Structure and expression of the Caenorhabditis elegans protein kinase C2 gene. Origins and regulated expression of a family of Ca2+-activated protein kinase C isoforms

A Necessary Role for PKC-2 and TPA-1 in Olfactory Memory and Synaptic AMPAR Trafficking in Caenorhabditis elegans

Protein kinase C (PKC) functions are essential for synaptic plasticity, learning, and memory. However, the roles of specific members of the PKC family in synaptic function, learning, and memory are poorly understood. Here, we investigated the role of individual PKC homologs for synaptic plasticity in Caenorhabditis elegans and found a differential role for pkc-2 and tpa-1, but not pkc-1 and pkc-3 in associative olfactory learning and memory. More specifically we show that PKC-2 is essential for associative learning and TPA-1 for short-term associative memory (STAM). Using endogenous labeling and cell-specific rescues, we show that TPA-1 and PKC-2 are required in AVA for their functions. Previous studies demonstrated that olfactory learning and memory in C. elegans are tied to proper synaptic content and trafficking of AMPA-type ionotropic glutamate receptor homolog GLR-1 in the AVA command interneurons. Therefore, we quantified synaptic content, transport, and delivery of GLR-1 in AVA and showed that loss of pkc-2 and tpa-1 leads to decreased transport and delivery but only a subtle decrease in GLR-1 levels at synapses. AVA-specific expression of both PKC-2 and TPA-1 rescued these defects. Finally, genetic epistasis showed that PKC-2 and TPA-1 likely act in the same pathway to control GLR-1 transport and delivery, while regulating different aspects of olfactory learning and STAM. Thus, our data tie together cell-specific functions of 2 PKCs to neuronal and behavioral outcomes in C. elegans, enabling comparative approaches to understand the evolutionarily conserved role of PKC in synaptic plasticity, learning, and memory.

A microbial metabolite synergizes with endogenous serotonin to trigger C. elegans reproductive behavior

Natural products are a major source of small-molecule therapeutics, including those that target the nervous system. We have used a simple serotonin-dependent behavior of the roundworm Caenorhabditis elegans, egg laying, to perform a behavior-based screen for natural products that affect serotonin signaling. Our screen yielded agonists of G protein-coupled serotonin receptors, protein kinase C agonists, and a microbial metabolite not previously known to interact with serotonin signaling pathways: the disulfide-bridged 2,5-diketopiperazine gliotoxin. Effects of gliotoxin on egg-laying behavior required the G protein-coupled serotonin receptors SER-1 and SER-7, and the Gq ortholog EGL-30. Furthermore, mutants lacking serotonergic neurons and mutants that cannot synthesize serotonin were profoundly resistant to gliotoxin. Exogenous serotonin restored their sensitivity to gliotoxin, indicating that this compound synergizes with endogenous serotonin to elicit behavior. These data show that a microbial metabolite with no structural similarity to known serotonergic agonists potentiates an endogenous serotonin signal to affect behavior. Based on this study, we suggest that microbial metabolites are a rich source of functionally novel neuroactive molecules.

TOR Signaling in Caenorhabditis elegans Development, Metabolism, and Aging

The Target of Rapamycin (TOR or mTOR) is a serine/threonine kinase that regulates growth, development, and behaviors by modulating protein synthesis, autophagy, and multiple other cellular processes in response to changes in nutrients and other cues. Over recent years, TOR has been studied intensively in mammalian cell culture and genetic systems because of its importance in growth, metabolism, cancer, and aging. Through its advantages for unbiased, and high-throughput, genetic and in vivo studies, Caenorhabditis elegans has made major contributions to our understanding of TOR biology. Genetic analyses in the worm have revealed unexpected aspects of TOR functions and regulation, and have the potential to further expand our understanding of how growth and metabolic regulation influence development. In the aging field, C. elegans has played a leading role in revealing the promise of TOR inhibition as a strategy for extending life span, and identifying mechanisms that function upstream and downstream of TOR to influence aging. Here, we review the state of the TOR field in C. elegans, and focus on what we have learned about its functions in development, metabolism, and aging. We discuss knowledge gaps, including the potential pitfalls in translating findings back and forth across organisms, but also describe how TOR is important for C. elegans biology, and how C. elegans work has developed paradigms of great importance for the broader TOR field.

