S100A11 plays a role in homologous recombination and genome maintenance by influencing the persistence of RAD51 in DNA repair foci

FLIM-FRET-based analysis of S100A11/annexin interactions in living cells

Proteins achieve their biological functions in cells by cooperation in protein complexes. In this study, we employed fluorescence lifetime imaging microscopy (FLIM)-based Förster resonance energy transfer (FRET) measurements to investigate protein complexes comprising S100A11 and different members of the annexin (ANX) family, such as ANXA1, ANXA2, ANXA4, ANXA5, and AnxA6, in living cells. Using an S100A11 mutant without the capacity for Ca2+ binding, we found that Ca2+ binding of S100A11 is important for distinct S100A11/ANXA2 complex formation; however, ANXA1-containing complexes were unaffected by this mutant. An increase in the intracellular calcium concentration induced calcium ionophores, which strengthened the ANXA2/S100A11 interaction. Furthermore, we were able to show that S100A11 also interacts with ANXA4 in living cells. The FLIM-FRET approach used here can serve as a tool to analyze interactions between S100A11 and distinct annexins under physiological conditions in living cells.

Evolution of gene expression signature in mammary gland stem cells from neonatal to old mice

During the lifetime of females, mammary epithelial cells undergo cyclical expansion and proliferation depending on the cyclical activation of mammary gland stem/progenitor cells (MaSCs) in response to the change of hormone level. The structural shrink of mammary duct tree and the functional loss of mammary gland occur along with inactivation of MaSCs in old females, even leading to breast cancer occasionally. However, the gene expression signature in MaSCs across the lifespan remains unclear. Herein, we tested the tissue regeneration ability of CD24⁺CD49f^high MaSCs over six time points from neonatal (4-day-old) to aged mice (360-day-old). Further RNA-seq analyses identified four clusters of gene signatures based on the gene expression patterns. A subset of stemness-related genes was identified, showing the highest level at day 4 of the neonatal age, and the lowest level at the old age. We also identified an aging-related gene signature showing significant change in the old mice, in which an association between aging process and stemness loss was indicated. The aging-related gene signature showed regulation of cancer signaling pathways, as well as aging-related diseases including Huntington disease, Parkinson disease, and Alzheimer disease. Moreover, 425, 1056, 418, and 1107 gene variants were identified at D20, D40, D90, and D180, respectively, which were mostly reported to associated with tumorigenesis and metastasis in cancer. In summary, the current study is the first to demonstrate the gene expression shift in MaSCs from neonatal to aging, which leads to stemness loss, aging, aging-related diseases, and even breast cancer in old mice.

The Calcium Binding Protein S100A11 and Its Roles in Diseases

The calcium binding protein S100 family in humans contains 21 known members, with each possessing a molecular weight between 10 and 14 kDa. These proteins are characterized by a unique helix-loop-helix EF hand motif, and often form dimers and multimers. The S100 family mainly exists in vertebrates and exerts its biological functions both inside cells as a calcium sensor/binding protein, as well as outside cells. S100A11, a member of the S100 family, may mediate signal transduction in response to internal or external stimuli and it plays various roles in different diseases such as cancers, metabolic disease, neurological diseases, and vascular calcification. In addition, it can function as chemotactic agent in inflammatory disease. In this review, we first detail the discovery of S100 proteins and their structural features, and then specifically focus on the tissue and organ expression of S100A11. We also summarize its biological activities and roles in different disease and signaling pathways, providing an overview of S100A11 research thus far.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Determination of the number of RAD51 molecules in different human cell lines

Knowledge about precise numbers of specific molecules is necessary for understanding and verification of biological pathways. The RAD51 protein is central in the repair of DNA double-strand breaks (DSBs) by homologous recombination repair and understanding its role in cellular pathways is crucial to design mechanistic DNA repair models. Here, we determined the number of RAD51 molecules in several human cell lines including primary fibroblasts. We showed that between 20000 to 100000 of RAD51 molecules are available per human cell that theoretically can be used for simultaneously loading at least 7 DSBs. Interestingly, the amount of RAD51 molecules does not significantly change after the induction of DNA damage using bleomycin or γ-irradiation in cells but an accumulation of RAD51 on the chromatin occurs. Furthermore, we generated an EGFP-RAD51 fusion under the control of HSV thymidine kinase promoter sequences yielding moderate protein expression levels comparable to endogenously expressed RAD51. Initial characterizations suggest that these low levels of ectopically expressed RAD51 are compatible with cell cycle progression of human cells. Hence, we provide parameters for the quantitative understanding and modeling of RAD51-involving processes.

Analysis of S100A11 in DNA Damage Repair

DNA damage possesses the capacity to threaten the genomic integrity of an organism. A multitude of proteins are involved in the detection and repair of DNA double-strand breaks (DSBs), a severe kind of DNA damage. The function of DNA repair proteins can be examined by biochemical assays in vitro as well as in cell-based studies. The Ca²⁺-binding protein S100A11 shows functional interactions with factors involved in the repair of DSBs by homologous recombination (HR), a high-fidelity DNA repair pathway, such as RAD51 and RAD54B. The key enzyme of the homologous recombination repair is RAD51 that catalyzes the invasion of single-stranded DNA (ssDNA) into double-stranded DNA (dsDNA) containing homologous regions and the exchange of these DNA molecules generating heteroduplex DNA (hDNA). In this chapter, we describe a protocol for the purification of S100A11 to near homogeneity. Using purified proteins, we show the ability of S100A11 to stimulate RAD51 in a DNA strand exchange assay. Additionally, we describe a protocol how S100A11 can be localized in sites of DNA repair by immunofluorescence staining. Furthermore, we present a protocol for assessment of chromosomal aberrations after depletion of S100A11 that illustrate the apparent involvement of S100A11 in genome integrity.