Conclusiones del capítulo: 38+

Between their seminal review of 2000 and subsequent update of 2011, Hanahan and Weinberg laid out a number of hallmarks of cancer (Hanahan & Weinberg, 2000, 2011). These included their six original hallmarks:

. Self-sufficiency in growth signals . Insensitivity to antigrowth signals . Limitless replicative potential . Sustained angiogenesis . Evading apoptosis

. Tissue invasion and metastasis

In terms of these hallmarks, UNR could immediately be linked to cancer in a general way. As an example, it could be postulated that a protein that controls the expression of a proto-oncogene like FOS, if mutated, could result in self-sufficiency in growth signals. Likewise, as UNR modulates the expression of the apoptosome scaffold protein, APAF1, a loss in that function could result in a cell potentially evading apoptosis. There are many such theoretical considerations that could link UNR to cancer but, in most cases, they are hypotheses based upon no experimental evidence whatsoever. That said, there is some circumstantial evidence in the literature that links UNR to cancer. For example, UNR has been shown to be differentially regulated or mutated in a number of cancers or during the development of the cancer phenotype.

Another of Hanahan and Weinberg’s classic hallmarks is invasion and metastasis. The UNR transcript was shown to be down-regulated in cases of metastatic gastric cancer (p value = 0.00228 by random permutation test) compared to non-metastatic tumours. Biopsies of resected advanced gastric tumours were taken from 56 patients who were then followed up for three years. The patients were noted to have shown peritoneal metastases or to be recurrence free (as tested by peritoneal lavage). They were then assigned to one of two groups with 30 (13 with metastasis, 17 without) or 24 (13 with metastasis, 11 without) patients, respectively. The first group was designated the ‘learning group’ and microarray analysis of data from those patients was used to make predictions of which of 2304 genes could potentially be used as diagnostic markers of metastatic potential. These predictions were then tested by examination of the second ‘validation group’ samples (Motoori et al., 2006). Conversely, with advanced

cervical cancer treated with radiotherapy, it was found thatUNRwas expressed approximately two times higher in samples from patients who went on to die from cancer within 3-23 months compared to those who showed no signs of cancer for at least 39 months, going up to over 102 months, depending on the individual patients within the course of the study (Harima et al., 2004). The genomic region containing theUNRgene was found to be a common region to show a gain of copy number in paediatric adrenocortical tumours, the authors consideringUNRto be important in adenomas but less so in carcinomas (Mateo et al., 2011). Interestingly, the region showed more frequent increases in copy number in carcinoma samples although the consensus length of amplification was slightly longer in carcinoma samples such that it included theNRAS gene.

1.6.1 UNR and cancer – COSMIC database search

There are other examples in the literature of UNR being associated with various cancers, mainly coming from high throughput experiments. The Catalogue Of Somatic Mutations In Cancer (COSMIC) database (version 70) listed 177 mutations in UNR found in different cancers, this equated to 95 changes in coding (Ray et al., 2015).

A more up to date version (v76) that used the GRCh38 version of the human genome was accessed on 16/02/2016 in order to obtain information about the amino acid mutations in UNR in cancer. It is worth pointing out that some observations from a given sample may have been coincidental and not related to the cancer,per se.

The first observation was that there appeared to be more arginines mutated than any other amino acid (Figure 1.6).

Figure 1.6: A bar chart showing the number of observed amino acid changes within the UNR protein recorded in the COSMIC database by affected amino acid residue. Changes include each mutation where the same residue has been recorded as being mutated into multiple amino acids and the introduction of stop codons but exclude silent mutations.

Taking the 844 amino acid version, there are 44 arginines in UNR, of which 20 were recorded as having at least one non-silent mutation. 17.1% of all recorded non-silent mutations were in arginine residues, more than both of the next most mutated amino acids (glutamine and glutamate at 7.7% each). This skew towards UNR having mutated arginines in cancer has been alluded to in the literature – e.g. it was noted that there are three recurrently mutated arginines within endometrial cancers (Bell, 2014). The reason for this overrepresentation of arginines is not known but it is easy to speculate that positively charged residues being mutated could alter, reduce or remove the capacity for UNR to bind to negatively charged molecules like RNA. Whilst pure speculation, it is considered unlikely that UNR-RNA binding would be rendered impossible as a result of these mutations. That is because it is believed that UNR binds RNA via its cold shock domains and these have particular highly conserved regions for binding nucleic acids (the RNP- 1 [Y/FGFI] and RNP-2 [FFH] motifs) and neither of these contain arginine. It is postulated here, therefore, that the mutations in arginine residues are more about altering the thermodynamic stability of specific UNR-RNA interactions and, thereby, possibly altering the set of RNAs involved in UNR-RNA interactions.

Mutations recorded in the COSMIC database from within the five canonical cold shock domains of UNR are shown below (Figure 1.7).

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