Neuroblastoma suppressor of tumorigenicity 1 is a circulating protein associated with progression to end-stage kidney disease in diabetes

Circulating proteins associated with transforming growth factor-β (TGF-β) signaling are implicated in the development of diabetic kidney disease (DKD). It remains to be comprehensively examined which of these proteins are involved in the pathogenesis of DKD and its progression to end-stage kidney disease (ESKD) in humans. Using the SOMAscan proteomic platform, we measured concentrations of 25 TGF-β signaling family proteins in four different cohorts composed in total of 754 Caucasian or Pima Indian individuals with type 1 or type 2 diabetes. Of these 25 circulating proteins, we identified neuroblastoma suppressor of tumorigenicity 1 (NBL1, aliases DAN and DAND1), a small secreted protein known to inhibit members of the bone morphogenic protein family, to be most strongly and independently associated with progression to ESKD during 10-year follow-up in all cohorts. The extent of damage to podocytes and other glomerular structures measured morphometrically in 105 research kidney biopsies correlated strongly with circulating NBL1 concentrations. Also, in vitro exposure to NBL1 induced apoptosis in podocytes. In conclusion, circulating NBL1 may be involved in the disease process underlying progression to ESKD, and its concentration in circulation may identify subjects with diabetes at increased risk of progression to ESKD.

Results of untargeted analysis using the SOMAscan proteomics platform indicates novel associations of circulating proteins with risk of progression to kidney failure in diabetes

This study applies a large proteomics panel to search for new circulating biomarkers associated with progression to kidney failure in individuals with diabetic kidney disease. Four independent cohorts encompassing 754 individuals with type 1 and type 2 diabetes and early and late diabetic kidney disease were followed to ascertain progression to kidney failure. During ten years of follow-up, 227 of 754 individuals progressed to kidney failure. Using the SOMAscan proteomics platform, we measured baseline concentration of 1129 circulating proteins. In our previous publications, we analyzed 334 of these proteins that were members of specific candidate pathways involved in diabetic kidney disease and found 35 proteins strongly associated with risk of progression to kidney failure. Here, we examined the remaining 795 proteins using an untargeted approach. Of these remaining proteins, 11 were significantly associated with progression to kidney failure. Biological processes previously reported for these proteins were related to neuron development (DLL1, MATN2, NRX1B, KLK8, RTN4R and ROR1) and were implicated in the development of kidney fibrosis (LAYN, DLL1, MAPK11, MATN2, endostatin, and ROR1) in cellular and animal studies. Specific mechanisms that underlie involvement of these proteins in progression of diabetic kidney disease must be further investigated to assess their value as targets for kidney-protective therapies. Using multivariable LASSO regression analysis, five proteins (LAYN, ESAM, DLL1, MAPK11 and endostatin) were found independently associated with risk of progression to kidney failure. Thus, our study identified proteins that may be considered as new candidate prognostic biomarkers to predict risk of progression to kidney failure in diabetic kidney disease. Furthermore, three of these proteins (DLL1, ESAM, and MAPK11) were selected as candidate biomarkers when all SOMAscan results were evaluated.

Comprehensive Search for Novel Circulating miRNAs and Axon Guidance Pathway Proteins Associated with Risk of ESKD in Diabetes

BACKGROUND

Mechanisms underlying the pro gression of diabetic kidney disease to ESKD are not fully understood.

METHODS

We performed global microRNA (miRNA) analysis on plasma from two cohorts consisting of 375 individuals with type 1 and type 2 diabetes with late diabetic kidney disease, and targeted proteomics analysis on plasma from four cohorts consisting of 746 individuals with late and early diabetic kidney disease. We examined structural lesions in kidney biopsy specimens from the 105 individuals with early diabetic kidney disease. Human umbilical vein endothelial cells were used to assess the effects of miRNA mimics or inhibitors on regulation of candidate proteins.

