Cell cycle models for molecular biology and molecular oncology: Exploring new dimensions

Prognostic Biomarkers of Cell Proliferation in Colorectal Cancer (CRC): From Immunohistochemistry to Molecular Biology Techniques

Colorectal cancer (CRC) is one of the most common and severe malignancies worldwide. Recent advances in diagnostic methods allow for more accurate identification and detection of several molecular biomarkers associated with this cancer. Nonetheless, non-invasive and effective prognostic and predictive testing in CRC patients remains challenging. Classical prognostic genetic markers comprise mutations in several genes (e.g., APC, KRAS/BRAF, TGF-β, and TP53). Furthermore, CIN and MSI serve as chromosomal markers, while epigenetic markers include CIMP and many other candidates such as SERP, p14, p16, LINE-1, and RASSF1A. The number of proliferation-related long non-coding RNAs (e.g., SNHG1, SNHG6, MALAT-1, CRNDE) and microRNAs (e.g., miR-20a, miR-21, miR-143, miR-145, miR-181a/b) that could serve as potential CRC markers has also steadily increased in recent years. Among the immunohistochemical (IHC) proliferative markers, the prognostic value regarding the patients' overall survival (OS) or disease-free survival (DFS) has been confirmed for thymidylate synthase (TS), cyclin B1, cyclin D1, proliferating cell nuclear antigen (PCNA), and Ki-67. In most cases, the overexpression of these markers in tissues was related to worse OS and DFS. However, slowly proliferating cells should also be considered in CRC therapy (especially radiotherapy) as they could represent a reservoir from which cells are recruited to replenish the rapidly proliferating population in response to cell-damaging factors. Considering the above, the aim of this article is to review the most common proliferative markers assessed using various methods including IHC and selected molecular biology techniques (e.g., qRT-PCR, in situ hybridization, RNA/DNA sequencing, next-generation sequencing) as prognostic and predictive markers in CRC.

Production and Stabilization of Specific Upregulated Long Noncoding RNA HOXD-AS2 in Glioblastomas Are Mediated by TFE3 and miR-661, Respectively

Differential expression of long noncoding RNAs (lncRNA) plays a key role in the development of gliomas. Because gliomas are the most common primary central nervous system tumor and glioblastomas have poor prognosis, it is urgent to develop new diagnostic methods. We have previously reported that lncRNA HOXD-AS2, which is specifically up-regulated in gliomas, can activate cell cycle and promote the development of gliomas. It is expected to be a new marker for molecular diagnosis of gliomas, but little is known about HOXD-AS2. Here, we demonstrate that TFE3 and miR-661 maintain the high expression level of HOXD-AS2 by regulating its production and degradation. We found that TFE3 acted as a transcription factor binding to the HOXD-AS2 promoter region and raised H3K27ac to activate HOXD-AS2. As the cytoplasmic-located lncRNA, HOXD-AS2 could be degraded by miR-661. This process was inhibited in gliomas due to the low expression of miR-661. Our study explains why HOXD-AS2 was specifically up-regulated in gliomas, helps to understand the molecular characteristics of gliomas, and provids insights for the search for specific markers in gliomas.

Integrative analysis of gene alterations and immunoexpression profiles of cell cycle checkpoints in oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) represents 95% of all cancers of the head and neck region. The five-year survival rate of OSCC patients is about 60% and has not gone throw significant improvements despite recent advances in molecular biology, or the identification of key pathways in its pathophysiology such as cell cycle.

OBJECTIVE

1) to analyse the inmunoexpression of cell cycle checkpoints (CPs) in an OSCC institutional cohort and to relate it to clinicopathological features and survival, and 2) to study CPs-related genes in the OSCC subset of the TCGA database.

METHODS

Immunohistochemistry (IHC) for p16INK4a, p21CIP1, cyclin D1 and p27KIP1 protein expression was quantified by tissue microarray analysis in 68 samples from OSCC patients. In order to analyse its correlation with genetic information, a cohort belonging to The Cancer Genome Atlas (TCGA) database was analysed.

RESULTS

Of 68 patients, 34 (50%) developed recurrence, and 36 (52.09%) died as a result of disease progression (mean survival 34.09 months). IHC staining for nuclear cyclin D1 was associated with worse staging and tobacco use. p16INK4a, p21CIP1, cyclin D1, and p27KIP1 expression was unrelated to overall survival. No statistically significant correlation linked the CPs-related genes mutations to OSCC overall survival in the TCGA database.

CONCLUSIONS

CPs variations at a phenotype and genotype level seem not to affect significantly clinicopathological features and survival in the studied OSCC cohorts.

