Thesis (M.S.)--Uniformed Services University of the Health Sciences, 2005. / Typescript (photocopy).

Abstract The β1-adrenergic receptor (β1AR) belongs to the large family of G protein-coupled receptors. It is activated by epinephrine and norepinephrine and thus has a central role in mediating the effects of the sympathetic nervous system. β1AR is the predominant adrenergic receptor in the heart, where it mediates positive inotropy and chronotropy. Thus, it is the most important target receptor for β-adrenergic antagonists, which are widely used in the treatment of cardiovascular diseases. Furthermore, β1AR is also expressed in the brain, where it has a crucial role in regulating memory formation and synaptic plasticity. Human β1AR (hβ1AR) has two polymorphisms, one at each terminus. The carboxyl-terminal (C-terminal) Arg389Gly8.56 polymorphism has previously been shown to have functional significance. Despite the clinical importance of hβ1AR, its biosynthetic profile and post-translational processing have not been well characterized to date. The aims of the present study were to shed light on these events, focusing on the limited proteolysis of hβ1AR and the impact of β-adrenergic ligands on receptor processing. In addition, the C-terminal polymorphism and its associations with certain parameters were investigated in a population consisting of survivors of acute myocardial infarction (AMI). By using a heterologous expression system, hβ1AR biosynthesis was revealed to be efficient and rapid. The N-terminus of the mature receptor was modified with O-glycans and one N-glycan, but despite these modifications it was subject to cleavage at the cell surface that resulted in two C-terminal fragments. The cleavage was mediated by a metalloproteinase, and importantly, it also occurred in vivo. Moreover, receptor activation enhanced the cleavage, which suggests that it represents a novel regulatory mechanism of hβ1AR. Interestingly, those ligands that enhanced the cleavage stabilized intracellular hβ1AR precursors, possibly via a pharmacological chaperone activity. Thus, the present study demonstrates that β-adrenergic ligands can have different regulatory effects on distinct hβ1AR forms. Among the AMI survivors, the Arg3898.56 homozygotes had significantly increased left ventricular mass indexes, when compared to the Gly3898.56 carriers, which suggests an association between Arg3898.56 and left ventricular hypertrophy (LVH). When euglycemic and diabetic patients were analyzed separately, the association existed among the euglycemic patients but was not present in diabetic patients. Diabetes is one of several risk factors that have previously been shown to influence the progression of LVH. Here, diabetes was shown to have a stronger effect on the development of LVH, when compared with the Arg3898.56 variant of hβ1AR. / Tiivistelmä β1-adrenerginen reseptori (β1AR) kuuluu laajaan G-proteiineihin kytkettyjen reseptorien perheeseen. β1AR on tärkeässä asemassa sympaattisen hermoston toiminnassa. Sydämessä β1AR on vallitseva adrenerginen reseptori, ja sydänlihaksen supistusvireys sekä -taajuus voimistuvat β1AR:n aktivaation kautta. Siten se edustaa sydän- ja verisuonisairauksissa käytettävien β-salpaajien tärkeintä kohdereseptoria. β1AR:n luontaisia agonisteja ovat lisämunuaisytimestä ja hermopäätteistä vapautuvat adrenaliini ja noradrenaliini. Sydänlihaksen lisäksi β1AR:a ilmennetään myös aivoissa, jossa reseptorilla on keskeinen asema muistin ja synaptisen muovautuvuuden kannalta. Ihmisen β1AR (hβ1AR) sisältää kaksi polymorfismia, joista toinen (Arg389Gly8.56) sijaitsee reseptorin karboksyyli- (C-) terminaalissa solulimassa. Tällä polymorfismilla on havaittu olevan toiminnallista merkitystä. Vaikka hβ1AR:n kliininen merkitys on huomattava, sen biosynteesistä ja translaationjälkeisestä muokkauksesta ei ole tähän mennessä ollut juurikaan tutkimustietoa. Tämän väitöskirjatyön tavoite oli kuvata näitä tapahtumia ja erityisesti keskittyä hβ1AR:n solunulkoisen amino- (N-) terminaalin rajoitettuun proteolyysiin. Lisäksi haluttiin tutkia, onko β-adrenergisillä ligandeilla vaikutusta reseptorin prosessointiin. Tutkimuksen kliinisessä osiossa kartoitettiin C-terminaalisen polymorfian yhteyttä valikoituihin muuttujiin aineistossa, joka koostui akuutin sydäninfarktin (AMI) sairastaneista potilaista. hβ1AR:n biosynteesin havaittiin olevan tehokas ja nopea heterologisessa systeemissä. Kypsän reseptorin N-terminaalissa havaittiin useita O-kytkennäisiä ja yksi N-kytkennäinen glykaani. Glykosyloinnista huolimatta N-terminaali pilkkoutui solun pinnalla, mikä tuotti kaksi solukalvolla sijaitsevaa, C-terminaalista reseptoripalasta. Pilkkoutumista, joka havaittiin myös in vivo, katalysoi metalloproteinaasi. Reseptorin aktivaatio kiihdytti pilkkoutumista, joka siten todennäköisesti edustaa uudenlaista hβ1AR:n säätelymekanismia. Ligandit, jotka kiihdyttivät pilkkoutumista, toisaalta stabiloivat solunsisäisiä hβ1AR:n epäkypsiä muotoja toimien luultavasti ns. farmakologisina kaperoneina. Näin ollen väitöskirjatyö osoittaa, että β-adrenergisillä ligandeilla voi olla erilaisia säätelyvaikutuksia eri hβ1AR-muotoihin. Kliinisessä tutkimuksessa Arg3898.56-homotsygooteilla potilailla havaittiin merkittävästi suurentunut vasemman kammion massaindeksi Gly3898.56-kantajiin verrattuina, mikä puoltaa Arg3898.56-polymorfismin ja vasemman kammion hypertrofian (LVH) välistä yhteyttä. Kun euglykeemisiä potilaita ja diabeetikkoja tutkittiin erikseen, yhteys ilmeni vain euglykeemisessä ryhmässä. Diabetes on riskitekijä, joka vaikuttaa LVH:n kehittymiseen. Tässä tutkimuksessa diabeteksellä havaittiin olevan voimakkaampi vaikutus LVH:n kehittymiseen Arg3898.56 -polymorfismiin verrattuna.