RESULTS

In the late diabetic kidney disease cohorts, we identified 17 circulating miRNAs, represented by four exemplars (miR-1287-5p, miR-197-5p, miR-339-5p, and miR-328-3p), that were strongly associated with 10-year risk of ESKD. These miRNAs targeted proteins in the axon guidance pathway. Circulating levels of six of these proteins-most notably, EFNA4 and EPHA2-were strongly associated with 10-year risk of ESKD in all cohorts. Furthermore, circulating levels of these proteins correlated with severity of structural lesions in kidney biopsy specimens. In contrast, expression levels of genes encoding these proteins had no apparent effects on the lesions. In in vitro experiments, mimics of miR-1287-5p and miR-197-5p and inhibitors of miR-339-5p and miR-328-3p upregulated concentrations of EPHA2 in either cell lysate, supernatant, or both.

CONCLUSIONS

This study reveals novel mechanisms involved in progression to ESKD and points to the importance of systemic factors in the development of diabetic kidney disease. Some circulating miRNAs and axon guidance pathway proteins represent potential targets for new therapies to prevent and treat this condition.

Circulating proteins protect against renal decline and progression to end-stage renal disease in patients with diabetes

Diabetic kidney disease (DKD) and its major clinical manifestation, progressive renal decline that leads to end-stage renal disease (ESRD), are a major health burden for individuals with diabetes. The disease process that underlies progressive renal decline comprises factors that increase risk as well as factors that protect against this outcome. Using untargeted proteomic profiling of circulating proteins from individuals in two independent cohorts with type 1 and type 2 diabetes and varying stages of DKD followed for 7 to 15 years, we identified three elevated plasma proteins-fibroblast growth factor 20 (OR, 0.69; 95% CI, 0.54 to 0.88), angiopoietin-1 (OR, 0.72; 95% CI, 0.57 to 0.91), and tumor necrosis factor ligand superfamily member 12 (OR, 0.75; 95% CI, 0.59 to 0.95)-that were associated with protection against progressive renal decline and progression to ESRD. The combined effect of these three protective proteins was demonstrated by very low cumulative risk of ESRD in those who had baseline concentrations above median for all three proteins, whereas the cumulative risk of ESRD was high in those with concentrations below median for these proteins at the beginning of follow-up. This protective effect was shown to be independent from circulating inflammatory proteins and clinical covariates and was confirmed in a third cohort of diabetic individuals with normal renal function. These three protective proteins may serve as biomarkers to stratify diabetic individuals according to risk of progression to ESRD and might also be investigated as potential therapeutics to delay or prevent the onset of ESRD.

Effect of TNFα stimulation on expression of kidney risk inflammatory proteins in human umbilical vein endothelial cells cultured in hyperglycemia

We recently identified a kidney risk inflammatory signature (KRIS), comprising 6 TNF receptors (including TNFR1 and TNFR2) and 11 inflammatory proteins. Elevated levels of these proteins in circulation were strongly associated with risk of the development of end-stage kidney disease (ESKD) during 10-year follow-up. It has been hypothesized that elevated levels of these proteins in circulation might reflect (be markers of) systemic exposure to TNFα. In this in vitro study, we examined intracellular and extracellular levels of these proteins in human umbilical vein endothelial cells (HUVECs) exposed to TNFα in the presence of hyperglycemia. KRIS proteins as well as 1300 other proteins were measured using the SOMAscan proteomics platform. Four KRIS proteins (including TNFR1) were down-regulated and only 1 protein (IL18R1) was up-regulated in the extracellular fraction of TNFα-stimulated HUVECs. In the intracellular fraction, one KRIS protein was down-regulated (CCL14) and 1 protein was up-regulated (IL18R1). The levels of other KRIS proteins were not affected by exposure to TNFα. HUVECs exposed to a hyperglycemic and inflammatory environment also showed significant up-regulation of a distinct set of 53 proteins (mainly in extracellular fraction). In our previous study, circulating levels of these proteins were not associated with progression to ESKD in diabetes.

Transcriptome analysis of proximal tubular cells (HK-2) exposed to urines of type 1 diabetes patients at risk of early progressive renal function decline

Background

In patients with Type 1 Diabetes (T1D) who develop microalbuminuria, progressive decline in glomerular filtration rate (GFR) may be initiated by leakage into the urine of toxic proteins (txUPs). This study tested this hypothesis.

Methods

After archiving baseline urine, we followed T1D patients with microalbuminuria for 8–12 years to distinguish those in whom GFR declined (Decliners) and those in whom it remained stable (Non-decliners). Human proximal tubular cells (HK-2 cells) were grown in serum-free medium enriched with pooled urines from Decliners or Non-decliners. We determined genome-wide expression profiles in extracted mRNA.