Imaging Tumor Proliferation in Breast Cancer: Current Update on Predictive Imaging Biomarkers

Uncontrolled growth is a hallmark of cancer; imaging cell proliferation can provides an early indicator of therapeutic response. This capability is especially well-matched to the emerging cell cycle-specific chemotherapeutics with the goal of identifying patients that benefit from these treatments early in the course of treatment to guide personalized therapy. This article focuses on investigational cell proliferation imaging PET radiotracers to evaluate tumor proliferation in the setting of cell cycle-targeted chemotherapy and endocrine therapy for metastatic breast cancer.

Novel Strategies for Breast Cancer Imaging: New Imaging Agents to Guide Treatment

The development of molecular therapies for cancer treatment has created a need to image biochemical and molecular processes to appropriately select tumors that express the drug target, thereby predicting a positive response to therapy. Biomarker-driven molecular imaging is complementary to pathologic analysis and offers a more direct measure of drug efficacy and treatment response, potentially providing early insight into therapeutic futility and allowing response-adapted treatment strategies. Imaging also allows a unique means of assessing the heterogeneity of both intra- and intertumoral targets as well as a mixed response to therapy; this information is important in the setting of metastatic disease. Here we review the development of novel molecular imaging probes and combinations of probes to guide therapy for two new targets and associated therapeutic agents: cyclin-dependent kinase inhibitors and poly(adenosine diphosphate-ribose) polymerase inhibitors.

PET Radiotracers for Imaging the Proliferative Status of Solid Tumors

Two different strategies have been developed for imaging the proliferative status of solid tumors with the functional imaging technique, Positron Emission Tomography (PET). The first strategy uses carbon-11 labeled thymidine and/or, more recently, fluorine-18 labeled thymidine analogs. These agents are a substrate for the enzyme thymidine kinase-1 (TK-1) and provide a pulse label of the number of cells in S phase. The second method for imaging the proliferative status of a tumor uses radiolabeled ligands that bind to the sigma-2 receptor which has a 10-fold higher density in proliferating (P) tumor cells versus quiescent (Q) tumor cells. This article compares and contrasts the two different strategies for imaging the proliferative status of solid tumors, and describes the strengths and weaknesses of each approach.

Oxygen-Driven Tumour Growth Model: A Pathology-Relevant Mathematical Approach

Xenografts -as simplified animal models of cancer- differ substantially in vasculature and stromal architecture when compared to clinical tumours. This makes mathematical model-based predictions of clinical outcome challenging. Our objective is to further understand differences in tumour progression and physiology between animal models and the clinic.

To achieve that, we propose a mathematical model based upon tumour pathophysiology, where oxygen -as a surrogate for endocrine delivery- is our main focus. The Oxygen-Driven Model (ODM), using oxygen diffusion equations, describes tumour growth, hypoxia and necrosis. The ODM describes two key physiological parameters. Apparent oxygen uptake rate (kR′) represents the amount of oxygen cells seem to need to proliferate. The more oxygen they appear to need, the more the oxygen transport. kR′ gathers variability from the vasculature, stroma and tumour morphology. Proliferating rate (k_p) deals with cell line specific factors to promote growth. The K_H,K_N describe the switch of hypoxia and necrosis. Retrospectively, using archived data, we looked at longitudinal tumour volume datasets for 38 xenografted cell lines and 5 patient-derived xenograft-like models.

Exploration of the parameter space allows us to distinguish 2 groups of parameters. Group 1 of cell lines shows a spread in values of kR′ and lower k_p, indicating that tumours are poorly perfused and slow growing. Group 2 share the value of the oxygen uptake rate (kR′) and vary greatly in k_p, which we interpret as having similar oxygen transport, but more tumour intrinsic variability in growth.

However, the ODM has some limitations when tested in explant-like animal models, whose complex tumour-stromal morphology may not be captured in the current version of the model. Incorporation of stroma in the ODM will help explain these discrepancies. We have provided an example. The ODM is a very simple -and versatile- model suitable for the design of preclinical experiments, which can be modified and enhanced whilst maintaining confidence in its predictions.

