We identified a human orthologue of tRNA:m5C methyltransferase from Saccharomyces cerevisiae, which has been previously shown to catalyse the specific modification of C34 in the intron-containing yeast pre-tRNA(CAA)Leu. Using transcripts of intron-less and intron-containing human tRNA(CAA)Leu genes as substrates, we have shown that m5C34 is introduced only in the intron-containing tRNA precursors when the substrates were incubated in the HeLa extract. m5C34 formation depends on the nucleotide sequence surrounding the wobble cytidine and on the structure of the prolongated anticodon stem. Expression of the human Trm4 (hTrm4) cDNA in yeast partially complements the lack of the endogenous Trm4p enzyme. The yeast extract prepared from the strain deprived of the endogenous TRM4 gene and transformed with hTrm4 cDNA exhibits the same activity and substrate specificity toward human pre-tRNALeu transcripts as the HeLa extract. The hTrm4 MTase has a much narrower specificity against the yeast substrates than its yeast orthologue: human enzyme is not able to form m5C at positions 48 and 49 of human and yeast tRNA precursors. To our knowledge, this is the first report showing intron-dependent methylation of human pre-tRNA(CAA)Leu and identification of human gene encoding tRNA methylase responsible for this reaction.

Toll-like receptors (TLRs) have been shown to play crucial role in the recognition of unicellular pathogens. We have shown the expression of three TLRs on tumor cells of human laryngeal carcinoma by means of immunohistochemistry. In the current study we searched presence of TLR1-10 on protein and molecular level in larynx carcinoma cell lines and the impact of respective TLR ligands on TLR expression. Larynx carcinoma cell lines have been used. Cell were subjected to immunocytochemistry. RNA isolated from the cells was tested by RT-PCR. Cells were cultured in the presence of respective TLR ligands. Cells than were harvested and subjected to flow cytometry, using anti TLR1-10 Moabs. The cells were evaluated of membrane and cytoplasmic cell staining. TLR reactivity varied in individual cell lines. RT-PCR allowed to show mRNA for all TLRs tested. After short-term cell culture each cell line exhibited distinct pattern of expression of TLRs following interaction with respective ligand. Cytoplasmic TLR staining had usually higher MFI value than membrane one, but after culture with ligand it became reversed. TLRs 7 and 9 showed highest expression in the majority of tumor cells tested. In conclusion, larynx carcinoma cell lines exhibit rather universal expression of TLRs, both on protein and molecular level. Culture of TLR expressing tumor cells with ligands points out for potential reactivity of tumor cells with TLR agonists, what may have therapeutic implications.

Pattern recognition receptors (PRRs) are a pivotal part of the immune system. They are distributed in almost every site of higher organisms, able to recognize foreign pathogens or unwanted remnants of metabolism and mount innate immune response. Moreover, PRRs create bridging signaling to initiate adaptive immunity. The liver being the largest organ of the body, exposed to myriads of foreign substances often being immunogenic, is well equipped with PRRs. They act as sentinels of the organ, both in health and disease. In viral hepatitis C at least two of them, RIG-1 and TLR3 sense HCV, induce protective interferon production and create proinflammatory status. The hepatitis B virus is apparently invisible to PRRs, which has recently been denied. Besides, they are active in the course of infection. In liver injury and hepatic fibrogenesis Toll-like receptors (TLRs), predominantly TLR4, TLR3 and TLR9 are associated with gut microflora-related products and DNA from dying hepatocytes, lead to the activation of hepatic stellate cells. The latter initiate production of fibrillar collagens, the main agents forming hepatic fibrosis. Tumor cells of primary liver cancer also express PRRs, mainly TLRs. In concert with non-resolving liver inflammation, they are considered pivotal factors leading to carcinogenesis.

Toll-like receptors (TLRs)

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