The lack of cyclin kinase inhibitor p27(Kip1) ameliorates progression of diabetic nephropathy

Cyclin kinase inhibitor p27(Kip(1)) (p27) has been shown to be upregulated in glomeruli of diabetic animals and mesangial cells cultured under high glucose. This study was an investigation of the role of p27 in the progression of diabetic nephropathy. Mice deficient in p27 (p27 -/-) and wild-type mice (p27 +/+) were studied 12 wk after diabetes induction by streptozotocin. Blood glucose and BP were comparable between diabetic p27 +/+ and p27 -/- mice. The kidney weight to body weight ratio and glomerular volume increased in diabetic p27 +/+ mice. In contrast, these parameters did not change in diabetic p27 -/- mice. Similarly, albuminuria developed in diabetic p27 +/+ mice but not in diabetic p27 -/- mice. The mesangial expansion was significantly milder in diabetic p27 -/- mice than that in diabetic p27 +/+ mice. These changes were associated with a similar increase in glomerular TGF-beta expression in diabetic p27 +/+ and p27 -/- mice. However, glomerular protein expression of fibronectin, a target of TGF-beta, increased only in diabetic p27 +/+ mice. In mesangial cells cultured from p27 +/+ mice, exposure to high glucose caused significant increases in total protein content and [(3)H]-leucine incorporation. On the other hand, high glucose caused a significant reduction in these parameters in cells from p27 -/- mice. Phosphorylation of 4E-BP1, the translation inhibitor, increased after exposure to high glucose in p27 +/+ cells. In p27 -/- cells, the level of phosphorylated 4E-BP1 was higher than that in control p27 +/+ cells and decreased under high glucose conditions. In conclusion, renal hypertrophy, glomerular hypertrophy, and albuminuria did not develop, and mesangial expansion was milder in diabetic p27 -/- mice despite glomerular TGF-beta upregulation. These results suggest that controlling p27 function may ameliorate diabetic nephropathy.     

Role of the CDK Inhibitor p27 (Kip1) in Mammary Development and Carcinogenesis: Insights from Knockout Mice

The cyclin-dependent kinase inhibitor p27 (Kip1) is an important cell cycle regulatory gene in breast cancer, and decreased p27 expression is associated with poor prognosis. Some investigations of its role in mammary development have demonstrated reduced cyclin D1 expression and consequent lack of lobuloalveolar development, but others have found increased cyclin E-Cdk2 activity and increased proliferation balanced by increased apoptosis. It is unclear at present why these apparently divergent results have been obtained. Mice with reduced p27 gene dosage alone do not develop mammary carcinomas but do display substantially shorter tumor latency upon overexpression of erbB2, consistent with a role for p27 as a mammary tumor suppressor gene. In this review we summarize these and other data addressing the role of p27 in normal mammary epithelium and experimental models of mammary carcinogenesis.     

Loss of p27(Kip1) accelerates DNA replication after partial hepatectomy in mice

BACKGROUND: Liver regeneration after partial hepatectomy (PH) is accomplished by a synchronous replication of hepatocytes. Both positive and negative regulators of cyclin-dependent protein kinase (Cdk) have been implicated in hepatocyte proliferation, but their specific roles in vivo remain to be clarified. To investigate the specific role of p27(Kip1), a member of the Cip/Kip family of Cdk inhibitors, in cell-cycle regulation during liver regeneration, p27-knockout mice were studied after PH. MATERIALS AND METHODS: Under ether anesthesia, mice were subjected to 70% PH. Animals were sacrificed at intervals after the surgery, and the remnant liver was harvested and analyzed. RESULTS: In p27-deficient mice, the timing of DNA synthesis was significantly accelerated with a perturbation in the ordered distribution of proliferating cells in the hepatic lobule. p27 deficiency, however, did not affect the whole population of cycling cells, the number of apoptotic cells, or liver injury and mortality after PH. CONCLUSION: These data provide in vivo evidence that p27 functions as a brake in the "start" of the hepatocyte cell cycle, thereby coordinating temporally and spatially the onset of DNA synthesis of hepatocytes within the hepatic lobules.     

