Demonstration of coordinate regulation of p75NTR and CRABP1, and CRABP1 knockdown-induced decrease in fenretinide efficacy in SH-EP1 cells caused us to examine whether these effects are also seen in the SK-N-AS epithelioid human neuroblastoma cell line.
To our surprise, in contrast to the case for SH-EP1 cells, stable knockdown of p75NTR in native SK-N-AS cells resulted in upregulation of CRABP1 (Figure 4(a)).
Effects of Manipulation of CRABP1 Expression on p75NTR Expression and Fenretinide Efficacy in Neuroblastoid Human Neuroblastoma Cell Lines.
Induction of expression of CRABP1 in SH-SY5Y cells did not alter expression of p75NTR (Figure 5).
CRABP1 binds to retinoids and thereby sequesters them in the cytoplasm and prevents their shuttling to the nucleus.
Our results demonstrate neuroblastoma cell line-dependence of the effects of manipulation of p75NTR expression on CRABP1 expression and the effects of CRABP1 expression on fenretinide-induced cell death.
The fact that p75NTR and CRABP1 expression differentially affect one another and the impact of treatment with fenretinide in different neuroblastomas makes p75NTR or CRABP1, at best, complex biomarkers for likely responsiveness to that drug.
Caption: Figure 1: Western blot (a) and RT-PCR (b) for p75NTR, CRABP1, and loading marker protein and mRNA, respectively, performed on lysates of different neuroblastoma cell lines.
Caption: Figure 2: (a) Western blot for CRABP1 in SH-EP1 cells transfected with an expression construct for p75NTR (OE) or the analogous empty vector (OE Ctrl).
Caption: Figure 3: Metabolic viability and cell number of SH-EP1 cells transfected with CRABP1 siRNA or a scrambled control construct after treatment with fenretinide.
Caption: Figure 4: p75NTR, CRABP1, and response to fenretinide in SK-N-AS neuroblastoma cells.