Ching Ching Ng

p53DINP1, a p53-Inducible Gene, Regulates p53-Dependent Apoptosis

Using the differential display method combined with a cell line that carries a well-controlled expression system for wild-type p53, we isolated a p53-inducible gene, termed p53DINP1 (p53-dependent damage-inducible nuclear protein 1). Cell death induced by DNA double-strand breaks (DSBs), as well as Ser46 phosphorylation of p53 and induction of p53AIP1, were blocked when we inhibited expression of p53DINP1 by means of an antisense oligonucleotide. Overexpression of p53DINP1 and DNA damage by DSBs synergistically enhanced Ser46 phosphorylation of p53, induction of p53AIP1 expression, and apoptotic cell death. Furthermore, the protein complex interacting with p53DINP1 was shown to phosphorylate Ser46 of p53. Our results suggest that p53DINP1 may regulate p53-dependent apoptosis through phosphorylation of p53 at Ser46, serving as a cofactor for the putative p53-Ser46 kinase.

A genome-wide association study identifies ITGA9 conferring risk of nasopharyngeal carcinoma

To identify a gene(s) susceptible to nasopharyngeal carcinoma (NPC), we carried out a genome-wide association study (GWAS) through genotyping of more than 500 000 tag single-nucleotide polymorphisms (SNPs), using an initial sample set of 111 unrelated NPC patients and 260 controls of a Malaysian Chinese population. We further evaluated the top 200 SNPs showing the smallest P-values, using a replication sample set that consisted of 168 cases and 252 controls. The combined analysis of the two sets of samples found an SNP in intron 3 of the ITGA9 (integrin-α 9) gene, rs2212020, to be strongly associated with NPC (P=8.27 × 10−7, odds ratio (OR)=2.24, 95% confidence intervals (CI)=1.59–3.15). The gene is located at 3p21 which is commonly deleted in NPC cells. We subsequently genotyped additional 19 tag SNPs within a 40-kb linkage disequilibrium (LD) block surrounding this landmark SNP. Among them, SNP rs189897 showed the strongest association with a P-value of 6.85 × 10−8 (OR=3.18, 95% CI=1.94–5.21), suggesting that a genetic variation(s) in ITGA9 may influence susceptibility to NPC in the Malaysian Chinese population.

p53RFP, a p53-inducible RING-finger protein, regulates the stability of p21WAF1.

The mechanisms by which p53 prevents development of cancer are much more complicated than previously thought. Under normal conditions, p53 is involved in cell-cycle arrest, Q1apoptosis, DNA repair, and inhibition of angiogenesis; it also promotes degradation of proteins through transcriptional regulation of certain target genes. Here we report the isolation of a novel transcriptional target of p53, designated p53RFP (p53-inducible RING-finger protein), whose product has E3 ubiquitin ligase activity. Its expression was negatively correlated to that of p21WAF1 protein; p53RFP is likely to play a role in the regulation of this protein, probably through interaction with, and ubiquitination of, p21WAF1. p53RFP appears to represent the second known example, the first being MDM2, of an E3 ubiquitin ligase as a p53 target. Our results further suggest that p53 might regulate the stability of p21WAF1 through transcriptional regulation of p53RFP, and this feature may represent a novel mechanism for a p53-dependent cell-cycle checkpoint.

Identification of NOD2/CARD15 mutations in Malaysian patients with Crohn's disease

OBJECTIVE:  The NOD2/CARD15 gene has been identified as an important susceptibility gene for Crohns disease (CD) but the three common disease predisposing mutations (DPM) found in developed countries have not been identified in Asian populations. The aim of our study was to look for the DPM in our multiracial population and to discover whether there were any differences in the three major ethnic groups; Malay, Chinese and Indian.

HLA-B*15:02 association with carbamazepine-induced Stevens-Johnson syndrome and toxic epidermal necrolysis in an Indian population: a pooled-data analysis and meta-analysis.

