The biochemical characterization of the DNA binding activity of pKi67

Investigation of the histopathological level of Ki-67, caspase-3 expressions of the effects of hesperidin on wound healing in the rat esophagus

PURPOSE

The effects of hesperidin application on the wound caused by esophageal burns were investigated in this study.

METHODS

Wistar albino rats were divided into three groups: Control group: only 1 mL of 0.09% NaCl was administered i.p. for 28 days; Burn group: An alkaline esophageal burn model was created with 0.2 mL of 25% NaOH orally by gavage-1 mL of 0.09% NaCl was administered i.p. for 28 days; Burn+Hesperidin group: 1 mL of 50 mL/kg of hesperidin was given i.p. for 28 days to rats after burn injury. Blood samples were collected for biochemical analysis. Esophagus samples were processed for histochemical staining and immunohistochemistry.

RESULTS

Malondialdehyde (MDA) and myeloperoxidase (MPO) levels were significantly increased in Burn group. Glutathione (GSH) content and histological scores of epithelialization, collagen formation, neovascularization was decreased. After hesperidin treatment, these values were significantly improved in the Burn+Hesperidin group. In the Burn group, epithelial cells and muscular layers were degenerated. Hesperidin treatment restored these pathologies in Burn+Hesperidin group. Ki-67 and caspase-3 expressions were mainly negative in control group; however, the expression was increased in the Burn group. In the Burn+Hesperidin group, Ki-67 and caspase-3 immune activities were reduced.

CONCLUSIONS

Hesperidin dosage and application methods can be developed as an alternative treatment for burn healing and treatment.

Dynamic chromosomal interactions and control of heterochromatin positioning by Ki-67

Ki-67 is a chromatin-associated protein with a dynamic distribution pattern throughout the cell cycle and is thought to be involved in chromatin organization. The lack of genomic interaction maps has hampered a detailed understanding of its roles, particularly during interphase. By pA-DamID mapping in human cell lines, we find that Ki-67 associates with large genomic domains that overlap mostly with late-replicating regions. Early in interphase, when Ki-67 is present in pre-nucleolar bodies, it interacts with these domains on all chromosomes. However, later in interphase, when Ki-67 is confined to nucleoli, it shows a striking shift toward small chromosomes. Nucleolar perturbations indicate that these cell cycle dynamics correspond to nucleolar maturation during interphase, and suggest that nucleolar sequestration of Ki-67 limits its interactions with larger chromosomes. Furthermore, we demonstrate that Ki-67 does not detectably control chromatin-chromatin interactions during interphase, but it competes with the nuclear lamina for interaction with late-replicating DNA, and it controls replication timing of (peri)centromeric regions. Together, these results reveal a highly dynamic choreography of genome interactions and roles for Ki-67 in heterochromatin organization.

The chromatin-binding domain of Ki-67 together with p53 protects human chromosomes from mitotic damage

Vertebrate mammals express a protein called Ki-67 which is most widely known as a clinically useful marker of highly proliferative cells. Previous studies of human cells indicated that acute depletion of Ki-67 can elicit a delay at the G1/S boundary of the cell cycle, dependent on induction of the checkpoint protein p21. Consistent with those observations, we show here that acute Ki-67 depletion causes hallmarks of DNA damage, and the damage occurs even in the absence of checkpoint signaling. This damage is not observed in cells traversing S phase but is instead robustly detected in mitotic cells. The C-terminal chromatin-binding domain of Ki-67 is necessary and sufficient to protect cells from this damage. We also observe synergistic effects when Ki-67 and p53 are simultaneously depleted, resulting in increased levels of chromosome bridges at anaphase, followed by the appearance of micronuclei. Therefore, these studies identify the C terminus of Ki-67 as an important module for genome stability.

Bridgin connects the outer kinetochore to centromeric chromatin

The microtubule-binding outer kinetochore is coupled to centromeric chromatin through CENP-C^Mif2, CENP-T^Cnn1, and CENP-U^Ame1 linker pathways originating from the constitutive centromere associated network (CCAN) of the inner kinetochore. Here, we demonstrate the recurrent loss of most CCAN components, including certain kinetochore linkers during the evolution of the fungal phylum of Basidiomycota. By kinetochore interactome analyses in a model basidiomycete and human pathogen Cryptococcus neoformans, a forkhead-associated domain containing protein “bridgin” was identified as a kinetochore component along with other predicted kinetochore proteins. In vivo and in vitro functional analyses of bridgin reveal its ability to connect the outer kinetochore with centromeric chromatin to ensure accurate chromosome segregation. Unlike established CCAN-based linkers, bridgin is recruited at the outer kinetochore establishing its role as a distinct family of kinetochore proteins. Presence of bridgin homologs in non-fungal lineages suggests an ancient divergent strategy exists to bridge the outer kinetochore with centromeric chromatin.

The kinetochore is a multi-complex structure that helps attach chromosomes to spindle microtubules, ensuring accurate chromosome segregation during cell division. Kinetochores are thought to be evolutionarily conserved, but which components are conserved is unclear. Here, the authors report that some members of the fungal phylum of Basidomycota lack many conventional kinetochore linker proteins. Instead, they possess a human Ki67-like protein that bridges the outer part of the kinetochore to centromere DNA, which may compensate for the loss of a conventional linker.

Nuclear co-expression of p21 and p27 induced effective cell-cycle arrest in T24 cells treated with BCG

A proposed mechanism underlying the effect of bacillus Calmette-Guérin (BCG) treatment for bladder cancer cells is as follows: BCG-induced crosslinking of cell-surface receptors results in the activation of signaling cascades, including cell-cycle regulators. However, the clinical significance of cell-cycle regulators such as p21 and p27 is controversial. Here we investigated the relationship between BCG exposure and p21 and p27. We used confocal laser microscopy to examine the expression levels of pKi67, p21 and p27 in T24 cells (derived from human urothelial carcinoma) exposed six times to BCG. We performed dual immunofluorescence staining methods for p21 and p27 and observed the localization of nuclear and cytoplasm expressions. We investigated the priority of p27 over p21 regarding nuclear expression by using p27 Stealth RNAi™ (p27-siRNA). With 2-h BCG exposure, the nuclear-expression level of p21 and p27 was highest, while pKi67 was lowest. The percentage of double nuclear-expression of p21 and p27 in BCG cells was significantly higher than that in control cells during the 1st to 6th exposure (P < 0.05), and the expression of pKi67 showed the opposite of this pattern. Approximately 10% of the nuclear p21 was independent of p27, whereas the cytoplasmic p21 was dependent on p27. Our results suggested that the nuclear co-expression of p21 and p27 caused effective cell-cycle arrest, and thus the evaluation of the nuclear co-expression of p21 and p27 might help determine the effectiveness of BCG treatment.

