Ca(2+)-dependent stimulation of retinoblastoma gene product phosphorylation and p34cdc2 kinase activation in serum-stimulated human fibroblasts

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Interplay of Ca2+ and K+ signals in cell physiology and cancer

The cytoplasmic Ca2+ concentration and the activity of K+ channels on the plasma membrane regulate cellular processes ranging from mitosis to oriented migration. The interplay between Ca2+ and K+ signals is intricate, and different cell types rely on peculiar cellular mechanisms. Derangement of these mechanisms accompanies the neoplastic progression. The calcium signals modulated by voltage-gated (KV) and calcium-dependent (KCa) K+ channel activity regulate progression of the cell division cycle, the release of growth factors, apoptosis, cell motility and migration. Moreover, KV channels regulate the cell response to the local microenvironment by assembling with cell adhesion and growth factor receptors. This chapter summarizes the pathophysiological roles of Ca2+ and K+ fluxes in normal and cancer cells, by concentrating on several biological systems in which these functions have been studied in depth, such as early embryos, mammalian cell lines, T lymphocytes, gliomas and colorectal cancer cells. A full understanding of the underlying mechanisms will offer a comprehensive view of the ion channel implication in cancer biology and suggest potential pharmacological targets for novel therapeutic approaches in oncology.

Regulation and role of calcium in cellular senescence

Cellular senescence is a state of stable cell proliferation arrest accompanied by a distinct secretory program impacting the senescent cell microenvironment. This phenotype can be induced by many stresses, including telomere shortening, oncogene activation, oxidative or genotoxic stress. Cellular senescence plays a key role in the organism throughout life, with beneficial effects at a young age for instance in embryonic development and wound healing, and deleterious effects during aging and in aging-related diseases. In the last decade calcium and calcium signaling have been established as critical factors in the implementation and regulation of cellular senescence. In this review we will present and discuss the main discoveries in this field, from the observation of an increased intracellular calcium concentration in senescent cells to the identification of calcium-binding proteins, calcium channels (TRP, ITPR, …) and MERCs (mitochondria-endoplasmic reticulum contact sites) as key players in this context.

Put in a “Ca2+ll” to Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a clonal disorder characterized by genetic aberrations in myeloid primitive cells (blasts) which lead to their defective maturation/function and their proliferation in the bone marrow (BM) and blood of affected individuals. Current intensive chemotherapy protocols result in complete remission in 50% to 80% of AML patients depending on their age and the AML type involved. While alterations in calcium signaling have been extensively studied in solid tumors, little is known about the role of calcium in most hematologic malignancies, including AML. Our purpose with this review is to raise awareness about this issue and to present (i) the role of calcium signaling in AML cell proliferation and differentiation and in the quiescence of hematopoietic stem cells; (ii) the interplay between mitochondria, metabolism, and oxidative stress; (iii) the effect of the BM microenvironment on AML cell fate; and finally (iv) the mechanism by which chemotherapeutic treatments modify calcium homeostasis in AML cells.

Mitochondrial Ca2+ Signaling in Health, Disease and Therapy

The divalent cation calcium (Ca²⁺) is considered one of the main second messengers inside cells and acts as the most prominent signal in a plethora of biological processes. Its homeostasis is guaranteed by an intricate and complex system of channels, pumps, and exchangers. In this context, by regulating cellular Ca²⁺ levels, mitochondria control both the uptake and release of Ca²⁺. Therefore, at the mitochondrial level, Ca²⁺ plays a dual role, participating in both vital physiological processes (ATP production and regulation of mitochondrial metabolism) and pathophysiological processes (cell death, cancer progression and metastasis). Hence, it is not surprising that alterations in mitochondrial Ca²⁺ (mCa²⁺) pathways or mutations in Ca²⁺ transporters affect the activities and functions of the entire cell. Indeed, it is widely recognized that dysregulation of mCa²⁺ signaling leads to various pathological scenarios, including cancer, neurological defects and cardiovascular diseases (CVDs). This review summarizes the current knowledge on the regulation of mCa²⁺ homeostasis, the related mechanisms and the significance of this regulation in physiology and human diseases. We also highlight strategies aimed at remedying mCa²⁺ dysregulation as promising therapeutical approaches.

Targeting the Calcium Signalling Machinery in Cancer

Cancer is caused by excessive cell proliferation and a propensity to avoid cell death, while the spread of cancer is facilitated by enhanced cellular migration, invasion, and vascularization. Cytosolic Ca²⁺ is central to each of these important processes, yet to date, there are no cancer drugs currently being used clinically, and very few undergoing clinical trials, that target the Ca²⁺ signalling machinery. The aim of this review is to highlight some of the emerging evidence that targeting key components of the Ca²⁺ signalling machinery represents a novel and relatively untapped therapeutic strategy for the treatment of cancer.

ER Ca2+ release and store-operated Ca2+ entry - partners in crime or independent actors in oncogenic transformation?

Ca²⁺ is a pleiotropic messenger that controls life and death decisions from fertilisation until death. Cellular Ca²⁺ handling mechanisms show plasticity and are remodelled throughout life to meet the changing needs of the cell. In turn, as the demands on a cell alter, for example through a change in its niche environment or its functional requirements, Ca²⁺ handling systems may be targeted to sustain the remodelled cellular state. Nowhere is this more apparent than in cancer. Oncogenic transformation is a multi-stage process during which normal cells become progressively differentiated towards a cancerous state that is principally associated with enhanced proliferation and avoidance of death. Ca²⁺ signalling is intimately involved in almost all aspects of the life of a transformed cell and alterations in Ca²⁺ handling have been observed in cancer. Moreover, this remodelling of Ca²⁺ signalling pathways is also required in some cases to sustain the transformed phenotype. As such, Ca²⁺ handling is hijacked by oncogenic processes to deliver and maintain the transformed phenotype. Central to generation of intracellular Ca²⁺ signals is the release of Ca²⁺ from the endoplasmic reticulum intracellular (ER) Ca²⁺ store via inositol 1,4,5-trisphosphate receptors (InsP₃Rs). Upon depletion of ER Ca²⁺, store-operated Ca²⁺ entry (SOCE) across the plasma membrane occurs via STIM-gated Orai channels. SOCE serves to both replenish stores but also sustain Ca²⁺ signalling events. Here, we will discuss the role and regulation of these two signalling pathways and their interplay in oncogenic transformation.

Targeting Ca2+ signalling through phytomolecules to combat cancer

Cancer is amongst the life-threatening public health issue worldwide, hence responsible for millions of death every year. It is affecting human health regardless of their gender, age, eating habits, and ecological location. Many drugs and therapies are available for its cure still the need for effective targeted drugs and therapies are of paramount importance. In the recent past, Ca²⁺ signalling (including channels/transporters/pumps) are being studied as a plausible target for combating the cancer menace. Many evidence has shown that the intracellular Ca²⁺ homeostasis is altered in cancer cells and the remodelling is linked with tumor instigation, angiogenesis, progression, and metastasis. Focusing on these altered Ca²⁺ signalling tool kit for cancer treatment is a cross-cutting and emerging area of research. In addition, there are numerous phytomolecules which can be exploited as a potential Ca²⁺ (channels/transporters/ pumps) modulators in the context of targeting Ca²⁺ signalling in the cancer cell. In the present review, a list of plant-based potential Ca²⁺ (channel/transporters/pumps) modulators has been reported which could have application in the framework of repurposing the potential drugs to target Ca²⁺ signalling pathways in cancer cells. This review also aims to gain attention in and support for prospective research in this field.

