Synthetic Lethality of Retinoblastoma Mutant Cells in the Drosophila Eye by Mutation of a Novel Peptidyl Prolyl Isomerase Gene

Abstract

Mutations that inactivate the retinoblastoma (Rb) pathway are common in human tumors. Such mutations promote tumor growth by deregulating the G1 cell cycle checkpoint. However, uncontrolled cell cycle progression can also produce new liabilities for cell survival. To uncover such liabilities in Rb mutant cells, we performed a clonal screen in the Drosophila eye to identify second-site mutations that eliminate Rbf Ϫ cells, but allow Rbf ϩ cells to survive. Here we report the identification of a mutation in a novel highly conserved peptidyl prolyl isomerase (PPIase) that selectively eliminates Rbf Ϫ cells from the Drosophila eye.A N important goal of novel cancer therapy is to elicit mutations in the RB1 locus itself, but do carry mutations that target the pathway through the loss of cyclin-depenthe death of mutant tumor cells in the patient, while allowing normal cells to survive. The identification dent kinase (Cdk) inhibitors or overexpression of Cyclin D1 or Cdk4 (reviewed in Sherr and McCormick 2002). of gene products required for tumor cell survival can provide highly validated drug targets for the developAdditionally, the transforming activities of DNA tumor virus oncoproteins are mediated via their interaction ment of therapeutic inhibitors. Ideally, targets could be identified that would kill cancer cells while sparing with RB1 (Helt and Galloway 2003). The RB1 protein acts as a critical regulator of G1/S normal cells. A synthetic lethal screen is one method of identifying such targets. In this type of screen, cells phase progression by binding to members of the E2F are genetically altered to model tumor cells and one family of transcription factors (Dyson 1998; Nevins then screens for mutations that eliminate the model 2001). E2F-RB1 complexes prevent entry into S phase tumor cells but have little or no effect on wild-type cells.by actively repressing transcription through the recruitOne way to model tumor cells is to functionally inactiment of histone deacetylases and other chromatin modvate the RB1 gene. In addition to being mutated in ifiers to E2F-responsive promoters (Harbour and Dean retinoblastomas, where it was initially discovered, RB12000; Ogawa et al. 2002). Progression from G1 through is mutated in many other cancers including prostate S phase occurs when RB1 is inactivated through phos- ), bladder (Miyamoto et al. 1995, phorylation by the Cdk complexes Cyclin D/Cdk4 or parathyroid (Cryns et al. 1994), and 90% of small cell Cyclin D/Cdk6 and Cyclin E/Cdk2 (Lundberg and lung cancers (SCLCs) (Minna et al. 2002) Rbf is that it itself is required for embryonic survival.To circumvent this issue, we generated mosaic animals required for DNA synthesis and metabolism (Stevaux and Dyson 2002). In addition to its effects on cell prolifthat carry clones of Rbf Ϫ tissue in the eye, whereas the rest of the animal is Rbf ϩ . We then generated overlaperation, loss of RB1 predisposes cells to apoptosis through the actions of E2F on p53 (reviewed in Chau and Wang ping clones of homozygous induced muta...

Identification and comparative analysis of the peptidyl‐prolyl cis/trans isomerase repertoires of H. sapiens, D. melanogaster, C. elegans, S. cerevisiae and Sz. pombe

“…In mammals, an FKBP12 knock‐out mouse showed normal skeletal muscle but suffered from severe cardiomyopathy and ventricular septal defects that mimic a human congenital heart disorder (Shou et al , 1998), an effect assigned to its modulation of calcium release activity of both skeletal and cardiac ryanodine receptors. Recently a mutation of the D. melanogaster cyclophilin CG3511, which severely truncates the protein, has been shown to confer a synthetic lethal phenotype on cells that lack the retinoblastoma (Rbf) protein (Edgar et al , 2005). Despite the high conservation of the PPIases throughout the eukaryotes and prokaryotes, it appears that they do not possess an essential function within many cells under normal growth conditions but may become essential in the absence of other cellular factors.…”

Synthetic lethality: the road to novel therapies for breast cancer

“…The progress in the molecular profiling of breast tumours means that there is now a working list of driver gene defects in the disease that in principle could be targeted with a synthetic lethal approach. For example, many of the tumour suppressor gene defects that recurrently occur in breast cancer, such as TP53, PTEN and RB1, might be amenable to synthetic lethal approaches; already a number of candidate synthetic lethal targets for these genes have been identified (Edgar et al 2005, Gordon & Du 2011, Reaper et al 2011, Mendes-Pereira et al 2012, Emerling et al 2013, Mereniuk et al 2013, Morandell et al 2013, Origanti et al 2013. Many of the efforts to identify synthetic lethal interactions that are relevant to breast cancer have been driven by advances in functional genomic approaches such as RNA interference screening and more recently CRISPR-based screens (Gilbert et al 2014, Wang et al 2015, Morgens et al 2016.…”

<b><i>Drosophila</i></b> as a Potential Model for Ocular Tumors

“…Using clonal genetic screens in the fly eye, loss-of-function mutations in the Tsc2 tumor suppressor [24] or a highly conserved peptidyl prolyl isomerase [25] were independently found to eliminate cells lacking rbf1 but allow wild-type cells to survive. It was subsequently found that inactivation of human Tsc2 in cancer cells inhibited the growth of RB1 mutant cells and induced cell death under stress conditions [24], suggesting potential therapeutic strategies for treating cancers in which RB1 has been inactivated.…”