Biology subjects

Lim, C. J.

Publications and source records attributed to Lim, C. J..

3 recordsLinked to original sources

bioRxiv2019

PDX models reflect the proteome landscape of pediatric acute lymphoblastic leukemia but divert in select pathways

Murine xenografts of pediatric leukemia are known to accurately recapitulate genomic aberrations. How this translates to the functional capacity of the proteome is unknown. Here, we studied global protein abundance, phosphorylation, and proteolytic processing in 11 pediatric B- and T-cell acute lymphoblastic leukemia patients and 19 corresponding xenografts. Protein level differences that stratified pediatric disease subtypes at diagnostic and relapse stages were largely recapitulated in xenograft models. Patient xenografts lacked multiple human leukocyte antigens, and complement proteins, and presented incomplete response mechanisms to the host immune system which is absent in the murine model. The dominant expression of MKI67 and cell cycle proteins indicated a high proliferative capacity of xenografted cells residing in the spleen. Structural genomic changes and mutations found in patients were reflected at the protein level. The post-translational modification landscape is shaped by leukemia type and host and only to a limited degree by the patient of origin. This study portrays how genomic and host factors shape protein and post-translational modification landscapes differently, and confirms murine patient-derived xenograft as competent model system while highlighting important areas of diverging biology.

cancer biology↗

bioRxiv2019

The cryo-EM structure of human CST reveals a two-megadalton decameric assembly bound to telomeric DNA

The single-stranded DNA-binding CTC1-STN1-TEN1 (CST) complex is essential for telomere maintenance and genome-wide replication recovery, processes that are critical for genome stability. Here, we report the 2.95 [A] cryo-EM structure of human CST bound to telomeric single-stranded DNA, which unexpectedly assembles as a decameric supercomplex. The atomic model of the 134 kDa CTC1, built almost entirely de novo, reveals the overall architecture of CST and the DNA-binding anchor site. In situ arrangements of STN1 and TEN1 are revealed, with STN1 interacting with CTC1 at two separated sites, allowing allosteric mediation of CST decameric assembly. Surprisingly, CTC1 lacks the anticipated structural homology to yeast Cdc13 but instead shares similarity with a form of Replication Protein A. The atomic-resolution model of human CST provides crucial mechanistic understanding of CST mutations associated with human diseases. Moreover, the decameric form of CST suggests the intriguing possibility of ssDNA architectural organization similar to what the nucleosome provides for dsDNA.\n\nOne Sentence SummaryHuman telomeric single-stranded DNA triggers the assembly of a decameric protein supercomplex solved by cryo-EM.

biophysics↗

bioRxiv2019

Set2-mediated alternative splicing of Srsf11 regulates cocaine reward behavior

Alternative splicing is a key mechanism for neuronal gene regulation, and is grossly altered in mouse brain reward regions following investigator-administered cocaine. It is well established that cocaine epigenetically regulates transcription, yet mechanism(s) by which cocaine-induced epigenetic modifications regulate alternative splicing is largely unexplored. Our group and others have previously identified the histone modification, H3K36me3, as a putative splicing regulator. However, it has not yet been possible to establish the direct causal relevance of this modification to alternative splicing in brain or any other context. We found that mouse cocaine self-administration caused widespread alternative splicing, concomitant with enrichment of H3K36me3 at splice junctions. Differentially spliced genes were enriched in the motif for splice factor, Srsf11, which was both differentially spliced and enriched in H3K36me3. Epigenetic editing led us to conclude that H3K36me3 functions directly in alternative splicing of Srsf11, and that Set2 mediated H3K36me3 bidirectionally regulates cocaine intake.

neuroscience↗