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

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)-kappaB pathways, major mechanisms controlling programmed cell death. To monitor the activity of p53 and NF-kappaB in mycoplasma-infected cells, we used a panel of reporter cell lines expressing the bacterial beta-galactosidase gene under the control of p53- or NF-kappaB-responsive promoters. Cells incubated with media conditioned with different species of mycoplasma showed constitutive activation of NF-kappaB 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 Ras-induced 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.

Nonactivated macrophage-induced nitric oxide production by tumor cells differing in tumorigenic and spontaneous metastatic activities

The ability of nonactivated peritoneal macrophages to induce nitric oxide (NO) secretion in transformed and tumor cells of the same origin differing in tumorigenic (TGA) and spontaneous metastatic activities (SMA) was examined. Low tumorigenic and nonmetastatic spontaneously transformed in vitro hamster embryo cells of the STHE strain in contact with macrophages, or their non-purified soluble product were the highest producers of NO. In vivo selected STHE cell variants characterized by middle or high TGA demonstrated low, or no NO production, respectively (independently of SMA- or SMA+). Two highly tumorigenic RSV-SR (v-src) transformed cell strains (SMA- and SMA+) were both negative in NO production. Thus, NO production by tumor cells appeared to be inversely correlated with TGA level and less dependent on SMA.

Bing de ling, a Chinese herbal formula, stimulates multifaceted immunologic responses in mice

Bing de ling is a Chinese herbal formula most commonly used in complementary medical settings against viral disorders. We have found that bing de ling potentiates upregulation of immune activity when administered to mice in dosages proportional to those used clinically. These mice demonstrated significant elevation of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) production in splenocytes and enhancement of macrophage, natural killer cell, and lymphokine-activated killer cell cytotoxicity. These data are consistent with bing de ling's clinically observed efficacy against viruses and identify the formula as a promising candidate for clinical trials against diverse diseases that may respond to increased immunologic activity.

Growth-regulating influence of nonactivated resident macrophages on transformed and tumor cells in the in vitro contact interactions

Susceptibility to cytostatic activity of nonactivated macrophages (Mph) of Syrian hamster embryo fibroblasts (HEF) transformed in vitro by BAV-3, SV40, RSV-SR, or spontaneously and of their in vivo selected variants was studied in dynamics (5 days of co-incubation). With the use of 3H-TdR incorporation test it was demonstrated that HEF transformed by BAV-3 appeared to be able to overcome the cytostasis at 4-5 day of the co-incubation with Mph, in contrast to deeply suppressed spontaneously transformed cells of STHE strain. HEF transformed by SV40, or RSV-SR appeared to be resistant to growth-inhibiting activity of Mph during almost all the 5-day period. The in vivo selected malignant variants of STHE cells were able to recover from cytostasis after 4-5 days of the co-incubation with nonactivated Mph, in contrast to low-malignant variant and to parental cell strain.