Inhibition of pro-cholecystokinin (CCK) sulfation by treatment with sodium chlorate alters its processing and decreases cellular content and secretion of CCK 8.
Pro-cholecystokinin (CCK) has three sulfated tyrosine residues. Sulfation of the tyrosine residue in CCK 8 is known to be important for its activity at CCK A receptors. The role of these sulfated tyrosines in the sorting and processing of pro-CCK was examined by treatment of CCK-secreting rat thyroid medullary carcinoma cells with 10 nM sodium chlorate (a non-toxic inhibitor of tyrosine sulfation). This treatment caused a 50% decrease in the cellular content of immunoreactive CCK and an 80% decrease in its secretion. Sephadex G-50 chromatography of cellular extracts and culture media showed a selective depletion of CCK 8. There was a comparative sparing of CCK 33 and larger molecular forms in cellular extracts which was not observed in the media. These results suggest that the sulfation of the tyrosines of pro-CCK is clearly important for the correct sorting and/or processing of pro-CCK. The pattern of immunoreactive CCK peptides seen with chlorate treatment is consistent with the substrate specificity of a recently identified putative CCK cleaving enzyme and suggests that unsulfated pro-CCK is not efficiently processed to CCK 8 in vivo. The large decrease in CCK content and secretion observed with sodium chlorate may also be due to inefficient sorting of unsulfated pro-CCK into secretory vesicles.
Beinfeld
M C
MC
Department of Pharmacological and Physiological Science, St Louis University School of Medicine, MO 63104.
D000818:Animals; D002277:Carcinoma / Q000378:metabolism; D002704:Chlorates / Q000494:pharmacology*; D002766:Cholecystokinin / Q000378:metabolism*; D003470:Culture Media; D011498:Protein Precursors / Q000378:metabolism*; D051381:Rats; D011949:Receptors, Cholecystokinin / Q000187:drug effects / Q000378:metabolism; D012844:Sincalide / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism; D013462:Sulfur Radioisotopes; D013964:Thyroid Neoplasms / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism / Q000502:physiology
D002704:Chlorates; D003470:Culture Media; D011498:Protein Precursors; D011949:Receptors, Cholecystokinin; D013431:Sulfates; D013462:Sulfur Radioisotopes; D014443:Tyrosine; C060249:procholecystokinin; D002766:Cholecystokinin; D012844:Sincalide; C032706:sodium chlorate