Both alleles of PSF1 are required for maintenance of pool size of immature hematopoietic cells and acute bone marrow regeneration

Progress of Psf1 and prospects in the tumor: A review

Partner of Sld5-1(Psf1) is a member of Gins complex, which was discovered in 2003. It consists of the predominantly α-helical A-domain and the massively β-stranded B-domain. Some researches indicate that Psf1 plays a prominent part in DNA replication through cell cycle regulation, and plays a key role in early embryo development and tissue regeneration. The overexpression of Psf1 in active proliferating cells is closely correlated with the occurrence of tumors. On the side, tumor cells with high Psf1 expression showed high heterogeneity and poor clinical prognosis. In this review, we will review the research progress of Psf1 in cell cycle regulation, immature cell proliferation and oncology.

Identification of GINS1 as a therapeutic target in the cancer patients infected with COVID-19: a bioinformatics and system biology approach

BACKGROUND

Coronavirus disease 2019 (COVID-19) caused a series of biological changes in cancer patients which have rendered the original treatment ineffective and increased the difficulty of clinical treatment. However, the clinical treatment for cancer patients infected with COVID-19 is currently unavailable. Since bioinformatics is an effective method to understand undiscovered biological functions, pharmacological targets, and therapeutic mechanisms. The aim of this study was to investigate the influence of COVID-19 infection in cancer patients and to search the potential treatments.

METHODS

Firstly, we obtained the COVID-19-associated genes from seven databases and analyzed the cancer pathogenic genes from Gene Expression Omnibus (GEO) databases, respectively. The Cancer/COVID-19-associated genes were shown by Venn analyses. Moreover, we demonstrated the signaling pathways and biological functions of pathogenic genes in Cancer/COVID-19.

RESULTS

We identified that Go-Ichi-Ni-San complex subunit 1 (GINS1) is the potential therapeutic target in Cancer/COVID-19 by GEPIA. The high expression of GINS1 was not only promoting the development of cancers but also affecting their prognosis. Furthermore, eight potential compounds of Cancer/COVID-19 were identified from CMap and molecular docking analysis.

CONCLUSION

We revealed the GINS1 is a potential therapeutic target in cancer patients infected with COVID-19 for the first time, as COVID-19 will be a severe and prolonged pandemic. However, the findings have not been verified actually cancer patients infected with COVID-19, and further studies are needed to demonstrate the functions of GINS1 and the clinical treatment of the compounds.

Partial loss-of-function mutations in GINS4 lead to NK cell deficiency with neutropenia

Human NK cell deficiency (NKD) is a primary immunodeficiency in which the main clinically relevant immunological defect involves missing or dysfunctional NK cells. Here, we describe a familial NKD case in which 2 siblings had a substantive NKD and neutropenia in the absence of other immune system abnormalities. Exome sequencing identified compound heterozygous variants in Go-Ichi-Ni-San (GINS) complex subunit 4 (GINS4, also known as SLD5), an essential component of the human replicative helicase, which we demonstrate to have a damaging impact upon the expression and assembly of the GINS complex. Cells derived from affected individuals and a GINS4-knockdown cell line demonstrate delayed cell cycle progression, without signs of improper DNA synthesis or increased replication stress. By modeling partial GINS4 depletion in differentiating NK cells in vitro, we demonstrate the causal relationship between the genotype and the NK cell phenotype, as well as a cell-intrinsic defect in NK cell development. Thus, biallelic partial loss-of-function mutations in GINS4 define a potentially novel disease-causing gene underlying NKD with neutropenia. Together with the previously described mutations in other helicase genes causing NKD, and with the mild defects observed in other human cells, these variants underscore the importance of this pathway in NK cell biology.

