There is hardly a cellular process that is not regulated in some way by phosphoinositides, which makes biochemical and physiological studies of these lipids extremely important. PI 3-kinases are key regulators of phosphoinositide metabolism and have been shown to affect a large variety of cellular responses. The key products of PI 3-kinases that have functional activity in higher eukaryotic cells are PI(3,4,5)P₃ and PI(3,4)P₂. PI(3,4,5)P₃ is universally accepted as one of the most important second messengers in signal transduction. However, our knowledge of the functions of PI(3,4)P₂ as a lipid second messenger is much less precise. In this dissertation, work was undertaken to elucidate the regulation of PI(3,4,5)P₃ and PI(3,4)P₂ production and downstream signaling in B cells. Cells with membrane targeted exogenous SHIP were utilized to manipulate phosphoinositide levels. The relationship of PI(3,4,5)P₃ and PI(3,4)P₂ levels to downstream PKB phosphorylation and activation was studied. PI(3,4,5)P₃ and PI(3,4)P₂ levels were found to closely correlate with PKB phosphorylation levels at Thr308 and Ser473, respectively. In addition, PI(3,4)P₂ levels determine the PKB activity in the cytosol; while PI(3,4,5)P₃ levels determine PKB activity at the plasma membrane. Different doses and different forms of B cell receptor (BCR) agonists were used for stimulation. PI 3-kinase activation was studied carefully following stimulation with low doses of anti-BCR antibody and F(ab')₂ fragments. Low concentrations of F(ab')₂ fragments produced higher levels of PI(3,4,5)P₃ than did a high concentration of F(ab')₂ fragments. Downstream PKB signaling was studied in these models. Similar conclusions were drawn from both SHIP over-expressing BJAB cells and dose-dependent BCR stimulations. We speculated that phosphoinositides’ regulation of the kinetics of PKB phosphorylation at Ser473 and Thr308 might be mediated by additional proteins. Investigation of plasma membrane-associated PKB showed that it formed a protein complex of around 400KD, which we attempted to characterize further with respect to PKB phosphorylation and association with lipids. In conclusion, phosphoinositide production is intricately regulated in vivo to control downstream signaling. The levels of PI(3,4)P₂ and PI(3,4,5)P₃ have precise and profound effects on PKB and other molecules such as TAPP and Bam32. This study has contributed new insight into the PI 3-kinase signaling pathway from the aspect of phosphoinositide lipid function.

<p><p>Hematopoiesis is the process in which billions of blood cells are produced on a daily basis, and is vital for sustaining life. This process is tightly regulated by a dynamic balance between hematopoietic stem cell (HSC) self-renewal and differentiation, and maintenance of this balance is of critical importance as dysregulation of HSCs can lead to hematopoietic deficiencies or malignancies such as leukemogenesis. While the signaling mechanisms that regulate HSC homeostasis and function are not well understood, our previous studies have identified a calcium/calmodulin (CaM)-dependent protein kinase, CaMKIV, that is intrinsically required for regulating normal proliferation and survival in HSCs. These findings suggest not only the importance of calcium-initiated pathways including CaMKIV-dependent signaling in hematopoietic cells, but also the potential for other calcium/CaM-dependent effector proteins such as other CaM-kinases to be involved in regulating HSCs and hematopoiesis.</p> </p><p><p>The first major section of this dissertation work presented herein was based on the usage of RNA interference (RNAi) technology to specifically deplete HSCs of growth factor erv1-like (Gfer), a gene whose expression appeared to be absent in CaMKIV null HSCs based on comparative microarray analysis with wild-type HSCs, and seemed a potential target of CaMKIV. We showed that depletion of Gfer in HSCs compromised their <i>in vivo</i> engraftment potential and triggered a hyper-proliferative response that led to their exhaustion. We further assessed Gfer-depleted HSCs by using microscopy techniques and found that these cells possessed significantly reduced levels of the cyclin-dependent kinase inhibitor (CDKI) p27^kip1. In contrast, ectopic over-expression of Gfer in HSCs resulted in significantly elevated total and nuclear p27^kip1. We next performed immunoprecipitation-immunoblot analyses to determine whether alteration of Gfer levels would affect p27^kip1's binding with its inhibitor, the COP9 signalosome subunit jun activation-domain binding protein 1 (Jab1), that would subsequently lead to its ubiquitination, and determined that depletion of Gfer resulted in enhanced binding of p27^kip1 to Jab1. Conversely, over-expression of Gfer resulted in its enhanced binding to Jab1 and inhibition of the Jab1-p27^kip1 interaction. Furthermore, normalization of p27^kip1 in Gfer-KD HSCs rescued their <i>in vitro</i> proliferation deficits. These results provide evidence for a novel Gfer-Jab1-p27^kip1 pathway present in HSCs that functions to restrict abnormal proliferation.