Synthesis, maturation and extracellular release of procathepsin D as influenced by cell proliferation or transformation.
The relationship between cell growth and intra- and extracellular accumulation of cathepsin D (CD), a lysosomal endopeptidase involved in cell protein breakdown, was examined in cultures of normal and transformed BALB/c mouse 3T3 fibroblasts grown at various cell densities. In crowded cultures of normal 3T3 cells (doubling time, Td, 53 hr) intracellular CD activity was 2-fold higher than in sparse, rapidly-growing (Td, 27 hr) cultures. In uncrowded (Td, 18 hr) and crowded (Td, 32 hr) cultures of benzo[a]pyrene-transformed cells intracellular CD levels were one third and two thirds, respectively, of those measured in hyperconfluent 3T3 cultures. Regardless of cell density, SV-40-virus-transformed cells (Td, 12 hr) contained one third of CD levels found in hyperconfluent 3T3 cells. Both transformed cell lines released into the medium a higher proportion of CD, compared with their untransformed counterpart, yet the amount secreted was not sufficient to account for the reduced intracellular level of the enzyme. Serum withdrawal induced a marked increase of both intra- and extracellular levels of CD activity. In both normal and virally or chemically transformed 3T3 cells CD comprised a precursor (52 kDa) and processed mature polypeptides; the latter were mostly represented by a 48-kDa peptide, but a minor part was in a double-chain form (31 and 16 kDa respectively). The proportion of mature enzyme vs. precursor was much higher in confluent, slowly-growing cells than in fast-growing cells, whether normal or transformed. In the latter, conversion of mature 48-kDa peptide into the double-chain form occurred more efficiently.
Isidoro
C
C
Dipartimento di Medicina el Oncologia Sperimentale, Università di Torino, Corso Raffaello, Italy.
Demoz
M
M
De Stefanis
D
D
Baccino
F M
FM
Bonelli
G
G
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport; D002402:Cathepsin D / Q000378:metabolism*; D002452:Cell Count; D002455:Cell Division; D002472:Cell Transformation, Viral; D016895:Culture Media, Serum-Free; D004792:Enzyme Precursors / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D013539:Simian virus 40
D016895:Culture Media, Serum-Free; D004792:Enzyme Precursors; C058345:procathepsin D; D002402:Cathepsin D