Phosphatidylinositol-3-kinase activation and atypical protein kinase C zeta phosphorylation characterize the DMSO signalling in erythroleukemia cells

Heterogeneous Off-Target Effects of Ultra-Low Dose Dimethyl Sulfoxide (DMSO) on Targetable Signaling Events in Lung Cancer In Vitro Models

Targetable alterations in cancer offer novel opportunities to the drug discovery process. However, pre-clinical testing often requires solubilization of these drugs in cosolvents like dimethyl sulfoxide (DMSO). Using a panel of cell lines commonly used for in vitro drug screening and pre-clinical testing, we explored the DMSO off-target effects on functional signaling networks, drug targets, and downstream substrates. Eight Non-Small Cell Lung Cancer (NSCLC) cell lines were incubated with three concentrations of DMSO (0.0008%, 0.002%, and 0.004% v/v) over time. Expression and activation levels of 187 proteins, of which 137 were kinases and downstream substrates, were captured using the Reverse Phase Protein Array (RPPA). The DMSO effect was heterogeneous across cell lines and varied based on concentration, exposure time, and cell line. Of the 187 proteins measured, all were statistically different in at least one comparison at the highest DMSO concentration, followed by 99.5% and 98.9% at lower concentrations. Only 46% of the proteins were found to be statistically different in more than 5 cell lines, indicating heterogeneous response across models. These cell line specific alterations modulate response to in vitro drug screening. Ultra-low DMSO concentrations have broad and heterogeneous effects on targetable signaling proteins. Off-target effects need to be carefully evaluated in pre-clinical drug screening and testing.

Combined inhibition of PI3K and activation of MAPK p38 signaling pathways trigger erythroid alternative splicing switch of 4.1R pre-mRNA in DMSO-induced erythroleukemia cells

There is increasing evidence showing that many extracellular cues modulate pre-mRNA alternative splicing, through different signaling pathways. We here show that 4.1R exon 16 splicing is altered in response to specific signals. The switch from erythroblastic isoform lacking exon 16 to mature erythrocytic isoform containing this exon is tightly regulated during late erythroid differentiation, and blocage of this splicing switch in erythroleukemia cells is seen as a consequence of the deregulation of important regulatory pathways. We support that combined inhibition of PI3K and activation of p38 signaling pathways impinge on erythroid 4.1R pre-mRNA alternative splicing switch, and on cell differentiation as witnessed by hemoglobin production. By contrast, MEK/ERK signaling appeared not to affect neither cell hemoglobin production nor erythroid 4.1R pre-mRNA splicing. We also found that the signal-induced alternative splicing is not typically distinctive of EPO-non-responsive cells, but operates in EPO-responsive cells as well. Pre-mRNA splicing is a major regulatory mechanism at the crossroad between transcription and translation. We here provide evidence that inhibition of PI3K activates the splicing switch in a promoter-dependent manner, whereas p38 activation induces this event in a promoter-independent fashion. Our data further support that constitutive activation of EPO-R by the viral protein gp55 and the short form of the tyrosine kinase receptor Stk, transduces PI3K proliferation signal, but not MAPK p38 differentiation signal. Concurrently, this work lend credence to the concept that DMSO triggers transient activation of p38 signaling and irreversible inhibition of PI3K/AKT signaling pathway, hence uncovering an old conundrum regarding the mechanism by which DMSO induces erythroleukemia cell differentiation.

Subtle distinct regulations of late erythroid molecular events by PI3K/AKT-mediated activation of Spi-1/PU.1 oncogene autoregulation loop