</p> </p><p><p>The second major section of this dissertation work describes our studies of a CaMKIV kinase, CaMKK2, and its role in HSCs and hematopoietic development. These studies were largely based on the usage of mice genetically ablated for the <i>Camkk2</i> gene in the germline. Herein, we identified a role for CaMKK2 in the restriction of granulocytic fate commitment and differentiation of myeloid progenitor cells. We performed bone marrow transplantation studies and discovered that engraftment by <i>Camkk2^-/-</i> donor cells resulted in the increased production of mature granulocytes in the bone marrow and peripheral blood. Similarly, we used fluorescence activated cell sorting (FACS) to determine that <i>Camkk2^-/-</i> mice possessed elevated numbers of common myeloid progenitor cells, and exhibited an accelerated granulopoietic phenotype in the bone marrow. Expression of ectopic CaMKK2 in <i>Camkk2^-/-</i> common myeloid progenitors was sufficient to rescue aberrant granulocyte differentiation, and when over-expressed in 32Dcl3 cells was also sufficient to impede granulocyte differentiation in a kinase activity-dependent manner. Collectively, our results reveal a novel role for CaMKK2 as an inhibitor of granulocytic fate commitment and differentiation in early myeloid progenitors.</p></p><p><p>While our original intent was to identify and link a downstream target and upstream kinase to CaMKIV in HSCs, our results ultimately did not suggest that Gfer or CaMKK2 function in the same pathway in HSCs as discussed in the following chapters. Nonetheless, our findings represent a considerable advance in identifying and characterizing the functions of two novel regulators, Gfer and CaMKK2, that are important for HSC proliferation and the commitment and early differentiation steps of granulopoiesis, respectively.</p></p> / Dissertation

Many signals involved in pathophysiology are controlled by hypoxia-inducible factors (HIFs), transcription factors that induce expression of hypoxia-responsive genes. HIFs are highly conserved master regulators of oxygen homeostasis. These factors are post-translationally regulated by a family of oxygen-dependent HIF hydroxylases, whose members include four prolyl 4-hydroxylases (PHD1-4) and an asparaginyl hydroxylase (FIH-1). All HIF hydroxylases require molecular oxygen, Fe(II), ascorbate, and 2-oxoglutarate as cofactors. We hypothesized that alterations in subcellular localization may provide an additional point of regulation for the HIF pathway in response to hypoxia. Most of these enzymes are abundant in resting liver, an organ which is itself unique due to its physiologic oxygen gradient, and they can exist in both nuclear and cytoplasmic pools. In this study, we analyzed the localization of endogenous HIFs and their regulatory hydroxylases in primary rat hepatocytes cultured under hypoxia-reoxygenation conditions. We observed an absence of nuclear HIF-1á activation in hypoxic hepatocytes, even though several known HIF target genes were upregulated, suggesting that HIF-2á and HIF-3á are the predominant isoforms in liver. We show that in hepatocytes, hypoxia-reoxygenation targets HIF-1á to the peroxisome rather than the nucleus, where it co-localizes with the von Hippel Lindau protein (VHL) and the HIF hydroxylases. Confocal immunofluorescence microscopy demonstrated that the HIF hydroxylases can translocate from the nucleus to the cytoplasm in response to hypoxia, with increased accumulation in peroxisomes upon reoxygenation. These results were confirmed via immuno-transmission electron microscopy and Western blotting. Surprisingly, in resting liver tissue, peri-venous localization of the HIF hydroxylases was detected, consistent with areas of low oxygenation. This was in contrast to nuclear HIF-1á, which was undetectable in a number of liver injury models. In conclusion, these studies establish the peroxisome as a highly relevant site of subcellular localization and function for the endogenous HIF pathway in hepatocytes.