High expression of PSF1 promotes drug resistance and cell cycle transit in leukemia cells

Escape of cancer cells from chemotherapy is a problem in the management of cancer patients. Research on chemotherapy resistance has mainly focused on the heterogeneity of cancer cells, multiple gene mutations, and quiescence of malignant cancer cells. However, some studies have indicated that interactions between cancer cells and vascular cells promote resistance to chemotherapy. Here, we established mouse leukemia models using the cell lines THP‐1 or MEG‐1. These were derived from acute and chronic myeloid leukemias, respectively, and highly expressed DNA replication factor PSF1, a member of the GINS complex. We found that, after anti‐cancer drug administration, surviving GFP‐positive leukemia cells in the bone marrow were located adjacent to blood vessels, as previously reported in a subcutaneous solid tumor transplantation model. Treating THP‐1 and MEG‐1 cells with anti‐cancer drugs in vitro revealed that those most strongly expressing PSF1 were most chemoresistant, suggesting that PSF1 induces not only cell cycle progression but also facilitates cell survival. Indeed, when PSF1 expression was suppressed by shRNA, the growth rate was reduced and cell death was enhanced in both cell lines. Furthermore, PSF1 knockdown in leukemia cells led to a change in their location at a distance from the blood vessels in a bone marrow transplantation model. These findings potentially reflect a mechanism of escape of leukemic cells from chemotherapy and suggest that PSF1 may be a possible therapeutic target to enhance the effect of chemotherapy.

Embryonic expression of GINS members in the development of the mammalian nervous system

The GINS (Go, Ichi, Nii, and San) complex contains four protein subunits (PSF1, PSF2, PSF3, and SLD5) and has been identified as a factor essential for the initiation and elongation stages of the DNA replication process. A previous study indicated that PSF2 participated in the developing central nervous system (CNS) of Xenopus laevis. However, the expression and function of GINS members in the mammalian developing nervous system remains unclear. Here, we examined the expression of GINS members in mice during nervous system development via immunofluorescence staining. At the beginning of neural development, PSF1 and SLD5 were highly expressed in neuroepithelial stem cells (NSCs) of the inner surface of neural tube (NT) and overlapped with proliferation marker Ki67. After entering the mid- and late-phase of neural development, PSF1 and SLD5 changed their regions of expression. These genes were highly expressed in dorsal root ganglion (DRG) progenitors, but they showed no overlap with Ki67 positive cells. Instead, a reduction of SLD5 expression promoted neuronal differentiation and maturation in the late-phase. PSF2 and PSF3 showed no tissue-specificity. PSF2 was constitutively and highly expressed whereas PSF3 was expressed at very low levels during neural development. In this study, we demonstrated variations in proteins and expression regions of the GINS members during mammalian CNS development and revealed a correlation between GINS expression and cell proliferation. Furthermore, we have suggested a novel function of GINS member SLD5, which regulates the differentiation of neural stem/progenitors.

Induced expression of GINS complex is an essential step for reactivation of quiescent stem-like tumor cells within the peri-necrotic niche in human glioblastoma

PURPOSE

Glioblastoma is still intractable despite the progress in therapies, and the intractability is attributable to a minor population of stem-like tumor cells. As a niche harboring quiescent stem-like tumor cells with potentially high tumorigenicity, we have specified an area around large ischemic necrosis, termed 'peri-necrotic niche', in glioblastoma. In this study, the behavior of tumor cells inside and outside the peri-necrotic niche was analyzed to find out molecules responsible for reactivation of quiescent stem-like tumor cells to proliferate outside the niche.

METHODS

Expression of Ki-67 and GINS complex composed of SLD5, PSF1, PSF2 and PSF3 was analyzed by immunohistochemistry in human glioblastoma tissue samples. Proliferation assays, immunoblotting and siRNA experiments were performed using a glioblastoma cell line.

RESULTS

Immunohistochemical analysis revealed quiescent and proliferative phenotypes of tumor cells inside and outside the niche, respectively, and the proliferation was spatially correlated with the expression of GINS components in tumor cells. To mimic the tissue microenvironment inside versus outside the niche, glioblastoma cells were cultured under hypoxic versus normoxic conditions, or without versus with serum. Quiescence and proliferation of tumor cells were reversibly determined by the microenvironment inside and outside the niche, respectively, and proliferative activities paralleled the expression levels of GINS components. Furthermore, the reactivation of proliferation after reoxygenation or serum replenishment was suppressed in quiescent tumor cells with PSF1 knockdown.

CONCLUSIONS

These findings indicate the essential role of GINS complex in the switch between quiescence and proliferation of tumor cells inside and outside the peri-necrotic niche.