Positive PCNA and Ki-67 Expression in the Testis Correlates with Spermatogenesis Dysfunction in Fluoride-Treated Rats

The present study aimed to evaluate the effect of fluoride (F) on spermatogenesis in male rats. F^- at 50 and 100 mg/L was administered for 70 days, after which the testicular and epididymis tissues were collected to observe the histopathological structure under a light microscope. The ultrastructure of the testis and sperm was also examined via transmission electron microscopy. The apoptosis of spermatogenic cells was measured through terminal deoxynucleotidyl transferase dUTP nick end labeling staining. The expression of proliferation factors, namely, proliferating cell nuclear antigen (PCNA) and Ki-67, in the testicular and epididymis tissues, were assayed through immunohistochemistry. F^- at 50 and 100 mg/L significantly damaged the structure of the testis and epididymis, and the testis and sperm ultrastructure exhibited various changes, including mitochondrial swelling and vacuolization, and apsilated and raised sperm membrane. F treatment significantly increased spermatogenic cell apoptosis in the testis. PCNA (P < 0.01) and Ki-67 (P < 0.01) also presented positive expression in the testis. By comparison, no significant changes occurred in the epididymis. In summary, excessive F intake results in spermatogenesis dysfunction by damaging the testicular structure and inducing spermatogenic cell apoptosis in male rats. The positive expression level of PCNA and Ki-67 was a good response to spermatogenesis dysfunction.

Study of Simple Immunohistochemical Cytocolorimetric Assay Application for More Accurate Assessment of Prognosis in Patients with Pituitary Adenomas

BACKGROUND

Immunohistochemistry is a basic diagnostic technique. Immunohistochemical examination results reflect mainly qualitative and less quantitative characteristics of proteomic status of cells. A combined approach with complex quantitative evaluation of marker expression using colorimetric analysis and computer technologies can expand the diagnostic capabilities of immunohistochemistry. We studied such an approach developed by using expression of the proliferative marker Ki-67 in pituitary adenomas.

METHODS

A retrospective, blind, randomized, comparative study was performed of Ki-67 expression activity in pituitary adenomas using the traditional Ki-67 labeling index and a simple immunohistochemical cytocolorimetric analysis developed by us with immunohistochemical cytocolorimetric index (ICI) estimation as predictors of relapse, assessing the relationships of these indicators with the time before relapse.

RESULTS

Mean Ki-67 labeling index was 3.87% ± 0.29% in the relapse-free group and 4.01% ± 0.29% in the relapse group; the difference was not statistically significant. The average Ki-67 ICI was 24.16% ± 0.51% in the relapse-free group and 30.68% ± 0.64% in the relapse group; the difference was statistically significant. The correlation coefficient of ICI values and time before relapse was -0.302, indicating the presence of a weak negative correlation.

CONCLUSIONS

We successfully tested an ICI estimation method developed by us to assess Ki-67 expression in pituitary adenomas. The ICI technique can be used both as a prognostic factor for relapse and, in combination with other modern proteomic and genetic methods, as the basis for creation of new multimodal analyzing systems for functional state assessment of cells and tissues.

Immunoexpression of Ki-67 and Endoglin Corroborating Hamartomatous Nature of Sialoangiolipoma

Mesenchymal neoplasms of salivary gland including adipocytes are relatively uncommon entity classified as monophasic and biphasic. Sialolipoma, a biphasic mesenchymal salivary gland neoplasm, with a prominent vascularity designated as sialoangiolipoma (SAL) is a recently discussed entity with debates on the hamartomatous nature of the lesion. We have endorsed the hamartomatous nature through evaluating the immunoexpression of Ki-67 and endoglin in SAL in hard palate of a 60-year-old patient. To the best of our knowledge, this would be the second case of SAL in hard palate in a global platform.

Ki-67 and the Chromosome Periphery Compartment in Mitosis

The chromosome periphery is a complex network of proteins and RNA molecules (many derived from nucleoli) that covers the outer surface of chromosomes and whose function remains mysterious. Although it was first described over 130 years ago, technological advances and the recent discovery that Ki-67 acts as an organiser of this region have allowed the chromosome periphery to be dissected in previously unattainable detail, leading to a revival of interest in this obscure chromosomal compartment. Here, we review the most recent advances into the composition, structure and function of the chromosome periphery, discuss possible roles of Ki-67 during mitosis and consider why this structure is likely to remain the focus of ongoing attention in the future.

Increase of poorly proliferated p63+ /Ki67+ basal cells forming multiple layers in the aberrant remodeled epithelium in nasal polyps

BACKGROUND

Aberrant epithelial remodeling with the ectopic expression of p63 (basal cell markers) is an important pathologic phenomenon seen in chronically inflamed airway epithelium such as in nasal polyps (NPs).

METHODS

Biopsies were obtained from 55 NP patients and 18 healthy controls (inferior turbinate). Among NP patients, 15 were treated with oral and nasal steroids, so that two sets of NP biopsies were taken before and after the treatments. p63, Ki67, type IV β-tubulin, and cell cycle markers were investigated in these specimens.

RESULTS

The number of p63⁺ cells is significantly higher in both hyperplastic (1.53-fold, P < 0.0001) and squamous metaplastic (2.02-fold, P < 0.0001) epithelium from NPs than from healthy controls. There are three types of proliferative basal cells (p63⁺ /Ki67⁺ ) which are in different phases of the cell cycle, such as G1 phase (type I cells), S to G2 phase (type II cells), and mitosis (type III cells). Of importance, some type I cells may arrest after proliferation although they may still be p63⁺ /Ki67⁺ . In healthy epithelium, the ratio of the type I and II cells is almost 50:50. However, less type II cells are found in hyperplastic epithelium (34.85%, P = 0.012) and in squamous metaplastic epithelium (30.77%, P = 0.02) together with the presence of type III cells (3.45%, P = 0.01). These findings were not changed after steroid treatments.

CONCLUSIONS

An increase of poorly proliferated basal cells forming multiple layers, which may stain for basal cell markers but does not form a proper epidermal barrier, is an important histopathologic phenomenon in aberrant remodeled epithelium of NPs.

