Modulation of Ca2+ channels is an important mechanism for regulation of synaptic strength. However, it is clear that some Ca2+ current types are insensitive to inhibitory modulation mediated by heterotrimeric G proteins (G protein inhibition), and among currents which are sensitive to G protein inhibition, there is great variation in the magnitude of Ca2+ current inhibition between cells of different origin. For the experiments in this dissertation, I utilized recently cloned Ca2+ channels to determine the minimal combination of Ca2+ channel subunits which would confer G protein sensitivity to the recombinant channels. In addition, I examined the role Ca2+ channel auxiliary subunits play in regulation of Ca2+ channel sensitivity to inhibitory G proteins, and whether channels which were sensitive to G protein inhibition were regulated equivalently by the auxiliary subunits. Finally, I investigated possible mechanisms by which these auxiliary subunits modulate G protein-mediated inhibition of Ca2+ channels. I found that α1A and α1B Ca2+ currents, when expressed in Xenopus oocytes, were sensitive to modulation by G proteins in the absence of any Ca2+ channel auxiliary subunits, while α1C currents were not modulated under the same conditions. I conclude from this data that Ca2+ channel α1 subunits are differentially sensitive to G protein modulation, and the α1 subunit of the class A and B Ca2+ channels is sufficient for G protein modulation. I also tested the ability of Ca2+ channel auxiliary subunits to modulate the magnitude of G protein-mediated inhibition Ca2+ currents. I found that the Ca2+ channel α2 subunit had no effect on the magnitude of G protein inhibition of α1A and α1B currents. However, the Ca2+ channel β3 subunit eliminated tonic G protein inhibition and sharply reduced the magnitude of muscarinic M2 receptor induced G protein inhibition of both α1A and α1B currents. I found, however, that while the magnitude of α1A and α1B current inhibition was equivalent in the absence of auxiliary subunits, the magnitude of inhibition was greater for the α1B channel after co-expression of the Ca2+ channel β3 subunit. These results indicate that the Ca2+ channel β3 subunit reduces the sensitivity of α1A and α1B Ca2+ channels to voltage-dependent G protein modulation, and does so to a greater extent for α1A channels when compared to α1B Ca2+ channels. I found that M2 receptor induced inhibition of α1B currents was more voltage-dependent after expression of the Ca2+ channel β3 subunit. Additionally, the rate relief of G protein inhibition dramatically increased after co-expression of the Ca2+ channel β3 subunit. I also co-expressed G protein subunits, and determined that inhibition of both α1B and α1Bβ3 currents was mediated by the G protein βγ subunit. Furthermore, the rate of voltage-dependent relief of G protein βγ subunit induced inhibition increased after co-expression of the Ca2+ channel β3 subunit, similar to the increased rate of relief of the M2 receptor induced G protein inhibition. These data, along with data which demonstrates that G protein inhibition results from the binding of the G protein βγ subunit to the Ca2+ channel (De Waard et al., 1997), indicate that the Ca2+ channel β3 subunit subunit reduces the magnitude of G protein inhibition of α1B Ca2+ currents by increasing the rate of dissociation of the G protein βγ subunit, such that moderate depolarizations used to activate the channel also relieve a large portion of the G protein inhibition.