Extracellular vesicles of Trypanosoma cruzi tissue-culture cell-derived trypomastigotes: Induction of physiological changes in non-parasitized culture cells

BACKGROUND

Trypanosoma cruzi is the obligate intracellular parasite that causes Chagas disease. The pathogenesis of this disease is a multifactorial complex process that involves a large number of molecules and particles, including the extracellular vesicles. The presence of EVs of T. cruzi was first described in 1979 and, since then, research regarding these particles has been increasing. Some of the functions described for these EVs include the increase in heart parasitism and the immunomodulation and evasion of the host immune response. Also, EVs may be involved in parasite adhesion to host cells and host cell invasion.

METHODOLOGY/PRINCIPAL FINDINGS

EVs (exosomes) of the Pan4 strain of T. cruzi were isolated by differential centrifugation, and measured and quantified by TEM, NTA and DLS. The effect of EVs in increasing the parasitization of Vero cells was evaluated and the ED50 was calculated. Changes in cell permeability induced by EVs were evaluated in Vero and HL-1 cardiomyocyte cells using cell viability techniques such as trypan blue and MTT assays, and by confocal microscopy. The intracellular mobilization of Ca2+ and the disruption of the actin cytoskeleton induced by EVs over Vero cells were followed-up in time using confocal microscopy. To evaluate the effect of EVs over the cell cycle, cell cycle analyses using flow cytometry and Western blotting of the phosphorylated and non-phosphorylated protein of Retinoblastoma were performed.

CONCLUSION/SIGNIFICANCE

The incubation of cells with EVs of trypomastigotes of the Pan4 strain of T. cruzi induce a number of changes in the host cells that include a change in cell permeability and higher intracellular levels of Ca2+ that can alter the dynamics of the actin cytoskeleton and arrest the cell cycle at G0/G1 prior to the DNA synthesis necessary to complete mitosis. These changes aid the invasion of host cells and augment the percentage of cell parasitization.

Calcium signaling and cell cycle: Progression or death

Cytosolic Ca²⁺ concentration levels fluctuate in an ordered manner along the cell cycle, in line with the fact that Ca²⁺ is involved in the regulation of cell proliferation. Cell proliferation should be an error-free process, yet is endangered by mistakes. In fact, a complex network of proteins ensures that cell cycle does not progress until the previous phase has been successfully completed. Occasionally, errors occur during the cell cycle leading to cell cycle arrest. If the error is severe, and the cell cycle checkpoints work perfectly, this results into cellular demise by activation of apoptotic or non-apoptotic cell death programs. Cancer is characterized by deregulated proliferation and resistance against cell death. Ca²⁺ is a central key to these phenomena as it modulates signaling pathways that control oncogenesis and cancer progression. Here, we discuss how Ca²⁺ participates in the exogenous and endogenous signals controlling cell proliferation, as well as in the mechanisms by which cells die if irreparable cell cycle damage occurs. Moreover, we summarize how Ca²⁺ homeostasis remodeling observed in cancer cells contributes to deregulated cell proliferation and resistance to cell death. Finally, we discuss the possibility to target specific components of Ca²⁺ signal pathways to obtain cytostatic or cytotoxic effects.

Calcium signaling and cellular senescence

Cellular senescence is a stable cell proliferation arrest induced by a variety of stresses including telomere shortening, oncogene activation and oxidative stress. This process plays a crucial role in many physiopathological contexts, especially during aging when cellular senescence favors development of age-related diseases, shortening lifespan. However, the molecular and cellular mechanisms controlling senescence are still a matter of active research. In the last decade, there has been emerging literature indicating a key involvement of calcium signaling in cellular senescence. In this review we will initially give an account of the direct evidence linking calcium and the regulation of senescence. We will then review our current knowledge on the role of calcium in some senescence-associated features and physiopathological conditions, which will shed light on additional ways in which calcium signaling is implicated in cellular senescence.

High ATP2A2 expression correlates with better prognosis of diffuse astrocytic tumor patients

Novel molecular markers are required for defining subsets of diffuse astrocytic tumor patients with differing prognoses. Here, we examined ATP2A2 expression in 109 human diffuse astrocytic tumor samples (39 grade II diffuse astrocytoma (DA), 19 grade III anaplastic astrocytoma (AA), 51 grade IV glioblastoma) and its correlation with patient clinicopathologic characteristics. ATP2A2 expression significantly correlated with tumor grade and survival (P<0.05). High ATP2A2 expression was detected in 35.3% (18/51) of glioblastoma patients, compared to 61.5% (24/39) in grade II, and 52.6% (10/19) in grade III astrocytoma patients (P=0.043). The median survival was 45±5.3 (95% CI, 34.7-55.3) months in patients with high ATP2A2 expression and 16±5.0 (95% CI, 6.3-25.7) months in patients with low ATP2A2 expression (P<0.0001). Additionally, high grade astrocytoma patients with high ATP2A2 expression showed longer survival (median, 31.0±4.9 months, 95% CI, 21.4-40.7) than those with low ATP2A2 expression (median: 13.0±1.6 months, 95% CI, 9.9-16.1; P=0.027). Furthermore, both ATP2A2 overexpression and IDH1 mutation were detected in secondary glioblastoma, AA developed from DA and oligodendrogiomas with IDH1 mutation. The MTT assays showed that lentiviral ATP2A2 overexpression significantly suppressed the clonogenic growth of glioblastoma U251MG cells (P<0.05). Xenografts stably overexpressing ATP2A2 were markedly smaller in size 4 weeks post inoculation (P<0.05). Our findings identified high ATP2A2 expression in a subset of astrocytoma patients that was associated with better prognosis and ATP2A2 suppressed astrocytoma growth.

Calcium alterations signal either to senescence or to autophagy induction in stem cells upon oxidative stress

Intracellular calcium ([Ca2+]i) has been reported to play an important role in autophagy, apoptosis and necrosis, however, a little is known about its impact in senescence. Here we investigated [Ca2+]i contribution to oxidative stress-induced senescence of human endometrium-derived stem cells (hMESCs). In hMESCs sublethal H2O2-treatment resulted in a rapid calcium release from intracellular stores mediated by the activation of PLC/IP3/IP3R pathway. Notably, further senescence development was accompanied by persistently elevated [Ca2+]i levels. In H2O2-treated hMESCs, [Ca2+]i chelation by BAPTA-AM (BAPTA) was sufficient to prevent the expansion of the senescence phenotype, to decrease endogenous reactive oxygen species levels, to avoid G0/G1 cell cycle arrest, and finally to retain proliferation. Particularly, loading with BAPTA attenuated phosphorylation of the main DNA damage response members, including ATM, 53BP1 and H2A.X and reduced activation of the p53/p21/Rb pathway in H2O2-stimulated cells. Next, we revealed that BAPTA induced an early onset of AMPK-dependent autophagy in H2O2-treated cells as confirmed by both the phosphorylation status of AMPK/mTORC1 pathway and the dynamics of the LC3 lipidization. Summarizing the obtained data we can assume that calcium chelation is able to trigger short-term autophagy and to prevent the premature senescence of hMESCs under oxidative stress.

