Prenatal ultrasonographic diagnosis of persistent hyperplastic primary vitreous

Persistent hyperplastic primary vitreous (PHPV) is a rare developmental malformation of the eye characterized by the presence of a vascular membrane located behind the lens. We report, for the first time in the literature, the identification on ultrasound examination of bilateral cataract and thickened hyaloid artery-lens junction, leading to a diagnosis of bilateral PHPV, in a fetus at 23 weeks' gestation. Histological examination at postmortem confirmed the prenatal diagnosis of bilateral PHPV and cataract. A thorough ultrasound examination of the fetal eye in cases with cataract is recommended.

Skp2 inversely correlates with p27 and tuberin in transformed cells

The cyclin-dependent kinase inhibitor p27Kip1 (p27) is a major gatekeeper of the mammalian cell cycle progression known to be regulated by both, its subcellular localization and its degradation. To allow entrance into S phase and thereby mammalian cell cycle progression p27 must be degraded by a skp2-containing E3 ubiquitin ligase whose task is to target p27 for degradation by the proteasome. The tumor suppressor gene product tuberin directly binds to p27 and protects it from degradation via skp2. Whereas, p27 and tuberin are known to be localized to both, the cytoplasm and the nucleus, the localization of skp2 remained elusive. Here we demonstrate that skp2 is a cytoplasmic and nuclear protein. In addition we found an inverse correlation of the endogenous protein levels of skp2 with p27 and tuberin in different transformed cells and under different growth conditions. These data allow new important insights into this molecular network of cell cycle control.

Microarray-based gene expression analysis during retinal maturation of albino rats

BACKGROUND

In recent years, the rat has become a commonly-used animal model for the study of retinal diseases. Similar to other tissues, the retina undergoes significant functional changes during maturation. Aiming to gain knowledge on additional aspects of retinal maturation, we performed gene expression and histological analyses of the rat retina during maturation.

METHODS

Rat retinas were dissected at three time points. Histological examination of the samples was performed, and the expression levels of retinal genes were evaluated using the rat whole-genome microarray system. Quantitative real-time PCR analysis was used to validate selected expression patterns. Various statistical and bioinformatic tools were used to identify differentially expressed genes.

RESULTS

The microarray analysis revealed a relatively high number of highly expressed non-annotated genes. We identified 603 differentially expressed genes, which were grouped into six clusters based on changes in expression levels during the first 20 weeks of life. A bioinformatic analysis of these clusters revealed sets of genes encoding proteins with functions that are likely to be relevant to retinal maturation (potassium, sodium, calcium, and chloride channels, synaptic vesicle transport, and axonogenesis). The histological analysis revealed a significant reduction of outer nuclear layer thickness and retinal ganglion cell number during maturation.

CONCLUSIONS

These data, taken together with our previously reported electrophysiological data, contribute to our understanding of the retinal maturation processes of this widely-used animal model.

Intratumoral IGF-I protein expression is selectively upregulated in breast cancer patients with BRCA1/2 mutations

BRCA1/2 mutations predispose to early onset breast and ovarian cancers. The phenotypic expression of mutant alleles, however, is thought to be modified by factors that are also involved in the pathogenesis of sporadic breast cancer. One such protein is IGF-I, one of the strongest mitogens to breast cancer cells in vitro. We have utilized immunohistochemistry to compare the intratumoral IGF-I and IGF-I receptor (IGF-IR) protein expression in 57 BRCA1/2 mutation carriers and 102 matched breast cancer patients without a family history in a nested case-control study. BRCA1 silencing by siRNA was used to investigate the effect of BRCA mutations on IGF-I protein expression. IGF-I protein expression was detected in tumoral epithelium and surrounding stroma, and was significantly upregulated in tumors of BRCA mutation carriers when compared with matched sporadic tumors (epithelial: 87.7% vs 61.8%, P=0.001; stromal: 73.7% vs 34.3%, P<0.001). By contrast, IGF-IR protein expression was confined to malignant epithelium and was unchanged in mutation carriers (52.6% vs 39.2%, P=0.310). While in mutation carriers IGF-IR protein expression was significantly correlated with both epithelial (P=0.003) and stromal IGF-I (P=0.02), this association was less pronounced in sporadic breast cancer (P=0.02 respectively). siRNA-mediated downregulation of BRCA1 in primary human mammary gland cells triggered upregulation of endogenous intracellular IGF-I in vitro. The increased intratumoral IGF-I protein expression in BRCA mutation carriers suggests an involvement of the IGF-I/IGF-IR axis in the biological behavior of breast cancers in this population and could define a potential therapeutic target.

