Potential role of N-myristoyltransferase in cancer.

Colorectal cancer is the second leading cause of malignant death, and better preventive strategies are needed. The treatment of colonic cancer remains difficult because of the lack of effective chemotherapeutic agents; therefore it is important to continue to search for cellular functions that can be disrupted by chemotherapeutic drugs resulting in the inhibition of the development and progression of cancer. The current knowledge of the modification of proteins by myristoylation involving myristoyl-CoA: protein N-myristoyltransferase (NMT) is in its infancy. This process is involved in the pathogenesis of cancer. We have reported for the first time that NMT activity and protein expression were higher in human colorectal cancer, gallbladder carcinoma and brain tumors. In addition, an increase in NMT activity appeared at an early stage in colonic carcinogenesis. It is conceivable therefore that NMT can be used as a potential marker for the early detection of cancer. These observations lead to the possibility of developing NMT specific inhibitors, which may be therapeutically useful. We proposed that HSC70 and/or enolase could be used as an anticancer therapeutic target. This review summarized the status of NMT in cancer which has been carried in our laboratory.

Calmodulin-dependent cyclic nucleotide phosphodiesterase (PDE1) splice variants from bovine cardiac muscle.

Calmodulin-dependent cyclic nucleotide phopshodiesterase (PDE1) has been extensively characterized and is a key enzyme involved in the complex interaction between cyclic nucleotide and Ca(2+) second-messenger systems. It is well established that PDE1 exists in different isozymes. For example, bovine brain tissue has two PDE1 isozymes (PDE1A2 and PDE1B1) whereas only one form (PDE1A1) is reported in bovine cardiac tissue. In this study, we report the cloning of two cDNA splice variants of PDE1: PDE1-small and PDE1-large, from bovine cardiac tissue. Their amino acid sequence similarity to PDE1 sequences from other mammalian species showed that all are very conserved, suggesting their importance in cellular functions. Interestingly, compared to other mammalian species, bovine PDE1A, PDE-small and PDE-large show a deletion at the C-terminal end of the catalytic domain of the gene. Although the significance of this deletion at this crucial location of the gene is not known, we have successfully over-expressed both PDE1-small and PDE1-large splice variants in E. coli and these splice variants are characterized in terms of Western blot, biotinylated calmodulin overlay and peptide mass fingerprinting. Results from these studies suggested that these two splice variants belong to the PDE1 superfamily. To our knowledge, this is the first report on cloning and characterization of these cDNA variants from bovine cardiac tissue. Since there are at least two isoforms of PDE1 in bovine heart tissue, this merits further in-depth study.

Regulation of calmodulin-stimulated cyclic nucleotide phosphodiesterase (PDE1): review.

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 Ca2+ 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 Ca2+ second messenger systems. Some PDE1 isozymes have similar kinetic and immunological properties but are differentially regulated by Ca2+ and calmodulin. Accumulating evidence suggests that the activity of PDE1 is selectively regulated by cross-talk between Ca2+ 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 ischemia-reperfusion.

Potential role of calmodulin-dependent phosphodiesterase in human brain tumor (review).

A wealth of knowledge exists regarding calmodulin-dependent phosphodiesterase (PDE1) in normal mammalian tissues. However, much remains to be known about the enzyme in human brain tumors (glioblastoma multiforme, GBM). PDE1 has not been investigated in GBM relative to normal brain and remains an important area of investigation. In this review, we have summarized the works that have been carried out in our laboratory on the potential role of PDE1 in GBM. In the normal brain, PDE1 is localized in all four principal parts of the brain: cerebrum, diencephalon, brainstem and cerebellum. Specifically, PDE1 is concentrated in anatomically distinct regions of the brain including the striatum, globus pallidus, substantia nigra, subiculum, Purkinjie cells, the external layer of the developing cerebellum and the cerebral cortex. In contrast, PDE1 is found to be very low in the GBM tissue compared to normal cerebral cortex tissue. However, the discovery of an inhibitor in the tumor tissue is interesting and definitely warrants further investigation, particularly, in relation to its possible interaction with PDE1.