Each member of the protein kinase C (PKC) family activates cell signaling pathways with different and sometimes opposing cell functions, such as cell division, migration, or death. Because of the importance of these processes in human diseases and disorders like cancer, stroke, and Alzheimer’s disease, there is a need for drugs which modify the action of PKC. However, drug design is difficult due to the complicated nature of PKC regulation. To better understand the differential regulation of PKC activity, these studies probe the structure, dynamics, and reactivity of one of the domains responsible for PKC regulation, C1B. C1B binds signaling molecules and translocates PKC to membranes in order to release the kinase domain from inhibition. Mutagenesis and ligand-binding assays monitored with fluorescence and nuclear magnetic resonance (NMR) techniques show that a single variable residue in C1B dramatically affects the sensitivity to signal activators. Investigation of the domain structure and dynamics using NMR revealed the identity of this residue alters the dynamics of the activator binding loops, without changing the structure. NMR studies of the C1B variants in membrane-mimicking micelles showed this residue also changes the interaction of the regulatory domain with lipids. These results demonstrate PKC isoforms have evolved specific functions by tuning dynamics and membrane affinity. Alternatively, PKC can be activated by reactive oxygen species by a mechanism that does not require binding of signaling molecules or membrane localization. To investigate the role of C1B in this type of signaling, the regulatory domain reactivity is monitored via NMR and gel electrophoresis. These studies reveal a particular cysteine residue in C1B that is most reactive, an alternative conformation of C1B in which this residue is more exposed, and modification of C1B leads to unfolding and zinc loss. Because the regulatory domains are responsible for auto-inhibition of the kinase domain, C1B unfolding provides a plausible explanation for activation of PKC by reactive oxygen species. The relation of the intrinsic C1B properties to the activation of PKC can be used to develop drugs with a single mechanism and to better understand how closely related signaling proteins develop specific functions.

The Src homology 3 domain (SH3) and cysteine rich domain (C1) 3 (Stac3) gene is a novel gene copiously expressed in skeletal muscle. The objective of this research was to determine the role of Stac3 in development, specifically in skeletal muscle. We achieved this objective by evaluating the phenotypic effects of Stac3 gene inactivation on development in mice. At birth homozygous Stac3 null (Stac3-/-) mice died perinatally and remained in fetal position with limp limbs, but possessed otherwise normal organs based on gross and histological evaluations. The primary phenotypes displayed at term in Stac3-/- mice were reduced late gestational body weights, increased prevalence of myotubes with centrally located nuclei and severe deformities throughout all skeletal muscles. At embryonic day 18.5 (E18.5) Stac3-/- mice displayed a 12.7% reduction (P < 0.001) in weight compared to wild type (Stac3+/+) or heterozygous (Stac3+/-) littermates while at E15.5 body weights and morphology were similar. At birth (P0) and at E17.5, Stac3-/- mice had 59% and 24% (P < 0.001) more myotubes with centrally located nuclei, respectively, than Stac3+/- or Stac3+/+ littermates. Stac3-/- mice also displayed increased myotube and myofiber cross sectional area at P0 (P < 0.001) and E17.5 (P < 0.05) with disorganized fiber bundling. Overall, these data show Stac3 is necessary for development of viable offspring and suggest Stac3 plays a critical role in fetal development where its primary phenotype is exhibited in skeletal muscle. / Master of Science