Calcium signaling and cell proliferation

Cell proliferation is orchestrated through diverse proteins related to calcium (Ca(2+)) signaling inside the cell. Cellular Ca(2+) influx that occurs first by various mechanisms at the plasma membrane, is then followed by absorption of Ca(2+) ions by mitochondria and endoplasmic reticulum, and, finally, there is a connection of calcium stores to the nucleus. Experimental evidence indicates that the fluctuation of Ca(2+) from the endoplasmic reticulum provides a pivotal and physiological role for cell proliferation. Ca(2+) depletion in the endoplasmatic reticulum triggers Ca(2+) influx across the plasma membrane in an phenomenon called store-operated calcium entries (SOCEs). SOCE is activated through a complex interplay between a Ca(2+) sensor, denominated STIM, localized in the endoplasmic reticulum and a Ca(2+) channel at the cell membrane, denominated Orai. The interplay between STIM and Orai proteins with cell membrane receptors and their role in cell proliferation is discussed in this review.

STIM and Orai proteins as novel targets for cancer therapy. A Review in the Theme: Cell and Molecular Processes in Cancer Metastasis

Calcium (Ca(2+)) regulates a plethora of cellular functions including hallmarks of cancer development such as cell cycle progression and cellular migration. Receptor-regulated calcium rise in nonexcitable cells occurs through store-dependent as well as store-independent Ca(2+) entry pathways. Stromal interaction molecules (STIM) and Orai proteins have been identified as critical constituents of both these Ca(2+) influx pathways. STIMs and Orais have emerged as targets for cancer therapeutics as their altered expression and function have been shown to contribute to tumorigenesis. Recent data demonstrate that they play a vital role in development and metastasis of a variety of tumor types including breast, prostate, cervical, colorectal, brain, and skin tumors. In this review, we will retrospect the data supporting a key role for STIM1, STIM2, Orai1, and Orai3 proteins in tumorigenesis and discuss the potential of targeting these proteins for cancer therapy.

Inhibition of cancer cell proliferation by midazolam by targeting transient receptor potential melastatin 7

Transient receptor potential melastatin 7 (TRPM7), a Ca²⁺-permeable channel, has been demonstrated to be present in cancer cells and involved in their growth and proliferation. The present study used midazolam, a benzodiazepine class anesthesic, to pharmacologically intervene in the expression of TRPM7 and to inhibit cancer cell proliferation. Midazolam significantly inhibited the growth and proliferation of FaDu human hypopharyngeal squamous cell carcinoma cells, concurring with the induction of G₀/G₁ cell cycle arrest and blockage of Rb activation. Central-type and peripheral-type benzodiazepine receptor antagonists did not abrogate proliferation inhibition by midazolam, while the specific TRPM7 agonist bradykinin reversed this effect. In addition, other benzodiazepines, diazepam and clonazepam also exhibited anti-proliferative activities. The inhibitory activity on cancer cell growth and proliferation, combined with the TRPM-dependent mechanism, reveals the anticancer potential of midazolam as a TRPM7 inhibitor and supports the suggestion that TRPM7 is a valuable target for pharmaceutical intervention.

Significance of calcium binding, tyrosine phosphorylation, and lysine trimethylation for the essential function of calmodulin in vertebrate cells analyzed in a novel gene replacement system

Calmodulin (CaM) was shown to be essential for survival of lower eukaryotes by gene deletion experiments. So far, no CaM gene deletion was reported in higher eukaryotes. In vertebrates, CaM is expressed from several genes, which encode an identical protein, making it difficult to generate a model system to study the effect of CaM gene deletion. Here, we present a novel genetic system based on the chicken DT40 cell line, in which the two functional CaM genes were deleted and one allele replaced with a CaM transgene that can be artificially regulated. We show that CaM is essential for survival of vertebrate cells as they die in the absence of CaM expression. Reversal of CaM repression or ectopic expression of HA-tagged CaM rescued the cells. Cells exclusively expressing HA-CaM with impaired individual calcium binding domains as well as HA-CaM lacking the ability to be phosphorylated at residues Tyr(99)/Tyr(138) or trimethylated at Lys(115) survived and grew well. CaM mutated at both Ca(2+) binding sites 3 and 4 as well as at both sites 1 and 2, but to a lesser degree, showed decreased ability to support cell growth. Cells expressing CaM with all calcium binding sites impaired died with kinetics similar to that of cells expressing no CaM. This system offers a unique opportunity to analyze CaM structure-function relationships in vivo without the use of pharmacological inhibitors and to analyze the function of wild type and mutated CaM in modulating the activity of different target systems without interference of endogenous CaM.

T-type Ca2+ channels in mouse embryonic stem cells: modulation during cell cycle and contribution to self-renewal

Ion channels participate in cell homeostasis and are involved in the regulation of proliferation and differentiation in several cell types; however, their presence and function in embryonic stem (ES) cells are poorly studied. We have investigated the existence of voltage-dependent inward currents in mouse ES cells and their ability to modulate proliferation and self-renewal. Patch-clamped ES cells had inactivating tetrodotoxin (TTX)-sensitive Na(+) currents as well as transient Ca(2+) currents abolished by the external application of Ni(2+). Biophysical and pharmacological data indicated that the Ca(2+) current is predominantly mediated by T-type (Ca(v)3.2) channels. The number of cells expressing T-type channels and Ca(v)3.2 mRNA levels increased at the G1/S transition of the cell cycle. TTX had no effect on ES cell proliferation. However, blockade of T-type Ca(2+) currents with Ni(2+) induced a decrease in proliferation and alkaline phosphatase positive colonies as well as reduced expression of Oct3/4 and Nanog, all indicative of loss in self-renewal capacity. Decreased alkaline phosphatase and Oct3/4 expression were also observed in cells subjected to small interfering RNA-induced knockdown for T-type (Ca(v)3.2) Ca(2+) channels, thus partially recapitulating the pharmacological effects on self-renewal. These results indicate that Ca(v)3.2 channel expression in ES cells is modulated along the cell cycle being induced at late G1 phase. They also suggest that these channels are involved in the maintenance of the undifferentiated state of mouse ES cells. We propose that Ca(2+) entry mediated by Ca(v)3.2 channels might be one of the intracellular signals that participate in the complex network responsible for ES cell self-renewal.

Ion channels and transporters in cancer. 1. Ion channels and cell proliferation in cancer

Progress through the cell mitotic cycle requires precise timing of the intrinsic molecular steps and tight coordination with the environmental signals that maintain a cell into the proper physiological context. Because of their great functional flexibility, ion channels coordinate the upstream and downstream signals that converge on the cell cycle machinery. Both voltage- and ligand-gated channels have been implicated in the control of different cell cycle checkpoints in normal as well as neoplastic cells. Ion channels mediate the calcium signals that punctuate the mitotic process, the cell volume oscillations typical of cycling cells, and the exocytosis of autocrine or angiogenetic factors. Other functions of ion channels in proliferation are still matter of debate. These may or may not depend on ion transport, as the channel proteins can form macromolecular complexes with growth factor and cell adhesion receptors. Direct conformational coupling with the cytoplasmic regulatory proteins is also possible. Derangement or relaxed control of the above processes can promote neoplasia. Specific types of ion channels have turned out to participate in the different stages of the tumor progression, in which cell heterogeneity is increased by the selection of malignant cell clones expressing the ion channel types that better support unrestrained growth. However, a comprehensive mechanistic picture of the functional relations between ion channels and cell proliferation is yet not available, partly because of the considerable experimental challenges offered by studying these processes in living mammalian cells. No doubt, such studies will constitute one of the most fruitful research fields for the next generation of cell physiologists.

