Quantitative proteomics reveals the basis for the biochemical specificity of the cell-cycle machinery.

Cyclin-dependent kinases comprise the conserved machinery that drives progress through the cell cycle, but how they do this in mammalian cells is still unclear. To identify the mechanisms by which cyclin-cdks control the cell cycle, we performed a time-resolved analysis of the in vivo interactors of cyclins E1, A2, and B1 by quantitative mass spectrometry. This global analysis of context-dependent protein interactions reveals the temporal dynamics of cyclin function in which networks of cyclin-cdk interactions vary according to the type of cyclin and cell-cycle stage. Our results explain the temporal specificity of the cell-cycle machinery, thereby providing a biochemical mechanism for the genetic requirement for multiple cyclins in vivo and reveal how the actions of specific cyclins are coordinated to control the cell cycle. Furthermore, we identify key substrates (Wee1 and c15orf42/Sld3) that reveal how cyclin A is able to promote both DNA replication and mitosis.

MicroRNA-874-mediated inhibition of the major G1/S phase cyclin, CCNE1, is lost in osteosarcomas.

The tumor microenvironment is characterized by nutrient-deprived conditions in which the cancer cells have to adapt for survival. Serum starvation resembles the growth factor deprivation characteristic of the poorly vascularized tumor microenvironment and has aided in the discovery of key growth regulatory genes and microRNAs (miRNAs) that have a role in the oncogenic transformation. We report here that miR-874 down-regulates the major G1/S phase cyclin, cyclin E1 (CCNE1), during serum starvation. Because the adaptation of cancer cells to the tumor microenvironment is vital for subsequent oncogenesis, we tested for miR-874 and CCNE1 interdependence in osteosarcoma cells. We observed that miR-874 inhibits CCNE1 expression in primary osteoblasts, but in aggressive osteosarcomas, miR-874 is down-regulated, leading to elevated CCNE1 expression and appearance of cancer-associated phenotypes. We established that loss of miR-874-mediated control of cyclin E1 is a general feature of osteosarcomas. The down-regulation of CCNE1 by miR-874 is independent of E2F transcription factors. Restoration of miR-874 expression impeded S phase progression, suppressing aggressive growth phenotypes, such as cell invasion, migration, and xenograft tumors, in nude mice. In summary, we report that miR-874 inhibits CCNE1 expression during growth factor deprivation and that miR-874 down-regulation in osteosarcomas leads to CCNE1 up-regulation and more aggressive growth phenotypes.

Centchroman induces redox-dependent apoptosis and cell-cycle arrest in human endometrial cancer cells.

Centchroman (CC) or Ormeloxifene has been shown to induce apoptosis and cell cycle arrest in various types of cancer cells. This has, however, not been addressed for endometrial cancer cells where its (CC) mechanism of action remains unclear. This study focuses on the basis of antineoplasticity of CC by blocking the targets involved in the cell cycle, survival and apoptosis in endometrial cancer cells. Ishikawa Human Endometrial Cancer Cells were cultured under estrogen deprived medium, exposed to CC and analyzed for proliferation and apoptosis. Additionally, we also analyzed oxidative stress induced by CC. Cell viability studies confirmed the IC50 of CC in Ishikawa cells to be 20 µM after 48 h treatment. CC arrests the cells in G0/G1 phase through cyclin D1 and cyclin E mediated pathways. Phosphatidylserine externalization, nuclear morphology changes, DNA fragmentation, PARP cleavage, and alteration of Bcl-2 family protein expression clearly suggest ongoing apoptosis in the CC treated cells. Activation of caspase 3 & 9, up-regulation of AIF and inhibition of apoptosis by z-VAD-fmk clearly explains the participation of the intrinsic pathway of programmed cell death. Further, the increase of ROS, loss of MMP, inhibition of antioxidant (MnSOD, Cu/Zn-SOD and GST) and inhibition of apoptosis with L-NAC suggests CC induced oxidative stress leading to apoptosis via mitochondria mediated pathway. Therefore, CC could be a potential therapeutic agent for the treatment of Endometrial Cancer adjunct to its utility as a contraceptive and an anti-breast cancer agent.

Phosphorylation of Mcm2 by Cdc7 promotes pre-replication complex assembly during cell-cycle re-entry.