The experimental data included in this thesis examines two events involved in signal transduction by the Epidermal Growth Factor Receptor. The first event (receptor oligomerization) occurs at the cell membrane and is proposed to be involved in activating the tyrosine protein kinase activity of the EGF receptor. Activation of the tyrosine protein kinase is an initial step in signal transduction by the EGF receptor. The second event examined (activation of an EGF stimulated serine/threonine protein kinase activity) occurs in the cytosol and may potentially be involved in final transmission of the EGF signal to the cell nucleus. The role of oligomerization in regulating the EGF receptor tyrosine protein kinase was examined by testing two hypotheses: 1) that PMA controls EGF receptor function by regulating the oligomeric state of the receptor and 2) that oligomerization is required to activate the EGF receptor tyrosine protein kinase. The oligomeric state of the EGF receptor was examined by chemical cross-linking and sucrose density gradient centrifugation analysis. It was determined that protein kinase C inhibition of the EGF receptor tyrosine protein kinase activity is independent of the oligomeric state of the receptor. It was also determined that the tyrosine protein kinase of the EGF receptor can be activated in the absence of receptor oligomerization. Threonine 669 is the major site of phosphorylation of the EGF receptor after treatment of cells with EGF. Phosphorylation of this site is also associated with the transmodulation of the EGF receptor caused by platelet-derived growth factor and phorbol ester. The kinetics of activation of this T669 kinase activity is rapid. Furthermore, it was demonstrated that EGF could activate the T669 kinase in the absence of detectable tyrosine kinase activity. Together, these data suggest that the T669 kinase has a role in intracellular signal transduction. Therefore, the T669 kinase was purified and characterized in order to help understand how EGF binding to its receptor at the cell membrane ultimately leads to signal transduction to the cell nucleus.

The cells and molecules that comprise the immune system are essential for mounting an effective response against microbes. A successful immune response limits pathology within the host while simultaneously eliminating the pathogen. The key to this delicate balance is the correct recognition of the pathogen and the appropriate response of immune cells. Cellular activation originates through receptors that relay information about the state of the microenvironment to different compartments within the cell. The rapid relay of information is called signal transduction and employs a network of signaling mediators such as kinases, phosphatases, adaptor molecules, and transcription factors. IL-2 inducible T cell kinase (Itk) is a non-receptor tyrosine kinase that is an integral component of signal transduction downstream of many immunoreceptors. This dissertation describes two distinct pathways that utilize Itk in both phases of the immune response. T cells use the TCR to sense a multitude of peptide-based ligands and to transmit signals inside the cell to activate cellular function. In this regard, the diversity of ligands the T cells encounter can be portrayed as analog inputs. Once a critical threshold is met, signaling events transpire in close proximity to the plasma membrane to activate major downstream pathways in the cell. The majority of these pathways are digital in nature resulting in the on or off activation of T cells. We find, however, that altering the TCR signal strength that a T cell receives can result in an analog-based response. Here, the graded expression of a transcription factor, IRF4, is modulated through the activity of Itk. We link this graded response to an NFAT-mediated pathway in which the digital vs. analog nature has been previously uncharacterized. Finally, we demonstrate that the repercussions of an analog signaling pathway is the altered expression of a second transcription factor, Eomes, which is important in the differentiation and function of T cells. These results suggest that Itk is crucial in the modulation of TCR signal strength. Mast cells primarily rely on the IgE-bound FcεR1 for pathogen recognition. Crosslinking this receptor activates mast cells and results in degranulation and cytokine production via an expansive signaling cascade. Upon stimulation, Itk is recruited to the plasma membrane and phosphorylated. Little else is known about how Itk operates inside of mast cells. We find that mast cells lacking Itk are hyperresponsive to FcεR1-mediated activation. This is most apparent in the amount of IL-4 and IL-13 produced in comparison to wild-type mast cells. Increased cytokine production was accompanied by elevated and sustained signaling downstream of the FcεR1. Finally, biochemical evidence demonstrates that Itk is part of an inhibitory complex containing the phosphatase SHIP-1. These results indicate a novel function for Itk as a negative regulator in FcεR1- mediated mast cell activation.

