Abstract
The insulin‐like growth factor (IGF) system is a key regulator of cell growth, survival and differentiation, and these functions are co‐modulated by other growth factors including fibroblast growth factor‐2 (FGF‐2). To investigate IGF/FGF interactions in neuronal cells, we employed neuroblastoma cells (SK‐N‐MC). In serum free conditions proliferation of the SK‐N‐MC cells was promoted by IGF‐I (25 ng/ml), but blunted by FGF‐2 (50 ng/ml). IGF‐I‐induced proliferation was abolished in the presence of FGF‐2 even when IGF‐I was used at 100 ng/ml. In addition to our previously described FGF‐2 induced proteolytic cleavage of IGFBP‐2, we found that FGF‐2 increased IGFBP‐6 levels in conditioned medium (CM) without affecting IGFBP‐6 mRNA abundance. Modulation of IGFBP‐2 and ‐6 levels were not significant mechanisms involved in the blockade of IGF‐I action since the potent IGF‐I analogues [QAYL]IGF‐I and des(1–3)IGF‐I (minimal IGFBP affinity) were unable to overcome FGF‐2 inhibition of cell proliferation. FGF‐2 treated cells showed morphological differentiation expressing the TUJ1 neuronal marker while cells treated with IGF‐I alone showed no morphological change. When IGF‐I was combined with FGF‐2, however, cell morphology was indistinguishable from that seen with FGF‐2 alone. FGF‐2 inhibited proliferation and enhanced differentiation was also associated with a 70% increase in cell death. Although IGF‐I alone was potently anti‐apoptotic (60% decreased), IGF‐I was unable to prevent apoptosis when administrated in combination with FGF‐2. Gene‐array analysis confirmed FGF‐2 activation of the intrinsic and extrinsic apoptotic pathways and blockade of IGF anti‐apoptotic signaling. FGF‐2, directly and indirectly, overcomes the proliferative and anti‐apoptotic activity of IGF‐I by complex mechanisms, including enhancement of differentiation and apoptotic pathways, and inhibition of IGF‐I induced anti‐apoptotic signalling. Modulation of IGF binding protein abundance by FGF‐2 does not play a significant role in inhibition of IGF‐I induced mitogenesis. © 2003 Wiley‐Liss, Inc.