Spi-1/PU.1 oncogene is downregulated as proerythroblasts undergo terminal differentiation. Insertion of the Friend virus upstream of the Spi-1/PU.1 locus leads to the constitutive upregulation of Spi-1/PU.1, and a subsequent block in the differentiation of the affected erythroblasts. We have shown that sustained overexpression of Spi-1/PU.1 also inhibits the erythroid splicing of protein 4.1R exon 16, irrespective of chemical induction of differentiation. Here, we show a positive feedback loop that couples constitutive phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling to high expression of Spi-1/PU.1 in Friend erythroleukemia cells. Inhibition of PI3K/AKT results in Spi-1/PU.1 downregulation in a stepwise manner and induces cell differentiation. Chromatin immunoprecipitation assays further supported the positive autoregulatory effect of Spi-1/PU.1. Mutational analysis indicated that Ser41, but not Ser148, is necessary for Spi-1/PU.1-mediated repression of hemoglobin expression, whereas both Ser residues are required for Spi-1/PU.1 inhibition of the erythroid splicing event. We further show that inhibition of the erythroid transcriptional and splicing events are strictly dependent on distinct Spi-1/PU.1 phosphorylation modifications rather than Spi-1/PU.1 expression level per se. Our data further support the fact that Spi-1/PU.1 inhibits 4.1R erythroid splicing through two different pathways, and bring new insights into the extracellular signal impact triggered by erythropoietin on late erythroid regulatory program, including pre-mRNA splicing.

The vitamin D receptor-mediated activation of phosphatidylinositol 3-kinase (PI3Kα) plays a role in the 1α,25-dihydroxyvitamin D3-stimulated increase in steroid sulphatase activity in myeloid leukaemic cell lines

In this article we show that 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) stimulates the activity of the class IA phosphatidylinositol 3-kinase PI3Kalpha and its downstream target Akt in HL60, U937 and THP-1 myeloid leukaemic cell lines. Furthermore, we show that the classical nuclear vitamin D receptor (VDR(nuc)) is involved in this activation of the PI3K/Akt signalling in these cell lines. We have previously shown that the activity of steroid sulphatase is stimulated in HL60, U937 and THP-1 myeloid leukaemic cell lines by 1alpha,25(OH)(2)D(3) (Hughes et al., [2001] Biochem J 355:361-371; Hughes et al., [2005] J Cell Biochem 94:1175-1189; Hughes and Brown [2006] J Cell Biochem 98:590-617). In this article we show that the 1alpha,25(OH)(2)D(3)-stimulated increase in signalling via the PI3K/Akt pathway plays a role in the increase in steroid sulphatase activity in the HL60 U937 and THP-1 cell lines. We used a variety of pharmacological and biochemical approaches to show that activation of PI3Kalpha mediates the 1alpha,25(OH)(2)D(3)-stimulated increase in steroid sulphatase activity in myeloid leukaemic cells. We also show that the PI3K/Akt dependent activation of NF-kappaB plays a role in the 1alpha,25(OH)(2)D(3)-stimulated increase in steroid sulphatase activity in myeloid leukaemic cells.

Parallel regulation of PKC-alpha and PKC-delta characterizes the occurrence of erythroid differentiation from human primary hematopoietic progenitors

OBJECTIVE

Erythroid differentiation is a process characterized by modulation of different proteins including phosphoinositide-related enzymes such as protein kinase C (PKC) isoforms. Because in different cell lines PKC-alpha and PKC-delta have been reported to be involved in the mechanisms controlling proliferation and differentiation, the aim of this study was to examine the relative involvement of these PKC isoforms in the development of CD235a+ erythroid cells from human healthy hematopoietic progenitors.

MATERIALS AND METHODS

Erythroid differentiation from human primary hematopoietic progenitor cells was achieved by adopting the human erythroblasts mass amplification culture. Expression and activity of PKC isoforms and their relationship with proliferation and differentiation were investigated by morphologic analysis, reverse-transcriptase polymerase chain reaction, Western blotting, multiparametric flow cytometry, and transfection experiments.

RESULTS

PKC-alpha was found expressed and phosphorylated in cells undergoing both proliferation and differentiation, although PKC-delta, largely expressed and activated during proliferation, was evidently downregulated during differentiation. Overexpression of PKC-delta-CAT scarcely influenced the development of glycophorin-A (CD235a)+ erythroid cells from hematopoietic progenitors, although overexpression of PKC-alpha-CAT strongly induced the development of CD235a+ erythroid cells. On the other hand, in PKC-alpha-CAT-transfected cells, pharmacologic inhibition of PKC-delta further increased the number of CD235a+ cells, although inhibition of PKC-alpha resulted in an evident impairment of the development of CD235a+ erythroid cells.

CONCLUSIONS

Our results indicate that the suppression or at least a strong downregulation of PKC-delta, concomitant to PKC-alpha expression and activity, might be a cofactor to be further investigated and might be involved in the events regulating erythropoietin-induced erythroid differentiation from human primary hematopoietic progenitor cells.

