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A functional screen identifies hDRIL1 as an oncogene that rescues RAS-induced senescence
Daniel S Peeper1, Avi Shvarts, Thijn Brummelkamp
1Division of Molecular Carcinogenesis and Center for Biomedical Genetics, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Abstract:
Primary fibroblasts respond to activated H-RAS(V12) by undergoing premature arrest, which resembles replicative senescence. This irreversible 'fail-safe mechanism' requires p19(ARF), p53 and the Retinoblastoma (Rb) family: upon their disruption, RAS(V12)-expressing cells fail to undergo senescence and continue to proliferate. Similarly, co-expression of oncogenes such as c-MYC or E1A rescues RAS(V12)-induced senescence. To identify novel genes that allow escape from RAS(V12)-induced senescence, we designed an unbiased, retroviral complementary DNA library screen. We report on the identification of DRIL1, the human orthologue of the mouse Bright and Drosophila dead ringer transcriptional regulators. DRIL1 renders primary murine fibroblasts unresponsive to RAS(V12)-induced anti-proliferative signalling by p19(ARF)/p53/p21(CIP1), as well as by p16(INK4a). In this way, DRIL1 not only rescues RAS(V12)-induced senescence but also causes these fibroblasts to become highly oncogenic. Furthermore, DRIL1 immortalizes mouse fibroblasts, in the presence of high levels of p16(INK4a). Immortalization by DRIL1, whose product binds the pRB-controlled transcription factor E2F1 (ref. 8), is correlated with induction of E2F1 activity. Correspondingly, DRIL1 induces the E2F1 target Cyclin E1, overexpression of which is sufficient to trigger escape from senescence. Thus, DRIL1 disrupts cellular protection against RAS(V12)-induced proliferation downstream of the p19(ARF)/p53 pathway.
Insights
The study identifies DRIL1 as a gene that allows cells to escape RAS(V12)-induced senescence, a critical safeguard against cancer. DRIL1 promotes fibroblast immortalization and oncogenic transformation by disrupting anti-proliferative signaling pathways.
Area of Science:
- Cellular senescence
- Oncogenesis
- Transcriptional regulation
Background:
- Primary fibroblasts normally arrest proliferation upon activation of oncogenic H-RAS(V12), a process resembling replicative senescence.
- This senescence pathway is a tumor-suppressive mechanism dependent on key regulators like p19(ARF), p53, and the Retinoblastoma (Rb) family.
- Oncogenes such as c-MYC or E1A can override RAS(V12)-induced senescence, indicating the existence of escape mechanisms.
Purpose of the Study:
- To identify novel genes that enable cells to evade RAS(V12)-induced senescence.
- To investigate the role of identified genes in cellular transformation and immortalization.
Main Methods:
- Utilized an unbiased retroviral complementary DNA library screen to identify genes conferring resistance to RAS(V12)-induced senescence.
- Assessed the impact of identified genes on fibroblast proliferation, senescence markers, oncogenic potential, and immortalization.
- Investigated the molecular mechanisms, including interactions with known senescence pathways and transcription factors like E2F1.
Main Results:
- Identified DRIL1, a transcriptional regulator, as a novel gene that allows escape from RAS(V12)-induced senescence.
- DRIL1 renders primary murine fibroblasts unresponsive to anti-proliferative signals mediated by p19(ARF)/p53/p21(CIP1) and p16(INK4a).
- DRIL1 expression leads to fibroblast immortalization and confers high oncogenic potential, correlating with induced E2F1 activity and Cyclin E1 expression.
Conclusions:
- DRIL1 acts downstream of the p19(ARF)/p53 pathway to disrupt cellular defenses against RAS(V12)-driven proliferation.
- DRIL1's ability to promote immortalization and oncogenesis highlights its significance in understanding cancer development.
- DRIL1's interaction with the E2F1 pathway provides a molecular basis for its senescence-evading and transforming properties.