Biology subjects

Mendillo, M. L.

Publications and source records attributed to Mendillo, M. L..

6 recordsLinked to original sources

bioRxiv2025

HSF1 remodels mitochondrial biogenesis and function in cancer cells via TIMM17A

Mitochondria play critical roles in energy production and cellular metabolism. Despite the Warburg effect, mitochondria are crucial for the survival and proliferation of cancer cells. Heat Shock Factor 1 (HSF1), a key transcription factor in the cellular heat shock response, promotes malignancy and metastasis when aberrantly activated. To understand the multifaceted roles of HSF1 in cancer, we performed a genome-wide CRISPR screen to identify epistatic interactors of HSF1 in cancer cell proliferation. The verified interactors of HSF1 include those involved in DNA replication and repair, transcriptional and post-transcriptional gene expression, and mitochondrial functions. Specifically, we found that HSF1 promotes cell proliferation, mitochondrial biogenesis, respiration, and ATP production in a manner dependent on TIMM17A, a subunit of the inner membrane translocase. HSF1 upregulates the steady-state level of the short-lived TIMM17A protein via its direct target genes, HSPD1 and HSPE1, which encode subunits of the mitochondrial chaperonin complex and are responsible for protein refolding once imported into the matrix. The HSF1- HSPD1/HSPE1-TIMM17A axis remodels the mitochondrial proteome to promote mitochondrial translation and energy production, thereby supporting robust cell proliferation. Our work reveals a mechanism by which mitochondria adjust protein uptake according to the folding capacity in the matrix by altering TIM complex composition.

cell biology↗

bioRxiv2025

Succinate dehydrogenase activity supports de novo purine synthesis

The de novo purine synthesis pathway is fundamental for nucleic acid production and cellular energetics, yet the role of mitochondrial metabolism in modulating this process remains underexplored. In many cancers, metabolic reprogramming supports rapid proliferation and survival, but the specific contributions of the tricarboxylic acid (TCA) cycle enzymes to nucleotide biosynthesis are not fully understood. Here, we demonstrate that the TCA cycle enzyme succinate dehydrogenase (SDH) is essential for maintaining optimal de novo purine synthesis in normal and cancer cells. Genetic or pharmacological inhibition of SDH markedly attenuates purine synthesis, leading to a significant reduction in cell proliferation. Mechanistically, SDH inhibition causes an accumulation of succinate, which directly impairs the purine biosynthetic pathway. In response, cancer cells compensate by upregulating the purine salvage pathway, a metabolic adaptation that represents a potential therapeutic vulnerability. Notably, co-inhibition of SDH and the purine salvage pathway induces pronounced antiproliferative and antitumoral effects in preclinical models. These findings not only reveal a signaling role for mitochondrial succinate in regulating nucleotide metabolism but also provide a promising therapeutic strategy for targeting metabolic dependencies in cancer.

biochemistry↗

bioRxiv2025

Distinct Control of histone H1 expression within the Histone Locus body by CRAMP1

Proper histone gene expression is critical to cell viability and maintaining genomic integrity. Multiple histone genes organized into three genomic loci encode for replication coupled core and linker histones. Histone gene expression and transcript processing is orchestrated in the histone locus body (HLB) within the nucleus. We identified human CRAMP1 as a selective regulator of linker histone H1 expression. CRAMP1 is recruited to the HLB in RPE1hTERT cells. Affinity purification shows that CRAMP1 physically associates the HLB component GON4L (a.k.a. YARP). We show that the PAH domains of GON4L interact with CRAMP1. CRAMP1 disruption results in a loss of histone H1 expression and a reduction in H1 protein. CRAMP1 occupies the unmethylated promoters of the replication coupled linker histone genes that reside within the histone locus body, and the replication independent histone H1 loci, which reside in a region of the genome without other histone genes. Together these data identify CRAMP1 as a novel and selective regulator of histone H1 gene expression.

genomics↗

bioRxiv2024

Dominant-negative TP53 mutations potentiated by the HSF1-regulatedproteostasis network

