Mycoplasmas and oncogenesis

Cancer determining information transmission and circulation

Cancer determining information transmission, typically oncogene transfer, is known in many cases of virus initiated tumors. Transmission of carcinogenic information, that stored in plasmids named T-DNAs, is also known to take place in one type of bacteria induced tumor, that caused by Agrobacterium tumefaciens in dicotyledon plants roots. Other mechanisms of carcinogenic information transmission have been more recently recognized, that involve horizontal transfer of genetic material among cells. Despite this latter issue is not new, insights in its mechanisms have just beginning to appear in the literature. Horizontal transfer processes, in addition to the well known vertical transfer from parental to daughter cancer cells, have been tentatively put together with a reductionistic approach in this work, leading to a unifying framework that summarizes the state of the art in carcinogenic information transmission and circulation in the world of cells. Counteracting vectors of carcinogenic information transmission and circulation, such as oncoviruses, has already been shown to be important both in the fields of cancer prevention and therapy. Investigating today unexplored ways of transmission could lead to implement new anticancer strategies.

Do mycoplasmas cause human cancer?

A linkage between mycoplasmas and malignancy was mainly proposed in the 1960s when human-associated mycoplasmas were becoming of interest given the novel characterization of the human respiratory pathogen Mycoplasma pneumoniae. Associations with leukemia and other malignancies, however, were largely ascribed to tissue-culture contamination, which is now recognized as a significant potential problem in molecular biology circles. A few epidemiological studies, however, continue to raise concern over such a linkage. As well, in vitro data have demonstrated the potential for some mycoplasmas to induce karyotypic changes and malignant transformation during chronic tissue-culture infestation. As cellular and molecular mechanisms for such transformation become studied, a resurgence of interest in this area is inevitable. A role for mycoplasmas in malignancy of any sort is conjectural, but there remains a need to continue with focussed epidemiological and laboratory investigations.Key words: mycoplasma, cancer, oncogenesis, leukemia.

Structural and functional properties of complement-activating protein M161Ag, a Mycoplasma fermentans gene product that induces cytokine production by human monocytes

Human malignant cells are targeted by homologous complement C3b if they express M161Ag, a 43-kDa protein with C3-activating property. cDNA of M161Ag cloned from human leukemia cell lines predicted M161Ag as a novel secretory protein comprised of 428 amino acids including 5 amino acids encoded by TGA codons (Matsumoto M., Takeda, J., Inoue, N., Hara, T., Hatanaka, M., Takahashi, K., Nagasawa, S., Akedo, H., and Seya, T. (1997) Nat. Med. 3, 1266-1270), although the origin of this gene was obscure. Here we clarified this point through genomic and biochemical analysis: 1) 5'-UT and genomic sequences represented the prokaryote promoter and ribosomal binding site; 2) the TGA codons in M161Ag cDNA were translated not into selenocysteines but into tryptophans; 3) M161Ag anchored onto the membrane secondary to its N-terminal palmitoylation like prokaryote lipoproteins; 4) genomic and cDNA clones of M161Ag were highly homologous to Mycoplasma fermentans gene encoding P48, a monocytic differentiation/activation factor, recently released in the data base, although the resultant proteins were different in the amino acid sequences. Additionally, purified soluble M161Ag efficiently provoked IL-1beta, tumor necrosis factor alpha, and IL-6 like P48, and further IL-10 and IL-12 in human peripheral blood monocytes. Thus, M161Ag originates from M. fermentans, and latently infected M. fermentans allows human cells to produce M161Ag. The liberated protein serves as a potent modulator of innate and cellular immune responses via its complement-activating and cytokine-producing activities.