Cyclic nucleotide response element binding (CREB) protein activation is involved in K562 erythroleukemia cells differentiation

K562 are human erythroleukemia cells inducible to differentiate into megakaryocytic or erythroid lineage by different agents. Cyclic nucleotide Response Element Binding (CREB) protein, a nuclear transcription factor which mediates c-AMP signaling, is a potential candidate involved in the occurrence of erythroid differentiation and adaptive response. Here we investigated signaling events in K562 cells induced with 30 microM hemin to undergo erythroid differentiation. CREB activation was detected early 1 h after hemin treatment and up to 4 and 6 days of treatment, when K562 terminal differentiation occurs together with caspase-3 maximal activation and PARP degradation. It was interesting to note that after hemin treatment in the presence of SB203580, p38 MAP kinase specific inhibitor, a reduced rate of CREB phosphorylation as well as a lower percentage of CD71/Gly+ (Glycophorin A) cells were detectable, demonstrating the p38 MAP kinase dependency of these phenomena. All in all these results document a novel relationship between CREB activation and differentiation-related apoptotic cell death and assign a role to p38 MAP kinase pathway in determining these events in K562 erythroleukemia cells.

Nuclear protein kinase C-delta: a possible check-point of cell cycle progression

Protein kinase Cs (PKCs) belong to a serine/threonine kinase family, ubiquitously expressed and claimed to be involved in physiological processes including apoptosis, cell growth and differentiation. The question of the subcellular localization and activity of PKCs remains to be clarified. Here we report that nuclear PKC-delta cooperates to regulate the S-G2/M phase transition of cell cycle, apparently being associated to chromosome condensation and alignment on the metaphase plate.

Erythroid cell differentiation is characterized by nuclear matrix localization and phosphorylation of protein kinases C (PKC) alpha, delta, and zeta

Protein kinases C (PKC) zeta expression and phosphorylation at nuclear level during dimethyl sulfoxide (DMSO)-induced differentiation in Friend erythroleukemia cells have been previously reported, suggesting a possible role of this PKC isoform in the DMSO-related signaling. In order to shed more light on this tantalizing topic, we investigated PKC intracellular and sub-cellular localization and activity during DMSO-induced erythroid differentiation. Results indicated that at least PKC alpha, zeta, and delta are strongly and temporally involved in the DMSO-induced differentiation signals since their expression and phosphorylation, though at different extents, were observed during treatments. Intriguingly, while PKC alpha and zeta associate to the nuclear matrix during the differentiation event, PKC delta appears to be residentially associated to the nuclear matrix. Furthermore, an evident downregulation of the beta-globin gene transcription (differentiation hallmark) was detected upon a progressive inhibition of these PKC isoforms by means of specific inhibitors, indicating, therefore, that PKC alpha, zeta, and delta phosphorylation play a crucial role in the control of erythroid differentiation.

Differential regulation of smooth muscle markers in human bone marrow-derived mesenchymal stem cells

OBJECTIVE

To study smooth-muscle differentiation and de-differentiation of human bone marrow-derived mesenchymal stem cells (MSCs), which have been shown to enter the circulation and to contribute to vascular repair and atherosclerosis.

DESIGN

Human MSCs from bone marrow were cultured with 20% fetal calf serum (FCS) or with 10% FCS and various concentrations of dimethyl sulfoxide (DMSO). Expression of smooth muscle markers was determined by Western blot analysis and immunofluorescence. For signalling studies, involvement of the mammalian target of rapamycin (mTOR) pathway was tested by treatment with rapamycin.

RESULTS

MSCs cultured with 20% FCS acquired a smooth muscle-like appearance and expressed the smooth muscle (sm) markers sm-alpha-actin, desmin, sm-calponin and myosin light chain kinase (MLCK). DMSO induced a spindle-like morphology with marked reduction of stress fibers. As judged by Western blot analysis, treatment with 2.5% DMSO strongly downregulated expression of sm-calponin (-85%), short MLCK (-98%) and sm-alpha-actin expression (-51%). Reduced calponin expression was detected by day 2 of treatment with 0.5-2.5% DMSO. After withdrawal of DMSO, MSCs regained high expression of sm-calponin. Treatment with 6 nmol/l rapamycin partly antagonized the effect of DMSO, indicating the involvement of mTOR in regulation of the smooth muscle phenotype of MSCs.