Growth factor-induced migration is a rate-limiting step in tumor invasiveness. The molecules that regulate this cellular behavior would represent novel targets for limiting tumor cell progression. Epidermal growth factor (EGF) receptor (EGFR)-mediated motility, present in both autocrine and paracrine modes in prostate carcinomas, requires de novo transcription to persist over times greater than a few hours. Therefore, we sought the specific signaling pathways that directly alter cellular transcription. We confirmed that STAT3 directly associates with, and is activated by EGFR in DU-145 and PC3 human prostate carcinoma cells in addition to the model NR6 fibroblast cell line. This correlated with electrophoretic motility shift of STAT3-selective oligonucleotides. Inhibition of STAT3 activity by antisense or siRNA down-regulation or expression of a dominant-negative construct limited cell motility as determined by an in vitro wound healing assay and invasiveness through a matrix barrier. The expression of constitutively activated STAT3 in the absence of EGF did not increase the migration. Together these data indicate that STAT3 is necessary but not sufficient for EGFR-mediated migration. An initial gene array detected a number of candidate operative molecules; the protein levels of both ENA/VASP, a repressor of cell motility, and caspase 3, a nexus of apoptotic signaling, were down regulated by EGF in a STAT3-dependent manner. Preliminary data show that EGF requires STAT3 functioning to inhibit the induction of apoptosis in the two human prostate cancer cell lines. This suggests that STAT3 signaling may be contributing to tumor progression in a second manner by rendering the cells resistant to death. Together, the sum of these findings suggest that STAT3 signaling may be a new target for both limiting prostate tumor cell invasion and enabling the tumor cells to be killed.

Melanoma, which accounts for only 4% of all skin cancers, but 75% of skin cancer-related deaths, continues to rise at an alarming rate worldwide. When a melanoma is detected and resected at an early stage, the cure rate for patients is favorable. However, the response rate of patients with metastatic melanoma to chemotherapy is less than 15%, and biological therapies have limited efficacy. Therefore, identification of genes that can serve as therapeutic targets for advanced-stage melanoma is crucial. The cell adhesion molecules N-cadherin, MCAM, and Beta3 integrin have been postulated to represent melanoma progression markers; yet, little is known regarding whether they may constitute valuable therapeutic targets for the disease. Furthermore, no studies conducted to date have examined the expression and function of these three molecules in concert in melanoma. The results of our whole-genome and tissue microarray profiling illustrate N-cadherin, MCAM, and Beta3 integrin expression in the distinct stages of melanoma progression. We demonstrate that N-cadherin and Beta3 integrin are melanoma progression markers, but MCAM is not. Furthermore, greater than 95% of metastatic melanomas analyzed in our study express at least one of the three adhesion molecules, and 50% express all three. Our next objective was to determine whether inhibition of N-cadherin, MCAM, or Beta3 integrin impairs melanoma cell proliferation, migration, and/or invasion. We hypothesized that due to redundancy in the functions of N-cadherin, MCAM, and Beta3 integrin, simultaneous inhibition of all three molecules may elicit the most effective therapeutic response. We demonstrate that inhibiting expression of N-cadherin, MCAM, or Beta3 integrin decreases melanoma cell proliferation. However, inhibiting their expression in parallel does not augment the anti-proliferative effect. In contrast, downregulation of N-cadherin, MCAM, and Beta3 integrin in parallel inhibits melanoma cell migration and invasion to a significantly greater extent than targeting each gene alone. Our results indicate that of the three adhesion molecules, MCAM and Beta3 integrin play the most pronounced role in migration and invasion, and therefore, in combination, may represent the most promising therapeutic targets. The data presented in this dissertation provide the foundation for future clinical studies that target adhesion molecules in advanced-stage melanoma patients.