Results

The two pooled urines induced differential expression of 312 genes. In terms of gene ontology, molecular functions of the 119 up-regulated genes were enriched for protein binding and peptidase inhibitor activities. Their biologic processes were enriched for defense response, responses to other organisms, regulation of cellular processes, or response to stress or stimulus, and programmed cell death. The 195 down-regulated genes were disproportionately represented in molecular functions of cation binding, hydrolase activity, and DNA binding. They were disproportionately represented in biological processes for regulation of metabolic processes, nucleic acid metabolic processes, cellular response to stress and macromolecule biosynthesis. The set of up-regulated genes in HK-2 cells overlaps significantly with sets of over-expressed genes in tubular and interstitial compartments of kidney biopsies from patients with advanced DN (33 genes in one study and 25 in the other compared with 10.3 expected by chance, p<10⁻⁹ and p<10⁻⁴, respectively). The overlap included genes encoding chemokines and cytokines. Overlap of down-regulated genes was no more than expected by chance.

Conclusions

Molecular processes in tubules and interstitium seen in advanced diabetic nephropathy can be induced in vitro by exposure to urine from patients with minimal microalbuminuria who subsequently developed progressive renal function decline, presumably due to putative txUPs.

Genome-wide association scan for diabetic nephropathy susceptibility genes in type 1 diabetes

OBJECTIVE

Despite extensive evidence for genetic susceptibility to diabetic nephropathy, the identification of susceptibility genes and their variants has had limited success. To search for genes that contribute to diabetic nephropathy, a genome-wide association scan was implemented on the Genetics of Kidneys in Diabetes collection.

RESEARCH DESIGN AND METHODS

We genotyped approximately 360,000 single nucleotide polymorphisms (SNPs) in 820 case subjects (284 with proteinuria and 536 with end-stage renal disease) and 885 control subjects with type 1 diabetes. Confirmation of implicated SNPs was sought in 1,304 participants of the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study, a long-term, prospective investigation of the development of diabetes-associated complications.

RESULTS

A total of 13 SNPs located in four genomic loci were associated with diabetic nephropathy with P < 1 x 10(-5). The strongest association was at the FRMD3 (4.1 protein ezrin, radixin, moesin [FERM] domain containing 3) locus (odds ratio [OR] = 1.45, P = 5.0 x 10(-7)). A strong association was also identified at the CARS (cysteinyl-tRNA synthetase) locus (OR = 1.36, P = 3.1 x 10(-6)). Associations between both loci and time to onset of diabetic nephropathy were supported in the DCCT/EDIC study (hazard ratio [HR] = 1.33, P = 0.02, and HR = 1.32, P = 0.01, respectively). We demonstratedexpression of both FRMD3 and CARS in human kidney.

CONCLUSIONS

We identified genetic associations for susceptibility to diabetic nephropathy at two novel candidate loci near the FRMD3 and CARS genes. Their identification implicates previously unsuspected pathways in the pathogenesis of this important late complication of type 1 diabetes.

A genome-wide linkage scan for genes controlling variation in renal function estimated by serum cystatin C levels in extended families with type 2 diabetes

We performed a variance components linkage analysis of renal function, measured as glomerular filtration rate (GFR), in 63 extended families with multiple members with type 2 diabetes. GFR was estimated from serum concentrations of cystatin C and creatinine in 406 diabetic and 428 nondiabetic relatives. Results for cystatin C were summarized because they are superior to creatinine results. GFR aggregates in families with significant heritability (h(2)) in diabetic (h(2) = 0.45, P < 1 x 10(-5)) and nondiabetic (h(2) = 0.36, P < 1 x 10(-3)) relatives. Genetic correlation (r(G) = 0.35) between the GFR of diabetic and nondiabetic relatives was less than one (P = 0.01), suggesting that genes controlling GFR variation in these groups are different. Linkage results supported this interpretation. In diabetic relatives, linkage was strong on chromosome 2q (logarithm of odds [LOD] = 4.1) and suggestive on 10q (LOD = 3.1) and 18p (LOD = 2.2). In nondiabetic relatives, linkage was suggestive on 3q (LOD = 2.2) and 11p (LOD = 2.1). When diabetic and nondiabetic relatives were combined, strong evidence for linkage was found only on 7p (LOD = 4.0). In conclusion, partially distinct sets of genes control GFR variation in relatives with and without diabetes on chromosome 2q, possibly on 10q and 18p in the former, and on 7p in both. None of these genes overlaps with genes controlling variation in urinary albumin excretion.

