Expression of genes belonging to the IGF-system in glial tumors

Increased expression of the insulin-like growth factor (IGF) family members, IGF1, IGF2, their receptors and binding proteins, or combinations thereof has been documented in various malignancies including gliomas. The results of multiple investigations suggest that the IGFs can play a paracrine and/or autocrine role in promoting tumor growth in situ during tumor progression but that these roles may vary depending on the tissue of origin. Enhanced IGF1 expression was not found in glioblastomas and it was supposed that IGF1 participation in the development of glial tumors may be substituted by protein products of highly expressed other genes, also participating in PI3K and MAPK pathways. Increased expression of IGF-binding protein genes in brain tumors makes the picture even more complicated. As other binding proteins, IGFBPs regulate the activity of their ligands by prolonging their half-life. The discrepancies arising from conflicting evidence on the results obtained by different laboratories in human gliomas are discussed. Our data highlight the importance of viewing the IGF-related proteins as a complex multifactorial system and show that changes in the expression levels of any one component of the system, in a given malignancy, should be interpreted with caution. As IGF targeting for anticancer therapy is rapidly becoming clinical reality, an understanding of this complexity is very timely.