Characterisation of LVI-1 (WDR76) as a candidate tumour suppressor gene

The central aim of this study was to characterise the expression of the candidate tumour suppressor gene, LV/-J (lentivirus integration-I) and its products. The LVI-J gene (WDR76) was discovered as a target for disruption by proviral insertional mutagenesis in a case of pre-B cell lymphoma in a FIV infected cat {Beatty, 1998 5 lid; Beatty, 2002 7 lid}. As LV/-J is highly conserved, my work focused on the human and murine orthologues to take advantage of the superior resources available for these species. My work showed potentially important differences in expression of the human and mouse genes with respect to promoter use and length of 3' untranslated sequences. The murine gene is transcribed mainly from the distal PI promoter, which appears to be a bi-directional element shared with the adjacent MJapJ gene, while the human gene transcripts are derived exclusively from the proximal P2 promoter. Direct analysis by RT-PCR showed that the murine gene could also be expressed from the P2 promoter. These findings have significant implications for Lvi-l protein expression as the P2 transcripts are predicted to express larger proteins with a distinct N-terminal sequence. To characterise the LV/-J gene products, rabbit polyclonal antisera were raised to GST fusion proteins expressed in bacteria. Use of the murine anti-ml.vi-I antiserum in Western blotting identified a protein of the expected size (58 kDa) based on translation of the major mRNA species from the PI promoter. Immunofluorescence and confocal microscopy suggested that this protein is localised mainly in the cytoplasm. Although the function of LVI-I is unknown, its closest relative in the human genome is DDB2, a protein involved in repair of UV-induced DNA damage. Regulation of LVI-I expression was examined after UV irradiation, providing preliminary evidence of responses at transcriptional and post-transcriptional levels. Further leads were followed by analogy with the yeast orthologue of LVI-I, YDLI56W, but no evidence of a complex between LVI-I and MSH6 was found. In conclusion, while function of the LVI-I gene remains to be establishes, it provides the basis for future characterisation of this highly conserved and potentially important eukaryotic gene.