Ras mediates cell survival by regulating tuberin

Mutational activation of Ras promotes oncogenesis by controlling cell cycle regulation and cell survival. Ras-mediated activation of both, the PI3K/AKT pathway and the MEK/ERK pathway, can trigger downregulation of the function of tuberin to block the activities of mTOR and p70S6K. Here we demonstrate that Ras-induced cell survival is accompanied by upregulation of p70S6K activity. Ras harbors the potential to negatively affect tuberin-induced apoptosis and p70S6K inactivation. These effects of Ras were found to depend on its potential to regulate the MEK/ERK pathway. Experiments using tuberin-negative fibroblasts revealed that the potential of Ras to counteract apoptosis depends on functional tuberin. Taken together, we provide evidence that the function of Ras to trigger inactivation of tuberin plays a major role in the regulation of cell survival upon mutational activation of the oncogene Ras. This is the first description of a functional interaction between the tumor suppressor tuberin and the oncogene Ras in regulating apoptosis.

Human amniotic fluid stem cells: a new perspective

The discovery of amniotic fluid stem cells initiated a new and very promising field in stem cell research. In the last four years amniotic fluid stem cells have been shown to express markers specific to pluripotent stem cells, such as Oct-4. Due to their high proliferation potential, amniotic fluid stem cell lineages can be established. Meanwhile, they have been shown to harbor the potential to differentiate into cells of all three embryonic germ layers. It will be a major aim for the future to define the potential of this new source of stem cells for therapies related to specific diseases.

Effect of Fourth-Generation Fluoroquinolones on the Healing Rate of Corneal Erosions in an Animal Model

PURPOSE

To compare the rate of epithelial healing of corneal erosion in an animal model with 2 commercial formulations of fourth-generation fluoroquinolones: 0.3% gatifloxacin and 0.5% moxifloxacin.

METHODS

Corneal erosions, 6 mm in diameter, were created in 28 rabbit eyes. The rabbits were randomized to receive topical gatifloxacin, moxifloxacin, or nonpreserved saline. Drops were administered every 15 minutes for 1 hour, then hourly for 3 hours, and then 4 times daily until the erosion reepithelialized. Eyes were examined with fluorescein drops and photographed every 12 hours with a cobalt blue-filtered light. When reepithelialization was observed, the rabbits were euthanized, and their eyes were enucleated for histopathologic evaluation.

RESULTS

Reepithelialization of the corneal erosions was fastest in the saline-treated eyes (57.3 +/- 8 hours), followed by moxifloxacin (62.7 +/- 11.7 hours) and gatifloxacin (66 +/- 8.5 hours). These differences in the time to closure of the erosions among the 3 groups were not statistically significant. Although significant differences were found among the healing progression curves when all 3 groups were compared (P = 0.042), the difference between the 2 antibiotic-treated groups was not significant.

CONCLUSIONS

Only slight differences in epithelial healing rates were found between the gatifloxacin-, moxifloxacin-, and saline-treated groups, suggesting that the 2 fluoroquinolones may have an equivalent role as prophylactic treatment of trauma- or surgery-induced corneal erosions.

Disability following kidney transplantation: the link to medication coverage

There is no uniformity regarding patient disability following kidney transplantation. Given improved results of patient and graft survival, and the link between insurance, medication coverage and disability, efforts must be made to define disability after a successful transplant. We conducted an individual questioner study of kidney transplant patients to determine factors relating to patient-perceived disability. Seventy patients participated in the study. Patient perception of disability did not correlate with education or ethnicity. Most patients believed they were disabled on dialysis and this did not change following transplantation. While 42 (60%) of the patients felt that they could work, either full-time or part-time, only 20 (28%) were actually working or in school. Most patients believe that working will eliminate disability status and, therefore, insurance and medication coverage. Patients considered disability more related to their status as a kidney transplant patient than any specific physical limitations. The link, whether real or perceived, between 'disability' and immunosuppressive medication coverage is a significant barrier for many patients. The transplant community must reach some degree of consensus regarding post-transplant activity restrictions. The transplant community needs to find a way to take an active role in post-transplant education and employment.

