Cervical Cancer Research – Dr Virna Leaner
Dr Virna Leaner
Title of the Project
The role of nuclear transport proteins in the development of cervical cancer
Highlights of the Project
Cancer development is a highly complex process involving the activation and suppression of numerous cell growth and tumor suppressor pathways. The activation of oncogenic kinases and transcription factors are reported to be essential, as it allows cancer cells to grow and develop in a near unchecked manner by overriding normal growth control mechanisms. These proteins rely on the nuclear transport proteins for their correct localisation within the cell pointing to a potentially critical role for the nuclear transport proteins in cancer cell development.
The nuclear transport proteins (karyopherins) are a family of proteins involved in the nucleo-cytoplasmic shuttling of proteins and RNA molecules into (import) and out of (export) the nucleus. Their functioning is critical for cellular processes including mitosis, replication and nuclear envelope assembly all of which are important for the maintenance of cancer cells. We have previously identified members of the nuclear
transport protein family as having high levels of expression in cervical cancer. Our studies suggest that overexpression of the nuclear importer protein Kpnβ1 is required for the survival and growth of cervical cancer cells as its inhibition with siRNA technologies results in cancer cell death. The identification of Kpnβ1 as a potential target for cancer therapy is a novel finding. The goal of the proposed study is thus to identify small molecule inhibitors that may serve to block nuclear import via Kpnβ1 and in this way inhibit the growth of cancer cells.
This project aims to develop effective inhibitors of Karopherin B1 (KpnB1), a protein on which cancer cells are highly dependent, yet normal cells are less reliant, as previously determined in our laboratory. We propose that the targeted inhibition of KpnB1 could have potential as a therapeutic approach for the treatment of cancer. To identify inhibitors of KpnB1 we have used a computational screening strategy, where compounds that potentially bind KpnB1 have been identified. Using a fluorescence-based assay which enables the identification of compounds that inhibit KpnB1 function we have identified a compound, C43 that shows potential to both inhibit the nuclear import function of KpnB1 as well as induce cancer cell death. Our results show that C43 treatment of cancer cells associate with apoptosis as the mechanism of cell death. C43 is effective at killing cancer cells of different origin including cervical, oesophageal and breast cancer. Investigations using derivatives of C43 show potential for these molecules as inhibitors of cancer cell growth. Ultimately, we hope to identify an inhibitor of KpnB1 that selectively kills cancer cells in both in vitro and in vivo models, thereby minimising the drug-associated side-effects that normally occur due to the killing of normal cells.
- Pauline J. van der Watt, Christopher P. Maske, Denver T. Hendricks, M. Iqbal Parker, Lynette Denny, Dhirendra Govender, Michael J. Birrer, and Virna D. Leaner., The Karyopherin proteins, Crm1 and Karyopherin b1, are overexpressed in cervical cancer and critical for cancer cell survival and proliferation. Int Journal of Cancer. Apr 15;124(8):1829-40 (2009).
- Pauline van der Watt and Virna D. Leaner., The nuclear exporter, Crm1, is regulated by NFY and Sp1 in cancer cells and repressed by p53 in response to DNA damage. Biochim Biophys Acta, Jul;1809(7):316-26 (2011).
- Pauline van der Watt, Ellen Ngarande, and Virna Leaner, Regulation of the nuclear importer proteins, KpnB1 and KpnA2 in cancer and transformed cells. PLoS One, Nov; 6(11):e27723 (2011).
- Michelle Ward, Pauline van der Watt, Gannie Tzoneva and Virna D. Leaner., Deregulated LAP2α expression in cervical cancer associates with aberrant E2F and p53 activities. IUBMB Life. (2011) Nov;63(11):1018-26.
- Pauline van der Watt, Catherine Stowell, and Virna D. Leaner, The nuclear import receptor KpnB1 and it’s potential as an anti-cancer therapeutic target. Critical Reviews in Eukaryotic Gene Expression, (in press) (2012).
Peer-reviewed published conference proceedings:
Pauline J. van der Watt, Christopher P. Maske, Denver T. Hendricks, M. Iqbal Parker, Lynette Denny, Dhirendra Govender, Michael J. Birrer, and Virna D. Leaner. A critical role for the karyopherin proteins, Crm1 and Kpn beta 1, in cancer cell survival and proliferation. FEBS JOURNAL Volume: 275 Pages: 468-468 Supplement: Suppl. 1 JUN 2008.
Pauline van der Watt, Christopher Maske, Denver Hendricks, M. Iqbal Parker, Lynette Denny, Dhirendra Govender, Michelle Birrer and Virna Leaner.The Karyopherin proteins Crm1 and Kpnβ1 are overexpressed and critical for the survival of cervical cancer cells., American Association for Cancer Research Annual Meeting, Denver, Colorado, USA, 18-22 April 2009.
Pauline van der Watt, Christopher Maske, Denver Hendricks, M. Iqbal Parker, Lynette Denny, Dhirendra Govender, Michelle Birrer and Virna Leaner.,Crm1 overexpression associates with cervical cancer and is critical for cell survival and proliferation. American Association for Cancer Research Centennial Meeting, Suntec, Singapore, 4-8 November 2007.
Pauline Forrester, Michael Birrer, Lynette Denny, Denver Hendricks, M. Iqbal Parker, and Virna Leaner, Transcriptional profiling identifies increased expression of nuclear transport proteins in cervical cancer. 97th American Association for Cancer Research Annual Meeting, Washington DC, USA., 1-5 April 2006.
How was this Project of value in the Struggle against Cancer?
The struggle against cancer is compounded by the fact that it is such a complex disease that progresses through a series of stages before the development of an advanced stage cancer which is often exceeding difficult to treat. Research into understanding cancer development and treatment has therefore largely focused on:
- the prevention of its occurrence
- the early detection of disease
- on identifying the most effective treatment strategies for patients who have the disease
The objective of our study has been to identify potential biomarkers for early detection as well identifying potential therapeutic targets. We obtained preliminary data using cervical cancer tissue specimens that suggested that proteins in the nuclear transport family (the karyopherins; Crm1, KpnA2 and KpnB1), may serve as both biomarkers and therapeutic targets. We tested our hypothesis that these proteins could be essential for the biology of cancer cells by using cell culture model systems. The main findings emanating from our research, suggest the all three of the proteins could serve as potential biomarkers as their expression levels were significantly elevated in the cancer group compared to controls.
Our results however, suggest that only two of the three proteins investigated, Crm1 and KpnB1 are potential therapeutic targets as inhibiting their expression and activity in a variety of cancer cell lines including; cervical, oesophageal and breast cancer resulted in a significant inhibition in the growth of these cancer cells. It is our belief that continued research into the potential of these proteins as anti-cancer targets may ultimately result in the identification of small molecules that could be used to inhibit their expression and activity and in this way interfere with the uncontrolled growth of cancer cells.
Future Plans with the Project
This project has yielded promising data that we are in the process of investigating further. Some of the questions we are asking include:
- can we identify small molecule inhibitors of the nuclear transport proteins (in particular KpnB1, as there is no known inhibitor to this protein identified to date)?
- should we identify a small molecule inhibitor how effective is it at inhibiting cancer cell growth as opposed to normal cells?
- why do these proteins become overexpressed in cancer cells (is it part cause or effect)?
- what are the mechanism that control its gene expression?
We thank CANSA for their support in funding our research and for providing a forum (the CANCER in Action conference) for Cancer Researchers in South Africa to interact on a national level.