This study aimed to investigate the prevalence and association of HLA‐B*15:02 with carbamazepine‐induced Stevens‐Johnson syndrome and toxic epidermal necrolysis (CBZ‐SJS/TEN) in the Indian population in Malaysia, which mostly originated from Southern India. HLA‐B alleles in five Indian case patients with CBZ‐SJS/TEN and 52 CBZ‐tolerant controls, and followed by a pooled sample of seven cases from two centers in Malaysia were analyzed. Positive association for HLA‐B*15:02 with CBZ‐SJS/TEN was detected in Indians (40% [2/5] vs. 3.8% [2/52], odds ratio [OR] 16.7, p = 0.0349), of which 80% (4/5) of the Indian patients originated from Southern India. A pooled sample of seven cases showed stronger association between HLA‐B*15:02 and CBZ‐SJS/TEN (57.1% [4/7] vs. 3.8% [2/52], OR 33.3, 95% confidence interval [CI] 4.25–162.21, p = 1.05 × 10−3). Subsequent meta‐analysis on Indians from Malaysia and India further demonstrated a significant and strong association between HLA‐B*15:02 and CBZ‐SJS/TEN (OR 38.54; 95% CI 6.83–217.34, p < 1.0 × 10−4). Our study is the first on Indians predominantly from Southern India that demonstrated HLA‐B*15:02 as a strong risk factor for CBZ‐SJS/TEN despite a low population allele frequency. This stressed the importance of testing for HLA‐B*15:02, irrespective of the ancestral background, including populations with low allele frequency.

Association of HLA-B*15:13 and HLA-B*15:02 with phenytoin-induced severe cutaneous adverse reactions in a Malay population.

Phenytoin (PHT) is a common cause of severe cutaneous adverse reactions (SCARs), including Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS). Although HLA-B*15:02 is associated with PHT-induced SJS/TEN (PHT-SJS/TEN) in Han Chinese and Thais, the genetic basis for susceptibility to PHT-induced SCARs (PHT-SCAR) in other populations remains unclear. We performed a case–control association study by genotyping the human leukocyte antigen (HLA)-B alleles of 16 Malay PHT-SCAR patients (13 SJS/TEN and 3 DRESS), 32 PHT-tolerant controls and 300 healthy ethnicity-matched controls. A novel genetic biomarker, HLA-B*15:13, showed significant association with PHT-SJS/TEN (53.8%, 7/13 cases) (odds ratio (OR) 11.28, P=0.003) and PHT-DRESS (100%, 3/3 cases) (OR 59.00, P=0.003) when compared with PHT-tolerant controls (9.4%, 3/32 controls). We also confirmed HLA-B*15:02 association with PHT-SJS/TEN (61.5%, 8/13 cases vs 21.9%, 7/32 controls; OR 5.71, P=0.016) when compared with PHT-tolerant controls. These alleles may serve as markers to predict PHT-SCAR in Malays.

HLA-A*24:02 as a common risk factor for antiepileptic drug–induced cutaneous adverse reactions

Objective: To investigate the involvement of human leukocyte antigen (HLA) loci in aromatic antiepileptic drug–induced cutaneous adverse reactions. Methods: A case-control study was performed to detect HLA loci involved in aromatic antiepileptic drug–induced Stevens-Johnson syndrome in a southern Han Chinese population. Between January 1, 2006, and December 31, 2015, 91 cases of Stevens-Johnson syndrome induced by aromatic antiepileptic drugs and 322 matched drug-tolerant controls were enrolled from 8 centers. Important genotypes were replicated in cases with maculopapular eruption and in the meta-analyses of data from other populations. Sequence-based typing determined the HLA-A, HLA-B, HLA-C, and HLA-DRB1 genotypes. Results: HLA-B*15:02 was confirmed as strongly associated with carbamazepine-induced Stevens-Johnson syndrome (p = 5.63 × 10−15). In addition, HLA-A*24:02 was associated significantly with Stevens-Johnson syndrome induced by the aromatic antiepileptic drugs as a group (p = 1.02 × 10−5) and by individual drugs (carbamazepine p = 0.015, lamotrigine p = 0.005, phenytoin p = 0.027). Logistic regression analysis revealed a multiplicative interaction between HLA-B*15:02 and HLA-A*24:02. Positivity for HLA-A*24:02 and/or HLA-B*15:02 showed a sensitivity of 72.5% and a specificity of 69.0%. The presence of HLA-A*24:02 in cases with maculopapular exanthema was also significantly higher than in controls (p = 0.023). Meta-analysis of data from Japan, Korea, Malaysia, Mexico, Norway, and China revealed a similar association. Conclusions: HLA-A*24:02 is a common genetic risk factor for cutaneous adverse reactions induced by aromatic antiepileptic drugs in the southern Han Chinese and possibly other ethnic populations. Pretreatment screening is recommended for people in southern China.

