Differences in targeting and secretion of cathepsins B and L by BALB/3T3 fibroblasts and Moloney murine sarcoma virus-transformed BALB/3T3 fibroblasts.
BALB/3T3 fibroblasts (3T3) were observed to secrete latent, pepsin-activatable forms of cathepsin B and cathepsin L as well as an active form of beta-glucuronidase when cultured in the absence of serum. The secretion of these proteins was stimulated by the cation ionophore monensin: cathepsin B, 4.3-fold; cathepsin L, 7.2-fold; and beta-glucuronidase, 3.1-fold. These increases were accompanied by a 50% decline in cellular levels of the active forms of these enzymes and by the cellular accumulation of latent forms of cathepsin B and cathepsin L. Latent forms of beta-glucuronidase were not detected. In contrast, Moloney murine sarcoma virus-transformed BALB/3T3 fibroblasts (MMSV) secreted greatly increased amounts of latent cathepsin B (17-fold) and latent cathepsin L (27-fold), and moderately increased amounts of active beta-glucuronidase (2-fold) in a manner which was not further increased by monensin. The increased monensin-insensitive secretion of these lysosomal enzymes by MMSV cells may be due to a transformation-induced decrease in mannose 6-phosphate receptors. Thus, 3T3 cells bound the neoglycoconjugate pentamannosyl 6-phosphate-bovine serum albumin at 4 degrees C in a pentamannosyl 6 phosphate and mannose 6-phosphate-inhibitable manner, whereas MMSV cells showed no measurable cell surface mannose 6-phosphate receptor binding activity.
Achkar
C
C
Department of Biochemistry, Loyola University of Chicago, Stritch School of Medicine, Maywood, Illinois 60153.
Gong
Q M
QM
Frankfater
A
A
Bajkowski
A S
AS
D000818:Animals; D002401:Cathepsin B / Q000096:biosynthesis / Q000378:metabolism*; D056668:Cathepsin L; D002403:Cathepsins / Q000096:biosynthesis / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D005347:Fibroblasts / Q000201:enzymology; D005966:Glucuronidase / Q000378:metabolism; D006600:Hexosephosphates / Q000378:metabolism*; D008247:Lysosomes / Q000201:enzymology; D008360:Mannosephosphates / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008980:Moloney murine sarcoma virus / Q000235:genetics*; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000378:metabolism*; D009053:Sarcoma Viruses, Murine / Q000235:genetics*
D006600:Hexosephosphates; D008360:Mannosephosphates; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D005966:Glucuronidase; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; D056668:Cathepsin L; C534278:Ctsl protein, mouse