Clinicopathological significance of PSF3 expression in uterine endometrial carcinomas

PSF3 (Partner of SLD Five 3) is a member of the heterotetrameric complex termed GINS. Previous studies have shown that PSF3 is up-regulated in several cancers and is associated with tumor malignancy. However, the clinicopathological significance of PSF3 expression in endometrial lesions is still poorly understood. To investigate whether PSF3 could serve as a useful biomarker for endometrial carcinomas, we performed immunohistochemical analysis of PSF3 expression. In 155 cases of endometrial carcinomas (ECs), the mean tumor proportion score of PSF3 expression was 30.7% in G1 endometrioid carcinoma, 55.0% in G2 endometrioid carcinoma, 59.0% in G3 endometrioid carcinoma, and 58.9% in nonendometrioid carcinomas. In 25 cases of atypical hyperplasia, the mean tumor proportion score of PSF3 expression was significantly lower (10.4%). High expression of PSF3 was associated with more advanced pathologic T stage (P = .000), lymphatic invasion (P = .001), and poor clinical outcomes such as shorter relapse-free survival (P = .000) and overall survival (P = .001). When we compared the immunostaining of PSF3 and Ki-67, the proportions of PSF3-positive cells in tumor epithelial cells were comparable to those of Ki-67-positive cells. However, PSF3-positive cells were selectively found in tumor cells, whereas Ki-67-positive cells were also found in tumor stromal cells. These results demonstrated that PSF3 immunostaining was valuable as a histopathologic marker for differential diagnosis between atypical hyperplasia and ECs, for tumor histologic grading, and for determining a patient's prognosis. PSF3 may play a crucial role in tumor progression in EC.

Soluble HLA-associated peptide from PSF1 has a cancer vaccine potency

Partner of sld five 1 (PSF1) is an evolutionary conserved DNA replication factor involved in DNA replication in lower species, which is strongly expressed in normal stem cell populations and progenitor cell populations. Recently, we have investigated PSF1 functions in cancer cells and found that PSF1 plays a significant role in tumour growth. These findings provide initial evidence for the potential of PSF1 as a therapeutic target. Here, we reveal that PSF1 contains an immunogenic epitope suitable for an antitumour vaccine. We analysed PSF1 peptides eluted from affinity-purified human leukocyte antigen (HLA) by mass spectrometry and identified PSF1_79-87 peptide (YLYDRLLRI) that has the highest prediction score using an in silico algorithm. PSF1_79-87 peptide induced PSF1-specific cytotoxic T lymphocyte responses such as the production of interferon-γ and cytotoxicity. Because PSF1 is expressed in cancer cell populations and highly expressed in cancer stem cell populations, these data suggest that vaccination with PSF1_79-87 peptide may be a novel therapeutic strategy for cancer treatment.

Inherited GINS1 deficiency underlies growth retardation along with neutropenia and NK cell deficiency

Inborn errors of DNA repair or replication underlie a variety of clinical phenotypes. We studied 5 patients from 4 kindreds, all of whom displayed intrauterine growth retardation, chronic neutropenia, and NK cell deficiency. Four of the 5 patients also had postnatal growth retardation. The association of neutropenia and NK cell deficiency, which is unusual among primary immunodeficiencies and bone marrow failures, was due to a blockade in the bone marrow and was mildly symptomatic. We discovered compound heterozygous rare mutations in Go-Ichi-Ni-San (GINS) complex subunit 1 (GINS1, also known as PSF1) in the 5 patients. The GINS complex is essential for eukaryotic DNA replication, and homozygous null mutations of GINS component-encoding genes are embryonic lethal in mice. The patients' fibroblasts displayed impaired GINS complex assembly, basal replication stress, impaired checkpoint signaling, defective cell cycle control, and genomic instability, which was rescued by WT GINS1. The residual levels of GINS1 activity reached 3% to 16% in patients' cells, depending on their GINS1 genotype, and correlated with the severity of growth retardation and the in vitro cellular phenotype. The levels of GINS1 activity did not influence the immunological phenotype, which was uniform. Autosomal recessive, partial GINS1 deficiency impairs DNA replication and underlies intra-uterine (and postnatal) growth retardation, chronic neutropenia, and NK cell deficiency.

PSF1 (Partner of SLD Five 1) is a Prognostic Biomarker in Patients with Non-small Cell Lung Cancer Treated with Surgery Following Preoperative Chemotherapy or Chemoradiotherapy

BACKGROUND

PSF1 (Partner of SLD Five 1) is an evolutionarily conserved DNA replication factor that is part of the GINS (Go, Ichi, Nii, and San) complex . The objective of this study was to evaluate the relationship between PSF1 expression and prognosis in patients with non-small cell lung cancer (NSCLC) treated with surgery following preoperative chemotherapy or chemoradiotherapy.

