Effect of growth factors and steroids on transglutaminase activity and expression in primary astroglial cell cultures

Type-2 transglutaminase (TG-2) is a multifunctional enzyme involved in the regulation of cell differentiation and survival that recently has been shown to play an emerging role in astrocytes, where it is involved in both proliferation and differentiation processes. Growth factors (GFs) such as EGF, basic fibroblast growth factor, insulin-like growth factor-I (IGF-I), and insulin (INS) are trophic and mitogenic peptides that participate in neuron-glia interactions and stimulate neuronal and astroglial proliferation and differentiation. Steroid hormones such as glucocorticoids and estrogens also play a pivotal role in neuronal and astroglial proliferation and differentiation and are key hormones in neurodegenerative and neuroprotective processes. We investigated the effects of the interaction of GFs with dexamethasone (DEX) or 17beta-estradiol (E(2)) on TG-2 activity and their expression in cultured astrocytes. We observed a significant increase in TG-2 activity and expression in astroglial cells treated for 24 hr with IGF-I, EGF, or INS. Priming of the cells with DEX or E(2), for 48 hr also led to an increase in TG-2 levels. When growth factors were present in the last 24 hr of the steroid treatment, a reduction in TG-2 expression and activity and a different subcellular TG-2 distribution were found. Our data indicate that steroid hormone-GF interaction may play an important role in astroglial function. The effect on TG-2 could be part of the regulation of intracellular pathways associated with the astrocyte response observed in physiological conditions and, possibly, also in neuropathological diseases.