Skeletal muscle is a complicated and heterogeneous striated muscle tissue that serves critical mechanical and metabolic functions in the organism. The process of generating skeletal muscle, myogenesis, is elaborately coordinated by members of the protein kinase family, which transmit diverse signals initiated by extracellular stimuli to myogenic transcriptional hierarchy in muscle cells. Mitogen-activated protein kinases (MAPKs) including p38 MAPK, c-Jun N terminal kinase (JNK) and extracellular signal-regulated protein kinase (ERK) are components of serine/threonine protein kinase cascades that play important roles in skeletal muscle differentiation. The exploration of MAPK upstream kinases identified mitogen activated protein kinase kinase kinase kinase 4 (MAP4K4), a serine/threonine protein kinase that modulates p38 MAPK, JNK and ERK activities in multiple cell lines. Our lab further discovered that Map4k4 regulates peroxisome proliferator-activated receptor γ (PPARγ) translation in cultured adipocytes through inactivating mammalian target of rapamycin (mTOR), which controls skeletal muscle differentiation and hypotrophy in kinase-dependent and -independent manners. These findings suggest potential involvement of Map4k4 in skeletal myogenesis. Therefore, for the first part of my thesis, I characterize the role of Map4k4 in skeletal muscle differentiation in cultured muscle cells. Here I show that Map4k4 functions as a myogenic suppressor mainly at the early stage of skeletal myogenesis with a moderate effect on myoblast fusion during late-stage muscle differentiation. In agreement, Map4k4 expression and protein kinase activity are declined with myogenic differentiation. The inhibitory effect of Map4k4 on skeletal myogenesis requires its kinase activity. Surprisingly, none of the identified Map4k4 downstream effectors including p38 MAPK, JNK and ERK is involved in the Map4k4-mediated myogenic differentiation. Instead, expression of myogenic regulatory factor Myf5, a positive mediator of skeletal muscle differentiation is transiently regulated by Map4k4 to partially control skeletal myogenesis. Mechanisms by which Map4k4 modulates Myf5 amount have yet to be determined. In the second part of my thesis, I assess the relationship between Map4k4 and IGF-mediated signaling pathways. Although siRNA-mediated silencing of Map4k4 results in markedly enhanced myotube formation that is identical to the IGF-induced muscle hypertrophic phenotype, and Map4k4 regulates IGF/Akt signaling downstream effector mTOR in cultured adipocytes, Map4k4 appears not to be involved in the IGF-mediated ERK1/2 signaling axis and the IGF-mediated Akt signaling axis in C2C12 myoblasts. Furthermore, Map4k4 does not affect endogenous Akt signaling or mTOR activity during C2C12 myogenic differentiation. The results presented here not only identify Map4k4 as a novel suppressor of skeletal muscle differentiation, but also add to our knowledge of Map4k4 action on multiple signaling pathways in muscle cells during skeletal myogenesis. The effects that Map4k4 exerts on myoblast differentiation, fusion and Myf5 expression implicate Map4k4 as a potential drug target for muscle mass growth, skeletal muscle regeneration and muscular dystrophy.