Cell-matrix and cell-cell adhesion proteins are of great significance for many fundamental cellular processes such as survival, differentiation, spreading, adhesion, migration as well as oncogenic transformation. In the present dissertation study, the role of different integrin-proximal protein complexes was investigated in vitro in cancer cells and in primary rat hepatocytes and in vivo in whole animals. First it was shown that migfilin, a newly identified cell-matrix adhesion protein, is also an important component of cell-cell junctions critical for the organization and strengthening of the adherens junctions. Next, Ras-Suppressor-1 (RSU-1), which interacts with the focal adhesion protein PINCH, was shown to regulate cell spreading and adhesion, although the exact mechanism is yet unclear. Furthermore, the role of Integrin-Linked Kinase (ILK) was investigated in vitro in the model system of matrix-induced hepatocyte differentiation. It was shown that ILK along with its binding partners PINCH and Ñ-parvin are dramatically down-regulated during the matrix-induced re-differentiation of hepatocytes. Thus, ILK and its binding partners likely play an important role in matrix-induced-hepatocyte differentiation. Finally, the role of ILK was examined in vivo by removing the protein from the whole animal or specifically from the liver. First ILK was removed from ILK-floxed mice following Cre-recombinase-adenoviral injections giving rise to animals with fulminant hepatitis characterized by massive apoptosis, abnormal mitoses, fatty change and necrosis in the liver. Then, ILK-floxed animals were crossbred with alpha-fetoprotein(AFP)-albumin, albumin, or Foxa3-Cre transgenic mice and thus ILK was genetically removed specifically from the liver. In all cases, the livers of the animals had disorganized liver architecture, absence of hepatocyte plates, increased fibrosis, absence of microvilli in the canaliculi, different degrees of malformations in the biliary system, apoptosis and compensatory proliferation. The present findings therefore, clearly show that ILK is critical for hepatocyte differentiation and survival and more importantly, this holds true in vivo where ILK is crucial for the maintainance of normal liver architecture and function. Thus, the present dissertation work highlights the importance of cell-matrix adhesion proteins in vitro and in vivo and enhances the scientific knowledge in the field of molecular, cellular, hepatocyte and liver biology.

Caveolin-1 (cav-1) has been reported to regulate apoptosis, lipid metabolism and endocytosis. In the present study, we demonstrate that cav-1 can act as a potent immunomodulatory molecule in murine macrophages and play an important role in the development of fibrosis. In murine alveolar and peritoneal macrophages, loss of function experiments using siRNA showed that down-regulating cav-1 expression increased lipopolysaccharide (LPS)-induced proinflammatory cytokine tumor necrosis factor-alpha (TNF-á) and interleukin-6 (IL-6) production but decreased anti-inflammatory cytokine interleukin-10 (IL-10) production. Gain of function experiments demonstrated that overexpression of cav-1 in RAW264.7 decreased LPS-induced TNF-á and IL-6 production and augmented IL-10 production. Cav-1 interacted with TLR4 as revealed by co-immunoprecipitation in peritoneal macrophages. Overexpressing cav-1 in RAW264.7 disrupted Toll like receptor 4 (TLR4) MyD88 and TRIF complex formation; regulated mitogen-activated protein kinase (MAPK) phosphorylation; and inhibited NF-êB activation. Furthermore, the anti-inflammatory modulation by cav-1 involved p38, since the administration of SB203580 significantly abrogated the effects of cav-1, and peritoneal macrophages isolated from MKK3 null mice did not demonstrate any modulation of cav-1. Interestingly, HO-1 translocated into caveolae after LPS stimulation. Carbon monoxide (CO), the gaseous byproduct of HO activity responsible for the anti-inflammatory effects of HO-1, did not regulate cytokines production in cav-1 null macrophages. We observed marked reduction of cav-1 expression in lung tissues and in primary pulmonary fibroblasts from IPF patients, compared to controls. Transforming growth factor-â1 (TGF-â1), the