Induction of intracellular Ca2+ and pH changes in Sf9 insect cells by rhodojaponin-III, a natural botanic insecticide isolated from Rhododendron molle

Many studies on intracellular calcium ([Ca²⁺]_i) and intracellular pH (pH_i) have been carried out due to their importance in regulation of different cellular functions. However, most of the previous studies are focused on human or mammalian cells. The purpose of the present study was to characterize the effect of Rhodojaponin-III (R-III) on [Ca²⁺]_i and pH_i and the proliferation of Sf9 cells. R-III strongly inhibited Sf9 cells proliferation with a time- and dose-dependent manner. Flow cytometry established that R-III interfered with Sf9 cells division and arrested them in G2/M. By using confocal scanning technique, effects of R-III on intracellular free calcium ([Ca²⁺]_i) and intracellular pH (pH_i) in Sf9 cells were determined. R-III induced a significant dose-dependent (1, 10, 100, 200 μg/mL) increase in [Ca²⁺]_i and pH_i of Sf9 cells in presence of Ca²⁺-containing solution (Hanks) and an irreversible decrease in the absence of extra cellular Ca²⁺. We also found that both extra cellular Ca²⁺ and intracellular Ca²⁺ stores contributed to the increase of [Ca²⁺]_i, because completely treating Sf9 cells with CdCl₂ (5 mM), a Ca²⁺ channels blocker, R-III (100 μg/mL) induced a transient elevation of [Ca²⁺]_i in case of cells either in presence of Ca²⁺ containing or Ca²⁺ free solution. In these conditions, pH_i showed similar changes with that of [Ca²⁺]_i on the whole. Accordingly, we supposed that there was a certain linkage for change of [Ca²⁺]_i, cell cycle arrest, proliferation inhibition in Sf9 cells induced by R-III.

Ca(2+) signaling, genes and the cell cycle

Changes in the concentration and spatial distribution of Ca(2+) ions in the cytoplasm constitute a ubiquitous intracellular signaling module in cellular physiology. With the advent of Ca(2+) dyes that allow direct visualization of Ca(2+) transients, combined with powerful experimental tools such as electrophysiological recordings, intracellular Ca(2+) transients have been implicated in practically every aspect of cellular physiology, including cellular proliferation. Ca(2+) signals are associated with different phases of the cell cycle and interfering with Ca(2+) signaling or downstream pathways often disrupts progression of the cell cycle. Although there exists a dependence between Ca(2+) signals and the cell cycle the mechanisms involved are not well defined and given the cross-talk between Ca(2+) and other signaling modules, it is difficult to assess the exact role of Ca(2+) signals in cell cycle progression. Two exceptions however, include fertilization and T-cell activation, where well-defined roles for Ca(2+) signals in mediating progression through specific stages of the cell cycle have been clearly established. In the case of T-cell activation Ca(2+) regulates entry into the cell cycle through the induction of gene transcription.

Regulation of store-operated Ca2+ entry during the cell cycle

Cytoplasmic Ca(2+) signals are central to numerous cell physiological processes, including cellular proliferation. Historically, much of the research effort in this area has focused on the role of Ca(2+) signals in cell-cycle progression. It is becoming clear, however, that the relationship between Ca(2+) signaling and the cell cycle is a 'two-way street'. Specifically, Ca(2+)-signaling pathways are remodeled during M phase, leading to altered Ca(2+) dynamics. Such remodeling probably better serves the large variety of functions that cells must perform during cell division compared with during interphase. This is clearly the case during oocyte meiosis, because remodeling of Ca(2+) signals partially defines the competence of the egg to activate at fertilization. Store-operated Ca(2+) entry (SOCE) is a ubiquitous Ca(2+)-signaling pathway that is regulated during M phase. In this Commentary, we discuss the latest advances in our understanding of how SOCE is regulated during cell division.

Calcium wave signaling in cancer cells

Ca(2+) functions as an important signaling messenger right from beginning of life to the final moments of the end of life. Ca(2+) is needed at several steps of the cell cycle such as early G(1), at the G(1)/S, and G(2)/M transitions. The Ca(2+) signals in the form of time-dependent changes in intracellular Ca(2+) concentrations, [Ca(2+)](i), are presented as brief spikes organized into regenerative Ca(2+) waves. Ca(2+)-mediated signaling pathways have also been shown to play important roles in carcinogenesis such as transformation of normal cells to cancerous cells, tumor formation and growth, invasion, angiogenesis and metastasis. Since the global Ca(2+) oscillations arise from Ca(2+) waves initiated locally, it results in stochastic oscillations because although each cell has many IP(3)Rs and Ca(2+) ions, the law of large numbers does not apply to the initiating event which is restricted to very few IP(3)Rs due to steep Ca(2+) concentration gradients. The specific Ca(2+) signaling information is likely to be encoded in a calcium code as the amplitude, duration, frequency, waveform or timing of Ca(2+) oscillations and decoded again at a later stage. Since Ca(2+) channels or pumps involved in regulating Ca(2+) signaling pathways show altered expression in cancer, one can target these Ca(2+) channels and pumps as therapeutic options to decrease proliferation of cancer cells and to promote their apoptosis. These studies can provide novel insights into alterations in Ca(2+) wave patterns in carcinogenesis and lead to the development of newer technologies based on Ca(2+) waves for the diagnosis and therapy of cancer.

Endogenous human CaMKII inhibitory protein suppresses tumor growth by inducing cell cycle arrest and apoptosis through down-regulation of the phosphatidylinositide 3-kinase/Akt/HDM2 pathway

Inhibition of calcium/calmodulin-dependent protein kinase II (CaMKII) results in hypophosphorylation of CaMKII substrates and in some cases suppresses cell growth. We previously presented the first report of the human CaMKII inhibitory protein, hCaMKIINbeta. Here we report the functional characterization of hCaMKIINbeta in ovarian cancer cells. We showed that hCaMKIINbeta was highly expressed in normal ovarian tissues but was not detected in human ovarian adenocarcinoma, indicating that decreased expression of hCaMKIINbeta may be involved in the pathogenesis of human ovarian adenocarcinoma. As an endogenous CaMKII inhibitor, hCaMKIINbeta could significantly inhibit the growth of human ovarian cancer cells in vitro. In vivo, hCaMKIINbeta decreased the tumorigenicity and growth of HO-8910PM human ovarian cancer cells and prolonged the survival of tumor-bearing mice. hCaMKIINbeta blocked cell cycle progression and induced apoptosis of HO-8910PM cells, which was correlated with the up-regulation of p21, p53, and Bax and the down-regulation of cyclin A, cyclin D1, cyclin E, CDK2, phosphorylated retinoblastoma, and Bcl-2. We further demonstrated that hCaMKIINbeta-mediated CaMKII inhibition suppressed Akt activation, leading to the down-regulation of HDM2, which was responsible for the up-regulation of p53 and p21 in human ovarian cancer cells. The tumor-suppressive effect and the negative expression in human ovarian cancer tissues suggest that hCaMKIINbeta may play an important role in the regulation of tumor cell growth, possibly contributing to the development of new therapeutic strategies for ovarian cancer.