12-脂氧化酶对糖尿病肾病鼠肾小球p27kip1表达的影响

目的 探讨12-脂氧化酶(12-LO)对糖尿病肾病肾小球内p27kip1表达的影响。方法 在有或无p38 MAPK（p38）抑制剂（SB203580,1 μmol/L）的条件下,用12-LO作用产物12羟二十烷四烯酸[ 12(S)-HETE,10－7 mmol/L]刺激系膜细胞24 h。雄性SD大鼠分为普通饮食对照组、普通饮食+12-LO抑制剂（CDC,8 mg/kg,3次/周,皮下注射）处理组、高脂饮食结合小剂量链脲菌素（STZ,35 mg/kg,腹腔注射）诱导2型糖尿病组、高脂饮食结合小剂量STZ诱导2型糖尿病+CDC处理组,连续皮下注射CDC 1个月。野生型和12-LO基因敲除C57BL/6小鼠随机分成野生型对照组、12-LO基因敲除组、野生型STZ（200 mg/kg,腹腔注射）诱导1型糖尿病组、12-LO基因敲除STZ诱导1型糖尿病组,饲养16周。实验结束后收集尿、血液、提取肾脏,用系列过筛方法分离肾小球。Western印迹和免疫组织化学方法检测p38 活性和p27kip1蛋白表达的变化。 结果 抑制p38 活性可有效阻断12(S)-HETE诱导的系膜细胞内p27kip1的表达（P < 0.01）。CDC可抑制2型糖尿病大鼠肾小球体积增大,降低尿白蛋白量（24 h）,阻止肾小球内p38 活性和p27kip1蛋白表达增加,与CDC未处理2型糖尿病大鼠比较差异均有统计学意义（均P < 0.01）。与野生型糖尿病小鼠比较,12-LO基因敲除糖尿病小鼠p38活性、p27kip1蛋白表达及细胞外基质积聚显著减少,差异有统计学意义（均P < 0.01）。 结论 12-LO可通过p38通路上调糖尿病肾小球内p27kip1的表达。     

Anomalous overexpression of p27(Kip1) in sporadic pancreatic endocrine tumors

BACKGROUND: Little is known about the cellular defects and molecular mechanisms leading to pancreatic endocrine tumors (PETs). p27(Kip1) is a universal cyclin-dependent kinase inhibitor (CDKI), which acts as a tumor suppressor and a negative regulator of cell cycle. From previous reports, quiescent cells show high levels of p27(Kip1) expression while neoplastic and proliferating cells show no detectable p27(Kip1) expression. We hypothesize that in malignant sporadic PETs, p27(Kip1) expression would be decreased compared with benign PETs and normal pancreatic tissue. METHODS: Western analysis was performed on 28 PETs (7 malignant, 21 benign), 2 nonendocrine cell lines, and 5 endocrine cell lines. Signal intensities were quantitated using densitometry and standardized to normal pancreas. RESULTS: Unexpectedly, increased p27(Kip1) expression as compared with control was seen in both benign and malignant tumors, as well as in all four pancreatic islet tumor cell lines, but not fibroblast or pituitary cell lines, evaluated. There was no difference in p27(Kip1) level between benign and malignant tumors. CONCLUSION: This represents the first report of anomalous p27(Kip1) overexpression in sporadic PETs, and is part of a growing literature describing the paradoxical overexpression of p27(Kip1) in human tumors that includes other endocrine tumors. These studies suggest a unique molecular pathway leading to endocrine tumorigenesis.     

Cell cycle inhibitors (p27Kip1 and p21CIP1) cause hypertrophy in LLC-PK1 cells.

