Expression and processing of procholecystokinin in a rat medullary thyroid carcinoma cell line.
A rat medullary thyroid carcinoma cell line, CA-77, was shown to express the cholecystokinin (CCK) gene. Measurements using a library of sequence-specific radioimmunoassays before and after enzymic treatment of extracts and chromatographic fractions showed that the cells contained 1.0 pmol of alpha-carboxyamidated cholecystokinins/10(6) cells, 0.4 pmol of glycine-extended intermediates/10(6) cells and 1.0 pmol of further C-terminal-extended pro-CCK/10(6) cells. Gel chromatography and reverse-phase h.p.l.c. revealed both sulphated and nonsulphated CCK-8 in the cells. The growth medium contained in addition alpha-amidated CCK-33, glycine-extended CCK-8 and pro-CCK. Exposure to 0.1 microM-dexamethasone for 6 days increased the cellular content and secretion of all of the described CCK peptides by 2-3-fold. The increase was first noted after 3 days of treatment. Monensin inhibited the synthesis of alpha-carboxyamidated CCK and the secretion of all of the CCK forms measured. Colchicine at a low concentration (0.2 mumol/l) apparently increased the synthesis and secretion of alpha-carboxyamidated CCK, whereas higher concentrations inhibited CCK synthesis. Finally, chloroquine inhibited the alpha-carboxyamidation of CCK. We conclude that the CA-77 cell line is a useful tool for studies of the expression and post-translational processing of pro-CCK.
Odum
L
L
Department of Clinical Chemistry, Rigshospitalet, University of Copenhagen, Denmark.
Rehfeld
J F
JF
D000818:Animals; D002277:Carcinoma / Q000378:metabolism*; D002738:Chloroquine / Q000494:pharmacology; D002766:Cholecystokinin / Q000235:genetics* / Q000378:metabolism; D002850:Chromatography, Gel; D003078:Colchicine / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D015870:Gene Expression; D005998:Glycine; D008985:Monensin / Q000494:pharmacology; D010446:Peptide Fragments / Q000032:analysis / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D012844:Sincalide / Q000032:analysis / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D010446:Peptide Fragments; D011498:Protein Precursors; D013431:Sulfates; C060249:procholecystokinin; D003907:Dexamethasone; D002738:Chloroquine; D002766:Cholecystokinin; D008985:Monensin; D012844:Sincalide; D003078:Colchicine; D005998:Glycine