Cytoplasmic/nuclear localization of tuberin in different cell lines

Tuberous sclerosis (TSC) is an autosomal dominantly inherited disease affecting 1 in 6000 individuals. The TSC gene products, hamartin and tuberin, form a complex, of which tuberin is assumed to be the functional component being involved in a wide variety of different cellular processes. Tuberin has been demonstrated to be localized to both, the cytoplasm and the nucleus. The cytoplasmic/nuclear localization of tuberin is known to be regulated by the serine/threonine protein kinase Akt. Akt also regulates the cytoplasmic/nuclear localization of the cyclin-dependent kinase inhibitor p27. In this study the localization of these two Akt-regulated proteins was analysed in different cell lines.

Nuclear/cytoplasmic localization of Akt activity in the cell cycle

The serine/threonine protein kinase Akt (also known as PKB) is a proto-oncogene and one of the most frequently hyperactivated kinases in human cancer. Its activation downstream of growth-factor-stimulated phosphatidylinositide-3'-OH kinase activity plays a role in the control of cell cycle, cell growth, apoptosis and cell energy metabolism. Akt phosphorylates some thousand downstream substrates, including typical cytoplasmic as well as nuclear proteins. Accordingly, it is not surprising that Akt activity can be found in both, the cytoplasm and the nucleus. Here we report the cell cycle regulation of nuclear and cytoplasmic Akt activity in mammalian cells. These data provide new insights into the regulation of Akt activity and have implications for future studies on the regulation of the wide variety of different nuclear and cytoplasmic Akt substrates.

Transplantation of newborn lacrimal gland cells in a rat model of reduced tear secretion

BACKGROUND

Decreased lacrimal gland output may cause dry eye syndrome. Using a rat model, we examined the feasibility of transplanting lacrimal gland cells from newborns.

OBJECTIVES

To restore lacrimal gland function in eyes with compromised tear production.

METHODS

A model of dry eye in adult rats was developed by unilateral surgical removal of the main lacrimal gland. Tear secretion in both eyes was then assessed by masked Schirmer's test. Lacrimal gland tissue from newborn rats was transplanted into the fibrous connective tissue in which the lacrimal gland had been embedded. Masked Schirmer's test was repeated 4, 8 and 12 weeks after transplantation.

RESULTS

Schirmer's test performed in 13 rats 10 days after unilateral lacrimal gland excision revealed significantly less wetting on the side with excised gland compared with the normal side (P < 0.003). The lack of secreting cells on the operated side was verified histologically. The reduction in tear secretion on the operated side remained significant for 8 weeks on average. In the six rats with transplanted lacrimal gland tissue however, there were no differences in tear reduction between the two eyes at 4, 8 or 12 weeks after the operation (P = 0.81, 0.56 and 0.8, respectively).

CONCLUSIONS

Transplantation of lacrimal gland tissue from newborn rats effectively restored eye wetting in this new model. Further research is needed to evaluate this new approach for treating lacrimal gland dysfunction. Using this model might also facilitate evaluation of potential clinical treatments for dry eyes.

Orbital marginal zone lymphomas: an immunohistochemical, polymerase chain reaction, and fluorescence in situ hybridization study

Many studies have been performed on chromosomal aberrations of extranodal marginal zone lymphomas. However, only a few have been published so far on ocular adnexal marginal zone lymphomas. We studied 18 cases of orbital lymphoid cell infiltrates. Using fluorescence in situ hybridization (FISH), we studied some of the most common chromosomal aberrations found in extranodal marginal zone lymphomas as: trisomies 3, and rearrangements of the 18q21 MALTI gene to detect the translocations t(11;18)(q21;q21) and t(14;18)(q32;q21)MALT1. Our goals were as follows: (1) study those aberrations in our material and compare them with the literature, (2) check their prognostic significance, and (3) check whether studying those aberrations with FISH can be used as a diagnostic tool to differentiate reactive from neoplastic infiltrates, in addition to immunohistochemistry and polymerase chain reaction. We found a high frequency of trisomies 3 (68%) and 18 (56.6%), the highest published so far in orbital lymphomas. On the other hand, no rearrangement was seen in any of our cases. The histologic picture and the clinical course were the same when there was one or more aberrations. As for the diagnostic significance, the presence of a prior, concurrent, or subsequent lymphoma in almost all the positive for aberrations cases suggests that either the orbital infiltrates in these cases are lymphomas, or they have, at least, a malignant potential or a genetic instability. Therefore, the demonstration of these numerical aberrations by FISH may be an additional sensitive, reliable, and relatively simple tool to differentiate reactive from neoplastic orbital lymphoid cell infiltrates when the immunohistochemistry and polymerase chain reaction, performed in a busy and routine-based histopathology laboratory, are unsatisfactory.

