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 b y IGF-II but not by IGF-I. We have studied the expression of IGF, IGFB P 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 g row 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 t en times greater than the CHP cell line. RNase protection assays were performed using P-32-labelled riboprobes and RNA that had been purifie d 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 hu man 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 expr essed IGFBP-5 mRNA. In addition, a 400 bases protected band was seen w ith the IGF-I receptor probe and a 260 bases protected band with the I GF-IIM6P receptor probe in either cell line. Interestingly, a 300 base s 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 radioimm unoassays SK-N-MC cells secreted 0.75+/-0.02 ng/ml IGF-I, 1.2+/-0.04 n g/ml TGF-II. and 149+/-2.1 ng/ml IGFBP-2 within 24 h, whereas Clip cel ls 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 wit h IGF-I (r=-0.9, P<0.01) in SK-N-MC cells. In conclusion, SK-N-MC cell s which grow rapidly and have a high plating efficiency, express TGF-I , while Clip cells that grow more slowly express IGF-II. We hypothesiz e that neuroblastoma cells depend upon autocrine stimulation by either IGF-I or IGF-II. Variable sensitivity to growth inhibitors or apoptot ic processes may be related to the differential expression of the IGF system. (C) 1997 Elsevier Science B.V.