Mycoplasmal infections prevent apoptosis and induce malignant transformation of interleukin-3-dependent 32D hematopoietic cells

The dual role of thymidine phosphorylase in cancer development and chemotherapy

Thymidine phosphorylase (TP), also known as "platelet-derived endothelial cell growth factor" (PD-ECGF), is an enzyme, which is upregulated in a wide variety of solid tumors including breast and colorectal cancers. TP promotes tumor growth and metastasis by preventing apoptosis and inducing angiogenesis. Elevated levels of TP are associated with tumor aggressiveness and poor prognosis. Therefore, TP inhibitors are synthesized in an attempt to prevent tumor angiogenesis and metastasis. TP is also indispensable for the activation of the extensively used 5-fluorouracil prodrug capecitabine, which is clinically used for the treatment of colon and breast cancer. Clinical trials that combine capecitabine with TP-inducing therapies (such as taxanes or radiotherapy) suggest that increasing TP expression is an adequate strategy to enhance the antitumoral efficacy of capecitabine. Thus, TP plays a dual role in cancer development and therapy: on the one hand, TP inhibitors can abrogate the tumorigenic and metastatic properties of TP; on the other, TP activity is necessary for the activation of several chemotherapeutic drugs. This duality illustrates the complexity of the role of TP in tumor progression and in the clinical response to fluoropyrimidine-based chemotherapy.

Exploring the link between microorganisms and oral cancer: a systematic review of the literature

The majority of cases of oral cancer have been related to tobacco use and heavy alcohol consumption. However, the incidence of oral cavity carcinoma appears to be increasing in many parts of the world in a manner that it is difficult to explain with traditional risk factors alone. Meanwhile, interest in the possible relationships between microorganisms and the different stages of cancer development has been rising and numerous mechanisms by which bacteria and yeast may initiate or promote carcinogenesis are currently under investigation. In particular, a persuasive body of evidence suggests a possible etiological role involving the metabolism and production of carcinogenic products, such as acetaldehyde. Other suggested mechanisms include the induction of chronic inflammation and direct interference with eukaryotic cell cycle and signaling pathways. This review aims to summarize the known associations between microbial infection and cancer and draw attention to how they may relate to oral carcinoma.

Persistent exposure to Mycoplasma induces malignant transformation of human prostate cells

Recent epidemiologic, genetic, and molecular studies suggest infection and inflammation initiate certain cancers, including those of the prostate. The American Cancer Society, estimates that approximately 20% of all worldwide cancers are caused by infection. Mycoplasma, a genus of bacteria that lack a cell wall, are among the few prokaryotes that can grow in close relationship with mammalian cells, often without any apparent pathology, for extended periods of time. In this study, the capacity of Mycoplasma genitalium, a prevalent sexually transmitted infection, and Mycoplasma hyorhinis, a mycoplasma found at unusually high frequency among patients with AIDS, to induce a malignant phenotype in benign human prostate cells (BPH-1) was evaluated using a series of in vitro and in vivo assays. After 19 weeks of culture, infected BPH-1 cells achieved anchorage-independent growth and increased migration and invasion. Malignant transformation of infected BPH-1 cells was confirmed by the formation of xenograft tumors in athymic mice. Associated with these changes was an increase in karyotypic entropy, evident by the accumulation of chromosomal aberrations and polysomy. This is the first report describing the capacity of M. genitalium or M. hyorhinis infection to lead to the malignant transformation of benign human epithelial cells and may serve as a model to further study the relationship between prostatitis and prostatic carcinogenesis.

Improvement of purine and pyrimidine antimetabolite-based anticancer treatment by selective suppression of mycoplasma-encoded catabolic enzymes

Most mycoplasmas are present as commensals, colonising the mucosa of our respiratory and gastrointestinal tract. Experimental data suggest that the long-term association of certain mycoplasma species with mammalian cells might favour host-cell transformation and malignancy. Moreover, increased mycoplasma infection has been noted in several cancers. Despite efforts to develop target-specific anticancer drugs, current cancer treatment still relies on the use of nucleobase or nucleoside-based analogues. Here, we provide experimental evidence that nucleoside-metabolising catabolic enzymes expressed by mycoplasmas substantially compromise the efficacy of nucleoside antimetabolites used in the treatment of cancer. We also suggest potential methods for improving future chemotherapy by suppressing mycoplasma-mediated catabolism of the anticancer nucleoside analogues.

Structural insights into the extracytoplasmic thiamine-binding lipoprotein p37 of Mycoplasma hyorhinis

The Mycoplasma hyorhinis protein p37 has been implicated in tumorigenic transformation for more than 20 years. Though there are many speculations as to its function, based solely on sequence homology, the issue has remained unresolved. Presented here is the 1.6-A-resolution refined crystal structure of M. hyorhinis p37, renamed the extracytoplasmic thiamine-binding lipoprotein (Cypl). The structure shows thiamine pyrophosphate (TPP) and two calcium ions are bound to Cypl and give the first insights into possible functions of the Cypl-like family of proteins. Sequence alignments of Cypl-like proteins between several different species of mycoplasma show that the thiamine-binding site is likely conserved and structural alignments reveal the similarity of Cypl to various binding proteins. While the experimentally determined function of Cypl remains unknown, the structure shows that the protein is a TPP-binding protein, opening up many avenues for future mechanistic studies and making Cypl a possible target for combating mycoplasma infections and tumorigenic transformation.

Interaction of Mycoplasma genitalium with host cells: evidence for nuclear localization

Mycoplasma genitalium (Mg) is a mollicute that causes a range of human urogenital infections. A hallmark of these bacteria is their ability to establish chronic infections that can persist despite completion of appropriate antibiotic therapies and intact and functional immune systems. Intimate adherence and surface colonization of mycoplasmas to host cells are important pathogenic features. However, their facultative intracellular nature is poorly understood, partly due to difficulties in developing and standardizing cellular interaction model systems. Here, we characterize growth and invasion properties of two Mg strains (G37 and 1019V). Mg G37 is a high-passage laboratory strain, while Mg 1019V is a low-passage isolate recovered from the cervix. The two strains diverge partially in gene sequences for adherence-related proteins and exhibit subtle variations in their axenic growth. However, with both strains and consistent with our previous studies, a subset of adherent Mg organisms invade host cells and exhibit perinuclear targeting. Remarkably, intranuclear localization of Mg proteins is observed, which occurred as early as 30 min after infection. Mg strains deficient in adherence were markedly reduced in their ability to invade and associate with perinuclear and nuclear sites.

