Biomedical subjects

Kristin A Waite

Publications and source records attributed to Kristin A Waite.

9 recordsLinked to original sources

PubMed2005

Phytoestrogen exposure elevates PTEN levels.

Epidemiological data suggest that consumption of phytoestrogens can be protective against the development of breast cancer. It may be logical to postulate that phytoestrogens may regulate proteins that control cellular division, such as the tumor suppressor PTEN. Germline, and more significantly, somatic PTEN mutations have been observed in a broad range of human cancers, especially those of the breast. Active PTEN results in decreased phosphorylation of Akt and MAPK, the up-regulation of p27 and down-regulation of cyclin D1 protein levels resulting in decreased proliferation and an increase in apoptosis. We hypothesized that phytoestrogen exposure regulates PTEN protein expression in the breast cancer cell line, MCF-7. When MCF-7 cells were stimulated with resveratrol, quercetin or genistein, there was an increase in PTEN protein levels. Concomitantly, phytoestrogen stimulation resulted in decreased Akt phosphorylation and an increase in p27 protein levels, indicating active PTEN lipid phosphatase activity. In contrast, we found that MAPK phosphorylation and cyclin D1 levels, which are regulated by PTEN's protein phosphatase activity, were not altered. Using semi-quantitative RT-PCR, we found that mRNA levels were slightly increased in cells stimulated by phytoestrogens, suggesting that the mechanism for increased PTEN protein expression is dependent upon transcription. Concurrently, our data provide evidence that a mechanism for phytoestrogens' protective nature is partially through increased PTEN expression. More importantly, it provides a novel target for the regulation of PTEN expression and suggests that dietary changes may be adjunctive to traditional preventive and therapeutic strategies against breast cancer.

Base Sequence↗

PubMed2004

Silencing of the maternally imprinted tumor suppressor ARHI contributes to follicular thyroid carcinogenesis.

The two most common subtypes of thyroid cancer, follicular thyroid carcinoma (FTC) and papillary thyroid carcinoma, have been extensively studied, but our fundamental understanding of the molecular events in thyroid epithelial oncogenesis is still limited. Unreported data from our previous published global gene expression analysis revealed that the tumor suppressor gene aplysia ras homolog I (ARHI) is frequently underexpressed in FTCs. In this study, we elucidated the frequency and mechanism of ARHI silencing in benign and malignant thyroid neoplasia. We demonstrated that underexpression of ARHI occurs principally in FTCs (P = 0.0018), including its oncocytic variant (11 of 13), even at minimally invasive stage but not classic papillary thyroid carcinoma (two of seven) or follicular adenoma (FA) (three of 14). FTCs show strong allelic imbalance with reduction in copy number/loss of heterozygosity (LOH) in 69%, compared with less than 10% for FAs. In combination with our LOH data, bisulfite sequencing in a subset of samples revealed that FA displays a symmetric methylation pattern, likely representing one unmethylated allele and one presumptively imprinted allele, whereas FTC shows a virtually complete methylation pattern, representing LOH of the nonimprinted allele with only the hypermethylated allele remaining. Furthermore, we showed that pharmacologic inhibition of histone deacetylation but not demethylation could reactivate ARHI expression in the FTC133 FTC cell line. Therefore, our data suggest that silencing of the putative maternally imprinted tumor suppressor gene ARHI, primarily by large genomic deletion in conjunction with hypermethylation of the genomically imprinted allele, serves as a key early event in follicular thyroid carcinogenesis.

Adenocarcinoma, Follicular↗

PubMed2004

Dimethylethanolamine does not prevent liver failure in phosphatidylethanolamine N-methyltransferase-deficient mice fed a choline-deficient diet.

