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TIMELESS haploinsufficiency induces a PARG-dependency that is rescued by nucleoside supplementation, thus mimicking intrinsic PARG inhibitor sensitivity of ovarian cancer cells

ABSTRACT: A subset of cancer cells are intrinsically sensitive to inhibitors targeting PARG, the poly(ADP-ribose) glycohydrolase that degrades PAR chains. Sensitivity is accompanied by persistent DNA replication stress, and can be induced by inhibition of TIMELESS, a replisome accelerator. However, the nature of the oncogenic vulnerability responsible for intrinsic sensitivity remains undetermined. To understand PARG activity dependency, we analyzed Timeless model systems and intrinsically sensitive ovarian cancer cells. We show that nucleoside supplementation rescues all phenotypes associated with PARG inhibitor sensitivity, including replisome speed and fork-restart ability, S-phase completion and mitotic entry, proliferation dynamics and clonogenic potential, in both a TIMELESShaploinsufficient model and intrinsically sensitive cells. Importantly nucleoside supplementation restores PARG inhibitor resistance without reverting PAR chain accumulation, indicating that sensitivity correlates with PAR chain intolerance. We show that inhibition of thymidylate synthase, an enzyme required for dNTP homeostasis, induces PARG-dependency, and, using label-free, quantitative proteomics, we show that PKMYT1, a negative regulator of CDK1, is overexpressed in PARG inhibitor-sensitive cells. Together, these observations suggest that PARG inhibitor sensitivity reflects an inability to control replisome speed and/or maintain helicase-polymerase coupling in response to nucleotide imbalances, in turn applying selective pressure on mitotic entry controls to maintain genome integrity.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Permanent Cell Line Cell, Cell Culture

DISEASE(S): Colon Cancer

SUBMITTER: Holda Anagho

LAB HEAD: Stephen S. Taylor

PROVIDER: PXD049682 | Pride | 2024-06-28

REPOSITORIES: Pride

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			Action	DRS
	20220601_LUMOS1_nLC4_HA_SA_RKO_D4_00h_r1_F1.raw	Raw
	20220601_LUMOS1_nLC4_HA_SA_RKO_D4_00h_r1_F2.raw	Raw
	20220601_LUMOS1_nLC4_HA_SA_RKO_D4_00h_r2_F1.raw	Raw
	20220601_LUMOS1_nLC4_HA_SA_RKO_D4_00h_r2_F2.raw	Raw
	20220601_LUMOS1_nLC4_HA_SA_RKO_D4_00h_r3_F1.raw	Raw

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Project description:To achieve the extreme nuclear condensation necessary for sperm function, most histones are replaced with protamines during spermiogenesis in mammals. Mature sperm retain only a small fraction of nucleosomes, which are, in part, enriched on gene regulatory sequences, and recent findings suggest that these retained histones provide epigenetic information that regulates expression of a subset of genes involved in embryo development after fertilization. We addressed this tantalizing hypothesis by analyzing two mouse models exhibiting abnormal histone positioning in mature sperm due to impaired poly(ADP-ribose) (PAR) metabolism during spermiogenesis and identified altered sperm histone retention in specific gene loci genome-wide using MNase digestion-based enrichment of mononucleosomal DNA. We then set out to determine the extent to which expression of these genes was altered in embryos generated with these sperm. For control sperm, most genes showed some degree of histone association, unexpectedly suggesting that histone retention in sperm genes is not an all-or-none phenomenon and that a small number of histones may remain associated with genes throughout the genome. The amount of retained histones, however, was altered in many loci when PAR metabolism was impaired. To ascertain whether sperm histone association and embryonic gene expression are linked, the transcriptome of individual 2-cell embryos derived from such sperm was determined using microarrays and RNA sequencing. Strikingly, a moderate but statistically significant portion of the genes that were differentially expressed in these embryos also showed different histone retention in the corresponding gene loci in sperm of their fathers. These findings provide new evidence for the existence of a linkage between sperm histone retention and gene expression in the embryo. Mnase sensitivity of sperm DNA, indicating nucleosomal, not protamine, packaging was altered in mice by manipulating poly(ADP-ribose) metabolism in adult males using a specific PARP inhibitor for 6 weeks. Abnormal sperm nucleosomal organization of males analyzed by these tiling arrays was compared with differential gene expression in 2 cell embryos fathered by these males analyzed by separate gene expression arrays and RNA sequencing.

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TIMELESS haploinsufficiency induces a PARG-dependency that is rescued by nucleoside supplementation, thus mimicking intrinsic PARG inhibitor sensitivity of ovarian cancer cells

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