Cyclin E has been shown to have a role in pre-replication complex (Pre-RC) assembly in cells re-entering the cell cycle from quiescence. The assembly of the pre-RC, which involves the loading of six MCM subunits (Mcm2-7), is a prerequisite for DNA replication. We found that cyclin E, through activation of Cdk2, promotes Mcm2 loading onto chromatin. This function is mediated in part by promoting the accumulation of Cdc7 messenger RNA and protein, which then phosphorylates Mcm2. Consistent with this, a phosphomimetic mutant of Mcm2 can bypass the requirement for Cdc7 in terms of Mcm2 loading. Furthermore, ectopic expression of both Cdc6 and Cdc7 can rescue the MCM loading defect associated with expression of dominant-negative Cdk2. These results are consistent with a role for cyclin E-Cdk2 in promoting the accumulation of Cdc6 and Cdc7, which is required for Mcm2 loading when cells re-enter the cell cycle from quiescence.

Cyclin E Deregulation and Genomic Instability.

Precise replication of genetic material and its equal distribution to daughter cells are essential to maintain genome stability. In eukaryotes, chromosome replication and segregation are temporally uncoupled, occurring in distinct intervals of the cell cycle, S and M phases, respectively. Cyclin E accumulates at the G1/S transition, where it promotes S phase entry and progression by binding to and activating CDK2. Several lines of evidence from different models indicate that cyclin E/CDK2 deregulation causes replication stress in S phase and chromosome segregation errors in M phase, leading to genomic instability and cancer. In this chapter, we will discuss the main findings that link cyclin E/CDK2 deregulation to genomic instability and the molecular mechanisms by which cyclin E/CDK2 induces replication stress and chromosome aberrations during carcinogenesis.

Analysis of Cyclin E1 Functions in Porcine Preimplantation Embryonic Development by Fluorescence Microscopy.

Cyclin E1 (CCNE1) is a core component of cell cycle regulation that drives the transition into the S phase. CCNE1 plays critical roles in cell cycle, cell proliferation, and cellular functions. However, the function of CCNE1 in early embryonic development is limited. In the present study, the function and expression of Ccne1 in porcine early parthenotes were examined. Immunostaining experiments showed that CCNE1 localized in the nucleus, starting at the four-cell stage. Knockdown of Ccne1 by double-stranded RNA resulted in the failure of blastocyst formation and induced blastocyst apoptosis. Ccne1 depletion increased expression of the pro-apoptotic gene Bax, and decreased the expression of Oct4 and the rate of inner cell mass (ICM)/trophectoderm formation. The results indicated that CCNE1 affects blastocyst formation by inducing cell apoptosis and ICM formation during porcine embryonic development.

Cyclin E as a potential therapeutic target in high grade serous ovarian cancer.

Cyclin E1 (CCNE1) gene amplification occurs in approximately 20% of ovarian high grade serous carcinoma (HGSC) and is associated with chemotherapy resistance and, in some studies, overall poor prognosis. The role of cyclin E1 in inducing S phase entry relies upon its interactions with cyclin dependent kinases (CDK), specifically CDK2. Therapies to target cyclin E1-related functions have centered on CDK inhibitors and proteasome inhibitors. While many studies have helped elucidate the functions and regulatory mechanisms of cyclin E1, further research utilizing cyclin E1 as a therapeutic target in ovarian cancer is warranted. This review serves to present the scientific background describing the role and function of cyclin E1 in cancer development and progression, to distinguish cyclin E1-amplified HGSC as a unique subset of ovarian cancer deserving of further therapeutic investigation, and to provide an updated overview on the studies which have utilized cyclin E1 as a target for therapy in ovarian cancer.

p21/Cyclin E pathway modulates anticlastogenic function of Bmi-1 in cancer cells.

Apart from regulating stem cell self-renewal, embryonic development and proliferation, Bmi-1 has been recently reported to be critical in the maintenance of genome integrity. In searching for novel mechanisms underlying the anticlastogenic function of Bmi-1, we observed, for the first time, that Bmi-1 positively regulates p21 expression. We extended the finding that Bmi-1 deficiency induced chromosome breaks in multiple cancer cell models. Interestingly, we further demonstrated that knockdown of cyclin E or ectopic overexpression of p21 rescued Bmi-1 deficiency-induced chromosome breaks. We therefore conclude that p21/cyclin E pathway is crucial in modulating the anticlastogenic function of Bmi-1. As it is well established that the overexpression of cyclin E potently induces genome instability and p21 suppresses the function of cyclin E, the novel and important implication from our findings is that Bmi-1 plays an important role in limiting genomic instability in cylin E-overexpressing cancer cells by positive regulation of p21.