Functional deficits resulting from laser-induced damage in the rat retina

BACKGROUND AND OBJECTIVES

To determine the threshold for electrophysiological detection of functional changes after laser photocoagulation in rats, and to correlate the functional damage with retinal morphology.

STUDY DESIGN/MATERIALS AND METHODS

Argon-laser lesions, covering a quarter or half of the retina, were produced in the right eyes of 25 rats. Eyes were evaluated by flash electroretinography (ERG) and histologically at 3, 21, and 60 days after lasering.

RESULTS

Lasering of half the retina, but not of a quarter, produced a significant decrease in signals at all time points. Some functional recovery was evident 60 days after injury, and was consistent with concurrent morphological healing.

CONCLUSIONS

In rats, lasering of half the retina, but not a quarter, leads to significant deficits in outer retinal functions over a 2-month period. Thereafter some recovery occurs, presumably as a result of migration of photoreceptors from undamaged areas and their retinal remodeling.

Experimental studies on nonpenetrating filtration surgery using the CO2 laser

BACKGROUND

This study evaluated the use of a CO2 laser for performing deep sclerectomy in nonpenetrating filtration surgery.

METHODS

Three experimental models were performed: enucleated sheep and cow eyes (n=18) to determine optimal irradiation parameters, live rabbit eyes (n=20) to test feasibility, and cadaver eyes (40 procedures in 20 eyes) to study effects in human eyes tissue. After a half-thickness scleral flap was created, deep sclerectomy was performed by CO2 laser applications on the scleral bed down to the trabeculo-Descemet's membrane.

RESULTS

Fluid percolation was repeatedly achieved without penetration in sheep and cow eyes using scanned laser energy of 5-10 W at a pulse duration of 200 micros and a working distance of 35 cm. In live rabbits, deep sclerectomy was achieved without perforation in 19/20 eyes. Intraocular pressure was significantly decreased on the first postoperative day (10.3+/-5.1 mmHg lower, on average, than in the nonoperated fellow eye; P<0.001), and this persisted for 21 days. Operations on all cadaver eyes resulted in effective fluid percolation. Penetration of the scleral wall occurred in five cases only after repeated laser applications with high energy. Histologically, a thin sclerocorneal intact wall was demonstrated at the sclerectomy bed. Collateral tissue damage did not extend beyond 100 microm, and adjacent structures remained unharmed.

CONCLUSIONS

CO2 laser-assisted deep sclerectomy is a feasible and apparently safe procedure.

Akt regulates nuclear/cytoplasmic localization of tuberin

The autosomal dominantly inherited disease tuberous sclerosis (TSC) affects approximately 1 in 6000 individuals and is characterized by the development of tumors, named hamartomas, in different organs. TSC1, encoding hamartin, and TSC2, encoding tuberin are tumor suppressor genes responsible for TSC. Hamartin and tuberin form a complex, of which tuberin is assumed to be the functional component. The TSC proteins have been implicated in the control of cell cycle by activating the cyclin-dependent kinase inhibitor p27 and in cell size regulation by inhibiting the mammalian target of rapamycin (mTOR)/p70S6K cascade. Phosphorylation of S939 and T1462 by Akt downregulates tuberin's potential to inhibit mTOR/p70S6K. Here, we show that this tuberin phosphorylation by Akt does not affect tuberin-mediated control of p27 protein amounts. This demonstrates that regulating p27 protein amounts and mTOR/p70S6K are separable functions of tuberin. Furthermore, we found that phosphorylation by Akt triggers upregulation of cytoplasmic and downregulation of nuclear tuberin. In cycling cells with high Akt activity, tuberin is predominantly localized to the cytoplasm. In arrested G0 cells with downregulated Akt activity, a significant proportion of tuberin is localized to the nucleus. Upon re-entry into the normal ongoing cell cycle, nuclear localization of tuberin is downregulated parallel to the activation of Akt. Recently, the mTOR/p70S6K cascade has been demonstrated to exist in both the cytoplasm and nucleus. We here also found that tuberin harbors the potential to regulate p70S6K activity in both the cytoplasm and nucleus. This description of functional tuberin in the cytoplasm and the nucleus together with our observation of Akt-controlled and cell cycle-regulated tuberin localization are of particular interest for a further understanding of tuberin's function as a gate keeper of the G0 cell status as well as of Akt's activity to control cell proliferation.