METHODS

Sixty-nine patients with NSCLC treated with surgery following preoperative chemotherapy or chemoradiotherapy who did not achieve pathologic complete response were enrolled. The status of PSF1 expression was evaluated by immunohistochemistry, and the relationship between expression of PSF1 and Ki-67 was determined, as well as correlations between PSF1 expression and prognosis.

RESULTS

We found that 27 of 69 patients' tumors (39 %) were positive for PSF1 expression. The Ki-67 index was significantly higher in the PSF1-positive versus the PSF1-negative group (p = 0.0026). Five-year, disease-free survival of the PSF1-positive group was significantly worse (17.7 vs. 44.3 %, p = 0.0088), and the 5-year overall survival also was worse (16.6 vs. 47.2 %, p = 0.0059). Moreover, PSF1 expression was found to be a significant independent prognostic factor for shorter survival by Cox multivariate analysis (hazard ratio 2.43, 95 % confidence interval 1.27-4.60, p = 0.0076).

CONCLUSIONS

PSF1 is a useful prognostic biomarker to stratify NSCLC patients treated with surgery following preoperative chemotherapy or chemoradiotherapy.

Tumor microenvironment for cancer stem cells

Tumor tissues consist of heterogeneous cancer cells including cancer stem cells (CSCs) that can terminally differentiate into cancer cells. Tissue-specific stem cells in normal organs maintain their stemness in a specific microenvironment, the stem cell niche; several studies have suggested that there are specific microenvironments that maintain CSCs in an immature phenotype. Cell types in a CSC niche vary from fibroblasts, to endothelial cells, immune cells, and so on; these non-cancer cells have been suggested to change their original features in the normal tissue/organ and to acquire a phenotype that protects CSCs from anticancer therapies. Therefore, to kill CSCs, we need to understand the cellular and molecular mechanisms involved in the maintenance of the immature phenotype of CSCs and in drug resistance.

Significant role of Psf3 expression in non-small-cell lung cancer

The GINS complex associates with cell division cycle (Cdc) protein 45 and mini‐chromosome maintenance (Mcm) proteins 2–7 to form the Cdc45–Mcm–GINS (CMG) complex, which is essential for DNA duplication. One member of the GINS complex is Psf3. We previously found that increased Psf3 expression was strongly associated with poor survival in lung adenocarcinoma. Here, we investigated the role of Psf3 expression in non‐small‐cell lung cancer (NSCLC). We verified Psf3 expression in human NSCLC tissues (180 patients) and cell lines. Immunohistochemical analysis revealed that the overexpression of Psf3 was significantly associated with vessel invasion (P = 0.016), lymphatic invasion (P = 0.002), and pleural invasion (P = 0.036). The overall survival rate in patients with Psf3 overexpression was significantly lower than that in patients without Psf3 overexpression (P = 0.006). Multivariate survival analysis revealed Psf3 expression to be an independent risk factor for an unfavorable outcome (P = 0.049). A proximal ligation assay showed interactions between Psf3 and other CMG components (such as Mcm2 and Cdc45) in both NSCLC specimens and cell lines, indicating that Psf3 acted as the CMG complex, which could lead to excessive proliferation. Knockdown of Psf3 inhibited the proliferation of both cell lines by delaying the S phase, which revealed that Psf3 played an important role in cancer proliferation. Thus, Psf3 acted as the CMG complex, promoting excessive proliferation. These results suggest that Psf3 inhibition might be a therapeutic target for NSCLC with Psf3 overexpression.

