Case report: Management of pediatric gigantism caused by the TADopathy, X-linked acrogigantism.

X-linked acrogigantism (X-LAG) is a rare form of pituitary gigantism that is associated with growth hormone (GH) and prolactin-secreting pituitary adenomas/pituitary neuroendocrine tumors (PitNETs) that develop in infancy. It is caused by a duplication on chromosome Xq26.3 that leads to the misexpression of the gene GPR101, a constitutively active stimulator of pituitary GH and prolactin secretion. GPR101 normally exists within its own topologically associating domain (TAD) and is insulated from surrounding regulatory elements. X-LAG is a TADopathy in which the duplication disrupts a conserved TAD border, leading to a neo-TAD in which ectopic enhancers drive GPR101 over-expression, thus causing gigantism. Here we trace the full diagnostic and therapeutic pathway of a female patient with X-LAG from 4C-seq studies demonstrating the neo-TAD through medical and surgical interventions and detailed tumor histopathology. The complex nature of treating young children with X-LAG is illustrated, including the achievement of hormonal control using a combination of neurosurgery and adult doses of first-generation somatostatin analogs.

Adipocyte-Breast Cancer Cell Co-Culture in Transwells.

Experiments with cell co-culture systems facilitate investigation of the effects of one cell population on another, when the cells are grown in close proximity. Here we describe co-culture of Simpson-Golabi-Behmel syndrome (SGBS) adipocyte cells with the MCF-7 breast cancer cell line using the Corning® Transwell® 12-mm, 0.4-µm pore polyester membrane insert cell culture system. The SGBS adipocyte cell line, which was developed from cells taken from an infant with Simpson-Golabi-Behmel syndrome is comparable, both functionally and biochemically, to primary preadipocytes. The MCF-7 breast cancer cell line is an ER+/PR+ and HER2- line used very commonly in studies of breast malignancy. Consisting of insert supports with a permeable membrane 'floor,' which sit suspended in wells, the Corning® Transwell® co-culture system allows communication between physically separate cells cultured on the membrane and in the well beneath. This co-culture procedure described here can be applied to analyze the effects of cancer cells on the process of adipogenesis and the changes in cancer cells due to adipocyte-secreted factors.

RET signalling provides tumorigenic mechanism and tissue specificity for AIP-related somatotrophinomas.

It is unclear how loss-of-function germline mutations in the widely-expressed co-chaperone AIP, result in young-onset growth hormone secreting pituitary tumours. The RET receptor, uniquely co-expressed in somatotrophs with PIT1, induces apoptosis when unliganded, while RET supports cell survival when it is bound to its ligand. We demonstrate that at the plasma membrane, AIP is required to form a complex with monomeric-intracellular-RET, caspase-3 and PKCδ resulting in PIT1/CDKN2A-ARF/p53-apoptosis pathway activation. AIP-deficiency blocks RET/caspase-3/PKCδ activation preventing PIT1 accumulation and apoptosis. The presence or lack of the inhibitory effect on RET-induced apoptosis separated pathogenic AIP variants from non-pathogenic ones. We used virogenomics in neonatal rats to demonstrate the effect of mutant AIP protein on the RET apoptotic pathway in vivo. In adult male rats altered AIP induces elevated IGF-1 and gigantism, with pituitary hyperplasia through blocking the RET-apoptotic pathway. In females, pituitary hyperplasia is induced but IGF-1 rise and gigantism are blunted by puberty. Somatotroph adenomas from pituitary-specific Aip-knockout mice overexpress the RET-ligand GDNF, therefore, upregulating the survival pathway. Somatotroph adenomas from patients with or without AIP mutation abundantly express GDNF, but AIP-mutated tissues have less CDKN2A-ARF expression. Our findings explain the tissue-specific mechanism of AIP-induced somatotrophinomas and provide a previously unknown tumorigenic mechanism, opening treatment avenues for AIP-related tumours.

A Case of Luscan-Lumish Syndrome: Possible Involvement of Enhanced GH Signaling.

