High Mobility Group Protein B1 Is an Activator of Apoptotic Response to Antimetabolite Drugs

Abstract

We explored the role of a chromatin-associated nuclear protein high mobility group protein B1 (HMGB1) in apoptotic response to widely used anticancer drugs. A murine fibroblast model system generated from Hmgb1 ϩ/ϩ and Hmgb1 Ϫ/Ϫ mice was used to assess the role of HMGB1 protein in cellular response to anticancer nucleoside analogs and precursors, which act without destroying the integrity of DNA. Chemosensitivity experiments with 5-fluorouracil, cytosine arabinoside (araC), and mercaptopurine (MP) demonstrated that Hmgb1 Ϫ/Ϫ mouse embryonic fibroblasts (MEFs) were 3 to 10 times more resistant to these drugs compared with Hmgb1 ϩ/ϩ MEFs. Hmgb1-deficient cells showed compromised cell cycle arrest and reduced caspase activation after treatment with MP and araC. Phosphorylation of p53 at Ser12 (corresponding to Ser9 in human p53) and Ser18 (corresponding to Ser15 in human p53), as well as phosphorylation of H2AX after drug treatment, was reduced in Hmgb1-deficient cells. trans-Activation experiments demonstrated diminished activation of proapoptotic promoters Bax, Puma, and Noxa in Hmgb1-deficient cells after treatment with MP or araC, consistent with reduced transcriptional activity of p53. We have demonstrated for the first time that Hmgb1 is an essential activator of cellular response to genotoxic stress caused by chemotherapeutic agents (thiopurines, cytarabine, and 5-fluorouracil), which acts at early steps of antimetaboliteinduced stress by stimulating phosphorylation of two DNA damage markers, p53 and H2AX. This finding makes HMGB1 a potential target for modulating activity of chemotherapeutic antimetabolites. Identification of proteins sensitive to DNA lesions that occur without the loss of DNA integrity provides new insights into the determinants of drug sensitivity in cancer cells.High mobility group protein B1 (HMGB1) is a versatile protein with intranuclear and extracellular functions. In the nucleus, it bends and plasticizes DNA; outside the cell, it acts as a cytokine mediator of inflammation. Despite its small size and a simple domain structure, HMGB1 facilitates numerous intranuclear processes, including transcription, replication, V(D)J recombination, and transposition (Hock et al., 2007). This versatility is achieved through the ability of HMGB1 to get involved in direct physical contacts with two distinct groups of macromolecules: HMGB1 reveals affinity with DNA cruciforms and bent, kinked, or chemically modified DNA; on the other hand, it interacts with a number of proteins, including p53, steroid hormone receptors, general and specific transcription factors, nuclear factor-B, DNA protein kinase (DNA-PK), etc. (Bianchi and Agresti, 2005). These two distinct groups of binding substrates suggest that HMGB1 may provide a molecular link between distorted DNA, and proteins involved in DNA metabolism or genotoxic stress response. Therefore, HMGB1 is a potential modulator of anticancer therapy targeted against DNA.Induction of apoptotic death in cancer cells via genotoxic stress by irradiation o...

Mutual enhancement between high-mobility group box-1 and NADPH oxidase-derived reactive oxygen species mediates diabetes-induced upregulation of retinal apoptotic markers

“…Furthermore, we demonstrate that diabetes upregulates PARP-1 and caspase-3 expression in the retinas and that administration of glycyrrhizin attenuates diabetes-induced PARP-1 and caspase-3 upregulation. Consistent with our findings, previous studies demonstrated that HMGB1 overexpession induces PARP-1 and caspase-3 expression [23,36] and that glycyrrhizin attenuates apoptosis induced by ischemia-reperfusion injury in rat brains [15]. Our findings suggest that the mechanism by which glycyrrhizin prevents diabetes-induced PARP-1 and caspase-3 expression in the diabetic retina could be through lowering ROS generation.…”

HMGB1 gene knockout in mouse embryonic fibroblasts results in reduced telomerase activity and telomere dysfunction

“…In this respect, HMGB1 could act either directly by interaction with the core telomerase subunits and/or indirectly via promotion of synthesis/folding of factor(s) participating in formation (assembly) of active telomerase (Collins 2008). The latter would be compatible with DNA microarrays revealing diminished expression of numerous heat shock proteins (chaperones) in HMGB1 −/− MEFs relative to the parental cells (Krynetskaia et al 2008), including Hsp90 mRNA as revealed by qRT-PCR (data not shown). Hsp90 protein has previously been shown to be an important factor in activation of telomerase (Holt et al 1999;Woo et al 2009).…”

High Mobility Group Box 1 (HMGB1) Phenotypic Role Revealed with Stress

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