Differences in targeting and secretion of cathepsins B and L by BALB/3T3 fibroblasts and Moloney murine sarcoma virus-transformed BALB/3T3 fibroblasts

• Published in: The Journal of biological chemistry 1990-08, Vol.265 (23), p.13650-13654
• Main Authors: ACHKAR, C, GONG, Q, FRANKFARTER, A, BAJKOWSKI, A. S
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Carcinogenesis, carcinogens and anticarcinogens; Cathepsin B - biosynthesis; Cathepsin B - metabolism; Cathepsin L; Cathepsins - biosynthesis; Cathepsins - metabolism; Cell Transformation, Neoplastic; Cells, Cultured; Cysteine Endopeptidases; Endopeptidases; Fibroblasts - enzymology; Glucuronidase - metabolism; Hexosephosphates - metabolism; Lysosomes - enzymology; Mannosephosphates - metabolism; Medical sciences; Mice; Mice, Inbred BALB C; Moloney murine sarcoma virus - genetics; Receptor, IGF Type 2; Receptors, Cell Surface - biosynthesis; Receptors, Cell Surface - metabolism; Sarcoma Viruses, Murine - genetics; Tumors; Viruses
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)77398-5

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.