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CHK1 Inhibitor Blocks Phosphorylation of FAM122A and Promotes Replication Stress.

ABSTRACT: While effective anti-cancer drugs targeting the CHK1 kinase are advancing in the clinic, drug resistance is rapidly emerging. Here, we demonstrate that CRISPR-mediated knockout of the little-known gene FAM122A/PABIR1 confers cellular resistance to CHK1 inhibitors (CHK1is) and cross-resistance to ATR inhibitors. Knockout of FAM122A results in activation of PP2A-B55α, a phosphatase that dephosphorylates the WEE1 protein and rescues WEE1 from ubiquitin-mediated degradation. The resulting increase in WEE1 protein expression reduces replication stress, activates the G2/M checkpoint, and confers cellular resistance to CHK1is. Interestingly, in tumor cells with oncogene-driven replication stress, CHK1 can directly phosphorylate FAM122A, leading to activation of the PP2A-B55α phosphatase and increased WEE1 expression. A combination of a CHK1i plus a WEE1 inhibitor can overcome CHK1i resistance of these tumor cells, thereby enhancing anti-cancer activity. The FAM122A expression level in a tumor cell can serve as a useful biomarker for predicting CHK1i sensitivity or resistance.

SUBMITTER: Li F

PROVIDER: S-EPMC7761918 | biostudies-literature |

REPOSITORIES: biostudies-literature

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CHK1 Inhibitor Blocks Phosphorylation of FAM122A and Promotes Replication Stress

Project description:While effective anti-cancer drugs targeting the CHK1 kinase are advancing in the clinic, drug resistance is rapidly emerging. Here, we demonstrate that CRISPR-mediated knockout of the little-known gene FAM122A confers cellular resistance to CHK1 inhibitors and cross-resistance to ATR inhibitors. Knockout of FAM122A results in activation of PP2A-B55α, a phosphatase which dephosphorylates the WEE1 protein and rescues WEE1 from Ubiquitin-mediated degradation. The resulting increase in WEE1 protein expression reduces replication stress, activates the G2/M checkpoint, and confers cellular resistance to CHK1 inhibitors. Interestingly, in tumor cells with oncogene-driven replication stress, CHK1 can directly phosphorylate FAM122A, leading to activation of the PP2A-B55α phosphatase and increased WEE1 expression. A combination of a CHK1 inhibitor plus a WEE1 inhibitor can overcome CHK1 inhibitor resistance of these tumor cells, thereby enhancing anti-cancer activity. The FAM122A expression level in a tumor cell can serve as a useful biomarker for predicting CHK1 inhibitor sensitivity or resistance.

2021-01-01 | GSE158338 | GEO

CHK1 Inhibitor Blocks Phosphorylation of FAM122A and Promotes Replication Stress

Project description:CHK1 Inhibitor Blocks Phosphorylation of FAM122A and Promotes Replication Stress

| PRJNA664943 | ENA

Human CTC1 promotes TopBP1 stability and CHK1 phosphorylation in response to telomere dysfunction and global replication stress.

Project description:CST (CTC1-STN1-TEN1) is a heterotrimeric, RPA-like complex that binds to single-stranded DNA (ssDNA) and functions in the replication of telomeric and non-telomeric DNA. Previous studies demonstrated that deletion of CTC1 results in decreased cell proliferation and telomere DNA damage signaling. However, a detailed analysis of the consequences of conditional CTC1 knockout (KO) has not been fully elucidated. Here, we investigated the effects of CTC1 KO on cell cycle progression, genome-wide replication and activation of the DNA damage response. Consistent with previous findings, we demonstrate that CTC1 KO results in decreased cell proliferation, G2 arrest and RPA-bound telomeric ssDNA. However, despite the increased levels of telomeric RPA-ssDNA, global ATR-dependent CHK1 and p53 phosphorylation was not detected in CTC1 KO cells. Nevertheless, we show that RPA-ssDNA does activate ATR, leading to the phosphorylation of RPA and autophosphorylation of ATR. Further analysis determined that inactivation of ATR, but not CHK1 or ATM, suppressed the accumulation of G2 arrested cells and phosphorylated RPA following CTC1 removal. These results suggest that ATR is localized and active at telomeres but is unable to elicit a global checkpoint response through CHK1. Furthermore, CTC1 KO inhibited CHK1 phosphorylation following hydroxyurea-induced replication stress. Additional studies revealed that this suppression of CHK1 phosphorylation, following replication stress, is caused by decreased levels of the ATR activator TopBP1. Overall, our results identify CST as a novel regulator of the ATR-CHK1 pathway.

| S-EPMC7781613 | biostudies-literature

Targeting Replication Stress Using CHK1 Inhibitor Promotes Innate and NKT Cell Immune Responses and Tumour Regression.

