Pro-neurotensin/neuromedin N expression and processing in human colon cancer cell lines

The regulatory peptide neurotensin NT has been proposed to exert an autocrine trophic effect on human colon cancers. In the present study, pro-neurotensin/neuromedin N (proNT/NN) expression and processing were investigated in 13 human colon cancer cell lines using a combination of radioimmunoassay and HPLC techniques. All 13 cell lines displayed low to moderate levels of proNT/NN ranging from 10 to 250 fmol/mg protein. However, only 6 (HCT8, LoVo, HT29, C119A, LS174T, and coloDM320) processed the precursor. Three of the latter (HCT8, LS174T, and coloDM320) were analysed in detail with regard to proNT/NN processing pattern and were found to produce NT and large precursor fragments ending with the NT or NN sequence. They had no detectable level of NN. Such a processing pattern resembles that generated by the prohormone convertase PC5. Northern and Western blot analysis of prohormone convertase expression in the 3 cell lines revealed that they were devoid of PC1 and PC2, whereas they all expressed PC5. These data indicate that proNT/NN is a good marker of human colon cancer cell lines while NT is found in only about half of the cell lines. They also suggest that, in addition to NT, several proNT/NN-derived products, possibly generated by PC5, might exert an autocrine positive effect on human colon cancer growth.