Concurrent deletion of cyclin E1 and cyclin-dependent kinase 2 in hepatocytes inhibits DNA replication and liver regeneration in mice.

UNLABELLED: The liver has a strong regenerative capacity. After injury, quiescent hepatocytes can reenter the mitotic cell cycle to restore tissue homeostasis. This G(0) /G(1) -S cell-cycle transition of primed hepatocytes is regulated by complexes of cyclin-dependent kinase 2 (Cdk2) with E-type cyclins (CcnE1 or CcnE2). However, single genetic ablation of either E-cyclin or Cdk2 does not affect overall liver regeneration. Here, we systematically investigated the contribution of CcnE1, CcnE2, and Cdk2 for liver regeneration after partial hepatectomy (PH) by generating corresponding double- and triple-knockout (KO) mouse mutants. We demonstrate that conditional deletion of Cdk2 alone in hepatocytes resulted in accelerated induction of CcnE1, but otherwise normal initiation of S phase in vivo and in vitro. Excessive CcnE1 did not contribute to a noncanonical kinase activity, but was located at chromatin together with components of the pre-replication complex (pre-RC), such as the minichromosome maintenance (MCM) helicase. Concomitant ablation of Cdk2 and CcnE1 in hepatocytes caused a defect in pre-RC formation and further led to dramatically impaired S-phase progression by down-regulation of cyclin A2 and cell death in vitro and substantially reduced hepatocyte proliferation and liver regeneration after PH in vivo. Similarly, combined loss of CcnE1 and CcnE2, but also the Cdk2/CcnE1/CcnE2 triple KO in liver, significantly inhibited S-phase initiation and liver mass reconstitution after PH, whereas concomitant ablation of CcnE2 and Cdk2 had no effect. CONCLUSION: In the absence of Cdk2, CcnE1 performs crucial kinase-independent functions in hepatocytes, which are capable of driving MCM loading on chromatin, cyclin A2 expression, and S-phase progression. Thus, combined inactivation of Cdk2 and CcnE1 is the minimal requirement for blocking S-phase machinery in vivo.

Cyclin E1 controls proliferation of hepatic stellate cells and is essential for liver fibrogenesis in mice.

UNLABELLED: Liver fibrogenesis is associated with the transition of quiescent hepatocytes and hepatic stellate cells (HSCs) into the cell cycle. Exit from quiescence is controlled by E-type cyclins (cyclin E1 [CcnE1] and cyclin E2 [CcnE2]). Thus, the aim of the current study was to investigate the contribution of E-type cyclins for liver fibrosis in man and mice. Expression of CcnE1, but not of its homolog, CcnE2, was induced in fibrotic and cirrhotic livers from human patients with different etiologies and in murine wild-type (WT) livers after periodical administration of the profibrotic toxin, CCl(4). To further evaluate the potential function of E-type cyclins for liver fibrogenesis, we repetitively treated constitutive CcnE1(-/-) and CcnE2(-/-) knock-out mice with CCl(4) to induce liver fibrosis. Interestingly, CcnE1(-/-) mice were protected against CCl(4)-mediated liver fibrogenesis, as evidenced by reduced collagen type I α1 expression and the lack of septum formation. In contrast, CcnE2(-/-) mice showed accelerated fibrogenesis after CCl(4) treatment. We isolated primary HSCs from WT, CcnE1(-/-), and CcnE2(-/-) mice and analyzed their activation, proliferation, and survival in vitro. CcnE1 expression in WT HSCs was maximal when they started to proliferate, but decreased after the cells transdifferentiated into myofibroblasts. CcnE1(-/-) HSCs showed dramatically impaired survival, cell-cycle arrest, and strongly reduced expression of alpha smooth muscle actin, indicating deficient HSC activation. In contrast, CcnE2-deficient HSCs expressed an elevated level of CcnE1 and showed enhanced cell-cycle activity and proliferation, compared to WT cells. CONCLUSIONS: CcnE1 and CcnE2 have antagonistic roles in liver fibrosis. CcnE1 is indispensable for the activation, proliferation, and survival of HSCs and thus promotes the synthesis of extracellular matrix and liver fibrogenesis.

Cyclin E facilitates dysplastic hepatocytes to bypass G1/S checkpoint in hepatocarcinogenesis.

