Membrane-spanning 4-domains subfamily A member 3 (MS4A3), also known as HTm4, is an hematopoietic modulator for the G1-S cell cycle transition []. HTm4 binds to the Cdk-associated Phosphatase (KAP)-Cdk2-Cyclin A complex, triggering the dissociation of cyclin A and facilitating dephosphorylation of Cdk2 by KAP [, ].