Sankar Kumar Ghosh

Epigenetic, Genetic and Environmental Interactions in Esophageal Squamous Cell Carcinoma from Northeast India

Background Esophageal squamous cell carcinoma (ESCC) develops as a result of complex epigenetic, genetic and environmental interactions. Epigenetic changes like, promoter hypermethylation of multiple tumour suppressor genes are frequent events in cancer, and certain habit-related carcinogens are thought to be capable of inducing aberrant methylation. However, the effects of environmental carcinogens depend upon the level of metabolism by carcinogen metabolizing enzymes. As such key interactions between habits related factors and carcinogen metabolizing gene polymorphisms towards modulating promoter methylation of genes are likely. However, this remains largely unexplored in ESCC. Here, we studied the interaction of various habits related factors and polymorphism of GSTM1/GSTT1 genes towards inducing promoter hypermethylation of multiple tumour suppressor genes. Methodology/Principal Findings The study included 112 ESCC cases and 130 age and gender matched controls. Conditional logistic regression was used to calculate odds ratios (OR) and multifactor dimensionality reduction (MDR) was used to explore high order interactions. Tobacco chewing and smoking were the major individual risk factors of ESCC after adjusting for all potential confounding factors. With regards to methylation status, significantly higher methylation frequencies were observed in tobacco chewers than non chewers for all the four genes under study (p<0.01). In logistic regression analysis, betel quid chewing, alcohol consumption and null GSTT1 genotypes imparted maximum risk for ESCC without promoter hypermethylation. Whereas, tobacco chewing, smoking and GSTT1 null variants were the most important risk factors for ESCC with promoter hypermethylation. MDR analysis revealed two predictor models for ESCC with promoter hypermethylation (Tobacco chewing/Smoking/Betel quid chewing/GSTT1 null) and ESCC without promoter hypermethylation (Betel quid chewing/Alcohol/GSTT1) with TBA of 0.69 and 0.75 respectively and CVC of 10/10 in both models. Conclusion Our study identified a possible interaction between tobacco consumption and carcinogen metabolizing gene polymorphisms towards modulating promoter methylation of tumour suppressor genes in ESCC.

Mitochondrial DNA Copy Number and Risk of Oral Cancer: A Report from Northeast India

Background Oral squamous cell carcinoma (OSCC) is the sixth most common cancer globally. Tobacco consumption and HPV infection, both are the major risk factor for the development of oral cancer and causes mitochondrial dysfunction. Genetic polymorphisms in xenobiotic-metabolizing enzymes modify the effect of environmental exposures, thereby playing a significant role in gene–environment interactions and hence contributing to the individual susceptibility to cancer. Here, we have investigated the association of tobacco - betel quid chewing, HPV infection, GSTM1-GSTT1 null genotypes, and tumour stages with mitochondrial DNA (mtDNA) content variation in oral cancer patients. Methodology/Principal Findings The study comprised of 124 cases of OSCC and 140 control subjects to PCR based detection was done for high-risk HPV using a consensus primer and multiplex PCR was done for detection of GSTM1-GSTT1 polymorphism. A comparative ΔCt method was used for determination of mtDNA content. The risk of OSCC increased with the ceased mtDNA copy number (Ptrend = 0.003). The association between mtDNA copy number and OSCC risk was evident among tobacco – betel quid chewers rather than tobacco – betel quid non chewers; the interaction between mtDNA copy number and tobacco – betel quid was significant (P = 0.0005). Significant difference was observed between GSTM1 - GSTT1 null genotypes (P = 0.04, P = 0.001 respectively) and HPV infection (P<0.001) with mtDNA content variation in cases and controls. Positive correlation was found with decrease in mtDNA content with the increase in tumour stages (P<0.001). We are reporting for the first time the association of HPV infection and GSTM1-GSTT1 null genotypes with mtDNA content in OSCC. Conclusion Our results indicate that the mtDNA content in tumour tissues changes with tumour stage and tobacco-betel quid chewing habits while low levels of mtDNA content suggests invasive thereby serving as a biomarker in detection of OSCC.

Identification and re-evaluation of freshwater catfishes through DNA barcoding.

