Interplay between BRCA1 and GADD45A and Its Potential for Nucleotide Excision Repair in Breast Cancer Pathogenesis

Abstract

A fraction of breast cancer cases are associated with mutations in the BRCA1 (BRCA1 DNA repair associated, breast cancer type 1 susceptibility protein) gene, whose mutated product may disrupt the repair of DNA double-strand breaks as BRCA1 is directly involved in the homologous recombination repair of such DNA damage. However, BRCA1 can stimulate nucleotide excision repair (NER), the most versatile system of DNA repair processing a broad spectrum of substrates and playing an important role in the maintenance of genome stability. NER removes carcinogenic adducts of diol-epoxy derivatives of benzo[α]pyrene that may play a role in breast cancer pathogenesis as their accumulation is observed in breast cancer patients. NER deficiency was postulated to be intrinsic in stage I of sporadic breast cancer. BRCA1 also interacts with GADD45A (growth arrest and DNA damage-inducible protein GADD45 alpha) that may target NER machinery to actively demethylate genome sites in order to change the expression of genes that may be important in breast cancer. Therefore, the interaction between BRCA1 and GADD45 may play a role in breast cancer pathogenesis through the stimulation of NER, increasing the genomic stability, removing carcinogenic adducts, and the local active demethylation of genes important for cancer transformation.

Keywords: BRCA1; DNA demethylation; GADD45A; NER; breast cancer; nucleotide excision repair.

Figure 1

Familial and non-familial breast cancer. The diagram on the left shows the approximate fraction of breast cancer cases with no family history (green) and family history associated with (yellow) or without (brown) the occurrence of BRCA1 (DNA repair associated, breast cancer type 1 susceptibility) and BRCA12 pathogenic variants. The right diagram presents the distribution of pathogenic mutations found in breast cancer cases with family history. Abbreviations are defined in the main text.

Figure 2

BRCA1 (BRCA1 DNA repair associated) gene and protein. The BRCA1 gene (upper panel) is located in 17q21.31, contains 24 exons, and encodes the BRCA1 protein (lower panel), which is important for genomic stability (clouds). The RING (really interesting new gene), NLS (nuclear localization signal), coiled-coil (C-C), SCD (serine cluster domain), and BRCT (BRCA1 C-terminal) domains are presented in a linear representation of BRCA1. BRCA1 is phosphorylated in response to DNA double-strand breaks (DSBs) and recruited at the DSB sites by the phosphorylated Abraxas protein. BRCA1 interacts with BARD1 (BRCA1-associated RING domain protein 1) through its N-terminal RING domain to activate its E3 ligase activity. A coiled-coil domain interacts with RAD51 (RAD51 recombinase), the main human recombinase, and its counterpart in PALB2 (partner and localizer of BRCA2). SCD is phosphorylated by the ATM (ataxia telangiectasia mutated)/ATR (ATR serine/threonine kinase) kinases. The BRCT repeats are responsible for multiple interactions of BRCA1 with other proteins. BACH1—BTB domain and CNC homolog 1, CtiP—RB bindfing protein, endonuclease, MRN—MRN complex interacting protein, TSS—transcription start site, UTR—untranslated region, P—a phosphate residue, HR—homologous recombination, and DSBR—double-strand break repair. Dotted lines represent DNA fragments non-essential for the BRCA1 gene.

Figure 3

Nucleotide excision repair (NER) in humans. In transcriptionally inactive DNA or non-transcribed strands of active genes, distortion of the DNA helix (red star) is recognized by XPC complexed with hRAD23B and CENT2 in GG-NER. This complex may be supplemented by the DDE complex. hRAD23 leaves the complex upon XPC binding. In the transcription-coupled NER, DNA damage is signalized by the stalling RNA polymerase II (RNA Pol II) during transcription elongation. A complex interaction of UVSSA, USP7, and CSB with RNA Pol II occurs during the elongation, but the stalling of the polymerase induces CSB binding by CSA, likely resulting in backward translocation of the polymerase and making room for the NER machinery. TFIIH, a transcription initiation complex is recruited to the damage in both NER subpathways. XPG, a structure-specific endonuclease, binds to the NER complex. The multiprotein complex TFIIH displays helicase activity and opens DNA around the damage. It also possesses the ATPase activity to DNA 5′→3′ unwind to verify the presence of chemically modified nucleotides in the site of damage by XPD assisted by XPA. Another structure-specific endonuclease, XPF-ERCC1, is directed to the damage by RPA and makes a strand break on its 5′ side, and XPG then makes a cut on the opposite side to the damage. PCNA is loaded onto XPF-ERCC1 and recruits DNA Pol δ/ε to fulfill the gap and DNA ligase 1 or 3 seals the nick, restoring the lacking phosphodiester bond and DNA integrity. Abbreviations are defined in the main text. Black straight arrows represent changes in DNA structure induced by a protein or protein complex (black curved arrows).

Figure 4

GADD45A (growth arrest and DNA damage-inducible 45 alpha) gene and protein. The GADD45A gene is located in 1p31.3 and contains four exons. The GADD45 protein interacts with many proteins to perform many functions in stress signaling, DNA repair, cell survival, cell cycle arrest, senescence, or apoptosis (clouds). TSS—transcription start site, UTR—untranslated region, MEKK4—mitogen-activated protein kinase 4, TAF12—TATA-box binding protein associated factor 12, ING1—inhibitor of growth family member 1, cdc2—cyclin dependent kinase 2, TDG—thymine DNA glycosylase, XPG—xeroderma pigmentosum group, G—complementary protein, and PCNA—proliferating cell nuclear antigen. Dotted lines represent DNA fragments non-essential for the GADD45A gene.

Figure 5

p53-dependent (upper panel) and independent (lower panel) regulation of GADD45A (growth arrest and DNA damage inducible 45 alpha) by BRCA1 (BRCA1 DNA repair associated, breast cancer type 1 susceptibility) in the presence and absence of DNA damage (yellow thunder). BRCA1 stimulates GADD45A when DNA damage is present. The BRCA1/ZNF350 (zinc finger protein 350)/Egr1 (early growth response protein 1) complex activates GADD45A by recruiting p53 to the p53 motif located at the GADD45A third intron. Ionizing radiation and other DSB-inducing agents promote GADD45A through the ATM (ataxia telangiectasia mutated) targeting p53, which accumulates and stimulates GADD45A transcription by binding the WT1 (Wilms tumor gene protein 1) protein, which directly binds the GADD45A promoter. In the absence of DNA damage, the BRCA1/ZNF350/Erg1 complex inhibits GADD45A. The regulation of GADD45A by non-DSB-inducing factors is independent of p53. In such a case, GADD45A regulation by BRCA1 is mediated by the interaction of Oct-1 (octamer-binding transcription factor 1) and NF-YA (nuclear transcription factor Y subunit alpha) with two elements present in the GADD45A promoter: OCT1 and CAAT box.

Figure 6

BRCA1 (BRCA1 DNA repair associated, breast cancer (BC) type 1 susceptibility protein) may stimulate nucleotide excision repair (NER) that may prevent or slow down breast carcinogenesis, increasing the genomic stability and removing BC-related DNA damages. Furthermore, BRCA1 may stimulate GADD45A, which can actively demethylate genes important in BC prevention and suppression.