Ca2+ signalling checkpoints in cancer: remodelling Ca2+ for cancer cell proliferation and survival

Increases in cytosolic free Ca2+ ([Ca2+]i) represent a ubiquitous signalling mechanism that controls a variety of cellular processes, including proliferation, metabolism and gene transcription, yet under certain conditions increases in intracellular Ca2+ are cytotoxic. Thus, in using Ca2+ as a messenger, cells walk a tightrope in which [Ca2+]i is strictly maintained within defined boundaries. To adhere to these boundaries and to sustain their modified phenotype, many cancer cells remodel the expression or activity of their Ca2+ signalling apparatus. Here, we review the role of Ca2+ in promoting cell proliferation and cell death, how these processes are remodelled in cancer and the opportunities this might provide for therapeutic intervention.

Membrane depolarization stimulates the proliferation of SH-SY5Y human neuroblastoma cells by increasing retinoblastoma protein (RB) phosphorylation through the activation of cyclin-dependent kinase 2 (Cdk2)

Membrane depolarization causes transmembrane ionic influxes that induce various gene expressions, and is involved in the processes of neuronal differentiation and apoptosis. However, the effect of membrane depolarization on neuronal proliferation has not been established. In this study, we aimed to investigate the effect of membrane depolarization on the proliferation of SH-SY5Y human neuroblastoma cells. Membrane depolarization induced by 50 mM KCl for 5 min significantly increased SH-SY5Y cell numbers and thymidine incorporation at 24 h after depolarization, and increased the phosphorylation and expression of retinoblastoma protein (RB), the activity of Cdk2 (without changing the activities of Cdk4 and Cdk6), and the expressions of cyclin A and cyclin E. Single and repeated depolarization (once a day for 6 days) had similar effects on RB, Cdks, and cyclins levels and activities. In summary, our results suggest that membrane depolarization may stimulate cellular proliferation by augmenting the expression of cyclin E leading to increases in Cdk2 activity and RB phosphorylation.

A calmodulin-binding site on cyclin E mediates Ca2+-sensitive G1/s transitions in vascular smooth muscle cells

Calcium transients are known to control several transition points in the eukaryotic cell cycle. For example, we have previously shown that a coordinate elevation in the intracellular free calcium ion concentration is required for G1- to S-phase cell cycle progression in vascular smooth muscle cells (VSMC). However, the molecular basis for this Ca2+ sensitivity was not known. Using buffers with differing [Ca2+], we found that the kinase activity of mouse and human cyclin E/CDK2, but not other G1/S-associated cell cycle complexes, was responsive to physiological changes in [Ca2+]. We next determined that this Ca2+-responsive kinase activity was dependent on a direct interaction between calmodulin (CaM), one of the major Ca2+-signal transducers of eukaryotic cells, and cyclin E. Pharmacological inhibition of CaM abrogated the Ca2+ sensitivity of cyclin E/CDK2 and retarded mouse VSMC proliferation by causing G1 arrest. We next defined the presence of a highly conserved 22 amino acid N-terminal CaM-binding motif in mammalian cyclin E genes (dissociation constant, 1.5+/-0.1 micromol/L) and showed its essential role in mediating Ca2+-sensitive kinase activity of cyclin E/CDK2. Mutant human cyclin E protein, lacking this CaM-binding motif, was incapable of binding CaM or responding to [Ca2+]. Taken together, these findings reveal CaM-dependent cyclin E/CDK2 activity as a mediator of the known Ca2+ sensitivity of the G1/S transition of VSMC.

A role for voltage gated T-type calcium channels in mediating “capacitative” calcium entry?

Calcium entry through plasma membrane calcium channels is one of the most important cell signaling mechanism involved in such diverse functions as secretion, contraction and cell growth by regulating gene expression, proliferation and apoptosis. The identity of plasma membrane calcium channels, the main regulators of calcium entry, involved in cell proliferation has been thus extensively sought. Among these, a calcium entry pathway called capacitative calcium entry (CCE), activated by calcium store depletion, is particularly important in non-excitable cells. Though this capacitative calcium entry is generally supposed to occur through TRP channels there is some evidence that voltage-dependent T-type calcium channels may contribute to calcium entry after store depletion. Here we show that though mibefradil, a T-type calcium channel blocker, is able to reduce capacitative calcium entry induced by either thapsigargin or ATP, this was not mimicked by any other T-type calcium channel inhibitors even in cells overexpressing alpha(1H) T-type calcium channels, leading us to conclude that T-type calcium channels are not responsible for the capacitative calcium entry observed in different cancer cell lines. On the contrary, we show that the action of mibefradil on capacitative calcium entry is due to an action on store-operated calcium channels.

Recent advances in Ca2+-dependent Ras regulation and cell proliferation

Our understanding of the mechanisms whereby growth factors stimulate cell proliferation through the Ras pathway stems largely from studies of the canonical pathway involving recruitment of Ras activators and inhibitors to the vicinity of receptor tyrosine kinases via phosphotyrosine-binding adaptor proteins. Ca(2+) has seldom joined the party, despite the identification of phospholipase Cgamma and Ca(2+) entry as receptor tyrosine kinase-dependent signals. Mechanisms by which Ca(2+) can directly influence Ras activity have remained relatively elusive. Similarly, the mechanisms whereby Ca(2+) modulates the cell cycle have been equally murky, and yet there are some interesting parallels in the role of Ras and Ca(2+) in cell cycle re-entry. This review focuses on a number of novel mechanisms that link Ca(2+) with the regulation of Ras activity and signaling output. Their collective discovery adds to the complexities of Ras regulation and raises further questions about the role of Ca(2+) signals in Ras-dependent cell proliferation.

Influence of DL-beta-hydroxybutyric acid on cell proliferation and calcium influx

Poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx), a member of the polyhydroxyalkanoate family of biopolyesters, has superior mechanical properties and biocompatibilities that enable it to meet diverse biomedical requirements. The main component of PHBHHx is DL-beta-hydroxybutyric acid (HB), a ketone body that is also produced in vivo. The effects of HB treatment on murine fibroblast L929 cells, human umbilical vein endothelial cells, and rabbit articular cartilages were investigated. HB (0.005-0.10 g/L) promoted cell proliferation for each cell line. Cell cycle analysis indicated that HB had a stimulatory effect on DNA synthesis. Flow cytometric analysis of L929 cells revealed changes in the [Ca2+]i for different stages of the cell cycle. In L929 cells, HB (0.02 g/L) stimulated a rapid increase in the concentration of cytosolic calcium that was blocked by verapamil and diltiazem, inhibitors of L-type Ca2+ channels. Finally, verapamil inhibited HB-induced L929 cell proliferation. Collectively, these results indicated that HB had a stimulatory effect on cell cycle progression that is mediated by a signaling pathway dependent upon increases in [Ca2+]i. This trophic effect may underlie the good biocompatibility observed for PHBHHx.

