A study of tetratricopeptide repeat domain12 (TTC12) methylation in leukemia

Abstract

We searched a candidate tumor suppressor gene of nasopharyngeal carcinoma (NPC) on the critical region of loss of heterozygosity on chromosome 11 q. Unexpectedly, we accidentally discovered that tetratricopeptide repeat domail (TTC12)m an NPC down regulated gene located in the LOH region, hypermethylated in leukemic cell lines. These cells included Daudi (B-lymphoblastoid line), Jurkat (acute T cell leukemia). Molt4 (acute lymphoblastic leukemia). No methylation was observed in K562 (chronic myelogenous leukemia) and those of epitherial cell lines, HN12 and Hela, were nonmethylated. Therefore, we hypothesized that the meythlation of TTC12 may be specific in leukemogenesis in vivo. To prove this hypothesis, we tested 29 acute lymphoblastic leukemia (ALL) in comparison with normal white blood cells (WBC) from 10 healthy volunteers using combined bisulfite restriction analysis (COBRA) technique. In ALL group, the results significant demonstrated hypermethylated than in normal WBC (p< 0.0001), and methylation level do not depend on ALL subtypes (p>0.1). The result were confirmed by cloning and sequencing. We tested TTC12 expression by RT-PCR, nonmethylated cells, K562, HN12 and Hela, expressed TTC12, whereas hypermethylated cells, Daudi, Jurkat and Molt4, did not express. The same situation has also detectable in vivo. We compared the proportion between TTC12 and GAPDH and found significant increase in expression of TTC12 in hypomethylated ALL when compared with hypermethylated cases (p<0.05). In addition, we tested TTC12 methylation in 8 remission ALL, 4 T cell lymphomas and 5 stem cells. The result showed different level of methylation each groups. The methylation on TTC12 expands through over 5’UTR. Therefore, hypermethylation in TTC12 may induce leukemogenesis by inhibiting its mRNA. Although the function of TTC12 has not been identified in silico, two conserved domains have been found including the tetratricopeptide repeat (TPR) domain and the armadillo repeat (ARM) domains. TTC12 might mediate protein-protein interaction with other proteins through TPR and ARM domains to trigger some cellular process including cell cycle control. Nevertheless, this hypothesis as well as the function(s) of TTC12 should be investigated and this will provide new knowledge of cancer biology that could be applied in cancer diagnosis as well as therapeutic in the future.