Reprogramming the Cell Cycle for Endoreduplication in Rodent Trophoblast Cells

Abstract

Differentiation of trophoblast giant cells in the rodent placenta is accompanied by exit from the mitotic cell cycle and onset of endoreduplication. Commitment to giant cell differentiation is under developmental control, involving down-regulation of Id1 and Id2, concomitant with up-regulation of the basic helix-loop-helix factor Hxt and acquisition of increased adhesiveness. Endoreduplication disrupts the alternation of DNA synthesis and mitosis that maintains euploid DNA content during proliferation. To determine how the mammalian endocycle is regulated, we examined the expression of the cyclins and cyclin-dependent kinases during the transition from replication to endoreduplication in the Rcho-1 rat choriocarcinoma cell line. We cultured these cells under conditions that gave relatively synchronous endoreduplication. This allowed us to study the events that occur during the transition from the mitotic cycle to the first endocycle. With giant cell differentiation, the cells switched cyclin D isoform expression from D3 to D1 and altered several checkpoint functions, acquiring a relative insensitivity to DNA-damaging agents and a coincident serum independence. The initiation of S phase during endocycles appeared to involve cycles of synthesis of cyclins E and A, and termination of S was associated with abrupt loss of cyclin A and E. Both cyclins were absent from gap phase cells, suggesting that their degradation may be necessary to allow reinitiation of the endocycle. The arrest of the mitotic cycle at the onset of endoreduplication was associated with a failure to assemble cyclin B/p34 cdk1 complexes during the first endocycle. In subsequent endocycles, cyclin B expression was suppressed. Together these data suggest several points at which cell cycle regulation could be targeted to shift cells from a mitotic to an endoreduplicative cycle.

Immunohistochemical Expression of Cell Cycle Proteins E2F-1, Cdk-2, Cyclin E, p27kip1, and Ki-67 in Normal Placenta and Gestational Trophoblastic Disease

“…The cyclin E-Cdk2 complex is essential for G 1 -S progression. As reported by others, we found cyclin E expression at moderate levels throughout normal placental development (20,21,30,31). We did not detect differences in the expression of cyclin E at the different stages of normal placental development.…”

Ectopic expression of cyclin E allows non-endomitotic megakaryoblastic K562 cells to establish re-replication cycles

“…Here, we have extended these data, showing that cyclin E is able to confer the ability to establish a re-replication cycle on di erentiating K562 cells which do not otherwise become polyploid after TPA treatment. These data are in accordance not only with the primary role of this cyclin, that is, the entrance into S phase Resnitzky et al, 1994), but also with its essential role in other re-replicating systems such as Drosophila embryonic cells (Duronio et al, 1996;Knoblich et al, 1994), maize endosperm (Gra® and Larkins, 1995), and mouse trophoblasts (MacAuley et al, 1998). Interestingly, our data also suggest that cyclin E is present in di erentiating cells undergoing re-replication cycles, in contrast with what occurs along a mitotic cycle of exponentially growing cells.…”

“…It is also expected that to undergo S phase, cells have to express cyclin A, as it has been established for proliferating cells (Ohtsubo et al, 1995;Zindy et al, 1992;Girard et al, 1991). Surprisingly, though, in other re-replicating systems including mouse trophoblasts (MacAuley et al, 1998;Sprenger et al, 1997), cyclin A appears not to be needed for extra S phases. This apparent discrepancy could be based upon fundamental di erences between the biological signi®cance of the respective re-replication cycles.…”

“…Genetic analyses have proved that cyclin E is directly implicated in the establishment of Drosophila endocycles (Duronio and O'Farrell, 1995;Knoblich et al, 1994;Lilly and Spradling, 1996;Richardson et al, 1993;Sauer et al, 1995), and that these can occur in the absence of mitotic cyclins A and B, cdc2 or string (Drosophila cdc25C), the phosphatase that ultimately activates the cyclin B-cdc2 at the G2/M transition (Lehner and O'Farrell, 1990;Smith and Orr-Weaver, 1991;Stern et al, 1993). Also, in mouse trophoblasts, cyclin E appears to be expressed during polyploidization, whereas expression of cyclins A and B, and cdc2 is abolished (MacAuley et al, 1998).…”

CCN1 (CYR61) and CCN3 (NOV) signaling drives human trophoblast cells into senescence and stimulates migration properties

“…37 Studies of murine trophoblast giant cells have shown that terminal differentiation is marked by endoreduplication. 38 However we did not detect an increase in the number of polyploid SGHPL-5 cells after treatment with either CCN. Instead, our results clearly showed that both CCN proteins induced cellular senescence in SGHPL-5 cells, as demonstrated by an increased expression of SAb-gal, and the increased expression of p16, both are wellestablished markers of cellular senescence.…”