A Calcium- and Diacylglycerol-Stimulated Protein Kinase C (PKC), Caenorhabditis elegans PKC-2, Links Thermal Signals to Learned Behavior by Acting in Sensory Neurons and Intestinal Cells

Ca²⁺- and diacylglycerol (DAG)-activated protein kinase C (cPKC) promotes learning and behavioral plasticity. However, knowledge of in vivo regulation and exact functions of cPKCs that affect behavior is limited. We show that PKC-2, a Caenorhabditis elegans cPKC, is essential for a complex behavior, thermotaxis. C. elegans memorizes a nutrient-associated cultivation temperature (T_c ) and migrates along the T_c within a 17 to 25°C gradient. pkc-2 gene disruption abrogated thermotaxis; a PKC-2 transgene, driven by endogenous pkc-2 promoters, restored thermotaxis behavior in pkc-2^-/- animals. Cell-specific manipulation of PKC-2 activity revealed that thermotaxis is controlled by cooperative PKC-2-mediated signaling in both AFD sensory neurons and intestinal cells. Cold-directed migration (cryophilic drive) precedes T_c tracking during thermotaxis. Analysis of temperature-directed behaviors elicited by persistent PKC-2 activation or inhibition in AFD (or intestine) disclosed that PKC-2 regulates initiation and duration of cryophilic drive. In AFD neurons, PKC-2 is a Ca²⁺ sensor and signal amplifier that operates downstream from cyclic GMP-gated cation channels and distal guanylate cyclases. UNC-18, which regulates neurotransmitter and neuropeptide release from synaptic vesicles, is a critical PKC-2 effector in AFD. UNC-18 variants, created by mutating Ser³¹¹ or Ser³²², disrupt thermotaxis and suppress PKC-2-dependent cryophilic migration.

The intestinal TORC2 signaling pathway contributes to associative learning in Caenorhabditis elegans

Several types of associative learning are dependent upon the presence or absence of food, and are crucial for the survival of most animals. Target of rapamycin (TOR), a kinase which exists as a component of two complexes, TOR complex 1 (TORC1) and TOR complex 2 (TORC2), is known to act as a nutrient sensor in numerous organisms. However, the in vivo roles of TOR signaling in the nervous system remain largely unclear, partly because its multifunctionality and requirement for survival make it difficult to investigate. Here, using pharmacological inhibitors and genetic analyses, we show that TORC1 and TORC2 contribute to associative learning between salt and food availability in the nematode Caenorhabditis elegans in a process called taste associative learning. Worms migrate to salt concentrations experienced previously during feeding, but they avoid salt concentrations experienced under starvation conditions. Administration of the TOR inhibitor rapamycin causes a behavioral defect after starvation conditioning. Worms lacking either RICT-1 or SINH-1, two TORC2 components, show defects in migration to high salt levels after learning under both fed and starved conditions. We also analyzed the behavioral phenotypes of mutants of the putative TORC1 substrate RSKS-1 (the C. elegans homolog of the mammalian S6 kinase S6K) and the putative TORC2 substrates SGK-1 and PKC-2 (homologs of the serum and glucocorticoid-induced kinase 1, SGK1, and protein kinase C-α, PKC-α, respectively) and found that neuronal RSKS-1 and PKC-2, as well as intestinal SGK-1, are involved in taste associative learning. Our findings shed light on the functions of TOR signaling in behavioral plasticity and provide insight into the mechanisms by which information sensed in the intestine affects the nervous system to modulate food-searching behaviors.