BACKGROUND AND AIM: By array-comparative genomic hybridization, we demonstrated cyclin E as one of seven genes associated with hepatocellular carcinoma (HCC) development in Ku70 DNA repair-deficient mice. We therefore explored the hypothesis that during hepatocarcinogenesis, cyclin E kinase can overcome the inhibitory effects of p53 and establish whether abnormal miRNA(mi-R)-34, a co-regulator of cyclin E and p53, can account for their interactions as "drivers" of HCC. METHODS: Dysplastic hepatocytes (DNs) and HCCs were generated from diethylnitrosamine (DEN)-injected C57BL/6 male mice at 3-12 months. RESULTS: Cyclin E/cdk2 was barely expressed in normal liver, but was readily detected in dysplastic hepatocytes, localizing to glutathione-S transferase pi-form positive cells dissected by laser-dissection. Cyclin E kinase activity preceded cyclin D1, proliferating cell nuclear antigen expression in DNs and HCCs despite maximal p53 and p21 expression. We confirmed that cyclin E, rather than cyclin D1, is the proliferative driver in hepatocarcinogenesis by immunoprecipitation experiments demonstrating preferential binding of p21 to cyclin D1, allowing cyclin E-mediated "escape" from G1/S checkpoint. We then showed cyclin E was responsible for regulating wild-type p53 by knockdown experiments in primary HCC cells; cyclin E-knockdown increased p53 and p21, diminished anti-apoptotic Bcl-XL and reduced cell viability. Conversely, blocking p53 augmented cyclin E, Bcl-XL expression and increased proliferation. Physiological interactions between cyclin E/p53/p21 were confirmed in primary hepatocytes. miR-34a,c were upregulated in dysplastic murine, human liver and HCCs compared with normal liver, and appeared to be linked to cyclin E/p53. CONCLUSION: Upregulation of functionally active cyclin E via miR34 with loss of p53 function is associated with cell-cycle checkpoint failure increasing proliferative drive that favors hepatocarcinogenesis.

A mouse model for cyclin E-dependent genetic instability and tumorigenesis.

Ubiquitination of murine cyclin E is triggered by phosphorylation on threonine 393. Cyclin E(T393A) knockin mice exhibited increased cyclin E stability, but no phenotypic abnormalities. Importantly, loss of the p53 pathway exacerbated the effect of the T393A mutation. Thus, in p21(-/-) cells the T393A mutation had an exaggerated effect on cyclin E abundance and its associated kinase activity, which caused abnormal cell cycle progression, and genetic instability involving chromosome breaks and translocations. Moreover, cyclin E(T393A) acted synergistically with p53 deficiency to accelerate tumorigenesis in cyclin E(T393A) p53(-/-) mice; Ras more readily transformed cyclin E(T393A) p53(-/-) cells than p53(-/-) cells in vitro; and cyclin E(T393A) mice had a greatly increased susceptibility to Ras-induced lung cancer.

Distinct roles for cyclins E and A during DNA replication complex assembly and activation.

Initiation of DNA replication is regulated by cyclin-dependent protein kinase 2 (Cdk2) in association with two different regulatory subunits, cyclin A and cyclin E (reviewed in ref. 1). But why two different cyclins are required and why their order of activation is tightly regulated are unknown. Using a cell-free system for initiation of DNA replication that is based on G1 nuclei, G1 cytosol and recombinant proteins, we find that cyclins E and A have specialized roles during the transition from G0 to S phase. Cyclin E stimulates replication complex assembly by cooperating with Cdc6, to make G1 nuclei competent to replicate in vitro. Cyclin A has two separable functions: it activates DNA synthesis by replication complexes that are already assembled, and it inhibits the assembly of new complexes. Thus, cyclin E opens a 'window of opportunity' for replication complex assembly that is closed by cyclin A. The dual functions of cyclin A ensure that the assembly phase (G1) ends before DNA synthesis (S) begins, thereby preventing re-initiation until the next cell cycle.

MAP kinase dependent cyclinE/cdk2 activity promotes DNA replication in early sea urchin embryos.