Tumour-bearing animal models of cancer are needed to discover new drugs to treat cancer. We aim in this article to capture—through mathematics- some underlying phenomena of tumour growth in animals. We propose a set of equations that, despite being very simple, describe tumour growth, hypoxia and necrosis. Cells under low oxygen levels change into a stress state called “hypoxia”, which will ultimately lead to tissue death, also known as “necrosis” and “apoptosis”. Hypoxic cells undergo a variety of changes which impact tumour growth, development, metastasis and -most importantly- response to therapy. Hence, oxygen distribution is important. We simulate oxygen profiles to locate hypoxic and necrotic tumour regions. Finally, this mathematical model allows us to compare and classify animal models from a grounded and physiological perspective, rather than a more convenient and empirical one. This will help us understand how well (or poorly) animal tumours mimic tumours in patients. The simplicity of our mathematical model allows us to obtain more information out of the same animal sets without any further experiments, hopefully saving time, money and animal usage.

Development of cell-cycle checkpoint therapy for solid tumors

Cellular proliferation is tightly controlled by several cell-cycle checkpoint proteins. In cancer, the genes encoding these proteins are often disrupted and cause unrestrained cancer growth. The proteins are over-expressed in many malignancies; thus, they are potential targets for anti-cancer therapies. These proteins include cyclin-dependent kinase, checkpoint kinase, WEE1 kinase, aurora kinase and polo-like kinase. Cyclin-dependent kinase inhibitors are the most advanced cell-cycle checkpoint therapeutics available. For instance, palbociclib (PD0332991) is a first-in-class, oral, highly selective inhibitor of CDK4/6 and, in combination with letrozole (Phase II; PALOMA-1) or with fulvestrant (Phase III; PALOMA-3), it has significantly prolonged progression-free survival, in patients with metastatic estrogen receptor-positive, HER2-negative breast cancer, in comparison with that observed in patients using letrozole, or fulvestrant alone, respectively. In this review, we provide an overview of the current compounds available for cell-cycle checkpoint protein-directed therapy for solid tumors.

Phosphorylation of the Retinoblastoma protein (Rb) on serine-807 is required for association with Bax

The recent finding that the Retinoblastoma protein (Rb) is able to regulate apoptosis in a non-transcriptional manner directly at the mitochondria by interaction with the pro-apoptotic protein Bax prompted this investigation of the complex formed between Rb and Bax. Because the function of Rb in the cellular processes of proliferation, apoptosis, senescence and differentiation is regulated by phosphorylation we endeavored to elucidate the phosphorylation status of Rb with respect to its association with Bax and its role in apoptosis. In this study we found that Rb phosphorylated on at least 4 C-terminal phosphorylation sites (S608, S795, S807/S811, and T821) is present at the mitochondria under non-stressed cellular conditions. An in vitro binding assay showed that Bax binds to Rb phosphorylated at S807/S811 in 3 cancer cell types. Physiologically relevant association between Bax and Rb phosphorylated on S807/S811 was demonstrated by reciprocal co-immunoprecipitation experiments using antibodies specific for Rb phosphorylated on S807/S811 and Bax. Mutant Rb proteins expressed in Rb-null C33A cells showed that phosphorylation of S807 of Rb promotes association with Bax and that mimicking phosphorylation at S807 of Rb can block the induction of apoptosis due to PNUTS downregulation. Finally using siRNA to activate phosphatase activity in MCF7 cells, Rb is dephosphorylated at several sites including S807/S811, dissociates from Bax and apoptosis is triggered. These studies show that phosphorylation of Rb regulates its association with Bax and its role in apoptosis.

Subcellular localization of p44/WDR77 determines proliferation and differentiation of prostate epithelial cells

The molecular mechanism that controls the proliferation and differentiation of prostate epithelial cells is currently unknown. We previously identified a 44-kDa protein (p44/wdr77) as an androgen receptor-interacting protein that regulates a set of androgen receptor target genes in prostate epithelial cells and prostate cancer. In this study, we found that p44 localizes in the cytoplasm of prostate epithelial cells at the early stage of prostate development when cells are proliferating, and its nuclear translocation is associated with cellular and functional differentiation in adult prostate tissue. We further demonstrated that cytoplasmic p44 protein is essential for proliferation of prostate epithelial cells, whereas nuclear p44 is required for cell differentiation and prostate- specific protein secretion. These studies suggest a novel mechanism by which proliferation and differentiation of prostate epithelial cells are controlled by p44's location in the cell.

Mathematical modeling as a tool for planning anticancer therapy

We review a large volume of literature concerning mathematical models of cancer therapy, oriented towards optimization of treatment protocols. The review, although partly idiosyncratic, covers such major areas of therapy optimization as phase-specific chemotherapy, antiangiogenic therapy and therapy under drug resistance. We start from early cell cycle progression models, very simple but admitting explicit mathematical solutions, based on methods of control theory. We continue with more complex models involving evolution of drug resistance and pharmacokinetic and pharmacodynamic effects. Then, we consider two more recent areas: angiogenesis of tumors and molecular signaling within and among cells. We discuss biological background and mathematical techniques of this field, which has a large although only partly realized potential for contributing to cancer treatment.

