Practice question

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.