Project description:Drugs selectively targeting replication stress have demonstrated significant preclinical activity, but this has not yet translated into an effective clinical treatment. Here we report that targeting increased replication stress with a combination of Checkpoint kinase 1 inhibitor (CHK1i) with a subclinical dose of hydroxyurea targets also promotes pro-inflammatory cytokine/chemokine expression that is independent of cGAS-STING pathway activation and immunogenic cell death in human and murine melanoma cells. In vivo, this drug combination induces tumour regression which is dependent on an adaptive immune response. It increases cytotoxic CD8+ T cell activity, but the major adaptive immune response is a pronounced NKT cell tumour infiltration. Treatment also promotes an immunosuppressive tumour microenvironment through CD4+ Treg and FoxP3+ NKT cells. The number of these accumulated during treatment, the increase in FoxP3+ NKT cells numbers correlates with the decrease in activated NKT cells, suggesting they are a consequence of the conversion of effector to suppressive NKT cells. Whereas tumour infiltrating CD8+ T cell PD-1 and tumour PD-L1 expression was increased with treatment, peripheral CD4+ and CD8+ T cells retained strong anti-tumour activity. Despite increased CD8+ T cell PD-1, combination with anti-PD-1 did not improve response, indicating that immunosuppression from Tregs and FoxP3+ NKT cells are major contributors to the immunosuppressive tumour microenvironment. This demonstrates that therapies targeting replication stress can be well tolerated, not adversely affect immune responses, and trigger an effective anti-tumour immune response.

| S-EPMC8345057 | biostudies-literature

Histone H3 Serine-57 phosphorylation by CHK1 promotes responses to DNA replication stress

Project description:Post-translational modifications (PTM) of chromatin control the genomic environment for transcription, DNA replication and repair in response to cell stimuli1–3. Replication stress in budding and fission yeasts leads to abundant acetylation of histone H3 on lysine-56 (H3K56ac)4–6, but only trace levels of H3K56ac are detected in human cells7,8, implying that other histone modifications promote a repair-permissive environment. In budding yeast, genetic interactions between histone H3 lysine-56 and serine-57 substitutions suggest a possible role for serine-57 (H3S57) in responses to replication poisons9. In this study, we identify a phosphorylated form of H3S57 (H3S57ph) using phosphoproteomics in replicating Xenopus egg extracts, and show that it is a highly conserved histone modification which promotes responses to DNA replication stress in human cells. A kinome screen and functional experiments identified Checkpoint kinase 1 (CHK1) as the H3S57ph kinase; CHK1 inhibition eliminates H3S57ph and arrests cells in S-phase. Induction of replication stress increases H3S57ph, while disrupting H3S57ph reduces stalling of replication forks upon replication stress, inducing DNA damage. We identified two distinct mechanisms of action. First, H3S57ph interacts with specific DNA repair proteins, notably Rad50. Second, atomistic molecular dynamics simulations of the nucleosome core particle and in vitro assays indicate that H3S57ph interacts with the unacetylated side-chain of K56, thus loosening DNA-histone contacts. Our results suggest that H3S57ph is an effector of CHK1 that assists in processing stalled replication forks by increasing nucleosome mobility and promoting interactions with repair machinery, thereby limiting DNA damage upon replication stress.

2022-02-10 | PXD011328 | Pride

Chk1 promotes replication fork progression by controlling replication initiation.

Project description:DNA replication starts at initiation sites termed replication origins. Metazoan cells contain many more potential origins than are activated (fired) during each S phase. Origin activation is controlled by the ATR checkpoint kinase and its downstream effector kinase Chk1, which suppresses origin firing in response to replication blocks and during normal S phase by inhibiting the cyclin-dependent kinase Cdk2. In addition to increased origin activation, cells deficient in Chk1 activity display reduced rates of replication fork progression. Here we investigate the causal relationship between increased origin firing and reduced replication fork progression. We use the Cdk inhibitor roscovitine or RNAi depletion of Cdc7 to inhibit origin firing in Chk1-inhibited or RNAi-depleted cells. We report that Cdk inhibition and depletion of Cdc7 can alleviate the slow replication fork speeds in Chk1-deficient cells. Our data suggest that increased replication initiation leads to slow replication fork progression and that Chk1 promotes replication fork progression during normal S phase by controlling replication origin activity.

| S-EPMC2941317 | biostudies-literature

Targeting radioresistant breast cancer cells by single agent CHK1 inhibitor via enhancing replication stress.

