| PKMYT1 is a membrane-associated serine/threonine kinase of the Wee1 family that localizes to Golgi and endoplasmic reticulum membranes and acts as a key negative regulator of cyclin-dependent kinase 1 at the G2/M checkpoint, controlling the timing of mitotic entry during DNA replication and repair. The kinase contains an N‑terminal regulatory region with multiple phosphorylation sites and protein–protein interaction motifs and a C‑terminal catalytic domain flanked by transmembrane segments that anchor PKMYT1 to intracellular membranes, positioning it to modulate cytoplasmic CDK1–cyclin B complexes before their nuclear accumulation. PKMYT1 directly phosphorylates CDK1 on Thr14 and Tyr15 within the ATP‑binding pocket, generating an inhibitory configuration that prevents activation of the CDK1–cyclin B complex and blocks formation of a fully active M phase–promoting factor until upstream checkpoints are satisfied. CDK1–cyclin B activity feeds back on PKMYT1 by phosphorylating N‑terminal threonine residues, which reduces its inhibitory potency, and PLK1-mediated phosphorylation promotes PKMYT1 degradation; together, these events participate in a switch that shifts the cell from a CDK1‑inactive G2 state to a CDK1‑active mitotic state. PKMYT1 cooperates with nuclear Wee1 to maintain CDK1 inhibition, with Wee1 acting predominantly in the nucleus and PKMYT1 acting on cytosolic and membrane-associated CDK1 pools, including sequestration of CDK1–cyclin complexes in the cytoplasm, while CDC25 phosphatases remove the inhibitory phosphates once DNA damage is resolved and the cell is committed to mitosis. High PKMYT1 expression is reported across multiple tumor types and correlates with poor prognosis and aggressive phenotypes in cancers such as gastric carcinoma and pancreatic ductal adenocarcinoma, where increased PKMYT1 levels associate with enhanced proliferation, apoptosis resistance, and activation of signaling pathways including Notch and NF‑κB. Pharmacologic inhibition or genetic suppression of PKMYT1 in these settings reduces CDK1 Thr14/Tyr15 phosphorylation, drives premature or forced mitotic entry in checkpoint-compromised tumor cells, and increases sensitivity to DNA-damaging agents. |
