Cell Line-Dependent Variability of Coordinate Expression of p75NTR and CRABP1 and Modulation of Effects of Fenretinide on Neuroblastoma Cells.

Neuroblastoma is a childhood neural crest tumor. Fenretinide, a retinoic acid analogue, induces accumulation of mitochondrial reactive oxygen species and consequent apoptosis in neuroblastoma cells. The p75 neurotrophin receptor (p75NTR) enhances the antineuroblastoma cell efficacy of fenretinide in vitro. We examined the role of the retinoid binding protein, CRABP1, in p75NTR-mediated potentiation of the efficacy of fenretinide. Knockdown and overexpression, respectively, of either p75NTR or CRABP1 were effected in neuroblastoma cell lines using standard techniques. Expression was determined by qRT-PCR and confirmed at the protein level by Western blot. Metabolic viability was determined by Alamar blue assay. While protein content of CRABP1 correlated roughly with that of p75NTR in the three neuroblastoid or epithelioid human neuroblastoma cell lines studied, manipulation of p75NTR expression resulted in cell line-dependent, variable change in CRABP1 expression. Furthermore, in some cell lines, induced expression of CRABP1 in the absence of p75NTR did not alter cell sensitivity to fenretinide treatment. The effects of manipulation of p75NTR expression on CRABP1 expression and the effects of CRABP1 expression on fenretinide efficacy are therefore neuroblastoma cell line-dependent. Potentiation of the antineuroblastoma cell effects of fenretinide by p75NTR is not mediated solely through CRABP1.

Induction of Expression of p75 Neurotrophin Receptor Intracellular Domain Does Not Induce Expression or Enhance Activity of Mitochondrial Complex II.

Fenretinide is a chemotherapeutic agent in clinical trials for the treatment of neuroblastoma, among the most common and most deadly cancers of childhood. Fenretinide induces apoptosis in neuroblastoma cells through accumulation of mitochondrial reactive oxygen species released from Complex II. The neurotrophin receptor, p75NTR, potentiates this effect. The signaling activity of p75NTR is dependent upon its cleavage to its intracellular domain, p75ICD, trafficking of p75ICD to the nucleus, and functioning of p75ICD as a transcription factor. Mitochondrial Complex II comprises 4 subunits, all of which are encoded by nuclear DNA. We therefore hypothesized that the fenretinide-potentiating effects of p75NTR are the result of transcriptional enrichment of Complex II by p75ICD. However, the present studies demonstrate that neither induced expression of p75ICD or its active fragments nor overexpression of p75NTR results in altered expression or activity of Complex II.