Crawford J M, Su Z, Varlamova O, Bresnick A R, Kiehart D P
Department of Cell Biology, Duke University Medical Center, Durham, NC 27708-1000, USA.
Eur J Cell Biol. 2001 Mar;80(3):240-4. doi: 10.1078/0171-9335-00156.
Microinjection of constitutively active Cdc42 (V12Cdc42) disrupts the actomyosin cytoskeleton during cellularization (Crawford et al., Dev. Biol., 204, 151-164 (1998)). The p21-activated kinase (PAK) family of Ser/Thr kinases are effectors of GTP-bound forms of the small GTPases, Cdc42 and Rac. Drosophila PAK, which colocalizes with actin and myosin-II during cellularization, concentrates at sites of V12Cdc42-induced actomyosin disruption. In vitro biochemical analyses demonstrate that PAK phosphorylates the regulatory light chain (RLC) of Drosophila nonmuscle myosin-II on Ser21, a site known to activate myosin-II function. Although activated PAK does not disrupt the actomyosin cytoskeleton, it induces increased levels of Ser21 phosphorylated RLC. These findings suggest that increased levels of RLC phosphorylation do not contribute to disruption of the actomyosin hexagonal array.
组成型激活的Cdc42（V12Cdc42）显微注射会在细胞化过程中破坏肌动球蛋白细胞骨架（Crawford等人，《发育生物学》，204，151 - 164（1998年））。丝氨酸/苏氨酸激酶的p21激活激酶（PAK）家族是小GTP酶Cdc42和Rac的GTP结合形式的效应器。果蝇PAK在细胞化过程中与肌动蛋白和肌球蛋白-II共定位，集中在V12Cdc42诱导的肌动球蛋白破坏位点。体外生化分析表明，PAK在丝氨酸21处磷酸化果蝇非肌肉肌球蛋白-II的调节轻链（RLC），该位点已知可激活肌球蛋白-II功能。虽然激活的PAK不会破坏肌动球蛋白细胞骨架，但它会诱导丝氨酸21磷酸化的RLC水平升高。这些发现表明，RLC磷酸化水平的升高不会导致肌动球蛋白六边形阵列的破坏。
