The mouse Kin-17 gene codes for a new protein involved in DNA transactions and is akin to the bacterial RecA protein

Roles and regulatory mechanisms of KIN17 in cancers (Review)

KIN17, which is known as a DNA and RNA binding protein, is highly expressed in numerous types of human cancers and was discovered to participate in several vital cell behaviors, including DNA replication, damage repair, regulation of cell cycle and RNA processing. Furthermore, KIN17 is associated with cancer cell proliferation, migration, invasion and cell cycle regulation by regulating pathways including the p38 MAPK, NF-κB-Snail and TGF-β/Smad2 signaling pathways. In addition, knockdown of KIN17 was found to enhance the sensitivity of tumor cells to chemotherapeutic agents. Immunohistochemical analysis revealed that there were significant differences in the expression of KIN17 between cancer tissues and adjacent tissues. Both the Kaplan-Meier survival analysis and multivariate Cox regression analysis indicated that KIN17 is aberrantly high expressed in various tumor tissues and is also associated with poor prognosis in patients with various tumor types. Taken together, KIN17 has key roles in tumorigenesis and cancer development. Investigating the relationship between KIN17 and neoplasms will provide a vital theoretical basis for KIN17 to serve as a diagnostic and prognostic biomarker for cancer patients and as a potential target for cancer therapy.

Lysine Methylation of the Valosin-Containing Protein (VCP) Is Dispensable for Development and Survival of Mice

Valosin-containing protein (VCP) is a homohexameric ATPase involved in a multitude cellular processes and it was recently shown that VCP is trimethylated at lysine 315 by the VCP lysine methyltransferase (VCPKMT). Here, we generated and validated a constitutive knockout mouse by targeting exon 1-4 of the Vcpkmt gene. We show that Vcpkmt is ubiquitously expressed in all tissues examined and confirm the sub-cellular localization to the cytoplasm. We show by (I) mass spectrometric analysis, (II) VCPKMT-mediated in vitro methylation of VCP in cell extracts and (III) immunostaining with a methylation specific antibody, that in Vcpkmt-/- mice the methylation of lysine 315 in VCP is completely abolished. In contrast, VCP is almost exclusively trimethylated in wild-type mice. Furthermore, we investigated the specificity of VCPKMT with in vitro methylation assays using as source of substrate protein extracts from Vcpkmt-/- mouse organs or three human Vcpkmt-/- cell lines. The results show that VCPKMT is a highly specific enzyme, and suggest that VCP is its sole substrate. The Vcpkmt-/- mice were viable, fertile and had no obvious pathological phenotype. Their body weight, life span and acute endurance capacity were comparable to wild-type controls. Overall the results show that VCPKMT is an enzyme required for methylation of K315 of VCP in vivo, but VCPKMT is not essential for development or survival under unstressed conditions.

8-oxoguanine DNA glycosylase, but not Kin17 protein, is translocated and differentially regulated by estrogens in rat brain cells

8-oxoguanine DNA glycosylase and Kin17 are proteins widely distributed and phylogenetically conserved in the CNS. 8-oxoguanine DNA glycosylase is a DNA repair enzyme that excises 7,8-dihydro-8-oxoguanine present in DNA damaged by oxidative stress. Kin17 protein is involved in DNA repair and illegitimate recombination in eukaryotic cells. The present study evaluates the effect of ovarian hormones on the expression of both proteins in the magnocellular paraventricular nucleus of the hypothalamus and the bed nucleus of the stria terminalis in female and male rat brains. In the paraventricular nucleus, ovariectomy induced a significant decrease in the number of 8-oxoguanine DNA glycosylase-positive nuclei as well as in their relative fluorescent intensity as compared with ovariectomized-estradiol treated and proestrous groups. Confocal microscopy observation demonstrated that oxoguanine DNA glycosylase protein is located in the Hoechst-dyed nuclei and cytoplasm in male and ovariectomized rats. Surprisingly, following estradiol administration to ovariectomized and proestrous rats, the 8-oxoguanine DNA glycosylase immunolabeling was observed in the nucleolus, the cytoplasm and the dendrites of cells, while Kin17 protein was always localized in the cell nuclei. In the bed nucleus of the stria terminalis, the number of 8-oxoguanine DNA glycosylase-positive nuclei during proestrous was significantly lower than the number obtained in males and ovariectomized rats and similar to the number of ovariectomized-estradiol-treated groups. In contrast to these observations, no significant differences were observed in the expression of kin17 protein. Our results suggest that estrogens differentially regulate the expression of 8-oxoguanine DNA glycosylase, but not that of Kin17 protein, in specific regions of the rat brain and that estradiol can translocate the 8-oxoguanine DNA glycosylase protein within nuclei and to other subcellular compartments.