Indiana University-Purdue University Indianapolis (IUPUI) / Many cells are involved in the orchestra that is bone homeostasis--particularly osteoclasts and osteoblasts, which mediate remodeling of bones. This creates a balance that must be kept in check, otherwise pathologies arise. The JAK-STAT signaling pathway is crucial to maintaining this balance. It has long been known that the transcription factor STAT3 has more profound effects on bone homeostasis than other members of the STAT family of proteins. Recently, a genetic condition called Job’s Syndrome has been specifically linked to point mutations in the Stat3 gene. These patients present with severe bone abnormalities, including prominent foreheads, broad nasal bridges, and abnormal eye spacing. For this reason, our lab has extensively studied conditional knockouts of Stat3 in all three types of bones cells in mice and observed severe deficiencies in numerous parameters of normal bone phenotypes. STAT3 seems to play a principal role in the signaling that takes place upon mechanical loading of bone tissues and calling cells into action where they are needed. Furthermore, STAT3 has been found to be up-regulated in the early-response gene cluster following mechanical loading. Our current approach to studying STAT3’s effects on bone includes both in vivo and in vitro comparisons of WT and KO STAT3 models. The conditional knock-out of STAT3 in 8-week old mice revealed significant phenotypic variations as compared to the WT controls, while no significant differences were observed in cKO newborn pups. We also looked at immortalized WT and STAT3 KO cell lines. The STAT3 KO cells had diminished proliferation rates and decreased differentiation capabilities. Furthermore, STAT3 KO cells showed significantly reduced mRNA levels of both Wnt3a and Wnt5a when exposed to fluid shear stress. By employing available ChIP-seq data, we were able to elucidate the genome-wide binding patterns of STAT3. From the peak distribution, we can begin to uncover novel downstream effectors of STAT3 signaling that are responsible for the observed phenotypes in our conditional knockout mouse model. A preliminary look at the ChIP-seq data reveals Wnt and Nrf2 signaling to be under the putative control of STAT3. In our further research, we endeavor to experimentally confirm the ChIP-seq data for STAT3 with RNA-seq experiments in the hopes of finding potential therapeutic targets for bone pathologies.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21341号 / 医博第4399号 / 新制||医||1031(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 小川 誠司, 教授 坂井 義治, 教授 武藤 学 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Environmental pollution represents one of the most pressing problems in developed countries and in recent years has raised concern and doubts also from the scientific perspective. In fact, an ever-growing number of epidemiologic-observational studies, carried out on population at risk, correlated the exposure to environmental chemicals with the incidence of several pathological conditions, ranging from metabolic to cardiological and reproductive diseases, until the development of cancers. These evidences have made more urgent the need for further investigations on the biological mechanism at the basis of pollutants toxicity. In particular, significant attention has been paid to evaluating the impact of organochlorine pesticides (OCPs) on human health. OCPs belong to a large class of organic compounds that the Stockholm Convention catalogued as “POPs” (Persistent Organic Pollutants). The list of banned chemicals includes dioxins and their derivatives, hexachlorocyclohexane, polychlorinated biphenyls and aldrin, whereas many other similar substances are subjected to restrictions. OCPs are widely distributed in the biosphere and their hazardousness is mostly related to physicochemical properties such as lipophilia and energetic stability, that allow these molecules to be resistant to biodegradation and to bio-accumulate into the adipose tissue. Information about the molecular mechanisms of the most popular OCPs (i.e. dioxins, DDT) is already present in scientific literature and several studies indicated them as endocrine disrupting chemicals as well as oncogenes. On the other hand, not much is known about a dangerous and widely diffused compound: the hexachlorocyclohexane. Hexachlorocyclohexane (HCH) is a chlorinated cyclic saturated hydrocarbon that exists in four isomers: α, β, γ and δ hexachlorocyclohexane. The g-isomer of HCH, also known as lindane, is a broad-spectrum insecticide that has been extensively used for the control of agricultural pests and for health purposes. Among HCH isomers, which are by-products of lindane