Deregulation of the ubiquitin system and p53 proteolysis modify the apoptotic response in B-CLL lymphocytes.
We recently reported increased sensitivity of B-cell chronic lymphocytic leukemia (B-CLL) lymphocytes to apoptotic death activation by the proteasome-specific inhibitor lactacystin. Here, we show that only specific-not nonspecific-proteasomal inhibitors can discriminate between malignant and normal lymphocytes in inducing the apoptotic death response. Indeed, lactacystin and its active metabolite clasto-lactacystin beta-lactone induced apoptotic death in CLL but not in normal lymphocytes. This difference was completely abolished when tripeptide aldehydes such as MG132 or LLnL (which can also inhibit calpains) were used as less specific proteasomal inhibitors. Moreover, B-CLL cells exhibited a constitutive altered ubiquitin-proteasome system, including a threefold higher chymotrypsin-like proteasomal activity and high levels of nuclear ubiquitin-conjugated proteins compared with normal lymphocytes. Interestingly, B-CLL cells also displayed altered proteolytic regulation of wild-type p53, an apoptotic factor reported to be a substrate for the ubiquitin-proteasome system. Nuclear wild-type p53 accumulated after lactacystin treatment used at the discriminating concentration in malignant, but not in normal, lymphocytes. In contrast, p53 was stabilized by MG132 or LLnL in malignant and normal cells undergoing apoptosis, indicating that in normal lymphocytes p53 is regulated mainly by calpains and not by the ubiquitin-proteasome system. This work raises the possibility that two different proteolytic pathways controlling p53 stability may be pathologically imbalanced. This could result in modification of apoptosis control, since in CLL-lymphocytes a highly upregulated ubiquitin-proteasome system, which controls p53 stability among other apoptotic factors, was correlated with an increased propensity of these cells to apoptosis triggered by lactacystin.
Masdehors
P
P
Laboratoire de Recherche Correspondant and Laboratoire de Radiopathologie, Institut Curie, Paris, France.
Merle-Béral
H
H
Maloum
K
K
Omura
S
S
Magdelénat
H
H
Delic
J
J
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000097:blood; D017209:Apoptosis / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000097:blood; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood / Q000276:immunology*; D008214:Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000502:physiology; D009097:Multienzyme Complexes / Q000097:blood; D009363:Neoplasm Proteins / Q000097:blood; D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D011518:Proto-Oncogene Proteins / Q000097:blood; D019253:Proto-Oncogene Proteins c-bcl-2; D051736:Proto-Oncogene Proteins c-mdm2; D012016:Reference Values; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014452:Ubiquitins / Q000502:physiology*; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000097:blood
D015853:Cysteine Proteinase Inhibitors; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D014452:Ubiquitins; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; C067713:lactacystin; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; D000111:Acetylcysteine