Background Catfishes are globally demanded as human food, angling sport and aquariums keeping thus are highly exploited all over the world. North-East India possess high abundance of catfishes and are equally exploited through decades. The strategies for conservation necessitate understanding the actual species composition, which is hampered due to sporadic descriptions of the species through traditional taxonomy. Therefore, actual catfish diversity in this region is important to be studied through the combined approach of morphological and molecular technique of DNA barcoding. Methodology/Principal Findings Altogether 75 native catfish specimens were collected from across the North-East India and their morphological features were compared with the taxonomic keys. The detailed taxonomic study identified 25 species belonging to 17 genera and 9 families. The cytochrome oxidase c subunit-I gene fragment were then sequenced from the samples in accordance with the standard DNA barcoding protocols. The sequences were compared with public databases, viz., GenBank and BOLD. Sequences developed in the current study and from databases of the same and related taxa were analyzed to calculate the congeneric and conspecific genetic divergences using Kimura 2-parameter distance model, and a Neighbor Joining tree was created using software MEGA5.1. The DNA barcoding approach delineated 21 distinct species showing 4.33 folds of difference between the nearest congeners. Four species, viz., Amblyceps apangi, Glyptothorax telchitta, G. trilineatus and Erethistes pusillus, showed high conspecific divergence; hence their identification through molecular approach remained inconclusive. On the other hand, the database sequences for three species, viz., Mystus horai, Bagarius yarrelli and Clarias batrachus, appeared mislabeled. Conclusion The efficiency of DNA barcoding was reaffirmed from its success by easily identifying the major share (84%) of the studied catfish into 21 distinct species. The study contributed 27 new barcodes for 7 species and confirmed the range expansion of 2 important species in NE India.

The Species Dilemma of Northeast Indian Mahseer (Actinopterygii: Cyprinidae): DNA Barcoding in Clarifying the Riddle

Background The taxonomic validity of Northeast Indian endemic Mahseer species, Tor progeneius and Neolissochilus hexastichus, has been argued repeatedly. This is mainly due to disagreements in recognizing the species based on morphological characters. Consequently, both the species have been concealed for many decades. DNA barcoding has become a promising and an independent technique for accurate species level identification. Therefore, utilization of such technique in association with the traditional morphotaxonomic description can resolve the species dilemma of this important group of sport fishes. Methodology/Principal Findings Altogether, 28 mahseer specimens including paratypes were studied from different locations in Northeast India, and 24 morphometric characters were measured invariably. The Principal Component Analysis with morphometric data revealed five distinct groups of sample that were taxonomically categorized into 4 species, viz., Tor putitora, T. progeneius, Neolissochilus hexagonolepis and N. hexastichus. Analysis with a dataset of 76 DNA barcode sequences of different mahseer species exhibited that the queries of T. putitora and N. hexagonolepis clustered cohesively with the respective conspecific database sequences maintaining 0.8% maximum K2P divergence. The closest congeneric divergence was 3 times higher than the mean conspecific divergence and was considered as barcode gap. The maximum divergence among the samples of T. progeneius and T. putitora was 0.8% that was much below the barcode gap, indicating them being synonymous. The query sequences of N. hexastichus invariably formed a discrete and a congeneric clade with the database sequences and maintained the interspecific divergence that supported its distinct species status. Notably, N. hexastichus was encountered in a single site and seemed to be under threat. Conclusion This study substantiated the identification of N. hexastichus to be a true species, and tentatively regarded T. progeneius to be a synonym of T. putitora. It would guide the conservationists to initiate priority conservation of N. hexastichus and T. putitora.

Role of DNA barcoding in marine biodiversity assessment and conservation: An update.