Regulation of cyclin D1/Cdk4 complexes by calcium/calmodulin-dependent protein kinase I

The selective inhibitor of the multifunctional calcium/calmodulin-dependent kinases (CaMK), KN-93, arrests a variety of cell types in G(1). However, the biochemical nature of this G(1) arrest point and the physiological target of KN-93 in G(1) remain controversial. Here we show that in WI-38 human diploid fibroblasts KN-93 reversibly arrested cells in late G(1) prior to detectable cyclin-dependent kinase 4 (cdk4) activation. At the KN-93 arrest point, we found that cyclin D1/cdk4 complexes had assembled with p21/p27, accumulated in the nucleus, and become phosphorylated on Thr-172, yet were relatively inactive. Additional examination of cdk4 complexes by gel filtration analysis demonstrated that, in late G(1), cyclin D1-containing complexes migrated toward lower molecular weight (M(r)) fractions and this altered migration was accompanied by the appearance of two peaks of cdk4 activity, at 150-200 and 70 kDa, respectively. KN-93 prevented both the activation of cdk4, and this shift in cyclin D1 migration and overexpression of cyclin D1/cdk4 overcame the KN-93 arrest. To determine which multifunctional CaMK acts in G(1), we expressed kinase-deficient forms of CaMKI and CaMKII. Overexpression of kinase-deficient CaMKI, but not CaMKII, prevented cdk4 activation, mimicking the KN-93 arrest point. Therefore, we hypothesize that KN-93 prevents a very late, uncharacterized step in cyclin D/cdk4 activation that involves CaMKI and follows complex assembly, nuclear entry, and phosphorylation.

Ca2+/calmodulin-dependent modulation of cell cycle elements pRb and p27kip1 involved in the enhanced proliferation of lymphoblasts from patients with Alzheimer dementia

Failure of cell cycle regulation in neurons might be critically involved in the process of neurodegeneration in Alzheimer's disease (AD). We present here evidence to support the hypothesis that cell cycle alterations occur in cells other than neurons in AD sufferers. Lymphocytes from AD patients immortalized with Epstein-Barr virus showed an enhanced rate of proliferation and increased phosphorylation of the retinoblastoma protein (pRb) and other members of the family of pocket proteins compared with cell lines derived from normal age-matched controls. The calmodulin antagonist calmidazolium, as well as W-7 and W-13, abrogated the enhanced activity of AD cells without altering the normal basal rate of proliferation. The effect of calmidazolium was accompanied by partially dephosphorylation of pRb. No changes were found in the expression levels of the G1 cyclin/Cdks complexes. However, lymphoblasts derived from AD patients showed reduced levels of the Cdk inhibitor p27(kip1), which were restored after anti-calmodulin treatment of the cultures. These observations suggest that in AD cells the enhanced rates of cell proliferation and phosphorylation of pRb and the intracellular content of p27(kip1) may be interrelated events controlled by a mechanism dependent on the Ca(2+)/calmodulin signaling pathway. The distinct functional features of lymphoblastoid cells from AD patients offer an invaluable, noninvasive tool to investigate the etiopathogenesis, and eventually, for the early diagnosis and prognosis of this devastating disease.

Effects of Ca(2+) influx through nonselective cation channel on noradrenaline-induced mitogenic responses

We have recently shown that noradrenaline induces extracellular Ca(2+) influx through nonselective cation channel (NSCC) in Chinese hamster ovary cells expressing alpha(1A)-adrenoceptors (CHO-alpha(1A)). Moreover, this NSCC is sensitive to (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]-acetamide (LOE 908) and resistant to 1-[b-(3-[4-Methoxyphenyl]propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride (SK&F 96365). In the present study, we characterized the effects of extracellular Ca(2+) influx through NSCC on noradrenaline-induced mitogenic responses and activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) of CHO-alpha(1A) using LOE 908 and SK&F 96365. Noradrenaline induced a mitogenic response in CHO-alpha(1A). LOE 908 completely inhibited the noradrenaline-induced mitogenesis, whereas SK&F 96365 did not inhibit it. The IC(50) value of LOE 908 for noradrenaline-induced mitogenesis was similar to that for the noradrenaline-induced increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)). Noradrenaline stimulated ERK1/2 activity. The magnitude of noradrenaline-induced ERK1/2 activity in the absence of extracellular Ca(2+) was 40% of that in the presence of extracellular Ca(2+). LOE 908 partially (60%) inhibited the noradrenaline-induced ERK1/2 activity, whereas SK&F 96365 did not inhibit it. The IC(50) value of LOE 908 for noradrenaline-induced ERK1/2 activity was similar to that for the noradrenaline-induced increase in [Ca(2+)](i). Collectively, these results demonstrate that extracellular Ca(2+) influx through LOE 908-sensitive and SK&F 96365-resistant NSCC may be essential for noradrenaline-induced mitogenesis in CHO-alpha(1A). Moreover, the noradrenaline-induced ERK1/2 activity involves two distinct pathways, one dependent on extracellular Ca(2+) influx through NSCC, whereas the other is independent of the influx.

Ca(2+) channels involved in endothelin-induced mitogenic response in carotid artery vascular smooth muscle cells

Endothelin (ET)-1 activates two types of Ca(2+)-permeable nonselective cation channels (NSCC-1 and NSCC-2) and a store-operated Ca(2+) channel (SOCC) in rabbit internal carotid artery (ICA) vascular smooth muscle cells (VSMCs) in addition to the voltage-operated Ca(2+) channel (VOCC). These channels can be discriminated using the Ca(2+) channel blockers SK&F-96365 and LOE-908. SK&F-96365 is sensitive to NSCC-2 and SOCC, and LOE-908 is sensitive to NSCC-1 and NSCC-2. On the basis of sensitivity to nifedipine, a specific blocker of the L-type VOCC, VOCCs have a minor role in ET-1-induced mitogenesis. Both LOE-908 and SK&F-96365 inhibited ET-1-induced mitogenesis in a concentration-dependent manner, and the combination of LOE-908 and SK&F-96365 abolished it. The IC(50) values of these blockers for ET-1-induced mitogenesis correlated well with those of the ET-1-induced intracellular free Ca(2+) concentration responses. These results indicate that the inhibitory action of these blockers on ET-1-induced mitogenesis may be mediated by blockade of NSCC-1, NSCC-2, and SOCC. Collectively, extracellular Ca(2+) influx through NSCC-1, NSCC-2, and SOCC may be essential for ET-1-induced mitogenesis in ICA VSMCs.

