Mycoplasma infection suppresses p53, activates NF-κB and cooperates with oncogenic Ras in rodent fibroblast transformation

Abstract

Prokaryotes of the genus Mycoplasma are the smallest cellular organisms that persist as obligate extracellular parasites. Although mycoplasma infection is known to be associated with chromosomal instability and can promote malignant transformation, the mechanisms underlying these phenomena remain unknown. Since persistence of many cellular parasites requires suppression of apoptosis in host cells, we tested the effect of mycoplasma infection on the activity of the p53 and nuclear factor (NF)-jB pathways, major mechanisms controlling programmed cell death. To monitor the activity of p53 and NF-jB in mycoplasma-infected cells, we used a panel of reporter cell lines expressing the bacterial b-galactosidase gene under the control of p53-or NF-jB-responsive promoters. Cells incubated with media conditioned with different species of mycoplasma showed constitutive activation of NF-jB and reduced activation of p53, common characteristics of the majority of human tumor cells, with M. arginini having the strongest effect among the species tested. Moreover, mycoplasma infection reduced the expression level and inducibility of an endogenous p53-responsive gene, p21 waf1 , and inhibited apoptosis induced by genotoxic stress. Infection with M. arginini made rat and mouse embryo fibroblasts susceptible to transformation with oncogenic H-Ras, whereas mycoplasma-free cells underwent irreversible p53-dependent growth arrest. Mycoplasma infection was as effective as shRNA-mediated knockdown of p53 expression in making rodent fibroblasts permissive to Rasinduced transformation. These observations indicate that mycoplasma infection plays the role of a p53-suppressing oncogene that cooperates with Ras in cell transformation and suggest that the carcinogenic and mutagenic effects of mycoplasma might be due to inhibition of p53 tumor suppressor function by this common human parasite.

Peptides genetically selected for NF-κB activation cooperate with oncogene Ras and model carcinogenic role of inflammation

“…This cell line has an undetectable background level of spontaneous transformation and has been shown to undergo senescence-like growth arrest in response to H-Ras V12 expression similar to MEFs (26,30). In addition, like MEFs, REF52 cells lacking p53 activity undergo transformation upon H-Ras V12 expression, which we confirmed using shRNA-mediated knockdown of p53 expression (26).…”

“…In this regard, NASPs resemble genetic suppressor elements described in our earlier work that encode fragments of p53 protein that act as dominantnegative p53 mutants also capable of cooperation with Ras (27). Even more relevant is our recent work on the association of mycoplasma infection with cancer predisposition where we found that the chronic, typically asymptomatic infections established by this class of bacteria lead to activation of NF-κB, suppression of p53, and promotion of oncogenic Ras-induced malignant transformation (30). Thus, sustained NF-κB activation resulting from infectious agents (such as mycoplasma) might promote cancer development not only through known NF-κB-induced factors (e.g., antiapoptotic factors and growth-promoting cytokines), but also through suppression of p53, which could impact multiple pathways of tumorigenesis, including sensitivity to oncogeneinduced transformation.…”

Inflammation and p53: A Tale of Two Stresses

“…These observations indicate that mycoplasma infection plays the role of a p53-suppressing oncogene that cooperates with Ras in cell transformation and suggest that the carcinogenic and mutagenic effects of mycoplasma might be due to NF-κB-mediated inhibition of p53. 65 The observed ability of mycoplasma infection to cooperate with a dominant oncogene in cell transformation is likely to be more than just a laboratory phenomenon. Inspired by our in vitro findings, we recently undertook a clinical study in which we looked at the presence of mycoplasma in the prostates of men suspected of having prostate cancer due to elevated prostate-specific antigen (PSA) levels.…”

Contamination of Tissue Cultures by Mycoplasmas

“…In some cases, mycoplasmas have been shown to induce the production of proteins that play essential roles in the development of malignancy. Examples are the mycoplasmal-promoted production in diverse types of cultured cells of bone morphogenetic protein 2 (BMP2) that enhances tumor growth by increasing cell proliferation [73]; mycoplasma-induced diminished activation of the tumor suppression protein p53, and enhanced fibroblast transformation by the oncogenic H-ras [74] ; promotion of cancer cell motility and migration by P37, the major immunogen of M. hyorhinis, through activation of the matrix metalloproteinase-2 [75].…”

“…The interaction with the receptors triggers cascades of cellular signals within the cell, and the complex pathways culminate in a variety of host cell responses. Mycoplasmas and mycoplasmal LPP are known to activate the transcription factors NF-B [74,79] and AP-1 [1 4], via TLRdownstream cascades involving kinases (MAPKKKs-IKKs and MAPKKKs-MAPKKsMAPKs). Known mycoplasma-affected target genes are mainly those responsible for proinflammatory proteins [4], and those involved in malignant cell transformation [72], with little information available on genes responsible for other proteins [53,79,80,81].…”