Modulation of POMC expression in human neuroectodermal cells

Neuroblastoma cell lines have been reported to contain two proopiomelanocortin (POMC) mRNA transcripts. We have now shown by immunocytochemistry and radioimmunoassay (RIA) that a number of neuroectodermally derived cell lines contain immunoreactive β-endorphin although cell concentrations were not characteristic of any tumour type. To explore further the functional significance of β-endorphin expression, we analysed neuroblastoma cell lines having intermediate (I), substrate adherent (S) and neuronal (N) phenotypes. No differences in cell β-endorphin content were detected. However, the expression of POMC mRNA and of immunoreactive β- endorphin was reduced within a few hours of treatment of these cell lines with retinoic acid. Culture of the cell lines in the presence of β-endorphin resulted in small but significant increases in growth. Although the POMC gene is in the same chromosomal segment as N-myc, which is normally amplified in neuroblastoma, no corresponding amplification of POMC could be demonstrated. The data suggest that POMC gene products may contribute to the autocrine/paracrine growth of neuroectodermal tumours.