Murine hematopoietic stem cell dormancy controlled by induction of a novel short form of PSF1 by histone deacetylase inhibitors

Hematopoietic stem cells (HSCs) can survive long-term in a state of dormancy. Little is known about how histone deacetylase inhibitors (HDACi) affect HSC kinetics. Here, we use trichostatin A (TSA), a histone deacetylase inhibitor, to enforce histone acetylation and show that this suppresses cell cycle entry by dormant HSCs. Previously, we found that haploinsufficiency of PSF1, a DNA replication factor, led to attenuation of the bone marrow (BM) HSC pool size and lack of acute proliferation after 5-FU ablation. Because PSF1 protein is present in CD34(+) transiently amplifying HSCs but not in CD34(-) long-term reconstituting-HSCs which are resting in a dormant state, we analyzed the relationship between dormancy and PSF1 expression, and how a histone deacetylase inhibitor affects this. We found that CD34(+) HSCs produce long functional PSF1 (PSF1a) but CD34(-) HSCs produce a shorter possibly non-functional PSF1 (PSF1b, c, dominantly PSF1c). Using PSF1a-overexpressing NIH-3T3 cells in which the endogenous PSF1 promoter is suppressed, we found that TSA treatment promotes production of the shorter form of PSF1 possibly by inducing recruitment of E2F family factors upstream of the PSF1 transcription start site. Our data document one mechanism by which histone deacetylase inhibitors affect the dormancy of HSCs by regulating the DNA replication factor PSF1.

Overexpression of PSF1 is correlated with poor prognosis in hepatocellular carcinoma patients

BACKGROUND

PSF1 is a subunit of the GINS complex which is essential for establishment of DNA replication forks, and the progression of the replisome. Previous studies have shown a close relationship between PSF1 and cell cycle in the proliferation of immature cells as well as tumors. The purpose of this study was to measure PSF1 expression in hepatocellular carcinoma (HCC) tissues, and determine the effects of down-regulation of PSF1 expression on growth of cancer cells, the cell cycle, apoptosis and cell invasiveness.

METHODS

Samples from 137 HCC tissues, 67 from adjacent nontumor tissue and 15 from normal liver were studied using immunochemistry. The HepG2 cell line was used for knockdown experiments studied by RT-PCR, real-time PCR, apoptosis and invasiveness assays.

RESULTS

PSF1 was overexpressed in HCC tissues compared with normal liver tissues. High PSF1 expression correlated with a more aggressive phenotype as well as worse prognosis in HCC patients. Knockdown of PSF1 expression using small interfering RNA (siRNA) slowed the growth of cancer cell by suppressing the cell cycle progression as well as increasing apoptosis, especially early apoptosis. In addition, the invasiveness of HepG2 cells was also reduced by down-regulation of PSF1.

CONCLUSIONS

These results suggest that the inhibition of PSF1 might provide new therapeutic approaches for HCC.

Partner of Sld five 3: a potential prognostic biomarker for colorectal cancer

BACKGROUND

Partner of Sld five 3 (PSF3) is a member of the evolutionarily conserved heterotetrameric complex "Go-Ichi-Ni-San" (GINS), which consists of SLD5, PSF1, PSF2, and PSF3. Previous studies have suggested that some GINS complex members are upregulated in cancer, but the status of PSF3 expression in colorectal cancer has not been investigated.

METHODS

We investigated the status of PSF3 expression in 137 consecutive resected colorectal caners by quantitative reverse-transcription polymerase chain reaction. Univariable and multivariable Cox regression analyses were performed to assess independent prognostic factors for overall survival in colorectal cancer.

RESULTS

In 137 restected colorectal cancer samples, median messenger RNA (mRNA) expression levels of PSF3 were significantly higher in tumor tissues (1.35 × 10(-3), range 2.88 × 10(-4) to 3.16 × 10(-2)) than in adjacent normal tissues (2.94 × 10(-4), range 5.48 × 10(-5) to 1.27 × 10(-3)) (P < 0.05). Moreover, high expression of PSF3 in tumor tissues was associated with shorter disease-free survival and overall survival. When analyzed with a Cox regression model, the PSF3 expression was an independent prognostic factor for overall survival. In addition, in patients with early stage (stage I and II) colorectal cancer, the overall survival rate of the high PSF3 expression group was significantly lower than that of the low PSF3 expression group (P < 0.001).

CONCLUSIONS

The PSF3 expression plays an important role in the progression of colorectal cancer and acts as a factor significantly affecting the prognosis of patients.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_217.