Effects of extracellular Ca2+ influx on endothelin-1-induced intracellular mitogenic cascades in C6 glioma cells

We have recently shown that endothelin-1 activates two types of Ca2+-permeable nonselective cation channels (NSCC-1 and NSCC-2) in C6 glioma cells. These channels can be distinguished by their sensitivity to blockers of the receptor-operated Ca2+ channel, 1-[b-(3-[4-methoxyphenyl]propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride (SK&F 96365) and (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]-acetamide (LOE 908). NSCC-1 is sensitive to LOE 908 and resistant to SK&F 96365, whereas NSCC-2 is sensitive to both LOE 908 and SK&F 96365. Moreover, extracellular Ca2+ influx through these channels plays an essential role in endothelin-1-induced mitogenesis in C6 glioma cells. The purpose of the present study was to investigate the effects of extracellular Ca2+ influx on intracellular pathways of endothelin-1-induced mitogenic responses in C6 glioma cells. We focused on extracellular signal-regulated kinase 1 and 2 (ERK1/2) in this context. An inhibitor of mitogen-activated protein kinase, 2-[2-amino-3-methoxyphenyl]-4H-1-benzopyran-4-one (PD 98059), abolished the endothelin-1-induced increase in ERK1/2 activity, but only partially suppressed the mitogenic response. ERK1/2 activation by endothelin-1 was partially suppressed in the absence of extracellular Ca2+. On the basis of the sensitivity to LOE 908 and SK&F 96365, Ca2+ influx through NSCC-1 and NSCC-2 plays an essential role in the extracellular Ca2+-dependent component of ERK1/2 activity. In contrast, Ca2+ influx through NSCC-2 is involved in the ERK1/2-independent component of endothelin-1-induced mitogenesis. These results indicate that (1) the endothelin-1-induced mitogenic response involves both ERK1/2-dependent and -independent mechanisms, (2) ERK1/2 activation by endothelin-1 involves an extracellular Ca2+ influx-dependent cascade as well as an extracellular Ca2+ influx-independent cascade, (3) because endothelin-1-induced mitogenesis is completely dependent on extracellular Ca2+ influx, extracellular Ca2+ influx also plays an important role in mitogenic pathways downstream of ERK1/2, (4) extracellular Ca2+ influx through NSCC-1 and NSCC-2 has an important role in the extracellular Ca2+ influx-dependent component of ERK1/2-dependent mitogenesis, (5) extracellular Ca2+ influx through NSCC-2 has an important role in ERK1/2-independent mitogenesis, and (6) Ca2+ influx through each Ca2+ channel may play a distinct role in intracellular mitogenic cascades.

Ca(2+) influx through nonselective cation channels plays an essential role in endothelin-1-induced mitogenesis in C6 glioma cells

Ca(2+) channels activated by endothelin-1 (ET-1) in C6 glioma cells (C6 cells) were characterized using whole-cell patch-clamps and by monitoring the intracellular free Ca(2+) concentration ([Ca(2+)](i)), when administering Ca(2+) channel blockers such as LOE 908 and SK&F 96365. Using this methodology, the Ca(2+) channels involved in ET-1-induced mitogenesis were identified. The patch-clamp study and [Ca(2+)](i) monitoring showed that 10 nM ET-1 activated two types of Ca(2+)-permeable nonselective cation channels (NSCC); one was sensitive to LOE 908 but resistant to SK&F 96365 (NSCC-1) and the other was sensitive to both LOE 908 and SK&F 96365 (NSCC-2). Conversely, 0.1 nM ET-1 activated only NSCC-1.ET-1-induced mitogenesis in a concentration-dependent manner, with the maximum effect arising at concentrations > or =10 nM. LOE 908 completely suppressed the 10 nM ET-1-induced mitogenesis, whereas SK&F 96365 only partially suppressed it. The IC(50) values of these blockers for the ET-1-induced mitogenesis were similar to those for the 10 nM ET-1-induced increase in [Ca(2+)](i). In contrast, LOE 908 completely suppressed 0.1 nM ET-1-induced mitogenesis, whereas SK&F 96365 did not affect it.Collectively, these results demonstrate that the sustained increase in [Ca(2+)](i), via NSCC-1 and NSCC-2, may be essential for ET-1-induced mitogenesis in C6 cells. Moreover, the sensitivity of NSCC-1 to ET-1 is higher than that of NSCC-2 to ET-1.

Calmodulin protects cells from death under normal growth conditions and mitogenic starvation but plays a mediating role in cell death upon B-cell receptor stimulation

Calmodulin (CaM) is the main intracellular Ca2+ sensor protein responsible for mediating Ca2+ triggered processes. Chicken DT40 lymphoma B cells express CaM from the two genes, CaMI and CaMII. Here we report the phenotypes of DT40 cells with the CaMII gene knocked out. The disruption of the CaMII gene causes the intracellular CaM level to decrease by 60%. CaMII-/- cells grow more slowly and die more frequently as compared to wild type (wt) cells but do not exhibit significant differences in their cell cycle profile. Both phenotypes are more pronounced at reduced serum concentrations. Upon stimulation of the B-cell receptor (BCR), the resting Ca2+ levels remain elevated after the initial transient in CaMII-/- cells. Despite higher Ca2+ resting levels, the CaMII-/- cells are partially protected from BCR induced apoptosis indicating that CaM plays a dual role in apoptotic processes.

Induction of replicative senescence biomarkers by sublethal oxidative stresses in normal human fibroblast

We tested the long-term effects of sublethal oxidative stresses on replicative senescence. WI-38 human diploid fibroblasts (HDFs) at early cumulative population doublings (CPDs) were exposed to five stresses with 30 microM tert-butylhydroperoxide (t-BHP). After at least 2 d of recovery, the cells developed biomarkers of replicative senescence: loss of replicative potential, increase in senescence-associated beta-galactosidase activity, overexpression of p21(Waf-1/SDI-1/Cip1), and inability to hyperphosphorylate pRb. The level of mRNAs overexpressed in senescent WI-38 or IMR-90 HDFs increased after five stresses with 30 microM t-BHP or a single stress under 450 microM H(2)O(2). These corresponding genes include fibronectin, osteonectin, alpha1(I)-procollagen, apolipoprotein J, SM22, SS9, and GTP-alpha binding protein. The common 4977 bp mitochondrial DNA deletion was detected in WI-38 HDFs at late CPDs and at early CPDs after t-BHP stresses. In conclusion, sublethal oxidative stresses lead HDFs to a state close to replicative senescence.

Rho kinase inhibitor HA-1077 prevents Rho-mediated myosin phosphatase inhibition in smooth muscle cells

In smooth muscle, a Rho-regulated system of myosin phosphatase exists; however, it has yet to be established whether Rho kinase, one of the downstream effectors of Rho, mediates the regulation of myosin phosphatase activity in vivo. In the present study, we demonstrate in permeabilized vascular smooth muscle cells (SMCs) that the vasodilator 1-(5-isoquinolinesulfonyl)-homopiperazine (HA-1077), which we show to be a potent inhibitor of Rho kinase, dose dependently inhibits Rho-mediated enhancement of Ca(2+)-induced 20-kDa myosin light chain (MLC(20)) phosphorylation due to abrogating Rho-mediated inhibition of MLC(20) dephosphorylation. By an immune complex phosphatase assay, we found that guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) stimulation of permeabilized SMCs caused a decrease in myosin phosphatase activity with an increase in the extent of phosphorylation of the 130-kDa myosin-binding regulatory subunit (MBS) of myosin phosphatase in a Rho-dependent manner. HA-1077 abolished both of the Rho-mediated events. Moreover, we observed that the pleckstrin homology/cystein-rich domain protein of Rho kinase, a dominant negative inhibitor of Rho kinase, inhibited GTPgammaS-induced phosphorylation of MBS. These results provide direct in vivo evidence that Rho kinase mediates inhibition of myosin phosphatase activity with resultant enhancement of MLC(20) phosphorylation in smooth muscle and reveal the usefulness of HA-1077 as a Rho kinase inhibitor.