KIN17 encodes an RNA-binding protein and is expressed during mouse spermatogenesis

Genotoxic agents deform DNA structure thus eliciting a complex genetic response allowing recovery and cell survival. The Kin17 gene is up-regulated during this response. This gene encodes a conserved nuclear protein that shares a DNA-binding domain with the bacterial RecA protein. The KIN17 protein binds DNA and displays enhanced expression levels in proliferating cultured cells, suggesting a role in nuclear metabolism. We investigated this by studying the expression profile of KIN17 protein during mouse spermatogenesis. As expected, the expression level of Kin17 is higher in proliferating than in differentiated cells. KIN17 is selectively extracted from this tissue by detergents and a fraction was tightly associated with the nuclear matrix. Germinal cells ubiquitously express Kin17 and the protein is located mainly in the nucleus except in elongated spermatids where cytoplasmic staining is also observed. Sertoli and germ cells that are no longer mitotically active express KIN17, suggesting a general role in all testicular cell types. In adult testis a significant proportion of KIN17 co-purifies with polyadenylated RNA. KIN17 directly binds RNA, preferentially poly(G) and poly(U) homopolymers. These results together with the identification of KIN17 as a component of the human spliceosome indicate that this protein may participate in RNA processing.

DNA repair in neural cells: basic science and clinical implications

As one part of a distinguished scientific career, Dr. Bryn Bridges focused his attention on the issue of DNA damage and repair in stationary phase bacteria. His work in this area led to his interest in DNA repair and mutagenesis in another non-dividing cell population, the neurons in the mammalian nervous system. He has specifically taken an interest in the magnocellular neurons of the central nervous system, and the possibility that somatic mutations may be occurring in these neurons. As part of this special issue dedicated to Bryn Bridges upon his retirement, I will discuss the various DNA repair pathways known to be active in the nervous system. The importance of DNA repair to the nervous system is most graphically illustrated by the neurological abnormalities observed in patients with hereditary diseases associated with defects in DNA repair. I will consider the mechanisms underlying the neurological abnormalities observed in patients with four of these diseases: xeroderma pigmentosum (XP), Cockayne's syndrome (CS), ataxia telangectasia (AT) and AT-like disorder (ATLD). I will also propose a mechanism for one of the observations indicating that somatic mutation can occur in the magnocellular neurons of the aging rat brain. Finally, as a parallel to Bridges inquiry into how much DNA synthesis is going on in stationary phase bacteria, I will address the question of how much DNA synthesis in going on in neurons, and the implications of the answer to this question for recent studies of neurogenesis in adult mammals.

Expression of Kin17 and 8-OxoG DNA glycosylase in cells of rodent and quail central nervous system

