Biology subjects

Tam, A. S.

Publications and source records attributed to Tam, A. S..

5 recordsLinked to original sources

bioRxiv2021

DYNLL1 mis-splicing is associated with replicative genome instability in SF3B1 mutant cells

Genome instability is a hallmark of cancer that arises through a panoply of mechanisms driven by oncogene and tumour-suppressor gene mutations. Oncogenic mutations in the core splicing factor SF3B1 have been linked to genome instability. Since SF3B1 mutations alter the selection of thousands of 3 splice sites affecting genes across biological pathways, it is not entirely clear how they might drive genome instability. Here we confirm that while R-loop formation and associated replication stress may account for some of the SF3B1-mutant genome instability, a mechanism involving changes in gene expression also contributes. An SF3B1-H662Q mutant cell line mis-splices the 5UTR of the DNA repair regulator DYNLL1, leading to higher DYNLL1 protein levels, mis-regulation of DNA repair pathway choice and PARP inhibitor sensitivity. Reduction of DYNLL1 protein in these cells restores genome stability. Together these data highlight how SF3B1 mutations can alter cancer hallmarks through subtle changes to the transcriptome.

cell biology↗

bioRxiv2020

Mis-splicing of Mdm2 leads to increased P53-activity and craniofacial defects in a MFDM Eftud2 mutant mouse model

EFTUD2, a GTPase and core component of the splicesome, is mutated in patients with mandibulofacial dysostosis with microcephaly (MFDM). We generated a mutant mouse line with conditional mutation in Eftud2 and used Wnt1-Cre2 to delete it in neural crest cells. Homozygous deletion of Eftud2 leads to neural crest cell death and malformations in the brain and craniofacial region of embryos. RNAseq analysis of embryonic mutant heads revealed a significant increase in exon skipping, in retained introns and enriched levels of Mdm2 transcripts lacking exon 3. Mutants also had increased nuclear P53, higher expression of P53-target genes, and increased cell death. Their craniofacial development was significantly improved when treated with Pifithrin-, an inihibitor of P53. We propose that craniofacial defects caused by mutations of EFTUD2 are a result of mis-splicing of Mdm2 and P53-associated cell death. Hence, drugs that reduce P53 activity may help prevent craniofacial defects associated with spliceosomopathies.

developmental biology↗

bioRxiv2020

Cdc48 regulates intranuclear quality control sequestration of the Hsh155 splicing factor

Cdc48/VCP is a highly conserved ATPase chaperone that plays an essential role in the assembly or disassembly of protein-DNA complexes and in degradation of misfolded proteins. We find that Cdc48 accumulates during cellular stress at intranuclear protein quality control (INQ) sites. Cdc48 function is required to suppress INQ formation under non-stress conditions and to promote recovery following genotoxic stress. Cdc48 physically associates with the INQ substrate and splicing factor Hsh155 and regulates its assembly with partner proteins. Accordingly, cdc48 mutants have defects in splicing and show spontaneous distribution of Hsh155 to INQ aggregates where it is stabilized. Overall, this study shows that Cdc48 regulates deposition of proteins at INQ and suggests a previously unknown role for Cdc48 in the regulation or stability of splicing subcomplexes.

molecular biology↗

bioRxiv2018

The yeast core spliceosome maintains genome integrity through R-loop prevention and alpha-tubulin expression

To achieve genome stability cells must coordinate the action of various DNA transactions including DNA replication, repair, transcription and chromosome segregation. How transcription and RNA processing enable genome stability is only partly understood. Two predominant models have emerged: one involving changes in gene expression that perturb other genome maintenance factors, and another in which genotoxic DNA:RNA hybrids, called R-loops, impair DNA replication. Here we characterize genome instability phenotypes in a panel yeast splicing factor mutants and find that mitotic defects, and in some cases R-loop accumulation, are causes of genome instability. Genome instability in splicing mutants is exacerbated by loss of the spindle-assembly checkpoint protein Mad1. Moreover, removal of the intron from the -tubulin gene TUB1 restores genome integrity. Thus, while R-loops contribute in some settings, defects in yeast splicing predominantly lead to genome instability through effects on gene expression.

cell biology↗

bioRxiv2017

Genotoxin-induced transcriptional repression regulates selective protein aggregation

Upon genotoxic stress, dynamic relocalization events control DNA repair, and alterations of the transcriptome and proteome enabling stress recovery. How these events may influence one another is only partly known. Beginning with a cytological screen for genome maintenance proteins that move under stress, we find that, upon alkylation stress, the splicing factor Hsh155 localizes to both intranuclear and cytoplasmic protein quality control aggregates. Under stress, an ordered sequestration of Hsh155 occurs at nuclear and then cytoplasmic aggregates in a manner that is regulated by molecular chaperones. This dynamic behavior is preceded by a decrease in splicing efficiency. While DNA replication stress signaling is not required for Hsh155 sequestration, Hsh155 aggregation is cell cycle and TOR pathway dependent. Indeed, loss of a TORC1 regulated ribosomal protein gene transcription factor Sfp1 allows general aggregate formation but prevents Hsh155 recruitment. Together, our analyses suggest a model in which some proteins evicted from chromatin undergoing transcriptional remodeling during stress are targeted to protein quality control sites.

cell biology↗