Clonal variation in cultured neuroblastoma cells. II. The relationship of increased intracellular cyclic amp content to increased anchorage requirement for growth and flattened morphology

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Abstract
Flat variant clones were isolated from both the N18 neuroblastoma cell line and from a subclone of the parent line exhibiting the typical round cell morphology. Several revertant clones exhibiting the round parental morphology were also isolated from one of the flat variant clones. The flat variants exhibit decreased cloning efficiency in suspension and increased amounts of myosin heavy chain when compared to the round cell clones. Intracellular cAMP levels were increased from two- to fivefold over those in clones representative of the parent line and in the round cell revertants. Treatment with the phosphodiesterase inhibitor RO20-1724 increased cAMP levels and reduced suspension cloning efficiency without altering doubling time or attached cloning efficiency. Increasing cAMP levels of two of the round cell clones by treatment with the phosphodiesterase inhibitor caused increased flattening of the cell body and increased myosin heavy chain content. Thus, even though increased cAMP level may be sufficient to explain the reduced cloning efficiency of the flat variants, it is not the sole cause of the flat morphology.