MCM2 and TIP30 are prognostic markers in squamous cell/adenosquamous carcinoma and adenocarcinoma of the gallbladder

The clinicopathological and biological characteristics of squamous cell/adenosquamous carcinoma (SC/ASC) of the gallbladder remain to be fully elucidated, due to the fact that it is a rare gallbladder cancer subtype. In the current study, the expression of minichromosome maintenance complex component 2 (MCM2) and HIV‑1 tat interactive protein 2 (TIP30) was measured in 46 cases of SC/ASC and 80 adenocarcinomas (AC) using immunohistochemistry. Positive MCM2 and negative TIP30 expression were significantly associated with large tumor size, high TNM stage, invasion, lymph node metastasis and lack of surgical curability in SC/ASC and AC. Positive MCM2 and negative TIP30 expression were significantly associated with poor differentiation in AC, whereas only MCM2 was correlated with differentiation in SC/ASC. Univariate Kaplan‑Meier analysis demonstrated that positive MCM2 and negative TIP30 expression, the degree of differentiation, tumor size, TNM stage, invasion, lymph node metastasis and surgical curability were significantly associated with post‑operative survival in patients with SC/ASC and AC. Multivariate Cox regression analysis demonstrated that positive MCM2 and negative TIP30 expression, the degree of differentiation, tumor size, TNM stage, invasion, lymph node metastasis and lack of surgical curability were also independent predictors of poor prognosis in patients with SC/ASC and AC. These data suggest that positive MCM2 and negative TIP30 expression are closely correlated with the clinical, pathological and biological parameters, in addition to poor prognosis in patients with gallbladder cancer.

The cell proliferation antigen Ki-67 organises heterochromatin

Antigen Ki-67 is a nuclear protein expressed in proliferating mammalian cells. It is widely used in cancer histopathology but its functions remain unclear. Here, we show that Ki-67 controls heterochromatin organisation. Altering Ki-67 expression levels did not significantly affect cell proliferation in vivo. Ki-67 mutant mice developed normally and cells lacking Ki-67 proliferated efficiently. Conversely, upregulation of Ki-67 expression in differentiated tissues did not prevent cell cycle arrest. Ki-67 interactors included proteins involved in nucleolar processes and chromatin regulators. Ki-67 depletion disrupted nucleologenesis but did not inhibit pre-rRNA processing. In contrast, it altered gene expression. Ki-67 silencing also had wide-ranging effects on chromatin organisation, disrupting heterochromatin compaction and long-range genomic interactions. Trimethylation of histone H3K9 and H4K20 was relocalised within the nucleus. Finally, overexpression of human or Xenopus Ki-67 induced ectopic heterochromatin formation. Altogether, our results suggest that Ki-67 expression in proliferating cells spatially organises heterochromatin, thereby controlling gene expression.

DOI:http://dx.doi.org/10.7554/eLife.13722.001

Living cells divide in two to produce new cells. In mammals, cell division is strictly controlled so that only certain groups of cells in the body are actively dividing at any time. However, some cells may escape these controls so that they divide rapidly and form tumors.

A protein called Ki-67 is only produced in actively dividing cells, where it is located in the nucleus – the structure that contains most of the cell’s DNA. Researchers often use Ki-67 as a marker to identify which cells are actively dividing in tissue samples from cancer patients, and previous studies indicated that Ki-67 is needed for cells to divide. However, the exact role of this protein was not clear. Before cells can divide they need to make large amounts of new proteins using molecular machines called ribosomes and it has been suggested that Ki-67 helps to produce ribosomes.

Now, Sobecki et al. used genetic techniques to study the role of Ki-67 in mice. The experiments show that Ki-67 is not required for cells to divide in the laboratory or to make ribosomes. Instead, Ki-67 alters the way that DNA is packaged in the nucleus. Loss of Ki-67 from mice cells resulted in DNA becoming less compact, which in turn altered the activity of genes in those cells.

Sobecki et al. also identified many other proteins that interact with Ki-67, so the next step following on from this research is to understand how Ki-67 alters DNA packaging at the molecular level. Another future challenge will be to find out if inhibiting the activity of Ki-67 can hinder the growth of cancer cells.

DOI:http://dx.doi.org/10.7554/eLife.13722.002

Expression of Ki-67 in normal oral epithelium, leukoplakic oral epithelium and oral squamous cell carcinoma

Aims and Objective:

To demonstrate the presence, location and pattern of cell proliferation in different histological grades of oral epithelial dysplasia (OED), oral squamous cell carcinoma (OSCC) and normal oral epithelium (NOE) using an antibody directed against the Ki-67 antigen and its intensity of staining evaluated respectively.

Materials and Methods:

A total number of 100 archival paraffin embedded blocks obtained from Department of Oral and Maxillofacial Pathology were studied. The case details were retrieved which consisted of histopathologically diagnosed cases of OSCC (n = 20), low risk OED (n = 30), high risk OED (n = 30) and normal appearing mucosa (n = 20) were taken as standard for comparison. Ki-67 immunostaining was detected. Ki-67 positive cells were counted in the five random high power fields in each case.

Results:

Ki-67 labeling Index (LI) was restricted to the basal and parabasal layers of the normal oral epithelium irrespective of age, sex and site whereas it was seen in the basal, suprabasal and spinous layers in OED. Ki-67 LI is increased in high risk cases than the low risk cases of OED. Ki-67 positive cells in OSCC were located in the periphery of the tumor nests than the center, where frequent mitoses were observed.

Conclusion:

The architectural alteration evaluated by Ki-67 antibody in proliferating cell distribution in the layers of epithelial dysplasias may provide useful information to evaluate the grading of OED. Ki-67 LI increased in high risk cases than low risk cases of OED. This study showed that over expression of Ki-67 antigen between well-differentiated and poorly differentiated OSCC was in accordance with histologic grade of malignancy but not in accordance with moderately differentiated OSCC.

Ki-67 is a PP1-interacting protein that organises the mitotic chromosome periphery

When the nucleolus disassembles during open mitosis, many nucleolar proteins and RNAs associate with chromosomes, establishing a perichromosomal compartment coating the chromosome periphery. At present nothing is known about the function of this poorly characterised compartment. In this study, we report that the nucleolar protein Ki-67 is required for the assembly of the perichromosomal compartment in human cells. Ki-67 is a cell-cycle regulated protein phosphatase 1-binding protein that is involved in phospho-regulation of the nucleolar protein B23/nucleophosmin. Following siRNA depletion of Ki-67, NIFK, B23, nucleolin, and four novel chromosome periphery proteins all fail to associate with the periphery of human chromosomes. Correlative light and electron microscopy (CLEM) images suggest a near-complete loss of the entire perichromosomal compartment. Mitotic chromosome condensation and intrinsic structure appear normal in the absence of the perichromosomal compartment but significant differences in nucleolar reassembly and nuclear organisation are observed in post-mitotic cells.DOI: http://dx.doi.org/10.7554/eLife.01641.001.

