Human neuroblastoma cells use either insulin-like growth factor-I or insulin-like growth factor-II in an autocrine pathway via the IGF-I receptor: Variability of IGF, IGF binding protein (IGFBP) and IGF receptor gene expression and IGF and IGFBP secretion in human neuroblastoma cells in relation to cellular proliferation

Neuroblastoma cells are thought to depend upon autocrine stimulation by IGF-II but not by IGF-I. We have studied the expression of IGF, IGFBP and IGF receptor mRNA in two human neuroblastoma cell lines, SK-N-MC and CHP and asked whether or not the expression of the IGF system in these malignant cells determines their growth pattern. SK-N-MC cells grow with a cell doubling time of 36 hours in medium supplemented with 10% fetal calf serum whereas CHP cells only grow with a doubling time of 72 h. In addition, the SK-N-MC cell line has a plating efficiency ten times greater than the CHP cell line. RNase protection assays were performed using P-32-labelled riboprobes and RNA that had been purified from SK-N-MC and Clip cells respectively. A 520 bases human IGF-I, a 556 bases human IGF-II, a 480 bases human IGF-I receptor and a 250 human IGF-II/mannose-6-phosphate (M6P) receptor probe were radiolabelled as were human IGFBP-1, -2, -3, -4, -5 and -6 probes. While both SKNMC and CHP neuroblastoma cells expressed mRNAs for IGFBP -2, -4, and -6 no signal was detected for IGFBP-1, and -3 and only SK-N-MC cells expressed IGFBP-5 mRNA. In addition, a 400 bases protected band was seen with the IGF-I receptor probe and a 260 bases protected band with the IGF-IIM6P receptor probe in either cell line. Interestingly, a 300 bases protected species was detected with the IGF-II probe in CHP cell RNA whereas SK-N-MC cells did not express IGF-II transcripts. Conversely, SK-N-MC cells expressed a 520 bases IGF-I transcript while CHP cells did not show IGF-I mRNA expression. As determined by specific radioimmunoassays SK-N-MC cells secreted 0.75+/-0.02 ng/ml IGF-I, 1.2+/-0.04 ng/ml TGF-II. and 149+/-2.1 ng/ml IGFBP-2 within 24 h, whereas Clip cells secreted 0.1+/-0.01 ng/ml IGF-I, but 6.2+/-0.1 ng/ml IGF-II and 254.8+/-5.5 ng/ml IGFBP-2 (N=5). IGFBP-2 secretion correlated positively with IGF-II secretion in CHP cells (r=0.85, P=0.05) and negatively with IGF-I (r=-0.9, P<0.01) in SK-N-MC cells. In conclusion, SK-N-MC cells which grow rapidly and have a high plating efficiency, express TGF-I, while Clip cells that grow more slowly express IGF-II. We hypothesize that neuroblastoma cells depend upon autocrine stimulation by either IGF-I or IGF-II. Variable sensitivity to growth inhibitors or apoptotic processes may be related to the differential expression of the IGF system. (C) 1997 Elsevier Science B.V.