The cytostatic activity of pyrimidine nucleosides is strongly modulated by Mycoplasma hyorhinis infection: Implications for cancer therapy

Nucleoside analogues are widely used as chemotherapeutic agents in the treatment of cancer. Several cancers are reported to be associated with mycoplasmas (i.e. Mycoplasma hyorhinis), which contain a number of nucleoside-metabolizing enzymes. Pyrimidine nucleoside analogues, such as 5-fluoro-2'-deoxyuridine (FdUrd), 5-trifluorothymidine (TFT) and 5-halogenated 2'-deoxyuridines can be degraded by thymidine phosphorylase (TP) to their inactive bases. We found in M. hyorhinis-infected MCF-7 breast carcinoma cells (MCF-7/HYOR) a mycoplasma-encoded TP that dramatically (20-150-fold) reduces the cytostatic activity of these compounds. The reduction in cytostatic activity could be fully restored in the presence of TPI (5-chloro-6-[1-(2-iminopyrrolidinyl)methyl]uracil hydrochloride), a known inhibitor of human TP. This observation is in agreement with the markedly decreased formation of active metabolite (i.e. FdUMP for FdUrd) or diminished drug incorporation into nucleic acids (i.e. for TFT and 5-bromo-2'-deoxyuridine) in MCF-7/HYOR cells compared with uninfected MCF-7 cells. Antimetabolite formation is fully restored in the presence of TPI. In contrast, 5-fluoro-5'-deoxyuridine (5'DFUR), an intermediate metabolite of capecitabine, was markedly more cytostatic in MCF-7/HYOR cells than in uninfected cells, due to the activation of this prodrug by the mycoplasma-encoded TP. Thus, our data reveal that M. hyorhinis expresses a TP that activates 5'DFUR but inactivates FdUrd, TFT and 5-halogenated 2'-deoxyuridines, and that is highly sensitive to the inhibitory effect of the TP inhibitor TPI. Given the association of M. hyorhinis with several human cancers, our findings suggest that pyrimidine nucleoside-based but not 5FU-based anti-cancer therapy might be more effective when combined with a mycoplasmal TP inhibitor.

Mycoplasma infection transforms normal lung cells and induces bone morphogenetic protein 2 expression by post-transcriptional mechanisms

Bone morphogenetic protein 2 (BMP2) is an essential growth factor and morphogen, whose pattern and level of expression profoundly influences development and physiology. We present the novel finding that mycoplasma infection induces BMP2 RNA production in six cell lines of diverse types (mesenchymal, epithelial, and myeloid). Mycoplasma infection triggered the expression of mature secreted BMP2 protein in BEAS-2B cells (immortalized human bronchial epithelial cells), which normally do not express BMP2, and further increased BMP2 production in A549 cells (lung adenocarcinoma cells). Indeed, mycoplasma is as strong an experimental inducer as inflammatory cytokines and retinoic acid. Second, we showed that post-transcriptional mechanisms including regulation of RNA stability, rather than transcriptional mechanisms, contributed to the increased BMP2 expression in mycoplasma-infected cells. Furthermore, a novel G-rich oligonucleotide, AS1411 that binds the post-transcriptional regulator nucleolin induced BMP2 exclusively in infected cells. Finally, BMP2 stimulated proliferation in BEAS-2B cells transformed by chronic mycoplasma infection, as demonstrated by treatment with Noggin, a BMP2 antagonist. These findings have important implications regarding the effects of mycoplasma on BMP2-regulated processes, including cell proliferation, differentiation, and apoptosis.

p37 from Mycoplasma hyorhinis promotes cancer cell invasiveness and metastasis through activation of MMP-2 and followed by phosphorylation of EGFR

High Mycoplasma infection in gastric cancer tissues suggests a possible association between Mycoplasma infection and tumorigenesis. By using human gastric cancer cells AGS and mouse melanoma cells B16F10 stably expressing p37, the major immunogen of Mycoplasma hyorhinis, we found that p37 enhanced cell motility, migration, and invasion in vitro. With experimental metastasis model in C57BL/6 mice, p37 adenovirus-infected B16F10 cells formed more metastasis lesions in the lung. Furthermore, p37 promoted the phosphorylation of epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase and the activity of matrix metalloproteinase-2 (MMP-2). Inhibitor of MMPs significantly blocked p37-induced EGFR but has little effect on extracellular signal-regulated kinase phosphorylation, whereas the p37-induced MMP-2 activation was only partially suppressed by inhibitor of MEK1/2 or by inhibitor of EGFR. However, all these inhibitors significantly reduced the p37-induced invasiveness of AGS cells. These results suggest that p37 may stimulate invasion by increasing the activity of MMP-2, thereby inducing EGFR phosphorylation and contributing to tumor metastasis on M. hyorhinis infection. p37 and its regulated molecules could be the potential targets for cancer therapy.

Apoptosis induced by lipid-associated membrane proteins from Mycoplasma penetrans is mediated by nuclear factor kappaB activation in mouse macrophage

Mycoplasma penetrans was shown to be involved in alteration of several eukaryotical cells functions and a causative agent in urogenital infectious diseases. Lipid-associated membrane proteins (LAMPs) may be responsible for the pathogenicity of some mycoplamas. In this study, we investigated whether M. penetrans LAMPs have pathogenic potential by inducing apoptosis in mouse macrophages. As analyzed by annexin-V - fluorescein isothiocyanate staining, significant early- and late-stage apoptosis was induced in M. penetrans LAMPs-challenged mouse macrophages. And agarose gel electrophoresis of the DNA of M. penetrans LAMPs-challenged cells revealed a ladder-like pattern of migration of DNA indicative of apoptosis. The possible molecular mechanisms responsible for the induction of apoptosis were also investigated by characterizing the activation of nuclear transcription factor kappaB (NFkappaB). NFkappaB was activated and translocated into the nucleus in mouse macrophages stimulated by M. penetrans LAMPs. The activation of NFkappaB and M. penetrans LAMPs-induced apoptosis in mouse macrophages was partially inhibited by the NFkappaB-specific inhibitor pyrrolidine dithiocarbamate. Thus, this study demonstrates that M. penetrans LAMPs may be an important etiological factor owing to their ability to induce apoptosis in mouse macrophages, which is probably mediated through the activation of NFkappaB.

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.