DNA damage enhanced by the attenuation of SLD5 delays cell cycle restoration in normal cells but not in cancer cells

SLD5 is a member of the GINS complex composed of PSF1, PSF2, PSF3 and SLD5, playing a critical role in the formation of the DNA replication fork with CDC45 in yeast. Previously, we had isolated a PSF1 orthologue from a murine hematopoietic stem cell DNA library and were then able to identify orthologues of all the other GINS members by the yeast two hybrid approach using PSF1 as the bait. These GINS orthologues may also function in DNA replication in mammalian cells because they form tetrameric complexes as observed in yeast, and gene deletion mutants of both PSF1 and SLD5 result in a lack of epiblast proliferation and early embryonic lethality. However, we found that PSF1 is also involved in chromosomal segregation in M phase, consistent with recent suggestions that homologues of genes associated with DNA replication in lower organisms also regulate cellular events other than DNA replication in mammalian cells. Here we analyzed the function of SLD5 other than DNA replication and found that it is active in DNA damage and repair. Attenuation of SLD5 expression results in marked DNA damage in both normal cells and cancer cells, suggesting that it protects against DNA damage. Attenuation of SLD5 delays the DNA repair response and cell cycle restoration in normal cells but not in cancer cells. These findings suggest that SLD5 might represent a therapeutic target molecule acting at the level of tumor stromal cells rather than the cancerous cells themselves, because development of the tumor microenvironment could be delayed or disrupted by the suppression of its expression in the normal cell types within the tumor.

Requirement of SLD5 for early embryogenesis

SLD5 forms a GINS complex with PSF1, PSF2 and PSF3, which is essential for the initiation of DNA replication in lower eukaryotes. Although these components are conserved in mammals, their biological function is unclear. We show here that targeted disruption of SLD5 in mice causes a defect in cell proliferation in the inner cell mass, resulting in embryonic lethality at the peri-implantation stage, indicating that SLD5 is essential for embryogenesis. Moreover, this phenotype of SLD5 mutant mice is quite similar compared with that of PSF1 mutant mice. We have previously reported that haploinsufficiency of PSF1 resulted in failure of acute proliferation of bone marrow hematopoietic stem cells (HSCs) during reconstitution of bone marrow ablated by 5-FU treatment. Since SLD5 was highly expressed in bone marrow, we investigated its involvement in bone marrow reconstitution after bone marrow ablation as observed in PSF1 heterozygous mutant mice. However, heterozygous deletion of the SLD5 gene was found not to significantly affect bone marrow reconstitution. On the other hand, abundant SLD5 expression was observed in human cancer cell lines and heterozygous deletion of the gene attenuated tumor progression in a murine model of spontaneous gastric cancer. These indicated that requirement and dependency of SLD5 for cell proliferation is different in different cell types.

Drosophila Psf2 has a role in chromosome condensation

The condensation state of chromosomes is a critical parameter in multiple processes within the cell. Failures in the maintenance of appropriate condensation states may lead to genomic instability, mis-expression of genes, and a number of disease states. During cell proliferation, replication of DNA represents an ongoing challenge for chromosome packaging as DNA must be unpackaged for replication and then faithfully repackaged. An integral member of the DNA replication machinery is the GINS complex which has been shown to stabilize the CMG complex which is required for processivity of the Mcm2-7 helicase complex during S phase. Through examination of the phenotypes associated with a null mutation in Psf2, a member of the evolutionarily conserved GINS complex, we find that Drosophila Psf2 likely has a role in establishing chromosome condensation and that the defects associated with this mis-condensation impact M phase progression, genomic stability, and transcriptional regulation.

Formation and regulation of the cancer stem cell niche

It is widely accepted that tumors contain cancer stem cells (CSC) possessing self-renewal potential as well as the ability to generate numerous cancer cells. Cancer stem cells are resistant to conventional cancer therapy and have greater invasive and metastatic behavior. It has been suggested that blood vessels provide a niche that maintains stemness in normal organs. This role also extends to the field of cancer biology. Cancer stem cells have been isolated from leukemias and solid cancers. Identification of these cells and their niche is critical for identifying molecular targets in order to inhibit their growth and to destroy their niche. For this purpose, sorting of living CSC is required to monitor their presence in the presumptive niche to establish whether a CSC candidate actually shows malignant features. Based on and referring to analyses in normal tissues, molecules including nitric oxide, Wnt, neuropilin-1, hepatocyte growth factor and others involved in the maintenance of CSC have been isolated. Stem cells might affect niche cells and niche cells produce stemness factors on such stimulation. Therefore, the niche might be flexible to support self-renewal or differentiation of stem cells even in the same niche cells.

