Expression of galectin‐3 in neuronally differentiating PC12 cells is regulated both via Ras/MAPK‐dependent and –independent signalling pathways

Abstract

Galectin-3 (gal-3) is a member of the galectin family of lectins whose expression strongly depends on the cellular state. Here we show that in PC12 cells the expression of gal-3 protein is regulated via Ras-and mitogen-activated protein kinase (MAPK)-dependent and -independent signalling pathways and correlates with nerve growth factor (NGF)-mediated neuronal differentiation. Gal-3 expression, activation of the MAPK ERK1/2 and neurite outgrowth are induced by NGF and basic fibroblast growth factor (bFGF), but not by ciliary neurotrophic factor (CNTF), epidermal growth factor, insulin or interleukin-6 (IL-6). In addition, in NGF-treated PC12 cells, gal-3 expression, ERK1/2 activation and neurite outgrowth could be specifically inhibited at the level of TrkA, Ras and MAPK-kinase, whereas expression of an oncogenic form of Ras leads to gal-3 expression and neurite outgrowth in the absence of growth factors. In NGF-primed PC12 cells, subsequent treatment with CNTF or IL-6 induces ERK1/2 activation and neurite outgrowth, but not gal-3 expression. Treatment of PC12 cells with staurosporine induces gal-3 expression and neurite outgrowth without ERK1/2 activation. NGF-and staurosporineinduced gal-3-expression is also regulated at the transcriptional level. Our data suggest the presence of complex induction mechanisms of gal-3 expression in neuronally differentiating PC12 cells involving NGF-, but not CNTF-and IL-6-driven (in NGF-primed cells) Ras/MAPK-related signalling pathways. Staurosporine, in contrast, induces gal-3 expression by a Ras/MAPK-independent mechanism. Keywords: ERK, galectin-3, interleukin-6, nerve growth factor, PC12 cells, Ras. Galectin-3 (gal-3) belongs to the galectin family of soluble lectins as defined by (i) amino acid sequence homology and (ii) their affinitiy to b-galactosidic carbohydrate structures (reviewed by Cooper 2002). Dependent on the cell type, gal-3 can be expressed intracellularly (cytoplasm and nucleus) and/or extracellularly (plasma membrane or extracellular space). The expression of gal-3 has been associated with a number of different normal biological and pathological processes, such as apoptotic cell death, differentiation, growth and transformation (reviewed by Rabinovich 1999). Thus, gal-3 expression generally correlates with alterations in the state of cell activation. In this context, a basic question concerns the mechanisms of regulation of gal-3 expression in different cell types (reviewed by Chiariotti et al. 1999). First investigated in mouse and human fibroblasts, the expression of gal-3, which is low or absent in quiescent growth-arrested cells, has been found to be induced after serum addition (reviewed by Kadrofske et al. 1998). In activated Schwann and microglial Received March 13, 2002; revised manuscript received July 2, 2003; accepted August 6, 2003. Address correspondence and reprint requests to Rainer Probstmeier, Neuro-and Tumor Cell Biology Group, Department of Nuclear Medicine, University of Bonn, Sigmund Freud Str. 25, 53105 Bonn, Germany. E-mai...

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