Retinoic Acid Receptor γ1 (RARγ₁) Levels Control RARβ₂ Expression in SK-N-BE2(c) Neuroblastoma Cells and Regulate a Differentiation-Apoptosis Switch

ABSTRACT

Vitamin A and its derivatives (retinoids) have profound effects on the proliferation and differentiation of many cell types and are involved in a diverse array of developmental and physiological regulatory processes, including those responsible for the development of the mature nervous system. Retinoid signals are mediated by retinoic acid (RA) receptors (RARs) and retinoid X receptors (RXRs), which show distinct spatio-temporal patterns of expression during development and in adult tissues. We have used SK-N-BE2(c) neuroblastoma cells to study the effects of reciprocal regulation of expression of various RARs. We show that in these cells RARγ₁ acts as a repressor of RARβ₂ transcription in the absence of an agonist. In the presence of RA, the expression of RARγ₁ is reduced and that of RARβ₂ is induced. Overexpression of RARγ₁ neutralizes the effects of RA on RARβ induction. Expression of an RARγ₁-specific antisense construct leads to the constitutive expression of RARβ₂. Although both overexpression of RARγ₁ and its reduction of expression can result in inhibition of cell proliferation, they induce different morphological changes. Reduction of RARγ₁ (and induction of RARβ) leads to increased apoptosis, whereas RARγ₁ overexpression leads to differentiation in the absence of apoptosis. Thus, RARγ₁ appears to control a differentiation-apoptosis switch in SK-N-BE2(c) neuroblastoma cells.

ACKNOWLEDGMENTS

We thank B. Shroot and J. M. Bernardon (CIRD Galderma) for supplying us with the antagonists and the Developmental Studies Hybridoma Bank for the 2H3 monoclonal antibody. We also thank Ulrich Pfeffer, Andrea Fanjul, and Javi Piedrafita for helpful discussions and Anna Briata and Francesco Campelli for excellent technical assistance.

This work was supported by grants from PF ACRO-CNR, Associazione Italiana per la Ricerca sul Cancro, Fondazione Italiana per la Ricerca sul Cancro (Luisa Santunione), Ministero della Sanità, CNRS. The work carried out at the Sidney Kimmel Cancer Center was supported by grant CA 55681 to M.P.