Diss. (sammanfattning) Umeå : Umeå universitet, 2008. / Härtill 5 uppsatser.

The c-Jun NH2-terminal kinase (JNK) group and the p38 group of mitogen-activated protein kinases (MAPK) are stress-activated protein kinases that regulate cell proliferation, differentiation, development, and apoptosis. These protein kinases are involved in a signal transduction cascade that includes a MAP kinase (MAPK), a MAP kinase kinase (MAP2K), and a MAP kinase kinase kinase (MAP3K). MAPK are phosphorylated and activated by the MAP2K, which are phosphorylated and activated by various MAP3K. The work presented in this dissertation focuses on understanding the regulation and function of the JNK and p38 MAPK pathways. Two different strategies were utilized. First, I used molecular and biochemical techniques to examine how MAP2K and MAP3K mediate signaling specificity and to define their role in the MAPK pathway. Second, I used gene targeted disruption studies to determine the in vivo role ofMAP2K and MAP3K in MAPK activation. I specifically used these approaches to examine: (1) docking interactions between p38 MAPK and MAP2K [MKK3 and MKK6 (Chapter II)]; (2) the differential activation of p38 MAPK by MAP2K [MKK3, MKK4, and MKK6 (Chapter III)]; and (3) the selective involvement of the mixed lineage kinase (MLK) group of MAP3K in JNK and p38 MAPK activation (Chapter IV and Appendix). In addition, I analyzed the role of the MKK3 and MKK6 MAP2K in cell proliferation and the role of the MLK MAP3K in adipocyte differentiation (Chapter III and Chapter IV). Together, these data provide insight into the regulation and function of the stress-activated MAPK signal transduction pathways.

The cytokine tumor necrosis factor α (TNFα) stimulates the NF-кB, SAPK/JNK, and p38 mitogen-activated protein (MAP) kinase pathways by recruiting Rip1 and Traf2 proteins to the tumor necrosis factor receptor 1 (TNFR1). Genetic studies have revealed that Rip1 links the TNFR1 to the IкB kinase (IKK) complex, whereas Traf2 couples the TNFR1 to the SAPK/JNK cascade. We found TNFα-induced p38 MAP kinase activation and interleukin-6 (IL-6) production is impaired in rip1-/- murine embryonic fibroblasts (MEF) but unaffected in traj2-/- MEF, demonstrating that Rip1 is also a specific mediator of the p38 MAP kinase response to TNFα. Moreover, we demonstrate that endogenous Rip1 associates with the MAP3K, Mekk3 in response to TNFα and that TNFα-induced p38 MAP kinase activation is impaired in mekk3-/- cells, indicating that Rip1 may mediate the p38 MAP kinase response to TNFα by recruiting Mekk3. We also demonstrate that Rip1 is phosphorylated and ubiquitinated in response to Tnfα and that Rip1 phosphorylation is not required for ubiquitination of Rip1. Furthermore, TNFα-induced ubiquitination of Rip1 is impaired in Traf2-/- cells, suggesting that Traf2 is the E3 ubiquitin ligase responsible for the TNFα-dependent ubiquitination of Rip1. Finally, recruitment of the ubiquitinated Tak1 complex is dependent on the presence of Rip1, suggesting that Rip1 ubiquitination rather than its phosphorylation is critical in TNFR1 signaling.

Arterial occlusive diseases are major causes of morbidity and mortality in industrialized countries and represent a huge economic burden. The extent of the native collateral circulation is an important determinant of blood perfusion restoration and therefore the severity of tissue damage and functional impairment that ensues following arterial occlusion. Understanding the mechanisms responsible for collateral artery development may provide avenues for therapeutic intervention. Here, we identify a critical requirement for mixed lineage kinase (MLK) – cJun-NH2-terminal kinase (JNK) signaling in vascular morphogenesis and native collateral artery development. We demonstrate that Mlk2-/-Mlk3-/- mice or mice with compound JNK-deficiency in the vascular endothelium display abnormal collateral arteries, which are unable to restore blood perfusion following arterial occlusion, leading to severe tissue necrosis in animal models of femoral and coronary artery occlusion. Employing constitutive and inducible conditional deletion strategies, we demonstrate that endothelial JNK acts during the embryonic development of collateral arteries to ensure proper patterning and maturation, but is dispensable for angiogenic and arteriogenic responses in adult mice. During developmental vascular morphogenesis, MLK – JNK signaling is required for suppression of excessive sprouting angiogenesis likely via JNK-dependent regulation of Dll4 expression and Notch signaling. This function of JNK may underlie its critical requirement for native collateral artery formation. Thus, this study introduces MLK – JNK signaling as a major regulator of vascular development. In contrast, we find that JNK in hematopoietic cells, which are thought to share a common mesodermally-derived precursor with endothelial cells, is cellautonomously dispensable for normal hematopoietic development and hematopoietic stem cell self-renewal, illustrating the highly context dependent function of JNK.

Dissertation (Ph.D.)--University of South Florida, 2008. / Title from PDF of title page. Document formatted into pages; contains 201 pages. Includes vita. Includes bibliographical references.

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.

No / Fibroblast growth factor receptors (FGFR) play key roles in proliferation, differentiation, and tumorigenesis. Many urothelial carcinomas contain activating point mutations or increased expression of FGFR3. However, little is known about the role of other FGFRs. We examined FGFR expression in telomerase-immortalized normal human urothelial cells, urothelial carcinoma cell lines, and tumor samples and showed that FGFR1 expression is increased in a high proportion of cell lines and tumors independent of stage and grade. To determine the role of FGFR1 in low-stage bladder cancer, we overexpressed FGFR1 in telomerase-immortalized normal human urothelial cells and examined changes in proliferation and cell survival in response to FGF2. FGFR1 stimulation increased proliferation and reduced apoptosis. To elucidate the mechanistic basis for these alterations, we examined the signaling cascades activated by FGFR1. FRS2alpha and PLCgamma were activated in response to FGF2, leading to activation of the mitogen-activated protein kinase pathway. The level of mitogen-activated protein kinase activation correlated with the level of cyclin D1, MCL1, and phospho-BAD, which also correlated with FGFR-induced proliferation and survival. Knockdown of FGFR1 in urothelial carcinoma cell lines revealed differential FGFR1 dependence. JMSU1 cells were dependent on FGFR1 expression for survival but three other cell lines were not. Two cell lines (JMSU1 and UMUC3) were dependent on FGFR1 for growth in soft agar. Only one of the cell lines tested (UMUC3) was frankly tumorigenic; here, FGFR1 knockdown inhibited tumor growth. Our results indicate that FGFR1 has significant effects on urothelial cell phenotype and may represent a useful therapeutic target in some cases of urothelial carcinoma.