Classical and Novel Prognostic Markers for Breast Cancer and their Clinical Significance

The use of biomarkers ensures breast cancer patients receive optimal treatment. Established biomarkers such as estrogen receptor (ER) and progesterone receptor (PR) have been playing significant roles in the selection and management of patients for endocrine therapy. HER2 is a strong predictor of response to trastuzumab. Recently, the roles of ER as a negative and HER2 as a positive indicator for chemotherapy have been established. Ki67 has traditionally been recognized as a poor prognostic factor, but recent studies suggest that measurement of Ki67-positive cells during treatment will more effectively predict treatment efficacy for both anti-hormonal and chemotherapy. p53 mutations are found in 20–35% of human breast cancers and are associated with aggressive disease with poor clinical outcome when the DNA-binding domain is mutated. The utility of cyclin D1 as a predictor of breast cancer prognosis is controversial, but cyclin D1b overexpression is associated with poor prognosis. Likewise, overexpression of the low molecular weight form of cyclin E1 protein predicts poor prognosis. Breast cancers from BRCA1/2 carriers often show high nuclear grades, negativity to ER/PR/HER2, and p53 mutations, and thus, are associated with poor prognosis. The prognostic values of other molecular markers, such as p14^ARF, TBX2/3, VEGF in breast cancer are also discussed. Careful evaluation of these biomarkers with current treatment modality is required to determine whether their measurement or monitoring offer significant clinical benefits.

[Ki-67 -- new faces of an old player]

The Ki-67 protein was isolated twenty-five years ago and has become the first histological marker of proliferating cells until now. This molecule with a unique structure possesses such fundamental biological functions that are essential for normal cell proliferation. Since the Ki-67 protein is present in every dividing cell (G1, S, G2/M phase) but is absent from the resting cells (G0 phase) it is very much suitable for identifying the proliferating fraction of cells. Thus, it provides essential information concerning the malignancy of a tumor and about the prediction of response to a certain therapy. Based on its important role in cell proliferation, the Ki-67 protein might also play a role in tumor genesis. In their present work the authors discuss the history and the properties of Ki-67, its role in cell cycle regulation and its prognostic importance in different malignant disorders.

Autospecies and post-myocardial infarction sera enhance the viability, proliferation, and maturation of 3D cardiac cell culture

The limited ability of cardiac muscle to regenerate after an extensive myocardial infarction (MI) and the scarcity of cardiac donors have fueled the field of cardiac tissue engineering as a potential therapeutic approach to enhance cardiac function in post-MI patients. We are exploring the ex vivo bioengineering of cardiac muscle tissue by seeding isolated cardiac cells within alginate scaffolds and supplementing the culture with "smart" media. The hypothesis investigated herein is that sera derived from autospecies and from post-MI animals contain agents that might induce cell proliferation, survival, and maturation in vitro. The results of the metabolic activity of the neonatal cardiac cell constructs (6.4-51x10(6) cells/cm(3)), as measured by MTT viability assay, indicated a significant advantage (p < 0.05) to the constructs supplemented with serum from normal and post-MI adult rats compared to fetal calf serum (FCS) supplementation. H&E staining and alpha-sarcomeric actin immunofluorescence staining revealed thick viable cardiac cell clusters (150-300 microm), with abundant 3D architecture in the cardiac cell constructs supplemented with post-MI and normal adult rat serum. The number of cells positively immunostained with Ki-67, a cell proliferation marker, was significantly higher in post-MI adult rat serum-supplemented cultures compared to negative results in the FCS-supplemented culture. The results presented in this study indicate that media supplemented with post-MI adult rat serum and normal adult rat serum compared to FCS have a significant advantage in the regeneration of injured cardiac tissue.

Sequential phosphorylation and multisite interactions characterize specific target recognition by the FHA domain of Ki67

The forkhead-associated (FHA) domain of human Ki67 interacts with the human nucleolar protein hNIFK, recognizing a 44-residue fragment, hNIFK226-269, phosphorylated at Thr234. Here we show that high-affinity binding requires sequential phosphorylation by two kinases, CDK1 and GSK3, yielding pThr238, pThr234 and pSer230. We have determined the solution structure of Ki67FHA in complex with the triply phosphorylated peptide hNIFK226-269(3P), revealing not only local recognition of pThr234 but also the extension of the beta-sheet of the FHA domain by the addition of a beta-strand of hNIFK. The structure of an FHA domain in complex with a biologically relevant binding partner provides insights into ligand specificity and potentially links the cancer marker protein Ki67 to a signaling pathway associated with cell fate specification.

Ki-67 protein is associated with ribosomal RNA transcription in quiescent and proliferating cells

The nuclear Ki-67 protein (pKi-67) has previously been shown to be exclusively expressed in proliferating cells. As a result, antibodies against this protein are widely used as prognostic tools in cancer diagnostics. Here we show, that despite the strong downregulation of pKi-67 expression in non-proliferating cells, the protein can nevertheless be detected at sites linked to ribosomal RNA (rRNA) synthesis. Although this finding does not argue against the use of pKi-67 as a proliferation marker, it has wide ranging implications for the elucidation of pKi-67 function. Employing the novel antibody TuBB-9, we could further demonstrate that also in proliferating cells, a fraction of pKi-67 is found at sites linked to the rRNA transcription machinery during interphase and mitosis. Moreover, chromatin immunoprecipitation (ChIP) assays provided evidence for a physical association of pKi-67 with chromatin of the promoter and transcribed region of the rRNA gene cluster. These data strongly suggest a role for pKi-67 in the early steps of rRNA synthesis.

