Basic fibroblast growth factor suppresses p53 activation in the neoplastic cells of a proportion of patients with chronic lymphocytic leukaemia

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 study was conducted to investigate the possibility that TP53 mRNA is variably expressed in chronic lymphocytic leukaemia (CLL) and that under-expression is associated with TP53 dysfunction and adverse outcome. Although TP53 mRNA levels did indeed vary among the 104 CLL samples examined, this variability resulted primarily from over-expression of TP53 mRNA in 18 samples, all of which lacked TP53 deletion/mutation. These patients had higher lymphocyte counts and shorter overall and treatment-free survival times compared to cases with low TP53 mRNA expression and no TP53 deletion/mutation. Furthermore, TP53 mRNA levels did not correlate with levels of TP53 protein or its transcriptional target CDKN1A. We speculated that the adverse outcome associated with TP53 mRNA over-expression might reflect variation in levels of MIR15A and MIR16-1, which are encoded on chromosome 13q14 and target TP53 and some oncogenes including BCL2. In keeping with our hypothesis, 13q14 copy number and levels of MIR15A/MIR16-1 correlated positively with one another but negatively with levels of TP53 mRNA and BCL2 mRNA. Our findings support a model in which loss of MIR15A/MIR16-1 at chromosome 13q14 results in adverse outcome due to de-repression of oncogenes such as BCL2, and up-regulation of TP53 mRNA as a bystander effect.

Angiogenic factors in chronic lymphocytic leukemia

Angiogenesis is a complex process controlled by the balance of a large number of regulating factors, the pro- and anti-angiogenic factors. Dysregulation of angiogenesis occurs in various pathologies and is one of the hallmarks for cancer. Recent emphasis on the microenvironment's influence in chronic lymphocytic leukemia (CLL) progression and drug resistance nurtures the interest in angiogenesis. Researchers have already identified a variety of angiogenic factors involved in the CLL, including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), angiopoietin-2(Ang-2), thrombospondin-1 (TSP-1), as well as extracellular proteinases such as matrix metalloproteinase-9 (MMP-9). Besides modulating neovascularization, angiogenic factors also participate in the regulation of pro-survival effects of CLL cells. However, the precise mechanism involved still needs to be elucidated further. At present, the levels of some angiogenic factors are regarded as prognostic markers of the progression of CLL, although it is not widely used. Several anti-VEGF agents are currently under clinical trial. Advances in the understanding of the bases of angiogenesis regulators will be benefit for the comprehension of CLL pathogenesis and help to conquer the disease.

Functional analysis of the ATM-p53-p21 pathway in the LRF CLL4 trial: blockade at the level of p21 is associated with short response duration

PURPOSE

This study sought to establish whether functional analysis of the ATM-p53-p21 pathway adds to the information provided by currently available prognostic factors in patients with chronic lymphocytic leukemia (CLL) requiring frontline chemotherapy.

EXPERIMENTAL DESIGN

Cryopreserved blood mononuclear cells from 278 patients entering the LRF CLL4 trial comparing chlorambucil, fludarabine, and fludarabine plus cyclophosphamide were analyzed for ATM-p53-p21 pathway defects using an ex vivo functional assay that uses ionizing radiation to activate ATM and flow cytometry to measure upregulation of p53 and p21 proteins. Clinical endpoints were compared between groups of patients defined by their pathway status.

RESULTS

ATM-p53-p21 pathway defects of four different types (A, B, C, and D) were identified in 194 of 278 (70%) samples. The type A defect (high constitutive p53 expression combined with impaired p21 upregulation) and the type C defect (impaired p21 upregulation despite an intact p53 response) were each associated with short progression-free survival. The type A defect was associated with chemoresistance, whereas the type C defect was associated with early relapse. As expected, the type A defect was strongly associated with TP53 deletion/mutation. In contrast, the type C defect was not associated with any of the other prognostic factors examined, including TP53/ATM deletion, TP53 mutation, and IGHV mutational status. Detection of the type C defect added to the prognostic information provided by TP53/ATM deletion, TP53 mutation, and IGHV status.