OppA, the ecto-ATPase of Mycoplasma hominis induces ATP release and cell death in HeLa cells

Background

In the facultative human pathogen Mycoplasma hominis, which belongs to the cell wall-less Mollicutes, the surface-localised substrate-binding domain OppA of the oligopeptide permease was characterised as the main ecto-ATPase.

Results

With the idea that extra-cellular ATP could only be provided by the infected host cells we analysed the ATP release of HeLa cells after incubation with different preparations of Mycoplasma hominis: intact bacterial cells, the membrane fraction with or without OppA, recombinant OppA as well as an ATPase-deficient OppA mutant. Release of ATP into the supernatant of the HeLa cells was primarily determined in all samples lacking ecto-ATPase activity of OppA. In the presence of the ATPase inhibitor DIDS the amount of ATP in the OppA-containing samples increased. This increase was maximal after incubation with fractions containing OppA protein indicating that OppA is involved in ATP release and subsequent hydrolysis. Real-time PCR analyses revealed that the proliferation of HeLa cells is reduced after infection with M. hominis and flow cytometry experiments established that OppA induces greater apoptosis than necrosis of HeLa cells whereas the preservation of ecto-ATPase activity of OppA induces apoptosis.

Conclusion

The OppA induced ATP-release and -hydrolysis induced cell death of M. hominis infected HeLa cells was predominantly due to apoptosis rather than necrosis. Future work will elucidate whether the induction of apoptosis is indispensable for survival of these non-invasive pathogen.

Exogenous mycoplasmal p37 protein alters gene expression, growth and morphology of prostate cancer cells

We previously showed that the Mycoplasma hyorhinis-encoded protein p37 can promote invasion of cancer cells in a dose-dependent manner, an effect that was blocked by monoclonal antibodies specific for p37. In this study, we further elucidated changes in growth, morphology and gene expression in prostate cancer cell lines when treated with exogenous p37 protein. Incubation with recombinant p37 caused significant nuclear enlargement, denoting active, anaplastic cells and increased the migratory potential of both PC-3 and DU145 cells. Microarray analysis of p37-treated and untreated cells identified eight gene expression clusters that could be broadly classified into three basic patterns. These were an increase in both cell lines, a decrease in either cell line or a cell line-specific differential trend. The most represented functional gene categories included cell cycle, signal transduction and metabolic factors. Taken together, these observations suggest that p37 potentiates the aggressiveness of prostate cancer and thus molecular events triggered by p37 maybe target for therapy.

Mycoplasmal membrane protein p37 promotes malignant changes in mammalian cells

Evidence of Mycoplasma hyorhinis infection in human gastric cancer tissues has been found in previous work. In this study, we demonstrate that the expression of p37, a membrane lipoprotein of M. hyorhinis, in mammalian cells induces antisenescence, enhances clonogenicity in soft agar, and co-operates with human epidermal growth factor receptor-related 2 to inhibit cell adhesion. Conversely, truncated p37 protein, with the first 28 amino acids deleted from its N terminal, promotes cell senescence. Taken together, our findings suggest that p37 promotes malignant changes in mammalian cells. With the identification of this molecular component, which is responsible for mycoplasma malignancy-promoting activity, it is possible that a better understanding of the relationship between M. hyorhinis infection and human gastric cancers will lead to novel diagnostics and therapeutics.

Effect of mycoplasmas on apoptosis of 32D cells is species-dependent

We previously showed that mycoplasmal infection effectively prevented apoptosis of infected cells, whereas other researchers have indicated that mycoplasmal infection promoted apoptosis. To understand the mechanism underlying this discrepancy, five different species of mycoplasmas were investigated for their effects on apoptosis of interleukin (IL)-3-dependent 32D cells. Results revealed that Mycoplasma fermentans and M. penetrans effectively supported continuous growth of 32D cells after IL-3 withdrawal. M. fermentans was more potent than M. penetrans. This effect was achieved by way of preventing apoptosis and stimulating cell proliferation. On the contrary, M. hominis and M. salivarium accelerated apoptosis of 32D cells. M. genitalium had no significant effect on apoptosis. The RNase protection assay indicated that the proapoptotic and antiapoptotic mycoplasmas altered the expression of major apoptosis regulatory genes differently. The difference in apoptosis regulatory gene expression induced by different species of mycoplasmas might be accountable for their effects on host cell apoptosis.

Interactions between mycoplasma lipid-associated membrane proteins and the host cells

Mycoplamas are a group of wall-less prokaryotes widely distributed in nature, some of which are pathogenic for humans and animals. There are many lipoproteins anchored on the outer face of the plasma membrane, called lipid-associated membrane proteins (LAMPs). LAMPs are highly antigenic and could undergo phase and size variation, and are recognized by the innate immune system through Toll-like receptors (TLR) 2 and 6. LAMPs can modulate the immune system, and could induce immune cells apoptosis or death. In addition, they may associate with malignant transformation of host cells and are also considered to be cofactors in the progression of AIDS.

Induction of Constitutive High-Level Expression of c-Myc in 32D Cells by Mycoplasmas is Associated with their Ability to Prevent Apoptosis and Induce Malignant Transformation

Our previous studies showed that mycoplasmas prevented apoptosis and induced the malignant transformation of mammalian cells. Other studies indicate that c-Myc plays an important role in promoting apoptosis and malignant transformation of cells. To understand the role of c-Myc in the mycoplasma induced apoptosis prevention and malignant cell transformation, 32D cells, an IL-3 dependent cell line, were infected and transformed by different species of mycoplasmas. The expression of Myc and ras gene families, apoptosis and the cell cycle during the infection and transformation were examined. Results showed that c-Myc expression was significantly increased in mycoplasma transformed 32D cells. Withdrawal of IL-3 substantially decreased c-Myc expression and led to cell cycle arrest at the G1 phase followed by rapid apoptosis. Infection by M. fermentans or M. penetrans not only alleviated the sharp decrease of c-Myc expression, rescued 32D cells from cell-cycle arrest and prevented apoptosis in IL-3-free culture, but also induced autonomous growth of 32D cells. Although M. hominis and M. salivarium had the ability neither to prevent apoptosis nor to induce malignant transformation, they were still able to rescue the cells from cell cycle arrest. The expression of ras family did not change significantly during the infection and transformation. These results suggest that constitutive expression of c-Myc appears to be associated with the continuous growth and malignant transformation of 32D cells induced by M. fermentans and M. penetrans, but not with rescuing the cell cycle arrest by the mycoplasmas.