BACKGROUND: Angiotensin II has been reported to induce renal tubular hypertrophy, but the mechanisms of this hypertrophy are not well known. We evaluated the roles of cyclin-dependent kinase (CDK) inhibitors in renal tubular hypertrophy. METHODS: To elucidate whether CDK inhibitors cause renal tubular hypertrophy, we produced adenovirus vectors containing coding sequences of the CDK inhibitors p27Kip1 (AxCAp27), p21CIP1 (AxCAp21), and p16INK4 (AxCAp16), and we investigated the effect of these gene transfers on epidermal growth factor (EGF)-induced proliferation in LLC-PK1 cells. We evaluated the cell cycle and hypertrophy by measurements of the [3H]-leucine and [3H]-thymidine incorporation, the protein:DNA ratio, flow cytometry, and CDK4 and CDK2 kinase assays. RESULTS: AxCAp27 and AxCAp21 caused significant increases in [3H]-leucine incorporation and the protein:DNA ratio but did not change the [3H]-thymidine incorporation. Conversely, AxCAp16 inhibited EGF-stimulated [3H]-thymidine incorporation but did not change the [3H]-leucine incorporation. AxCAp27, AxCAp21, and AxCAp16 all inhibited EGF-stimulated CDK4 kinase activity (to 15.6, 14.1, and 21.9% of control, respectively). Forward light-scatter analysis demonstrated that AxCAp27 and AxCAp21 increased the cell size but that AxCAp16 effected no change in cell size. CONCLUSION: These findings suggest that p27Kip1 and p21CIP1 may play an important role in hypertrophy of renal tubule cells by reducing pRb phosphorylation. On the other hand, p16INK4 was not found to cause hypertrophic changes in EGF-treated LLC-PK1 cells.     

Genetics of diabetic nephropathy: lessons from mice

Although diabetic nephropathy occurs only in a minority of diabetic patients (approximately 30%), it is the major single cause of end-stage renal disease in the United States. Hyperglycemia and hypertension are important factors predisposing patients to nephropathy, however, accumulating evidence points to critical genetic factors that predispose only a subset of diabetic patients to nephropathy. Defining the genes responsible for nephropathy risk in human populations has proven challenging. Comparative genomics using the robust genetic reagents available in the laboratory mouse should provide a complementary approach to defining genes that may predispose to diabetic nephropathy in mice and human beings. In this article we review studies that have started to identify genetic risk factors for diabetic nephropathy in mice and the multiple approaches that may be used to elucidate the genetic pathogenesis of this disorder.     

Identification of a common risk haplotype for diabetic nephropathy at the protein kinase C-beta1 (PRKCB1) gene locus

Abnormal activation of protein kinase C-beta isoforms in the diabetic state has been implicated in the development of diabetic nephropathy. It is thus plausible that DNA sequence differences in the protein kinase C-beta1 gene (PRKCB1), which encodes both betaI and betaII isoforms, may influence susceptibility to nephropathy. Nine single-nucleotide polymorphisms (SNP) in PRKCB1 were tested for association with diabetic nephropathy in type I diabetes mellitus, by using both case-control and family-study designs. Allele and genotype distributions of two SNP in the promoter (--1504C/T and --546C/G) differed significantly between case patients and control patients (P < 0.05). These associations were particularly strong with diabetes mellitus duration of <24 yr (P = 0.002). The risk of diabetic nephropathy was higher among carriers of the T allele of the --1504C/T SNP, compared with noncarriers (odds ratio, 2.54; 95% confidence interval, 1.39 to 4.62), and among carriers of the G allele of the --546C/G SNP (odds ratio, 2.45; 95% confidence interval, 1.37 to 4.38). Among individuals with diabetes mellitus duration of >/==" BORDER="0">24 yr, these two SNP were not associated with diabetic nephropathy. These positive findings were confirmed by using the family-based transmission disequilibrium test. The T-G haplotype, with both risk alleles, was transmitted more frequently than expected from heterozygous parents to offspring who developed diabetic nephropathy during the first 24 yr of diabetes mellitus. It is concluded that DNA sequence differences in the promoter of PRKCB1 contribute to diabetic nephropathy susceptibility in type I diabetes mellitus.     

Low expression of p27(Kip1) in advanced mucoepidermoid carcinomas of head and neck