Protein kinase C and extracellular signal-regulated kinase regulate movement, attachment, pairing and egg release in Schistosoma mansoni

Protein kinases C (PKCs) and extracellular signal-regulated kinases (ERKs) are evolutionary conserved cell signalling enzymes that coordinate cell function. Here we have employed biochemical approaches using ‘smart’ antibodies and functional screening to unravel the importance of these enzymes to Schistosoma mansoni physiology. Various PKC and ERK isotypes were detected, and were differentially phosphorylated (activated) throughout the various S. mansoni life stages, suggesting isotype-specific roles and differences in signalling complexity during parasite development. Functional kinase mapping in adult worms revealed that activated PKC and ERK were particularly associated with the adult male tegument, musculature and oesophagus and occasionally with the oesophageal gland; other structures possessing detectable activated PKC and/or ERK included the Mehlis' gland, ootype, lumen of the vitellaria, seminal receptacle and excretory ducts. Pharmacological modulation of PKC and ERK activity in adult worms using GF109203X, U0126, or PMA, resulted in significant physiological disturbance commensurate with these proteins occupying a central position in signalling pathways associated with schistosome muscular activity, neuromuscular coordination, reproductive function, attachment and pairing. Increased activation of ERK and PKC was also detected in worms following praziquantel treatment, with increased signalling associated with the tegument and excretory system and activated ERK localizing to previously unseen structures, including the cephalic ganglia. These findings support roles for PKC and ERK in S. mansoni homeostasis, and identify these kinase groups as potential targets for chemotherapeutic treatments against human schistosomiasis, a neglected tropical disease of enormous public health significance.

Parasitic blood flukes, also called schistosomes, cause human schistosomiasis, a neglected tropical disease and major public health problem in developing countries, especially sub-Saharan Africa. Sustainable control of schistosomiasis is difficult, mainly because the complex life cycle of the parasite involves a freshwater snail host, and the ability of the parasite to evade the immune response of the human host and to survive for many years. Little is yet known about the cellular mechanisms in schistosomes and how they regulate parasite homeostasis, development and behaviour. In this paper, the nature of intracellular signalling by protein kinases C (PKCs) and extracellular signal-regulated kinases (ERKs) in schistosomes is studied and these proteins are found to be vital for the coordination of processes fundamental to parasite survival, such as muscular activity and reproductive function. Our results contribute to an understanding of molecular events regulating schistosome function and identify PKCs and ERKs as possible targets for the development of new chemotherapeutic treatments against schistosomiasis.

A genetic program promotes C. elegans longevity at cold temperatures via a thermosensitive TRP channel

Both poikilotherms and homeotherms live longer at lower body temperatures, highlighting a general role of temperature reduction in lifespan extension. However, the underlying mechanisms remain unclear. One prominent model is that cold temperatures reduce the rate of chemical reactions, thereby slowing the rate of aging. This view suggests that cold-dependent lifespan extension is simply a passive thermodynamic process. Here, we challenge this view in C. elegans by showing that genetic programs actively promote longevity at cold temperatures. We find that TRPA-1, a cold-sensitive TRP channel, detects temperature drop in the environment to extend lifespan. This effect requires cold-induced, TRPA-1-mediated calcium influx and a calcium-sensitive PKC that signals to the transcription factor DAF-16/FOXO. Human TRPA1 can functionally substitute for worm TRPA-1 in promoting longevity. Our results reveal a previously unrecognized function for TRP channels, link calcium signaling to longevity, and, importantly, demonstrate that genetic programs contribute to lifespan extension at cold temperatures.