Sea urchins provide an excellent model for studying cell cycle control mechanisms governing DNA replication in vivo. Fertilization and cell cycle progression are tightly coordinated by Ca(2+) signals, but the mechanisms underlying the onset of DNA replication after fertilization remain less clear. In this study we demonstrate that calcium-dependent activation of ERK1 promotes accumulation of cyclinE/cdk2 into the male and female pronucleus and entry into first S-phase. We show that cdk2 activity rises quickly after fertilization to a maximum at 4 min, corresponding in timing to the early ERK1 activity peak. Abolishing MAP kinase activity after fertilization with MEK inhibitor, U0126, substantially reduces the early peak of cdk2 activity and prevents cyclinE and cdk2 accumulation in both sperm pronucleus and zygote nucleus in vivo. Both p27(kip1) and roscovitine, cdk2 inhibitors, prevented DNA replication suggesting cdk2 involvement in this process in sea urchin. Inhibition of cdk2 activity using p27(kip1) had no effect on the phosphorylation of MBP by ERK, but completely abolished phosphorylation of retinoblastoma protein, a cdk2 substrate, indicating that cdk2 activity is downstream of ERK1 activation. This pattern of regulation of DNA synthesis conforms to the pattern observed in mammalian somatic cells.

ST14 (suppression of tumorigenicity 14) gene is a target for miR-27b, and the inhibitory effect of ST14 on cell growth is independent of miR-27b regulation.

MicroRNAs are noncoding, endogenous small RNAs that regulate target genes by cleavage of the targeted mRNA or translational repression. We investigated the microRNAome using 2-color microarrays in a highly invasive human breast cancer cell line, MDA-MB-231 (subline 4175) and a noninvasive breast epithelial cell line, MCF10A. We found 13 microRNAs that were up-regulated, and nine were down-regulated significantly in 4175 cells (p < 0.05, -fold change >2) compared with MCF10A cells. Interestingly, miR-27b and its putative target gene, ST14 (suppressor of tumorigenicity 14), had inverse expression pattern in breast cancer cells. The 3'-untranslated region of ST14 contains a regulatory element for miR-27b, and our luciferase experiments indicate that antisense miR-27b enhances ST14 expression in cancer cells. Furthermore, antagomir of miR-27b suppressed cell invasion in 4175 cells, whereas pre-miR-27b stimulated invasion in moderately invasive ZR75 breast cancer cells. In addition, ST14 reduces cell proliferation as well as cell migration and invasion. Analysis of human breast tumors revealed that miR-27b expression increases during cancer progression, paralleling a decrease in ST14 expression. Furthermore, our data indicate that ST14 inhibits cells from entering into S phase by up-regulating p27, which results in down-regulation of cyclin E-CDK2 complexes, suggesting ST14 reduces cell growth through its effects on cell cycle-related proteins. Introduction of miR-27b into ST14-expressing cells did not suppress the effect on cell growth. These findings suggest that ST14 plays an important role in several biological processes, and some effects are not completely dependent on miR-27b regulation.

Response gene to complement 32, a novel hypoxia-regulated angiogenic inhibitor.

BACKGROUND: Response gene to complement 32 (RGC-32) is induced by activation of complement and regulates cell proliferation. To determine the mechanism of RGC-32 in angiogenesis, we examined the role of RGC-32 in hypoxia-related endothelial cell function. METHODS AND RESULTS: Hypoxia/ischemia is able to stimulate both angiogenesis and apoptosis. Hypoxia-inducible factor-1/vascular endothelial growth factor is a key transcriptional regulatory pathway for angiogenesis during hypoxia. We demonstrated that the increased RGC-32 expression by hypoxia was via hypoxia-inducible factor-1/vascular endothelial growth factor induction in cultured endothelial cells. However, overexpression of RGC-32 reduced the proliferation and migration and destabilized vascular structure formation in vitro and inhibited angiogenesis in Matrigel assays in vivo. Silencing RGC-32 had an opposing, stimulatory effect. RGC-32 also stimulated apoptosis as shown by the increased apoptotic cells and caspase-3 cleavage. Mechanistic studies revealed that the effect of RGC-32 on the antiangiogenic response was via attenuating fibroblast growth factor 2 expression and further inhibiting expression of cyclin E without affecting vascular endothelial growth factor and fibroblast growth factor 2 signaling in endothelial cells. In the mouse hind-limb ischemia model, RGC-32 inhibited capillary density with a significant attenuation in blood flow. Additionally, treatment with RGC-32 in the xenograft tumor model resulted in reduced growth of blood vessels that is consistent with reduced colon tumor size. CONCLUSIONS: We provide the first direct evidence for RGC-32 as a hypoxia-inducible gene and antiangiogenic factor in endothelial cells. These data suggest that RGC-32 plays an important homeostatic role in that it contributes to differentiating the pathways for vascular endothelial growth factor and fibroblast growth factor 2 in angiogenesis and provides a new target for ischemic disorder and tumor therapies.

