Regulation of Growth Inhibitory Factor Expression by Epidermal Growth Factor and Interleukin-1β in Cultured Rat Astrocytes

Growth inhibitory factor (GIF) is highly expressed in the CNS under physiological conditions, but its expression is reduced in neurodegenerative diseases, such as Alzheimer's disease. The results of this study show that the levels of GIF and GIF mRNA were not influenced by neuroglial interactions. GIF was highly expressed in confluent astrocytes, but the expression was down-regulated in low-density growing astrocytes. A high level of GIF was not observed in serum-starved low-density cultures. These findings suggest that GIF is a quiescent state-specific protein and that two different mechanisms may exist for the cells to enter the quiescent state. Among interleukin-1beta (IL-1beta), fibroblast growth factor-2, epidermal growth factor (EGF), amyloid beta1-42, and 50% O2, only EGF and IL-1beta altered the level of GIF in confluent astrocytes: EGF increased both GIF mRNA and protein, and IL-1beta decreased GIF mRNA, but did not alter GIF protein. Kinetic analysis of the GIF mRNA level revealed the biphasic regulation of GIF mRNA expression by IL-1beta, i.e., a transient up-regulation followed subsequently by down-regulation, explaining in part the discrepancy between the levels of GIF mRNA and protein in astrocytes treated with IL-1beta.