Background:

Graduated from the University of Leicester in 1997 with a BSc (Hons) in Biological Sciences (Molecular Biology).
Completed a PhD in Biochemistry at the University of Leicester in 2001.
Postdoctoral research fellow at the University of Sussex (2001-2008).
Joined the University of Southampton as a lecturer in the summer of 2008.

Research Interests:

Throughout my research career, I have been investigating eukaryotic post-transcriptional control, in particular the initiation phase of translation. This key point in gene expression (Figure 1) can rapidly alter the temporal and spatial expression of either the whole transcriptome or specific mRNAs, without requiring new transcription.

Figure 1 Overview of eukaryotic gene expression

The major mechanism of translation initiation in eukaryotic cells requires the assembly of the ribosome and associated eukaryotic translation initiation factors (eIFs) at the m 7GTP cap structure at the 5’ end of an mRNA (Figure 2). However, more recently it has become clear that the cap-independent phenomenon of internal ribosome entry, first discovered for viral mRNAs, including poliovirus and HIV, also occurs on cellular mRNAs. This phenomenon allows the continued translation of these mRNAs during conditions when overall protein synthesis is inhibited due to viral infection or environmental stresses. During my PhD I was one of the first researchers to identify internal ribosome entry segments (IRESs) in the 5’ untranslated regions of cellular mRNAs and during my time as a postdoctoral research fellow I investigated the regulation of eIF4GI.

Figure 2 Formation of the 48S preinitiation complex showing the central role of the scaffold protein eIF4G

Central to cap- and IRES-dependent translation initiation are the multi-domain eIF4GI/II, which act as a scaffold for the assembly of the initiation complex via contacts with the mRNA cap-binding protein eIF4E, the RNA helicase, eIF4A, the ribosome-binding eIF3; the eIF4E kinase, Mnk; and the poly(A)-binding protein (PABP). The eIF4GI scaffold protein can be cleaved during apoptosis and some viral infections and while studying the localisation of fragments that arise from these viral protease or caspase cleavages in mammalian cells, I identified a nuclear localisation signal in the N-terminus of the protein using indirect immunofluorescence microscopy.

Furthermore, eIF4GI is expressed as five isoforms arising from alternative translation start sites, and I have used RNA interference to reduce the expression of endogenous eIF4GI protein, which resulted in alterations in the morphology and physiology of cells. More recent work rescued some of the effects of the siRNAs by expressing eIF4GI cDNAs that are immune to silencing, with the different translational isoforms having differing activities. eIF4GII is also expressed as a number of different isoforms and I am currently examining these in more detail.

Research Projects:

Central to translation initiation is the selection of the initiation codon, which is usually an AUG. However, other codons may be used for translation giving rise to N-terminally extended or truncated polypeptides. We are investigating the usage and regulation of these alternative initiation codons in order to examine the importance of alternative initiation codon selection in the generation of protein isoform diversity, a previously neglected aspect of gene expression. This work will modify and extend our understanding of the protein-coding potential of all eukaryotic genomes, as the underlying mechanisms of translational control are conserved across species.

Selection of the correct initiation codon is mediated by several initiation factors, and part of this project explores the regulation of AUG usage versus non-AUG initiation codons. It is clear that the selection of certain initiation codons may have beneficial or detrimental effects on the cell and it is important to establish in which stages of cell growth and/or disease progression that this form of translational control occurs. Deregulation of the appropriate selection of translation initiation codons may be important in the status of certain diseases, including cancer.

Selected Publications:

Dobbyn, H.C., Hill, K., Hamilton, T.L., Spriggs, K.A., Pickering, B.M., Coldwell, M.J., de Moor, C.H., Bushell, M. and Willis, A.E. (2008) Regulation of BAG-1-IRES-mediated translation following chemotoxic stress. Oncogene. 27: 1167-1174

Morley, S.J. and Coldwell, M.J. (2007) Matters of Life and Death: Translational aspects of apoptosis. in: Mathews, M.B. Sonenberg, N. and Hershey, J.W.B. (eds.) Translational Control in Biology and Medicine . Cold Spring Harbor Laboratory Press, pp 433-458.

Hinton, T.M., Coldwell, M.J., Carpenter, G.A., Morley, S.J. and Pain, V.M. (2007) Functional Analysis of Individual Binding Activities of the Scaffold Protein eIF4G. J. Biol. Chem. 282: 1695-1708.

Coldwell, M.J., Morley, S.J. (2006) Specific isoforms of translation initiation factor 4GI show differences in translational activity. Mol. Cell. Biol. 26: 8448-8460.

Morley, S.J., Coldwell, M.J. and Clemens, M.J. (2005) Initiation Factor Modifications in the Pre‑Apoptotic Phase. Cell Death Differ. 12: 571-84.

Coldwell, M.J. , Hashemzadeh-Bonehi, L., Hinton, T.M., Morley, S.J. and Pain, V.M. (2004) Expression of fragments of translation initiation factor eIF4GI reveals a nuclear localisation signal within the N-terminal apoptotic cleavage fragment N-FAG. J. Cell Sci. 117: 2545-2555.

Mitchell, S.A., Spriggs, K.A., Coldwell, M.J., Jackson, R.J. and Willis, A.E. (2003) The Apaf‑1 internal ribosome entry segment attains the correct structural conformation for function via interactions with PTB and unr. Mol. Cell 11: 757-771.

Mitchell, S.A., Brown, E.C., Coldwell, M.J., Jackson, R.J. and Willis, A.E. (2001) Protein factor requirements of the Apaf-1 internal ribosome entry segment: roles of polypyrimidine tract binding protein and upstream of N-ras. Mol. Cell. Biol. 21: 3364-3374.

Coldwell, M.J. , deSchoolmeester, M.L., Fraser, G.A., Pickering, B.M., Packham, G. and Willis, A.E. (2001) The p36 isoform of BAG-1 is translated by internal ribosome entry following heat shock. Oncogene 20: 4095-4100.

Coldwell, M.J. , Mitchell, S.A., Stoneley, M., MacFarlane, M., and Willis, A.E . (2000). Initiation of Apaf‑1 translation by internal ribosome entry. Oncogene 19: 899-905.

Stoneley, M., Subkhankulova, T., Le Quesne, J.P.C., Coldwell, M.J., Jopling, C.L., Belsham, G.J., and Willis, A.E. (2000). Analysis of the c-myc IRES; a potential role for cell-type specific trans-acting factors and the nuclear compartment. Nuc. Acids Res. 28: 687-694.

Created November 2008