Coxsackievirus targets proliferating neuronal progenitor cells in the neonatal CNS

Type B coxsackieviruses (CVB) frequently infect the CNS and, together with other enteroviruses, are the most common cause of viral meningitis in humans. Newborn infants are particularly vulnerable, and CVB also can infect the fetus, leading to mortality, or to neurodevelopmental defects in surviving infants. Using a mouse model of neonatal CVB infection, we previously demonstrated that coxsackievirus B3 (CVB3) could infect neuronal progenitor cells in the subventricular zone (SVZ). Here we extend these findings, and we show that CVB3 targets actively proliferating (bromodeoxyuridine+, Ki67+) cells in the SVZ, including type B and type A stem cells. However, infected cells exiting the SVZ have lost their proliferative capacity, in contrast to their uninfected companions. Despite being proliferation deficient, the infected neuronal precursors could migrate along the rostral migratory stream and radial glia, to reach their final destinations in the olfactory bulb or cerebral cortex. Furthermore, infection did not prevent cell differentiation, as determined by cellular morphology and the expression of maturation markers. These data lead us to propose a model of CVB infection of the developing CNS, which may explain the neurodevelopmental defects that result from fetal infection.

Novel retinoblastoma binding protein RBBP9 modulates sex-specific radiation responses in vivo

Retinoblastoma (RB) tumor suppressor is a key regulator of apoptosis, a central mediator of the proliferative block induced by ionizing radiation (IR) and a binding target for a variety of proteins that regulate its activity. One of the recently discovered and the least investigated of these is the novel Rb-binding protein RBBP9/BOG. We studied the effects of acute and chronic low dose radiation (LDR) exposure on the induction of RBBP9 and RB signaling pathway in vivo in mouse spleen and found that RBBP9 played a pivotal role in IR responses in vivo. We observed that chronic LDR exposure led to a significant increase of RBBP9 expression in males and a significant decrease in females. Elevated RBBP9 expression in males was paralleled by a pronounced dephosphorylation of RB and a significant drop of PCNA and cyclin A expression. On the contrary, chronic exposure in females led to decreased levels of RBBP9 and increased levels of hyperphosphorylated RB (ppRB) in spleen. Decreased levels of ppRB in spleen of chronically exposed males were correlated with strongly elevated apoptotic rates. In females, the radiation-induced increase of apoptotic index was much less pronounced. Quite surprisingly, the observed sex-specific signaling changes did not result in the sex-specificity of cellular proliferation. The molecular mechanisms and possible repercussions of the radiation-induced sex differences in cellular proliferation and apoptosis are discussed.

Proteolytic digest derived from bovine Ligamentum Nuchae stimulates deposition of new elastin-enriched matrix in cultures and transplants of human dermal fibroblasts

BACKGROUND

Diverse topical products and injectable fillers used for correcting facial wrinkles induce rather short-lived effects because they target replacement of dermal collagen and hyaluronan, matrix components of limited biologic durability.

OBJECTIVE

Present studies were aimed at stimulation of fully differentiated human dermal fibroblasts to resume deposition of new extracellular matrix rich of elastin, the most durable and metabolically inert component of dermal ECM.

METHODS

We have created a novel proteolytic digest of bovine ligamentum nuchae (ProK-60), and tested its potential biological effect on dermal fibroblasts derived from females of different ages. Northern blots, quantitative immunohistochemistry and metabolic assays were used to assess effects of ProK-60 on proliferation and matrix production in primary cultures of dermal fibroblasts, in cultures of skin explants and after implantation of stimulated fibroblasts into the skin of athymic nude mice.

RESULTS

ProK-60 increased proliferation (25-30%) of cultured dermal fibroblasts and significantly enhanced their production of new elastic fibers (>250%) and collagen fibers (100%). These effects were mostly mediated by stimulation of cellular elastin receptor. In contrast, ProK-60 inhibited production of fibronectin (-30%) and chondroitin sulfate proteoglycans (-50%). ProK-60 also activated proliferation of dermal fibroblasts, mostly derived from the stratum basale and induced deposition of elastic fibers in cultures of skin explants. Moreover, human fibroblasts pre-treated with ProK-60 produced abundant elastic fibers after their injection into the skin of athymic nude mice.

CONCLUSION

The described biological effects of ProK-60, including its unique elastogenic property, encourage use of this compound in cosmetic formulations stimulating rejuvenation of aged skin.

Proliferation marker pKi-67 occurs in different isoforms with various cellular effects

The Ki-67 antigen, pKi-67, is a commonly used proliferation marker in research and pathology. It has been recognized that the protein exists in two different splice variants that differ in one exon. In the current work, we present three new splice variants of human pKi-67 consisting of two naturally occurring isoforms and one atypical version. Additionally, data is presented indicating that alternative splicing of the pKi-67 N-terminus is common in tumor cell lines. Analyzing 93 tissues mainly consisting of brain tumor specimens, we found evidence that long and short isoform can be expressed independently of each other. Induction of mitosis in human peripheral blood mononuclear cells revealed that short pKi-67 appears earlier in the cell cycle than the long isoform and reaches its expression maximum when transcription of the latter sets in. Finally, transfection of mammalian culture cells with exon 7 (specific for the long pKi-67 isoform and not present in the short isoform) in a tetracycline regulated expression system decreased the rate of cell proliferation without affecting the cell cycle. In summary, we present evidence that the pKi-67 N-terminus is differentially spliced resulting in at least five different isoforms with different functions.

High-level mRNA quantification of proliferation marker pKi-67 is correlated with favorable prognosis in colorectal carcinoma

PURPOSE

The present study retrospectively examines the expression of pKi-67 mRNA and protein in colorectal carcinoma and their correlation to the outcome of patients.

METHODS

Immunohistochemistry and quantitative RT-PCR were used to analyze the expression of pKi-67 in 43 archival specimens of patients with curatively resected primary colorectal carcinoma, who were not treated with neo-adjuvant therapy.

RESULTS

We determined a median pKi-67 (MIB-1) labeling index of 31.3% (range 10.3-66.4%), and a mean mRNA level of 0.1769 (DeltaC(T): range 0.01-0.69); indices and levels did not correlate. High pKi-67 mRNA DeltaC(T) values were associated with a significantly favorable prognosis, while pKi-67 labeling indices were not correlated to prognostic outcome. A multivariate analysis of clinical and biological factors indicated that tumor stage (UICC) and pKi-67 mRNA expression level were independent prognostic factors.

CONCLUSION

Quantitatively determined pKi-67 mRNA can be a good and new prognostic indicator for primary resected colorectal carcinoma.