Newly identified c-KIT receptor tyrosine kinase ITD in childhood AML induces ligand-independent growth and is responsive to a synergistic effect of imatinib and rapamycin

Activating mutations of c-KIT lead to ligand-independent growth. Internal tandem duplications (ITDs) of exon 11, which encodes the juxtamembrane domain (JMD), are constitutively activating mutations found in 7% of gastrointestinal stromal tumors (GISTs) but have not been described in childhood acute myeloid leukemia (AML). DNA and cDNA from 60 children with AML were screened by polymerase chain reaction (PCR) for mutations of the JMD. A complex ITD (kit cITD) involving exon 11 and exon 12 was identified with a relative frequency of 7% (4/60). The human kit cITDs were inserted into the murine c-Kit backbone and expressed in Ba/F3 cells. KIT cITD induced factorindependent growth and apoptosis resistance, and exhibited constitutive autophosphorylation. KIT cITD constitutively activated the PI3K/AKT pathway and phosphorylated STAT1, STAT3, STAT5, and SHP-2. Imatinib (IM) or rapamycin (Rap) led to complete inhibition of growth, with IC50 values at nanomolar levels. IM and Rap synergistically inhibited growth and surmounted KIT cITD-induced apoptosis resistance. IM but not LY294002 inhibited phosphorylation of STAT3 and STAT5, suggesting aberrant cross talk between PI3K- and STAT-activating pathways. The findings presented may have immediate therapeutic impact for a subgroup of childhood AML-expressing c-KIT mutations.

The inhibitory effect of Mycoplasma fermentans on tumour necrosis factor (TNF)-alpha-induced apoptosis resides in the membrane lipoproteins

Mycoplasma have been shown to be involved in the alteration of several eukaryotic cell functions, such as cytokine production, gene expression and more. We have previously reported that infection of human myelomonocytic U937 cell line with live Mycoplasma fermentans (M. fermentans) inhibited tumour necrosis factor (TNF-alpha)-induced apoptosis. Mycoplasmal membrane lipoproteins are considered to be the most potent initiators of inflammatory reactions in mycoplasmal infections. The aim of this study was to clarify whether the inhibitory effect on TNFalpha-induced apoptosis is exerted by M. fermentans lipoproteins (LPMf). A significant reduction in TNFalpha-induced apoptosis was demonstrated by stimulation of U937 cells with M. fermentans total proteins, LPMf or MALP-2 (M. fermentans synthetic lipopeptide), but not with M. fermentans hydrophilic protein preparation (AqMf). To investigate the mechanism of M. fermentans antiapoptotic effect, the reduction of mitochondrial transmembrane potential (delta psi m) was measured. M. fermentans total proteins LPMf and MALP-2, but not AqMf, inhibited the reduction of delta psi m. In addition, M. fermentans total proteins LPMf and MALP-2, but not AqMf, downregulated the formation of active caspase-8. NF-kappaB was transactivated in cells treated with M. fermentans lipoproteins, and was essential for host cell survival, but not for the inhibition of TNFalpha-induced apoptosis by LPMf. Our results suggest that the inhibitory effect exerted by M. fermentans on TNFalpha-induced apoptosis in U937 cells is due to the membrane lipoproteins of these bacteria.

Recruitment of insulin receptor substrate-1 and activation of NF-kappaB essential for midkine growth signaling through anaplastic lymphoma kinase

Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase in the insulin receptor superfamily. We recently demonstrated that the growth factors pleiotrophin (PTN) and midkine (MK) are ligands for ALK and that upon ALK activation, insulin receptor substrate-1 (IRS-1) and other substrates are phosphorylated. Here, the role of IRS-1 in ligand-mediated ALK signaling is investigated in interleukin-3 (IL-3)-dependent 32D murine myeloid cells. These cells do not express ALK and IRS family members, and do not respond to exogenously added PTN or MK. We show that expression of ALK plus IRS-1 renders these cells independent of IL-3 owing to the activation of ALK by endogenous MK. Mutational analysis reveals that this transformed phenotype of 32D cells requires kinase-active ALK as well as the interaction of ALK with IRS-1. Furthermore, 32D/IRS-1/ALK cells display an enhanced activation of mitogen-activated protein kinase and PI3-kinase pathways, and a selective transcriptional activation of nuclear factor (NF)-kappaB. Small interfering RNA-mediated knockdown of the endogenous MK or p65/NF-kappaB revealed that both these are rate limiting for the transformed phenotype induced by ALK plus IRS-1. We conclude that the recruitment of IRS-1 to activated ALK and the activation of NF-kappaB are essential for the autocrine growth and survival signaling of MK.

Alteration of gene expression profiles during mycoplasma-induced malignant cell transformation

BACKGROUND

Mycoplasmas are the smallest microorganisms capable of self-replication. Our previous studies show that some mycoplasmas are able to induce malignant transformation of host mammalian cells. This malignant transformation is a multistage process with the early infection, reversible and irreversible stages, and similar to human tumor development in nature. The purpose of this study is to explore mechanisms for this malignant transformation.

METHODS

To better understand mechanisms for this unique process, we examined gene expression profiles of C3H cells at different stages of the mycoplasma-induced transformation using cDNA microarray technology. A total of 1185 genes involved in oncogenesis, apoptosis, cell growth, cell-cycle regulation, DNA repair, etc. were examined. Differences in the expression of these genes were compared and analyzed using the computer software AtlasImage.

RESULTS

Among 1185 genes screened, 135 had aberrant expression at the early infection stage, 252 at the reversible stage and 184 at the irreversible stage. At the early infection stage, genes with increased expression (92 genes) were twice more than those with decreased expression (42 genes). The global gene expression at the reversible stage appeared to be more volatile than that at any other stages but still resembled the profile at the early infection stage. The expression profile at the irreversible stage shows a unique pattern of a wide range of expression levels and an increased number of expressing genes, especially the cancer-related genes. Oncogenes and tumor suppressors are a group of molecules that showed significant changes in expression during the transformation. The majority of these changes occurred in the reversible and irreversible stages. A prolonged infection by mycoplasmas lead to the expression of more cancer related genes at the irreversible stage.

CONCLUSION

The results indicate that the expression profiles correspond with the phenotypic features of the cells in the mycoplasma induced transformation process. The early mycoplasma infection stage shares a common phenomenon with many other acute infections, genes with increased expression significantly outnumbering those with decreased expression. The reversible stage is a transition stage between benignancy and malignancy at the molecular level. Aberrant expression of oncogenes and tumor repressors plays a key role in mycoplasma-induced malignant transformation.