A genome-wide linkage scan for genes controlling variation in urinary albumin excretion in type II diabetes

The main hallmark of diabetic nephropathy is elevation in urinary albumin excretion. We performed a genome-wide linkage scan in 63 extended families with multiple members with type II diabetes. Urinary albumin excretion, measured as the albumin-to-creatinine ratio (ACR), was determined in 426 diabetic and 431 nondiabetic relatives who were genotyped for 383 markers. The data were analyzed using variance components linkage analysis. Heritability (h2) of ACR was significant in diabetic (h2=0.23, P=0.0007), and nondiabetic (h2=0.39, P=0.0001) relatives. There was no significant difference in genetic variance of ACR between diabetic and nondiabetic relatives (P=0.16), and the genetic correlation (rG=0.64) for ACR between these two groups was not different from 1 (P=0.12). These results suggested that similar genes contribute to variation in ACR in diabetic and nondiabetic relatives. This hypothesis was supported further by the linkage results. Support for linkage to ACR was suggestive in diabetic relatives and became significant in all relatives for chromosome 22q (logarithm of odds, LOD=3.7) and chromosome 7q (LOD=3.1). When analyses were restricted to 59 Caucasian families, support for linkage in all relatives increased and became significant for 5q (LOD=3.4). In conclusion, genes on chromosomes 22q, 5q and 7q may contribute to variation in urinary albumin excretion in diabetic and nondiabetic individuals.

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.

Molecular events in radiation transformation

Studies of human tumor cell lines have revealed alterations in the regulation of a number of cell cycle-related genes, associated in some cases with a TP53-independent loss of the radiation-induced G(1)-phase arrest. It is not clear, however, whether these are early or late events in tumor development, or they arise in tumor cell lines during growth in culture. Since the oncogenic transformation of an individual cell is thought to be an early event in tumor development, we have used a model system of normal and radiation-transformed C3H 10T(1/2) mouse fibroblast cell clones to address this issue. Transformed clones derived from type III foci were compared with clones derived from parental, wild-type cells. Approximately 25% of transformed clones showed Trp53 mutations in exon 5; however, preliminary results based on in situ immunofluorescence studies with an antibody recognizing mutant Trp53 indicate that the appearance of such mutations in transformed clones occurs late in the process of transformation and is unlikely to represent an initiating event. The remaining transformed clones and all clones derived from parental cells expressed wild-type Trp53. Radiation-induced G(1)-phase arrest was either absent or significantly reduced in all of the transformed clones, independent of Trp53 status. Constitutive expression of Cdkn1a protein was significantly increased in most of the transformed clones. Also, the majority of transformed clones showed elevated levels of cyclin D1, and two clones overexpressed cyclin E. These results indicate that loss of G(1)-phase checkpoint control, independent of Trp53 status, and altered expression of cell cycle regulatory proteins may represent early events in the process of radiation-induced carcinogenesis that are associated with the malignant transformation of individual cells.

Overexpression of p21 protein in radiation-transformed mouse 10T(1/2) cell clones

In order to investigate the hypothesis that aberrant expression of cell-cycle regulatory proteins may represent early events in the process of carcinogenesis, levels of expression of the negative regulators p21(waf1/cip1) (p21), p27(kip1) (p27), and p16(ink4a) (p16) and/or the positive regulators cyclin D(1) and cyclin E were examined by western blot analysis in cells transformed in vitro by ionizing radiation. The levels of these proteins in 12 independently derived mouse 10T(1/2) cell clones transformed by 1.5 Gy of alpha radiation were compared with those in nine similarly derived nontransformed control clones. Constitutive levels of p21 were very low in all control clones, whereas p21 expression was significantly elevated in nine of 12 transformed clones. Two of the three transformed clones displaying low levels of p21 expressed increased levels of p53. p21 regulation was also altered in response to radiation in transformed clones as compared with controls, only minimal induction was observed 4 h following gamma irradiation. Western blot analysis indicated a constant expression of p27 protein but slightly decreased levels of p16 in these transformed clones. Cyclin D(1) was overexpressed in 11 of 12 transformed clones; in only two of these were the levels of cyclin E elevated. Overall, the results suggest that alterations in the expression of cell cycle regulatory proteins may represent important events in radiation-induced oncogenic transformation in vitro. Although the specific alterations vary among different transformed clones, overexpression and aberrant regulation of p21 appear to be the most frequent ones.

