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#Wee1 kinase

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Cell Cycle Regulation

Wee1 kinase inhibition in G2 phase leads to:

G2 progression is gated by inhibitory phosphorylation of master mitotic kinase CDK1 that prevents premature mitotic entry while last preparations complete. Nuclear kinase Wee1 and membrane-associated Myt1 phosphorylate CDK1 subunit within cyclin B-CDK1 complex at Tyr15 and Thr14 within ATP-binding loop, rendering kinase catalytically inactive despite abundant cyclin B synthesized during G2, allowing centrosome maturation, Golgi segregation, and DNA repair synthesis to proceed. At G2/M border, dual-specificity phosphatases Cdc25A/B/C remove these phosphates, causing explosive autoamplification where CDK1 phosphorylates Cdc25 to activate it and phosphorylates Wee1 to inhibit it. Pharmacologic inhibition or siRNA depletion of Wee1 eliminates inhibitory phosphate, leading to immediate activation of cyclin B-CDK1 before replication fully completed or damage repaired, driving cells into mitosis with under-replicated DNA, premature chromosome condensation, pulverization, and activation of mitotic catastrophe program. This vulnerability underlies therapy where Wee1 inhibitors enhance genotoxic chemotherapy efficacy in p53-deficient cancers. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.

Ref: Harper & Elledge, Mol Biol Cell 2007, Wee1 Control. Alberts 7th ed., Chapter 17, CDK1 Regulation.

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Cell Cycle Regulation

What is the role of Wee1 kinase in CDK regulation?

G2/M commitment governed by antagonism between inhibitory Wee1/Myt1 kinases and activating Cdc25 phosphatases acting on CDK1-Cyclin B. Wee1 encodes nuclear tyrosine kinase belonging to WEE family capable of phosphorylating both threonine and tyrosine. Active during S and G2 phases, Wee1 phosphorylates CDK1 at conserved glycine rich loop residues Thr14 and Tyr15 positioned near ATP binding cleft. These phosphates sterically hinder ATP orientation and substrate catalysis maintaining low activity even though cyclin B accumulates to high levels, effectively preventing premature mitotic entry while replication completes. Inhibition reinforced by Myt1 membrane associated kinase adding Thr14 modification. At mitotic threshold, rising Plk1 and CDK1 phosphorylate Wee1 creating phosphodegron recognized by SCF-betaTrCP ligase for ubiquitination and degradation plus nuclear export, while concurrently activating Cdc25C. Cdc25 removes Thr14/Tyr15 phosphates reversing inhibition. DNA damage checkpoint activates Chk1 which phosphorylates Cdc25 isoforms causing 14-3-3 sequestration and stabilizes Wee1 to enforce G2 arrest. Pharmacological Wee1 inhibitors like adavosertib force premature mitosis in cancer cells with accumulated damage causing mitotic catastrophe. Additional feedback loops involving polo-like kinases, phosphatases and SCF-mediated degradation reinforce irreversibility and protect against premature progression that would compromise genome integrity and viability.

Ref: Morgan, Cell Cycle Control: Wee1 Regulation of CDK1, Principles of Control, Chapter 3; Mueller et al., Wee1 Kinase in DNA Damage G2 Checkpoint.

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