Lipoprotein p37 from Mycoplasma hyorhinis inhibiting mammalian cell adhesion

p37 protein is a membrane lipoprotein of Mycoplasma hyorhinis, and our previous work showed that there was high ratio of M. hyorhinis infection in human gastric carcinoma. To investigate the possible functions of p37 in cancer development, the nucleotide sequence of p37 gene was modified and expressed well in transfected cells. We found that p37 localized at the Golgi apparatus and could be secreted out of the cell. Human gastric cancer cells AGS, after being transfected with the p37 gene, were smaller, more spherical and easy to detach from each other. Their adhesion to matrix was also diminished and cytoskeleton in these stable p37 AGS cell was rearranged and transcription co-factor beta-actin was transferred to nucleolus with down-regulation of ICAM-1 and integrin beta1. These findings will be helpful for us to elucidate the effects of p37 on eukaryotic cells as well as to better understand the potential relationship between cancer and mycoplasma infection.

Can mycoplasma-mediated oncogenesis be responsible for formation of conventional renal cell carcinoma?

OBJECTIVES

To investigate the association between Mycoplasma sp. infection and conventional renal cell carcinoma (RCC).

METHODS

Normal kidney, renal intratubular neoplasia, and tumor tissue samples from 33 patients with RCC and 35 healthy controls were studied. Molecular DNA analysis was done after nested polymerase chain reaction performed in two steps with seven primers (four outer and three inner) that can recognize at least 15 different Mycoplasma sp.

RESULTS

Mycoplasma sp. DNA was detected in normal kidney, renal intratubular neoplasia, and tumor tissue samples at a ratio of 36%, 67%, and 82%, respectively. In 6 of the 33 patients with RCC, no Mycoplasma sp. was detected from any of the three tissue samples. Mycoplasma sp. DNA was detected in only 5 (14%) of the 35 samples from the control group.

CONCLUSIONS

The relationship between mycoplasma infection and conventional RCC has been investigated for the first time, and a significantly high existence of Mycoplasma sp. DNA was found in the tissues of patients with conventional RCC compared with that found in a healthy control group. This suggests that mycoplasma-mediated multistage carcinogenesis may play a role in the development of RCC.

Mycoplasma fermentans inhibits tumor necrosis factor alpha-induced apoptosis in the human myelomonocytic U937 cell line

Mycoplasma fermentans (M. fermentans) was shown to be involved in the alteration of several eukaryotic cell functions (i.e. cytokine production, gene expression), and was suggested as a causative agent in arthritic diseases involving impaired apoptosis. We investigated whether M. fermentans has a pathogenic potential by affecting tumor necrosis factor (TNF)alpha-induced apoptosis in the human myelomonocytic U937 cell line. A significant reduction in the TNFalpha-induced apoptosis (approximately 60%) was demonstrated upon either infection with live M. fermentans or by stimulation with non-live M. fermentans. To investigate the mechanism of M. fermentans antiapoptotic effect, the reduction of mitochondrial transmembrane potential (DeltaPsim) and the protease activity of caspase-8 were measured. In the infected cells, the reduction of DeltaPsim was inhibited (approximately 75%), and an approximately 60% reduction of caspase-8 activity was measured. In conclusion, M. fermentans significantly inhibits TNFalpha-induced apoptosis in U937 cells, and its effect is upstream of the mitochondria and upstream of caspase-8.

Trypanosoma cruzi trans-sialidase as a new therapeutic tool in the treatment of chronic inflammatory diseases: possible action against mycoplasma and chlamydia

The present paper proposes a new therapy using Trypanosoma cruzi trans-sialidase to treat diseases with unclear pathogenesis that present in common chronic inflammation and fibrosis. This hypothesis is based on recent findings that co-infection with mycoplasma and chlamydia is present in many of these diseases and that this enzyme was capable to eliminate or decrease the co-infection from the host. We identified that mycoplasmas and chlamydias are present in atherosclerosis, aortic valve stenosis, dilated cardiomyopathy, chronic chagasic myocarditis and cancer. We hypothetized that mycoplasmal infection may induce immunodepression in the host, favoring proliferation of pre-existent chlamydial infection and that elimination of mycoplasma would lead to improvement of the immune system resistance and the control of chlamydial proliferation. Mycoplasma has a particular parasitic relationship with host cells, involving strong adherence of their membranes, making it extremely difficult to eradicate mycoplasmal infection from the host. A new therapeutic approach is suggested using one or more agents that prevent or inhibit the adherence of mycoplasma to host cell membranes by removing sialic acid residues and preventing oxidation of the cells. The use of a neuraminidase enzyme, particularly the T. cruzi trans-sialidase enzyme, associated with treatment using anti-oxidating agents is proposed. Preliminary experimental animal and laboratory tests showed good results. The proposal that trans-sialidase from T. cruzi is efficient in combating co-infection of mycoplasma and chlamydia is based, at least in part, on the observation that chagasic patients suffering from T. cruzi infection present less mycoplasma and chlamydia infection in their tissues. Also, a lower incidence of the diseases above described to be related to mycoplasma infection is observed in chagasic patients. It is also hypothesized that co-infection with mycoplasma and chlamydia may induce oxidation of the host cells. Anti-oxidants such as those present in plant extracts may also be used in the treatment. Other diseases such as chronic hepatitis, glomerulonephritis, Multiple Sclerosis, Alzheimer's Syndrome and idiopathic encephalitis are other examples of chronic diseases where mycoplasma and chlamydia might be present, as they have the characteristics of unknown etiology, persistent chronic inflammation and fibrosis.

Mycoplasma fermentans infection promotes immortalization of human peripheral blood mononuclear cells in culture

Chronic infection or colonization by mycoplasma(s) could gradually and significantly alter many biologic properties of mammalian host cells in culture, including induction of malignant transformation. We examined effects of Mycoplasma fermentans infection on the continuing survival and immortality of human peripheral blood mononuclear cells (PBMCs) from healthy blood donors. Without specific supplemental growth factors, human PBMCs normally die rapidly, with few cells other than macrophages/monocytes surviving after 2 weeks in cultures. Only occasional Epstein-Barr virus (EBV)–positive B lymphocytes would continue to proliferate and undergo spontaneous immortalization. Our present study revealed that infection of human PBMCs in culture with the incognitus and PG18 strains of M fermentans, but surprisingly not with some other strains tested in parallel, markedly enhanced the rate of EBV-positive B lymphocytes to undergo immortalization (74% vs 17%). Compared with spontaneously immortalized PBMCs, the PBMCs immortalized in cultures infected with the mycoplasmas often had prominent karyotype changes with chromosomal loss, gain, or translocations. Furthermore, many of these immortalized B lymphocytes were found to be monoclonal in nature. The in vitro findings would be of relevance to lymphoproliferative disorders that occurred in patients with immune suppression. The mycoplasma-mediated promotional effect in cell immortalization and its potential clinical implications warrant further study.

