To understand the effects of the interaction between Mycoplasma and cells on the host cellular function, it is important to elucidate the influences of
infection of cells with Mycoplasma on nuclear
enzymes such as
DNA Topoisomerase type I (
Topo I). Human
Topo I participates in
DNA transaction processes and is the target of anti-
cancer drugs, the camptothecins (CPTs). Here we investigated the mechanism by which
infection of human
tumor cells with Mycoplasma fermentans affects the activity and expression of cellular
Topo I, and the anti-
cancer efficacy of
CPT. Human
cancer cells were infected or treated with live or sonicated M. fermentans and the activity and expression of
Topo I was determined. M. fermentans significantly reduced (by 80%)
Topo I activity in the infected/treated
tumor cells without affecting the level of
Topo I
protein. We demonstrate that this reduction in
enzyme activity resulted from ADP-ribosylation of the
Topo I
protein by
Poly-ADP-ribose polymerase (PARP-1). In addition, pERK was activated as a result of the induction of the MAPK signal transduction pathway by M. fermentans. Since PARP-1 was shown to be activated by pERK, we concluded that M. fermentans modified the cellular
Topo I activity by activation of PARP-I via the induction of the MAPK signal transduction pathway. Moreover, the
infection of
tumor cells with M. fermentans diminished the inhibitory effect of
CPT. The results of this study suggest that modification of
Topo I activity by M. fermentans may alter cellular gene expression and the response of
tumor cells to
Topo I inhibitors, influencing the anti-
cancer capacity of
Topo I antagonists.