The dynamics of tumour-vasculature interaction suggests low-dose, time-dense anti-angiogenic schedulings

OBJECTIVES

The administration schedule appears to be a particularly relevant factor in determining the effectiveness of an antiangiogenic drug. A better quantitative knowledge of the interactions between tumour growth and the development of its vasculature could help to design effective therapies.

MATERIAL AND METHODS

Biological and clinical inferences were derived from the analysis of a mathematical model proposed by Hahnfeldt et al. (1999), and some of its variants. In particular, we compared the effect of constant continuous infusion of an anti-angiogenic drug that induces vascular loss, to the effect of periodic, bolus-based therapy.

RESULTS AND CONCLUSIONS

The role of drug elimination rate and of dose fractionation was investigated, and we show that different schedulings, guaranteeing the same mean value of drug concentration, may exhibit very different long-term responses according to their concentration vs. time profile. For a large class of tumour growth laws, the profiles that approach the constant one are the most effective. This behaviour appears to depend on the 'cooperativity' of the tumour-vasculature interaction and on the functional form of the relationship between tumour growth and vasculature extent. Moreover, we suggest that a therapy approaching constant drug infusion might be advantageous also in the case of cytostatic anti-angiogenic drugs.

Enhanced proliferation of monolayer cultures of embryonic stem (ES) cell-derived cardiomyocytes following acute loss of retinoblastoma

Background

Cardiomyocyte (CM) cell cycle analysis has been impeded because of a reliance on primary neonatal cultures of poorly proliferating cells or chronic transgenic animal models with innate compensatory mechanisms.

Methodology/Principal Findings

We describe an in vitro model consisting of monolayer cultures of highly proliferative embryonic stem (ES) cell-derived CM. Following induction with ascorbate and selection with puromycin, early CM cultures are >98% pure, and at least 85% of the cells actively proliferate. During the proliferative stage, cells express high levels of E2F3a, B-Myb and phosphorylated forms of retinoblastoma (Rb), but with continued cultivation, cells stop dividing and mature functionally. This developmental transition is characterized by a switch from slow skeletal to cardiac TnI, an increase in binucleation, cardiac calsequestrin and hypophosphorylated Rb, a decrease in E2F3, B-Myb and atrial natriuretic factor, and the establishment of a more negative resting membrane potential. Although previous publications suggested that Rb was not necessary for cell cycle control in heart, we find following acute knockdown of Rb that this factor actively regulates progression through the G1 checkpoint and that its loss promotes proliferation at the expense of CM maturation.

Conclusions/Significance

We have established a unique model system for studying cardiac cell cycle progression, and show in contrast to previous reports that Rb actively regulates both cell cycle progression through the G1 checkpoint and maturation of heart cells. We conclude that this in vitro model will facilitate the analysis of cell cycle control mechanisms of CMs.

Identification of age-structured models: cell cycle phase transitions

A methodology is developed that determines age-specific transition rates between cell cycle phases during balanced growth by utilizing age-structured population balance equations. Age-distributed models are the simplest way to account for varied behavior of individual cells. However, this simplicity is offset by difficulties in making observations of age distributions, so age-distributed models are difficult to fit to experimental data. Herein, the proposed methodology is implemented to identify an age-structured model for human leukemia cells (Jurkat) based only on measurements of the total number density after the addition of bromodeoxyuridine partitions the total cell population into two subpopulations. Each of the subpopulations will temporarily undergo a period of unbalanced growth, which provides sufficient information to extract age-dependent transition rates, while the total cell population remains in balanced growth. The stipulation of initial balanced growth permits the derivation of age densities based on only age-dependent transition rates. In fitting the experimental data, a flexible transition rate representation, utilizing a series of cubic spline nodes, finds a bimodal G(0)/G(1) transition age probability distribution best fits the experimental data. This resolution may be unnecessary as convex combinations of more restricted transition rates derived from normalized Gaussian, lognormal, or skewed lognormal transition-age probability distributions corroborate the spline predictions, but require fewer parameters. The fit of data with a single log normal distribution is somewhat inferior suggesting the bimodal result as more likely. Regardless of the choice of basis functions, this methodology can identify age distributions, age-specific transition rates, and transition-age distributions during balanced growth conditions.