PKC-2 phosphorylation of UNC-18 Ser322 in AFD neurons regulates temperature dependency of locomotion

Diacylglycerol (DAG)/protein kinase C (PKC) signaling plays an integral role in the regulation of neuronal function. This is certainly true in Caenorhabditis elegans and in particular for thermosensory signaling and behavior. Downstream molecular targets for transduction of this signaling cascade remain, however, virtually uncharacterized. We investigated whether PKC phosphorylation of Munc18-1, an essential protein in vesicle trafficking and exocytosis, was the downstream effector for DAG regulation of thermosensory behavior. We demonstrate here that the C. elegans ortholog of Munc18-1, UNC-18, was phosphorylated in vitro at Ser322. Transgenic rescue of unc-18-null worms with Ser322 phosphomutants displayed altered thermosensitivity. C. elegans expresses three DAG-regulated PKCs, and blocking UNC-18 Ser322 phosphorylation was phenocopied only by deletion of calcium-activated PKC-2. Expression of nonphosphorylatable UNC-18 S322A, either pan-neuronally or specifically in AFD thermosensory neurons, converted wild-type worms to a pkc-2-null phenotype. These data demonstrate that an individual DAG-dependent thermosensory behavior of an organism is effected specifically by the downstream PKC-2 phosphorylation of UNC-18 on Ser322 in AFD neurons.

Neuronal and intestinal protein kinase d isoforms mediate Na+ (salt taste)-induced learning

Ubiquitously expressed protein kinase D (PKD) isoforms are poised to disseminate signals carried by diacylglycerol (DAG). However, the in vivo regulation and functions of PKDs are poorly understood. We show that the Caenorhabditis elegans gene, dkf-2, encodes not just DKF-2A, but also a second previously unknown isoform, DKF-2B. Whereas DKF-2A is present mainly in intestine, we show that DKF-2B is found in neurons. Characterization of dkf-2 null mutants and transgenic animals expressing DKF-2B, DKF-2A, or both isoforms revealed that PKDs couple DAG signals to regulation of sodium ion (Na+)-induced learning. EGL-8 (a phospholipase Cbeta4 homolog) and TPA-1 (a protein kinase Cdelta homolog) are upstream regulators of DKF-2 isoforms in vivo. Thus, pathways containing EGL-8-TPA-1-DKF-2 enable learning and behavioral plasticity by receiving, transmitting, and cooperatively integrating environmental signals targeted to both neurons and intestine.

Actors of the tyrosine kinase receptor downstream signaling pathways in amphioxus

One of the major goals of evo-developmentalists is to understand how the genetic mechanisms controlling embryonic development have evolved to create the current diversity of bodyplans that we encounter in the animal kingdom. Tyrosine kinase receptors (RTKs) are transmembrane receptors present in all metazoans known to control several developmental processes. They act via the activation of various cytoplasmic signaling cascades, including the mitogen-activated protein kinase (MAPK), the PI3K/Akt, and the phospholipase C-gamma (PLCgamma)/protein kinase C (PKC) pathways. In order to address the evolution of these three pathways and their involvement during embryogenesis in chordates, we took advantage of the complete genome sequencing of a key evolutionarily positioned species, the cephalochordate amphioxus, and searched for the complete gene set of the three signaling pathways. We found that the amphioxus genome contains all of the most important modules of the RTK-activated cascades, and looked at the embryonic expression of two genes selected from each cascade. Our data suggest that although the PI3K/Akt pathway may have ubiquitous functions, the MAPK and the PLCgamma/PKC cascades may play specific roles in amphioxus development. Together with data known in vertebrates, the expression pattern of PKC in amphioxus suggests that the PLCgamma/PKC cascade was implicated in neural development in the ancestor of all chordates.

Protein kinase D is an essential regulator of C. elegans innate immunity

Protein kinase D (PKD) mediates signal transduction downstream from phospholipase C and diacylglycerol (DAG). PKDs are activated by hormones and stress in cell lines, but little is known about PKD functions and regulation in vivo. Here, we show that DKF-2, a C. elegans PKD, regulates innate immunity. Animals lacking DKF-2 were hypersensitive to killing by bacteria that are pathogens of C. elegans and humans. DKF-2 induced 85 mRNAs, which encode antimicrobial peptides and proteins that sustain intestinal epithelium. Induction of immune effector mRNAs by DKF-2 proceeded via PMK-1 (p38 Map-kinase)-dependent and -independent pathways. TPA-1, a PKCdelta homolog, regulated activation and functions of DKF-2 in vivo. Therefore, DKF-2 provides a molecular link that couples DAG signaling to regulation of immunity. This intersection between DAG-TPA-1-DKF-2 and PMK-1 pathways enables integrated immune responses to multiple stimuli. Thus, a PKD mobilizes activation of host immune defenses against pathogens by previously unappreciated signaling pathways and mechanisms.