Breast cancer, as the most prevalent cancer in women, is responsible for more than 15% of new cancer cases and about 6.9% of all cancer-related death in the US. A major cause of therapeutic failure in breast cancer is the development of resistance to chemotherapy, especially for triple-negative breast cancer (TNBC). Therefore, how to overcome chemoresistance is the major challenge to improve the life expectancy of breast cancer patients. Our studies demonstrate that TNBC cells surviving the chronic treatment of chemotherapeutic drugs show significantly higher expression of the dual serine/threonine and tyrosine protein kinase (DSTYK) than non-treated parental cells. In our in vitro cellular models, DSTYK knockout via the CRISPR/Cas9-mediated technique results in apoptotic cell death of chemoresistant cells upon drug treatment. Moreover, DSTYK knockout promotes chemotherapeutic drug-induced tumor cell death in an orthotopic mouse model. These findings suggest that DSTYK exerts an important and previously unknown role in promoting chemoresistance. Our studies provide fundamental insight into the role of DSTYK in chemoresistance in TNBC cells and lay the foundation for the development of new strategies targeting DSTYK for improving TNBC therapy.

No / Recent studies have revealed extensive cortical demyelination in patients with progressive multiple sclerosis (MS). Demyelination in gray matter lesions is associated with activation of microglia. Macrophages and microglia are known to express myeloperoxidase (MPO) and generate reactive oxygen species during myelin phagocytosis in the white matter. In the present study we examined the extent of microglial activation in the cerebral cortex and the relationship of microglial activation and MPO activity to cortical demyelination. Twenty-one cases of neuropathologically confirmed multiple sclerosis, with 34 cortical lesions, were used to assess microglial activation. HLA-DR immunolabeling of activated microglia was significantly higher in demyelinated MS cortex than control cortex and, within the MS cohort, was significantly greater within cortical lesions than in matched non-demyelinated areas of cortex. In homogenates of MS cortex, cortical demyelination was associated with significantly elevated MPO activity. Immunohistochemistry revealed MPO in CD68-positive microglia within cortical plaques, particularly toward the edge of the plaques, but not in microglia in adjacent non-demyelinated cortex. Cortical demyelination in MS is associated with increased activity of MPO, which is expressed by a CD68-positive subset of activated microglia, suggesting that microglial production of reactive oxygen species is likely to be involved in cortical demyelination.

