Delisle, M.-B. | bioRxiv Science

bioRxiv2024

A non-catalytic function for Rad18 in sustaining glioblastoma proliferation

The Rad18 E3 ubiquitin ligase, a non-essential gene, is a key regulator of DNA damage tolerance that also functions in repair of DNA double strand breaks. Rad18 is overexpressed in the aggressive brain cancer glioblastoma (GBM) and its downregulation sensitizes glioblastoma cells to DNA damaging agents. Here we show that Rad18 has an essential role in GBM cells proliferation in the absence of external damage, surprisingly independent of its catalytic activity. Rad18 downregulation leads to cell cycle arrest in the G1 phase in the absence of apparent DNA damage. We also show that Rad18 sustains GBM stem cells self-renewal and survival, as well as the growth of tumor orthotropic xenografts in mice. We also show that increased Rad18 expression enhances the growth of non-transformed cells and induces features of oncogenic transformation. Mechanistically, we show that Rad18 downregulation negatively regulates the Hippo pathway by interfering with the nuclear retention of the YAP1 transcription factor. Altogether, these data show that Rad18 has an essential, non-catalytic function, in GBM proliferation, and propose Rad18 as a key target to sensitize GBM to therapy.

cancer biology↗

bioRxiv2019

Ephrin-B1 blocks adult cardiomyocyte proliferation and heart regeneration

AimsDeciphering the innate mechanisms governing the blockade of proliferation in adult cardiomyocytes (CMs) is challenging for mammalian heart regeneration. Despite the exit of CMs from the cell cycle during the postnatal maturation period coincides with their morphological switch to a typical adult rod-shape, whether these two processes are connected is unknown. Here, we examined the role of ephrin-B1, a CM rod-shape stabilizer, in adult CM proliferation and cardiac regeneration.\n\nMethods and resultsTransgenic- or AAV9-based ephrin-B1 repression in adult mouse heart led to substantial proliferation of resident CMs and tissue regeneration to compensate for apex resection, myocardial infarction (MI) and senescence. Interestingly, in the resting state, CMs lacking ephrin-B1 did not constitutively proliferate, indicative of no major cardiac defects. However, they exhibited proliferation-competent signature, as indicated by higher mononucleated state and a dramatic decrease of miR-195 mitotic blocker, which can be mobilized under neuregulin-1 stimulation in vitro and in vivo. Mechanistically, the post-mitotic state of the adult CM relies on ephrin-B1 sequestering of inactive phospho-Yap1, the effector of the Hippo-pathway, at the lateral membrane. Hence, ephrin-B1 repression leads to phospho-Yap1 release in the cytosol but CM quiescence at resting state. Upon cardiac stresses (apectomy, MI, senescence), Yap1 could be activated and translocated to the nucleus to induce proliferation-gene expression and consequent CM proliferation\n\nConclusionsOur results identified ephrin-B1 as a new natural locker of adult CM proliferation and emphasize that targeting ephrin-B1 may prove a future promising approach in cardiac regenerative medicine for HF treatment.\n\nSignificanceThe mammalian adult heart is unable to regenerate due to the inability of cardiomyocytes (CMs) to proliferate and replace cardiac tissue lost. Exploiting CM-specific transgenic mice or AAV9-based gene therapy, this works identifies ephrin-B1, a specific rod-shape stabilizer of the adult CM, as a natural padlock of adult CM proliferation for compensatory adaptation to different cardiac stresses (apectomy, MI, senescence), thus emphasizing a new link between the adult CM morphology and their proliferation potential. Moreover, the study demonstrates proof-of-concept that targeting ephrin-B1 may be an innovative therapeutic approach for ischemic heart failure.

physiology↗