A rat model for acute rise in intraocular pressure: immune modulation as a therapeutic strategy

PURPOSE

To establish a rat model of acute increase in intraocular pressure (IOP) and to investigate the therapeutic window for protection against death of retinal ganglion cells (RGCs) by vaccination with glatiramer acetate (Cop-1) or by treatment with brimonidine or MK-801.

DESIGN

Animal study, laboratory investigation.

METHODS

IOP was transiently increased in anesthetized Lewis rats by infusing normal saline (0.9%) into the anterior chamber of the eye for one hour. RGC survival was assessed one week and two weeks later by counting the RGCs retrogradely labeled with rhodamine dextran.

MAIN OUTCOME MEASURES

RGC survival.

RESULTS

IOP rose to 100 cm H(2)O (76 mm Hg) and returned to baseline after 24 hours. The RGC count decreased by 23% a week after the insult and by a further 7% after the second week. Vaccination with Cop-1 on the day of the insult prevented 50% of the IOP-induced RGC loss. Similar neuroprotection was achieved by daily intraperitoneal injections of brimonidine, but not with MK-801.

CONCLUSIONS

A transient increase in IOP to 100 cm H(2)O causes death of RGCs in rats. A single immunization with Cop-1 or daily injections of brimonidine protected up to 50% of potentially doomed RGCs from IOP-induced death, suggesting that not all of the cell death in the untreated model results from the IOP insult directly, but that some of it is caused by insult-induced environmental cytotoxicity, which is unrelated to glutamate toxicity or at least to NMDA receptors. These findings can be applied immediately as a basis for acute glaucoma therapy.

Tuberin negatively affects BCL-2’s cell survival function

Uncontrolled cell cycle progression and cell growth are key properties of tumor cells. The tumor suppressor genes responsible for the autosomal dominantly inherited disease tuberous sclerosis (TSC) have been demonstrated to control both, cell cycle and cell size regulation. Hamartin, encoded by TSC1, and tuberin, encoded by TSC2, form a complex, of which tuberin is assumed to be the functional component. Loss of TSC genes function triggers hamartoma development in TSC patients. However, in vivo mostly tumor cell development is rapidly terminated via apoptosis. BCL-2, the founding member of the BCL-2 family of proteins, is well known for its anti-apoptotic properties. Here we show that pro-apoptotic actinomycin D cannot interfere with BCL-2's cell survival functions. However, we found tuberin to negatively regulate BCL-2's anti-apoptotic effects on low serum-induced apoptosis. These findings warrant further investigations to elucidate the molecular mechanism underlying tuberin's negative effects on cell survival.

Tuberin activates the proapoptotic molecule BAD

TSC1, encoding hamartin, and TSC2, encoding tuberin, are tumor suppressor genes responsible for the autosomal dominantly inherited disease tuberous sclerosis (TSC). TSC affects approximately 1 in 6000 individuals and is characterized by the development of tumors, named hamartomas, in different organs. Hamartin and tuberin form a complex, of which tuberin is assumed to be the functional component. The TSC proteins have been implicated in the control of cell cycle and cell size. In addition to enhanced growth, reduced death rates can lead to tumor development. Therefore, defects in the apoptosis-inducing pathways contribute to neoplastic cell expansion. Here, we show that tuberin triggers apoptosis, accompanied by downregulation of p70S6K activity and of phosphorylation of BAD on residue Ser136, and by upregulation of the interaction of BAD/BCL-2 and BAD/BCL-XL. AKT phosphorylation negatively regulates tuberin's potential to trigger apoptosis. Experiments with BAD-/- cells demonstrate BAD to be a mediator of tuberin's effects on the regulation of apoptosis. Tuberin interferes with insulin-like growth factor-1-induced BAD Ser136 phosphorylation and cell survival. Our work proposes a model in which tuberin-mediated inhibition of p70S6K activates BAD to heterodimerize with BCL-2 and BCL-XL to promote apoptosis. A mutation of TSC2--as it occurs in TSC patients--attenuates this proapoptotic potential, underscoring the relevance of our findings for human pathophysiology.

