Biology subjects

Nikolaev, S.

Publications and source records attributed to Nikolaev, S..

6 recordsLinked to original sources

bioRxiv2024

Effect of MisMatch Repair Deficiency on metastasis occurrence modelized in a syngeneic mouse model

Mismatch repair deficiency leads to high mutation rates and microsatellite instability (MSI-H), associated with immune infiltration and responsiveness to immunotherapies. In early stages, MSI-H tumors generally have a better prognosis and lower metastatic potential than microsatellite-stable (MSS) tumors, especially in colorectal cancer. However, in advanced stages, MSI-H tumors lose this survival advantage for reasons that remain unclear. We developed a syngeneic mouse model of MSI cancer by knocking out the MMR gene Msh2 in the metastatic 4T1 breast cancer cell line. This model mirrored genomic features of MSI-H cancers and showed reduction in metastatic incidence compared to their MSS counterparts. In MSI-H tumors, we observed an enrichment of immune gene-signatures that negatively correlated with metastasis incidence. Importantly, a hybrid epithelial-mesenchymal signature, related to aggressiveness was detected only in metastatic MSI-H tumors which may explain the worse outcomes after recurrence of MSI tumors compared to MSS. Interestingly, we identified immature myeloid cells at primary and metastatic sites in MSI-H tumor-bearing mice, suggesting that MMR deficiency elicits specific immune responses beyond T-cell activation. SignificanceA novel syngeneic mouse model of MSI cancer demonstrates that the immune system regulates MSI cancer cell dissemination, offering an important tool to model advanced stages of human MSI-driven disease.

cancer biology↗

bioRxiv2024

Mitochondrial sites of contact with the nucleus aid in chemotherapy evasion of glioblastoma cells

Glioblastoma (GBM) is the most common form of a malignant primary brain tumour in adults for which therapeutic options are minimal. The rapid onset of the resistance mechanisms against the chemotherapeutic agent Temozolomide (TMZ), the first line of pharmacological care for patients, prevents the long-term validity of this approach. The underpinning biology for this remains poorly understood thus compromising the efficacy of this approach. The Translocator Protein (TSPO) is an 18kDa ubiquitous cholesterol-binding molecule on the outer membrane of mitochondria (OMM). Upregulated in cancers TSPO is required to form contacts between mitochondria and the nucleus termed: Nucleus Associated Mitochondria (NAM). In GBM tissues as well as in 2D and 3D cell cultures we assayed patterns of TSPO expression (i), autophagy/mitophagy (ii), transcription factors (iii) and susceptibility to TMZ-induced demise (iv). Confocal and ultrastructural imaging detailed the organization and redistribution of the mitochondrial network (v). Our findings show that TMZ exploits mitochondria via TSPO to aid the formation of NAM which couples the expression of the nuclear transcription factor Sterol regulatory element-binding transcription factor 1 (SREBP1) and the stabilization of YAP/TAZ. Pharmacological modulation of TSPO counteracts all the above and re-instates susceptibility to TMZ-induced demise. NAM is therefore proposed as a variable in the engagement and execution of pro-survival mechanisms in GBM thus offering a means to both insight into the pathophysiology of this disease and offer novel therapeutic strategies. Key PointsO_LITMZ exploits TSPO to curb mitochondrial quality control in glioblastoma cells. C_LIO_LITMZ-mediated MRR is associated with the relocation of mitochondria to the nucleus and modulation of transcriptional factors involved in cholesterol metabolism and adaptation to aggressive growth. C_LIO_LITSPO represents a pharmacological target to revert chemoresistance in glioblastoma cells. C_LI Importance of the StudyThis study elucidates a mitochondrion-driven mechanism of chemoresistance in human glioblastoma cells, which depends on the mitochondrial translocator protein TSPO. The administration of TSPO ligands restores susceptibility to TMZ by influencing the dynamics of transcriptional factors associated with cholesterol metabolism and mechanical transduction.

cancer biology↗

bioRxiv2021

Mitochondrial mutational spectrum is associated with mammalian longevity: a novel signature of oxidative damage.

