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Cell cycle and DNA damage response regulation by Spy1, and the intersection of FGFR and NFkappaB pathways


Understanding the activation and regulatory functions of cyclin dependent kinases and their inhibitors is of great importance to cancer biology. Experiments from our lab and others have identified the Speedy/RINGO family of proteins as important regulators of mammalian cell cycle control. I show that Spy1 activates CDKs and stimulates p27Kip¹ degradation, thereby relieving an important cell cycle progression restraint. Using in vitro purified proteins in defined reactions, I demonstrate that Spy1 can directly activate CDK2 to phosphorylate p27 on Thr187, thereby targeting it for degradation and promoting S-phase entry. We also show that Spy1 is a component of the mammalian DNA damage response, preventing the DNA damage response and enhancing the survival of cells treated with DNA damaging agents. We show that Spy1 expression suppresses apoptosis in a p53- and p21-dependent fashion, allows for UV irradiation resistant DNA synthesis (UVDS), and inhibits the S- and G₂/M- checkpoints through inhibition of checkpoint response proteins. This leads to DNA damage tolerance and prevention of repair cyclobutane pyrimidine dimers through nucleotide excision repair suppression. Knockdown of Spy1 activates intrinsic damage responses, indicating that Spy1 is required to promote tolerance of endogenous and exogenous damage. The novel modes of CDK regulation by Speedy/RINGO proteins may be important during cell cycle transitions, in the tolerance of normal intrinsic damage or in response to exogenous DNA damage. Misregulation of FGFR signaling can lead to uncontrolled downstream signaling associated with many developmental syndromes and cancers. NF[kappa]B also regulates apoptosis and proliferation of many human cancers, and activation of inflammatory responses. Interestingly, our research identifies a novel link between FGFR signaling and the NF[kappa]B pathway. We show FGFR2 and FGFR4 interact with IKK[beta], a critical component of NF[kappa]B signaling. We demonstrate tyrosine phosphorylation of IKK[beta] resulting from FGFR4 or FGFR2 expression, and show suppressed NF[kappa]B signaling upon FGFR activation, which is dependent upon FGFR kinase activity. This work provides a unique model of NFkappaB inactivation and implicates FGFR4 as a tumor suppressor in prostate cancer and indicates FGFR2 may play dual roles as a tumor promoter and a tumor suppressor in breast cancer cell lines

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