Variations of mitochondrial D-loop region plus downstream gene 1 2S rRNA-tRNA(phe) and gastric carcinomas

Abstract

Aim: To explore the instabilities, polymorphisms and other variations of mitochondrial D-loop region and downstream gene 12S rRNA-tRNA(phe) in gastric cancers, and to study their relationship with gastric cancer.

Methods: Three adjacent regions (D-loop, tRNA(phe) and 12S rRNA) were detected for instabilities, polymorphisms and other variations via PCR amplification followed by direct DNA sequencing in 22 matched gastric cancerous tissues and para-cancerous normal tissues.

Results: PolyC or (CA) (n) instabilities were detected in 13/22(59.1 %) gastric cancers and 9/22(40.9 %) in the control (P>0.05). There existed 2/12(16.7 %) and 6/10(60 %) alterations of 12S rRNA-tRNA(phe) in well differentiated gastric cancers and poorly differentiated ones, respectively (P<0.05). Some new variations were found, among which np 318 and np 321 C-T transitions in D-loop region were two of the five bases for H-strand replication primer. np 523 AC-deletion and np 527 C-T transition occurred at mtTF1 binding site (mtTFBS), which were associated with the transcription of downstream mitochondrial genome. Seven samples showed the np 16 182 polyC instabilities, five of which simultaneously showed np 16 189 T-C transitions.

Conclusion: There is no statistic significance of instabilities and polymorphisms in mitochondrial D-loop region between gastric cancerous and para-cancerous normal tissues, which suggests that the instability might relate to heredity or be dependent on aging. There is a significant correlation between differentiation degree of gastric cancer and variant frequencies of 12S rRNA-tRNA(phe). The poorly differentiated gastric cancers are more prone to 12S rRNA-tRNA(phe) variations, or gastric cancers with 12S rRNA-tRNA(phe) variations are more likely to be poorly differentiated. np 16 189 T-C transition may be one of the important reasons for polyC instability in gastric cancer.

Figure 1

Sequencing results of instabilities and some variations in D-loop and 12S rRNA-tRNA^phe.

Figure 2

Elements of transcription and translation for mitochondrial coding region 12S rRNA-tRNA^phe and non-coding D-loop region. Non-coding D-loop region and genes encoding 12S rRNA and tRNA^phe are shown with boxes on the H-strand and L-strand of mtDNA. H1 and H2 are start sites for transcription of H-strand. L is start site for transcription of L-strand. O_H is the primary origin of H-strand. mt3, mt4 and mt5 are control elements. TAS: termination-associated sequence. CSB: Conserved Sequence Block.