Properties, Regulation, and in Vivo Functions of a Novel Protein Kinase D

Protein kinase D (PKD) isoforms are protein kinase C effectors in signaling cascades controlled by diacylglycerol (DAG). All PKDs are regulated by DAG/phorbol 12-myristate 13-acetate-binding C1 domains and an activation loop (A-loop). To understand how PKD isoforms diversify DAG signaling networks, it is essential to determine redundant and novel properties of their regulatory domains, characterize factors controlling PKD gene expression, and discover their in vivo physiological roles. Studies on a novel PKD, Caenorhabditis elegans DKF-2 (D kinase family-2), addressed these topics. The C1b domain mediates phorbol 12-myristate 13-acetate-induced translocation and activation of DKF-2. However, when DAG is elevated, C1a and C1b contribute equally to targeting/activation of DKF-2. DKF-2 C1 domains do not inhibit catalytic activity; they mediate delivery of DKF-2 to a membrane where protein kinase C phosphorylates Ser(925) and Ser(929) in the A-loop. This potently stimulates DKF-2 catalytic activity. Phosphorylation of Ser(925) alone switches on 70% of maximal kinase activity. Persistent phosphorylation of Ser(929) tags DKF-2 for proteasomal degradation; Ser(P)(925) plays a minor role in DKF-2 degradation. GATA enhancer sequences govern DKF-2 expression in intestine in vivo. Adult life span increases 40% in animals lacking DKF-2. In thermally stressed wild type animals, the DAF-16 transcription factor is segregated from the nuclei of adult intestinal cells. In contrast, DAF-16 enters adult intestinal nuclei of DKF-2-deficient, thermally stressed animals, where it can trigger gene transcription that protects against various insults. The results suggest a mechanism for increased longevity and show that a PKD links DAG signals to regulation of stress responses and life span.

SmPKC1, a new protein kinase C identified in the platyhelminth parasite Schistosoma mansoni

Schistosoma mansoni signal transduction pathways are promising sources of target molecules for the development of novel control strategies against this platyhelminth parasite of humans. Members of the protein kinase C (PKC) family play key roles in such pathways activated by both receptor tyrosine kinases and other receptors, controlling a variety of physiological processes. Here, we report the cloning and molecular characterization of the first PKC identified in S. mansoni. Structural analysis indicated that SmPKC1 exhibits all the features typical of the conventional PKC subfamily. The gene structure was determined in silico and found to comprise a total of 15 exons and 14 introns. This structure is highly conserved; all intron positions are also present in the human PKCbeta gene and most of the exon sizes are identical. Using PCR on genomic DNA we were able to show that putative orthologues of SmPKC1 are present in 9 Schistosoma species. SmPKC1 expression is developmentally regulated with the highest level of transcripts in miracidia, whereas SmPKC1 protein expression is higher in the sporocyst. The localization of SmPKC1 on the sporocyst ridge cyton and in schistosomula acetabular glands suggests that the enzyme plays a role in signal transduction pathways associated with larval transformation.

