC3), that is differentially expressed in cancer cells. Expression of this gene is usually limited to fetal mesodermal tissue, and its inactivation has been found to be responsible for the X-linked Simpson-Golabi-Behmel overgrowth syndrome. Here, we show that GPC3 mRNA is present in several neuroblastomas and all Wilms' tumors tested to date but not in medulloblastoma. GPC3 was not expressed in normal kidney tissues obtained from the corresponding Wilms' tumor patients, suggesting that in these cancer cells expression was not repressed (or was activated). No correlation was found between expression of GPC3 and the known indicator of neuroblastoma prognosis MYCN mRNA. However, all samples that expressed GPC3 also expressed IGF-II, coding for a growth factor important in the survival and growth of many cancer types. Although the biological significance of this relationship remains unclear, our results suggest that GPC3 may be implicated in the development of embryonal tumors through a signaling pathway that appears to involve IGF-II.