industrial synthesis, β-HCH is the most recalcitrant because of its higher energetic stability due to the equatorial position of all six chlorine atoms in the chair cyclohexane conformation; in addition, few reports are available about its metabolic breakdown. For this characteristic, it is usually the predominant isomer remaining in soils and in animal tissue and can still be detected at low background environmental levels. The improper disposal of huge amounts of β-HCH led to the generation of contaminated sites in several parts of the world (Italy, Turkey, Spain, Kazakhstan, Canada, India, China, Russia, Poland, Germany, Argentine): this classifies “lindane’s contamination” as one of the environmental catastrophe of global proportions on the planetary scale. A detailed epidemiological study, ongoing since 2006, has found correlation between high blood levels of β-HCH and the occurrence of a wide range of diseases in a sample of 660 exposed patients living close the Valle del Sacco, south of Rome. The Valle del Sacco, in fact, is characterized by the presence of a large industrial conglomerate in which lindane production has been stopped in 70’s. Although the biomonitoring study highlighted a link between β-HCH contamination and the incidence of several pathological conditions, few data are currently available in the scientific literature regarding the molecular mechanism of β-HCH. For this reason, our laboratory is investigating since 2015 the intracellular effects of β-HCH with a particular focus on its impact on cancer cells. In a first published study, experiments were carried out on a panel of cells representing different human tumor types (i.e. liver, lungs, prostate, breast) associated with the expression and activation of specific receptors or kinases that are related to STAT3 activity. The experimental concentration of 10 µM for β-HCH was chosen averaging across all the plasma concentration values detected in patients under the biomonitoring study carried out in the Valle del Sacco, in order to reproduce the real exposure conditions. After evaluating the effects of β-HCH on cellular viability, different types of analysis were performed to identify the transduction cascades involved in the molecular responses to β-HCH. Obtained results established that β-HCH can activate cell-line specific pathways that all converge in STAT3 activation. Then, a special focus was placed on investigating the putative role of β-HCH in prostate cancer progression; in fact, literature data, together with our previous findings, suggest that β-HCH could have an endocrine disrupting activity by interfering with Androgen Receptor (AR) signaling. To confirm this hypothesis, LNCaP cells (hormone-sensitive prostate cancer cell line) were treated with β-HCH or testosterone in the presence or absence of the chemotherapeutic agent bicalutamide. The outcomes show that AR nuclear translocation occurs upon both β-HCH and testosterone treatment, whereas is inhibited in the presence of bicalutamide, as evidenced by immunoblotting analysis on nuclear extracts and immunofluorescence experiments. Subsequently, was verified whether β-HCH could affect the activity of AhR (Aryl Hydrocarbon Receptor), the xenobiotic sensor par excellence, in both hormone-dependent and independent tumor types. Immunofluorescence analysis evidenced the capability of β-HCH to induce AhR nuclear translocation. In addition, immunoblotting analysis were performed on cells treated with β-HCH in the presence or not of MG-132 (proteasome inhibitor) and CH223191 (AhR inhibitor) and obtained results clearly highlighted the influence of β-HCH on AhR signaling. Then, experiments were performed to investigate whether β-HCH, on par with other organochlorine pesticides, can induce oxidative stress. For this purpose, ROS production and GSSG/GSH ratio were measured, evidencing the impact of β-HCH on cellular redox homeostasis. In parallel, variations in cellular bioenergetic profile were monitored, demonstrating that β-HCH promote a metabolic shift toward aerobic glycolysis. In this altered context, β-HCH can also induce DNA damage through H2AX phosphorylation. Subsequently, the potential role of β-HCH as a contributor in tumor initiation was inspected. Experiments were carried out on a continuous normal bronchial epithelium cell line to investigate whether β-HCH could trigger cellular malignant transformation toward cancer development. For this reason, β-HCH impact was evaluated on cells viability and morphology and some markers for tumorigenesis, as Ki67 positive-cells and EGF secretion, were studied along with β-HCH activation pathways. Experimental outcomes strongly support the oncogenic potential of this molecule. Considering