Major role of cathepsin L for producing the peptide hormones ACTH, beta-endorphin, and alpha-MSH, illustrated by protease gene knockout and expression.
The pituitary hormones adrenocorticotropic hormone (ACTH), beta-endorphin, and alpha-melanocyte stimulating hormone (alpha-MSH) are synthesized by proteolytic processing of their common proopiomelanocortin (POMC) precursor. Key findings from this study show that cathepsin L functions as a major proteolytic enzyme for the production of POMC-derived peptide hormones in secretory vesicles. Specifically, cathepsin L knock-out mice showed major decreases in ACTH, beta-endorphin, and alpha-MSH that were reduced to 23, 18, and 7% of wild-type controls (100%) in pituitary. These decreased peptide levels were accompanied by increased levels of POMC consistent with proteolysis of POMC by cathepsin L. Immunofluorescence microscopy showed colocalization of cathepsin L with beta-endorphin and alpha-MSH in the intermediate pituitary and with ACTH in the anterior pituitary. In contrast, cathepsin L was only partially colocalized with the lysosomal marker Lamp-1 in pituitary, consistent with its extralysosomal function in secretory vesicles. Expression of cathepsin L in pituitary AtT-20 cells resulted in increased ACTH and beta-endorphin in the regulated secretory pathway. Furthermore, treatment of AtT-20 cells with CLIK-148, a specific inhibitor of cathepsin L, resulted in reduced production of ACTH and accumulation of POMC. These findings demonstrate a prominent role for cathepsin L in the production of ACTH, beta-endorphin, and alpha-MSH peptide hormones in the regulated secretory pathway.
Funkelstein
Lydiane
L
Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093, USA.
Toneff
Thomas
T
Mosier
Charles
C
Hwang
Shin-Rong
SR
Beuschlein
Felix
F
Lichtenauer
Urs D
UD
Reinheckel
Thomas
T
Peters
Christoph
C
Hook
Vivian
V
D000324:Adrenocorticotropic Hormone / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D056668:Cathepsin L; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D008247:Lysosomes / Q000201:enzymology; D051379:Mice; D018345:Mice, Knockout; D010902:Pituitary Gland / Q000166:cytology / Q000201:enzymology*; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000201:enzymology*; D000521:alpha-MSH / Q000235:genetics / Q000378:metabolism*; D001615:beta-Endorphin / Q000235:genetics / Q000378:metabolism*
D000521:alpha-MSH; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D056668:Cathepsin L; C534278:Ctsl protein, mouse