DR-nm23 gene expression in neuroblastoma cells: Relationship to integrin expression, adhesion characteristics, and differentiation

Abstract

Background: Neuroblastoma, a childhood tumor originating from cells of the embryonic neural crest, retains the ability to differentiate, yielding cells with epithelial-Schwann-like, neuronal, or melanocytic characteristics. Since nm23 gene family members have been proposed to play a role in cellular differentiation, as well as in metastasis suppression, we investigated whether and how DR-nm23, a recently identified third member of the human nm23 gene family, might be involved in neuroblastoma differentiation. Methods: Three neuroblastoma cell lines (human LAN-5, human SK-N-SH, and murine N1E- 115) were used in these experiments; cells from two of the lines (SK-N-SH and N1E-115) were also studied after being stably transfected with a plasmid containing a full-length DR-nm23 complementary DNA. Cellular expression of specific messenger RNAs and proteins was assessed by use of standard techniques. Cellular adhesion to a variety of protein substrates was also evaluated. Results: DR-nm23 messenger RNA levels in nontransfected LAN-5 and SK-N-SH cells generally increased with time after exposure to differentiation-inducing conditions; levels of the other two human nm23 messenger RNAs (nm23-H1 and nm23-H2) remained essentially constant. Transfected SK-NSH cells overexpressing DR-nm23 exhibited some characteristics of differentiated cells (increased vimentin and collagen type IV expression) even in the absence of differentiation-inducing conditions. Compared with control cells, DR-nm23 transfected cells exposed to differentiation-inducing conditions showed a greater degree of growth arrest (SK-N-SH cells) and greater increases in integrin protein expression, especially of integrin β1 (N1E-115 cells). DR-nm23 transfected N1E-115 cells also showed a marked increase in adhesion to collagen type I-coated tissue culture plates that was inhibited by preincubation with an anti- integrin β1 antibody. Conclusions: DR-nm23 gene expression appears to be associated with differentiation in neuroblastoma cells and may affect cellular adhesion through regulation of integrin protein expression.