CONCLUSIONS

DMSO strongly downregulates the smooth muscle markers sm-calponin, short MLCK and sm-alpha-actin in human MSCs, indicating a transition from a smooth muscle-like phenotype to an undifferentiated state by an mTOR-dependent mechanism. Regulating the phenotype of human MSCs may be of relevance for novel therapeutic approaches in atherosclerosis and intimal hyperplasia after vascular injury.

PI3 kinase is important for Ras, MEK and Erk activation of Epo-stimulated human erythroid progenitors

Background

Erythropoietin is a multifunctional cytokine which regulates the number of erythrocytes circulating in mammalian blood. This is crucial in order to maintain an appropriate oxygen supply throughout the body. Stimulation of primary human erythroid progenitors (PEPs) with erythropoietin (Epo) leads to the activation of the mitogenic kinases (MEKs and Erks). How this is accomplished mechanistically remained unclear.

Results

Biochemical studies with human cord blood-derived PEPs now show that Ras and the class Ib enzyme of the phosphatidylinositol-3 kinase (PI3K) family, PI3K gamma, are activated in response to minimal Epo concentrations. Surprisingly, three structurally different PI3K inhibitors block Ras, MEK and Erk activation in PEPs by Epo. Furthermore, Erk activation in PEPs is insensitive to the inhibition of Raf kinases but suppressed upon PKC inhibition. In contrast, Erk activation induced by stem cell factor, which activates c-Kit in the same cells, is sensitive to Raf inhibition and insensitive to PI3K and PKC inhibitors.

Conclusions

These unexpected findings contrast with previous results in human primary cells using Epo at supraphysiological concentrations and open new doors to eventually understanding how low Epo concentrations mediate the moderate proliferation of erythroid progenitors under homeostatic blood oxygen levels. They indicate that the basal activation of MEKs and Erks in PEPs by minimal concentrations of Epo does not occur through the classical cascade Shc/Grb2/Sos/Ras/Raf/MEK/Erk. Instead, MEKs and Erks are signal mediators of PI3K, probably the recently described PI3K gamma, through a Raf-independent signaling pathway which requires PKC activity. It is likely that higher concentrations of Epo that are induced by hypoxia, for example, following blood loss, lead to additional mitogenic signals which greatly accelerate erythroid progenitor proliferation.

Inhibition of PI-3 kinase sensitizes human leukemic cells to histone deacetylase inhibitor-mediated apoptosis through p44/42 MAP kinase inactivation and abrogation of p21CIP1/WAF1 induction rather than AKT inhibition

Effects of the PI-3 kinase inhibitor LY294002 (LY) have been examined in relation to responses of human leukemia cells to histone deacetylase inhibitors (HDIs). Coexposure of U937 cells for 24 h to marginally toxic concentrations of LY294002 (e.g., 30 microM) and sodium butyrate (SB; 1 mM) resulted in a marked increase in mitochondrial damage (e.g., cytochrome c and Smac/DIABLO release, loss of DeltaPsi(m)), caspase activation, and apoptosis. Similar results were observed in Jurkat, HL-60, and K562 leukemic cells and with other HDIs (e.g., SAHA, MS-275). Exposure of cells to SB/LY was associated with Bcl-2 and Bid cleavage, XIAP and Mcl-1 downregulation, and diminished CD11b expression. While LY blocked SB-mediated Akt activation, enforced expression of a constitutively active (myristolated) Akt failed to attenuate SB/LY-mediated lethality. Unexpectedly, treatment of cells with SB+/-LY resulted in a marked reduction in phosphorylation (activation) of p44/42 mitogen-activated protein (MAP) kinase. Moreover, enforced expression of a constitutively active MEK1 construct partially but significantly attenuated SB/LY-induced apoptosis. Lastly, cotreatment with LY blocked SB-mediated induction of p21(CIP1/WAF1); moreover, enforced expression of p21(CIP1/WAF1) significantly reduced SB/LY-mediated apoptosis. Together, these findings indicate that LY promotes SB-mediated apoptosis through an AKT-independent process that involves MEK/MAP kinase inactivation and interference with p21(CIP1/WAF1) induction.

