1. Academic Validation
  2. Non-canonical pathway for Rb inactivation and external signaling coordinate cell-cycle entry without CDK4/6 activity

Non-canonical pathway for Rb inactivation and external signaling coordinate cell-cycle entry without CDK4/6 activity

  • Nat Commun. 2023 Nov 29;14(1):7847. doi: 10.1038/s41467-023-43716-y.
Mimi Zhang # 1 Sungsoo Kim # 1 2 Hee Won Yang 3 4
Affiliations

Affiliations

  • 1 Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032, USA.
  • 2 Herbert Irving Comprehensive Cancer Center, Columbia University, New York, NY, 10032, USA.
  • 3 Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032, USA. hy2602@cumc.columbia.edu.
  • 4 Herbert Irving Comprehensive Cancer Center, Columbia University, New York, NY, 10032, USA. hy2602@cumc.columbia.edu.
  • # Contributed equally.
Abstract

Cyclin-dependent kinases 4 and 6 (CDK4/6) are critical for initiating cell proliferation by inactivating the retinoblastoma (Rb) protein. However, mammalian cells can bypass CDK4/6 for Rb inactivation. Here we show a non-canonical pathway for Rb inactivation and its interplay with external signals. We find that the non-phosphorylated Rb protein in quiescent cells is intrinsically unstable, offering an alternative mechanism for initiating E2F activity. Nevertheless, this pathway incompletely induces Rb-protein loss, resulting in minimal E2F activity. To trigger cell proliferation, upregulation of mitogenic signaling is required for stabilizing c-Myc, thereby augmenting E2F activity. Concurrently, stress signaling promotes Cip/Kip levels, competitively regulating cell proliferation with mitogenic signaling. In Cancer, driver mutations elevate c-Myc levels, facilitating adaptation to CDK4/6 inhibitors. Differentiated cells, despite Rb-protein loss, maintain quiescence through the modulation of c-Myc and Cip/Kip levels. Our findings provide mechanistic insights into an alternative model of cell-cycle entry and the maintenance of quiescence.

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  • HY-114277
    99.94%, KRAS G12C Inhibitor
    Ras