Differentiation of normal and adenovirus-12 E1 transformed human embryo retinal cells

Following the treatment with dibutyryl cyclic AMP (dbcAMP) in the absence of serum, a proportion of cultured human embryo retinoblasts will differentiate rapidly. This is characterized by cell rounding and the extension of neuritic-type processes. A transformed cell line (Ad 12 HER 10), developed by transfection of human embryo retinoblasts with adenovirus 12 (Ad 12) early region 1 (E1) DNA, forms retinoblastoma-like tumours in athymic nude mice and retains the ability to extend neuritic-like processes after treatment with dbcAMP in the absence of serum. This response, which occurs in almost all cells (over 98%), is accompanied by growth arrest and reverses rapidly after re-exposure to serum. Other agents known to increase intracellular cAMP also mediate differentiation. Ad 12 HER 10 cells were shown to contain the neuronal markers, neurone-specific enolase and protein gene product 9.5, but not the glial cell marker glial fibrillary acidic protein (GFAP). Activity of the neurotransmitter enzyme acetylcholinesterase was also detected and found to increase after differentiation. Interestingly, the expression of the Ad 12 E1 transforming proteins did not change throughout differentiation. These results show first, that the Ad 12 HER 10 cell line can differentiate in a similar manner to that observed in a proportion of primary retinoblasts and second, that the expression of transforming proteins does not preclude at least part of that differentiative capacity. This is the first demonstration of in vitro differentiation in an adenovirus-transformed human cell line, as well as offering a useful system for the study of factors controlling growth and differentiation of tumorigenic human retinoblasts.