Biology subjects

MacMillan, D.

Publications and source records attributed to MacMillan, D..

4 recordsLinked to original sources

bioRxiv2025

Mutant p53 binds RNA to drive mitochondrial dysfunction

Tumor suppressor protein 53 (p53) is a transcription factor that is deregulated in 50% of cancers. Often termed the guardian of the genome, p53 is responsible for maintenance of genomic stability, cell cycle arrest, DNA repair, senescence, and apoptosis. In cancer cells, deregulation of p53 often occurs through mutations in the DNA binding domain which lead to a loss of the transcriptional activity. While 100s of somatic mutations in the DNA binding domain are known, a small number of mutants are enriched in cancer, suggesting a gain-of-function role. Here we deploy an intein-based approach to localize {micro}Map photoproximity labeling to p53 to define novel interactions contributing to the loss and gain of function roles of 5 separate hotspot mutants. These data revealed that G245S and R273H binds to RNA through its C-terminal domain. We show through CLIP experiments that mutant p53 has an RNA binding motif that conserved across mutants and is enriched in 3UTRs, promoting ribosomal localization and labeling of proteins at the mitochondrial surface. We further demonstrate that the RNA binding ability of mutant p53 promotes altered miRNA processing and mitochondrial dysfunction providing mechanistic rationale for historically reported but poorly understood phenotypes.

molecular biology↗

bioRxiv2025

Micromapping (μMap) of HER2 Across Human Breast Cancers: Photocatalytic Proximity Labeling Identifies Primary Resistance Mechanisms and Functional Interactors

Interactions among receptor tyrosine kinases (RTKs), particularly HER2, are critical in driving the growth of certain breast cancer subtypes. However, the mechanisms of HER2 dependency and resistance to targeted therapies remain unclear. Using photocatalytic micromapping ({micro}Map) proximity labeling, we profiled the HER2 interactome across human breast cancer lines. We identify galectin family proteins as uniquely enriched in trastuzumab-resistant models, and show that genetic and pharmacological inhibition of galectins restores trastuzumab sensitivity. Mechanistically, galectin inhibition destabilized HER2 and other RTKs and enhanced antibody-mediated receptor degradation. Galectin inhibition in combination with trastuzumab triggered mitochondrial and endoplasmic reticulum stress pathways, revealing new mechanisms underlying HER2 signaling, dependency, and resistance in breast cancer. We also identified protein tyrosine phosphatase F (PTPRF) as a pan-cancer HER2 interactor, which is broadly upregulated and whose knockdown suppresses proliferation in HER2-low cancers. This work provides an extensive new interactomic resource and underscores the utility of proximity labeling for mapping complex cancer networks and identifying new therapeutic targets.

cancer biology↗

bioRxiv2021

HIV proviral burden, genetic diversity and dynamics in viremic controllers who subsequently initiated suppressive antiretroviral therapy

Curing HIV will require eliminating the reservoir of integrated, replication-competent proviruses that persist despite antiretroviral therapy (ART). Understanding the burden, genetic diversity and longevity of persisting proviruses in diverse individuals with HIV is critical to this goal, but these characteristics remain understudied in some groups. Among them are viremic controllers, individuals who naturally suppress HIV to low levels but for whom therapy is nevertheless recommended. We reconstructed within-host HIV evolutionary histories from longitudinal single-genome amplified viral sequences in four viremic controllers who eventually initiated ART, and used this information to characterize the age and diversity of proviruses persisting on therapy. We further leveraged these within-host proviral age distributions to estimate rates of proviral turnover prior to ART. This is an important yet understudied metric, since pre-ART proviral turnover dictates reservoir composition at ART initiation (and thereafter), which is when curative interventions, once developed, would be administered. Despite natural viremic control, all participants displayed significant within-host HIV evolution pre-therapy, where overall on-ART proviral burden and diversity broadly reflected the extent of viral replication and diversity pre-ART. Consistent with recent studies of non-controllers, the proviral pools of two participants were skewed towards sequences that integrated near ART initiation, suggesting dynamic proviral turnover during untreated infection. In contrast, proviruses recovered from the two other participants dated to time-points that were more evenly spread throughout infection, suggesting slow or negligible proviral decay following deposition. HIV cure strategies will need to overcome within-host proviral diversity, even in individuals who naturally controlled HIV replication before therapy. ImportanceHIV therapy is life-long because integrated, replication-competent viral copies persist within long-lived cells. To cure HIV, we need to understand when these viral reservoirs form, how large and genetically diverse they are, and how long they endure. Elite controllers, individuals who naturally suppress HIV to undetectable levels, are being intensely studied as models of HIV remission, but viremic controllers, individuals who naturally suppress HIV to low levels, remain understudied even though they too may hold valuable insights. We combined phylogenetics and mathematical modeling to reconstruct proviral seeding and decay from infection to therapy-mediated suppression in four viremic controllers. We recovered diverse proviruses persisting during therapy that broadly reflected HIVs within-host evolutionary history, where the estimated half-lives of the persistent proviral pool during untreated infection ranged from <1 year to negligible. Cure strategies will need to contend with proviral diversity and between-host heterogeneity, even in individuals who naturally control HIV.

microbiology↗

bioRxiv2017

Pan-cancer analysis reveals complex tumor-specific alternative polyadenylation

Alternative polyadenylation (APA) of 3 untranslated regions (3 UTRs) has been implicated in cancer development. Earlier reports on APA in cancer primarily focused on 3 UTR length modifications, and the conventional wisdom is that tumor cells preferentially express transcripts with shorter 3 UTRs. Here, we analyzed the APA patterns of 114 genes, a select list of oncogenes and tumor suppressors, in 9,939 tumor and 729 normal tissue samples across 33 cancer types using RNA-Seq data from The Cancer Genome Atlas, and we found that the APA regulation machinery is much more complicated than what was previously thought. We report 77 cases (gene-cancer type pairs) of differential 3 UTR cleavage patterns between normal and tumor tissues, involving 33 genes in 13 cancer types. For 15 genes, the tumor-specific cleavage patterns are recurrent across multiple cancer types. While the cleavage patterns in certain genes indicate apparent trends of 3 UTR shortening in tumor samples, over half of the 77 cases imply 3 UTR length change trends in cancer that are more complex than simple shortening or lengthening. This work extends the current understanding of APA regulation in cancer, and demonstrates how large volumes of RNA-seq data generated for characterizing cancer cohorts can be mined to investigate this process.

genomics↗