Endodermal differentiation of murine embryonic carcinoma cells by retinoic acid requires JLP, a JNK-scaffolding protein

Retinoic acid (RA) is a morphogen that induces endodermal differentiation of murine P19 embryonic carcinoma cells. RA-induced differentiation of P19 cells has been used as a model system to define the differentiation programs of pluripotent stem cells. Using this system it has been shown that Gα₁₃-the α-subunit of the heterotrimeric G protein G ₁₃-and its activation of JNK-module are critically required for the endodermal differentiation of P19 cells. However, the mechanism through which Gα₁₃ is linked to JNK-module is unknown. Here, we report that RA stimulates the expression of JNK-interacting leucine zipper protein (JLP), a newly identified JNK-scaffolding protein and its critical role in RA-mediated endodermal differentiation. Our results indicate that there is a physical association between JLP and Gα₁₃ in RA-stimulated P19 cells. More interestingly, silencing JLP abrogates RA-mediated endodermal differentiation of P19 cells analogous to the effects seen with the silencing of Gα₁₃ or JNK. Therefore, our studies presented here identify for the first time, a novel role for a newly identified scaffolding protein in RA-mediated endodermal differentiation, providing a new signaling conduit to transmit signals from RA to JNK module.