Terminal differentiation in vitro of patient-derived post-TMD megakaryoblastic AML cells

Differentiation induction is a therapeutic principle in acute promyelocytic leukemia (AML) using all- trans retinoic acid. In cell lines with properties of AML M6/M7 (K562 and CMK), differentiation towards megakaryopoietic and erythropoietic phenotypes can be induced in vitro. Transitory myeloproliferative disorder (TMD) is a self-limited disorder of newborn infants with Down syndrome, phenotypically resembling acute myeloid leukemia of megakaryoblastic lineage. Despite spontaneous disappearance of blasts from blood and bone marrow, in about 10% of the patients, overt acute megakaryoblastic leukemia (AML M7) develops up to 4 years later. Recently, mutations of the GATA1 transcription factor have been identified in the megakaryoblastic leukemia of Down syndrome. Here, we studied cells from a patient suffering from megakaryoblastic AML at the age of 2.5 years after spontaneous remission of neonatal TMD. In vitro, terminal differentiation towards a megakaryocyte-like phenotype could be induced by phorbol myristate acetate (PMA), with typical morphological features, upregulation of platelet-specific and downregulation of erythroid antigens, going along with downregulation of c-myc. Whether spontaneous resolution of TMD is a process due to terminal differentiation is still open; however, here we give evidence that in vitro differentiation can be induced even in blasts deriving from an overt AML French-American-British (FAB) M7 after TMD.

NF-kappaB activation plays an antiapoptotic role in human leukemic K562 cells exposed to ionizing radiation

Exposure of cells to ionizing radiation (IR) determines cellular lesions, such as DNA and membrane damage, which involve a coordinate network of signal transduction pathways responsible for resistance to or delay of apoptosis, depending on cell type and administered dose. Since, after IR exposure, the apoptotic profile appeared different in the two chosen cell lines K562 and Jurkat along with caspase-3 activation, we paid attention to the influence exerted by Protein kinase C delta on transcription factor NF-kappaB activation. Interestingly, K562 resist to IR carrying out a survival strategy which includes PKC delta/NF-kappaB pathway activation, probably mediated by novel IKKs and a role for PI-3-kinase in activating PKC delta at Thr 505 by PDK-1 phosphorylation is suggested. In addition, since caspase-3 is not activated in these cells upon ionizing radiation exposure, it could be supposed that NF-kappaB antagonizes apoptosis induction interfering with pathways which lead to caspase activation, may be by inducing expression of IAP, caspases 3, 7, 9, inhibitor. Thus NF-kappaB activation explains the resistance displayed by K562 to IR and drug potential interference directed to this protein could overcome apoptosis resistance in clinical settings.

Simultaneous changes in the function and expression of beta 1 integrins during the growth arrest of poorly differentiated colorectal cells (LISP-1)

Cells usually lose adhesion and increase proliferation and migration during malignant transformation. Here, we studied how proliferation can affect the other two characteristics, which ultimately lead to invasion and metastasis. We determined the expression of beta 1 integrins, as well as adhesion and migration towards laminin-1, fibronectin, collagens type I and type IV presented by LISP-1 colorectal cancer cells exposed to 2.5% dimethyl sulfoxide (DMSO), an agent capable of decreasing proliferation in this poorly differentiated colorectal cell line. Untreated cells (control), as shown by flow cytometry and monoclonal antibodies, expressed alpha 2 (63.8 11.3% positive cells), alpha 3 (93.3 7.0%), alpha 5 (50.4 12.0%) and alpha 6 (34.1 4.9%) integrins but not alpha1, alpha 4, alpha v or 4. Cells adhered well to laminin-1 (73.4 6.0%) and fibronectin (40.0 2.0%) substrates but very little to collagens. By using blocking monoclonal antibodies, we showed that alpha 2, alpha 3 and alpha 6 mediated laminin-1 adhesion, but neither alpha 3 nor alpha 5 contributed to fibronectin adherence. DMSO arrested cells at G0/G1 (control: 55.0 2.4% vs DMSO: 70.7 2.5%) while simultaneously reducing alpha 5 (24.2 19%) and alpha 6 (14.3 10.8%) expression as well as c-myc mRNA (7-fold), the latter shown by Northern blotting. Although the adhesion rate did not change after exposure to DMSO, alpha 3 and alpha 5 played a major role in laminin-1 and fibronectin adhesion, respectively. Migration towards laminin-1, which was clearly increased upon exposure to DMSO (control: 6 2 cells vs DMSO: 64 6 cells), was blocked by an antibody against alpha 6. We conclude that the effects of DMSO on LISP-1 proliferation were accompanied by concurrent changes in the expression and function of integrins, consequently modulating adhesion/migration, and revealing a complex interplay between function/expression and the proliferative state of cells.