BACKGROUND: p27(Kip1), a cyclin-dependent kinase inhibitor, negatively regulates the G1 phase progression of the cell cycle by binding to the cyclin E/cyclin-dependent kinase 2 complex. This study was done to investigate the expression of p27(Kip1) in mucoepidermoid carcinomas and its usefulness as an indicator in tumor progression, aggressiveness, and prognosis. METHODS: Thirty-one patients with mucoepidermoid carcinomas who had surgical resection were studied retrospectively. Clinicopathologic features, including histologic types, T stage, nodal status, perineural invasion, overall AJCC stage, and survival data, were obtained from medical records. Immunohistochemical staining with monoclonal antibodies against p27(Kip1) was performed on the formalin-fixed, paraffin-embedded specimens from each patient. The percentage of tumor cells expressing p27(Kip1) (labeling index) was evaluated by counting 1000 cells per slide in at least four different areas and comparing with the patients' clinicopathologic features and survival rates. RESULTS: Significant correlation was found between low p27(Kip1) expression and tumors with high-grade, advanced T stages, positive nodal status, and advanced clinical stages (p =.001 for all) except perineural invasion. Multivariate analysis indicated that p27(Kip1) expression (p =.030) was the most significant, and gender (p =.048) was the next significant predictor of overall survival among the variables. Also patients with low p27(Kip1) expression showed poor prognosis (p =.002). CONCLUSIONS: We suggest that p27(Kip1) is a reliable independent marker of tumor progression, invasiveness, and prognosis in the mucoepidermoid carcinomas.     

Molecular mechanisms of renal hypertrophy: role of p27Kip1.

There are two fundamentally different growth responses for cells comprising the nephron: hyperplasia or hypertrophy. Cells that progress through the normal cell cycle double their DNA content and eventually divide during mitosis. Those cells that hypertrophy stop the growth process in the G1-phase of the cell cycle; while they increase in size, protein and RNA content, they cannot duplicate their set of chromosomes because they never pass through the S-phase of the cell cycle. Hypertrophy may be an early compensatory mechanism to initially replace the loss of functioning tissue, however, this maladaptive process eventually fosters progressive loss of renal function. Since progression of the cell through the G1 to S-phases is regulated by cyclins D, E and A, which in turn bind and activate cyclin dependent kinases (CDKs), evidence has been accumulating on a particular CDK-inhibitor protein, p27Kip1, which is speculated to be a key to the complex process of the G1/S cell cycle transition. This article examines the mechanisms of the proliferative growth response following acute tubular necrosis, and compensatory hypertrophy of glomerular and tubule cells, with a particular focus on the protein p27Kip1.     

Survivin和p27~(Kip1)蛋白在结肠癌中的表达及临床意义

目的 探讨Survivin和p27Kip1蛋白在结肠癌中的表达及其相互关系.方法 应用免疫组织化学方法检测83例结肠癌标本和10例正常结肠黏膜组织中Survivin、p27Kip1的表达.分析Survivin、p27Kip1的表达与临床病理参数的关系.结果 Survivin在结肠癌组织中阳性表达率83.1%(69/83)明显高于在正常结肠黏膜组织中的0.0%(0/10)(P<0.01).结肠癌中Survivin的表达与临床病理参数无关(P>0.05).p27Kip1在结肠癌组织中阳性表达率41.0%(34/83)明显低于在正常结肠黏膜组织中的90%(9/10)(P<0.01).远处转移组p27Kip1阳性率(16.7%,3/18)明显低于远处无转移组(47.7%,31/65)(P<0.05).结肠癌p27Kip1表达与组织分化、肠壁浸润深度、Dukes分期有关(P<0.05).结肠癌组织中Survivin表达与p27Kip1表达未见明显相关性(P>0.05).结论 Survivin和p27Kip1蛋白在结肠癌组织中存在异常表达,提示两者在结肠癌的发生发展中起着重要的作用.结肠癌中Survivin的表达与p27Kip1蛋白的表达无相关性.     

Polymorphisms of the glucose transporter (GLUT1) gene are associated with diabetic nephropathy

