Acciones del ácido retinoico en la diferenciación de células de neuroblastoma humano.

Abstract

Administration of Retinoic Acid (RA) to SH-SY5Y neuroblastoma cells results in activation of phosphatidyl-inositol-3-kinase (PI3K) signalling pathway, and this activation is required for RA-induced differentiation. Here we show that RA activates PI3K and ERK1/2 MAP Kinase signalling pathways through a rapid, non-genomic mechanism that does not require new gene transcription or newly synthesized proteins. Activation of PI3K by RA appears to involve the nuclear receptor RAR, on the basis of the pharmacological profile of the activation. In addition, activation of PI3K in RA-treated COS-7 cells was strongly increased by transfection of a RAR? expression vector. The intracellular localization of RAR resulted to be relevant for PI3K activation. A chimerical RAR receptor fusing c-Src myristylation domain to the N-terminal of RAR? (Myr-RAR?) was targeted to plasma membrane. Transfection of Myr-RAR? to COS-7 cells results in strong activation of PI3K signalling pathway, although both in the absence as well in the presence of RA. This result would argue for a role of ligand binding in the localization of RAR to plasma membrane, allowing there interactions with components of the signal transduction machinery that result in PI3K activation. By means of biochemical fractionation experiments we demonstrated that the levels of RAR? in the membrane fractions (microsomal and purified plasma membrane fractions) were rapidly increased upon RA administration to NIH-3T3 cells. Immunoprecipitation experiments showed a physical interaction between RAR? and p85, the regulatory subunit of PI3K, both in the absence as well in the presence of RA. Ligand administration increased the association of p110, the catalytic subunit of PI3K, to this complex. The results shown here suggest a model in which RAR forms a stable complex with p85-PI3K. Ligand binding to RAR promotes targeting of this complex to plasma membrane, facilitating the association with p110-PI3K and resulting in increased PI3K activity.