Associations between DRDs and schizophrenia in a Korean population: multi-stage association analyses

The dysregulation of the dopaminergic system has been implicated in the pathophysiology of major psychosis, including schizophrenia, with dopamine receptor genes (DRDs) presently targeted as the most promising candidate genes. We investigated DRD1-5 for association with schizophrenia using a multi-stage approach in a Korean sample. One hundred forty-two SNPs in DRD1-5 were selected from the dbSNP, and the associations of each SNP were then screened and typed by MALDI-TOF mass spectrometry using pooled DNA samples from 150 patients with major psychosis and 150 controls. Each of the suggested SNPs was then genotyped and tested for an association within the individual samples comprising each pool. Finally, the positively associated SNPs were genotyped in an extended sample of 270 patients with schizophrenia and 350 controls. Among the 142 SNPs, 88 (62%) SNPs in our Korean population were polymorphic. At the pooling stage, 10 SNPs (DRD1: 2, DRD2: 3, and DRD4: 5) were identified (P < 0.05). SNPs rs1799914 of DRD1 (P = 0.046) and rs752306 of DRD4 (P = 0.017) had significantly different allele frequencies in the individually genotyped samples comprising the pool. In the final stage, with the extended sample, the suggestive association of DRD4 with rs752306 was lost, but the association of DRD1 with rs1799914 gained greater significance (P = 0.017). In these large-scale multi-stage analyses, we were able to find a possible association between DRD1 and schizophrenia. These findings suggested the potential contribution of a multi-step strategy for finding genes related to schizophrenia.

Characterization of mitosis-specific phosphorylation of tumor-associated microtubule-associated protein

Tumor-associated microtubule-associated protein (TMAP), also known as cytoskeleton associated protein 2 (CKAP2), has been recently shown to be involved in the assembly and maintenance of mitotic spindle and also plays an essential role in maintaining the fidelity of chromosome segregation during mitosis. We have previously reported that TMAP is phosphorylated at multiple residues specifically during mitosis, and characterized the mechanism and functional importance of phosphorylation at one of the mitosis-specific phosphorylation residues (i.e., Thr-622). However, the phosphorylation events at the remaining mitotic phosphorylation sites of TMAP have not been fully characterized in detail. Here, we report on generation and characterization of phosphorylated Thr-578- and phosphorylated Thr-596-specific antibodies. Using the antibodies, we show that phosphorylation of TMAP at Thr-578 and Thr-596 indeed occurs specifically during mitosis. Immunofluorescent staining using the antibodies shows that these residues become phosphorylated starting at prophase and then become rapidly dephosphorylated soon after initiation of anaphase. Subtle differences in the kinetics of phosphorylation between Thr-578 and Thr-596 imply that they may be under different mechanisms of phosphorylation during mitosis. Unlike the phosphorylation-deficient mutant form for Thr-622, the mutant in which both Thr-578 and Thr-596 had been mutated to alanines did not induce significant delay in progression of mitosis. These results show that the majority of mitosis-specific phosphorylation of TMAP is limited to pre-anaphase stages and suggest that the multiple phosphorylation may not act in concert but serve diverse functions.

Candidate gene polymorphisms for diabetes mellitus, cardiovascular disease and cancer are associated with longevity in Koreans

Long-lived people may have a unique genetic makeup that makes them more resistant than the general population to prevalent age-related diseases; however, not much is known about genes involved in the longevity. To identify susceptibility variants controlling longevity, we performed a high-throughput candidate gene study using 137 Koreans over 90 yr old and 213 young healthy Koreans. We evaluated 463 informative markers located in 176 candidate genes mostly for diabetes mellitus, cardiovascular disease and cancer under five genetic models. We estimated the odds ratios for each allele, genotype, haplotype, and gene-gene interaction using logistic regression analysis. Associations between 13 genes and longevity were detected at a P-value less than 0.01. Particularly, the rs671 (A) allele of the aldehyde dehydrogenase 2 family (mitochondrial) (ALDH2) gene was associated with longevity only in men (OR 2.11, P = 0.008). Four genes, proprotein convertase subtilisin/kexin type 1 (PCSK1, P = 0.008), epidermal growth factor receptor (EGFR, P = 0.003), paired box 4 (PAX4, P = 0.008), and V-yes-1 Yamaguchi sarcoma viral related oncogene homolog (LYN, P = 0.002) consistently yielded statistical evidence for association with longevity. The findings of the current study may provide a starting point for future studies to unravel genetic factors controlling longevity in Koreans.