Quantitative analysis of the Ge concentration in a SiGe quantum well: comparison of low-energy RBS and SIMS measurements

The germanium concentration and the position and thickness of the quantum well in molecular beam epitaxy (MBE)-grown SiGe were quantitatively analyzed via low-energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). In these samples, the concentrations of Si and Ge were assumed to be constant, except for the quantum well, where the germanium concentration was lower. The thickness of the analyzed quantum well was about 12 nm and it was situated at a depth of about 60 nm below the surface. A dip showed up in the RBS spectra due to the lower germanium concentration in the quantum well, and this was evaluated. Good depth resolution was required in order to obtain quantitative results, and this was obtained by choosing a primary energy of 500 keV and a tilt angle of 51 degrees with respect to the surface normal. Quantitative information was deduced from the raw data by comparing it with SIMNRA simulated spectra. The SIMS measurements were performed with oxygen primary ions. Given the response function of the SIMS instrument (the SIMS depth profile of the germanium delta (delta) layer), and using the forward convolution (point-to-point convolution) model, it is possible to determine the germanium concentration and the thickness of the analyzed quantum well from the raw SIMS data. The aim of this work was to compare the results obtained via RBS and SIMS and to show their potential for use in the semiconductor and microelectronics industry. The detection of trace elements (here the doping element antimony) that could not be evaluated with RBS in low-energy mode is also demonstrated using SIMS instead.

Forecasting the Prognosis of Choroidal Melanoma with an Artificial Neural Network

PURPOSE

To develop an artificial neural network (ANN) that will forecast the 5-year mortality from choroidal melanoma.

DESIGN

Retrospective, comparative, observational cohort study.

PARTICIPANTS

One hundred fifty-three eyes of 153 consecutive patients with choroidal melanoma (age, 58.4+/-14.6 years) who were treated with ruthenium 106 brachytherapy between 1988 and 1998 at the Department of Ophthalmology, Hadassah University Hospital, Jerusalem, Israel.

METHODS

Patients were observed clinically and ultrasonographically (A- and B-mode standardized ultrasonography). Metastatic screening included liver function tests and liver imaging. Backpropagation ANNs composed of 3 or 4 layers of neurons with various types of transfer functions and training protocols were assessed for their ability to predict the 5-year mortality. The ANNs were trained on 77 randomly selected patients and tested on a different set of 76 patients. Artificial neural networks were compared based on their sensitivity, specificity, forecasting accuracy, area under the receiver operating curves, and likelihood ratios (LRs). The best ANN was compared with the results of logistic regression and the performance of an ocular oncologist.

MAIN OUTCOME

The ability of the ANNs to forecast the 5-year mortality from choroidal melanoma.

RESULTS

Thirty-one patients died during the follow-up period of metastatic choroidal melanoma. The best ANN (one hidden layer of 16 neurons) had 84% forecasting accuracy and an LR of 31.5. The number of hidden neurons significantly influenced the ANNs' performance (P<0.001). The performance of the ANNs was not significantly influenced by the training protocol, the number of hidden layers, or the type of transfer function. In comparison, logistic regression reached 86% forecasting accuracy, with a very low LR (0.8), whereas the human expert forecasting ability was <70% (LR, 1.85).

CONCLUSIONS

Artificial neural networks can be used for forecasting the prognosis of choroidal melanoma and may support decision-making in treating this malignancy.

14-3-3 proteins are involved in the regulation of mammalian cell proliferation

The 14-3-3 proteins are a family of abundant, widely expressed acidic polypeptides. The seven isoforms interact with over 70 different proteins. 14-3-3 isoforms have been demonstrated to be involved in the control of positive as well as negative regulators of mammalian cell proliferation. Here we used the approach of inactivating 14-3-3 protein functions via overexpression of dominant negative mutants to analyse the role of 14-3-3 proteins in mammalian cell proliferation. We found 14-3-3 dominant negative mutants to downregulate the proliferation rates of HeLa cells. Overexpression of these dominant negative mutants triggers upregulation of the protein levels of the cyclin-dependent kinase inhibitor p27, a major negative cell cycle regulator. In addition, they downregulate the protein levels of the important cell cycle promoter cyclin D1. These data provide new insights into mammalian cell proliferation control and allow a better understanding of the functions of 14-3-3 proteins.