No / Resveratrol is a polyphenolic phytoestrogen that has been shown to exhibit potent anti-oxidant, anti-inflammatory, and anti-catabolic properties. Increased osteoclastic and decreased osteoblastic activities result in bone resorption and loss of bone mass. These changes have been implicated in pathological processes in rheumatoid arthritis and osteoporosis. Receptor activator of NF-kappaB ligand (RANKL), a member of the TNF superfamily, is a major mediator of bone loss. In this study, we investigated the effects of resveratrol on RANKL during bone morphogenesis in high density bone cultures in vitro. Untreated bone-derived cell cultures produced well organized bone-like structures with a bone-specific matrix. Treatment with RANKL induced formation of tartrate-resistant acid phosphatase-positive multinucleated cells that exhibited morphological features of osteoclasts. RANKL induced NF-kappaB activation, whereas pretreatment with resveratrol completely inhibited this activation and suppressed the activation of IkappaBalpha kinase and IkappaBalpha phosphorylation and degradation. RANKL up-regulated p300 (a histone acetyltransferase) expression, which, in turn, promoted acetylation of NF-kappaB. Resveratrol inhibited RANKL-induced acetylation and nuclear translocation of NF-kappaB in a time- and concentration-dependent manner. In addition, activation of Sirt-1 (a histone deacetylase) by resveratrol induced Sirt-1-p300 association in bone-derived and preosteoblastic cells, leading to deacetylation of RANKL-induced NF-kappaB, inhibition of NF-kappaB transcriptional activation, and osteoclastogenesis. Co-treatment with resveratrol activated the bone transcription factors Cbfa-1 and Sirt-1 and induced the formation of Sirt-1-Cbfa-1 complexes. Overall, these results demonstrate that resveratrol-activated Sirt-1 plays pivotal roles in regulating the balance between the osteoclastic versus osteoblastic activity result in bone formation in vitro thereby highlighting its therapeutic potential for treating osteoporosis and rheumatoid arthritis-related bone loss.

No / Vitiligo is characterized by a patchy loss of inherited skin color affecting approximately 0.5% of individuals of all races. Despite the absence of the protecting pigment and the overwhelming evidence for hydrogen peroxide (H(2)O(2))-induced oxidative stress in the entire epidermis of these patients, there is neither increased photodamage/skin aging nor a higher incidence for sun-induced nonmelanoma skin cancer. Here we demonstrate for the first time increased DNA damage via 8-oxoguanine in the skin and plasma in association with epidermal up-regulated phosphorylated/acetylated p53 and high levels of the p53 antagonist p76(MDM2). Short-patch base-excision repair via hOgg1, APE1, and polymerasebeta DNA repair is up-regulated. Overexpression of Bcl-2 and low caspase 3 and cytochrome c levels argue against increased apoptosis in this disease. Moreover, we show the presence of high epidermal peroxynitrite (ONOO(-)) levels via nitrotyrosine together with high nitrated p53 levels. We demonstrate by EMSA that nitration of p53 by ONOO(-) (300 x 10(-6) M) abrogates DNA binding, while H(2)O(2)-oxidized p53 (10(-3) M) enhances DNA binding capacity and prevents ONOO(-)-induced abrogation of DNA binding. Taken together, we add a novel reactive oxygen species to the list of oxidative stress inducers in vitiligo. Moreover, we propose up-regulated wild-type p53 together with p76(MDM2) as major players in the control of DNA damage/repair and prevention of photodamage and nonmelanoma skin cancer in vitiligo.

No / Bone morphogenetic proteins (BMPs) are a large family of multi-functional secreted signalling molecules. Previously BMP2/4 were shown to inhibit skin pigmentation by downregulating tyrosinase expression and activity in epidermal melanocytes. However, a possible role for other BMP family members and their antagonists in melanogenesis has not yet been explored. In this study we show that BMP4 and BMP6, from two different BMP subclasses, and their antagonists noggin and sclerostin were variably expressed in melanocytes and keratinocytes in human skin. We further examined their involvement in melanogenesis and melanin transfer using fully matched primary cultures of adult human melanocytes and keratinocytes. BMP6 markedly stimulated melanogenesis by upregulating tyrosinase expression and activity, and also stimulated the formation of filopodia and Myosin-X expression in melanocytes, which was associated with increased melanosome transfer from melanocytes to keratinocytes. BMP4, by contrast, inhibited melanin synthesis and transfer to below baseline levels. These findings were confirmed using siRNA knockdown of BMP receptors BMPR1A/1B or of Myosin-X, as well as by incubating cells with the antagonists noggin and sclerostin. While BMP6 was found to use the p38MAPK pathway to regulate melanogenesis in human melanocytes independently of the Smad pathway, p38MAPK, PI3-K and Smad pathways were all involved in BMP6-mediated melanin transfer. This suggests that pigment formation may be regulated independently of pigment transfer. These data reveal a complex involvement of regulation of different members of the BMP family, their antagonists and inhibitory Smads, in melanocytes behaviour.