Activation of large form galanin-LI by extracellular processing in small cell lung carcinoma tissue

Galanin is a neuropeptide that is widely distributed in the central and peripheral nervous systems. Some small cell lung carcinoma (SCLC) cell lines such as SBC-3A release only the high-molecular-mass form, with lower molecular mass forms being undetectable. To investigate the mechanism of processing of progalanin to active peptide, we studied galanin-LI in both the culture media of SBC-3A cells and in extracts from in vivo mouse SBC-3A tumors. SBC-3A cells were found to release high molecular mass galanin, but did not release active peptides. In contrast, tumor extract contained both high-molecular-mass galanin, and a cleaved lower-molecular-mass form of the peptide (8, 5 and 2 kDa). The lower-molecular-mass peptide was identified as galanin(1-20) by MALDI-TOF mass spectrometry. We then looked at MMP-2 and MMP-9 release from SBC-3A cells and tumor tissue treated with galanin and progalanin, as revealed by gelatin zymography. Galanin elicited pro-MMP-2 and pro-MMP-9 release from SBC-3A cells and tumor tissue; however, recombinant progalanin induced pro-MMP-2 and pro-MMP-9 release from tumor tissue only. This study has shown that the galanin-LI released from SCLC SBC-3A cells consisted of the high-molecular-mass peptide form, and was processed extracellularly to galanin(1-20). Furthermore, galanin was seen to induce pro-MMP-2 and pro-MMP-9 release from SBC-3A cells.