Genetic redundancy in human cervical carcinoma cells: Identification of cells with “normal” properties

Abstract

Although it is generally assumed that cancer arises from a singular cell, a tumor must be considered as a dynamic and emergent biological structure, whose organizing principle is determined by genetic and epigenetic modifications, occurring variably in response to microenvironmental selection conditions. As previously shown, HPV-positive cervical carcinoma cells have lost their ability to induce IFN-b upon TNF-a treatment. However, regarding cancer as a non-linear system, which may, even in the absence of an apparent selection pressure, fluctuate between different ''metastable'' phenotypes, we demonstrate that TNF-a mediated IFN-b induction is not irreversibly disturbed in all cells. Using the IFN-b sensitive Encephalomyocarditis virus (EMCV) as a tool to monitor antiviral activity in long-term established malignant HeLa cells, rare IFN-b expressing clones were rescued from a population of non-responsive and EMCV-sensitive cells. Antiviral activity was mediated by the re-expression of IRF-1 and p48 (IRF-9), both key regulatory molecules normally found to be suppressed in cervical carcinoma cells. Upon inoculating of selected clones into immunocompromised animals, a reduced or even an absence of tumorigenicity of initially highly malignant cells could be discerned. These data indicate that both the absence of interferon signaling and the ability to form tumors were reversed in a minority of cells. We provide a paradigm for the existence of innate genetic redundancy mechanisms, where a particular phenotype persists and can be isolated without application of drugs generally changing the epigenetic context. ' 2007 Wiley-Liss, Inc.Key words: human papillomaviruses; interferon-b regulation; EMCVcytolysis; tumor necrosis factor alpha; redundancy mechanisms; oscillation; chaotic cell systems; tumorigenicity Infections with certain types of human papillomaviruses (HPV) are the major cause for the development of cervical cancer. 1 Epidemiological studies show that immunodeficient women have a significantly higher risk of developing a tumor than age-matched controls. Hence, cancer of the cervix uteri is the final outcome of a long term selection and escape process, where HPV positive cells are no longer controlled by immunological surveillance. 2 Consequently, a physiological intact communication route between inflammatory and HPV-containing cells is an indispensable prerequisite for a proper antiviral response. 3 Targeting IFN-signaling actually provides a general selective advantage for tumor formation, because it favors the disruption of the intercellular cross-talk between HPV positive and immunological effector cells. 4 In a previous investigation, we demonstrated that the antiviral effect of TNF-a, which is mediated by IFN-b gene activation, 5 is disturbed in HPV positive cervical carcinoma cells. 6 The reason for this failure is the lack of interferon-regulatory factor (IRF)-1 and p48 (IRF-9) expression, two key regulators, tightly involved in the transcriptional control of the intermediate and the delayed interfero...

Epigenetic Silencing of Interferon-κ in Human Papillomavirus Type 16–Positive Cells

“…Similar to IFN-κ (Fig. 1A), we showed previously that cervical carcinoma cells also lacked or have reduced IFN-β expression (9,10). Although it has been reported that HPV16 E7 inhibits TLR9 transcription (20), IFN-β can be alternatively induced through the RIG-1/Mda5-dependent pathway (21) when cells were infected with RNA viruses (22).…”

“…As shown previously, cervical carcinoma cells lack the ability to express IFN-β on TNF-α treatment, which was mainly attributed to the absence of the IRF-1, an important trans-acting activator of the IFN-β promoter (9,10). However, IFN-β as intermediate-early IFN (40) can be reactivated after infection with RNA viruses (21,22), where IRF-3 is replacing IRF-1 in building up the IFN-β enhanceosome (41).…”

“…HPV18 E6 impairs Jak-STAT1/2 tyrosine phosphorylation (7), whereas HPV16 E6 physically interacts with the IFN-regulatory factor (IRF)-3, a central transcription factor in the primary antiviral response (8). However, there is still a matter of controversy because these results do not explain why exogenously added IFN-α or IFN-β induces an antiviral state or why RNA virus infection can activate IRF-3 and, in turn, an immediate-early IFN response in cervical carcinoma cells despite E6 and E7 expression (9,10).…”

The Emerging Role of Histone Deacetylase Inhibitors in Cervical Cancer Therapy

“…Some studies also focus on the synergistic effects of sodium butyrate with diverse therapeutic agents. Bachmann et al pretreated HeLa cells with sodium butyrate prior to TNF-a addition and, surprisingly, reported a lack of interferon ( IFN )- β gene inducibility [ 103 ]. Additionally, Decrion-Barthod et al combined sodium butyrate with 7-hydroxystaurosporine (UCN-01), which led to increased caspase-3 and poly (ADP-ribose) polymerase cleavage in vitro after p21, Bcl-2, Bcl-2-associated X protein, and B-cell lymphoma-extra large (Bcl-xL) modulation.…”