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Institute of Molecular Cancer Research Lopes Lab

  • Overexpression of oncogenes like Cyclin E or CDC25A rapidly induces replication fork slowing, as detected by DNA fiber assays (left), accompanied by frequent fork remodeling into four-way junctions, as detected by electron microscopy (right) (from Neelsen et al., JCB 2013).

  • The regressed arm of reversed forks (arrow) is remarkably similar to a DNA double-strand break. Upon fork stalling by hydroxyurea (HU), these DNA ends may represent entry points for extensive degradation of newly replicated DNA (detected by DNA fiber assays), unless protected by key homologous recombination factors (e.g. BRCA2). Preventing reversed fork formation (e.g. by RAD51 inactivation) suppresses fork degradation in BRCA2-defective cells (from Mijic et al., Nature Comms 2017).

  • Direct microscopic investigation of condensed chromosomes in mitotic cells allows monitoring chromosomal breaks and aberrations (red arrows) induced by cancer chemotherapeutic treatments, genetic defects and other conditions associated with increased DNA replication stress (e.g. downregulation of BRCA2 and XRCC3).

  • Besides BRCA2, also other homologous recombination factors – i.e. RAD51, and RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3) – participate in remodeling, protection and restart of stalled replication forks, together with specialized fork remodeling enzymes (ZRANB3, SMARCAL1, HLTF). From Berti et al., Nature Comms 2020).

Oncogenes and oncosuppressors in the replication stress response


Replication stress has emerged as an early causative event in tumorigenesis, frequently detectable already in precancerous lesions and promoted by activation of well-known oncogenes. These yet-elusive alterations of the replication program activate checkpoint pathways that delay or prevent cell cycle progression in most precancerous lesions, thus representing a crucial barrier against full malignant transformation. At the same time, replication stress creates selective pressure for further mutations that occasionally inactivate checkpoint control, leading to more aggressive cancers. Several tumour suppressors – already well-known as DNA repair factors - were also recently found to play central roles at stalled replication forks, genetically and mechanistically distinct from their function in DNA damage repair. Uncovering how oncogenes and tumour suppressors specifically operate upon endogenous and exogenous replication stress is of key relevance to obtain full mechanistic understanding of cancer onset, especially in individuals carrying known mutations predisposing to cancer.



The goal of this research line is to use our portfolio of imaging and molecular approaches to investigate the role of known oncogenes and tumour suppressors in the replication stress response. We aim to uncover how specific oncogenes exacerbate endogenous sources of genome instability and/or affect the cellular responses to these challenges. Similarly, we attempt to identify novel roles of known tumour suppressors in the replication stress response and to characterize how genetic alterations associated with increased cancer susceptibility impact on genome integrity during replication.


Ongoing and future work

Our work in this area uncovered replication fork remodelling as common and rapid consequence of the activation of multiple oncogenes (e.g. Cyclin E, CDC25A) and identified an important role in fork remodelling and protection of several tumour suppressors, well known in the context of homologous recombination repair (BRCA2, RAD51, RAD51 paralogs, etc.). We now aim to identify endogenous and exogenous sources of genotoxic stress which may potentially engage these factors in limiting fragility of replicating chromosomes, thereby explaining their role in cancer avoidance and chemotherapy response. We also aim to clarify whether, in cell types or tissues particularly exposed to replication stress, even partial inactivation of certain tumour suppressors may lead to increased genomic instability, contributing to the associated cancer susceptibility.


Selected publications

K.J. Neelsen, I.M.Y. Zanini, S. Mijic, R. Herrador, R. Zellweger, A. Ray Chaudhuri, K.D. Creavin, J.J. Blow and M. Lopes (2013). Deregulated origin licensing leads to chromosomal breaks by re-replication of a gapped DNA template. Genes and Development, 27:2537-42.

K. J. Neelsen, I. M. Y. Zanini, R. Herrador and M. Lopes (2013). Oncogenes induce genotoxic stress by mitotic processing of unusual replication intermediates. Journal of Cell Biology, 6: 699-708.

M. Vujanovic, J. Krietsch, M.C. Raso, N. Terraneo, R. Zellweger, J.A. Schmid, A. Taglialatela, J.W. Huang, C.L. Holland, K. Zwicky, R. Herrador, H. Jacobs, D. Cortez, A. Ciccia, L. Penengo and M. Lopes (2017). Replication Fork Slowing and Reversal upon DNA Damage Require PCNA Polyubiquitination and ZRANB3 DNA Translocase Activity. Molecular Cell, 67:882-890.

S. Mijic, R. Zellweger, N. Chappidi, M. Berti, K. Jacobs, K. Mutreja, S. Ursich, A. Ray Chaudhuri, A. Nussenzweig, P. Janscak and M. Lopes (2017). Replication fork reversal triggers fork degradation in BRCA2-defective cells. Nature Communications, 8(1):859.


M. Berti, F. Teloni, S. Mijic, S. Ursich, J. Fuchs, M. D. Palumbieri, J. Krietsch, J. A. Schmid, E. B. Garcin, S. Gon, M. Modesti, M. Altmeyer, and M. Lopes (2020). Sequential role of RAD51 paralog complexes in replication fork remodeling and restart. Nature Communications, 11(1):3531.