Ongoing projects deal with basic and translational aspects of the following topics:

1.) HPVs and the Host Cell Metabolism

Tumor viruses, such as oncogenic HPV types, are important human carcinogens. On the other hand, it becomes increasingly clear that cancer cells exhibit metabolic alterations that contribute to their malignant growth behaviour. Understanding and modulating tumor cell-specific metabolic alterations may identify an “Achilles heel” of cancer and ultimately allow the development of novel strategies for targeted cancer therapy.
Interestingly, there is relatively little known about the possible interactions between oncogenic HPVs and the host cell metabolism. We thus are interested in answering two major questions:
(i) Do tumor viruses lead to cancer by manipulating the host cell metabolism and
(ii) does the metabolic state of the host cell affect the activity of tumor viruses?

Using HPV-linked cancers as a model system to study the mutual interaction between tumor viruses and the host cell metabolism, focusing on hypoxia (low O2-content) as well as on iron (Fe)- and glutamine (Glut.) metabolism.

Experimentally, we concentrate on the crosstalk between oncogenic HPVs and three metabolic systems which can be altered in tumor cells:
a) Hypoxia
Many cancers, including HPV-positive cervical and head & neck cancers, are often characterized by regions with low oxygen (O2) content („hypoxia“). This can affect the growth behaviour of tumor cells and hypoxic tumors often exhibit a worsened clinical prognosis. We investigate the effects of HPVs on cellular factors involved in the response to hypoxia and, vize versa, the influence of O2 supply on the activities of the HPV oncogenes. (Hoppe-Seyler et al., 2017) (Press release DKFZ).
b) Iron Metabolism
The proliferation and survival of tumor cells may profit from an increased intracellular iron availability. We study the effect of HPVs on key regulators of iron metabolism and the influence of intracellular iron availability on the function of the HPV oncogenes.
c) Glucose Metabolism
Tumor cells typically exhibit an increased rate of aerobic glycoloysis (“Warburg effect”) for the generation of energy (ATP) and intermediates for tumor cell growth (e.g. nucleic acid precursors, lipids) from glucose. We study whether the HPV oncogenes may affect this tumor-linked metabolic process (Hoppe-Seyler et al., Oncotarget, 2017).

2.) Targeted inhibition of the HPV E6 oncoprotein.

The HPV E6 oncoprotein plays a crucial role for the survival of HPV-transformed cells. We have identified a small peptide that blocks E6 in HPV-positive cancer cells, leading to apoptotic cell death (Dymalla et al., 2009). By biochemical and biophysical studies, we recently have identified the E6 region which is bound by the peptide (Zanier, Stutz et al., PLoS ONE, 2014; Stutz et al., PLoS ONE, 2015). As proof of concept, these studies show that E6 is “druggable” in that its anti-apoptotic actvity can be blocked by molecules targeting a specific E6 domain. The E6-binding peptide could form a basis to generate therapeutically useful agents (“small molecules” or therapeutic peptides) in order to eliminate HPV-positive tumor cells.

Apoptotic cell death in HPV-positive cancer cells (SiHa) induced by an E6-binding peptide (pep11). Green: pep11-expressing cells. Red: Apoptosis measured by TUNEL assay.

3.) Identification of cellular targets for oncogenic HPVs

We have identified novel cellular genes (e.g. BTG2, EZH2, LEDGF) which are deregulated by the HPV E6/E7 oncoproteins. For example, we recently found that the cellular LEDGF gene is activated by the HPV oncogenes (Leitz et al., 2014). As a “survival gene”, LEDGF protects tumor cells against different forms of cellular stress, including the effects of radio- and chemotherapy. Thus, LEDGF could play a major role for the therapeutic resistance of tumors in the clinic.
(see also DKFZ press release)

HPVs stimulate expression of the cellular survival protein LEDGF (brown staining) in cervical cancer cells (also see: Leitz et al., 2014, PLoS Pathog.) . Immunohistochemical staining of a section from a cervical cancer biopsy. © Miriam Reuschenbach, Universitätsklinikum Heidelberg.

4.) Deregulation of the cellular and exosomal miRNA networks by the HPV oncogenes

By comprehensive deep sequencing analyses, we recently have analyzed the effects of HPV E6/E7 oncogene expression on the cellular microRNA (miRNA) network. Interestingly, the viral oncogenes induce profound alterations of the intracellular miRNA composition, increasing the amounts of pro-tumorigenic and decreasing the amounts of anti-tumorigenic miRNAs (Honegger et al., PLoS Pathog., 2015). This indicates that the deregulation of miRNAs by HPVs contributes to viral oncogenesis and raises the possibility that the correction of HPV-induced miRNA alterations could possess therapeutic potential.

We also found that the viral oncogenes strongly affect the miRNA composition of exosomes. Exosomes are small vesicles secreted by many cells, including tumor cells. They can serve as intercellular shuttles, transporting functionally active proteins, mRNAs, and miRNAs from tumor cells into recipient cells (Honegger et al., Int. J. Cancer, 2013).

Exosomes are small extracellular vesicles of endosomal origin. They can transport bioactive molecules (proteins, mRNAs, noncoding RNAs) from tumor cells into recipient cells. Electron microscopy. (Fig. from: Honegger et al., 2013, Int. J. Cancer, 133: 1631-1642).

We identified an E6/E7-dependent miRNA signature in exosomes secreted from HPV-positive tumor cells (Honegger et al., PLoS Pathog., 2015). The further investigation of this issue could provide insights into the cell-to-cell communication of HPV-positive cancer cells and open novel diagnostic opportunities.

Our work is supported by the Wilhelm Sander-Stiftung and by the Deutsche Krebshilfe.

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