Microarray analysis of gene expression after transverse aortic constriction in mice

Cardiac hypertrophy is a compensatory response initially beneficial to heart function but can ultimately lead to cardiac decompensation. It is an integrated process involving multiple cellular signaling pathways and their cross talk. Microarray GeneChip technology is a powerful new tool to identify gene expression profiles of cardiac hypertrophy. To identify well-characterized as well as novel adaptive mechanisms, we utilized a murine model of compensated pressure overload hypertrophy (transverse aortic constriction, TAC). At 48 h, 10 days, and 3 wk, hearts were harvested and total RNA hybridized to Affymetrix U74Av2 GeneChips, which contain a 12,488-gene/EST probe set. Verification of gene expression was performed by SYBR quantitative real-time RT-PCR (QRT-PCR) for selected genes. A rigorous evaluation of the adequacy of the control condition was also performed. For statistical analysis we generated a four-step filtering criteria. Our results show an upregulation of 38 genes (48 h), 269 genes (10 days), and 203 genes (3 wk) and downregulation of 15 genes (48 h), 160 genes (10 days), and 124 genes (3 wk). Transcripts differentially expressed after TAC were categorized into 12 functional groups and revealed the presence of several intriguing transcripts, e.g., cell proliferation-related Ki-67 and several apoptosis-related genes. Overall changes in QRT-PCR were in accordance with GeneChip data, with the highest correlation for genes with the largest up- or downregulation with TAC. Thus TAC results in altered expression of genes in several pathways regulating both cardiac structure and function. However, for in vivo gene microarray experiments, it is critical to define adequate controls, perform rigorous statistical analysis, and provide validation by alternative methods.

Detection of mutations in the cDNA of the proliferation marker Ki-67 protein in four tumor cell lines

The Ki-67 protein has an essential role in cell proliferation. It is present in all dividing cells of normal and tumor tissues, but absent in resting cells. At present, no data are available about any alterations in the gene of this protein that could contribute to its altered structure and function, resulting in tumor development. We therefore searched for mutations in the Ki-67 gene (MKI67). cDNAs from four tumor cell lines derived from carcinoma of the cervix (HeLa), colon (CXF94, SW480), and lung (A549) were prepared. Defined parts of the cDNA were amplified by specific primers, cloned into pCRII-Blunt-TOPO vector, and replicated in Escherichia coli. The sequence of the amplified products were determined by automated fluorescence sequencing. Eight different mutations were characterized in the four cell lines tested. One is a deletion of a single base at position 1496 causing a truncated protein, the second is a A433T exchange is a silent mutation, and the remaining six mutations result in an amino acid change that might alter the conformation of the protein. Our results show that several mutations exist within the Ki-67 protein's cDNA in four tumor cell lines. These mutations might provide a genetic basis for tumor development.

Myocyte growth in the failing heart

Adult ventricular myocytes can undergo mitotic division, resulting in an increase in the aggregate number of cells in the heart. The improvement in the methodological approach to the analysis of tissue sections by immunostaining and confocal microscopy has defeated the dogma that myocyte regeneration cannot occur in the adult heart. Most importantly, primitive and progenitor cells have been identified in the human heart. These cells express telomerase and have the capability of undergoing lineage commitment and rapid cell division, expanding significantly the contracting ventricular myocardium. These cell populations possess all the molecular components regulating the entry and progression through the cell cycle, karyokinesis, and cytokinesis. The recognition that myocyte hypertrophy and regeneration, as well as myocyte necrosis and apoptosis, occur in cardiac diseases has contributed to enhancing our understanding of the plasticity of the human heart.

Proliferation marker pKi-67 affects the cell cycle in a self-regulated manner

The proliferation marker pKi-67 is commonly used in research and pathology to detect proliferating cells. In a previous work, we found the protein to be associated with regulators of the cell cycle, controlling S-phase progression, as well as entry into and exit from mitosis. Here we investigate whether pKi-67 has a regulative effect on the cell cycle itself. For that purpose we cloned four fragments of pKi-67, together representing nearly the whole protein, and an N-terminal pKi-67 antisense oligonucleotide into a tetracycline inducible gene expression system. The sense fragments were C-terminally modified by addition of either a nuclear localization sequence (NLS) or a STOP codon to address the impact of their intracellular distribution. FACS based cell cycle analysis revealed that expression of nearly all pKi-67 domains and the antisense oligonucleotide led to a decreased amount of cells in S-phase and an increased number of cells in G(2)/M- and G(1)-phase. Subsequent analysis of the endogenous pKi-67 mRNA and protein levels revealed that the constructs with the most significant impact on the cell cycle were able to silence pKi-67 transcription as well. We conclude from the data that pKi-67 influences progression of S-phase and mitosis in a self-regulated manner and, therefore, effects the cell cycle checkpoints within both phases. Furthermore, we found pKi-67 mediates an anti-apoptotic effect on the cell and we verified that this marker, although it is a potential ribosomal catalyst, is not expressed in differentiated tissues with a high transcriptional activity.

Three-dimensional organization of pKi-67: a comparative fluorescence and electron tomography study using FluoroNanogold

The monoclonal antibody (MAb) Ki-67 is routinely used in clinical studies to estimate the growth fraction of tumors. However, the role of pKi-67, the protein detected by the Ki-67 MAb, remains elusive, although some biochemical data strongly suggest that it might organize chromatin. To better understand the functional organization of pKi-67, we studied its three-dimensional distribution in interphase cells by confocal microscopy and electron tomography. FluoroNanogold, a single probe combining a dense marker with a fluorescent dye, was used to investigate pKi-67 organization at the optical and ultrastructural levels. Observation by confocal microscopy followed by 3D reconstruction showed that pKi-67 forms a shell around the nucleoli. Double labeling experiments revealed that pKi-67 co-localizes with perinucleolar heterochromatin. Electron microscopy studies confirmed this close association and demonstrated that pKi-67 is located neither in the fibrillar nor in the granular components of the nucleolus. Finally, spatial analyses by electron tomography showed that pKi-67 forms cords 250-300 nm in diameter, which are themselves composed of 30-50-nm-thick fibers. These detailed comparative in situ analyses strongly suggest the involvement of pKi-67 in the higher-order organization of perinucleolar chromatin.

Cell-cycle-dependent three-dimensional redistribution of nuclear proteins, P 120, pKi-67, and SC 35 splicing factor, in the presence of the topoisomerase I inhibitor camptothecin

Topoisomerase I (Topo I) is mostly known for its role in DNA relaxation, which is required for duplication and transcription. Topo I acts as a protein kinase mainly directed to the mRNA splicing factor SC35. Camptothecin is one of the specific Topo I inhibitors and is effective on the two functions of the enzyme. In this study we demonstrated that treatment of KB cells with camptothecin for only 30 min induced the 3D reorganization and redistribution of three proteins involved in the nucleus machinery, P 120, pKi-67, and SC 35, and this occurred in a cell cycle-dependent manner. Our data were obtained from confocal microscopic studies after immunolabeling, 3D reconstruction, and measurement of the nuclear components volumes. In the presence of camptothecin, P 120, which occupied the nucleolar volume, lost its reticulation and pKi-67 was redistributed within the nucleoplasm and even into the cytoplasm. Finally, for SC 35 the fusion of its dots into bigger volumes was observed specifically during the G1 phase. Variations of volumes were also observed for the nucleolus and for the nucleus. These results pointed out that, depending on the cell cycle phase, Topo I functions were selective toward the three different proteins.

