THE PC12 RAT PHEOCHROMOCYTOMA CELL-LINE EXPRESSES THE PRODYNORPHIN GENE AND SECRETES THE 8 KDA DYNORPHIN PRODUCT

Most adrenal chromaffin cells synthesize opioids derived from proenkep halin but not from prodynorphin. However, human pheochromocytomas and the PC12 rat pheochromocytoma cell line synthesize dynorphins. The aim of this study was to confirm the presence of the authentic prodynorph in transcript and its dynorphin product in PC12 cells. We have found t hat the sequence of a 458 bp cDNA fragment derived from RT-PCR amplifi cation of total PC12 RNA was in complete accordance with the published sequence of the equivalent region of the prodynorphin gene. It encode s the potent endogenous kappa opioid agonists alpha-neo-endorphin, dyn orphin A and dynorphin B. Furthermore, immunoaffinity-purified PC12 ce ll extracts were subjected to RP-HPLC. Most of its IR-dynorphin eluted on a peak exhibiting the retention time of similarly treated rat ante rior pituitary. The expression of the prodynorphin gene in pheochromoc ytomas can be explained as either the result of (a) the process of ded ifferentiation of chromaffin cells to pheochromocytoma which may thus cause the expression of a previously unexpressed prodynorphin or that (b) those pheochromocytomas expressing the prodynorphin gene derive fr om the few, centrally located chromaffin cells, which express this gen e even under normal conditions.