Loss of normal G1 checkpoint control is an early step in carcinogenesis, independent of p53 status

Recent studies have described a diminished radiation-induced G1 arrest in some wild-type (wt) p53 human tumor cell lines compared to normal human fibroblasts. However, the significance of this finding was unclear, particularly because tumor cell lines may have accumulated additional genetic changes after long periods in culture. Because malignant transformation of individual cells is thought to be an early step in carcinogenesis, we have used a model system of normal and transformed mouse fibroblast 10T1/2 cell clones to examine whether loss of G1 checkpoint control may be an early event in tumor development and to study the relationships between G1 arrest, radiosensitivity, and genetic alterations. Twelve transformed clones were established from type III foci induced by irradiation of normal 10T1/2 cells and were compared with six clones derived from wt 10T1/2 cells. Three of the transformed clones expressed mutant p53; two of these had the same point mutation at codon 132 (exon 5), and one had a point mutation at codon 135. The remaining transformed and normal clones had wt p53 status. The radiosensitivity of transformed clones, as measured by a clonogenic assay, was similar to that of normal clones; the three clones with mutant p53 did not differ from the others. There was no relationship between G1 arrest and radiosensitivity. Normal 10T1/2 cell clones showed a transient G1 arrest lasting approximately 9 h after 6 Gy of irradiation. This G1 arrest was either absent or markedly reduced in all of the transformed clones, regardless of p53 status. These results suggest that diminished G1 checkpoint control is an early event in the process of carcinogenesis that is associated with the malignant transformation of individual cells and is independent of p53 status.

Phosphorylation and activity of Na+/H+ exchanger isoform 1 of immortalized lymphoblasts in diabetic nephropathy

In both essential hypertension and diabetic nephropathy (DN), the ubiquitous cellular Na+/H+ exchanger (NHE) exhibits altered kinetics with increased transport activity. The mechanism for this phenotype and its dependence on the presence of serum are unknown, but increased lymphoblast NHE activity in DN has been attributed to a defect in post-translational processing of NHE-1 rather than an increased cellular exchanger number. Phosphorylation of NHE-1 has been proposed to play a role in its activation in a variety of cell models. We have examined, therefore, the role of NHE-1 phosphorylation and the effect of serum in determining the increased NHE-1 activity in lymphoblasts from patients with DN. Cells from these patients exhibited increased NHE activity in the presence and absence of fetal calf serum (range 42-59%, P < 0.005, analysis of variance) and an increased proliferation rate (P < 0.01) when compared with cells from both normoalbuminuric diabetic patients and non-diabetic control subjects. However, NHE-1 abundance was very similar among all groups in the presence and absence of serum, indicating that increased NHE activity in cells of nephropathy patients was due to an increased turnover number. This nephropathy phenotype was not accompanied by an increased net phosphorylation of NHE-1 in the presence or absence of serum. Our findings suggest that increased NHE-1 activity in cells of DN patients is independent of the presence of serum and is not attributable to altered NHE-1 phosphorylation. Additional post-translational mechanisms for activation of NHE-1, therefore, may be involved.

Na(+)-H+ antiporter phenotype, abundance, and phosphorylation of immortalized lymphoblasts from humans with hypertension