Random discrete competing events vs. dynamic bistable switches in cell proliferation in differentiation.

Several recent experiments related to fundamental aspects of cell behaviour, such as passing of the restriction point of cell cycle, which are generally interpreted in accordance with the dynamic paradigm implying the use of differential equations operating with the concentrations of cellular components and rate constants of their interactions, are shown in the present paper to be consistent with a simple model based on discrete competing stochastic events interpreted as assembly of alternative complexes of transcription factors at gene promoters. The model conforms to the transition probability model of cell cycle and to the stochastic approaches to cell differentiation and integrates them with the restriction point concept.

Integrated genome-wide DNA copy number and expression analysis identifies distinct mechanisms of primary chemoresistance in ovarian carcinomas.

PURPOSE: A significant number of women with serous ovarian cancer are intrinsically refractory to platinum-based treatment. We analyzed somatic DNA copy number variation and gene expression data to identify key mechanisms associated with primary resistance in advanced-stage serous cancers. EXPERIMENTAL DESIGN: Genome-wide copy number variation was measured in 118 ovarian tumors using high-resolution oligonucleotide microarrays. A well-defined subset of 85 advanced-stage serous tumors was then used to relate copy number variation to primary resistance to treatment. The discovery-based approach was complemented by quantitative-PCR copy number analysis of 12 candidate genes as independent validation of previously reported associations with clinical outcome. Likely copy number variation targets and tumor molecular subtypes were further characterized by gene expression profiling. RESULTS: Amplification of 19q12, containing cyclin E (CCNE1), and 20q11.22-q13.12, mapping immediately adjacent to the steroid receptor coactivator NCOA3, was significantly associated with poor response to primary treatment. Other genes previously associated with copy number variation and clinical outcome in ovarian cancer were not associated with primary treatment resistance. Chemoresistant tumors with high CCNE1 copy number and protein expression were associated with increased cellular proliferation but so too was a subset of treatment-responsive patients, suggesting a cell-cycle independent role for CCNE1 in modulating chemoresponse. Patients with a poor clinical outcome without CCNE1 amplification overexpressed genes involved in extracellular matrix deposition. CONCLUSIONS: We have identified two distinct mechanisms of primary treatment failure in serous ovarian cancer, involving CCNE1 amplification and enhanced extracellular matrix deposition. CCNE1 copy number is validated as a dominant marker of patient outcome in ovarian cancer.

P53, cyclin-dependent kinase and abnormal amplification of centrosomes.

Centrosomes play a critical role in formation of bipolar mitotic spindles, an essential event for accurate chromosome segregation into daughter cells. Numeral abnormalities of centrosomes (centrosome amplification) occur frequently in cancers, and are considered to be the major cause of chromosome instability, which accelerates acquisition of malignant phenotypes during tumor progression. Loss or mutational inactivation of p53 tumor suppressor protein, one of the most common mutations found in cancers, results in a high frequency of centrosome amplification in part via allowing the activation of the cyclin-dependent kinase (CDK) 2-cyclin E (as well as CDK2-cyclin A) which is a key factor for the initiation of centrosome duplication. In this review, the role of centrosome amplification in tumor progression, and mechanistic view of how centrosomes are amplified in cells through focusing on loss of p53 and aberrant activities of CDK2-cyclins will be discussed.

Regulation of growth by ploidy in Caenorhabditis elegans.

Some animals, such as the larvae of Drosophila melanogaster, the larvae of the Appendicularian chordate Oikopleura, and the adults of the nematode Caenorhabditis elegans, are unusual in that they grow largely by increases in cell size. The giant cells of such species are highly polyploid, having undergone repeated rounds of endoreduplication. Since germline polyploid strains tend to have large cells, it is often assumed that endoreduplication drives cell growth, but this remains controversial. We have previously shown that adult growth in C. elegans is associated with the endoreduplication of nuclei in the epidermal syncitium, hyp 7. We show here that this relationship is causal. Manipulation of somatic ploidy both upwards and downwards increases and decreases, respectively, adult body size. We also establish a quantitative relationship between ploidy and body size. Finally, we find that TGF-beta (DBL-1) and cyclin E (CYE-1) regulate body size via endoreduplication. To our knowledge, this is the first experimental evidence establishing a cause-and-effect relationship between somatic polyploidization and body size in a metazoan.