CONCLUSION

Our findings implicate blockade of the ATM-p53-p21 pathway at the level of p21 as a hitherto unrecognized determinant of early disease recurrence following successful cytoreduction.

Present status and perspectives in functional analysis of p53 in chronic lymphocytic leukemia

Aberrations of TP53 (mutations and/or deletions) are associated with a dismal prognosis in chronic lymphocytic leukemia (CLL). Complete loss of ATM is another mechanism of failed DNA damage response and also associated with poorer prognosis in CLL. However, p53 dysfunction may arise through alternative mechanisms unrelated to structural aberrations (deletion and/or mutation) of TP53 or ATM, and thus be undetectable by traditional DNA-directed approaches (fluorescence in situ hybridization [FISH], sequencing, karyotyping). In order to address the latter changes, and also to better understand the consequences of TP53/ATM aberrations, p53 functional assays have recently been developed. The purpose of dynamic assessment of p53 response in CLL is to carry out a comprehensive analysis of all mechanisms causing p53-deficient phenotype, including those unrelated to genomic aberrations of TP53 and ATM. The present review focuses on the current knowledge of p53 function assays in CLL, including important features such as technical issues, correlation with structural aberrations and clinical value.

Human telomerase catalytic subunit (hTERT) suppresses p53-mediated anti-apoptotic response via induction of basic fibroblast growth factor

Although human telomerase catalytic subunit (TERT) has several cellular functions including telomere homeostasis, genomic stability, cell proliferation, and tumorigenesis, the molecular mechanism underlying anti-apoptosis regulated by TERT remains to be elucidated. Here, we show that ectopic expression of TERT in spontaneously immortalized human fetal fibroblast (HFFS) cells, which are a telomerase- and p53-positive, leads to increases of cell proliferation and transformation, as well as a resistance to DNA damage response and inactivation of p53 function. We found that TERT and a mutant TERT (no telomerase activity) induce expression of basic fibroblast growth factor (bFGF), and ectopic expression of bFGF also allows cells to be resistant to DNA-damaging response and to suppress activation of p53 function under DNA-damaging induction. Furthermore, loss of TERT or bFGF markedly increases a p53 activity and DNA-damage sensitivity in HFFS, HeLa and U87MG cells. Therefore, our findings indicate that a novel TERT-bFGF axis accelerates the inactivation of p53 and consequent increase of resistance to DNA-damage response.

Vascular endothelial growth factor stimulates protein kinase CbetaII expression in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is a malignant disease of mature B lymphocytes. We have previously shown that a characteristic feature of CLL cells are high levels of expression and activity of protein kinase CbetaII (PKCbetaII), and that this might influence disease progression by modulating signaling in response to B-cell receptor engagement. The aim of the present work was to investigate the factors involved in stimulating PKCbetaII expression in CLL cells. Here we show that the activation of PKCbetaII in CLL cells stimulated with vascular endothelial growth factor (VEGF) can drive expression of the gene for PKCbeta, PRKCB1. We found that this effect of VEGF on PRKCB1 transcription is paralleled by high expression of PKCbetaII protein and therefore probably contributes to the malignant phenotype of CLL cells. Taken together, the data presented in this study demonstrate that VEGF, in addition to its role in providing prosurvival signals, also plays a role in overexpression of PKCbetaII, an enzyme with a specific pathophysiologic role in CLL.

