The differential processing of proenkephalin A in mouse and human breast tumour cell lines

We have carried out an investigation into the processing of the enkephalin- like immunoreactivity reported in breast tissue using two human breast tumo ur cell lines and a mouse tumour cell line. A 46 kDa form of proenkephalin (PE) has been observed in the cell lysates of two human breast tumour cell Lines (MCF-7, ZR-75-1) and the mouse androgen-responsive Shionogi breast ca rcinoma cell line (SC115). PE processing in the cell lysates of these cells was assessed by a specific met-enkephalin RIA. The basal levels of process ed PE in the MCF-7, ZR-75-1 and SC115 cell lysates were 30, 30 and 76% resp ectively. The processing enzymes PC1 and PC2, which have been implicated in the differential processing of PE, were detected by immunoblot analysis in these cells. PC1 was found within the cell extracts of all three cell line s. PC2 was only observed in the SC115 cell line, which may account for the higher percentage of processed PE measured, The cDNA of PC2 has been transf ected into ZR-75-1 cells and this was accompanied by an increase in the lev el of processed PE from 30 to 76%. These breast tumour cell lines may provi de a useful insight into the function of enkephalin-containing peptides in breast cancer.