microRNA and stress tolerance in cancer models

Among small non-coding RNAs, microRNAs have demonstrated a variety of essential functions under both physiological and pathological conditions. The vast majority of them have not been functionally characterized so far. Involved in cell cycle progression, apoptosis, oncogenic transformation or cell migration, microRNAs may play a major role in cellular stress adaptation. To date, no systematic analysis of their contribution to stress tolerance has been performed. In the present project, the functional role of differentially expressed candidate microRNAs in stress tolerance is investigated in different cancer models from colon, cervix and breast cancer with acquired multi- stage resistance to antineoplastic agents. Thus, we propose the following hypotheses: 1. microRNAs are differentially regulated in malignant cells under stress; 2. microRNAs are key players in drug resistance. To test the first hypothesis, cells will be subjected to different forms of stress including oxidative and DNA oriented stress monitoring the dynamics of microRNA response by differential expression profiling and - in case of microRNA suppression - assessing epigenetic silencing. To test the second hypothesis, the expression of microRNAs is modulated at the cellular level to quantify their impact on stress response (survival, senescence, apoptosis or necrosis), on interaction between microRNA and survival pathways (e.g. PI3K - Akt - mTOR) and on identified microRNA target genes. Finally, proof-of-principle studies in selected models may indicate novel intervention strategies in drug resistant tumours. Previous work from our team has demonstrated the orchestrated response of cancer cells to xenobiotics at the molecular level. In order to assess differentially regulated microRNAs in cancer cells under chronic stress, we tested a multi-stage colon cancer system with increasing degrees of resistance to the antimetabolite 5-fluorouracil. Using microarrays and qPCR, we already validated 9 differentially expressed microRNA candidate molecules. The candidates selected for further investigations are: miR-10b, miR-19a, miR-19b, miR-130a, miR-141, miR-200a, miR-200b, miR-200c, and miR-375. Stress tolerance is a vital function in every living organism. To survive, cancer cells have developed a flexible strategy to cope with stress including immune resistance and therapeutic challenge. This endurance makes cancer cells an exceptionally well suited model to study microRNA as a central regulator of stress tolerance by using three multi-stage models. As resistance to systemic cancer therapy is still the major cause of cancer death, this knowledge should have direct relevance for translational cancer therapy research. Neighbouring fields such as neurodegenerative and cardiovascular diseases - all associated with cellular stress conditions - may benefit from this project as the regulatory role of microRNAs may well extend to other types of cells under unphysiological conditions.

Living cells have to tolerate a variety of different types of stress during their life span. This applies to normal cells but all the more to cancer cells. To survive, cancer cells learn how to adapt to the challenge of anticancer treatment. In this project, we show how very small pieces of RNA, termed microRNA, are altered when cancer cells becomes drug resistant and how they support cancer cells when exposed to a variety of therapeutic agents. First, microRNA levels in the cancer cell are significantly changed upon exposure to therapeutic medicines. Second, some of them are not only altered, but help the stressed cancer cell to survive. This microRNA response seems to be specific for the different type of cancer cell as investigated in four different models: cervical cancer, colon cancer, breast cancer and melanoma. Moreover, microRNA are transferred from the drug resistant cancer cell in small droplets (nanoparticles), called exosomes. These exosomes are shedded from the cancer cell and transport molecular information from cell to cell: this is one way how cells speak to each other, particularly under stress. Most interestingly, drug resistant cancer cells have a deleterious message to provide to other cells: this is a very hot area for future research.