The HINT1 tumor suppressor regulates both γ-H2AX and ATM in response to DNA damage

Hint1 is a haploinsufficient tumor suppressor gene and the underlying molecular mechanisms for its tumor suppressor function are unknown. In this study we demonstrate that HINT1 participates in ionizing radiation (IR)–induced DNA damage responses. In response to IR, HINT1 is recruited to IR-induced foci (IRIF) and associates with γ-H2AX and ATM. HINT1 deficiency does not affect the formation of γ-H2AX foci; however, it impairs the removal of γ-H2AX foci after DNA damage and this is associated with impaired acetylation of γ-H2AX. HINT1 deficiency also impairs acetylation of ATM and activation of ATM and its downstream effectors, and retards DNA repair, in response to IR. HINT1-deficient cells exhibit resistance to IR-induced apoptosis and several types of chromosomal abnormalities. Our findings suggest that the tumor suppressor function of HINT1 is caused by, at least in part, its normal role in enhancing cellular responses to DNA damage by regulating the functions of both γ-H2AX and ATM.

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The tumor suppressor activity of DLC1 requires the interaction of its START domain with Phosphatidylserine, PLCD1, and Caveolin-1

Molecular Cancer ◽

10.1186/s12943-021-01439-y ◽

2021 ◽

Vol 20 (1) ◽

Author(s):

Beatriz Sanchez-Solana ◽

Dunrui Wang ◽

Xiaolan Qian ◽

Parthibane Velayoudame ◽

Dhirendra K. Simanshu ◽

...

Keyword(s):

Tumor Suppressor ◽

Molecular Mechanisms ◽

Structural Model ◽

Suppressor Gene ◽

Lipid Transfer ◽

Tumor Suppressor Function ◽

Suppressor Activity ◽

Caveolin 1 ◽

Suppressor Function ◽

Start Domain

Abstract Background DLC1, a tumor suppressor gene that is downregulated in many cancer types by genetic and nongenetic mechanisms, encodes a protein whose RhoGAP and scaffolding activities contribute to its tumor suppressor functions. The role of the DLC1 START (StAR-related lipid transfer; DLC1-START) domain, other than its binding to Caveolin-1, is poorly understood. In other START domains, a key function is that they bind lipids, but the putative lipid ligand for DLC1-START is unknown. Methods Lipid overlay assays and Phosphatidylserine (PS)-pull down assays confirmed the binding of DLC1-START to PS. Co-immunoprecipitation studies demonstrated the interaction between DLC1-START and Phospholipase C delta 1 (PLCD1) or Caveolin-1, and the contribution of PS to those interactions. Rho-GTP, cell proliferation, cell migration, and/or anchorage-independent growth assays were used to investigate the contribution of PS and PLCD1, or the implications of TCGA cancer-associated DLC1-START mutants, to DLC1 functions. Co-immunoprecipitations and PS-pull down assays were used to investigate the molecular mechanisms underlying the impaired functions of DLC1-START mutants. A structural model of DLC1-START was also built to better understand the structural implications of the cancer-associated mutations in DLC1-START. Results We identified PS as the lipid ligand for DLC1-START and determined that DLC1-START also binds PLCD1 protein in addition to Caveolin-1. PS binding contributes to the interaction of DLC1 with Caveolin-1 and with PLCD1. The importance of these activities for tumorigenesis is supported by our analysis of 7 cancer-associated DLC1-START mutants, each of which has reduced tumor suppressor function but retains wildtype RhoGAP activity. Our structural model of DLC1-START indicates the mutants perturb different elements within the structure, which is correlated with our experimental findings that the mutants are heterogenous with regard to the deficiency of their binding properties. Some have reduced PS binding, others reduced PLCD1 and Caveolin-1 binding, and others are deficient for all of these properties. Conclusion These observations highlight the importance of DLC1-START for the tumor suppressor function of DLC1 that is RhoGAP-independent. They also expand the versatility of START domains, as DLC1-START is the first found to bind PS, which promotes the binding to other proteins.

