Naslov
EARLY CLEAVAGE OF p27Kip1 BY CASPASES IN CHRONIC LYMPHOCYTIC LEUKEMIA CELLS UNDERGOING APOPTOSIS

Autori
Sanhes, L. ; Delmer, A. ; Tang, R.P. ; Vrhovac, Radovan ; Faussat, A.M. ; Zittoun, R. ; Marie, J.P. ; Ajchenbaum-Cymbalista, F.

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Blood / - , 1998

Skup
ASH 40th Annual Meeting

Mjesto i datum
Miami (FL), Sjedinjene Američke Države, 04.12.1998. - 08.12.1998

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Sažetak
B-cell chronic lymphocytic leukemia (B-CLL) is generally considered as a malignant disorder characterized by an accumulation of resting clonal B lymphocytes related to defective apoptosis. The cyclin dependent kinase inhibitor p27kip1 is known to play an important role in G0/G1 cell cycle arrest. We reported recently that high p27 expression was strongly correlated with a shorter doubling time and associated with a poorer prognosis in B-CLL (Blood, 91, 4694, 1998). In vitro, we observed an increased spontaneous survival of B-CLL cells expressing high p27 levels in contrast to cells that expressed low p27 levels. Interleukin-4 (IL4), which promotes B cell survival, was found to upregulate p27 in B-CLL cells in vitro. Conversely, after a 5 day exposure to fludarabine, which induces apoptosis, there was a decrease in p27 expression. When considering earlier times of culture, before any significant decrease of p27 protein level, we noticed the expression of a protein running at approximately 23 kDa. This protein was detected on Western blot analysis when using an antibody against p27 N terminus, but an antibody against the C terminus of p27 failed to detect it. Therefore p23 was likely to correspond to a p27 molecule truncated at the C terminus. The p23 was undetectable in samples studied before culture or in the presence of IL4. In these conditions, percentage of apoptotic cells, as assessed by TUNEL method and by FITC-annexin V staining, was less than 5%. Expression of p23 was not specific of fludarabine, as p23 was detected in samples exposed to other proapoptotic drugs such as etoposide or corticosteroids. This proteolytic cleavage was associated with the apoptotic process and appeared as soon as after a 6 hours drug exposure. Recently, caspases (cysteine aspartate specific proteases) were shown to play a central role in apoptosis. Recent studies report that cleavage of cell cycle regulator proteins may contribute to the apoptosis process. We found that p23 results from the proteolytic cleavage of p27 by caspases: a site of potential cleavage for CPP32 is present in the C terminal region of p27, and 2 inhibitors of these caspases (i.e. z-VAD-fmk and ac-DEVD-CHO) prevented truncation of p27 as well as apoptosis in B-CLL cells exposed to fludarabine. The p23 protein lacks the C terminal region of p27 which contains a nuclear localization signal and Western blot analysis on nuclear and cytoplasmic extracts revealed that p23 was strictly intracytoplasmic. Conversely, the cdk binding site, located in the amino-terminal region, is unaffected. This could suggest a putative role for p23 in cell cycle control and apoptosis. In samples exposed to fludarabine, we found a substantial cdk-4 activity contrasting with undetectable activity in untreated cells. As cdk-4 in B-CLL appears mostly cytoplasmic, p23 is likely to prevent p27 access to cdk-4 and subsequently its inhibition. Therefore, we hypothesize that, after proapoptotic drug exposure, p23 might actively contribute to the onset of apoptosis.

Izvorni jezik
Engleski

Znanstvena područja
Kliničke medicinske znanosti

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