Kin17 and 8-Oxoguanine DNA glycosylase (Ogg1) are proteins, respectively, involved in illegitimate recombination and DNA repair in eukaryotic cells. To characterize the expression of these proteins in cell types of rodent and avian brains, we combined immunocytochemistry for either Kin17 or Ogg1 proteins with glial fibrillary acidic protein (GFAP, an astrocyte marker) immunodetection on the same tissue section. Both Kin17 and Ogg1 proteins were localized in cell nuclei and were extensively distributed in neuronal populations of quail and rodent brains. However, GFAP-immunoreactive cells were never labeled by Kin17 protein. This was observed in nerve fiber tracts, in the cerebral cortex, the hippocampal formation, the hypothalamic region, and the periventricular regions of the brain of both species studied. These results were confirmed by combining in situ hybridization of kin17 mRNA and GFAP immunodetection. On the contrary, GFAP-immunoreactive cells were often labeled by the Ogg1 protein in brain structures such as fiber tracts, the cortical surface, the cerebellum, and the ependymal surface of both quail and mouse brains. Our results suggest that the expression of the Kin17 protein (observed in neurons) and that of the Ogg1 protein (observed in neurons and glial cells) is conserved in brain phylogeny.

Molecular cloning and characterization of the human KIN17 cDNA encoding a component of the UVC response that is conserved among metazoans

We describe the cloning and characterization of the human KIN17 cDNA encoding a 45 kDa zinc finger nuclear protein. Previous reports indicated that mouse kin17 protein may play a role in illegitimate recombination and in gene regulation. Furthermore, overproduction of mouse kin17 protein inhibits the growth of mammalian cells, particularly the proliferation of human tumour-derived cells. We show here that the KIN17 gene is remarkably conserved during evolution. Indeed, the human and mouse kin17 proteins are 92.4% identical. Furthermore, DNA sequences from fruit fly and filaria code for proteins that are 60% identical to the mammalian kin17 proteins, indicating conservation of the KIN17 gene among metazoans. The human KIN17 gene, named (HSA)KIN17, is located on human chromosome 10 at p15-p14. The (HSA)KIN17 RNA is ubiquitously expressed in all the tissues and organs examined, although muscle, heart and testis display the highest levels. UVC irradiation of quiescent human primary fibroblasts increases (HSA)KIN17 RNA with kinetics similar to those observed in mouse cells, suggesting that up-regulation of the (HSA)KIN17 gene after UVC irradiation is a conserved response in mammalian cells. (HSA)kin17 protein is concentrated in intranuclear focal structures in proliferating cells as judged by indirect immunofluorescence. UVC irradiation disassembles (HSA)kin17 foci in cycling cells, indicating a link between the intranuclear distribution of (HSA)kin17 protein and the DNA damage response.

Overexpression of kin17 protein disrupts nuclear morphology and inhibits the growth of mammalian cells

UVC or ionizing radiation of mammalian cells elicits a complex genetic response that allows recovery and cell survival. Kin17 gene, which is highly conserved among mammals, is upregulated during this response. Kin17 gene encodes a 45 kDa protein which binds to DNA and presents a limited similarity with a functional domain of the bacterial RecA protein. Kin17 protein is accumulated in the nucleus of proliferating fibroblasts and forms intranuclear foci. Using expression vectors, we show that overexpression of kin17 protein inhibits cell-cycle progression into S phase. Our results indicate that growth inhibition correlates with disruption of the nuclear morphology which seems to modify the intranuclear network required during the early steps of DNA replication. We report that a mutant encoding a protein deleted from the central domain of kin17 protein enhanced these effects whereas the deletion of the C-terminal domain considerably reduced them. These mutants will be used to elucidate the molecular mechanism by which kin17 protein alters cell growth and DNA replication.

Ectopic expression of (Mm)Kin17 protein inhibits cell proliferation of human tumor-derived cells