CONTEXT: Luscan-Lumish syndrome (LLS) is characterized by postnatal overgrowth, obesity, Chiari I malformation, seizures, and intellectual disability. SET domain-containing protein 2 (SETD2) is a histone methyltransferase, where mutations in the gene are associated with the development of LLS. However, mechanisms underlying LLS remain unclear. CASE DESCRIPTION: A 20-year-old man was referred to our hospital because of tall stature. His body height was 188.2 cm (+3.18 SD) and he showed obesity with a body mass index of 28.4 kg/m2. He exhibited acral overgrowth, jaw malocclusion, and prognathism, but no history of seizures, intellectual disability, or speech delay. Serum growth hormone (GH), insulin-like growth factor 1 (IGF-1), and nadir GH levels after administration of 75 g oral glucose were within normal range. Pituitary magnetic resonance imaging showed no pituitary adenoma, but Chiari I malformation. Whole exome sequencing analysis of the proband revealed a de novo heterozygous germline mutation in SETD2 (c.236T>A, p.L79H). Skin fibroblasts derived from the patient grew faster than those from his father and the control subject. In addition, these cells showed enhanced tyrosine phosphorylation and transcriptional activity of signal transducer and activator of transcription 5b (STAT5b) and increased IGF-1 expression induced by GH. CONCLUSION: This is a mild case of LLS with a novel mutation in SETD2 without neurological symptoms. LLS should be differentiated in a patient with gigantism without pituitary tumors. Although further investigation is necessary, this is the first study to suggest the involvement of aberrant GH signaling in the development of LLS.

CD90 Is Dispensable for White and Beige/Brown Adipocyte Differentiation.

Brown adipose tissue (BAT) is a thermogenic organ in rodents and humans. In mice, the transplantation of BAT has been successfully used to combat obesity and its comorbidities. While such beneficial properties of BAT are now evident, the developmental and cellular origins of brown, beige, and white adipocytes have remained only poorly understood, especially in humans. We recently discovered that CD90 is highly expressed in stromal cells isolated from human white adipose tissue (WAT) compared to BAT. Here, we studied whether CD90 interferes with brown or white adipogenesis or white adipocyte beiging. We applied flow cytometric sorting of human adipose tissue stromal cells (ASCs), a CRISPR/Cas9 knockout strategy in the human Simpson-Golabi-Behmel syndrome (SGBS) adipocyte model system, as well as a siRNA approach in human approaches supports the hypothesis that CD90 affects brown or white adipogenesis or white adipocyte beiging in humans. Taken together, our findings call the conclusions drawn from previous studies, which claimed a central role of CD90 in adipocyte differentiation, into question.

GPR101 drives growth hormone hypersecretion and gigantism in mice via constitutive activation of Gs and Gq/11.

Growth hormone (GH) is a key modulator of growth and GH over-secretion can lead to gigantism. One form is X-linked acrogigantism (X-LAG), in which infants develop GH-secreting pituitary tumors over-expressing the orphan G-protein coupled receptor, GPR101. The role of GPR101 in GH secretion remains obscure. We studied GPR101 signaling pathways and their effects in HEK293 and rat pituitary GH3 cell lines, human tumors and in transgenic mice with elevated somatotrope Gpr101 expression driven by the rat Ghrhr promoter (GhrhrGpr101). Here, we report that Gpr101 causes elevated GH/prolactin secretion in transgenic GhrhrGpr101 mice but without hyperplasia/tumorigenesis. We show that GPR101 constitutively activates not only Gs, but also Gq/11 and G12/13, which leads to GH secretion but not proliferation. These signatures of GPR101 signaling, notably PKC activation, are also present in human pituitary tumors with high GPR101 expression. These results underline a role for GPR101 in the regulation of somatotrope axis function.

Pseudoacromegaly.

Individuals with acromegaloid physical appearance or tall stature may be referred to endocrinologists to exclude growth hormone (GH) excess. While some of these subjects could be healthy individuals with normal variants of growth or physical traits, others will have acromegaly or pituitary gigantism, which are, in general, straightforward diagnoses upon assessment of the GH/IGF-1 axis. However, some patients with physical features resembling acromegaly - usually affecting the face and extremities -, or gigantism - accelerated growth/tall stature - will have no abnormalities in the GH axis. This scenario is termed pseudoacromegaly, and its correct diagnosis can be challenging due to the rarity and variability of these conditions, as well as due to significant overlap in their characteristics. In this review we aim to provide a comprehensive overview of pseudoacromegaly conditions, highlighting their similarities and differences with acromegaly and pituitary gigantism, to aid physicians with the diagnosis of patients with pseudoacromegaly.

