Heterogeneity of p53-pathway Protein Expression in Chemosensitive Chronic Lymphocytic Leukemia: A Pilot Study

Abstract

The presence of p53-pathway dysfunction in chronic lymphocytic leukemia (CLL) can be used to identify patients with chemotherapy-refractory disease. Therapeutic responses are known to vary between patients with chemosensitive CLL and may relate to differences in p53-pathway activity. We hypothesized that the magnitude or type of p53-pathway protein expression is heterogeneous in patients with chemosensitive disease and could associate with white cell responses. In this pilot study, changes in p53 and its transcriptional targets, p21/waf1 and MDM2 were analyzed by immunoblotting and densitometry in CLL cells from 10 patients immediately prior to the start of chemotherapy, and after culture for 24 hours (h) with fludarabine (n=7) or chlorambucil (n=3). The in vitro response was also compared to that in vivo in circulating cells pre-treatment, and at 24h and 96h of chemotherapy. Disease responses were evident in all patients after the first treatment-cycle. Significant p53 induction was observed in CLL cells treated in vitro and in vivo. Greater heterogeneity in the expression-intensity was observed in vivo (σ2=45.15) than in vitro (σ2=1.33) and the results failed to correlate (r2=0.18, p=0.22). p21/waf1 and MDM2 expression-profiles were also dissimilar in vitro and in vivo. Higher in vivo (but not in vitro) responses associated with changes in white cell count (p=0.026). Thus, heterogeneity of p53-pathway activity exists in chemosensitive CLL; in unselected patients, in vivo changes do not correlate with those in vitro, but may associate with post-treatment white cell responses.

Loss of MIR15A and MIR16‐1 at 13q14 is associated with increased TP53 mRNA, de‐repression of BCL2 and adverse outcome in chronic lymphocytic leukaemia

“…This observation was contrary to expectations and could not be adequately explained by differences in other clinical or laboratory variables. Furthermore, no correlation was observed between TP53 mRNA levels and TP53 protein expression and function (measured as CDKN1A protein expression), even when the putative TP53‐activating effect of prior chemotherapy (Groves et al , ) was taken into account. This lack of correlation between TP53 mRNA and TP53 protein levels is likely to reflect the dominant role of post‐translational regulation in determining TP53 protein expression (Kruse & Gu, ).…”

p53 and cell cycle independent dysregulation of autophagy in chronic lymphocytic leukaemia

“…Following image capture, slides were washed before being permeabilised in sodium thiocyanate (Abbott, Abbott Park, IL, USA) at 80 °C for 15 min. Following further washes in distilled water and sodium citrate buffer (pH 7.0), slides were treated with protease solution (Abbott) for 10 min at 37 °C after which in situ hybridisation with the CEP17/ TP53 (17p13.1) (Abbott) probes was performed as described previously (Groves et al , 2012). Fluorescence was captured from cells in the same microscopy field-settings as for LC3 determination, enabling simultaneous analysis of LC3 fluorescence and TP53 signals in 50 individual cells.…”

p21WAF1 modulates drug-induced apoptosis and cell cycle arrest in B-cell precursor acute lymphoblastic leukemia

“…16 TP53 mutations represent another mechanism that leads to drug resistance and perturbed initiation of apoptosis in cancer cells, 17 although in diseases such as childhood acute lymphoblastic leukemia (ALL), 18,19 apoptosis can also be inhibited by alternative mechanisms, including ATM inactivation, 20 overexpression of Hdm-2, 21 expression of anti-apoptotic proteins, 22 or dysfunction in the p53-p21 WAF1 axis. 23,24 Upregulation of p21 WAF1 and disruption of the cytotoxic response can occur irrespective of TP53 gene mutations. 20,24,25 In addition, the induction of p21 WAF1 that occurs after exposure to various cytotoxic stimuli can inhibit the apoptosis process in malignant hematopoietic cells [26][27][28] and solid tumor cells.…”

“…23,24 Upregulation of p21 WAF1 and disruption of the cytotoxic response can occur irrespective of TP53 gene mutations. 20,24,25 In addition, the induction of p21 WAF1 that occurs after exposure to various cytotoxic stimuli can inhibit the apoptosis process in malignant hematopoietic cells [26][27][28] and solid tumor cells. 5,29 In the clinical setting, elevated p21 WAF1 expression has been associated with chemotherapy resistance and poor prognosis in acute myeloid leukemia, 30,31 while an association with p21 WAF1 induction and poor clinical outcome in ALL has been proposed.…”