Correlation between Ca(2+) oscillation and cell proliferation via CCK(B)/gastrin receptor

Gastrin stimulates cell proliferation through the CCK(B) receptor coupled to Gq-protein, whereas the m3 muscarinic receptor, which also couples to Gq, has no trophic effects. In order to elucidate the cause of the difference, we stably transfected CHO cells with human CCK(B) and m3 receptors. Stimulation of the CCK(B), but not the m3 receptor increased cell growth. Activation of MAP kinase via the m3 receptor was to the same extent as that via CCK(B), indicating that there is an initial signaling common to both receptors. Stimulation of either receptor induced a transient increase in [Ca(2+)](i) followed by a sustained plateau phase. After 2 h of stimulation, the [Ca(2+)](i) response to the m3 receptor disappeared, whereas that to the CCK(B) receptor remained as a [Ca(2+)](i) oscillation. Removal of extracellular Ca(2+), which abolished [Ca(2+)](i) oscillation, completely inhibited DNA synthesis via CCK(B). When the C-terminal part of the CCK(B) receptor was truncated, the trophic effect as well as the [Ca(2+)](i) response after 2 h of stimulation disappeared, whereas the chimeric CCK(B) receptor with the C-terminal region of the m3 receptor preserved its ability to elicit both DNA synthesis and [Ca(2+)](i) oscillation. These results suggest that desensitization might be a principal determinant of cell proliferation, and the persistence of the [Ca(2+)](i) response as [Ca(2+)](i) oscillation could be essential for this type of signal transduction.

rab5 GTPase regulates adenovirus endocytosis

Adenovirus interaction with alphav integrins is important for virus entry. We have examined the effects of adenovirus attachment on intracellular signaling in HeLa cells, with an emphasis on pathways known to be activated following integrin interaction with other ligands. We found no evidence for [Ca(2+)](c)-mediated signaling or for tyrosine phosphorylation of pp125(FAK), p130(CAS), and paxillin. However, adenovirus attachment is known to activate phosphatidylinositol-3 kinase, which in turn may regulate endocytosis via rab5 GTPase. We found that adenovirus uptake was increased by overexpression of wild-type rab5 and decreased by dominant-negative rab5. These results indicate a role for rab5 in adenovirus entry.

Downregulation of delta CaM kinase II in human tumor cells

Over two dozen alternative splice variants of CaMK-II, the type II Ca(2+)/CaM-dependent protein kinase, are encoded from four genes (alpha, beta, gamma and delta) in mammalian cells. Isozymes of alpha and beta CaMK-II are well characterized in brain; however, an understanding of the relative endogenous levels of CaMK-II isozymes in a wide variety of non-neuronal cells has not yet been described. In this study, we have demonstrated that CaMK-II consists primarily of the 54 kDa delta CaMK-II (delta(2) or delta(C)) isozyme in rodent fibroblasts. beta and gamma CaMK-II isozymes are minor and alpha CaMK-II was not expressed. The primary delta CaMK-II in human fibroblasts and the MCF10A mammary epithelial cell line was the 52 kDa delta(4) CaMK-II, an isozyme identical to delta(2) except for a missing 21-amino-acid C-terminal tail. delta CaMK-II levels were diminished in both human and rodent fibroblasts after SV40 transformation and in the mammary adenocarcinoma MCF7 cell line when compared to MCF10A cells. In fact, most tumor cells exhibited CaMK-II specific activities which were two- to tenfold lower than in untransformed fibroblasts. We conducted complementary CaMK-II studies on the NGF-induced differentiation of rat PC-12 cells. Although no new synthesis of CaMK-II occurs, neurite outgrowth in these cells is accompanied by a preferential activation of delta CaMK-II. Endogenous delta CaMK-II has a perinuclear distribution in fibroblasts and extends along neurites in PC-12 cells. These findings point to a role for delta CaMK-II isozymes in cellular differentiation.

Calmodulin binds to p21(Cip1) and is involved in the regulation of its nuclear localization

p21(Cip1), first described as an inhibitor of cyclin-dependent kinases, has recently been shown to have a function in the formation of cyclin D-Cdk4 complexes and in their nuclear translocation. The dual behavior of p21(Cip1) may be due to its association with other proteins. Different evidence presented here indicate an in vitro and in vivo interaction of p21(Cip1) with calmodulin: 1) purified p21(Cip1) is able to bind to calmodulin-Sepharose in a Ca(2+)-dependent manner, and this binding is inhibited by the calmodulin-binding domain of calmodulin-dependent kinase II; 2) both molecules coimmunoprecipitate when extracted from cellular lysates; and 3) colocalization of calmodulin and p21(Cip1) can be detected in vivo by electron microscopy immunogold analysis. The carboxyl-terminal domain of p21(Cip1) is responsible for the calmodulin interaction, since p21(145-164) peptide is also able to bind calmodulin and to compete with full-length p21(Cip1) for the calmodulin binding. Because treatment of cells with anti-calmodulin drugs decreases the nuclear accumulation of p21(Cip1), we hypothesize that calmodulin interaction with p21(Cip1) is important for p21(Cip1), and in consequence for cyclin D-Cdk4, translocation into the cell nucleus.

Fibroblast growth factor signaling regulates growth and morphogenesis at multiple steps during brain development

The fibroblast growth factor (FGF) family comprises several members with distinct patterns of expression in the developing central nervous system. FGFs regulate the early specification and the subsequent growth of central nervous system regions. These different actions require the coordinated activation of distinct sets of target genes by FGFs at the appropriate stage of development. The role of FGF2 in the growth and morphogenesis of the cerebral cortex is reviewed in detail. The cellular and molecular mechanisms that underlie the action of FGF2 on cortical development are discussed.

The retinoblastoma susceptibility gene product/Sp1 signalling pathway is modulated by Ca2+/calmodulin kinases II and IV activity

To investigate the possible link between Ca2+ signalling and cell cycle control we analysed Ca2+/calmodulin kinases (CamK) interaction with the retinoblastoma susceptibility gene product/SP1 pathway. CamK II and IV activate c-fos transcription through a short promoter region (-99 to -53) containing the retinoblastoma control element (RCE) and a cAMP response element (CRE) related sequences. Deletion analysis revealed that the RCE is a major CamK responsive element and is sufficient to confer CamK and Ca2+ regulation to a minimal promoter. Direct interactions between SP1 and RCE were confirmed by gel shift experiments. Using transient transfection experiments, we show that CamK-dependent transcription is regulated by the retinoblastoma (Rb) susceptibility gene product and the p107 Rb related protein. However, the stimulatory effects of CamKs and Rb on c-fos are blocked by overexpression of both proteins. These effects appear to be directly mediated by SP1 as shown by the use of a Gal4/SP1 fusion proteins. In conclusion, CamK II and IV, two major Ca2+-dependent intracellular effectors, may represent a molecular link between this second messenger transduction pathway and effectors that control cell cycle progression through Rb/SP1 signalling pathway.