Chronic fatigue syndrome: intracellular immune deregulations as a possible etiology for abnormal exercise response

The exacerbation of symptoms after exercise differentiates Chronic fatigue syndrome (CFS) from several other fatigue-associated disorders. Research data point to an abnormal response to exercise in patients with CFS compared to healthy sedentary controls, and to an increasing amount of evidence pointing to severe intracellular immune deregulations in CFS patients. This manuscript explores the hypothetical interactions between these two separately reported observations. First, it is explained that the deregulation of the 2-5A synthetase/RNase L pathway may be related to a channelopathy, capable of initiating both intracellular hypomagnesaemia in skeletal muscles and transient hypoglycemia. This might explain muscle weakness and the reduction of maximal oxygen uptake, as typically seen in CFS patients. Second, the activation of the protein kinase R enzyme, a characteristic feature in atleast subsets of CFS patients, might account for the observed excessive nitric oxide (NO) production in patients with CFS. Elevated NO is known to induce vasidilation, which may limit CFS patients to increase blood flow during exercise, and may even cause and enhanced postexercise hypotension. Finally, it is explored how several types of infections, frequently identified in CFS patients, fit into these hypothetical pathophysiological interactions.

Presence of human mycoplasma DNA in gastric tissue samples from Korean chronic gastritis patients

We aimed to determine whether mycoplasmas are present in Korean chronic gastritis, and to understand their roles in gastric cancer tumorigenesis, because mycoplasmas resemble Helicobacter pylori in terms of ammonia production and induction of inflammatory cytokines in immune and non-immune cells. The presence and identity of mycoplasmas were assessed by semi-nested PCR and sequencing, and the results were compared with pathologic data. Fifty-six samples collected from Korean chronic gastritis patients were used for this study. Twenty-three (41.1%) were positive for mycoplasmas. Eighteen sequenced samples contained a single human mycoplasma or two mycoplasmas, which were identified as Mycoplasma faucium (13/18), M. fermentans (3/18), M. orale (1/18), M. salivarium (2/18), and M. spermatophilum (1/18). Mycoplasma-infected chronic gastritis samples showed significantly more severe neutrophil infiltration than non-infected samples (P = 0.0135). Mycoplasma profiles in the oral cavity (M. salivarium is major) and stomach were different, and the presence of significant proinflammatory responses in mycoplasma-positive patients suggests that the mycoplasmas are not simply contaminants. Further studies are required to understand whether mycoplasmas play a role in gastric tumorigenesis.

Identification of antigens by monoclonal antibody PD4 and its expression in Escherichia coli

AIM

To clone and express the antigen of monoclonal antibody (MAb) PD4 for further investigation of its function.

METHODS

MGC803 cDNA expression library was constructed and screened with PD4 as probes to clone the antigen. After failed in the library screening, immunoprecipitation and SDS-polyacrylamide gel electrophoresis were applied to purify the antigen for sequence analysis. The antigen coming from Mycoplasma hyorhinis (M. hyorhinis) was further confirmed with Western blot analysis by infecting M. hyorhinis -free HeLa cells and eliminating the M. hyorhinis from MGC803 cells. The full p37 gene was cloned by PCR and expressed successfully in Escherichia coli after site-directed mutations. Immunofluorescence assay was used to demonstrate if p37 protein could directly bind to gastric tumor cell AGS.

RESULTS

The cDNA library constructed with MGC803 cells was screened by MAb PD4 as probes. Unfortunately, the positive clones identified with MAb PD4 were also reacted with unrelated antibodies. Then, immunoprecipitation was performed and the purified antigen was identified to be a membrane protein of Mycoplasma hyorhinis (M. hyorhinis) by sequencing of N-terminal amino acid residues. The membrane protein was intensively verified with Western blot by eliminating M. hyorhinis from MGC803 cells and by infecting M. hyorhinis-free HeLa cells. The full p37 gene was cloned and expressed successfully in Escherichia coli after site-directed mutations. Immunofluorescence demonstrated that p37 protein could directly bind to gastric tumor cell AGS.

CONCLUSION

The antigen recognized by MAb PD4 is from M. hyorhinis, which suggests the actions involved in MAb PD4 is possibly mediated by p37 protein or M. hyorhinis. As p37 protein can bind directly to tumor cells, the pathogenic role of p37 involved in tumorigenesis justifies further investigation.

APAF-1-ALT, a novel alternative splicing form of APAF-1, potentially causes impeded ability of undergoing DNA damage-induced apoptosis in the LNCaP human prostate cancer cell line

We have found a novel alternative splicing product of the apoptotic protease activating factor 1 (APAF-1), termed APAF-1-ALT, in the LNCaP human prostate cancer cell line. APAF-1-ALT harbors the caspase recruitment domain and an incomplete CED-4 like/ATPase domain, but lacks the WD-40 repeat units. The LNCaP cell expressed the full-length APAF-1 weakly and APAF-1-ALT rather abundantly, especially after mycoplasma infection. LNCaP underwent a retarded DNA damage-induced apoptosis, which was independent of caspase 9 activity. APAF-1-ALT functioned less effectively in inducing apoptosis than did APAF-1-XL, the full-length APAF-1, in transient transfection. Moreover, APAF-1-ALT interfered with APAF-1-XL's ability to induce apoptosis in transient double transfection experiment. These results indicate that APAF-1-ALT is a molecule that is deficient and impeded for mediating apoptosis and that it may contribute to the resistance to DNA damage-induced treatment observed in LNCaP.

