Apoptosis as a hallmark Flashcards
Kerr, Wyllie and Currie in 1972
Described apoptosis as a new form of cell death
Noticed it was a morphologically distinct form of cell death - used electron microscopy
Evan et al 1992
Overexpressed c-myc in Rat-1 fibroblasts constitutively via preparation of recombinant retroviruses. They found that the growth curves of all cells was very similar, irrespectibe of whether the cells were constiutively expressing c-myc or in they were controls. This indicated that constituive c-myc expression has no effect on the ability of Rat-1 cells to slow growth in low serum levels. IN order to confirm this, they examined the growth of WT Rat-1 cells and Rat-1/myc cells cells by DNA content BrdU incorporation by flow cytometry. Paradoxical outcome - there was a complete block of growth arrest in cells expressing c-myc. Microscopic inspection revealed cells were dying in low serum. and further time-lapse microscopy determined this to be due to apoptosis.
Sulston 1976
In this organism, 1090 somatic cells are generated in the formation of the adult worm, of which 131 undergo apoptosis or ‘programmed cell death’. These 131 cells die at particular points in the development process, which is essentially invariant between worms, demonstrating the remarkable accuracy and control in this system.
Horvitz et al 1983
Identified two genes in C.elegans, which impaired this programmed cell death - ced-3 and ced-4. The showed that functional ced-3 and ced-4 genes are a prerquiste for cell death to be executed.This was the first evidence that programmed cell death was genetically encoded. We now know that most genes involved in controlling cell death in C.elegans have counterparts in humans
Hockenbery et al 1990
Provided a direct link between BCL-2 and apoptosis with the obervation that BCL-2 did not simply have a prosurival function, but rather specifically prevented apoptotic death in cells deprived of GF. Transfected BCL-2 into a murine lymphocyte line. Found that this overexpression significantly extended the lifespan of these cells when deprived of GFs, in comparison to those that those that were no overexpressing it. Examination of the dead cells revealed death was characteristic of apoptosis
Strasser et al 1990
Identified that BCL-2 blocked an apoptotic death induced by myc. They showed that mice overexpressing bcl-1 and myc show hyperproliferation of pre-B and B cells and develop tumours much faster that only myc-overexpressing mice
Beroukhim et al 2010
Studied copy number alterations using an Affymetrix array - comparing signal intensities from each array to >1000 paired normal tissue specimens. Looked at 3131 cancer specimens across more than two dozen cancer types. Found amplification of MCL1 and BCL2L1 among the most frequent chromosomal gains - these are anti-apoptotic.
Caveat - Doesn’t distinguish between the alterations that driver cancer growth from those accumulating during tumorigenesis
Blombery et al 2019
Analysed paired pre-ventoclax and progression samples from 15 patients with CLL progression enrolled on ventoclax clinical trials. Used targeted amplicon NGS on paired samples assessing the entire coding region of BCL2. The novel Gly101Val mutation in BCL2 was identified at progression in 7 pts but not at study entry. They used digital droplet PCR to characterise the emergence of the mutation in serial archived samples from these patients - was first detectable after 19-42 months of therapy. They found that Gly101Val reduces the affinity of BCL2 for venetoclax by ~180-fold in vitro in competition surface plasmon resonance assays
Cav - There was a wide range of subclonality of Gly101Val in the cohort, suggesting that other aquired changes must confer resistance in non-BCL2 mutation-bearing subclones. They only looked at the coding region of BCL2 for mutations - whole exome/ whole genome seq would be better
Future - Would be interesting to see if this BCL2 Gly101Val mutation exists in other hematologic malignancies and solid tumours which are responsive to venetoclax - their identification early in the development process has the potential to lead to strategies to overcome them. The Gly101Val mutation could potentially serve as an early biomarker of resistance - could then use another drug with a different mechanism of action
He et al 2007
Examined miRNA expression profiles in WT and p53-deficient mouse embryonic fibroblasts. Used semi-quantitative RT-qPCR to measure expression of a panel of 150 mouse miRNA in WT of p53 KO MEFs. The expression of miR-34 was found to be precisely correlated with p53 status. THen did CHiP - in WT MEFs follwoing induction of p53 activity through DNA damage,regions of the genes encoding miR-34 that contained putative p53 binding sites were enriched in p53 immunoprecipitates. This enrichment was absent from p53 KO MEFs. So miR34 is a durect transcriptional target of p53. Althoguh the data was not show, authors state that delivery of miR34 sensitised MEFs to apoptosis in response to genotoxic stress - however they did not show a role on Bcl-2 directly. However, later that year another group showed that miR-34 induction in SW480 cells, this was correlated with downregulation of transcript levels of BCL2, though again this was only correlative
Daige et al 2014
Systemic (IV) delivery of MRX34 (miR-34 mimetic) in mice bearing liver tumour xenografts resulted in about 1000-fold increased expression of miR-34a and the inhibition of tumour growth. Furthermore, MRX43 induced tumour regression in more than 1/3 of mice. They did not observed toxicity in at any dose tested.
Caveat - They used an orthotopic liver cancer cell model - used immortalised human cancer cell lines - in vitro passaging of cells and lead to unrepresentative tumour histology and heterogeneity - poor predictive relevance in later clinical development
Wodarz et al 2007
Describe a relation between cell death and generation of mutant cells within a population after a furst wave of clonal expansion. In their mathematical model, they find that less cell death correlates with fewer divisions during clonal expansion, thus leading to a less variable cell population. In contrast, hgih death rates correlate with more cell divisions during expansion causing appearence of many different mutants. With increasing sub-clonal variability, the risk that individual cells overcome selective barriers and progress towards malignancy increases. Do these in silico models on cell-death stimulated tumour progression find counterparts in vivo?
