Proto-oncogene expression in cAMP and TPA-mediated neuronal differentiation in a human retinal cell line KGLDMSM

A human retinal cell line, KGLDMSM, developed by SV-40T antigen gene transfection, is stable in culture for a long period, unlike the primary cells. The cell line shows some degree of morphological differentiation with limited extension of stublike neurites upon transfer to defined medium. In our effort to explore genes implicated in neuritic extension and neuronal differentiation seen in response to cAMP and TPA, we have analyzed time dependent induction of a variety of proto-oncogenes: c-myc, H-ras, c-ras, and c-fos.

Cells were adapted to grow in defined media and exposed to differentiation inducing agents cAMP, TPA, Retinoic Acid, and sodium butyrata. Cells were assessed for phenotypic changes and altered expression of proto-oncogenes as evaluated by Northern Blot analysis and immunocytochemistry.

Exposure of the cells to cAMP and TPA induced dramatic changes, with 100% of the cells extending neuritic processes. However, other differentiation inducing agents such as retinoic acid and sodium butyrata failed to elicit any response. We report that agents that promote neuritic extension also induce expression of c-fos. Transcriptional activation of c-fos in response to cAMP (30 min) and TPA (1hr) is also accompanied by expression of fos gene product as evaluated by using fos antibody. No fos expression was seen in uninduced cells.

In retinal cell line KGLDMSM, agents that enhance neuronal differentiation (cAMP, TPA) also induce c-fos expression. Expression of c-fos may be a necessary prerequisite in neuronal differentiation and the established retinal cell line offers an excellent cell model for dissecting the molecular events underlying neuronal differentiation.