A model with 'growth retardation' for the kinetic heterogeneity of tumour cell populations

In the present paper we propose a continuous cell population model based on Shackney's idea of growth retardation. Cells are characterized by two state variables: the cell maturity x, 0 < or = x < or = 1, and a state variable T that identifies the rate of maturation along cell cycle. During their life span, cells can change T at random by jump transitions to T values corresponding to slower maturation rates, while at each jump the maturity x is conserved. Both the time evolution of the population and the exponential stationary solution are numerically computed. The distribution of the cell cycle transit time in asynchronous exponential growth is investigated by Monte Carlo simulation. An approximated formula for the distribution of cell cycle time is also provided.

Phosphorylation by MAPK Regulates Simian Immunodeficiency Virus Vpx Protein Nuclear Import and Virus Infectivity

Transport of the viral genome into the nucleus required phosphorylation of components in the preintegration complex by virion-associated host cellular kinases. In this study, we showed that ERK-2/MAPK is associated with simian immunodeficiency virus (SIV) virions and regulated the nuclear transport of Vpx and virus replication in non-proliferating target cells by phosphorylating Vpx. Suppression of the virion-associated ERK-2 activity by MAPK pathway inhibitors impaired both Vpx nuclear import and viral infectivity without affecting virus particle maturation and release. In addition, mutation analysis indicated that the inactivation of Vpx phosphorylation precluded nuclear import and reduced virus replication in macrophage cultures, even when functional integrase and Gag matrix proteins implicated in viral preintegration complex nuclear import are present. In this study, we also showed that co-localization of Vpx with Gag precursor in the cytoplasm is a prerequisite for Vpx incorporation into virus particles. Substitution of hydrophobic Leu-74 and Ile-75 with serines in the helical domain abrogated Vpx nuclear import, and its incorporation into virus particles, despite its localization in the cytoplasm, suggested that the structural integrity of helical domains is critical for Vpx functions. Taken together, these studies demonstrated that the host cell MAPK signal transduction pathway regulated an early step in SIV infection.

Phosphorylated retinoblastoma protein complexes with pp32 and inhibits pp32-mediated apoptosis

The retinoblastoma gene product (Rb) is a tumor suppressor that affects apoptosis paradoxically. Most sporadic cancers inactivate Rb by preferentially targeting the pathway that regulates Rb phosphorylation, resulting in resistance to apoptosis; this contrasts with Rb inactivation by mutation, which is associated with high rates of apoptosis. How phosphorylated Rb protects cells from apoptosis is not well understood, but there is evidence that Rb may sequester a pro-apoptotic nuclear factor. pp32 (ANP32A) is a pro-apoptotic nuclear phosphoprotein, the expression of which is commonly increased in cancer. We report that hyperphosphorylated Rb interacts with pp32 but not with the closely related proteins pp32r1 and pp32r2. We further demonstrate that pp32-Rb interaction inhibits the apoptotic activity of pp32 and stimulates proliferation. These results suggest a mechanism whereby cancer cells gain both a proliferative and survival advantage when Rb is inactivated by hyperphosphorylation.

Cadmium at a non-toxic dose alters gene expression in mouse testes

The testes are important targets of cadmium (Cd)-induced toxicity and carcinogenicity in rodents. Exposure to Cd at environmentally relevant low levels is a significant human health concern, but the effects of Cd on the rodent testes at doses that do not cause overt lesions are poorly defined. We used cDNA microarray and quantitative real-time RT-PCR assays to determine gene expression profiles in the testes of CD-1 mice 12-72 h after a single s.c. injection of 5 micromol/kg CdCl2. This dose of Cd did not produce overt histopathological changes, but clearly altered the expression of some genes that are likely to be important in toxicity responses. The most significant changes in gene expression occurred 24 h after treatment, corresponding to when the highest level of Cd was detected in the testes. Increased expression of the C-myc and Egr1 genes strongly suggests acute stress responses. Repressed expression of cell cycle-regulated cyclin B1 and CDC2 proteins indicates a potential for causing G2/M arrest and disturbance of meiosis. Decreased expression of pro-apoptotic genes, particularly Casp3, and DNA repair genes possibly contributes to Cd-induced carcinogenesis. These results indicate that changes in gene expression occur well before overt effects of Cd-induced testicular toxicity and carcinogenicity are apparent.

Proliferation models in tumours

Cell cycle models can be helpful in understanding the organization and kinetics of cellular proliferation. Until recently, models tended to fall into two classes, those assuming that cells normally reside in a quiescent state and are recruited into and through the cell cycle, and those that attempted to accommodate the heterogeneity seen in human tumours. The proliferation plane model combines these two approaches into a unified model encompassing recruitment and retardation in the cell cycle. It provides a framework to re-evaluate current thinking about the factors and mechanisms that contribute to failure in radiotherapy.