BACKGROUND: Diabetic nephropathy (DN) is a major cause of morbidity and mortality in patients with type 1 diabetes mellitus. Recent studies suggest that genetic factors, including polymorphisms in the flanking region of the aldose reductase gene (5'ALR2), play an important role in the pathogenesis of nephropathy. Glucose transporter (GLUT1) activity has been implicated in renal hypertrophy and extracellular matrix formation in mesangial cells. The aim was to investigate the frequency of a polymorphism within the GLUT1 gene in 186 Caucasoid patients with type 1 diabetes and 104 normal controls. METHODS: Amplimers flanking the Xba-I polymorphic site in the second intron were employed to amplify DNA from subjects. The amplified DNA was restricted with endonuclease Xba-I, separated by gel electrophoresis, and visualized. In the absence of an Xba-I site, a fragment of 1.1 kilobase was seen, whereas fragments of 0.9 and 0.2 were generated if the Xba-I site was present. RESULTS: There was a highly significant increase in the frequency of the 1.1 allele in those patients with nephropathy (N = 70) compared with those with no proteinuria or retinopathy after 20 years of diabetes (uncomplicated N = 44, 61.4 vs. 40.9%, respectively, P < 0.001). The 1.1/1.1 genotype was also significantly increased in the nephropathy group compared with the uncomplicated group of patients (37.1 vs. 13.6%, respectively, P < 0.01). The frequency of the 1.1/1.1 genotype was similar in 30 patients with retinopathy but not nephropathy when compared with the uncomplicated group of patients (13.6 vs. 16.7%). Furthermore, only 8 out of 49 patients with DN had the Z+2 5'ALR2 DN "protective" allele and the 0.9 GLUT1 allele in contrast to 21 out of 39 uncomplicated patients (P < 0.0002). CONCLUSION: These results suggest that the GLUT1 gene together with the aldose reductase gene are associated with susceptibility to DN in patients with type 1 diabetes.     

HbA(1c) levels are genetically determined even in type 1 diabetes: evidence from healthy and diabetic twins.

HbA(1c), a measure of blood glucose regulation, reflects glucose levels in the preceding months. In diabetes, HbA(1c) levels predict the risk of microvascular complications. The aim of this study was to determine whether genetic factors could influence HbA(1c) levels in normal subjects and type 1 diabetic patients. We performed a classical twin study of HbA(1c) in healthy nondiabetic female twins and 42 monozygotic (MZ) and 47 dizygotic (DZ) pairs. Interclass correlations (r) were higher in MZ (r = 0.77) compared with DZ (r = 0.53) twin pairs, suggesting a substantial genetic effect; this was confirmed by quantitative genetic model fitting. Additive genetic effects (heritability) explained 62% (95% CI 47-75) of population variance in HbA(1c); the remainder was attributable to the influence of unique environment (23% [15-36]) and age (14% [5-28]). Multivariate modeling showed that genetic factors also have a substantial influence on fasting glucose levels (51%). However, HbA(1c) heritability could not be explained by genes in common with fasting glucose. In the patients with type 1 diabetes, HbA(1c) levels were correlated in 33 MZ twins concordant for diabetes (r = 0.68; P < 0.001) but also in 45 MZ twins discordant for the disease (r = 0.52; P < 0.001). These significant correlations for HbA(1c) in both concordant and discordant pairs indicate a diabetes-independent familial effect. Thus, HbA(1c) levels are largely genetically determined and independent of the genes influencing fasting glucose. Even in type 1 diabetes, familial (i.e., diabetes-independent) factors influence protein glycation, implying that familial factors may explain, in part, the risk for microvascular complications, as indicated by high HbA(1c) levels.     

Multifunctionality of PAI-1 in fibrogenesis: evidence from obstructive nephropathy in PAI-1-overexpressing mice

BACKGROUND: Plasminogen activator inhibitor-1 (PAI-1) has been implicated in the pathogenesis of chronic kidney disease based on its up-regulated expression and on the beneficial effects of PAI-1 inhibition or depletion in experimental models. PAI-1 is a multifunctional protein and the mechanisms that account for its profibrotic effects have not been fully elucidated. METHODS: The present study was designed to investigate PAI-1-dependent fibrogenic pathways by comparing the unilateral ureteral obstruction model (UUO) (days 3, 7, and 14) in PAI-1-overexpressing mice (PAI-1 tg) to wild-type mice, both on a C57BL6 background. RESULTS: Following UUO, total kidney PAI-1 mRNA and/or protein levels were significantly higher in the PAI-1 tg mice (N= 6 to 8/group) and fibrosis severity was significantly worse (days 3, 7, and 14), measured both as Sirius red-positive interstitial area (e.g., 10 +/- 3.2% vs. 4.5 +/- 1.0%) (day 14) and total kidney collagen (e.g., 11.1 +/- 1.7 vs. 6.2 +/- 1.3 microg/mg) (day 14). By day 14, the expression of two normal tubular proteins, E-cadherin and Ksp-cadherin, were significantly lower in the PAI-1 tg mice (3.2 +/- 0.5% vs. 11.7 +/- 5.9% and 2.6 +/- 1.6) vs. 6.2 +/- 0.8%, respectively), implying more extensive tubular damage. At least four fibrogenic pathways were differentially expressed in the PAI-1 tg mice. First, interstitial macrophage recruitment was more intense (P < 0.05 days 3 and 14). Second, interstitial myofibroblast density was greater (P < 0.05 days 3 and 7) despite similar numbers of proliferating tubulointerstitial cells. Third, transforming growth factor-beta1 (TGF-beta1) and collagen I mRNA were significantly higher. Finally, urokinase activity was significantly lower (P < 0.05 days 7 and 14) despite similar mRNA levels. Gene microarray studies documented that that the deletion of this single profibrotic gene had far-reaching consequences on renal cellular responses to chronic injury. CONCLUSION: These data provide further evidence that PAI-1 is directly involved in interstitial fibrosis and tubular damage via two primary overlapping mechanisms: early effects on interstitial cell recruitment and late effects associated with decreased urokinase activity.     

