Cathepsin L Colocalizes with Chromogranin A in Chromaffin Vesicles to Generate Active Peptides

• DOI: 10.1210/en.2008-1613
• Publication Date: 2009-04-17T00:46:33Z
• Authors: Nilima Biswas; Juan L. Rodriguez...; Maite Courel; Jiaur R. Gayen; Sucheta M. Vainga...; Manjula Mahata; Justin W. Torpey; Laurent Taupenot; Daniel T. O'Connor; Sushil K. Mahata
• Keywords: Chromogranin A

Chromogranin A (CgA), the major soluble protein in chromaffin granules, is proteolytically processed to generate biologically active peptides including catecholamine release inhibitory peptide catestatin. Here we sought determine whether cysteine protease cathepsin L (CTSL), a novel enzyme for proteolytic processing of neuropeptides, acts like well-established serine proteases [prohormone convertase (PC)1/3 or PC2] catestatin by CgA. We found that endogenous CTSL colocalizes with CgA secretory vesicles primary rat cells. Transfection PC12 cells an expression plasmid encoding directed toward vesicles. Deconvolution fluorescence microscopy suggested greater colocalization than lysosomal marker LGP110. The overexpression caused cleavage full-length also cleaved vitro, time- and dose-dependent fashion, specificity process was documented through E64 (thiol reagent) inhibition. Mass spectrometry on CTSL-digested recombinant identified catestatin-region peptide, corresponding CgA360–373. pool generated from inhibited nicotine-induced secretion region diminished naturally occurring variants, especially Pro370Leu Gly364Ser. Among CTSL-generated peptides, subset matched those vivo. These findings indicate can be substrate both vitro cella, their within granules cella suggests likelihood enzyme/substrate relationship