Wild-type p53 is required for apoptosis induced by growth factor deprivation in factor-dependent leukaemic cells

Abstract

Summary The p53 gene is a growth control gene, abnormalities of which have been implicated in a variety of cancers. Recently wild-type p53 has been shown to exist in two interchangeable conformational variants, which can be distinguished by specific p53 monoclonal antibodies. One conformation acts as a suppressor (PAb240-/PAbl620+) and one acts as a promoter (PAb240+/PAbl620-) of cell proliferation; the latter conformation is also that of mutant p53. We have previously shown that acute myeloblastic leukaemia (AML) blasts which proliferate autonomously in vitro express only p53 in the promoter conformation. In contrast, expression of PAb 1620 was found only in blasts with non-autocrine growth in vitro and was diminished following stimulation by exogenous growth factors when there was a switch to p53 in the promoter (PAb240+) conformation. As AML blasts with non-autocrine growth undergo apoptosis when deprived of exogenous growth factors, we studied whether this was mediated by wild-type p53. Antisense oligonucleotides to p53 were used to suppress p53 protein expression in blasts with non-autocrine growth and also the factor-dependent human erythroleukaemia cell line TF-1. Following growth factor deprivation for 48 h, 20.6-53.6% of control blasts were apoptotic and demonstrated a typical 'ladder' on DNA electrophoresis characteristic of internucleosomal degradation of DNA. In the presence of p53 antisense, apoptosis was suppressed despite the absence of growth factor, however cell proliferation was not stimulated. We conclude that apoptosis occurring in factor-dependent AML blasts following growth factor deprivation is mediated by wild-type p53 (PAb 1620+), and that conformational change of p53 to the PAb240+ conformation occurring either by mutation or by the action of autocrine growth factors would permit leukaemic cell survival by suppressing apoptosis.

p53 status of newly established acute myeloid leukaemia cell lines

“…Based on the present findings and according to the previously published studies (Zhang et al, 1992;Zhu et al, 1993Zhu et al, , 1994, it is probable that inactivation of the wt p53 protein in AML is due to a change in the protein conformation. In order to improve AML treatment, it would be plausible to try to develop drugs that are able to convert the inactive p53 protein conformation to an active one.…”

“…it was in a mutational or promoter conformation. Apart from in AML cells (Rivas et al, 1992;Zhang et al, 1992;Zhu et al, 1993Zhu et al, , 1994, the mutational p53 conformation has also been detected in OU-AML-3 96 ± 4 8 9 ± 15 0 ± 0 OU-AML-4 96 ± 4 8 5 ± 17 2 ± 2 OU-AML-5 99 ± 2 8 3 ± 23 1 ± 1 OU-AML-7 91 ± 10 77 ± 25 0 ± 0 OU-AML-8 92 ± 6 6 6 ± 19 1 ± 1 normal haematopoietic progenitor cells (Rivas et al, 1992;Zhang et al, 1992;Bi et al, 1994). This conformation may represent a condition whereby wt p53 is in an inactive form and permits cell proliferation instead of acting as a suppressor of the cell cycle.…”

“…Ab3 anti-p53 antibody has been used in flow cytometric analysis (Zhu et al, 1993(Zhu et al, ,1994Bi et al, 1994). It recognizes both mutated p53 and wt protein in mutational, i.e.…”

Induction of Mdm2 and enhancement of cell survival by bFGF

“…Its overexpression can trigger apoptosis in a wide array of cell types (Yonish-Rouach et al, 1991, 1994Shaw et al, 1992;Johnson et al, 1993;Ryan et al, 1993;Keren Tal et al, 1995;Haupt et al, 1995;reviewed in Oren, 1994). Depending on cellular context, wild type (wt) p53 may facilitate apoptosis upon withdrawal of certain survival factors (Lotem and Sachs, 1993;Gottlieb et al, 1994;Zhu et al, 1994;Blandino et al, 1995;Eizenberg et al, 1996;Xiang et al, 1996), as well as in response to the excess activity of several viral and cellular oncoproteins (Debbas and White, 1993;Hermeking and Eick, 1994;Wagner et al, 1994;Wu and Levine, 1994). Apoptosis induced by DNA damaging agents is particularly dependent on p53, especially at low to moderate doses of DNA damage Lowe et al, 1993a, b;Gottlieb et al, 1994).…”

New Strategies in the Treatment of Acute Myelogenous Leukemia (AML): In Vitro Culture of AML Cells—The Present Use in Experimental Studies and the Possible Importance for Future Therapeutic Approaches

“…First, all AML cells in the native population are characterized by identical genetic abnormalities that are regarded as fundamental in the pathogenesis of AML, and one would therefore expect that the characteristics of the total cell population reflect important disease characteristics. The clinical relevance of cell population characteristics is also demonstrated by two observations: A) detection of autocrine proliferation in assays based on characterization of the whole native AML population in short-term culture can be used as a prognostic parameter in AML [7][8][9][10][11][12], and B) autocrine proliferation is also associated with decreased in vitro apoptosis [63][64][65], and expression levels of apoptosis-regulatory genes in the whole AML population seem to be a predictor of survival/AML relapse after intensive chemotherapy [66][67][68]. Furthermore, a recent study described that the two most important prognostic factors (i.e., predictors of later leukemia relapse) in AML were cytogenetics (a population characteristic) and the achievement of complete hematological remission after the first induction course [30].…”