Skin healing and scale regeneration in fed and unfed sea bream, Sparus auratus

Background

Fish scales are an important reservoir of calcium and phosphorus and together with the skin function as an integrated barrier against environmental changes and external aggressors. Histological studies have revealed that the skin and scales regenerate rapidly in fish when they are lost or damaged. In the present manuscript the histological and molecular changes underlying skin and scale regeneration in fed and fasted sea bream (Sparus auratus) were studied using a microarray 3 and 7 days after scale removal to provide a comprehensive molecular understanding of the early stages of these processes.

Results

Histological analysis of skin/scales revealed 3 days after scale removal re-epithelisation and formation of the scale pocket had occurred and 53 and 109 genes showed significant up or down-regulation, respectively. Genes significantly up-regulated were involved in cell cycle regulation, cell proliferation and adhesion, immune response and antioxidant activities. 7 days after scale removal a thin regenerated scale was visible and only minor changes in gene expression occurred. In animals that were fasted to deplete mineral availability the expression profiles centred on maintaining energy homeostasis. The utilisation of fasting as a treatment emphasised the competing whole animal physiological requirements with regard to barrier repair, infection control and energy homeostasis.

Conclusions

The identification of numerous genes involved in the mitotic checkpoint and cell proliferation indicate that the experimental procedure may be useful for understanding cell proliferation and control in vertebrates within the context of the whole animal physiology. In response to skin damage genes of immune surveillance were up-regulated along with others involved in tissue regeneration required to rapidly re-establish barrier function. Additionally, candidate fish genes were identified that may be involved in cytoskeletal re-modelling, mineralization and stem cells, which are of potential use in aquaculture and fish husbandry, as they may impact on the ability of the fish to produce structural proteins, such as muscle, efficiently.

The GINS complex from the thermophilic archaeon, Thermoplasma acidophilum may function as a homotetramer in DNA replication

The eukaryotic GINS heterotetramer, consisting of Sld5, Psf1, Psf2, and Psf3, participates in "CMG complex" formation with mini-chromosome maintenance (MCM) and Cdc45 as a key component of a replicative helicase. There are only two homologs of the GINS proteins in Archaea, and these proteins, Gins51 and Gins23, form a heterotetrameric GINS with a 2:2 molar ratio. The Pyrococcus furiosus GINS stimulates the ATPase and helicase activities of its cognate MCM, whereas the Sulfolobus solfataricus GINS does not affect those activities of its cognate MCM, although the proteins bind each other. Intriguingly, Thermoplasma acidophilum, as well as many euryarchaea, have only one gene encoding the sequence homologous to that of archaeal Gins protein (Gins51) on the genome. In this study, we investigated the biochemical properties of the gene product (TaGins51). A gel filtration and electron microscopy revealed that TaGins51 forms a homotetramer. A physical interaction between TaGins51 and TaMcm was detected by a surface plasmon resonance analysis. Unexpectedly, TaGins51 inhibited the ATPase activity, but did not affect the helicase activity of its cognate MCM. These results suggest that another factor is required to form a stable helicase complex with MCM and GINS at the replication fork in T. acidophilum cells.

Up-regulation of PSF1 promotes the growth of breast cancer cells

PSF1 is a subunit of the GINS complex that functions along with the MCM2-7 complex and Cdc45 in eukaryotic DNA replication. Although mammalian PSF1 is predominantly expressed in highly proliferating cells and organs, little is known about the roles of PSF1 in mature cells or cancer cells. We found that PSF1 was expressed at relatively high levels in breast tumor cells, but at low levels in normal breast cells. Knockdown of PSF1 expression using small interfering RNA (siRNA) slowed the growth of breast cancer cell lines by delaying DNA replication but did not affect proliferation of normal human mammary epithelial cells. Reduced PSF1 expression also inhibited anchorage-independent growth in breast cancer cell lines. These results suggest that PSF1 over-expression is specifically involved in breast cancer cell growth. Therefore, PSF1 inhibition might provide new therapeutic approaches for breast cancer.