In vitro profiling of volatile organic compounds released by Simpson-Golabi-Behmel syndrome adipocytes.

Breath analysis offers a non-invasive and rapid diagnostic method for detecting various volatile organic compounds that could be indicators for different diseases, particularly metabolic disorders including type 2 diabetes mellitus. The development of type 2 diabetes mellitus is closely linked to metabolic dysfunction of adipose tissue and adipocytes. However, the VOC profile of human adipocytes has not yet been investigated. Gas chromatography with mass spectrometric detection and head-space needle trap extraction (two-bed Carbopack X/Carboxen 1000 needle traps) were applied to profile VOCs produced and metabolised by human Simpson Golabi Behmel Syndrome adipocytes. In total, sixteen compounds were identified to be related to the metabolism of the cells. Four sulphur compounds (carbon disulphide, dimethyl sulphide, ethyl methyl sulphide and dimethyl disulphide), three heterocyclic compounds (2-ethylfuran, 2-methyl-5-(methyl-thio)-furan, and 2-pentylfuran), two ketones (acetone and 2-pentanone), two hydrocarbons (isoprene and n-heptane) and one ester (ethyl acetate) were produced, and four aldehydes (2-methyl-propanal, butanal, pentanal and hexanal) were found to be consumed by the cells of interest. This study presents the first profile of VOCs formed by human adipocytes, which may reflect the activity of the adipose tissue enzymes and provide evidence of their active role in metabolic regulation. Our data also suggest that a previously reported increase of isoprene and sulphur compounds in diabetic patients may be explained by their production by adipocytes. Moreover, the unique features of this profile, including a high emission of dimethyl sulphide and the production of furan-containing VOCs, increase our knowledge about metabolism in adipose tissue and provide diagnostic potential for future applications.

Impact of X-ray Exposure on the Proliferation and Differentiation of Human Pre-Adipocytes.

Radiotherapy is a widely used treatment option for cancer patients as well as for patients with musculoskeletal disorders. Adipocytes, the dominant cell type of adipose tissue, are known to constitute an active part of the tumor microenvironment. Moreover, adipocytes support inflammatory processes and cartilage degradation in chronic inflammatory diseases, i.e., rheumatoid and osteoarthritis. Since the production of inflammatory factors is linked to their differentiation stages, we set out to explore the radiation response of pre-adipocytes that may influence their inflammatory potential and differentiation capacity. This is the first study investigating the effects of X-ray irradiation on the proliferation and differentiation capacity of human primary pre-adipocytes, in comparison to Simpson⁻Golabi⁻Behmel Syndrome (SGBS) pre-adipocytes, an often-used in vitro model of human primary pre-adipocytes. Our results demonstrate a dose-dependent reduction of the proliferation capacity for both cell strains, whereas the potential for differentiation was mostly unaffected by irradiation. The expression of markers of adipogenic development, such as transcription factors (PPARγ, C/EBPα and C/EBPß), as well as the release of adipokines (visfatin, adiponectin and leptin) were not significantly changed upon irradiation. However, after irradiation with high X-ray doses, an increased lipid accumulation was observed, which suggests a radiation-induced response of adipocytes related to inflammation. Our results indicate that pre-adipocytes are radio-resistant, and it remains to be elucidated whether this holds true for the overall inflammatory response of adipocytes upon irradiation.

Simpson-Golabi-Behmel syndrome human adipocytes reveal a changing phenotype throughout differentiation.

The Simpson-Golabi-Behmel syndrome (SGBS) cell strain is widely considered to be a representative in vitro model of human subcutaneous white pre-adipocytes. These cells achieve a transient expression of classical brown markers, such as uncoupling protein 1, peaking at day 14 of differentiation and decreasing thereafter. Adipocyte browning process involves dynamic changes in lipid droplet (LD) dimension, in mitochondria morphology, and in the expression of brown-specific marker genes. This study analyzes SGBS transient phenotypic transformation by quantifying the heterogeneity of LDs, mitochondrial dynamics, and a panel of genes involved in adipocyte differentiation and browning. LDs at 21 days of differentiation were larger than in the previous stages, without any change in the number per cell. The expression of genes such as peroxisome peroxisome proliferator-activated receptor γ, leptin, and lipase E significantly raised from 0 to 21 days. Adiponectin was significantly upregulated at 14 days of differentiation. Brown-specific marker PR domain containing 16 was highly expressed at D0. The variability of mitochondrial shape and interconnectivity reflects differences in the relative rates of fusion and fission, resulting in a significant shift from a networked shape at D7 to a fragmented and swollen one at D14 and D21. The transient phenotype experienced by this cellular model should be considered whether used in studies involving the stimulation of adipocyte browning and could be an interesting human model to further elucidate the browning process in the absence of any stimulation.