Interaction of mycoplasmas with host cells

The mycoplasmas form a large group of prokaryotic microorganisms with over 190 species distinguished from ordinary bacteria by their small size, minute genome, and total lack of a cell wall. Owing to their limited biosynthetic capabilities, most mycoplasmas are parasites exhibiting strict host and tissue specificities. The aim of this review is to collate present knowledge on the strategies employed by mycoplasmas while interacting with their host eukaryotic cells. Prominant among these strategies is the adherence of mycoplasma to host cells, identifying the mycoplasmal adhesins as well as the mammalian membrane receptors; the invasion of mycoplasmas into host cells including studies on the role of mycoplasmal surface molecules and signaling mechanisms in the invasion; the fusion of mycoplasmas with host cells, a novel process that raises intriguing questions of how microinjection of mycoplasma components into eukaryotic cells subvert and damage the host cells. The observations of diverse interactions of mycoplasmas with cells of the immune system and their immunomodulatory effects and the discovery of genetic systems that enable mycoplasmas to rapidly change their surface antigenic composition have been important developments in mycoplasma research over the past decade, showing that mycoplasmas possess an impressive capability of maintaining a dynamic surface architecture that is antigenically and functionally versatile, contributing to the capability of the mycoplasmas to adapt to a large range of habitats and cause diseases that are often chronic in nature.

How bacteria could cause cancer: one step at a time

Helicobacter pylori highlighted the potential for bacteria to cause cancer. It is becoming clear that chronic infection with other bacteria, notably Salmonella typhi, can also facilitate tumour development. Infections caused by several bacteria (e.g. Bartonella spp., Lawsonia intracellularis and Citrobacter rodentium) can induce cellular proliferation that can be reversed by antibiotic treatment. Other chronic bacterial infections have the effect of blocking apoptosis. However, the underlying cellular mechanisms are far from clear. Conversely, several bacterial toxins interfere with cellular signalling mechanisms in a way that is characteristic of tumour promoters. These include Pasteurella multocida toxin, which uniquely acts as a mitogen, and Escherichia coli cytotoxic necrotizing factor, which activates Rho family signalling. This leads to activation of COX2, which is involved in several stages of tumour development, including inhibition of apoptosis. Such toxins could provide valuable models for bacterial involvement in cancer, but more significantly they could play a direct role in cancer causation and progression.

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.

Suppression of apoptosis and granulocyte colony-stimulating factor-induced differentiation by an oncogenic form of Cbl

OBJECTIVE

The retroviral oncogene v-Cbl causes pre-B cell lymphomas and myeloid leukemias in mice, and its Drosophila homologue is oncogenic, causing enhanced receptor tyrosine kinase signaling. The human Cbl gene resides at 11q23. The aim of this study is to determine the effect of oncogenic Cbl on growth-regulating responses.

MATERIALS AND METHODS

The oncogenic mutant of Cbl (CblDelta1-357) was transfected into factor-dependent 32Dcl3 myeloid cells. Consequently, cell survival and differentiation were measured. Lyn, Syk, MAP kinase, and phosphatidylinositol 3'(PI3')-kinase activities, protein phosphorylation, Bcl-2 promoter activity, ubiquitination, and levels of Bcl-2, Bax, Bad, and Bcl-x(L) were determined. In addition, the effect of v-Cbl on TF-1 cell survival upon granulocyte-macrophage colony-stimulating factor withdrawal was studied.

RESULTS

32Dcl3 and TF-1 cells expressing v-Cbl showed resistance to apoptosis upon growth factor withdrawal, and 32Dcl3 cells completely failed to respond to granulocyte colony-stimulating factor's induction of differentiation. Basal activities of Lyn, Syk, and PI3'-kinase were elevated in the v-Cbl line. There was neither enhanced tyrosine phosphorylation of cellular protein content, Cbl, or Jak2, nor serine phosphorylation of MAP kinase or Akt. After factor withdrawal, the level of Bcl-2 was greater in v-Cbl cells than in control cells.

CONCLUSIONS

Neither increased Bcl-2 promoter activity nor decreased ubiquitination of Bcl-2 could account for increased Bcl-2 levels. v-Cbl-expressing 32Dcl3 cells were resistant to differentiation. v-Cbl suppresses apoptosis and differentiation, possibly through enhancement of Lyn, Syk, and PI3'-kinase activities and Bcl-2.

Expression of interferon consensus sequence binding protein induces potent immunity against BCR/ABL-induced leukemia

Mice deficient in the interferon consensus sequence binding protein (ICSBP) develop a disease resembling chronic myeloid leukemia (CML), which in humans is caused by the BCR/ABL oncoprotein. Interferon-α (IFN-α) induces ICSBP expression and is an effective therapy for CML. This study examined whether enforced expression of ICSBP might antagonize BCR/ABL-induced leukemia; results demonstrated that ICSBP-modified cells generated a protective CD8+ cytotoxic T-cell response against BCR/ABL-transformed BaF3 cells in a murine leukemia model. ICSBP expression represents a novel means of stimulating a host immune response to BCR/ABL+ leukemia cells and a potential strategy for immunotherapy of CML.

Mycoplasma infections and different human carcinomas

AIM: To explore relationships between human carcinomas and mycoplasma infection.

METHODS: Monoclonal antibody PD4, which specifically recognizes a distinct protein from mycoplasma hyorhinis, was used to detect mycoplasma infection in different paraffin embedded carcinoma tissues with immunohistochemistry. PCR was applied to amplify the mycoplasma DNA from the positive samples for confirming immunohistochemistry.

RESULTS: Fifty of 90 cases (56%) of gastric carcinoma were positive for mycoplasma hyorhinis. In other gastric diseases, the mycoplasma infection ratio was 28% (18/49) in chronic superficial gastritis, 30% (14/46) in gastric ulcer and 37% (18/49) in intestinal metaplasia. The difference is significant with gastric cancer (χ² = 12.06, P < 0.05). In colon carcinoma, the mycoplasma infection ratio was 55.1% (32/58),but it was 20.9% (10/ 49) in adenomarous polyp (χ² = 13.46, P < 0.005). Gastric and colon cancers with high differentiation had a higher mycoplasma infection ratio than those with low differentiation (P < 0.05). Mycoplasma infection in esophageal cancer, lung cancer, breast cancer and glioma was 50.9% (27/53), 52.6% (31/ 59), 39.7% (25/63)and 41% (38/91), respectively. The mycoplasma DNA was successfully amplified with the DNA extracted from the cancer tissues that were positive for mycoplasma infection (detected with antibody PD4).

CONCLUSION: There was high correlation between mycoplasma infection and different cancers, which suggests the possibility of an association between the two. The mechanism involved in oncogenesis by mycoplasma remains unknown.

