Retinoic acid modulation of transmembrane signaling: Analysis in F9 teratocarcinoma cells

F9 embryonal mouse teratocarcinoma cells were differentiated to a primitive endoderm-like phenotype by retinoic acid and to a parietal endoderm-like phenotype by retinoic acid in combination with dibutyryl cyclic AMP. The secretion of tissue plasminogen activator (tPA) is a characteristic of the cells displaying the differentiated phenotypes. The fundamental question of whether tPA secretion is regulated acutely by G-protein-mediated transmembrane signaling was explored. Cells differentiated to primitive and parietal endoderm demonstrated a rapid tPA response to stimulation by β-adrenergic agonist (isoproterenol). Adenylyl cyclase activity in response to isoproterenol and GTP, but not forskolin, was greater in primitive and parietal endoderm than F9 stem cells. Both primitive and parietal endoderm cells, but not F9 stem cells, displayed β-adrenergic stimulation of cyclic AMP accumulation. Retinoic acid induced F9 stem cells to the primitive endoderm phenotype and increased β-adrenergic receptor levels 3-fold. G_iα2 levels declined, G_β-subunits increased, and G_iα, levels were unchanged following differentiation to primitive endoderm. In parietal endoderm cells β-adrenergic receptors increased 2-fold over F9 stem cells, G_iα2 levels declined even further than in primitive endoderm, G_β-subunits increased compared to F9 stem cells, and G_iα levels again were unchanged. The marked potentiation of short-term stimulation of tPA secretion in the differentiated state may be best explained by the retinoic acid-induced increase in expression of β-adrenergic receptors coupled with a decline in G_iα2 levels. Short-term regulation by G-protein-linked receptors represents a novel mode for the control of tPA secretion.