Characterization of a novel protein kinase D: Caenorhabditis elegans DKF-1 is activated by translocation-phosphorylation and regulates movement and growth in vivo

Protein kinase D (PKD) isoforms are protein kinase C (PKC) effectors in diacylglycerol (DAG)-regulated signaling pathways. Key physiological processes are placed under DAG control by the distinctive substrate specificity and intracellular distribution of PKDs. Comprehension of the roles of PKDs in homeostasis and signal transduction requires further knowledge of regulatory interplay among PKD and PKC isoforms, analysis of PKC-independent PKD activation, and characterization of functions controlled by PKDs in vivo. Caenorhabditis elegans and mammals share conserved signaling mechanisms, molecules, and pathways Thus, characterization of the C. elegans PKDs could yield insights into regulation and functions that apply to all eukaryotic PKDs. C. elegans DKF-1 (D kinase family-1) contains tandem DAG binding (C1) modules, a PH (pleckstrin homology) domain, and a Ser/Thr protein kinase segment, which are homologous with domains in classical PKDs. DKF-1 and PKDs have similar substrate specificities. Phorbol 12-myristate 13-acetate (PMA) switches on DKF-1 catalytic activity in situ by promoting phosphorylation of a single amino acid Thr(588) in the activation loop. DKF-1 phosphorylation and activation are unaffected when PKC activity is eliminated by inhibitors. Both phosphorylation and kinase activity of DKF-1 are extinguished by substituting Ala for Thr(588) or Gln for Lys(455) ("kinase dead") or incubating with protein phosphatase 2C. Thus, DKF-1 is a PMA-activated, PKC-independent D kinase. In vivo, dkf-1 gene promoter activity is evident in neurons. Both dkf-1 gene disruption (null phenotype) and RNA interference-mediated depletion of DKF-1 protein cause lower body paralysis. Targeted DKF-1 expression corrected this locomotory defect in dkf-1 null animals. Supraphysiological expression of DKF-1 limited C. elegans growth to approximately 60% of normal length.

Regulation of the ABC kinases by phosphorylation: protein kinase C as a paradigm

Phosphorylation plays a central role in regulating the activation and signalling lifetime of protein kinases A, B (also known as Akt) and C. These kinases share three conserved phosphorylation motifs: the activation loop segment, the turn motif and the hydrophobic motif. This review focuses on how phosphorylation at each of these sites regulates the maturation, signalling and down-regulation of PKC as a paradigm for how these sites control the function of the ABC kinases.

Genomic organization and chromosomal localization of the mouse protein kinase C alpha gene

Protein kinase C (PKC) is a family of ten isoforms of phospholipid-dependent serine/threonine kinases, which participate in many cellular responses including cell growth, differentiation, and tumorigenesis. Of the isoforms, PKC alpha is distributed ubiquitously in almost all tissues and involved in various signal transductions. Furthermore, PKC alpha plays an important role in the growth and malignant progression of some tumor cell lines. Elucidating the roles of PKC alpha in vivo would lead to understanding of the mechanism of tumorigenesis and other biological functions. In this study, we isolated and characterized genomic DNA clones of the mouse PKC alpha gene (Prkca). The Prkca gene was a unigene consisting of 17 exons and spanning at least 116 kb. All the exon-intron boundaries followed the GT/AG rule. The genomic structure of PKC alpha was markedly conserved among the mouse, human, and fly. By radiation hybrid mapping, the Prkca gene was closely linked to sequence-tagged site marker D11Mit258 that locates 65.0 cM from the centromere of chromosome 11, and its transcription was towards the centromere. This study shows that generation of PKC alpha-mutant mice may reveal the PKC alpha function in vivo.

Structural properties and mechanisms that govern association of C kinase adapter 1 with protein kinase C3 and the cell periphery

