RETINOIC ACID STIMULATES PROTEIN-KINASE A-ASSOCIATED G-PROTEINS DURING HUMAN TERATOCARCINOMA DIFFERENTIATION

Retinoic acid (RA) treatment of F9 murine teratocarcinoma (TC) cells r educes the expression of the protein kinase A (PKA)-associated G prote in, G(alpha i2). The present study reveals interactions between the RA and PKA pathways during differentiation of the multipotent human TC c ell line NTERA-2 clone D1 (abbreviated NT2/D1) which differ from prior reports in F9 TC cells. Compared to untreated NT2/D1 cells, different iated NT2/D1 cells expressed increased levels of G(alpha S) and G(alph a il,2) proteins as shown by both immunoblot analysis and cholera toxi n- and pertussis toxin-induced ADP ribosylation. To further explore co operation between these pathways during human TC differentiation, we e xamined the effects of cyclic adenosine monophosphate (cAMP) on RA-res ponsive genes and of RA treatment on the transcriptional activation of a cAMP response element (CRE). Compared to RA alone, combined treatme nt with RA and cAMP augmented the expression of the RA nuclear recepto r-beta (RAR-beta). Also, transient transfection assays revealed that c AMP and RA cooperated to enhance CRE transcriptional activation. The c AMP-induced enhancement of RA actions in NT2/D1 cells extended to immu nophenotypic changes typical of the neuronal differentiation program i nduced by RA. In contrast to these findings in NT2/D1 cells, prior wor k in F9 TC cells showed that cAMP inhibits the RA-mediated augmentatio n of RAR-beta expression and switches the differentiation program from visceral to parietal endoderm. Thus, unlike murine TC cells, in human NT2/D1 cells RA stimulates PKA-associated G proteins and PKA pathway activation enhances RA-mediated TC differentiation.