Expression of trkA cDNA in neuroblastomas mediates differentiation in vitro and in vivo.

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Abstract
The human trkA cDNA was transfected into a malignant human neuroblastoma (NB) cell line (HTLA230) to investigate its role in NB growth and differentiation. This cell line lacks expression of both endogenous trkA and gp75NGFR genes. Transfectants expressing the trkA mRNA and surface-bound receptors transcriptionally activate immediate-early genes (c-fos, c-jun, and jun-B) following nerve growth factor (NGF) stimulation. NGF treatment induces growth arrest as well as down-regulation of the amplified N-myc oncogene. Genes selectively expressed in mature neurons (SCG-10, ret proto-oncogene, GAP-43, etc.) are transcriptionally activated, and neurite outgrowth further demonstrates differentiation of transfectants following NGF stimulation. trkA-expressing NB cells remain tumorigenic in nude mice; however, subcutaneous treatment of tumor-bearing mice with NGF induces Schwannian and neuronal cell differentiation similar to the induction seen in human ganglioneuroblastomas. Thus, trkA expression in HTLA230 cells is sufficient to generate a functional NGF receptor complex that leads to growth-arrested and differentiated NB cells in vitro and in vivo in the presence of NGF. Hence, NGF may play a crucial role in NB cell differentiation and regression in vivo.