VE-cadherin expression and clustering maintain low levels of survivin in endothelial cells.

Survivin is strongly expressed in embryonic organs and in tumor cells but is low or absent in differentiated normal tissues. Resting endothelium expresses low levels of survivin but can up-regulate its synthesis on activation to proliferate. The mechanisms responsible for survivin down-regulation in resting conditions are still unknown. We report here that confluence and vascular endothelial-cadherin (VE-cadherin) expression induce contact inhibition of cell growth and survivin down-regulation in the endothelium. Using beta-catenin null and positive isogenic endothelial cell lines we found that the effect requires beta-catenin expression and its association to VE-cadherin cytoplasmic tail. Furthermore, in allantois organ cultures, survivin expression is up-regulated in areas of growing vessels where VE-cadherin is partially dismantled from junctions or in VE-cadherin -/- specimens. Overall, these data indicate that VE-cadherin and beta-catenin may negatively regulate survivin synthesis in endothelial cells. Consistently, in epidermal and pancreatic cell lines or ovarian tumors, epithelial-cadherin (E-cadherin) and survivin expression is inversely related, suggesting a non-cell-specific role of cadherins in reducing survivin synthesis.

Alpha(v)beta3 integrin expression up-regulates cdc2, which modulates cell migration.

The alphavbeta3 integrin has been shown to promote cell migration through activation of intracellular signaling pathways. We describe here a novel pathway that modulates cell migration and that is activated by alphavbeta3 and, as downstream effector, by cdc2 (cdk1). We report that alphavbeta3 expression in LNCaP (beta3-LNCaP) prostate cancer cells causes increased cdc2 mRNA levels as evaluated by gene expression analysis, and increased cdc2 protein and kinase activity levels. We provide three lines of evidence that increased levels of cdc2 contribute to a motile phenotype on integrin ligands in different cell types. First, increased levels of cdc2 correlate with more motile phenotypes of cancer cells. Second, ectopic expression of cdc2 increases cell migration, whereas expression of dominant-negative cdc2 inhibits migration. Third, cdc2 inhibitors reduce cell migration without affecting cell adhesion. We also show that cdc2 increases cell migration via specific association with cyclin B2, and we unravel a novel pathway of cell motility that involves, downstream of cdc2, caldesmon. cdc2 and caldesmon are shown here to localize in membrane ruffles in motile cells. These results show that cdc2 is a downstream effector of the alphavbeta3 integrin, and that it promotes cell migration.

Regulation of microtubule stability and mitotic progression by survivin.

Survivin is a member of the inhibitor of apoptosis (IAP) gene family, which has been implicated in both preservation of cell viability and regulation of mitosis in cancer cells. Here, we show that HeLa cells microinjected with a polyclonal antibody to survivin exhibited delayed progression in prometaphase (31.5 +/- 6.9 min) and metaphase (126.8 +/- 73.8 min), as compared with control injected cells (prometaphase, 21.5 +/- 3.3 min; metaphase, 18.9 +/- 4.5 min; P < 0.01). Cells injected with the antibody to survivin displayed short mitotic spindles severely depleted of microtubules and occasionally underwent apoptosis without exiting the mitotic block or thereafter. Forced expression of survivin in HeLa cells profoundly influenced microtubule dynamics with reduction of pole-to-pole distance at metaphase (8.57 +/- 0.21 microm versus 10.58 +/- 0.19 microm; P < 0.0001) and stabilization of microtubules against nocodazole-induced depolymerization in vivo. These data demonstrate that survivin functions at cell division to control microtubule stability and assembly of a normal mitotic spindle. This pathway may facilitate checkpoint evasion and promote resistance to chemotherapy in cancer.

Survivin exists in immunochemically distinct subcellular pools and is involved in spindle microtubule function.

Survivin is a member of the inhibitor of apoptosis gene family that has been implicated in both apoptosis inhibition and regulation of mitosis. However, the subcellular distribution of survivin has been controversial and variously described as a microtubule-associated protein or chromosomal passenger protein. Here, we show that antibodies directed to the survivin sequence Ala(3)-Ile(19) exclusively recognized a nuclear pool of survivin that segregated with nucleoplasmic proteins, but not with outer nuclear matrix or nuclear matrix proteins. By immunofluorescence, nuclear survivin localized to kinetochores of metaphase chromosomes, and to the central spindle midzone at anaphase. However, antibodies to Cys(57)-Trp(67) identified a cytosolic pool of survivin, which associated with interphase microtubules, centrosomes, spindle poles and mitotic spindle microtubules at metaphase and anaphase. Polyclonal antibodies recognizing survivin epitopes Ala(3)-Ile(19), Met(38)-Thr(48), Pro(47)-Phe(58) and Cys(57)-Trp(67) identified both survivin pools within the same mitotic cell. A ratio of approximately 1:6 for nuclear versus cytosolic survivin was obtained by quantitative subcellular fractionation. In synchronized cultures, cytosolic survivin abruptly increased at mitosis, physically associated with p34(cdc2), and was phosphorylated by p34(cdc2) on Thr(34), in vivo. By contrast, nuclear survivin began to accumulate in S phase, was not complexed with p34(cdc2) and was not phosphorylated on Thr(34). Intracellular loading of a polyclonal antibody to survivin caused microtubule defects and resulted in formation of multipolar mitotic spindles, but did not interfere with cytokinesis. These data demonstrate that although both reported localizations of survivin exist in mitotic cells, the preponderant survivin pool is associated with microtubules and participates in the assembly of a bipolar mitotic spindle.