Rho GTPases and their regulators such as guanosine exchange factors (GEFs) and GTPase activating proteins (GAPs) represent an important class of molecules controlling dendritic spine plasticity. Although they are typically described as cytoskeletal modulators, roles for the GTPases in endocytosis and cell polarity establishment have also been defined. The neuronal proteins a1- and a2-chimaerins belong to a group of Rac and Cdc42 GAPs that inactivate these GTPases; in addition to a GAP domain, the a-chimaerins share a phosphokinase C (PKC)-like C1 domain but have distinct N-terminal domains (NTDs). My project has explored the importance of specific domains of a1-chimaerin both in induction of a morphological cellular protrusion collapse phenotype ('circularisation') and in interactions with partner proteins that may help to explain the phenotype. The results described in my thesis show that a1-chimaerin possesses a previously undescribed C-terminal domain (CTD) that is indispensable for the ability of the protein to induce collapse of protrusions, and consequent circularisation, in various cell types; moreover, an intact CTD is also important for association of a1-chimaerin with its known effector EphA4, and potentially with other undefined membrane proteins, in a C1-domain- dependent manner. In addition, my results show that a1-chimaerin associates via its NTD with the Src kinase Fyn, and via its C1 domain with the NR2A subunit of the NMDA receptor. Further experiments explored a1-chimaerin effects on EphA4 and NMDA receptor cell surface expression, as well as binding to other putative partners - including the adaptor protein p35 and the polarity protein PAR6. Finally, I have shown that inhibition of a pathway involving the Rho-associated coiled-coil containing protein kinase (ROCK) reverts circularisation induced by a1- chimaerin, and that a blocking peptide based on the CTD may be employed to partially counteract the phenotype. These results uncover a novel domain in a1-chimaerin that may have a crucial importance for the induction of cellular process collapse by a1-chimaerin with a potential relevance to the EphA4-induced dendritic spine retraction, EphA4 receptor endocytosis, and cell surface expression of NR2A-containing NMDA receptors. This suggests a model of a multi-protein signalling complex involving a1-chimaerin that coordinates cellular process remodelling, and that is likely to be important both for adult neuronal circuit plasticity and for neurodegenerative diseases.

La Proteína Quinasa C (PKC) juega un papel fundamental en la regulación del crecimiento celular. Estas proteínas están implicadas en diferentes vías intracelulares que son consideradas como dianas para el tratamiento contra el cáncer. Atendiendo a las propiedades enzimáticas, las PKC se clasifican en tres grandes subfamilias: clásicas, nuevas y atípicas. En las PKC clásicas, el dominio C2&#61537; es un motivo regulador que responde a señales de Ca2+ intracelulares. Este dominio presenta un motivo denominado región rica en lisinas que interacciona con fosfolípidos acídicos. Los resultados de esta tesis demuestran que la afinidad de este dominio por fosfolípidos como el PIP2 es mayor frente a otros de la misma naturaleza. El dominio C2&#61541; de las PKC nuevas se une a fosfolípidos cargados negativamente de modo Ca2+-independiente. Nuestro estudio demuestra que la interacción de este dominio con las membranas es principalmente electrostática con una pequeña contribución de interacciones hidrofóbicas. Por otra parte, el estudio de la estructura secundaria del dominio catalítico de la PKC&#61562; mostró una elevada proporción de hélice &#61537;. La adición de Mg2+-ATP provocó un mayor efecto protector frente a la desnaturalización térmica. / Protein kinase C (PKC) is a family of related protein kinases that plays an important role in regulating cell growth. These protein kinases are involved in several intracellular pathways that end in transcription and are considered to be potential targets for anticancer therapy. The mammalian isoenzymes have been grouped into three subfamilies according to their enzymatic properties: classical, novel and atypical.The C2&#61537; domain is a regulatory sequence motif and is a targeting domain that responds to intracellular Ca2+ signals in classical protein kinases. This domain presents a motif named the lysine-rich cluster that interacts with acidic phospholipids. The results demonstrate that PIP2 interacts with the C2 domain of PKC&#945; in a different way to that described for other phospolipids.C2 domain in novel PKC binds to negatively charged phospholipid vesicles in a Ca2+-independent manner. Our study confirms that the main way in which C2-PKC&#61541; interacts with membranes is electrostatic in nature, with a very small contribution on the part of hydrophobic interactions.The secondary structure of catalytic domain from atypical PKC&#61562; showed a high contribution of &#61537;-helix component. In addition, Mg2+-ATP significantly altered the denaturation pattern of this domain because it protected against denaturation.