ABSTRACT
Overexpression of the cyclin-dependent kinase inhibitor p27(Kip1) has been demonstrated to induce cell cycle arrest and apoptosis in various cancer cell lines, but has also been associated with the opposite effect of enhanced survival of tumor cells and increased resistance towards chemotherapeutic treatment. To address the question of how p27(Kip1) expression is related to apoptosis induction, we studied doxycycline-regulated p27(Kip1) expression in K562 erythroleukemia cells. p27(Kip1) expression effectively retards proliferation, but it is not sufficient to induce apoptosis in K562 cells. p27(Kip1)-expressing K562 cells, however, become resistant to apoptosis induction by the proteasome inhibitors PSI, MG132 and epoxomicin, in contrast to wild-type K562 cells that are efficiently killed. Cell cycle arrest in the S phase by aphidicolin, which is not associated with an accumulation of p27(Kip1) protein, did not protect K562 cells against the cytotoxic effect of the proteasome inhibitor PSI. The expression levels of p27(Kip1) thus constitute an important parameter, which decides on the overall sensitivity of cells against the cytotoxic effect of proteasome inhibitors.
Subject(s)
Cell Cycle Proteins/biosynthesis , Cell Cycle Proteins/physiology , Tumor Suppressor Proteins/biosynthesis , Tumor Suppressor Proteins/physiology , Antibiotics, Antineoplastic/pharmacology , Aphidicolin/pharmacology , Apoptosis , Blotting, Western , Caspases/metabolism , Cell Cycle , Cell Division , Cell Nucleus/metabolism , Cell Separation , Cyclin-Dependent Kinase Inhibitor p27 , Cysteine Endopeptidases , Cysteine Proteinase Inhibitors/pharmacology , Dose-Response Relationship, Drug , Doxorubicin/pharmacology , Flow Cytometry , Genetic Vectors , Hemoglobins/metabolism , Humans , K562 Cells , Leupeptins/pharmacology , Microscopy, Fluorescence , Models, Genetic , Multienzyme Complexes/antagonists & inhibitors , Oligopeptides/pharmacology , Proteasome Endopeptidase Complex , Retroviridae/genetics , S Phase/drug effects , Time Factors , TransfectionABSTRACT
The ability of p53 to activate or repress transcription suggests that its biological function as tumor suppressor is in part accomplished by regulating a number of genes including such required for inhibition of cell growth. We here give evidence that p53 also may regulate genes responsible for the proteolytic degradation of the extracellular matrix, which is considered a crucial feature for local invasion and metastasis of neoplastic cells. An important and highly regulated cascade of such proteolytic events involves the plasminogen activator system. We show that wild-type p53 represses transcription from the enhancer and promoter of the human urokinase-type (u-PA) and the tissue-type plasminogen activator (t-PA) gene through a non-DNA binding mechanism. Oncogenic mutants lost the repressing activity. In contrast, wild-type but not mutant p53 specifically binds to and activates the promoter of the plasminogen activator inhibitor type-1 (PAI-1) gene. Interestingly, one of the p53 mutants (273his) inhibited PAI-1 promoter activity. Our results suggest that altered function of oncogenic forms of p53 may lead to altered expression of the plasminogen activators and their inhibitor(s) and thus to altered activation of the plasminogen/plasmin system during tumor progression.