Assessment of the ultrastructural and proliferative properties of human embryonic stem cell-derived cardiomyocytes

Assessment of early ultrastructural development and cell-cycle regulation in human cardiac tissue is significantly hampered by the lack of a suitable in vitro model. Here we describe the possible utilization of human embryonic stem cell (ES) lines for investigation of these processes. With the use of the embryoid body (EB) differentiation system, human ES cell-derived cardiomyocytes at different developmental stages were isolated and their histomorphometric, ultrastructural, and proliferative properties were characterized. Histomorphometric analysis revealed an increase in cell length, area, and length-to-width ratio in late-stage EBs (>35 days) compared with early (10–21 days) and intermediate (21–35 days) stages. This was coupled with a progressive ultrastructural development from an irregular myofibrillar distribution to an organized sarcomeric pattern. Cardiomyocyte proliferation, assessed by double labeling with cardiac-specific antibodies and either [3H]thymidine incorporation or Ki-67 immunolabeling, demonstrated a gradual withdrawal from cell cycle. Hence, the percentage of positively stained nuclei in early-stage cardiomyocytes ([3H]thymidine: 60 ± 10%, Ki-67: 54 ± 23%) decreased to 36 ± 7% and 9 ± 16% in intermediate-stage EBs and to <1% in late-stage cardiomyocytes. In conclusion, a reproducible temporal pattern of early cardiomyocyte proliferation, cell-cycle withdrawal, and ultrastructural maturation was noted in this model. Establishment of this unique in vitro surrogate system may allow to examine the molecular mechanisms underlying these processes and to assess interventions aiming to modify these properties. Moreover, the detailed characterization of the ES cell-derived cardiomyocyte may be crucial for the development of future cell replacement strategies aiming to regenerate functional myocardium.

Chromatin preferences of the perichromosomal layer constituent pKi-67

The proliferation-associated nuclear protein pKi-67 relocates from the nucleolus to the chromosome surface during the G2/M transition of the cell cycle and contributes to the formation of the 'perichromosomal layer'. We investigated the in-vivo binding preferences of pKi-67 for various chromatin blocks of the mitotic chromosomes from the human and two mouse species, Mus musculus and M. caroli. All chromosomes were decorated with pKi-67 but displayed a gap of pKi-67 decoration in the centromere and NOR regions. pKi-67 distribution in a rearranged mouse chromosome showed that the formation of the centromeric gap was controlled by the specific chromatin in that region. While most chromatin served as a substrate for direct or indirect binding of pKi-67, we identified three types of chromatin that bound less or no pKi-67. These were: (1) the centromeric heterochromatin defined by the alpha satellite DNA in the human, by the mouse minor satellite in M. musculus and the 60- and 79-bp satellites in M. caroli; (2) the pericentromeric heterochromatin in M. musculus defined by the mouse major satellite, and (3) NORs in the human and in M. musculus defined by rDNA repeats. In contrast, the conspicuous blocks of pericentromeric heterochromatin in human chromosomes 1, 9 and 16 containing the 5-bp satellite showed intense pKi-67 decoration. The centromeric gap may have a biological significance for the proper attachment of the chromosomes to the mitotic spindle. In this context, our results suggest a new role for centromeric heterochromatin: the control of the centromeric gap in the perichromosomal layer.

The proliferation marker pKi-67 organizes the nucleolus during the cell cycle depending on Ran and cyclin B

The proliferation marker pKi-67 ('Ki-67 antigen') is commonly used in clinical and research pathology to detect proliferating cells, as it is only expressed during cell-cycle progression. Despite the fact that this antigen has been known for nearly two decades, there is still no adequate understanding of its function. This study has therefore identified proteins that interact with pKi-67, using a yeast two-hybrid system. A mammalian two-hybrid system and immunoprecipitation studies were used to verify these interactions. Among other cell-cycle regulatory proteins, two binding partners associated with the small GTPase Ran were identified. In addition, DNA-structural and nucleolus-associated proteins binding to pKi-67 were found. Moreover, it was demonstrated that the N-terminal domain of pKi-67 is capable of self-binding to its own repeat region encoded by exon 13. Since RanBP, a protein involved in the transport of macromolecules over the nuclear lamina, was found to be a binding partner, a possible effect of pKi-67 on the localization of cell-cycle regulatory proteins was proposed. To test this hypothesis, a tetracycline-responsive gene expression system was used to induce the pKi-67 fragments previously used for the two-hybrid screens in HeLa cells. Subsequent immunostaining revealed the translocation of cyclin B1 from cytoplasm to nucleoli in response to this expression. It is suggested that pKi-67 is a Ran-associated protein with a role in the disintegration and reformation of the nucleolus and thereby in entry into and exit from the M-phase.

Interaction of the chromatin compaction-inducing domain (LR domain) of Ki-67 antigen with HP1 proteins

BACKGROUND

The LR domain of marsupial chmadrin is defined by its C-terminal amino acid sequence, which contains several pairs of leucine (L) and arginine (R) residues. The LR domain of chmadrin causes a significant compaction of chromatin over the entire length of chromosomes when it is overproduced. The possible human homologue of chmadrin, Ki-67 antigen (pKi-67), also has a stretch of LR pairs, but with no obvious overall similarity, at its C-terminus.

RESULTS

The LR domain of human pKi-67 also induced chromatin compaction, both in human and marsupial cells. A yeast two-hybrid assay and an in vitro binding assay demonstrated that the human LR domain binds to heterochromatin protein 1 (HP1), a well-characterized molecule as a mediator of heterochromatin formation. In fixed cells stained with specific antibodies, the pKi-67 was found to be co-localized partially with HP1 at foci on chromosomes in an early G1 phase. Time-lapse observation in living cells co-expressing the fluorescently tagged proteins showed that the LR domain formed foci on chromosomes over a limited period of the cell cycle from the telophase to early G1 phase and that HP1 subsequently accumulated at these foci of the LR domain.