More than two third area of our planet is covered by oceans and assessment of marine biodiversity is a challenging task. With the increasing global population, there is a tendency to exploit marine resources for food, energy and other requirements. This puts pressure on the fragile marine environment and necessitates sustainable conservation efforts. Marine species identification using traditional taxonomical methods is often burdened with taxonomic controversies. Here we discuss the comparatively new concept of DNA barcoding and its significance in marine perspective. This molecular technique can be useful in the assessment of cryptic species which is widespread in marine environment and linking the different life cycle stages to the adult which is difficult to accomplish in the marine ecosystem. Other advantages of DNA barcoding include authentication and safety assessment of seafood, wildlife forensics, conservation genetics and detection of invasive alien species (IAS). Global DNA barcoding efforts in the marine habitat include MarBOL, CeDAMar, CMarZ, SHARK-BOL, etc. An overview on DNA barcoding of different marine groups ranging from the microbes to mammals is revealed. In conjugation with newer and faster techniques like high-throughput sequencing, DNA barcoding can serve as an effective modern tool in marine biodiversity assessment and conservation.

An assessment of the DNA barcodes of Indian freshwater fishes

Freshwater fishes in India are poorly known and plagued by many unresolved cryptic species complexes that masks some latent and endemic species. Limitations in traditional taxonomy have resulted in this crypticism. Hence, molecular approaches like DNA barcoding, are needed to diagnose these latent species. We have analyzed 1383 barcode sequences of 175 Indian freshwater fish species available in the databases, of which 172 sequences of 70 species were generated. The congeneric and conspecific genetic divergences were calculated using Kimuras 2 parameter distance model followed by the construction of a Neighbor Joining tree using the MEGA 5.1. DNA barcoding principle at its first hand approach, led to the straightforward identification of 82% of the studied species with 2.9% (S.E=0.2) divergence between the nearest congeners. However, after validating some cases of synonymy and mislabeled sequences, 5% more species were found to be valid. Sequences submitted to the database under different names were found to represent single species. On the other hand, some sequences of the species like Barilius barna, Barilius bendelisis and Labeo bata were submitted to the database under a single name but were found to represent either some unexplored species or latent species. Overall, 87% of the available Indian freshwater fish barcodes were diagnosed as true species in parity with the existing checklist and can act as reference barcode for the particular taxa. For the remaining 13% (21 species) the correct species name was difficult to assign as they depicted some erroneous identification and cryptic species complex. Thus, these barcodes will need further assay and inclusion of barcodes of more specimens from same and sister species.

Promoter Hypermethylation Profiling Identifies Subtypes of Head and Neck Cancer with Distinct Viral, Environmental, Genetic and Survival Characteristics

Background Epigenetic and genetic alteration plays a major role to the development of head and neck squamous cell carcinoma (HNSCC). Consumption of tobacco (smoking/chewing) and human papilloma virus (HPV) are also associated with an increase the risk of HNSCC. Promoter hypermethylation of the tumor suppression genes is related with transcriptional inactivation and loss of gene expression. We investigated epigenetic alteration (promoter methylation of tumor-related genes/loci) in tumor tissues in the context of genetic alteration, viral infection, and tobacco exposure and survival status. Methodology The study included 116 tissue samples (71 tumor and 45 normal tissues) from the Northeast Indian population. Methylation specific polymerase chain reaction (MSP) was used to determine the methylation status of 10 tumor-related genes/loci (p16, DAPK, RASSF1, BRAC1, GSTP1, ECAD, MLH1, MINT1, MINT2 and MINT31). Polymorphisms of CYP1A1, GST (M1 & T1), XRCC1and XRCC2 genes were studied by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and multiplex-PCR respectively. Principal Findings Unsupervised hierarchical clustering analysis based on methylation pattern had identified two tumor clusters, which significantly differ by CpG island methylator phenotype (CIMP), tobacco, GSTM1, CYP1A1, HPV and survival status. Analyzing methylation of genes/loci individually, we have found significant higher methylation of DAPK, RASSF1, p16 and MINT31genes (P = 0.031, 0.013, 0.031 and 0.015 respectively) in HPV (+) cases compared to HPV (-). Furthermore, a CIMP-high and Cluster-1 characteristic was also associated with poor survival. Conclusions Promoter methylation profiles reflecting a correlation with tobacco, HPV, survival status and genetic alteration and may act as a marker to determine subtypes and patient outcome in HNSCC.

