Effect of monensin on secretion of t-PA from melanoma (Bowes).
The secretion of tissue-type plasminogen activator (t-PA) from melanoma cells (Bowes) was investigated with or without monensin treatment. Monensin inhibited secretion of t-PA from the cells to the medium in a dose-and time-dependent manner. The inhibition was accompanied by an intracellular accumulation of t-PA. Electrophoretic enzymography of the cell homogenate showed the main lytic zone at 72 kDa, which reacted with the IgG of anti-t-PA. Analysis of the cell organelles using ultracentrifugation with a discontinuous sucrose density gradient revealed that the activity and the antigen of t-PA were observed near the discontinuous phase of the sucrose gradient. Analysis of 3H-mannose- and 35S-methionine-labeled t-PA in the cell organelles revealed that the radioactivity of each was increased by monensin treatment, and that such treatment increased the ratio of 3H-mannose-related glycoprotein to 35S-methionine-related protein. The sugar chain of intracellular t-PA was analyzed with endoglycosidase H and N-glycanase, which reduced the molecular weight of t-PA by 4.5-10 kDa, indicating the intracellular presence of a high-mannose type sugar chain and a complex-type sugar chain of t-PA. t-PA secreted from the monensin-treated cells possesses a high-mannose type sugar chain only. Therefore, monensin alters the secretion of t-PA by abnormal glycosylation.
Fukao
H
H
Department of Physiology, Kinki University, School of Medicine, Osakasayama, Japan.
Ueshima
S
S
Sakai
T
T
Okada
K
K
Matsuo
O
O
D001693:Biological Transport, Active; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D008358:Mannose / Q000378:metabolism; D008545:Melanoma / Q000378:metabolism*; D008985:Monensin / Q000494:pharmacology*; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D006023:Glycoproteins; D008985:Monensin; D010959:Tissue Plasminogen Activator; D008358:Mannose