well-known pro-fibrotic cytokine, decreased cav-1 expression in human pulmonary fibroblasts. Cav-1 was able to suppress TGF-â1-induced extracellular matrix (ECM) production in cultured fibroblasts through the regulation of the c-Jun N-terminal kinase (JNK) pathway. Interestingly, highly activated JNK was detected in IPF and bleomycin (BLM)-instilled lung tissue samples, which was dramatically suppressed by adenovirus cav-1 infection. Moreover, JNK1 null fibroblasts showed reduced Smads cascades signaling, mimicking the effects of cav-1. We also demonstrated that cav-1 markedly ameliorated BLM-induced pulmonary fibrosis as evidenced by histological analysis, hydroxyproline content and immunoblot analysis. In summary, our data suggest that cav-1 acts as a potent immunomodulatory and anti-fibrotic effector molecule. Cav-1 may mediate the anti-inflammatory effects of HO-1/CO in immune cells involving the MKK3/p38 MAPK pathway. Cav-1 also plays a pivotal role in ECM regulation and the development of fibrosis, possibly through the MAPK and Smads pathway. This study suggests cav-1 as a novel therapeutic target for patients with fibrosis and inflammation.

Disruption in important cell survival signaling pathways may represent a central mechanism in neurodegenerative disease processes. 6-Hydroxydopamine (6-OHDA) is an oxidative neurotoxin that is commonly used to injure catecholaminergic cells of the central and peripheral nervous systems, and has been used extensively to model Parkinsons Disease. Although it has been documented that 6-OHDA elicits phosphorylation of several kinases, downstream transcriptional effects that influence neuronal cell death are not well defined. The cAMP response element (CRE) is present in the promoter sequences of several important neuronal survival factors. Treatment of catecholaminergic neuronal cell lines (B65 and SH-SY5Y) with 6-OHDA resulted in repression of basal CRE transactivation, and message levels of CRE-mediated genes such as brain derived neurotrophic factor and the survival factor Bcl-2 were decreased in 6-OHDA-treated cells. Message levels of genes lacking CRE sequences were not affected. Interestingly, repression of CRE could be reversed by delayed treatment with cAMP several hours after initiation of 6-OHDA injury. Furthermore, this restoration of CRE-driven transcription, even up to 2 hours post 6-OHDA treatment, was associated with significant neuroprotection. In contrast to observations in other model systems, the mechanism of CRE repression did not involve decreased phosphorylation of its binding protein CREB. Instead, increased phospho-CREB was observed in 6-hydroxydopamine-treated cells, as both total CREB and phospho-CREB were markedly increased in the cytoplasm after treatment. Nuclear expression of p-CREB showed a different pattern, and was decreased in the nucleus of 6-hydroxydopamine-treated cells. 6-OHDA also decreased nuclear phospho-CREB in dopaminergic neurons of primary mouse midbrain cultures. Co-treatment with cAMP promoted/restored nuclear localization of phospho-CREB in both immortalized and primary culture systems, a trend that was associated with protection in both B65 and SY5Y cell lines. Additionally, when human Parkinsons/Lewy body brain tissue was examined, an intense clumped or granular distribution of cytoplasmic phospho-CREB was observed in degenerating substantia nigra neurons, with little to no cytoplasmic staining seen in age-matched controls. Overall, these studies suggest a common theme of impaired nuclear-cytoplasmic trafficking during oxidative neuronal injury processes, with disruption in CREB sub-cellular localization being a recurring trend. It is interesting to note that cytoplasmic accumulation of upstream CREB kinases has previously been observed in both 6-hydroxydopamine-treated cells and in degenerating Parkinson's disease neurons, further supporting a potential role for impaired nuclear import of phosphorylated signaling proteins in neuronal injury processes. These studies present important insight into oxidant-mediated modulation of survival signaling pathways in neuronal cells, may offer potential relevance to the pathogenic mechanisms underlying the progression of neurodegenerative disease.