Accumulation of mutations over the complete mitochondrial genome in tobacco-related oral cancer from northeast India

Northeast India has one of the worlds highest incidences of oral cancer and 90% of them are related to tobacco. We examined the complete mitochondrial genome to determine hot spot mutations in oral cancer. The complete mitochondrial genome was sequenced using PGM™ from 10 patients matched blood and tumour tissue. Overall, 26 somatic mutations were found of which nine mutations in d-loop and 17 mutations in the coding region. The mutations at nucleotide positions 16294, 16325 and 16463 in d-loop and 4136, 13542 and 13869 in coding region are probably an indication to be a hot spot mutation in oral cancer. The knowledge about role, patterns and timing of mitochondrial mutations may serve to be facilitating clinical applications and hot spot mutations may be helpful in assessing cancer risk in tumour.

Association of mitochondrial D-loop mutations with GSTM1 and GSTT1 polymorphisms in oral carcinoma: A case control study from Northeast India

OBJECTIVES Mitochondrial dysfunction is a hallmark of cancer cells. Tobacco consumption in various forms is one of the major risk factors for the development of oral squamous cell carcinoma which makes the mitochondrial DNA susceptible to damage by reactive oxygen species. The GSTT1 and GSTM1 members of the glutathione S-transferase multigene family are candidate carcinogen metabolizing genes. Here we determined the hot spot mutations in the D-loop region and revealing correlation if any, with clinical parameters, along with analysing the genetic polymorphism of GSTT1 and GSTM1 and its susceptibility towards oral cancer. MATERIALS AND METHODS To determine the hot spot mutations 25 matched tissue samples of OSCC patients with 25 control subjects were used for PCR and direct sequencing. Analysis for GSTM1 and GSTT1 gene polymorphism was done by multiplex PCR. RESULTS Several mutations were found within the D-loop region among which mutations at nt146, nt152 and nt196 are found to be hot spot (P<0.0001, P<0.0001 and P<0.001 respectively). A significant association was found between the numbers of D-loop mutation and GSTM1 (OR=2.03; 95% CI, 1.04-3.96, P=0.003), GSTT1 (OR=1.73; 95% CI, 1.10-2.71, P=0.0027) null genotypes respectively. We observed a significant correlation between the increased number of D-loop mutations with the advancement in tumour stage of the patients (P=0.009, r=0.48). CONCLUSION The association of null genotypes and mutations can be used as a possible biomarker for early detection and preventive measure of oral cancer for those habituated to tobacco consumption.

Epigenetic response in mice mastitis: Role of histone H3 acetylation and microRNA(s) in the regulation of host inflammatory gene expression during Staphylococcus aureus infection

BackgroundThere is renewed interest towards understanding the host-pathogen interaction in the light of epigenetic modifications. Although epithelial tissue is the major site for host-pathogen interactions, there is handful of studies to show how epithelial cells respond to pathogens. Bacterial infection in the mammary gland parenchyma induces local and subsequently systemic inflammation that results in a complex disease called mastitis. Globally Staphylococcus aureus is the single largest mastitis pathogen and the infection can ultimately result in either subclinical or chronic and sometimes lifelong infection.ResultsIn the present report we have addressed the differential inflammatory response in mice mammary tissue during intramammary infection and the altered epigenetic context induced by two closely related strains of S. aureus, isolated from field samples. Immunohistochemical and immunoblotting analysis showed strain specific hyperacetylation at histone H3K9 and H3K14 residues. Global gene expression analysis in S. aureus infected mice mammary tissue revealed a selective set of upregulated genes that significantly correlated with the promoter specific, histone H3K14 acetylation. Furthermore, we have identified several differentially expressed known miRNAs and 3 novel miRNAs in S. aureus infected mice mammary tissue by small RNA sequencing. By employing these gene expression data, an attempt has been made to delineate the gene regulatory networks in the strain specific inflammatory response. Apparently, one of the isolates of S. aureus activated the NF-κB signaling leading to drastic inflammatory response and induction of immune surveillance, which could possibly lead to rapid clearance of the pathogen. The other strain repressed most of the inflammatory response, which might help in its sustenance in the host tissue.ConclusionTaken together, our studies shed substantial lights to understand the mechanisms of strain specific differential inflammatory response to S. aureus infection during mastitis. In a broader perspective this study also paves the way to understand how certain bacteria can evade the immune surveillance and cause sustained infection while others are rapidly cleared from the host body.