Role of nuclear PKC delta in mediating caspase-3-upregulation in Jurkat T leukemic cells exposed to ionizing radiation

The response of Jurkat T cells to ionizing radiation (IR) includes cell cycle arrest and DNA damage, which lead to the occurrence of apoptosis. Here, we try to elucidate some of the early intracellular signals which control the induction of such a process upon IR exposure, addressing to examine the specific role of several PKC isoforms (delta, epsilon, zeta) and their subcellular distribution. Attention has been focused on the connections between nuclear PKC delta activation and the expression of cell death regulators (Bcl-2 family proteins Bad, Bax and Bcl-2) and cell death effector caspase-3 (CPP32) which lead to the cleavage of cytoskeletal and nuclear proteins and induction of apoptosis. Altogether these results let us to conclude that PKC delta, potentiating the pro-apoptotic effect of caspase 3, plays a key role in the cellular response to IR and thus can be considered a molecular target for therapy.

Protein kinase C zeta nuclear translocation mediates the occurrence of radioresistance in friend erythroleukemia cells

Friend erythroleukemia cells require high doses (15 Gy) of ionizing radiation to display a reduced rate of proliferation and an increased number of dead cells. Since ionizing radiation can activate several signaling pathways at the plasma membrane which can lead to the nuclear translocation of a number of proteins, we looked at the intranuclear signaling system activated by Protein Kinases C, being this family of enzymes involved in the regulation of cell growth and death. Our results show an early and dose-dependent increased activity of zeta and epsilon isoforms, although PKC zeta is the only isoform significantly active and translocated into the nuclear compartment upon low (1.5 Gy) and high (15 Gy) radiation doses. These observations are concomitant and consistent with an increase in the anti-apoptotic protein Bcl-2 level upon both radiation doses. Our results point at the involvement of the PKC pathway in the survival response to ionizing radiation of this peculiar cell line, offering PKC zeta for consideration as a possible target of pharmacological treatments aimed at amplifying the effect of such a genotoxic agent.

Role of PKCalpha in feedback regulation of Na(+) transport in an electrically tight epithelium

It has long been known that Na(+) channels in electrically tight epithelia are regulated by homeostatic mechanisms that maintain a steady state and allow new levels of transport to be sustained in hormonally challenged cells. Little is known about the potential pathways involved in these processes. In addition to short-term effect, recent evidence also indicates the involvement of PKC in the long-term regulation of the epithelial Na(+) channel (ENaC) at the protein level (40). To determine whether stimulation of ENaC involves feedback regulation of PKC levels, we utilized Western blot analysis to determine the distribution of PKC isoforms in polarized A6 epithelia. We found the presence of PKC isoforms in the conventional (alpha and gamma), novel (delta, eta, and epsilon), and atypical (iota, lambda, and zeta) groups. Steady-state stimulation of Na(+) transport with aldosterone was accompanied by a specific decrease of PKCalpha protein levels in both the cytoplasmic and membrane fractions. Similarly, overnight treatment with an uncharged amiloride analog (CDPC), a procedure that through feedback regulation causes a stimulation of Na(+) transport, also decreased PKCalpha levels. These effects were additive, indicating separate mechanisms that converge at the level of PKCalpha. These effects were not accompanied by changes of PKCalpha mRNA levels as determined by Northern blot analysis. We propose that this may represent a novel regulatory feedback mechanism necessary for sustaining an increase of Na(+) transport.

