Spontaneously immortalized adult mouse Schwann cells secrete autocrine and paracrine growth‐promoting activities

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Abstract
We established spontaneously immortalized Schwann cell lines from long‐term cultures of adult mouse dorsal root ganglia and peripheral nerves. One of the cell lines, designated IMS32, responded to mitogenic stimuli by platelet‐derived growth factor (PDGF)‐BB, acidic and basic fibroblast growth factors (aFGF, bFGF), and transforming growth factors (TGF)‐b̃1 and ‐b̃2, as determined by bromodeoxyuridine (BrdU) incorporation and double immunofluorescence for S100 and BrdU. Furthermore, conditioned media (CM) obtained from IMS32 cells showed mitogenic activity for both IMS32 cells and long‐term cultured Schwann cells. Western blot analysis revealed TGF‐b̃‐like molecule in the CM, and the activity was absorbed with anti‐TGF‐b̃ neutralizing antibody. Reverse transcription followed by polymerase chain reaction (RT‐PCR) of IMS32 RNA revealed that these cells expressed TGF‐b̃1, b̃2, and ‐b̃3 transcripts. When rat pheochromocytoma PC 12 cells were incubated with the CM, they developed neurite growth. Coculture of PC12 and IMS32 cells also showed neurite growth of PC12 cells. RNA transcripts of nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT3), ciliary neurotrophic factor (CNTF), and glial cell line‐derived neurotrophic factor (GDNF) were detected from IMS32 cells by RT‐PCR. In these, we sequenced the mouse GDNF cDNA coding region and observed 97% and 90% homologies to corresponding rat and human cDNA sequences, respectively. These results indicate that the immortalized Schwann cell line mitotically responds to various growth factors and secretes autocrine and paracrine growth‐promoting activities in vitro.