The mutational spectrum of the mitochondrial DNA (mtDNA) does not resemble any of the known mutational signatures of the nuclear genome and variation in mtDNA mutational spectra between different organisms is still incomprehensible. Since mitochondria is tightly involved in aerobic energy production, it is expected that mtDNA mutational spectra is affected by the oxidative damage. Assuming that oxidative damage increases with age, we analyze mtDNA mutagenesis of different species. Analysing (i) dozens thousands of somatic mtDNA mutations in samples of different age (ii) 70053 polymorphic synonymous mtDNA substitutions, reconstructed in 424 mammalian species with different generation length and (iii) synonymous nucleotide content of 650 complete mitochondrial genomes of mammalian species we observed that the frequency of AH>GH substitutions (H - heavy chain notation) is twice higher in species with high versus low generation length making their mtDNA more AH poor and GH rich. Considering that AH>GH substitutions are also sensitive to the time spent single stranded (TSSS) during asynchroniuos mtDNA replication we demonstrated that AH>GH substitution rate is a function of both species-specific generation length and position specific TSSS. We propose that AH>GH is a mitochondria-specific signature of oxidative damage associated with both aging and TSSS.

bioinformatics↗

bioRxiv2020

XPC deficiency increases risk of hematologic malignancies through mutator phenotype and characteristic mutational signature

Recent studies demonstrated a dramatically increased risk of leukemia in patients with a rare genetic disorder, Xeroderma Pigmentosum group C (XP-C), characterized by constitutive deficiency of global genome nucleotide excision repair (GG-NER). However, the genetic mechanisms of non-skin cancers in XP-C patients remain unexplored. In this study, we analyzed a unique collection of internal XP-C tumor genomes including 6 leukemias and 2 sarcomas. We observed an average of 25-fold increase of mutation rates in XP-C vs. sporadic leukemia which we presume leads to its elevated incidence and early appearance. In all XP-C tumors predominant mutational process is characterized by a distinct mutational signature, highlighting a specific mutational pattern in the context of GG-NER deficiency. We observed a strong mutational asymmetry with respect to transcription and the direction of replication in XP-C tumors suggesting association of mutagenesis with bulky purine DNA lesions of probably endogenous origin. These findings suggest existence of a balance between formation and repair of bulky DNA lesions by GG-NER in human body cells which is disrupted in XP-C patients leading to internal cancers.

cancer biology↗

bioRxiv2019

RAS mutations drive proliferative chronic myelomonocytic leukemia via activation of a novel KMT2A-PLK1 axis

ABSTRACTChronic myelomonocytic leukemia (CMML) is an aggressive hematological malignancy with limited treatment options. Whole exome (WES) and targeted sequencing of several independent cohorts of CMML patients, comparing dysplastic (dCMML) to proliferative (pCMML) CMML, as well as paired chronic phase disease and acute leukemic transformation (LT), associate acquisition of oncogenic RAS pathway mutations, the most common being NRASG12D, with aggressive disease and with disease progression. Using patient derived progenitor colony assays and a NRASG12D-Vav-Cre mouse model, we further demonstrate the role of mutant RAS signaling in driving and maintaining pCMML phenotype. RNA-sequencing links RAS pathway mutations with an increased expression of genes encoding the mitotic checkpoint kinases PLK1 and WEE1. Further, we dmeoinstrated that non-mutated lysine methyltransferase KMT2A (MLL1) acts as mediator of NRAS-induced PLK1 and WEE1 expression. Finally, we demonstrate the translational value of our findings by showing that pharmacological PLK1 inhibition decreases monocytosis and hepatosplenomegaly while improving hematopoiesis in RAS mutant patient-derived xenografts. Hence, we define severe CMML as oncogenic RAS pathway-enriched malignancies, with a unique gene expression profile regulated by KMT2A, amenable to therapeutic intervention.

cancer biology↗

bioRxiv2019

Mitochondrial mutational spectrum provides an universal marker of cellular and organismal longevity

Mutational spectrum of the mitochondrial genome (mtDNA) does not resemble signatures of any known mutagens and variation in mtDNA mutational spectra between different tissues and organisms is still incomprehensible. Since mitochondria is tightly involved in aerobic energy production, it is expected that mtDNA mutational spectra may be affected by the oxidative damage which is increasing with cellular and organismal aging. However, the well-documented mutational signature of the oxidative damage, G>T substitutions, is typical only for the nuclear genome while it is extremely rare and age-independent in mtDNA. Thus it is still unclear if there is a mitochondria - specific mutational signature of the oxidative damage. Here, reconstructing mtDNA mutational spectra for human cancers originated from 21 tissues with various cell turnover rate, human oocytes fertilized at different ages, and 424 mammalian species with variable generation length which is a proxy for oocyte age, we observed that the frequency of AH>GH substitutions (H - heavy chain notation) is positively correlated with cellular and organismal longevity. Moreover, this mutational bias from AH to GH affects nucleotide content at the fourfold degenerative synonymous positions leading to a deficit of AH and excess of GH, which is especially pronounced in long-lived mammals. Taking into account additionally, that AH>GH is sensitive to time being single stranded during mtDNA asynchronous replication and A>G is associated with oxidative damage of single-stranded DNA in recent bacterial experiments we propose that AH>GH is a mutational signature of oxidative damage in mtDNA.

genomics↗