To characterize the biological role of Kin17 protein, a mammalian nuclear protein which participates in the response to UV and ionizing radiation and binds to curved DNA, EBV-derived vectors carrying (Mm)Kin17 cDNA were constructed and transfected in tumorigenic cells harboring different p53 profiles (HeLa, H1299, and HCT116) and in immortalized HEK 293 cells. (Mm)Kin17 protein expression induced a tremendous decrease in cell proliferation of the three tumorigenic cell lines 2 weeks after transfection. Transfection of HEK 293 cells with an pEBVCMV(Mm)Kin17 plasmid gave rise to numerous (Mm)Kin17-expressing cells which constantly disappeared with time, preventing the establishment of (Mm)Kin17-expressing cells. Several independent clones were isolated from HEK 293 cells carrying a pEBVMT(Mm)Kin17 vector. The two clones described here (B223.1 and B223.2) exhibited different (Mm)Kin17 protein levels and displayed a gradual decrease in their proliferative capacities. In B223.1 cells, the basal expression of (Mm)Kin17 greatly reduced plating efficiency and cell growth. B223.1 cell morphology was altered, with numerous round-shaped cells whose spreading on the culture support was hampered. We observed giant multinucleated cells or cells containing micronuclei-like structures and/or multilobed nuclei. To conclude, (Mm)Kin17 overexpression reduced the proliferation of tumorigenic cells independently of their p53 status and modified cell growth and cell morphology of established HEK 293 cells producing (Mm)Kin17 protein. It is likely that (Mm)Kin17 may interfere with DNA replication.

Expression of Kin, a nuclear protein binding to curved DNA, in mammal and avian brains

Kin is a nuclear protein which presents cross-immunoreactivity with the bacterial RecA protein and which efficiently binds to curved DNA. This genomic interaction could be implied in DNA repair and illegitimate recombination in eukaryotic cells. Using immunocytochemistry with anti-RecA antibodies, we report the ubiquitous presence of the Kin protein in the CNS of mice and quails. However, some brain structures such as the hippocampal area, the locus coeruleus and Purkinje cells are preferentially immunolabelled and show some homologies between the two species. In conclusion, the expression of the Kin protein is preserved in the phylogeny of the brain of higher vertebrates.

Overexpression of kin17 protein forms intranuclear foci in mammalian cells

We used antibodies against E coli RecA protein to identify in mouse cells a 45-kDa DNA-binding protein called kin17, which has an active zinc finger and a nuclear localisation signal. Kin17 protein produced in E coli binds preferentially to the curved DNA of a bacterial promoter in vivo and in vitro, suggesting a transcriptional regulation activity. The fact that in rodent cells kin17 protein levels increase after gamma-irradiation suggests its participation in a cellular response to ionising radiation. We raised polyclonal antibodies against the whole kin17 protein and against its derived synthetic peptides. We report the detection of kin17 protein and of truncated forms of the protein by Western blot or by immunocytochemistry after transient overexpression in cultured human cells. Our results indicate that the cross-reactivity with the anti-RecA antibodies is due to an antigenic determinant located in the core of kin17 protein, between residues 129 and 228. The kin17 protein is located in the nucleus and is concentrated in small nuclear dot-like structures throughout the nucleoplasm. The RecA homologous region seems to play an essential role in the localisation of kin17 protein since the deletion of this particular region dramatically changes the form and the distribution of the intranuclear foci. We hypothesise that these dot-like structures reflect nuclear metabolism compartmentalization.

Preferential expression of kin, a nuclear protein binding to curved DNA, in the neurons of the adult rat

The KIN17 gene product has been identified by cross immunoreactivity with anti-RecA antibodies and by DNA recombination techniques, and is probably part of the DNA recombination-repair machinery. Following Western blotting and immunocytochemistry using anti-RecA antibodies, and in situ hybridization with specific KIN17 cDNA probes, we here report the detection of high levels of KIN protein and KIN17 mRNA in the CNS of adult rats. The RecA cross-reacting protein has an apparent molecular weight of 41 kDa and is located in the nucleus of brain cells. Both the KIN17 transcript and the protein were found to be widespread, but they were present in different proportions, depending on the type of brain cells. High levels of KIN protein were seen in neurons of the motor nuclei of the brainstem, the locus coeruleus, hippocampal formation, entorhinal cortex, Purkinje cells, pyramidal cells of the cortex and mitral cells. In contrast, using a combination of KIN17 mRNA in situ hybridization and GFAP immunocytochemistry (a marker of glial cells) showed that the KIN17 messenger is preferentially transcribed in neurons, the post-mitotic and long lived brain cells. We postulate that KIN17 play a role in the illegitimate recombination of DNA sequences and/or the repair of alterations of the genome in neurons.