Association of an atypical protein kinase C (aPKC) with an adapter protein can affect the location, activity, substrate specificity, and physiological role of the phosphotransferase. Knowledge of mechanisms that govern formation and intracellular targeting of aPKC.adapter protein complexes is limited. Caenorhabditis elegans protein kinase C adapter proteins (CKA1 and CKA1S) bind and target aPKCs and provide prototypes for mechanistic analysis. CKA1 binds an aPKC (PKC3) via a phosphotyrosine binding (PTB) domain. A distinct, Arg/Lys-rich N-terminal region targets CKA1 to the cell periphery. We discovered that a short segment ((212)GGIDNGAFHEHEI(224)) of the V(2) (linker) region of PKC3 creates a binding surface that interacts with the PTB domain of CKA1/CKA1S. The docking domain of PKC3 differs from classical PTB ligands by the absence of Tyr and Pro. Substitution of Ile(214), Asn(216), or Phe(219) with Ala abrogates binding of PKC3 with CKA1; these residues cooperatively configure a docking site that complements an apolar surface of the CKA1 PTB domain. Phosphorylation site domains (PSD1, residues 11-25; PSD2, residues 61-77) in CKA1 route the adapter (and tethered PKC3) to the cell periphery. Phosphorylation of Ser(17) and Ser(65) in PSDs 1 and 2 elicits translocation of CKA1 from the cell surface to cytoplasm. Activities of DAG-stimulated PKCs and opposing protein Ser/Thr phosphatases can dynamically regulate the distribution of adapter protein between the cell periphery and cytoplasm.

Aspartic proteases from the nematode Caenorhabditis elegans. Structural organization and developmental and cell-specific expression of asp-1

A Caenorhabditis elegans gene (asp-1) and cDNA that encode a homologue of cathepsin D aspartic protease were cloned and characterized. The asp-1 mRNA is transcribed from a single exon, and it begins with the SL1 trans-splice leader sequence. The protein (ASP-1) is expressed as a 396-amino acid, 42.7-kDa pre-pro-peptide that is post-translationally processed into a approximately 40-kDa lysosomal protein. ASP-1 shares approximately 60% sequence identity with the aspartic protease precursor from the nematode Strongyloides stercoralis. The amino acid sequences adjacent to the two active site aspartic acid residues in ASP-1 are 100% identical to those in other eukaryotic aspartic proteases. In addition, ASP-1 contains conserved, potential disulfide bond-forming cysteine residues and N-glycosylation sites. The asp-1 gene is exclusively transcribed in the intestinal cells, with the highest levels of expression observed at late embryonic and early larval stages of development. asp-1 transcription is not observed in adult nematodes or mature larvae. Furthermore, transcription predominantly occurs in eight anterior cells of the intestine (int6-int8). Analyses of ASP-1 nucleotide and amino acid sequences revealed the presence of five additional C. elegans aspartic proteases.

Mammalian homologue of the Caenorhabditis elegans UNC-76 protein involved in axonal outgrowth is a protein kinase C zeta-interacting protein

By the yeast two-hybrid screening of a rat brain cDNA library with the regulatory domain of protein kinase C zeta (PKCzeta) as a bait, we have cloned a gene coding for a novel PKCzeta-interacting protein homologous to the Caenorhabditis elegans UNC-76 protein involved in axonal outgrowth and fasciculation. The protein designated FEZ1 (fasciculation and elongation protein zeta-1) consisting of 393 amino acid residues shows a high Asp/Glu content and contains several regions predicted to form amphipathic helices. Northern blot analysis has revealed that FEZ1 mRNA is abundantly expressed in adult rat brain and throughout the developmental stages of mouse embryo. By the yeast two-hybrid assay with various deletion mutants of PKC, FEZ1 was shown to interact with the NH2-terminal variable region (V1) of PKCzeta and weakly with that of PKCepsilon. In the COS-7 cells coexpressing FEZ1 and PKCzeta, FEZ1 was present mainly in the plasma membrane, associating with PKCzeta and being phosphorylated. These results indicate that FEZ1 is a novel substrate of PKCzeta. When the constitutively active mutant of PKCzeta was used, FEZ1 was found in the cytoplasm of COS-7 cells. Upon treatment of the cells with a PKC inhibitor, staurosporin, FEZ1 was translocated from the cytoplasm to the plasma membrane, suggesting that the cytoplasmic translocation of FEZ1 is directly regulated by the PKCzeta activity. Although expression of FEZ1 alone had no effect on PC12 cells, coexpression of FEZ1 and constitutively active PKCzeta stimulated the neuronal differentiation of PC12 cells. Combined with the recent finding that a human FEZ1 protein is able to complement the function of UNC-76 necessary for normal axonal bundling and elongation within axon bundles in the nematode, these results suggest that FEZ1 plays a crucial role in the axon guidance machinery in mammals by interacting with PKCzeta.

