Growth hormone and insulin-like growth factor-I: effects on the growth of glioma cell lines

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are known to be mitogens for many types of neoplasms. To investigate their role in tumors of glial origin, in vitro and in vivo experiments were performed with a panel of immortalized glioma cell lines (D54, SNB-19, U87, U251 and U373). Initial analysis for mRNA expression demonstrated the following: GH receptor (5/5 cell lines positive), IGF-I (0/5), IGF-II (0/5), IGF-I receptor (5/5), IGF-II receptor (2/5). Thus, each cell line expressed the necessary receptors to respond to GH and the IGFs but there was no autocrine IGF production by the tumors themselves. IGF-I stimulated mitogenesis as measured by [(3)H]thymidine uptake experiments in U251 and U373 cells. However, when these two IGF-responsive cell lines were xenografted into mice, tumor development and growth rates were not significantly different in GH-deficient animals (despite having IGF-I serum concentrations only 31% of normal). Because our studies were performed in immunocompromised animals, GH or IGF effects on immune surveillance, known to be important from some syngeneic glioma models, would not be likely to contribute to our findings. Nevertheless, these studies are important because they demonstrate that the growth of glioma cell lines in an in vivo environment can remain robust in a GH/IGF-I-deficient setting, even if in vitro experiments indicate that IGF-I is mitogenic.