|3-D Model of the ornithine decarboxylase|
|X-Ray Model of the ornithine decarboxylase|
We have shown that a mouse neuroblastoma variant, DF-40, whose ornithine decarboxylase (ODC) gene has been amplified 40-fold, cannot be induced to differentiate by cAMP analogs, most likely due to its high polyamine contents as we have predicted. To our surprise, however, we found that DF-40 cells can differentiate in the absence of serum in spite of its high polyamine contents. We speculate that polyamines (putrescine, spermidine, and spermime) may be sequestered in the absence of serum and that a certain growth factor(s) present in serum can either mobilize the sequestered polyamines or is needed for the growth-stimulatory action of polyamines. Since very little is known about the compartmentalization and trafficking of polyamines inside mammalian cells, the serum-dependent differentiation of DF-40 cells may offer a unique system to investigate polyamine compartmentalization and utilization.