Protein kinase C-zeta overexpression induces erythroid phenotype in the monocytic leukaemia cell line U937

Previous studies have established that protein kinase C-zeta (PKC-zeta) is critical for neuronal cell differentiation. However, the role of PKC-zeta in haematopoietic cell differentiation is less clear. In this study, we have investigated the influence of PKC-zeta overexpression on the phenotype of the human monocytic U937 leukaemic cells. In two PKC-zeta-overexpressing clones (U937 zetaJ and U937 zetaB), PKC-zeta expression levels and activity were three to fourfold higher, and the enzyme accumulated both in the cytoplasm and in the nucleus compared with U937 control cells. PKC-zeta-overexpressing U937 cells exhibited an erythroid phenotype characterized by high levels of glycophorin A, cell haemoglobinization, increased GATA-1 transcripts and protein expression, compared with controls. Immunoprecipitation studies revealed that GATA-1 protein was constitutively phosphorylated in PKC-zeta-overexpressing cells. Moreover, GATA-1 did not interact with PKC-zeta but interacted with ERK1, which was constitutively activated and accumulated in the nucleus of U937 zetaJ. However, ERK1 phosphorylation inhibition by PD098059 did not influence either GATA-1 phosphorylation or GATA-1/ERK1 interaction. Collectively, these results suggest a model in which PKC-zeta induces MEK-dependent ERK1 activation, ERK1 translocation to the nucleus, GATA-1/ERK1 interaction and ERK1-independent GATA-1 phosphorylation resulting in GATA-1 accumulation. To conclude, this study provides evidence for the role of PKC-zeta in erythroid gene regulation.

Age-related death-survival balance in myocardium: an immunohistochemical and biochemical study

During ageing, the occurrence of apoptosis is due to a progressive impairment of normal functions, leading to eliminate redundant, damaged or infected cells. Here we report that also in myocardial tissue, ageing, besides reduction of the number of myocytes and of specialized conduction tissue cells, reduction in Ca(++) transport across the membrane, includes the establishment of apoptosis. In particular, the occurrence of this process, which is less represented than we would have expected, is mediated by the balance between the well known Bcl-2 protein family members, Bad, Bax and Bcl-2, related to the pathway PI-3-kinase/AKT-1, which is known to deliver a survival signal. In fact, aged myocardial cells disclose a suboptimal response, which underlines the possibility that they can become more sensitive to damaging factors or diseases, more frequently occurring during ageing, probably due to an exploited molecular control of apoptosis.

Skin pigmentation enhancers

The highest incidences of cancer are found in the skin, but endogenous pigmentation is associated with markedly reduced risk. Agents that enhance skin pigmentation have the potential to reduce both photodamage and skin cancer incidence. The purpose of this review is to evaluate agents that have the potential to increase skin pigmentation. These include topically applied substances that simulate natural pigmentation: dihydroxyacetone and melanins; and substances that stimulate the natural pigmentation process: psoralens with UVA (PUVA), dimethylsulfoxide (DMSO), L-tyrosine, L-Dopa, lysosomotropic agents, diacylglycerols, thymidine dinucleotides, DNA fragments, melanocyte stimulating hormone (MSH) analogs, 3-isobutyl-1-methylxanthine (IBMX), nitric oxide donors, and bicyclic monoterpene (BMT) diols. These agents are compared with regards to efficacy when administered to melanoma cells, normal human epidermal melanocytes, animal skin, and human skin. In addition, mechanisms of action are reviewed since these may reveal issues related to both efficacy and safety. Both dihydroxyacetone and topically applied melanins are presently available to the consumer, and both of these have been shown to provide some photoprotection. Of the pigmentation stimulators, only PUVA and MSH analogs have been tested extensively on humans, but there are concerns about the safety and side effects of both. At least some of the remaining pigmentation stimulators under development have the potential to safely induce a photoprotective tan.

Ultrastructural modifications and phosphatidylinositol-3-kinase expression and activity in myocardial tissue deriving from rats in different experimental conditions

Oxygen supply is essential in the maintenance of the physiological cell metabolism. In fact, both lower and higher O2 concentrations induce modifications of the enzymatic activity of the cell which determine, in turn, morphological changes at nuclear and cytoplasmic level. Among the molecules involved in the maintenance of the cellular homeostasis, the signal transduction pathway PI-3-kinase/AKT-1 should be included. Here we suggest a relationship between the modulation of this pathway and the morphological modifications occurring "in vivo" in myocardial tissue upon hypoxic and hyperoxic stress. In particular, down regulation of this pathway, which when activated is known to deliver an anti-apoptotic signal, is concomitant to the maintenance of the apoptotic events occurring in these cells in response to oxidative stresses.