Protein mutational landscapes are shaped by how amino acid substitutions affect stability and folding or aggregation kinetics. These properties are modulated by cellular proteostasis networks. Heat shock factor 1 (HSF1) is the master regulator of cytosolic and nuclear proteostasis. Chronic HSF1 ac-tivity upregulation is a hallmark of cancer cells, potentially because upregulated proteostasis factors fa-cilitate the acquisition and maintenance of oncogenic mutations. Here, we assess how HSF1 activation influences mutational trajectories by which p53 can escape cytotoxic pressure from nutlin-3, an inhibitor of the p53 regulator MDM2. HSF1 activation broadly increases the fitness of dominant-negative p53 substitutions, particularly non-conservative, biophysically unfavorable amino acid changes within buried regions of the p53 DNA-binding domain. These findings demonstrate that HSF1 activation reshapes the oncogenic mutational landscape by preferentially supporting the emergence and persistence of bio-physically disruptive, cancer-associated p53 substitutions, linking proteostasis network activity directly to oncogenic evolution.

molecular biology↗

bioRxiv2022

Beyond BRCA: Discovery of novel causes and consequences of homologous recombination deficiencies

Since the discovery of BRCA1 and BRCA2 mutations as cancer risk factors, we have gained substantial insight into their role in maintaining genomic stability through homologous recombination (HR) DNA repair. However, upon pan-cancer analysis of tumors from The Cancer Genome Atlas (TCGA), we found that mutations in BRCA1/2 and other classical HR genes only identified 10-20% of tumors that display genomic evidence of HR deficiency (HRD), suggesting that the cause of the vast majority of HR defects in tumors is unknown. As HRD both predisposes individuals to cancer development and leads to therapeutic vulnerabilities, it is critical to define the spectrum of genetic events that drive HRD. Here, we employed a network-based approach leveraging the abundance of molecular characterization data from TCGA to identify novel drivers of HRD. We discovered that over half of putative genes driving HRD originated outside of canonical DNA damage response genes, with a particular enrichment for RNA binding protein (RBP)-encoding genes. These novel drivers of HRD were cross-validated using an independent ICGC cohort, and were enriched in GWAS loci associated with cancer risk. Experimental approaches validated over 90% of our predictions in a panel of 50 genes tested by siRNA and 31 additional engineered mutations identified from TCGA patient tumors. Moreover, genetic suppression of identified RBPs or pharmacological inhibition of RBPs induced PARP inhibition. Further mechanistic studies indicate that some RBPs are recruited to sites of DNA damage to facilitate repair, whereas others control the expression of canonical HR genes. Overall, this study greatly expands the repertoire of known drivers of HRD and their contributions to DNA damage repair, which has implications for not only future mechanistic studies, but also for genetic screening and therapy stratification. HIGHLIGHTSO_LIThe majority of HR deficiencies detected cannot be directly attributed to aberrations in canonical HR genes. C_LIO_LIIntegrated network analysis identifies RNA binding proteins (RBPs) as a novel driver of HR deficiency in patient tumors. C_LIO_LIRBP dysfunction can produce HR deficiencies through both dysregulation of canonical HR genes and action at sites of DNA damage. C_LI

systems biology↗

bioRxiv2019

Coessential Genetic Networks Reveal the Organization and Constituents of a Dynamic Cellular Stress Response

The interrelated programs essential for cellular fitness in the face of stress are critical to understanding tumorigenesis, neurodegeneration, and aging. However, modelling the combinatorial landscape of stresses experienced by diseased cells is challenging, leaving functional relationships within the global stress response network incompletely understood. Here, we leverage genome-scale fitness screening data from 625 cancer cell lines, each representing a unique biological context, to build a network of "coessential" gene relationships centered around master regulators of the response to proteotoxic, oxidative, hypoxic, and genotoxic stress. This approach organizes the stress response into functional modules, identifies genes connecting distinct modules, and reveals mechanisms underlying cellular dependence on individual modules. As an example of the power of this approach, we discover that the previously unannotated HAPSTR (C16orf72) promotes resilience to diverse stressors as a stress-inducible regulator of the E3 ligase HUWE1. Altogether, we present a broadly applicable framework and interactive tool (http://fireworks.mendillolab.org/) to interrogate biological networks using unbiased genetic screens.

genetics↗