Previous studies have demonstrated an elevated Na(+)-H+ exchanger activity in various cell types from patients with essential hypertension. The phenotype of an increased maximal transport capacity is preserved in Epstein-Barr virus immortalized lymphoblasts from hypertensive patients. The mechanisms underlying this abnormality are unclear. In this study, we used lymphoblasts from hypertensive patients and normotensive control subjects with and without a family history of hypertension to determine (1) Na(+)-H+ exchanger activity using fluorometry with the pH indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, (2) Na(+)-H+ exchanger isoform 1 abundance with specific polyclonal antibodies, and (3) Na(+)-H+ exchanger phosphorylation by immunoprecipitation of the 32P-labeled transporter. Na(+)-H+ exchanger activity (in millimoles per liter per minute) measured when pHi was clamped at 6.0 was significantly higher in cells from hypertensive patients (18.8 +/- 0.6, P < .001) and those subjects with a family history of hypertension (16.4 +/- 0.6, P < .001) compared with normotensive control subjects (12.9 +/- 0.6). Exchanger abundance was identical in all three groups of subjects, indicating that increased activity in the hypertensive group was due to an elevated turnover number of the exchanger. Na(+)-H+ exchanger phosphorylation in quiescent cells was significantly elevated in cells from hypertensive patients (1.58 +/- 0.16, P < .001) compared with control subjects (1.00 +/- 0.07), and cells from normotensive subjects with a hypertensive family history showed intermediate values (1.23 +/- 0.14). Identical changes in Na(+)-H+ exchanger function and phosphorylation have been demonstrated in vascular smooth muscle cells from spontaneously hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose-induced changes in turnover of Na+/H+ exchanger of immortalized lymphoblasts from type I diabetic patients with nephropathy

Increased cellular Na+/H+ exchanger (NHE) activity has been demonstrated in type I diabetic patients with nephropathy. Such patients also have a previous history of poor glycemic control. The interaction between hyperglycemia and changes in NHE activity remains obscure. Therefore, we examined the effects of media containing 5 and 25 mmol/l glucose on the increased NHE activity and turnover number in Epstein-Barr virus-transformed lymphoblasts from patients with diabetic nephropathy compared with normoalbuminuric diabetic and nondiabetic control subjects. NHE activity was determined fluorometrically, and NHE isoform 1 (NHE-1) density was measured with specific polyclonal antibodies. In the presence of 5 mmol/l glucose, cells from patients with diabetic nephropathy exhibited higher NHE activity with intracellular pH clamped to 6.0 compared with diabetic and nondiabetic control subjects (P < 0.005 for both), due to a higher turnover number of NHE-1. Incubation in 25 mmol/l glucose for 48 h caused an increase in NHE activity (P < 0.001) and turnover number (P < 0.01) in the diabetic nephropathy group only, with no significant change in the diabetic or nondiabetic control groups. The rate constants for cell proliferation and NHE activity or turnover number were correlated when cells were cultured in 5 mmol/l glucose (r = 0.34 and 0.32, respectively; P < 0.05) or 25 mmol/l glucose media (r = 0.66 and 0.65, respectively; P < 0.001). We conclude that only lymphoblasts from the diabetic nephropathy group show an increase in NHE activity and turnover number under conditions mimicking hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal Na+/H+ antiporter phenotype and turnover of immortalized lymphoblasts from type 1 diabetic patients with nephropathy

Cellular Na+/H+ exchanger (NHE) activity is elevated in type 1 diabetic patients with nephropathy and patients with essential hypertension. The characteristics of this NHE phenotype in hypertension (raised Vmax and a lowered Hill coefficient) are preserved in Epstein-Barr virus-transformed lymphoblasts from hypertensive patients. In this study, we have determined NHE kinetics in cultured lymphoblasts from diabetic patients with and without nephropathy, with nondiabetic controls, using fluorometry with the pH indicator 2,7'-bis-(carboxyethyl)-5,6-carboxyfluorescein and estimation of NHE isoform 1 (NHE-1) density with specific polyclonal antibodies. The Vmax of NHE was elevated significantly, and the Hill coefficient for internal H+ binding was lowered in cells from patients with diabetic nephropathy compared with both normal controls and normoalbuminuric diabetic patients. NHE-1 density as measured by Western blotting was similar in all groups. The turnover number of NHE-1 was thus elevated in cells from nephropathy patients. This phenotype in cells from diabetic nephropathy patients resembles that in essential hypertension and suggests that such patients may have a predisposition to hypertension. Moreover, as these changes persist in cultured lymphoblasts in vitro, these cells should provide a cell culture model to further define the basic mechanisms leading to NHE activation in diabetic nephropathy.

