Retinoic Acid Induces Neuroblastoma Cell Death by Inhibiting Proteasomal Degradation of Retinoic Acid Receptor α

Abstract

To seek a novel therapeutic approach to neuroblastoma (NBL), we used three NBL cell lines (SK-N-DZ, NH12, and SK-N-SH) to examine the underlining molecular mechanisms of cellular reactions and sensitivity to all-trans-retinoic acid (ATRA). SK-N-DZ cells expressed relatively high levels of retinoic acid receptor ␣ (RAR-␣) and underwent ATRA-induced cell death that was blocked by an RAR-␣ antagonist. By contrast, RAR-␣ expression gradually decreased in NH12 and SK-N-SH cells, which did not experience increased cell death in response to ATRA. We report here the ubiquitin-dependent down-regulation of RAR-␣ expression during ATRA treatment. Our data suggest that SK-N-DZ cells have a defect in RAR-␣ down-regulation, resulting in sustained high expression of RAR-␣ that confers high sensitivity to ATRA. Accordingly, treatment with a proteasome inhibitor dramatically increased ATRA-induced cell death in NH12 and SK-N-SH cell lines. Our results reveal the crucial involvement of the RAR-␣ signaling pathway in NBL cell death and show that three NBL cell lines are differentially sensitive to ATRA. These data suggest a potential novel therapy for NBL involving retinoic acid treatment combined with the inhibition of RAR-␣ degradation.

Resistance to the atypical retinoid ST1926 in SK-N-AS cells selected the subline rAS-ST with enhanced sensitivity to ATRA mediated by not conventional mechanisms: DNA damage, G2 accumulation and late telomerase inhibition

“…Intriguingly, in the ST1926-resistant subline, ATRA treatment enhanced the expression of both RARa and total RARb, with early accumulation in G2 phase. This modulation of RARs' expression was consistent with reported lines of evidence showing a correlation between RA sensitivity and inhibition of RARa-catabolism, amplification of RARa-transcription (Nagai et al, 2004) and to increased expression of RARb in NB cells (Perez-Juste and Aranda, 1999). Furthermore, there are reported lines of evidence that inhibition of proteasome by MG132 enhances ATRA responsivity (Nagai et al, 2004).…”

“…5B). Proteasome inhibition by MG132 was reported to enhance the cellular responsivity to ATRA (Nagai et al, 2004). Therefore, we explored a possible role for the proteasome in our model of ATRA-sensitivity shown by the retinoid resistant subline.…”

Bcl-2 is a key regulator for the retinoic acid-induced apoptotic cell death in neuroblastoma

“…All-trans-retinoic acid activates phosphatidylinositol 3 0 -kinase-Akt pathway that plays an important role in neuronal differentiation (Encinas et al, 1999;Lopez-Carballo et al, 2002), and it reduces the expression levels of MYCN (Thiele et al, 1985) and upregulates the cyclin-dependent kinase (CDK) inhibitor p27 KIP1 in association with the ATRA-induced cell cycle arrest in neuroblastoma cells (Lee et al, 1996;Nakamura et al, 2003). In addition, certain neuroblastoma cells underwent apoptosis in response to ATRA (Piacentini et al, 1992;Takada et al, 2001;Nagai et al, 2004). Consistent with these observations, 13-cis-RA treatment after intensive chemotherapy improved an event-free survival rate of the patients with aggressive neuroblastomas with 17% increase (Villablanca et al, 1995;Matthay et al, 1999).…”

p38 Mitogen‐activated protein kinase‐dependent regulation of SRC‐3 and involvement in retinoic acid receptor α signaling in embryonic cortical neurons

“…It has been demonstrated that the effect of RA, in terms of inducing or inhibiting degradation of RARa, is cell type specific (30)(31)(32). We observed that ATRA caused a decrease in RARa levels in the cultured neurons, and this decrease was not altered by p38 MAPK inhibition.…”