Biological response to radiation therapy

In an investigation by the Swedish Cancer Society, the present status, critical issues and future aspects and potentials were described by an expert group for each of nine major areas of radiation therapy research. This article deals with biological response to radiation. Separate sections deal with molecular responses to radiation, the stem cell and clonogenic cell concepts and the importance of cell proliferation, cell and tissue responses to doses above and below 1 Gy, respectively, the potential role of intercellular signalling pathways, the so-called bystander effect and radiation biology-based therapy planning and treatment optimization.

Distinct mechanisms for regulating the tumor suppressor and antiapoptotic functions of Rb

The retinoblastoma protein, Rb, suppresses tumorigenesis by inhibiting cell proliferation and promoting senescence and differentiation. Paradoxically, Rb also inhibits apoptosis, which would seem to oppose its tumor suppressor function. Further, most human cancer cells inactivate Rb by hyperphosphorylation and demonstrate increased proliferative capacity but not high levels of apoptosis. As a potential explanation for these findings, we show here that the tumor suppressor and antiapoptotic functions of Rb are regulated by distinct phosphorylation events. Phosphorylation of sites in the C terminus occurs efficiently every cell cycle and regulates proliferation. Phosphorylation of Ser567 is inefficient and does not occur during the normal cell cycle. However, high cyclin-dependent kinase activity promotes phosphorylation of Ser567 by inducing an intramolecular interaction that leads to release of E2F, degradation of Rb, and susceptibility to apoptosis. Thus, phosphorylation of Ser567 may limit excessive proliferation by triggering cell death under hyperproliferative conditions. These findings suggest that the antiproliferative and antiapoptotic activities of Rb may represent complementary functions that work in concert to maintain the proliferation rate of cells within certain limits. As a survival strategy, some cancer cells may exploit this dual role of Rb by phosphorylating sites that regulate tumor suppression but avoiding phosphorylation of Ser567 and consequent apoptotic stimulus.

Negative regulation of beta-catenin signaling by tyrosine phosphatase SHP-1 in intestinal epithelial cells

Protein-tyrosine phosphatase SHP-1 is expressed at high levels in hematopoietic cells and at moderate levels in many other cell types including epithelial cells. Although SHP-1 has been shown to be a negative regulator of multiple signaling pathways in hematopoietic cells, very little is known about the biological role of SHP-1 in epithelial cells. In order to elucidate the mechanism(s) responsible for the loss of proliferative potential once committed intestinal epithelial cells begin to differentiate, the role and regulation of SHP-1 were analyzed in both intact epithelium as well as in well established intestinal cell models recapitulating the crypt-villus axis in vitro. Results show that SHP-1 was expressed in the nuclei of all intestinal epithelial cell models as well as in epithelial cells of intact human fetal jejunum and colon. Expression and phosphatase activity levels of SHP-1 were much more elevated in confluent growth-arrested intestinal epithelial cells and in differentiated enterocytes as well. Overexpression of SHP-1 in intestinal epithelial crypt cells significantly inhibited dhfr, c-myc, and cyclin D1 gene expression but did not interfere with c-fos gene expression. In contrast, a mutated inactive form of SHP-1 had no effect on these genes. SHP-1 expression significantly decreased beta-catenin/TCF-dependent transcription in intestinal epithelial crypt cells. Immunoprecipitation experiments revealed that beta-catenin is one of the main binding partners and a substrate for SHP-1. Taken together, our results indicate that SHP-1 may be involved in the regulation of beta-catenin transcriptional function and in the negative control of intestinal epithelial cell proliferation.

Cancer cell dynamics in presence of telomerase inhibitors: analysis of in vitro data

The inhibition of telomerase activity in actively dividing cells leads to suppression of cell growth after a time delay (inhibitory delay) required to reach a threshold telomeric DNA size. We developed a mathematical model of the dynamics of telomere size distribution and cell growth in the presence of telomere inhibitors that allowed quantification of the inhibitory delay. The model based on the solution of a system of differential equations described quantitatively recent experimental data on dynamics of cultured cells in presence of telomerase inhibitors. The analysis of the data by this model suggested the existence of at least two distinct subpopulations of cells with different proliferative activity. Size distribution of telomeres, fraction of proliferating cells, and tumor doubling times are of critical importance for the dynamics of cancer cells growth in presence of telomerase inhibitors. Rapidly growing cells with large telomeric DNA heterogeneity and small proliferating fractions as well as those with very short homogeneous telomeres would be the most sensitive to telomerase inhibitors.