Project description:Radiotherapy (RT) remains a standard therapeutic modality for breast cancer patients. However, intrinsic or acquired resistance limits the efficacy of RT. Here, we demonstrate that CHK1 inhibitor AZD7762 alone significantly inhibited the growth of radioresistant breast cancer cells (RBCC). Given the critical role of ATR/CHK1 signaling in suppressing oncogene-induced replication stress (RS), we hypothesize that CHK1 inhibition leads to the specific killing for RBCC due to its abrogation in the suppression of RS induced by oncogenes. In agreement, the expression of oncogenes c-Myc/CDC25A/c-Src/H-ras/E2F1 and DNA damage response (DDR) proteins ATR/CHK1/BRCA1/CtIP were elevated in RBCC. AZD7762 exposure led to significantly higher levels of RS in RBCC, compared to the parental cells. The mechanisms by which CHK1 inhibition led to specific increase of RS in RBCC were related to the interruptions in the replication fork dynamics and the homologous recombination (HR). In summary, RBCC activate oncogenic pathways and thus depend upon mechanisms controlled by CHK1 signaling to maintain RS under control for survival. Our study provided the first example where upregulating RS by CHK1 inhibitor contributes to the specific killing of RBCC, and highlight the importance of the CHK1 as a potential target for treatment of radioresistant cancer cells.

| S-EPMC5085184 | biostudies-literature

Extensive RPA2 hyperphosphorylation promotes apoptosis in response to DNA replication stress in CHK1 inhibited cells.

Project description:The replication protein A (RPA)-ssDNA complex formed at arrested replication forks recruits key proteins to activate the ATR-CHK1 signalling cascade. When CHK1 is inhibited during DNA replication stress, RPA2 is extensively hyperphosphorylated. Here, we investigated the role of RPA2 hyperphosphorylation in the fate of cells when CHK1 is inhibited. We show that proteins normally involved in DNA repair (RAD51) or control of RPA phosphorylation (the PP4 protein phosphatase complex) are not recruited to the genome after treatment with CHK1 and DNA synthesis inhibitors. This is not due to RPA2 hyperphosphorylation as suppression of this response does not restore loading suggesting that recruitment requires active CHK1. To determine whether RPA2 hyperphosphorylation protects stalled forks from collapse or induction of apoptosis in CHK1 inhibited cells during replication stress, cells expressing RPA2 genes mutated at key phosphorylation sites were characterized. Mutant RPA2 rescued cells from RPA2 depletion and reduced the level of apoptosis induced by treatment with CHK1 and replication inhibitors however the incidence of double strand breaks was not affected. Our data indicate that RPA2 hyperphosphorylation promotes cell death during replication stress when CHK1 function is compromised but does not appear to be essential for replication fork integrity.

| S-EPMC4787776 | biostudies-literature

Chk1 phosphorylation of Metnase enhances DNA repair but inhibits replication fork restart.

Project description:Chk1 both arrests replication forks and enhances repair of DNA damage by phosphorylating downstream effectors. Although there has been a concerted effort to identify effectors of Chk1 activity, underlying mechanisms of effector action are still being identified. Metnase (also called SETMAR) is a SET and transposase domain protein that promotes both DNA double-strand break (DSB) repair and restart of stalled replication forks. In this study, we show that Metnase is phosphorylated only on Ser495 (S495) in vivo in response to DNA damage by ionizing radiation. Chk1 is the major mediator of this phosphorylation event. We had previously shown that wild-type (wt) Metnase associates with chromatin near DSBs and methylates histone H3 Lys36. Here we show that a Ser495Ala (S495A) Metnase mutant, which is not phosphorylated by Chk1, is defective in DSB-induced chromatin association. The S495A mutant also fails to enhance repair of an induced DSB when compared with wt Metnase. Interestingly, the S495A mutant demonstrated increased restart of stalled replication forks compared with wt Metnase. Thus, phosphorylation of Metnase S495 differentiates between these two functions, enhancing DSB repair and repressing replication fork restart. In summary, these data lend insight into the mechanism by which Chk1 enhances repair of DNA damage while at the same time repressing stalled replication fork restart.

| S-EPMC3963179 | biostudies-literature

Fos-dependent induction of Chk1 protects osteoblasts from replication stress.

Project description:Stable Fos expression in the osteoblast lineage results in the development of osteosarcomas (OS) in mice, yet the underlying mechanisms are poorly understood. Using a genetic system in which Fos expression can be induced in osteoblasts in a doxycycline-dependent manner and through subsequent RNA sequencing and gene set enrichment analysis, we were able to identify novel transcriptional targets of Fos in osteoblasts. These included a distinct activation of cellular response toward replication stress (RS), exemplified by a Fos-dependent induction of the RS-suppressing Chk1 kinase. Importantly, Fos expression protects osteoblasts from RS and DNA damage likely through upregulation of Chk1 and facilitates transformation by Ras/E1A oncogenes. These data reveal a novel function of Fos in safeguarding genome stability during replication, which is particularly relevant in conditions of oncogene-induced S-phase entry.

| S-EPMC4111761 | biostudies-literature

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