Squamous cell carcinoma of the head and neck (SCCHN) is the 5th most common cancer worldwide. Signal transducer and activator of transcription 3 (STAT3) is overexpressed in SCCHN and associated with decreased survival. A transcription factor decoy was designed to bind to the DNA binding domain of STAT3, abrogating expression of downstream target genes. The antitumor mechanisms of transcription factor decoys, including the STAT3 decoy, are incompletely understood. STAT3 forms heterodimers with STAT1 suggesting that the STAT3 decoy may interact with STAT1. We determined that the STAT1 pathway was functional in SCCHN cell lines. The STAT3 decoy inhibited STAT1-mediated expression of the target gene, IRF-1. Stimulation of the STAT1 pathway with IFN-× did not mitigate STAT3 decoy-mediated growth inhibition. STAT3 decoy-mediated inhibition of STAT1 signaling did not abrogate its antitumor effects in vitro. Studies using STAT3 knockout cells indicated that STAT3 is necessary for decoy-mediated growth inhibition. The STAT3 decoy was then studied in combination with an EGFR inhibitor and/or a Bcl-XL inhibitor as a therapeutic strategy for SCCHN. Targeting this pathway at several levels¡Xthe upstream receptor (EGFR), the intracellular transcription factor (STAT3), and the downstream target gene (Bcl-XL)¡Xhas not been previously investigated. Combined targeting of EGFR and STAT3 using erlotinib and the STAT3 decoy enhanced growth inhibition of SCCHN cells in vitro. The STAT3 decoy in combination with gossypol, a Bcl-XL inhibitor, resulted in enhanced growth inhibition. The triple combination of all 3 agents enhanced growth inhibition in vitro. These results indicate that targeting the EGFR-STAT3-Bcl-XL pathway at three distinct levels may be a promising treatment strategy for SCCHN.

Select epidermal growth factor (EGF)-like (EGFL) repeats of human tenascin cytotactin can stimulate EGF receptor (EGFR) signaling, but activation requires micromolar concentrations of soluble EGFL repeats in contrast to subnanomolar concentrations of EGF. Using in silico homology modeling techniques, we generated a structure for one such repeat, the 14th EGFL repeat (Ten14). Ten14 assumes a tight EGF-like fold with truncated loops, consistent with circular dichroism studies. We generated bound structures for Ten14 with EGFR using two different approaches, resulting in two distinctly different conformations. Normal mode analysis of both structures indicated that the binding pocket of EGFR exhibits significantly higher mobility in Ten14-EGFR complex compared to the EGF-EGFR complex; we attributed this to loss of key high-affinity interactions within the Ten14-EGFR complex. We proved the efficacy of our in silico models by in vitro experiments. Surface plasmon resonance measurements yielded equilibrium constant KD of 74µM for Ten14, approximately three orders of magnitude weaker than that of EGF. In accordance with our predicted bound models, Ten14 in monomeric form does not bind EGFR with sufficient stability to induce degradation of receptor, or undergo EGFR-mediated internalization. This transient interaction of Ten14 with the receptor on the cell surface is in marked contrast to other EGFR ligands which cause EGFR transit through, and signaling from intracellular locales in addition to cell surface signaling. We investigated whether Ten14-mediated surface restriction of EGFR resulted in altered cellular responses compared to EGF. Activation of PLCã and m-calpain, molecules associated with migration, were noted even at sub-saturating doses of Ten14. However, activation of ERK/MAPK, p90RSK and Elk1, factors affecting proliferation, remained low even at high Ten14 concentrations. Similar activation profiles were observed for EGF-treated cells at 4&#x00B0;C, a maneuver that limits receptor internalization. We demonstrated a direct concurrent effect of such altered signaling on overall biophysical responses - sustained migration was observed at lower levels of Ten14 that activated PLCã, but proliferation remained basal. We present a novel class of EGFR ligands that can potentially signal as a part of the matrix, triggering select signaling cascades leading to a directed cellular response from an otherwise pleiotropic receptor.