Bioavailability and efficacy of antisense morpholino oligomers targeted to c-myc and cytochrome P-450 3A2 following oral administration in rats

Antisense phosphorodiamidate Morpholino oligomers (PMO) are resistant to degradation by cellular hydrolases, DNases, RNases, and phosphodiesterases, but remain sensitive to prolonged exposure to low pH. The present studies evaluate the oral fractional bioavailability, stability, and efficacy of two distinct PMO sequences targeted to c-myc and cytochrome P-450 (CYP) 3A2. The c-myc antisense 20-mer, AVI-4126 (5'-ACGTTGAGGGGCATCGTCGC-3'), slowed the regenerative process in the rat liver after a 70% partial hepatectomy (PH). Rats were administered 3.0 mg/kg AVI-4126 in 0.1 mL saline via a bolus intravenous injection or in 0.5 mL sterile phosphate-buffered saline via gavage immediately following PH. The areas under the plasma concentration versus time curves revealed a fractional oral availability of 78.8% over a period of 10 min through 24 h. Immunoblot analysis of liver tissue from rats treated orally with AVI-4126 demonstrated a sequence-specific reduction in the target protein c-Myc, as well as secondary proliferation markers: proliferating cell nuclear antigen (PCNA), cyclin D1, and p53. The CYP3A2 antisense 22-mer AVI-4472 (5'-GAGCTGAAAGCAGGTCCATCCC-3') caused a sequence-dependent reduction of approximately five-fold in the rat liver CYP3A2 protein levels and erythromycin demethylation activity in 24 h following oral administration at a dose of 2 mg/kg. It is concluded that oral administration of PMOs can inhibit c-myc and CYP3A2 gene expression in rat liver by an antisense-based mechanism of action. These studies highlight the potential for development of PMOs as orally administered therapeutic agents.

Modelling of cell proliferation: nuclear versus membrane labelling

Cell proliferation is a fundamental process involved in growth, development and oncogenesis. Monitoring and quantification of proliferation are essential to analyse the behaviour of cells drug-treated or not. Flow cytometry assessment of cell proliferation requires mathematical models to extract information of interest from fluorescence distributions. Various methods are available for cell cycle analysis, including estimation of cell phase durations and doubling time. In this context, we compare widely used flow cytometric methods based on nuclear labelling (using BrdUrd incorporation in combination with DNA content) to membrane labelling (using intercalating dyes PKH).

p27(Kip1) is important in modulating pulmonary artery smooth muscle cell proliferation

Vascular remodeling due to pulmonary arterial smooth muscle cell (PASMC) proliferation is central to the development of pulmonary hypertension. Cell proliferation requires the coordinated interaction of cyclins and cyclin-dependent kinases (cdk) to drive cells through the cell cycle. Cdk inhibitors can bind cyclin-cdk complexes and cause G(1) arrest. To determine the importance of the cdk inhibitor p27(Kip1) in PASMC proliferation we studied [(3)H]thymidine incorporation, changes in cell cycle, cell proliferation, and protein expression of p27(Kip1) following serum stimulation in early passage rat PASMC. p27(Kip1) expression decreased to 40% of baseline after serum stimulation, which was associated with an increase in both [(3)H]thymidine incorporation and the percent of cells in S phase. p27(Kip1) binding to cyclin E decreased at 24 h, and this correlated with an increase in phosphorylation of retinoblastoma both in vivo and in vitro. Overexpression of p27(Kip1) decreased [(3)H]thymidine incorporation and reduced cell counts at 5 d compared with controls. PASMC obtained from p27(Kip1-/-) mice showed a 2-fold increase in [(3)H]thymidine incorporation (at 24 h) and cell proliferation compared with p27(Kip1+/+) PASMC when cultured in 10% fetal bovine serum (FBS). These results suggest an important role for p27(Kip1) in regulating PASMC mitogenesis and proliferation.

From consensus sequence peptide to high affinity ligand, a "library scan" strategy

A wide variety of proteins have been shown to recognize and bind to specific amino acid sequences on other proteins. These sequences can be readily identified using combinatorial peptide libraries. However, peptides containing these preferred sequences ("consensus sequence peptides") typically display only modest affinities for the consensus sequence-binding site on the intact protein. In this report, we describe a parallel synthesis strategy that transforms consensus sequence peptides into high affinity ligands. The work described herein has focused on the Lck SH2 domain, which binds the consensus peptide acetyl-Tyr(P)-Glu-Glu-Ile-amide with a K(D) of 1.3 micrometer. We employed a strategy that creates a series of spatially focused libraries that challenge specific subsites on the target protein with a diverse array of functionality. The final lead compound identified in this study displayed a 3300-fold higher affinity for the Lck SH2 domain than the starting consensus sequence peptide.

