Protein N-myristoylation is a cotranslational lipidic modification specific to the alpha-amino group of an N-terminal glycine residue of many eukaryotic and viral proteins. The ubiquitous eukaryotic enzyme, N-myristoyltransferase, catalyzes the myristoylation process. Precisely, attachment of a myristoyl group increases specific protein–protein interactions leading to subcellular localization of myristoylated proteins with its signaling partners. The birth of the field of myristoylation, a little over three decades ago, has led to the understanding of the significance of protein myristoylation in regulating cellular signaling pathways in several biological processes especially in carcinogenesis and more recently immune function. This review discusses myristoylation as a prerequisite step in initiating many immune cell signaling cascades. In particular, we discuss the hitherto unappreciated implication of myristoylation during myelopoiesis, innate immune response, lymphopoiesis for T cells, and the formation of the immunological synapse. Furthermore, we discuss the role of myristoylation in inducing the virological synapse during human immunodeficiency virus infection as well as its clinical implication. This review aims to summarize existing knowledge in the field and to highlight gaps in our understanding of the role of myristoylation in immune function so as to further investigate into the dynamics of myristoylation-dependent immune regulation.

No abstract

N-Myristoyltransferase (NMT) transfers myristate to an amino-terminal glycine of many eukaryotic proteins. In yeast, worms, and flies, this enzyme is essential for viability of the organism. Humans and mice possess two distinct but structurally similar enzymes, NMT1 and NMT2. These two enzymes have similar peptide specificities, but no one has examined the functional importance of the enzymes in vivo. To address this issue, we performed both genetic and biochemical studies. Northern blots with RNA from adult mice and in situ hybridization studies of day 13.5 embryos revealed widespread expression of both Nmt1 and Nmt2. To determine whether the two enzymes are functionally redundant, we generated Nmt1-deficient mice carrying a ␤-galactosidase marker gene. ␤-Galactosidase staining of tissues from heterozygous Nmt1-deficient (Nmt1؉/؊) mice and embryos confirmed widespread expression of Nmt1. Intercrosses of Nmt1؉/؊ mice yielded no viable homozygotes (Nmt1؊/؊), and heterozygotes were born at a less than predicted frequency. Nmt1؊/؊ embryos died between embryonic days 3.5 and 7.5. Northern blots revealed lower levels of Nmt2 expression in early development than at later time points, a potential explanation for the demise of Nmt1؊/؊ embryos. To explore this concept, we generated Nmt1؊/؊ embryonic stem (ES) cells. The Nmt2 mRNA could be detected in Nmt1؊/؊ ES cells, but the total NMT activity levels were reduced by ϳ95%, suggesting that Nmt2 contributes little to total enzyme activity levels in these early embryo cells. The Nmt1؊/؊ ES cells were functionally abnormal; they yielded small embryoid bodies in in vitro differentiation experiments and did not contribute normally to organogenesis in chimeric mice. We conclude that Nmt1 is not essential for the viability of mammalian cells but is required for development, likely because it is the principal N-myristoyltransferase in early embryogenesis.

No abstract

No abstract

No abstract

N-myristoyltransferase (NMT) exists in two isoforms, NMT1 and NMT2, that catalyze myristoylation of various proteins crucial in signal transduction, cellular transformation, and oncogenesis. We have recently demonstrated that NMT1 is essential for the early development of mouse embryo. In this report, we have demonstrated that an invariant consequence of NMT1 knock out is defective myelopoesis. Suppressed macrophage colony forming units were observed in M-CSF-stimulated bone marrow cells from heterozygous (+/–) Nmt1-deficient mice. Homozygous (−/−) Nmt1-deficient mouse embryonic stem cells resulted in drastic reduction of macrophages when stimulated to differentiate by M-CSF. Furthermore, to understand the requirement of NMT1 in the monocytic differentiation we investigated the role of NMT, pp60c−Src (NMT substrate) and heat shock cognate protein 70 (inhibitor of NMT), during PMA-induced differentiation of U937 cells. Src kinase activity and protein expression increased during the differentiation process along with regulation of NMT activity by hsc70. NMT1 knock down in PMA treated U937 cells showed defective monocytic differentiation. We report in this study novel observation that regulated total NMT activity and NMT1 is essential for proper monocytic differentiation of the mouse bone marrow cells.

The response of living cells to change in cell environment depends on the action of second messenger molecules. The two second messenger molecules cAMP and Ca 2+ regulate a large number of eukaryotic cellular events. Calmodulin-stimulated cyclic nucleotide phosphodiesterase (PDE1) is one of the key enzymes involved in the complex interaction between cAMP and Ca 2+ second messenger systems. Some PDE1 isozymes have similar kinetic and immunological properties but are differentially regulated by Ca 2+ and calmodulin. Accumulating evidence suggests that the activity of PDE1 is selectively regulated by cross-talk between Ca 2+ and cAMP signalling pathways. These isozymes are also further distinguished by various pharmacological agents. We have demonstrated a potentially novel regulation of PDE1 by calpain. This study suggests that limited proteolysis by calpain could be an alternative mechanism for the activation of PDE1. We have also shown PDE1 activity, expression and effect of calpain in the rat model in vitro of cardiac ischemiareperfusion. Contents 1. Introducton 2. Kinetic properties of various PDE1 isozymes 3. Differential regulation of PDE1 by CaM and Ca 2+ 4. Coupling between Ca 2+ and cAMP second messengers in the regulation of PDE1 5. Role of autophosphorylation of PDE1B1 by CaMdependent protein kinase II 6. Differential inhibition of PDE1 isozymes and its therapeutic applications 7. Role of proteolysis in regulating PDE1A2 8. Role of PDE1A1 in ischemic-reperfused heart 9. Conclusion