the capability of β-HCH to promote cell growth and tumor progression, the next question to answer is whether the exposure to β-HCH may lead to a loss of response to chemotherapeutic agents such as tyrosine kinases inhibitors. Experiments carried out on a HER2-positive lung cancer cell line revealed that β-HCH can counteract the inhibitory activity of lapatinib, leading to a higher cell proliferation rate via STAT3 activation. Further investigations were conducted using other chemotherapeutic agents (cisplatin, camptothecin and paclitaxel) and preliminar results seem to confirm the loss of sensitivity to drugs in the presence of β-HCH. From an environmental point of view, the persistence of β-HCH still represents an open question for the presence of massive illegal repositories all around the world. For this reason, β-HCH degradation through a copper-based Fenton-like method was explored by setting up a HPLC protocol under different experimental conditions. The process focused on the quantitative degradation of the parental β-HCH, since the detection of its breakdown products or transformed molecules would need a mass-spectrometry for their qualitative characterization. In parallel with the β-HCH research topic, the role of the protein STAT3 in prostate cancer was further deepened. STAT3 (Signal Transducer and Activator of Transcription 3) is a converging point for many signaling cascades and has been reported constitutively activated in a wide range of solid tumors and hematological malignancies. STAT3 is a latent cytosolic transcription factor and upregulates the expression of genes involved in cell survival and proliferation upon a wide variety of stimuli, including cytokines, oncogenes, growth factors or cytosolic kinases. The dynamic biological behavior of STAT3 can explain the higher proliferation rate triggered by β-HCH through the activation of STAT3-mediated pathways. STAT3 fulfils its multifaceted molecular functions through two different intracellular mechanisms, generally referred as canonical and non-canonical pathways. The canonical activation of STAT3 is strictly dependent on its phosphorylation at the tyrosine residue 705; upon phosphorylation at Y705, induced by the binding of a ligand to its receptor, STAT3 undergoes homodimerization to form an active dimer that can translocate to nucleus and mediates its transcriptional activity. Besides its well-described canonical signaling, STAT3 can be subjected to alternative post-translational modifications. In addition, recent studies assessed the involvement of STAT3, by means of both its canonical and non-canonical pathway, in the metabolic shift toward aerobic glycolysis known as Warburg Effect, which is typical of the more aggressive tumor phenotypes. On the basis of these premises, the existence of a link between PTMs and specific STAT3-mediated pathways was investigated in LNCaP (less aggressive PCa form) and DU-145 (more aggressive) cells performing experiments that simulated inflammatory and oxidative-stress conditions. Cells were treated with IL-6 to induce an inflammatory response, whereas tert-butyl hydroperoxide (t-BHP) was used to simulate oxidative stress. Obtained results on cellular models confirmed the relationship between STAT3 PTMs and cellular conditions, thereby reinforcing the hypothesis that PTMs can drive intracellular responses through STAT3-mediated signaling pathways. Thus, it is possible to identify STAT3 PTMs and STAT3 modulators as suitable markers or targets for PCa prevention, diagnosis and therapy. Then the role of STAT3 in prostate cancer energy metabolism was further investigated, with particular focus on the protein SHMT2 (Serine-Hydroxymethyltransferase). Results indicate that SHMT2 is an active player in STAT3 signaling and that its expression is upregulated by the JAK2/STAT3 canonical pathway upon IL-6 stimulation. Experiments were carried out on two different prostate cancer cell lines, LNCaP (less aggressive) and DU145 (more aggressive). The observation was extended to PCa formalin-fixed paraffin-embedded (FFPE) tissue sections obtained from total prostatectomies: collected specimens are characterized by a different Gleason score, ranging from 6 (less aggressive) to 9 (more aggressive). In both cell lines, STAT3 activation mode, the amount and distribution of PKM2, SHMT2, and HIF-1a proteins, as well as the cellular metabolic conditions, were evaluated in the presence or absence of IL-6-induced inflammation. Expression levels of PKM2, SHMT2, and HIF-1a, together with interleukin-6, were also analyzed utilizing normal and tumor FFPE tissues. / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

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