Expression of intermediate filaments and synaptophysin show neuronal properties and lack of glial characteristics in Y79 retinoblastoma cells

The expression of intermediate filaments and synaptophysin in Y79 retinoblastoma cells was studied. The cells grew normally in suspension as floating aggregates. Sodium butyrate and dibutyryl cyclic AMP induced adherence and rapid spreading of Y79 cells on laminin-coated substratum and many of the cells presented long cellular extensions. As judged by immunostaining with monoclonal and polyclonal antibodies, most untreated Y79 cells expressed synaptophysin, whereas only vimentin intermediate filaments were detected in a few cells. A more bright fibrillar vimentin-positivity, which responded by coiling to disruption of microtubules, could be seen in the spread cells. Furthermore, especially when exposed to butyrate, a distinct fibrillar positivity could be revealed in some of the spread cells with antibodies recognizing a phosphorylated epitope in neurofilaments. Western blotting results showed the presence of the molecular weight 57,000 vimentin polypeptide and the molecular weight 38,000 synaptophysin polypeptide in both undifferentiated and spread Y79 cells, and a phosphorylated molecular weight 200,000 neurofilament polypeptide in spread cells only. In contrast, both immunostaining and Western blotting results with several antibodies indicated lack of glial fibrillary acidic protein in Y79 cells suggesting hence, a lack of glial differentiation. The present results do not support the hypothesis that retinoblastomas would originate from a common precursor cell of neurons and glia, and show the presence of mainly neuronal features in Y79 retinoblastoma cells.