DEHP deregulates adipokine levels and impairs fatty acid storage in human SGBS-adipocytes.

DEHP is a plasticizer which has been used in plastic products of everyday use for decades. Studies in mice and murine cell culture models identified DEHP as an endocrine disruptor that may also act as an obesogen. As this is of high concern in respect of the worldwide obesity epidemic, our aim is the translation of these findings into a human model system. On the basis of DOHaD, we investigated the influence of an environmentally relevant dose of DEHP [50 µg/ml] on adipogenesis in the human cell culture model SGBS. Pre-adipocytes were exposed to DEHP and differentiated into mature adipocytes. At different stages of differentiation, markers of adipogenesis like GLUT4, FABP4, LPL and PPARs, and of signaling pathways like AMPK/ACC2, JAK/STAT and MAPK were analyzed. Functional markers like adipokine secretion and triglyceride content as well as ROS production were measured in mature adipocytes. We found significantly lower expression levels of adipogenic markers, a reduction in lipid accumulation, higher leptin- and reduced adiponectin levels in the supernatant of treated adipocytes. Moreover, ROS production was significantly elevated after DEHP-exposure. In conclusion, DEHP led to lower grade of adipogenic differentiation in human SGBS-adipocytes under the chosen conditions.

miR-146a-mediated suppression of the inflammatory response in human adipocytes.

The obesity-associated inflammation of white adipose tissue (WAT) is one of the factors leading to the development of related diseases such as insulin resistance and liver steatosis. Recently, microRNAs (miRNAs) were identified as important regulators of WAT functions. Herein, we cultured human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes with macrophage-conditioned medium (MacCM) and performed an Affimetrix miRNA array to identify miRNAs differentially expressed under inflammatory conditions. We identified 24 miRNAs differentially expressed upon inflammation in human adipocytes and miR-146a was the most up-regulated miRNA species. In subcutaneous WAT, miR-146a was elevated in both human and murine obesity. Transfection of miR-146a mimics prevented the MacCM-induced inflammatory response in SGBS adipocytes as seen by reduced levels of IL-8 and MCP-1 mRNA and protein. We identified IRAK1 and TRAF6 as targets of miR-146a in human adipocytes and detected a reduced inflammation-induced activation of JNK and p38 upon miR-146a transfection. Taken together, we could show that miR-146a reduces the inflammatory response in human adipocytes. In a negative feedback loop miR-146a might contribute to the regulation of inflammatory processes in WAT and possibly prevent an overwhelming inflammatory response.

Delayed Intervention With Pyridoxamine Improves Metabolic Function and Prevents Adipose Tissue Inflammation and Insulin Resistance in High-Fat Diet-Induced Obese Mice.

Obesity is associated with an increased risk for the development of type 2 diabetes and vascular complications. Advanced glycation end products are increased in adipose tissue and have been associated with insulin resistance, vascular dysfunction, and inflammation of adipose tissue. Here, we report that delayed intervention with pyridoxamine (PM), a vitamin B6 analog that has been identified as an antiglycating agent, protected against high-fat diet (HFD)-induced body weight gain, hyperglycemia, and hypercholesterolemia, compared with mice that were not treated. In both HFD-induced and db/db obese mice, impaired glucose metabolism and insulin resistance were prevented by PM supplementation. PM inhibited the expansion of adipose tissue and adipocyte hypertrophy in mice. In addition, adipogenesis of murine 3T3-L1 and human Simpson-Golabi-Behmel Syndrome preadipocytes was dose- and time-dependently reduced by PM, as demonstrated by Oil Red O staining and reduced expression of adipogenic differentiation genes. No ectopic fat deposition was found in the liver of HFD mice. The high expression of proinflammatory genes in visceral adipose tissue of the HFD group was significantly attenuated by PM. Treatment with PM partially prevented HFD-induced mild vascular dysfunction. Altogether, these findings highlight the potential of PM to serve as an intervention strategy in obesity.