A GWAS meta-analysis and replication study identifies a novel locus within CLPTM1L/TERT associated with nasopharyngeal carcinoma in individuals of Chinese ancestry

Background: Genetic loci within the major histocompatibility complex (MHC) have been associated with nasopharyngeal carcinoma (NPC), an Epstein-Barr virus (EBV)-associated cancer, in several GWAS. Results outside this region have varied. Methods: We conducted a meta-analysis of four NPC GWAS among Chinese individuals (2,152 cases; 3,740 controls). Forty-three noteworthy findings outside the MHC region were identified and targeted for replication in a pooled analysis of four independent case–control studies across three regions in Asia (4,716 cases; 5,379 controls). A meta-analysis that combined results from the initial GWA and replication studies was performed. Results: In the combined meta-analysis, rs31489, located within the CLPTM1L/TERT region on chromosome 5p15.33, was strongly associated with NPC (OR = 0.81; P value 6.3 × 10−13). Our results also provide support for associations reported from published NPC GWAS—rs6774494 (P = 1.5 × 10−12; located in the MECOM gene region), rs9510787 (P = 5.0 × 10−10; located in the TNFRSF19 gene region), and rs1412829/rs4977756/rs1063192 (P = 2.8 × 10−8, P = 7.0 × 10−7, and P = 8.4 × 10−7, respectively; located in the CDKN2A/B gene region). Conclusions: We have identified a novel association between genetic variation in the CLPTM1L/TERT region and NPC. Supporting our finding, rs31489 and other SNPs in this region have been reported to be associated with multiple cancer sites, candidate-based studies have reported associations between polymorphisms in this region and NPC, the TERT gene has been shown to be important for telomere maintenance and has been reported to be overexpressed in NPC, and an EBV protein expressed in NPC (LMP1) has been reported to modulate TERT expression/telomerase activity. Impact: Our finding suggests that factors involved in telomere length maintenance are involved in NPC pathogenesis. Cancer Epidemiol Biomarkers Prev; 25(1); 188–92. ©2015 AACR.

Differential expression of a subset of ribosomal protein genes in cell lines derived from human nasopharyngeal epithelium.

Extraribosomal functions of human ribosomal proteins (RPs) include the regulation of cellular growth and differentiation, and are inferred from studies that linked congenital disorders and cancer to the deregulated expression of RP genes. We have previously shown the upregulation and downregulation of RP genes in tumors of colorectal and nasopharyngeal carcinomas (NPCs), respectively. Herein, we show that a subset of RP genes for the large ribosomal subunit is differentially expressed among cell lines derived from the human nasopharyngeal epithelium. Three such genes (RPL27, RPL37a and RPL41) were found to be significantly downregulated in all cell lines derived from NPC tissues compared with a nonmalignant nasopharyngeal epithelial cell line. The expression of RPL37a and RPL41 genes in human nasopharyngeal tissues has not been reported previously. Our findings support earlier suspicions on the existence of NPC-associated RP genes, and indicate their importance in human nasopharyngeal organogenesis.

HLA-A SNPs and amino acid variants are associated with nasopharyngeal carcinoma in Malaysian Chinese

Nasopharyngeal carcinoma (NPC) arises from the mucosal epithelium of the nasopharynx and is constantly associated with Epstein–Barr virus type 1 (EBV‐1) infection. We carried out a genome‐wide association study (GWAS) of 575,247 autosomal SNPs in 184 NPC patients and 236 healthy controls of Malaysian Chinese ethnicity. Potential association signals were replicated in a separate cohort of 260 NPC patients and 245 healthy controls. We confirmed the association of HLA‐A to NPC with the strongest signal detected in rs3869062 (p = 1.73 × 10−9). HLA‐A fine mapping revealed associations in the amino acid variants as well as its corresponding SNPs in the antigen peptide binding groove (pHLA‐A‐aa‐site‐99 = 3.79 × 10−8, prs1136697 = 3.79 × 10−8) and T‐cell receptor binding site (pHLA‐A‐aa‐site‐145 = 1.41 × 10−4, prs1059520 = 1.41 × 10−4) of the HLA‐A. We also detected strong association signals in the 5′‐UTR region with predicted active promoter states (prs41545520 = 7.91 × 10−8). SNP rs41545520 is a potential binding site for repressor ATF3, with increased binding affinity for rs41545520‐G correlated with reduced HLA‐A expression. Multivariate logistic regression diminished the effects of HLA‐A amino acid variants and SNPs, indicating a correlation with the effects of HLA‐A*11:01, and to a lesser extent HLA‐A*02:07. We report the strong genetic influence of HLA‐A on NPC susceptibility in the Malaysian Chinese.