Splicing defects caused by exonic mutations in PKD1 as a new mechanism of pathogenesis in autosomal dominant polycystic kidney disease.

The correct splicing of precursor-mRNA depends on the actual splice sites plus exonic and intronic regulatory elements recognized by the splicing machinery. Surprisingly, an increasing number of examples reveal that exonic mutations disrupt the binding of splicing factors to these sequences or generate new splice sites or regulatory elements, causing disease. This contradicts the general assumption that missense mutations disrupt protein function and that synonymous mutations are merely polymorphisms. Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder caused mainly by mutations in the PKD1 gene. Recently, we analyzed a substantial number of PKD1 missense or synonymous mutations to further characterize their consequences on pre-mRNA splicing. Our results showed that one missense and 2 synonymous mutations induce significant defects in pre-mRNA splicing. Thus, it appears that aberrant splicing as a result of exonic mutations is a previously unrecognized cause of ADPKD.

TP53 lacks tetramerization and N-terminal domains due to novel inactivating mutations detected in leukemia patients.

BACKGROUND: TP53 is a highly conserved tumor suppressor gene present on chromosome 17 and comprised 11 exons and 12 introns. The TP53 protein maintained the genomic integrity of the cell by regulating different pathways. The association of TP53 with leukemia and the increasing prevalence of leukemia in Pakistan instigated us to initiate the current study. MATERIALS AND METHODS: The TP53 gene of acute myeloid leukemia patients (n = 23) and normal individuals (n = 30) was amplified through polymerase chain reaction (PCR). The PCR amplified products of 3 samples 1 normal (NC-30) and 2 cancerous (LK-6 and LK-19) were subjected to deoxyribonucleic acid (DNA) sequence analysis. Bioinformatics analysis of the obtained DNA sequences helped to identify nature, type, and functional impact of mutations, if any. RESULTS: Results revealed 2 novel mutations in Case No. 1 (c. G >A10987 and c. InsA13298_13299) and Case No. 2 (c. InsC13284_13285, c. T >A13365) which generate a premature codon (ocher) at position 239 and lead to truncated TP53 protein. In Case No. 3, 16 novel mutations were identified and c. delC11093 mutation created a premature codon (opal) at 59th position. Hence, the resultant protein will lack its tetramerization and N-terminal domain required for its normal functioning. Moreover, some intronic mutations were noticed and found to have a negative impact on splicing related regulatory sequences. CONCLUSION: Results suggest the role of TP53 inactivating mutations in pathogenesis of leukemia.