Weight loss-induced stress in subcutaneous adipose tissue is related to weight regain.

Initial successful weight loss is often followed by weight regain after the dietary intervention. Compared with lean people, cellular stress in adipose tissue is increased in obese subjects. However, the relation between cellular stress and the risk for weight regain after weight loss is unclear. Therefore, we determined the expression levels of stress proteins during weight loss and weight maintenance in relation to weight regain. In vivo findings were compared with results from in vitro cultured human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes. In total, eighteen healthy subjects underwent an 8-week diet programme with a 10-month follow-up. Participants were categorised as weight maintainers or weight regainers (WR) depending on their weight changes during the intervention. Abdominal subcutaneous adipose tissue biopsies were obtained before and after the diet and after the follow-up. In vitro differentiated SGBS adipocytes were starved for 96 h with low (0·55 mm) glucose. Levels of stress proteins were determined by Western blotting. WR showed increased expressions of ß-actin, calnexin, heat shock protein (HSP) 27, HSP60 and HSP70. Changes of ß-actin, HSP27 and HSP70 are linked to HSP60, a proposed key factor in weight regain after weight loss. SGBS adipocytes showed increased levels of ß-actin and HSP60 after 96 h of glucose restriction. The increased level of cellular stress proteins in the adipose tissue of WR probably resides in the adipocytes as shown by in vitro experiments. Cellular stress accumulated in adipose tissue during weight loss may be a risk factor for weight regain.

Functional characterization of retromer in GLUT4 storage vesicle formation and adipocyte differentiation.

Insulin-stimulated translocation of glucose transporter 4 (GLUT4) storage vesicles (GSVs), the specialized intracellular compartments within mature adipocytes, to the plasma membrane (PM) is a fundamental cellular process for maintaining glucose homeostasis. Using 2 independent adipocyte cell line models, human primary Simpson-Golabi-Behmel syndrome and mouse 3T3-L1 fibroblast cell lines, we demonstrate that the endosome-associated protein-sorting complex retromer colocalizes with GLUT4 on the GSVs by confocal microscopy in mature adipocytes. By use of both confocal microscopy and differential ultracentrifugation techniques, retromer is redistributed to the PM of mature adipocytes upon insulin stimulation. Furthermore, stable knockdown of the retromer subunit-vacuolar protein-sorting 35, or the retromer-associated protein sorting nexin 27, by lentivirus-delivered small hairpin RNA impaired the adipogenesis process when compared to nonsilence control. The knockdown of retromer decreased peroxisome proliferator activated receptor γ expression during differentiation, generating adipocytes with decreased levels of GSVs, lipid droplet accumulation, and insulin-stimulated glucose uptake. In conclusion, our study demonstrates a role for retromer in the GSV formation and adipogenesis.

GHRH excess and blockade in X-LAG syndrome.

X-linked acrogigantism (X-LAG) syndrome is a newly described form of inheritable pituitary gigantism that begins in early childhood and is usually associated with markedly elevated GH and prolactin secretion by mixed pituitary adenomas/hyperplasia. Microduplications on chromosome Xq26.3 including the GPR101 gene cause X-LAG syndrome. In individual cases random GHRH levels have been elevated. We performed a series of hormonal profiles in a young female sporadic X-LAG syndrome patient and subsequently undertook in vitro studies of primary pituitary tumor culture following neurosurgical resection. The patient demonstrated consistently elevated circulating GHRH levels throughout preoperative testing, which was accompanied by marked GH and prolactin hypersecretion; GH demonstrated a paradoxical increase following TRH administration. In vitro, the pituitary cells showed baseline GH and prolactin release that was further stimulated by GHRH administration. Co-incubation with GHRH and the GHRH receptor antagonist, acetyl-(d-Arg(2))-GHRH (1-29) amide, blocked the GHRH-induced GH stimulation; the GHRH receptor antagonist alone significantly reduced GH release. Pasireotide, but not octreotide, inhibited GH secretion. A ghrelin receptor agonist and an inverse agonist led to modest, statistically significant increases and decreases in GH secretion, respectively. GHRH hypersecretion can accompany the pituitary abnormalities seen in X-LAG syndrome. These data suggest that the pathology of X-LAG syndrome may include hypothalamic dysregulation of GHRH secretion, which is in keeping with localization of GPR101 in the hypothalamus. Therapeutic blockade of GHRH secretion could represent a way to target the marked hormonal hypersecretion and overgrowth that characterizes X-LAG syndrome.