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The trefoil factor 1 participates in gastrointestinal cell differentiation by delaying G1-S phase transition and reducing apoptosis

The Journal of Cell Biology ◽

10.1083/jcb200108056 ◽

2002 ◽

Vol 157 (5) ◽

pp. 761-770 ◽

Cited By ~ 116

Author(s):

Carine Bossenmeyer-Pourié ◽

Rama Kannan ◽

Stéphane Ribieras ◽

Corinne Wendling ◽

Isabelle Stoll ◽

...

Keyword(s):

Phase Transition ◽

Cell Differentiation ◽

Tumor Suppressor ◽

Molecular Mechanisms ◽

Kinase Inhibitors ◽

Active Form ◽

Suppressor Gene ◽

Trefoil Factor ◽

Altered Expression ◽

Induced Apoptosis

Trefoil factor (TFF)1 is synthesized and secreted by the normal stomach mucosa and by the gastrointestinal cells of injured tissues. The link between mouse TFF1 inactivation and the fully penetrant antropyloric tumor phenotype prompted the classification of TFF1 as a gastric tumor suppressor gene. Accordingly, altered expression, deletion, and/or mutations of the TFF1 gene are frequently observed in human gastric carcinomas. The present study was undertaken to address the nature of the cellular and molecular mechanisms targeted by TFF1 signalling. TFF1 effects were investigated in IEC18, HCT116, and AGS gastrointestinal cells treated with recombinant human TFF1, and in stably transfected HCT116 cells synthesizing constitutive or doxycycline-induced human TFF1. We observed that TFF1 triggers two types of cellular responses. On one hand, TFF1 lowers cell proliferation by delaying G1-S cell phase transition. This results from a TFF1-mediated increase in the levels of cyclin-dependent kinase inhibitors of both the INK4 and CIP subfamilies, leading to lower E2F transcriptional activity. On the other hand, TFF1 protects cells from chemical-, anchorage-free–, or Bad-induced apoptosis. In this process, TFF1 signalling targets the active form of caspase-9. Together, these results provide the first evidence of a dual antiproliferative and antiapoptotic role for TFF1. Similar paradoxical functions have been reported for tumor suppressor genes involved in cell differentiation, a function consistent with TFF1.

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Genetic analysis of Ikaros target genes and tumor suppressor function in BCR-ABL1+ pre–B ALL

Journal of Experimental Medicine ◽

10.1084/jem.20160049 ◽

2017 ◽

Vol 214 (3) ◽

pp. 793-814 ◽

Cited By ~ 15

Author(s):

Hilde Schjerven ◽

Etapong F. Ayongaba ◽

Ali Aghajanirefah ◽

Jami McLaughlin ◽

Donghui Cheng ◽

...

Keyword(s):

Tumor Suppressor ◽

Target Genes ◽

Lymphoblastic Leukemia ◽

Suppressor Gene ◽

Tumor Suppressor Function ◽

Gene Encoding ◽

Specific Expression ◽

Suppressor Function ◽

Genome Wide ◽

Conserved Gene

Inactivation of the tumor suppressor gene encoding the transcriptional regulator Ikaros (IKZF1) is a hallmark of BCR-ABL1+ precursor B cell acute lymphoblastic leukemia (pre–B ALL). However, the mechanisms by which Ikaros functions as a tumor suppressor in pre–B ALL remain poorly understood. Here, we analyzed a mouse model of BCR-ABL1+ pre–B ALL together with a new model of inducible expression of wild-type Ikaros in IKZF1 mutant human BCR-ABL1+ pre–B ALL. We performed integrated genome-wide chromatin and expression analyses and identified Ikaros target genes in mouse and human BCR-ABL1+ pre–B ALL, revealing novel conserved gene pathways associated with Ikaros tumor suppressor function. Notably, genetic depletion of different Ikaros targets, including CTNND1 and the early hematopoietic cell surface marker CD34, resulted in reduced leukemic growth. Our results suggest that Ikaros mediates tumor suppressor function by enforcing proper developmental stage–specific expression of multiple genes through chromatin compaction at its target genes.

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