Structure and function of the GINS complex, a key component of the eukaryotic replisome

High-fidelity chromosomal DNA replication is fundamental to all forms of cellular life and requires the complex interplay of a wide variety of essential and non-essential protein factors in a spatially and temporally co-ordinated manner. In eukaryotes, the GINS complex (from the Japanese go-ichi-ni-san meaning 5-1-2-3, after the four related subunits of the complex Sld5, Psf1, Psf2 and Psf3) was recently identified as a novel factor essential for both the initiation and elongation stages of the replication process. Biochemical analysis has placed GINS at the heart of the eukaryotic replication apparatus as a component of the CMG [Cdc45-MCM (minichromosome maintenance) helicase-GINS] complex that most likely serves as the replicative helicase, unwinding duplex DNA ahead of the moving replication fork. GINS homologues are found in the archaea and have been shown to interact directly with the MCM helicase and with primase, suggesting a central role for the complex in archaeal chromosome replication also. The present review summarizes current knowledge of the structure, function and evolution of the GINS complex in eukaryotes and archaea, discusses possible functions of the GINS complex and highlights recent results that point to possible regulation of GINS function in response to DNA damage.

PSF3 marks malignant colon cancer and has a role in cancer cell proliferation

PSF3 (partner of Sld five 3) is a member of the tetrameric complex termed GINS, composed of SLD5, PSF1, PSF2, and PSF3, and well-conserved evolutionarily. Previous studies suggested that some GINS complex members are upregulated in cancer, but PSF3 expression in colon carcinoma has not been investigated. Here, we established a mouse anti-PSF3 antibody, and examined PSF3 expression in human colon carcinoma cell lines and colon carcinoma specimens. We found that PSF3 is expressed in the crypt region in normal colonic mucosa and that many PSF3-positive cells co-expressed Ki-67. This suggests that PSF3-positivity of normal mucosa is associated with cell proliferation. Expression of the PSF3 protein was greater in carcinoma compared with the adjacent normal mucosa, and even stronger in high-grade malignancies, suggesting that it may be associated with colon cancer progression. PSF3 gene knock-down in human colon carcinoma cell lines resulted in growth inhibition characterized by delayed S-phase progression. These results suggest that PSF3 is a potential biomarker for diagnosis of progression in colon cancer and could be a new target for cancer therapy.

The initiation step of eukaryotic DNA replication

Eukaryotic initiation of DNA replication is a tightly regulated process. In the yeasts, S-phase-specific cyclin Cdk1 complex as well as Dfb4-Cdc7 kinase phosphorylate the initiation factors Sld2 and Sld3. These factors form a ternary complex with another initiation factor Dbp11 in their phosphorylated state, and associate with the origin of replication. This complex mediates the loading of Cdc45. A second complex called GINS and consisting of Sld5 and Psf1, 2 and 3 is also loaded onto the origin during the initiation process, in an interdependent manner with the Sld2/Sld3/Dpb11 complex. Both complexes cooperate in the recruitment of the replicative DNA polymerases, thus executing the initiation and subsequent establishment of the replication fork. Cdc45 and GINS are essential, well-conserved factors that are retained at the elongating replication fork. They form a stable helicase complex with MCM2-7 and mediate its contact to the replicative DNA polymerases. In contrast, the Sld2/Sld3/Dpb11 complex critical for the initiation is not retained by the elongating replication fork. Sld2 displays limited homology to the amino-terminal region of RecQL4 helicase, which may represent its metazoan orthologue, whereas Sld3 homologues have been identified only in fungi. Dbp11 and its fission yeast homologue Cut5 are members of a large family of BRCT-containing proteins including human TopBP1 and fruit fly Mus101. Similar principles of regulation apply also to human initiation of DNA replication, despite obvious differences in the detailed mechanisms. The regulatory initiation cascade is intimately intertwined with the cell cycle apparatus as well as the checkpoint control.

Balancing dormant and self-renewing hematopoietic stem cells

The mouse hematopoietic stem cell (HSC) is probably the best-understood somatic stem cell in higher organisms. Recent studies have shown that the highest self-renewal potential is most likely contained within an exceedingly small number of deeply dormant bone marrow HSCs. These stem cells are housed in individual niches that preserve their dormancy via signaling molecules such as Thrombopoietin, Angiopoietins, and Stem Cell Factor. In response to injury cues, dormant HSCs are efficiently activated and produce numerous progenitors and mature cells. A series of intracellular regulatory molecules including FoxOs, mTORC1, Fbw7, Egr1, Pbx1, pRb, c-Cbl, Myc, and Bmi1 mediate the processes of dormancy, cycling, self-renewal, differentiation, and survival, all of which control the behavior of HSCs.