Transient phosphorylation of tumor associated microtubule associated protein (TMAP)/cytoskeleton associated protein 2 (CKAP2) at Thr-596 during early phases of mitosis

Tumor associated microtubule associated protein (TMAP), also known as cytoskeleton associated protein 2 (CKAP2) is a mitotic spindle-associated protein whose expression is cell cycle-regulated and also frequently deregulated in cancer cells. Two monoclonal antibodies (mAbs) against TMAP/CKAP2 were produced: B-1-13 and D-12-3. Interestingly, the reactivity of mAb D-12-3 to TMAP/CKAP2 was markedly decreased specifically in mitotic cell lysate. The epitope mapping study showed that mAb D-12-3 recognizes the amino acid sequence between 569 and 625 and that phosphorylation at T596 completely abolishes the reactivity of the antibody, suggesting that the differential reactivity originates from the phosphorylation status at T596. Immunofluorescence staining showed that mAb D-12-3 fails to detect TMAP/CKAP2 in mitotic cells between prophase and metaphase, but the staining becomes evident again in anaphase, suggesting that phosphorylation at T596 occurs transiently during early phases of mitosis. These results suggest that the cellular functions of TMAP/CKAP2 might be regulated by timely phosphorylation and dephosphorylation during the course of mitosis.

Downregulation of regenerating islet-derived 3 alpha (REG3A) in primary human gastric adenocarcinomas

Gastric carcinoma is considered to be one of the most prevalent cancers worldwide. We have performed differential-display polymerase chain reaction (DD-PCR) in order to compare the gene expression profile of gastric carcinoma and that of a normal stomach, in an attempt to identifiy differentially expressed genes associated with primary human gastric cancers. One of the down-regulated genes in gastric cancers was identified as regenerating islet-derived 3 alpha (REG3A), also known as hepatocarcinoma-intestine-pancreas/ pancreatitis-associated protein (HIP/PAP). REG3A exhibited relatively high expression levels in normal gastric mucosa. However, REG3A was found to be down-regulated in 67% (20 out of 30 samples) of primary human gastric cancers, as determined by RT-PCR. In addition, REG3A mRNA expression was not detected in stomach cancer cell lines, SNU cells. Immunohistochemical analysis further confirmed the down-regulation of REG3A expression in primary human gastric cancers. Treatment with the demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dC) resulted in the restoration of REG3A mRNA expression in the gastric cancer cell line, indicating that the transcriptional silencing of REG3A in SNU cell lines was caused by DNA methylation. Taken together, these data indicate that REG3A is down-regulated in most primary human gastric cancer cells, and might be useful in the diagnosis of gastric cancer. Further characterization of the differentially expressed gene, REG3A, should lead to a better understanding of the changes occurring at the molecular level during the development and progression of primary human gastric cancer.

AMPA, not NMDA, activates RhoA GTPases and subsequetly phosphorylates moesin

Glutamate induced rapid phosphorylation of moesin, one of ERM family proteins involved in the ligation of membrane to actin cytoskeleton, in rat hippocampal cells (JBC, 277:16576-16584, 2002). However, the identity of glutamate receptor has not been explored. Here we show that a-amino- 3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor is responsible for glutamate-induced RhoA activation and phosphorylation of moesin. Glutamate induced phosphorylation at Thr-558 of moesin was still detectible upon chelation of Ca(2+), suggesting involvement of AMPA receptor instead of N-methyl D-Aspartate (NMDA) receptor in this phosphorylation of moesin. AMPA but not NMDA- induced moesin phosphorylation was independent of Ca(2+). Both AMPA and NMDA but not Kainate induced moesin phosphorylation at similar levels. However, the kinetics of phosphorylation varied greatly between AMPA and NMDA where AMPA treatment rapidly increased phosphomoesin, which reached a maximum at 10 min after treatment and returned to a basal level at 30 min. In contrast, NMDA-induced phosphorylation of moesin reached a maximum at 30 min after treatment and was remained at higher levels at 60 min. A possible involvement of RhoA and its downstream effector, Rho kinase in the AMPA receptor-triggered phosphorylation of moesin was also explored. The kinetics for the glutamate- induced membrane translocation of RhoA was similar to that of moesin phosphorylation induced by AMPA. Moreover, Y-27632, a specific Rho kinase inhibitor, completely blocked AMPA-induced moesin phosphorylation but had no effect on NMDA-induced moesin phosphorylation. These results suggest that glutamate-induced phosphorylation of moesin may be mediated through the AMPA receptor/RhoA/Rho kinase pathway.