Search for oncogene mutations in X-ray-transformed mouse 10T1/2 cells by denaturing gradient gel electrophoresis blotting

We have sought evidence for possible mutations within the c-myc, c-Ha-ras and c-Ki-ras loci of X-ray-transformed mouse C3H10T1/2 cell clones using the denaturing gradient gel electrophoresis (DGGE) blot technique. This highly sensitive method was developed to detect any mutations (e.g. single base changes, small deletions) in genomic DNA, by measuring differences in the melting behaviour of short DNA fragments (50-800 bp) obtained by digestion of genomic DNA with several specific 4 bp recognition site restriction enzymes. In this study, genomic DNAs derived from 23 X-ray-transformed clones were digested with several restriction enzymes, electrophorezed on denaturing gradient gel and hybridized to c-myc, c-Ha-ras and c-Ki-ras cDNA probes. No alterations in melting patterns were observed for any of these oncogenes as compared with DNA from 18 control, non-irradiated wild-type 10T1/2 cell clones, suggesting that transformation was not associated with mutation of these genes nor with changes in their patterns of methylation. However, our screening of the large portion of exons 2 and 3 of c-myc as well as of exons 1 and 2 of c-Ha-ras gene cannot exclude the possibility that some sequence differences in the high melting domains of examined fragments were not detected by this assay.

Application of denaturing gradient gel blots to detect p53 mutations in X-ray-transformed mouse C3H 10T1/2 clones

The denaturing-gradient gel electrophoresis (DGGE) blot technique is a highly sensitive method developed to detect sequence differences (e.g., single base changes and small deletions) in genomic DNA. We used this method to screen for mutations within the p53 locus of independent X-ray-transformed C3H 10T1/2 cell clones. Genomic DNA from 29 transformed clones was digested with Haell and Hinfl endonucleases, electrophoresed on denaturing gradient gels, electroblotted onto nylon membranes, and hybridized to a radioactive p53 cDNA probe. Changes in the melting pattern of p53 were observed in DNAs from 9 of 29 X-ray-transformed clones examined. No changes were found in untransformed, wild-type 10T1/2 cell clones. These results indicate that X-ray-induced p53 mutations may contribute to cell transformation.

High-frequency DNA sequence polymorphisms in the insulin receptor gene detected by denaturing gradient gel blots

A limiting factor in the study of genetic determinants of human disorders is the availability of informative DNA markers. In this report, we describe an application of the denaturing gradient gel blot method for detecting high-frequency DNA sequence polymorphisms in the human insulin receptor locus. Using two restriction enzymes and cDNA probes for the insulin receptor, we found five DNA polymorphisms. The probe that contained exons 4-10 of the insulin receptor gene detected two two-allelic polymorphisms in HinfI digests, one at denaturant concentrations of 38%/39% and the other at 46%/48%. The probe that contained exons 14-22 detected three two-allelic polymorphisms in Sau96I digests, the first at denaturant concentrations of 34%/35%, the second at 38%/39%, and the third at 46%/47%. All these DNA polymorphisms segregated in families in a Mendelian fashion, and the allelic distribution for each of them did not deviate from Hardy-Weinberg equilibrium. The identified polymorphisms were in linkage equilibrium and provided sufficient genetic information to determine parental haplotypes at the insulin receptor locus in small two-generation families. The denaturing gradient gel blot method is a very sensitive technique for identifying sequence polymorphisms in genomic DNA; its application will facilitate the search for genes involved in the development of many inherited disorders.

Molecular analysis of DNA isolated from the different stages of x-ray-induced transformation in vitro

A major challenge in radiation carcinogenesis is to identify the cellular gene or genes involved in initiating the process. We examined the transforming activities of DNAs obtained from C3H10T1/2 cells during x-ray-induced morphological transformation. DNAs extracted from mass cultures of 10T1/2 cells at different times after irradiation with 600 rad and from type III-transformed foci were transfected into NIH 3T3 cells. The results indicate that certain oncogenes are activated beginning 3 wk after irradiation, well before the appearance of macroscopically visible transformed foci. For DNA isolated from x-ray-transformed 10T1/2 cells (type III foci), the frequencies of transfection were 0.003-0.11 foci/microgram of genomic DNA with NIH 3T3 cells and 0.004-0.04 foci/microgram genomic DNA using 10T1/2 cells as recipients. Southern blot analysis of DNAs obtained from 23 primary transfectants and from 23 x-ray-transformed cell lines indicated no gross rearrangements or amplification of any of the 14 oncogenes screened (v-Ha-ras, v-Ki-ras, N-ras, v-myc, v-raf, v-src, v-fes, v-abl, v-mos, v-erbA, v-erbB, v-myb, v-fos, v-sis). This suggests that x-irradiation may activate as yet unidentified oncogenes. The occurrence of positive transfection 3 wk after irradiation is discussed in terms of the hypothesis that transformation may not occur as a direct consequence of the exposure to x-rays but develops as a rare event in the progeny of the irradiated cells at some later time, as a consequence of the delayed activation of certain genes.

