Hypomodification of transfer RNA in cancer with respect to queuosine.

Queuosine is a highly modified nucleoside analogue of guanosine. It is present only in the first position of anticodon loop of specific tRNA i.e., tRNA(his), tRNA(asp), tRNA(asn) and tRNA(tyr) and post transcriptionally modified with base-for-base exchange of guanine to queuine. The transfer RNA modifying enzyme transfer RNA guanine transglycosylase (TGTase) catalyzes the modification of tRNAs. Transfer RNA is completely modified with respect to queuosine in mature tissue, however modification is often incomplete in mitotically active cells. Hypomodification of transfer RNA is correlated with cell proliferation and malignancy. In the present study queuosine modification of transfer RNA and TGTase activity is compared in normal, Dalton's lymphoma ascites transplanted (DLAT) cancerous and queuine treated DLAT cancerous mouse liver. Transfer RNA of cancerous mouse is hypomodified in terms of queuosine modification. TGTase activity of cancerous mouse is found to decrease to less then half of enzyme activity of normal mouse; suggesting that the enzyme may be responsible for transfer RNA hypomodification. Exogenous treatment of queuine during development of cancer improves the queuosine modification of transfer RNA. The activators NaPP and ATP enhance TGTase activity of normal and DLAT cancerous mouse, where as 7mG inhibits the TGTase activity.