Parathyroid Hormone is Related to Dysplasia and a Higher Rate of Distal Colorectal Adenoma in Women but Not Men.

Molecular and clinical observations provide evidence for a potential role of parathyroid hormone (PTH) in colorectal cancer development. We therefore aimed to assess the association of PTH with regard to colorectal cancer precursor lesions. A cohort of 1432 participants, 777 men, 58.4 ± 9.6 years and 701 women, 59.1 ± 10.6 years, undergoing screening colonoscopy were allocated to PTH serum concentrations either above or below 55 ng/L. The number, localization, size, and histology of the polypoid lesions detected during screening colonoscopy were recorded according to PTH serum concentrations. Serum PTH concentrations were not different between men and women. Women with PTH serum concentrations above the cut-off had significantly more adenomas (13/40; 32.5%) of the distal colon compared to women below the cut-off (91/659; 13.8%; P = 0.001). Additionally, the rate of dysplasia in adenomas of the distal colon was higher in women with high compared to low PTH concentrations (P = 0.001). These findings remained robust after adjustments for serum vitamin D, age, plasma creatinine, BMI, diabetes, and liver steatosis. No associations were observed between serum PTH concentrations and colorectal lesions in men. These data suggest that elevated PTH serum concentrations might have a role in colorectal cancer development as indicated by higher rates of adenomas, specifically with dysplasia, in women. The role of PTH in colon carcinogenesis and its sex specificity deserve further study.

TNF-related apoptosis-inducing ligand promotes human preadipocyte proliferation via ERK1/2 activation.

Upon obesity, adipose tissue is excessively expanded and characterized by pathologic processes like hypoxia, fibrosis, and inflammation. Death ligands belonging to the TNF superfamily such as TNF-α are important contributors to these derangements and exert a pronounced influence on the metabolic and cellular homeostasis of adipose tissue. Here, we sought to identify the effect of the death ligand TNF-related apoptosis-inducing ligand (TRAIL) on the adipose tissue precursor cell pool and therefore investigated its influence on preadipocyte proliferation. Treatment of human preadipocytes with TRAIL resulted in a time- and dose-dependent increase in proliferation (EC50 3.4 ng/ml) comparable to IGF-1. Although no apoptosis was observed, TRAIL triggered a rapid cleavage of caspase-8 and -3. Neither inhibition of caspase activity by zVAD.fmk (20 µM) nor ablation of caspase-8 expression by lentivirus-delivered small hairpin RNA (shRNA) abolished the proliferative response. TRAIL triggered a delayed and sustained activation of ERK1/2, leaving Akt, p38, JNK, and NF-κB unaffected. Importantly, inhibition of ERK1/2 activation by PD0325901 (300 nM) or AZD6244 (5 or 10 µM) completely abolished the proliferative response. We thus reveal a hitherto unknown function of TRAIL in regulating adipose tissue homeostasis by promoting the proliferation of tissue-resident precursor cells.

Genetic characterization of p27(kip1) and stathmin in controlling cell proliferation in vivo.

The CDK inhibitor p27(kip1) is a critical regulator of cell cycle progression, but the mechanisms by which p27(kip1) controls cell proliferation in vivo are still not fully elucidated. We recently demonstrated that the microtubule destabilizing protein stathmin is a relevant p27(kip1) binding partner. To get more insights into the in vivo significance of this interaction, we generated p27(kip1) and stathmin double knock-out (DKO) mice. Interestingly, thorough characterization of DKO mice demonstrated that most of the phenotypes of p27(kip1) null mice linked to the hyper-proliferative behavior, such as the increased body and organ weight, the outgrowth of the retina basal layer and the development of pituitary adenomas, were reverted by co-ablation of stathmin. In vivo analyses showed a reduced proliferation rate in DKO compared to p27(kip1) null mice, linked, at molecular level, to decreased kinase activity of CDK4/6, rather than of CDK1 and CDK2. Gene expression profiling of mouse thymuses confirmed the phenotypes observed in vivo, showing that DKO clustered with WT more than with p27 knock-out tissue. Taken together, our results demonstrate that stathmin cooperates with p27(kip1) to control the early phase of G1 to S phase transition and that this function may be of particular relevance in the context of tumor progression.