Atypical protein kinase C cooperates with PAR-3 to establish embryonic polarity in Caenorhabditis elegans

Asymmetric cell divisions, critically important to specify cell types in the development of multicellular organisms, require polarized distribution of cytoplasmic components and the proper alignment of the mitotic apparatus. In Caenorhabditis elegans, the maternally expressed protein, PAR-3, is localized to one pole of asymmetrically dividing blastomeres and is required for these asymmetric divisions. In this paper, we report that an atypical protein kinase C (PKC-3) is essential for proper asymmetric cell divisions and co-localizes with PAR-3. Embryos depleted of PKC-3 by RNA interference die showing Par-like phenotypes including defects in early asymmetric divisions and mislocalized germline-specific granules (P granules). The defective phenotypes of PKC-3-depleted embryos are similar to those exhibited by mutants for par-3 and another par gene, par-6. Direct interaction of PKC-3 with PAR-3 is shown by in vitro binding analysis. This result is reinforced by the observation that PKC-3 and PAR-3 co-localize in vivo. Furthermore, PKC-3 and PAR-3 show mutual dependence on each other and on three of the other par genes for their localization. We conclude that PKC-3 plays an indispensable role in establishing embryonic polarity through interaction with PAR-3.

The extended protein kinase C superfamily

Members of the mammalian protein kinase C (PKC) superfamily play key regulatory roles in a multitude of cellular processes, ranging from control of fundamental cell autonomous activities, such as proliferation, to more organismal functions, such as memory. However, understanding of mammalian PKC signalling systems is complicated by the large number of family members. Significant progress has been made through studies based on comparative analysis, which have defined a number of regulatory elements in PKCs which confer specific location and activation signals to each isotype. Further studies on simple organisms have shown that PKC signalling paradigms are conserved through evolution from yeast to humans, underscoring the importance of this family in cellular signalling and giving novel insights into PKC function in complex mammalian systems.

Structure, expression, and properties of an atypical protein kinase C (PKC3) from Caenorhabditis elegans. PKC3 is required for the normal progression of embryogenesis and viability of the organism

Little is known about differential expression, functions, regulation, and targeting of "atypical" protein kinase C (aPKC) isoenzymes in vivo. We have cloned and characterized a novel cDNA that encodes a Caenorhabditis elegans aPKC (PKC3) composed of 597 amino acids. In post-embryonic animals, a 647-base pair segment of promoter/enhancer DNA directs transcription of the 3.6-kilobase pair pkc-3 gene and coordinates accumulation of PKC3 protein in approximately 85 muscle, epithelial, and hypodermal cells. These cells are incorporated into tissues involved in feeding, digestion, excretion, and reproduction. Mammalian aPKCs promote mitogenesis and survival of cultured cells. In contrast, C. elegans PKC3 accumulates in non-dividing, terminally differentiated cells that will not undergo apoptosis. Thus, aPKCs may control cell functions that are independent of cell cycle progression and programmed cell death. PKC3 is also expressed during embryogenesis. Ablation of PKC3 function by microinjection of antisense RNA into oocytes yields disorganized, developmentally arrested embryos. Thus, PKC3 is essential for viability. PKC3 is enriched in particulate fractions of disrupted embryos and larvae. Immunofluorescence microscopy revealed that PKC3 accumulates near cortical actin cytoskeleton/plasma membrane at the apical surface of intestinal cells and in embryonic cells. A candidate anchoring/targeting protein, which binds PKC3 in vitro, has been identified.