Effect of duration of exposure to benzo(a)pyrene diol-epoxide on neoplastic transformation, mutagenesis, cytotoxicity, and total covalent binding to DNA of rodent cells

We examined the effect of different durations of exposure (20 sec to 24 hr) to (+/-) 7-beta,8 alpha-dihydroxy-9 alpha, 10 alpha -epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE I) on the induction of transformation in C3H/10T 1/2 cells and of mutations to 6-thioguanine resistance in Chinese hamster ovary cells (CHO), as well as on BPDE I-DNA binding in these two cell lines. A 20-sec exposure of the cells to BPDE I was sufficient to induce mutations and morphological transformation in vitro. However, the transformation frequency in CH3 mouse-embryo-derived 10T 1/2 cells increased twofold and the frequency of mutations in CHO cells sixfold when the exposure time to BPDE I was increased from 20 sec to 8 h. Cytotoxicity increased under similar conditions. A large number of BPDE I-DNA adducts were formed in both cell lines within the first 15-min of exposure of the cells to this ultimate carcinogen. The total covalent binding did not increase with longer than 15-min incubation times. These results suggest that in addition to its covalent binding to DNA, BPDE I may influence other cellular mechanism(s) that are responsible for the initiation of transformation and mutagenesis.

Effect of aliphatic amides on oncogenic transformation, sister chromatid exchanges, and mutations induced by cyclopenta[cd]-pyrene and benzo[a]pyrene

We examined the effects of the aliphatic amides isopropyl-valeramide (IVA) and allylisopropylacetamide (AIA) on oncogenic transformation and sister chromatid exchanges (SCE) induced by cyclopenta[cd]pyrene (CPP) and benzo[a]pyrene (B[a]P) in C3H/10T1/2 cells and on B[a]Pdiol-epoxide (BPDE)-induced mutation at the HGPRT locus in Chinese hamster ovary (CHO) cells. IVA and AIA significantly suppressed B[a]P and CPP transformation in vitro. Both amides were effective when given just prior to, simultaneously with, or 24 h after carcinogen exposure. On the other hand, IVA and AIA did not affect cytotoxicity, the frequencies of SCE induced by CPP or B[a]P, nor BPDE-induced mutations in CHO cells. These and previous results suggest that the mechanism of inhibition of transformation by IVA or AIA may be very specific and probably not related to the early initiation event in oncogenic transformation in vitro.

Influence of isopropylvaleramide and allylisopropylacetamide on transformation of C3H/10T1/2 cells induced by benzo[a]pyrene derivatives

We examined the effect of aliphatic amides isopropylvaleramide (IVA) and allylisopropylacetamide (AIA) on the oncogenic transformation of C3H/10T1/2 cells induced by benzo[a]pyrene (B[a]P) or its proximate and ultimate metabolites (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-diol) and (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene (B[a]P-diol-epoxide), respectively. IVA and AIA given prior to, simultaneously with, or for 24 h intervals beginning up to 48 h after removal of carcinogens significantly suppressed transformation induced by B[a]P or the 7,8-diol metabolite. Both modifiers were most effective when added for 24 h immediately following carcinogen exposure. IVA and AIA were also very potent inhibitors of B[a]P-diol-epoxide transformation; however they were most effective when added for 24 h simultaneously with the B[a]P-diol-epoxide. No significant difference in B[a]P-diol-epoxide binding to DNA in C3H/10T1/2 cells was observed during 1 or 24 h exposure to this carcinogen in the presence or absence of IVA or AIA. Neither modifier affected X-ray transformation when added for 24 h immediately following X-irradiation of C3H/10T1/2 cells. These results suggest that AIA and especially IVA might be important tools in studies directed at non-metabolic aspects of B[a]P carcinogenesis.