Differentiation of trophoblast stem cells into giant cells is triggered by p57/Kip2 inhibition of CDK1 activity

Abstract

Genome endoreduplication during mammalian development is a rare event for which the mechanism is unknown. It first appears when fibroblast growth factor 4 (FGF4) deprivation induces differentiation of trophoblast stem (TS) cells into the nonproliferating trophoblast giant (TG) cells required for embryo implantation. Here we show that RO3306 inhibition of cyclin-dependent protein kinase 1 (CDK1), the enzyme required to enter mitosis, induced differentiation of TS cells into TG cells. In contrast, RO3306 induced abortive endoreduplication and apoptosis in embryonic stem cells, revealing that inactivation of CDK1 triggers endoreduplication only in cells programmed to differentiate into polyploid cells. Similarly, FGF4 deprivation resulted in CDK1 inhibition by overexpressing two CDK-specific inhibitors, p57/KIP2 and p21/CIP1. TS cell mutants revealed that p57 was required to trigger endoreduplication by inhibiting CDK1, while p21 suppressed expression of the checkpoint protein kinase CHK1, thereby preventing induction of apoptosis. Furthermore, Cdk2 −/− TS cells revealed that CDK2 is required for endoreduplication when CDK1 is inhibited. Expression of p57 in TG cells was restricted to G-phase nuclei to allow CDK activation of S phase. Thus, endoreduplication in TS cells is triggered by p57 inhibition of CDK1 with concomitant suppression of the DNA damage response by p21.[Keywords: Endoreduplication; placentomegaly; trophoblast giant cell; p57; CDK1; DNA replication] Supplemental material is available at http://www.genesdev.org.

Cyclin-dependent kinase 1 (Cdk1) is essential for cell division and suppression of DNA re-replication but not for liver regeneration

“…Inhibition of Cdk1 activity via mutagenesis (28,31) or selective drug inhibitors (26) has been shown to result in increased endoreduplication. Corroborating this hypothesis, p57-mediated inhibition of Cdk1 activity in an endogenous system, trophoblast giant cells, has been shown to be essential for repeated rounds of endoreduplication that take place during their maturation (32); in the same system, the authors have also shown that Cdk2 is required for endoreduplication.…”

p57Kip2 and Cancer: Time for a Critical Appraisal

“…In particular, CKI is able to stabilize MyoD, a transcription factor that is highly specific for muscle involved in myogenic differentiation. p57 Kip2 is also involved in the differentiation of several other cell phenotypes, including podocytes (79), placental cells (65,80,81), keratinocytes (82), pancreatic cells (83), hepatocytes (84,85), T-lymphocytes (86), spermatozoa (87,88), Leydig cells (88), chondrocytes (89)(90)(91), and adrenal cortex cells (92).…”

“…Moreover, coordinated changes of p57 Kip2 , p27 Kip1 , and p21 Cip1 have been shown clearly during keratinocyte maturation (76) and human placenta development (65,80,81).…”

Fundamental differences in endoreplication in mammals and Drosophila revealed by analysis of endocycling and endomitotic cells

“…Other highly expressed genes included scavenger receptor class B, member 1 (Scarb 1), required for the phagocytic activity of TGCs (38,39), and the Cdk1 inhibitor p57 (Cdkn1c), required for TGC endoreplication (22). We analyzed the E9.5 TGC mRNA-Seq profile with the GOrilla gene ontology (GO) tool (http://www.ncbi.nim.nih.gov/pubmed/ 19192299), which uses an algorithm that precludes the choice of an arbitrary P value cutoff.…”

“…Mouse TGCs can be differentiated in culture from trophoblast stem cells by the absence of fibroblast growth factor 4, and a rat trophoblast cell culture line exists that becomes polyploid in culture, attaining up to 64C ploidy (19,20). Analysis of these models revealed that the cyclindependent kinase (CDK) inhibitor p57 is necessary for the onset of the endocycle (21,22). Differential DNA replication, however, was not examined in these cell culture models.…”