Cyclin D1 and E2F-1 immunoreactivity in bone marrow biopsy specimens of multiple myeloma: relationship to proliferative activity, cytogenetic abnormalities and DNA ploidy

Cyclin D1, encoded by the CCND1 gene, is immunohistochemically detectable in up to one-third of cases of multiple myeloma (MM). To examine the mechanism of cyclin D1 overexpression, we compared cyclin D1 immunoreactivity with the results of conventional cytogenetics to determine if the t(11;14)(q13;q32) or other abnormalities of 11q11-14 explained cyclin D1 overexpression. Karyotypic abnormalities were found in 45 out of 67 (67%) MM cases; the t(11;14) was present in seven cases (10%). Additional 11q11-14 abnormalities were not identified. The t(11;14) correlated with cyclin D1 upregulation in low to intermediately proliferative MM, but was not present in highly proliferative tumours (assessed using bromodeoxyuridine labelling index). Cyclin D1 indirectly activates the transcription factor E2F-1. In the bone marrow biopsy specimens of MM cases, E2F-1 was concurrently expressed with cyclin D1 (P = 0.001), indicating that cyclin D1 is functional. However, as neither E2F-1 nor cyclin D1 expression correlated with proliferative activity, the speculation that t(11;14) upregulates the CCND1 gene to induce higher proliferation and possibly more aggressive disease is not supported. We conclude that in low to intermediately proliferative MM cases, cyclin D1 is probably upregulated by t(11;14), but an alternative mechanism is more probable in highly proliferative MM.

Differential modulation and subsequent blockade of mitogenic signaling and cell cycle progression by Pasteurella multocida toxin

The intracellularly acting protein toxin of Pasteurella multocida (PMT) causes numerous effects in cells, including activation of inositol 1,4,5-trisphosphate (IP(3)) signaling, Ca(2+) mobilization, protein phosphorylation, morphological changes, and DNA synthesis. The direct intracellular target of PMT responsible for activation of the IP(3) pathway is the G(q/11)alpha-protein, which stimulates phospholipase C (PLC) beta1. The relationship between PMT-mediated activation of the G(q/11)-PLC-IP(3) pathway and its ability to promote mitogenesis and cellular proliferation is not clear. PMT stimulation of p42/p44 mitogen-activated protein kinase occurs upstream via G(q/11)-dependent transactivation of the epidermal growth factor receptor. We have further characterized the effects of PMT on the downstream mitogenic response and cell cycle progression in Swiss 3T3 and Vero cells. PMT treatment caused dramatic morphological changes in both cell lines. In Vero cells, limited multinucleation, nuclear fragmentation, and disruption of cytokinesis were also observed; however, a strong mitogenic response occurred only with Swiss 3T3 cells. Significantly, this mitogenic response was not sustained. Cell cycle analysis revealed that after the initial mitogenic response to PMT, both cell types subsequently arrested primarily in G(1) and became unresponsive to further PMT treatment. In Swiss 3T3 cells, PMT induced up-regulation of c-Myc; cyclins D1, D2, D3, and E; p21; PCNA; and the Rb proteins, p107 and p130. In Vero cells, PMT failed to up-regulate PCNA and cyclins D3 and E. We also found that the initial PMT-mediated up-regulation of several of these signaling proteins was not sustained, supporting the subsequent cell cycle arrest. The consequences of PMT entry thus depend on the differential regulation of signaling pathways within different cell types.

Phosphorylation of human immunodeficiency virus type 1 Vpr regulates cell cycle arrest

Human immunodeficiency virus type 1 (HIV-1) Vpr regulates nuclear transport of the viral preintegration complex, G(2) cell cycle arrest, and transcriptional transactivation. We asked whether phosphorylation could affect Vpr activity. Vpr was found to be phosphorylated on serine residues in transiently transfected and infected cells. Residues 79, 94, and 96 were all found to be phosphorylated, as assessed by alanine mutations. Mutation of Ser-79 to Ala abrogated effects of Vpr on cell cycle progression, whereas mutation of Ser-94 and Ser-96 had no effect. Simultaneous mutation of all three Vpr serine residues attenuated HIV-1 replication in macrophages, whereas single and double Ser mutations had no effect.