Abstract A33: Dysfunction of subtelomeric methylation and telomere length in different grades of gallbladder cancer
Authors: Poojary Satish , Mishra Gunja , Gupta Sanjiv , Shrivastav Braj Raj , Tiwari Pramod Kumar 
Published: May 2016

Background: Gallbladder cancer (GBC), although a rare cancer, has a very high incidence in certain parts of the world including North Central India. A recent report from our lab has shown a very high incidence in the Gwalior-Chambal region of North Central India, ranking fourth among all cancers and first among gastrointestinal tract cancers. Due to its highly aggressive nature and inadequate therapeutic alternatives, its mortality is very high while prognosis is poor. Gallstones, which are an important risk factor, are present in most of the tumor cases. Telomeres are known to protect the organism against chromosomal instability and its dysfunction has been reported to be an early and common event in pre-cancerous lesions. Subtelomeric repeats, which are located adjacent to telomeres, include sequences, such as D4Z4 and DNF92. Subtelomeric methylation has been recently reported to negatively regulate telomere length in various diseases, including cancer. However, there is no report on the influence of subtelomeric methylation in telomere dysfunction in GBC and whether this is affected by the presence of gall stones.

Materials and Methods: Monochrome multiplex quantitative PCR was used to determine telomere length in 37 pairs of adjacent non tumor and adenocarcinoma tissues and 37 gall stone tissues. Methylation status of 2 subtelomeric sequences, D4Z4 and DNF92 was assessed by bisulfite sequencing in 24 samples of different tissue grades. Comparison was made between normal, gallstone and different grades of cancer tissues with regard to their telomere length and methylation status. To calculate statistical significance of the observed differences in telomere length and methylation status, Mann-Whitney Rank Sum test and Chi square test was applied, respectively. Linear regression analysis was applied to test the correlation between telomere length and subtelomeric methylation.

Results: Telomere length was observed to be shortened significantly in early grade GBC (p &lt; 0.001) and not in late grade. Also, D4Z4 and DNF92 sequences were found to be hyper- and hypo-methylated, respectively, in GBC (D4Z4, p = 0.01; DNF92, p = 0.01), with their levels significantly differing only in early grades of GBC (D4Z4, p = 4x10-6; DNF92, p = 0.01). Surprisingly, no correlation could be found between subtelomeric methylation levels and telomere length. Interestingly, telomere length and subtelomeric methylation differed significantly in tumor tissues without gallstones and not in tumor tissues with gallstones (telomere length, p=0.02; D4Z4, p = 0.005; DNF92, p = 0.009).

Conclusion: This study, thus, suggests that telomere dysfunction and changes in methylation levels occurs earlier in the progression of GBC and presence of gall stones may have no effect on telomere length as well as methylation levels.

Citation Format: Satish Poojary, Gunja Mishra, Sanjiv Gupta, Braj Raj Shrivastav, Pramod Kumar Tiwari. Dysfunction of subtelomeric methylation and telomere length in different grades of gallbladder cancer. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr A33.