Suppression of apoptosis induced by growth factor withdrawal by an oncogenic form of c-Cbl

The v-Cbl oncogene induces myeloid and B-cell leukemia; however, the mechanism by which transformation occurs is not understood. An oncogenic form of c-Cbl (Cbl-DeltaY371) was expressed in the interleukin-3 (IL-3)-dependent cell line 32Dcl3 to determine whether it was able to induce growth factor-independent proliferation. We were unable to isolate clones of transfected 32Dcl3 cells expressing Cbl-DeltaY371 that proliferated in the absence of IL-3. In contrast, 32Dcl3/Cbl-DeltaY371 cells did not undergo apoptosis like parental 32Dcl3 cells when cultured in the absence of IL-3. Both 32Dcl3 and 32D/CblDeltaY371 cells arrested in G(1) when cultured in the absence of IL-3. Approximately 18% of the 32Dcl3 cells cultured in the absence of IL-3 for 24 h were present in a sub-G(1) fraction, while only 4% of the 32D/Cbl-DeltaY371 and 2% of the 32D/Bcl-2 cells were found in a sub-G(1) fraction. There was no difference in the pattern of tyrosine-phosphorylated proteins observed following stimulation of either cell type with IL-3. The phosphorylation of JAK2, STAT5, and endogenous c-Cbl was identical in both cell types. No differences were detected in the activation of Akt, ERK1, or ERK2 in unstimulated or IL-3-stimulated 32D/Cbl-DeltaY371 cells compared with parental 32Dcl3 cells. Likewise, there was no difference in the pattern of phosphorylation of JAK2, STAT5, ERK1, ERK2, or Akt when 32Dcl3 and 32D/CblDY371 cells were withdrawn from medium containing IL-3. The protein levels of various Bcl-2 family members were examined in cells grown in the absence or presence of IL-3. We observed a consistent increased amount of Bcl-2 protein in five different clones of 32D/Cbl-DeltaY317 cells. These data suggest that the Cbl-DeltaY371 mutant may suppress apoptosis by a mechanism that involves the overexpression of Bcl-2. Consistent with this result, activation of caspase-3 was suppressed in 32D/Cbl-DeltaY371 cells cultured in the absence of IL-3 compared with 32Dcl3 cells cultured under the same conditions.

Intracellular DNA replication and long-term survival of pathogenic mycoplasmas

We examined intracellular survival and growth of pathogenic mycoplasmas (Mycoplasma penetrans, Mycoplasma pneumoniae and Mycoplasma genitalium) in cultured human cells. By using the eukaryotic nuclear DNA synthesis inhibitor, aphidicolin, we detected the selective synthesis of mycoplasma (My) and mitochondria (Mt) DNA, which could be further differentiated by restriction enzyme analyses. Also, intracellular M. pneumoniae and M. penetrans infectivity of human cells was detected over 6 months using subfractionation of infected cells and determination of mycoIplasma colony forming units (cfu). For M. genitalium, which we failed to re-grow from infected cells, species-specific PCR primers were used to implicate long-term mycoplasma survivability. Data indicated that pathogenic mycoplasmas reside and replicate intracellularly over extended periods in human cells, consistent with the ability of mycoplasmas to circumvent antibiotic therapy and immune surveillance and establish chronic infections.

Progressive changes in the leukemogenic signaling in BCR/ABL-transformed cells

Our previous study indicated that BCR/ABL SH2 domain and BCR/ABL SH3 domain+SH2 domain complex are required for immediate activation of the phosphatidylinositol-3 kinase PI-3k)--> Akt serine/threonine kinase pathway and of the signal transducer and activator of transcription 5 (STAT5), respectively, in hematopoietic cells. We show here that the defect in activation of PI-3k/Akt by BCR/ABL DeltaSH2 mutant (SH2 domain deleted) and of STAT5 by BCR/ABL DeltaSH3+DeltaSH2 mutant (SH3 and SH2 domains deleted) is not permanent and both Akt and STAT5 could be 're-activated' by in vitro culture. This phenomenon was responsible for increased resistance to apoptosis, growth factor-independent proliferation and leukemogenesis in SCID mice. Incubation of cells with BCR/ABL tyrosine kinase inhibitor STI571 abrogated the 're-activation' of Akt or STAT5 by BCR/ABL SH3+SH2 mutants in some clones, in the others Akt and STAT5 activation became independent on BCR/ABL kinase activity. The immediate upstream activators of Akt and STAT5 such as PI-3k and Jak-2 were also activated. In addition, the common beta subunit of IL-3/IL-5/GM-CSF receptor was tyrosine phosphorylated in the clones in which 're-activation' was dependent on the BCR/ABL kinase activity. These results suggested that 're-activation' of Akt and STAT5, in the absence of functional BCR/ABL SH3+SH2 domains, may be achieved by two different mechanisms: (i) BCR/ABL kinase-dependent activation of alternative pathway(s) and (ii) additional genetic changes stimulating Akt and STAT5 independently of BCR/ABL. Oncogene (2000) 19, 4117 - 4124

Insulin receptor substrate-1, p70S6K, and cell size in transformation and differentiation of hemopoietic cells

After an initial burst of cell proliferation, the type 1 insulin-like growth factor receptor (IGF-IR) induces granulocytic differentiation of 32D IGF-IR cells, an interleukin-3-dependent murine hemopoietic cell line devoid of insulin receptor substrate-1 (IRS-1). The combined expression of the IGF-IR and IRS-1 (32D IGF-IR/IRS-1 cells) inhibits IGF-I-mediated differentiation, and causes malignant transformation of 32D cells. Because of the role of IRS-1 in changing the fate of 32D IGF-IR cells from differentiation (and subsequent cell death) to malignant transformation, we have looked for differences in IGF-IR signaling between 32D IGF-IR and 32D IGF-IR/IRS-1 cells. In this report, we have focused on p70(S6K), which is activated by the IRS-1 pathway. We find that the ectopic expression of IRS-1 and the inhibition of differentiation correlated with a sustained activation of p70(S6K) and an increase in cell size. Phosphorylation in vivo of threonine 389 and, to a lesser extent, of threonine 421/serine 424 of p70(S6K) seemed to be a requirement for inhibition of differentiation. A role of IRS-1 and p70(S6K) in the alternative between transformation or differentiation of 32D IGF-IR cells was confirmed by findings that inhibition of p70(S6K) activation or IRS-1 signaling, by rapamycin or okadaic acid, induced differentiation of 32D IGF-IR/IRS-1 cells. We have also found that the expression of myeloperoxidase mRNA (a marker of differentiation, which sharply increases in 32D IGF-IR cells), does not increase in 32D IGF-IR/IRS-1 cells, suggesting that the expression of IRS-1 in 32D IGF-IR cells causes the extinction of the differentiation program initiated by the IGF-IR, while leaving intact its proliferation program.