RNA interference of LRRK2-microarray expression analysis of a Parkinson's disease key player

The protein leucine-rich repeat kinase 2 (LRRK2) is a key player in the pathogenesis of Parkinson's disease (PD). Mutations in the LRRK2 gene account for up to 10% of all autosomal dominant forms of familiar and for approximately 1-3% of sporadic PD patients. Although the LRRK2 protein has many functional domains like a leucine-rich repeat domain, a Roc-GTPase domain, a kinase domain of the tyrosine kinase-like subfamily and multiple protein interaction domains (armadillo, ankyrin, WD40), the exact biological role of LRRK2 in the human brain is elusive. To gain more insight into the biological function of this protein, we monitored the changes in the expression profiles of SH-SY5Y cells, a dopaminergic neuroblastoma cell line, induced by a depletion of LRRK2 levels by RNA interference (RNAi) with Affymetrix U133 Plus 2.0 microarrays. A total of 187 genes were differentially regulated by at least a 1.5-fold change with 94 transcripts being upregulated and 93 transcripts being downregulated compared to scrambled control siRNA transfected cells. Key players of the interaction networks were independently verified by qRT-PCR. The differentially expressed gene products are involved in axonal guidance, nervous system development, cell cycle, cell growth, cell differentiation, cell communication, MAPKKK cascade, and Ras protein signal transduction. Defined gene expression networks will now serve to look more closely for candidates affected by LRRK2 reduction and how they might be altered in other forms of familial or sporadic PD.

Genetic alteration associated with chronic lymphocytic leukemia

The genetics of B-cell chronic lymphocytic leukemia (B-CLL) differ considerably from most other forms of hematologic malignancy which are usually characterized by chromosome translocations. B-CLL typically contains chromosomal deletions and chromosomes 13q14 and 11q22-->q23 are the most common. These two regions appear to share a common ancestral origin (Auer et al., 2007b). Overall, chromosomal abnormalities can be found in the majority of patients with B-CLL when using sensitive techniques (Dohneret al., 2000) and possibly reflects an underlying predisposition, with a small but significant number of familial cases. Although single and consistent abnormalities are most common, multiple rearrangements can occur, often with disease progression (Feganetal., 1995; Dohner et al., 2000). Regions of recurrent deletion suggest the presence of tumor suppressor genes if following Knudson's theoretical 2-hit model. However, despite extensive sequencing analysis over the last decade and lack of pathogenic mutations identified, there has been a move away from this suggested hypothesis and alternative mechanisms of gene inactivation involving epigenetic silencing or haploinsufficiency may be considered as more likely in this disease. This review focuses on the common genetic abnormalities in B-CLL and relates them to some of the more recent hypotheses on inactivation of genes within these regions of deletion.

Hsp90 inhibition has opposing effects on wild-type and mutant p53 and induces p21 expression and cytotoxicity irrespective of p53/ATM status in chronic lymphocytic leukaemia cells

In chronic lymphocytic leukaemia (CLL), mutation/deletion of TP53 is strongly associated with early disease progression, resistance to chemotherapy and short patient survival. Consequently, there is a pressing need to develop novel treatment protocols for this high-risk patient group. The present study was performed to evaluate Hsp90 inhibition as a possible therapeutic approach for such patients. Primary CLL cells of defined ataxia telangiectasia mutated (ATM)/p53 status were incubated with the Hsp90 inhibitor geldanamycin (GA) and analysed by western blotting for the expression of p53, p21, MDM2 and Akt. GA downregulated overexpressed mutant p53 protein (an oncogene) and upregulated wild-type (wt) p53 (a tumour suppressor). The upregulation of wt p53 by GA was independent of ATM and was accompanied by downregulation of Akt and the active form of MDM2, indicating a possible mechanism. GA also produced a p53/ATM-independent increase in the levels of p21-a potent inducer of cell-cycle arrest. In-vitro cytotoxicity studies showed that GA killed cultured CLL cells in a dose- and time-dependent fashion irrespective of their p53/ATM status and more effectively than normal blood mononuclear cells. In summary, our findings reveal important consequences of inhibiting Hsp90 in CLL cells and strongly support the therapeutic evaluation of Hsp90 inhibitors in poor-prognosis patients with p53 defects.