Our work is currently focused on post-transcriptional aspects of gene regulation, and specifically how these differ between cancer cells and their normal counterparts. In 2000 we identified Cid1, a nucleotidyl transferase required for cell cycle checkpoint activation when replicative DNA polymerases are inhibited in fission yeast. Our subsequent studies showed that Cid1 is a cytoplasmic protein with poly(A) polymerase activity in vitro, but our more recent data suggest that it uridylates mRNAs in vivo. This modification forms the basis of a widespread but previously unappreciated pathway of mRNA decapping that is independent of poly(A) tail shortening. Human cells contain two Cid1 orthologues, one of which (ZCCHC11) we have found to be responsible for uridylation of replication-dependent histone mRNAs. The uridylation of histone mRNAs targets them for degradation after exposure of cells to hydroxyurea, an anti-cancer drug that inhibits DNA replication. Remarkably, ZCCHC11 is also responsible for the modification of tumour suppressor micro-RNA precursors and mature micro-RNAs. Inhibition of ZCCHC11 expression in cancer cells has been shown to block some of the aspects of the cancer phenotype in vivo, and recent data suggest that ZCCHC11 over-expression predicts disease progression in breast cancer. Together, these findings suggest that targeting the ZCCHC11 uridylation pathway may be of therapeutic value in a variety of cancers. Our recent collaborative study of the relationship between the structure of Cid1 and its function suggests ways in which RNA uridylyl transferases might be targeted therapeutically.
We are also studying aspects of the control of protein synthesis that are deregulated during tumorigenesis. Efforts in this area are mainly focused on the translation initiation factor eIF3e (also known as INT6) which we identified through its capacity to induce multi-drug resistance in the fission yeast model, and which was identified independently as a site of MMTV integration in murine tumours. Our recent work has shown that high levels of eIF3e/INT6 in primary breast cancer are positively correlated with tumour grade. Using siRNA knock-down we have found that eIF3e/INT6 selectively regulates the translation, and in some cases the abundance, of mRNAs encoding a number of key regulators of tumour invasion and metastasis.