Parathyroid hyperplasia, adenomas, and carcinomas: differential expression of p27Kip1 protein

The histologic spectrum of proliferative parathyroid lesions (hyperplasia, adenoma, and carcinoma) often overlap, and differentiation between these lesions may at times be difficult. p27kip1 (p27) is a cyclin-dependent kinase inhibitor that helps regulate the transition from the G1 to the S phase of the cell cycle. Significantly higher levels of p27 expression have been detected in some normal tissues than in their neoplastic counterparts. The authors analyzed a series of parathyroid lesions to determine if expression of this cell cycle protein may be useful in distinguishing between parathyroid hyperplasia, adenomas, and carcinomas. Formalin-fixed paraffin-embedded tissues from randomly selected patients (22 histologically normal parathyroid glands, 33 cases of hyperplasia, 43 adenomas, and 17 carcinomas) were analyzed for expression of p27 by immunostaining. All cases were also immunostained for Ki67 with antibody MIB-1. The distribution of immunoreactivity was analyzed by quantifying the percentage of positive nuclei that was expressed as the labeling index (LI). In situ hybridization (ISH) for p27 mRNA was done using a cRNA probe with 30 of these cases. Normal parathyroid glands had the highest p27 LI (89.6 +/- 1.4), followed by hyperplasia (69.6 +/- 7.5), adenomas (56.8 +/- 3.4), and carcinomas (13.9 +/- 2.6). ISH showed no differences in p27 mRNA, indicating that the expression of the p27 gene was controlled at a posttranslational level in parathyroid tissues. Ki67 expression was significantly higher in carcinomas (LI = 8.4 +/- 1.9) than in adenomas (LI = 2.7 +/- 0.2) and hyperplasia (LI = 3.3 +/- 0.4). These results suggest that both p27 and Ki67 may be helpful in the diagnosis of histologically difficult parathyroid lesions.     

Scrutiny of the glutamine-fructose-6-phosphate transaminase 1 (GFPT1) locus reveals conserved haplotype block structure not associated with diabetic nephropathy

Glutamine-fructose-6-phosphate transaminase 1 (GFAT) is the rate-limiting enzyme of the hexosamine pathway that has been implicated in the pathogenesis of diabetic nephropathy. As such, we hypothesized that GFPT1, which encodes for GFAT, may confer genetic susceptibility to this complication among Caucasians. Screening of all known functional regions of GFPT1 revealed six single nucleotide polymorphisms (SNPs) that were located in the promoter, introns, and 3' untranslated region. The approximately 60 kb GFPT1 locus was encompassed in a single conserved haplotype block, and two tagging SNPs were sufficient to capture >90% of the haplotype diversity. Analysis of these SNPs in a case-control study made up of type 1 diabetic subjects (324 case subjects with diabetic nephropathy and 289 control subjects with normoalbuminuria despite >15 years of diabetes) revealed no significant association even after stratification by sex, diabetes duration, glucose control, and blood pressure. Similar results were obtained among type 2 diabetic subjects (202 case and 114 control subjects). Genetic variation in GFPT1 is thus unlikely to have a major impact on susceptibility to diabetic nephropathy.