Retrovirus-mediated expression of an artificial beta-endorphin precursor in primary fibroblasts

Peptides are of potential interest in the field of gene therapy but require modification by genetic engineering to facilitate their secretion. Amino terminal addition of a signal peptide is not always sufficient to achieve this goal, as found in this study for beta-endorphin. To overcome this problem, addition of the pre-pro-sequence of mouse nerve growth factor to beta-endorphin was tested. Retrovirus-mediated expression of a hybrid construct of the pre-pro-sequence of nerve growth factor and human beta-endorphin in primary fibroblasts resulted in the secretion of beta-endorphin immunoreactivity at a rate of 620 pg/h/10(6) cells. Analysis of the secreted beta-endorphin immunoreactivity with reverse-phase HPLC, immunoassays using three different antibodies, and an assay for the specific displacement of [3H][D-Ala2,N-MePhe4,Gly-ol5]enkephalin from mu-opioid receptors suggests that the pre-pro-sequence is cleaved off from the pre-pro-sequence/beta-endorphin construct prior to secretion, resulting in bona fide beta-endorphin. Transplantation of beta-endorphin-secreting cells into brain or spinal cord may provide a gene therapy approach for the treatment of chronic, opioid-sensitive pain states.