CONCLUSIONS

Marsupial chmadrin and human pKi-67 induce chromatin compaction across species, possibly via the interaction of its LR domain with HP1.

Analysis of the Ki-67 antigen at the invasive tumour front of human oral squamous cell carcinoma

BACKGROUND

It is hypothesised that cell proliferation, as measured by the Ki-67 labelling index (LI) at the invasive tumour front (ITF) was directly related to the histological grade in human oral squamous cell carcinomas (SCCs).

METHODS

Tissues from 42 human oral SCCs were collected and stained with an antibody directed against the Ki-67 antigen using an advanced polymer staining system. Quantitation of the immunopositive cells was performed on two parallel sections at the invasive tumour front (ITF), using an image analyser. The Ki-67 LI was expressed as the number of positive nuclei/mm2 of epithelium. The control tissue used was normal epithelium at the excision margin.

RESULTS

The mean Ki-67 LI for oral SCCs at the ITF was significantly greater than that for the excision margin tissue (P < 0.0001). There was a positive association between increasing Ki-67 LI and increasing Broders' grade (P < 0.05), with a well-differentiated tumour having the lowest mean Ki-67 LI (1549 +/- 806) and a poorly differentiated tumour having the highest value (2232 +/- 771). A similar trend was observed between the mean Ki-67 LI and Bryne's multifactorial grading system.

CONCLUSIONS

It was concluded from this study that cell proliferation (as measured by the Ki-67 antigen) at the ITF had a strong positive relationship with histological grading in human oral SCC.

The N-terminal basic domain of human parvulin hPar14 is responsible for the entry to the nucleus and high-affinity DNA-binding

We have studied the cellular localization and the DNA-binding capability of human peptidyl-prolyl cis/trans isomerase hPar14. The cellular expression pattern shows an uneven distribution of the protein between cytoplasm and nucleus. To determine the nuclear localization of hPar14 in vivo the molecule was fused to green fluorescent protein and expressed in human HeLa cells. Deletion mutants of hPar14 were used to restrict a sequence, necessary for nuclear targeting, to Ser7-Lys14 of the N terminus of the protein. DNA-cellulose affinity experiments were performed to demonstrate that hPar14, which is present in the nuclear fraction, could bind to double-stranded native DNA in vitro. On the basis of homologies and similarities of hPar14 to members of the high-mobility group proteins, double-stranded DNA constructs were developed and tested for their hPar14 binding affinity in fluorescence titration assays. The protein binds preferentially to bent A-tract sequences. The binding interface of the protein was determined by 1-D and 2-D NMR studies of the complex of unlabeled DNA and uniformly 15N-labeled hPar14((1-131)). Experiments with a truncated hPar14((25-131)) showed that the unstructured N-terminal 25 amino acid residues are necessary for high-affinity binding to DNA. These findings in connection with sequence and structural homologies of hPar14 to members of the HMGB/HMGN protein family suggest a function of hPar14 in cell-cycle regulation or gene transcription.

Myocyte growth and cardiac repair

Introduced several decades ago, the dogma persists that ventricular myocytes are terminally differentiated cells and cardiac repair by myocyte regeneration is completely inhibited shortly after birth. On the basis that cardiac myocytes are unable to divide in the adult heart, myocyte growth under physiologic and pathologic conditions is believed to be restricted to cellular hypertrophy. Evidence is presented to indicate that this old paradigm has to be changed to include myocyte replication as a significant component of the cellular processes of ventricular remodeling. Importantly, myocyte death, apoptotic and necrotic in nature, has to be regarded as an additional critical variable of the multifactorial events implicated in the alterations of cardiac anatomy and myocardial structure of the decompensated heart. Methodologies are currently available to recognize and measure quantitatively the contribution of myocyte size, number and death to the adaptation of the overloaded heart and its progression to cardiac failure.

The Ki-67 protein interacts with members of the heterochromatin protein 1 (HP1) family: a potential role in the regulation of higher-order chromatin structure

The expression of the nuclear protein Ki-67 (pKi-67) is strictly correlated with cell proliferation. Because of this, anti-Ki-67 antibodies can be used as operational markers to estimate the growth fraction of human neoplasia in situ. For a variety of tumours, the assessment of pKi-67 expression has repeatedly been proven to be of prognostic value for survival and tumour recurrence, but no cellular function has yet been ascribed to the Ki-67 protein. This study shows that a C-terminal domain of pKi-67 (Kon21) is able to bind to all three members of the mammalian heterochromatin protein 1 (HP1) family in vitro and in vivo. This interaction can be manipulated in living cells, as evidenced by ectopic expression of GFP-tagged HP1 proteins in HeLa cells, which results in a dramatic relocalization of endogenous pKi-67. Taken together, the data presented in this study suggest a role for pKi-67 in the control of higher-order chromatin structure.

Evidence that human cardiac myocytes divide after myocardial infarction

BACKGROUND

The scarring of the heart that results from myocardial infarction has been interpreted as evidence that the heart is composed of myocytes that are unable to divide. However, recent observations have provided evidence of proliferation of myocytes in the adult heart. Therefore, we studied the extent of mitosis among myocytes after myocardial infarction in humans.

METHODS

Samples from the border of the infarct and from areas of the myocardium distant from the infarct were obtained from 13 patients who had died 4 to 12 days after infarction. Ten normal hearts were used as controls. Myocytes that had entered the cell cycle in preparation for cell division were measured by labeling of the nuclear antigen Ki-67, which is associated with cell division. The fraction of myocyte nuclei that were undergoing mitosis was determined, and the mitotic index (the ratio of the number of nuclei undergoing mitosis to the number not undergoing mitosis) was calculated. The presence of mitotic spindles, contractile rings, karyokinesis, and cytokinesis was also recorded.

RESULTS

In the infarcted hearts, Ki-67 expression was detected in 4 percent of myocyte nuclei in the regions adjacent to the infarcts and in 1 percent of those in regions distant from the infarcts. The reentry of myocytes into the cell cycle resulted in mitotic indexes of 0.08 percent and 0.03 percent, respectively, in the zones adjacent to and distant from the infarcts. Events characteristic of cell division--the formation of the mitotic spindles, the formation of contractile rings, karyokinesis, and cytokinesis--were identified; these features demonstrated that there was myocyte proliferation after myocardial infarction.

CONCLUSIONS

Our results challenge the dogma that the adult heart is a postmitotic organ and indicate that the regeneration of myocytes may be a critical component of the increase in muscle mass of the myocardium.