Mice that lack phosphatidylethanolamine-N-methyltransferase (PEMT) and are fed a choline-deficient (CD) diet suffer severe liver damage and do not survive. Since phosphatidyldimethylethanolamine (PDME) has physical properties similar to those of phosphatidylcholine (PC), we hypothesized that dimethylethanolamine (DME) would be converted into PDME that might substitute for PC, and therefore abrogate the liver damage in the Pemt -/- mice fed a CD diet. We fed Pemt -/- mice either a CD diet, a CD diet supplemented with choline, or a CD diet supplemented with DME (CD + DME). Pemt -/- mice fed the CD diet developed severe liver failure by 4 days while CD + DME-fed mice developed severe liver failure by 5 days. The hepatic PC level in choline-supplemented (CS) mice was 67 +/- 4 nmol/mg protein, whereas the PC content was reduced in CD- and CD + DME-fed mice (49 +/- 3 and 30 +/- 3 nmol/mg protein, respectively). Upon supplementation of the CD diet with DME the amount of hepatic PDME was 81 +/- 9 nmol/mg protein so that the hepatic content of PC + PDME combined was 111 nmol/mg protein. Moreover, plasma apolipoprotein B100 and Al levels were markedly lower in mice fed the CD + DME diet compared to mice fed the CS diet, as was the plasma content of PC. Thus, despite replacement of the deficit in hepatic PC with PDME in Pemt -/- mice fed a CD diet, normal liver function was not restored. We conclude that although PC and PDME exhibit similar physical properties, the three methyl groups of choline are required for hepatic function in mice.

Animals↗

PubMed2003

Enhanced expression and activation of CTP:phosphocholine cytidylyltransferase beta2 during neurite outgrowth.

During differentiation neurons increase phospholipid biosynthesis to provide new membrane for neurite growth. We studied the regulation of phosphatidylcholine (PC) biosynthesis during differentiation of two neuronal cell lines: PC12 cells and Neuro2a cells. We hypothesized that in PC12 cells nerve growth factor (NGF) would up-regulate the activity and expression of the rate-limiting enzyme in PC biosynthesis, CTP:phosphocholine cytidylyltransferase (CT). During neurite outgrowth, NGF doubled the amount of cellular PC and CT activity. CTbeta2 mRNA increased within 1 day of NGF application, prior to the formation of visible neurites, and continued to increase during neurite growth. When neurites retracted in response to NGF withdrawal, CTbeta2 mRNA, protein, and CT activity decreased. NGF specifically activated CTbeta2 by promoting its translocation from cytosol to membranes. In contrast, NGF did not alter CTalpha expression or translocation. The increase in both CTbeta2 mRNA and CT activity was inhibited by U0126, an inhibitor of mitogen-activated kinase/extracellular signal-regulated kinase kinase 1/2 (MEK1/2). In Neuro2a cells, retinoic acid significantly increased CT activity (by 54%) and increased CTbeta2 protein, coincident with neurite outgrowth but did not change CTalpha expression. Together, these data suggest that the CTbeta2 isoform of CT is specifically up-regulated and activated during neuronal differentiation to increase PC biosynthesis for growing neurites.

Animals↗

PubMed2003

Germline PTEN promoter mutations and deletions in Cowden/Bannayan-Riley-Ruvalcaba syndrome result in aberrant PTEN protein and dysregulation of the phosphoinositol-3-kinase/Akt pathway.

Germline intragenic mutations in PTEN are associated with 80% of patients with Cowden syndrome (CS) and 60% of patients with Bannayan-Riley-Ruvalcaba syndrome (BRRS). The underlying genetic causes remain to be determined in a considerable proportion of classic CS and BRRS without a polymerase chain reaction (PCR)-detectable PTEN mutation. We hypothesized that gross gene deletions and mutations in the PTEN promoter might alternatively account for a subset of apparently mutation-negative patients with CS and BRRS. Using real time and multiplex PCR techniques, we identified three germline hemizygous PTEN deletions in 122 apparently mutation-negative patients with classic CS (N=95) or BRRS (N=27). Fine mapping suggested that one deletion encompassed the whole gene and the other two included exon 1 and encompassed exons 1-5 of PTEN, respectively. Two patients with the deletion were diagnosed with BRRS, and one patient with the deletion was diagnosed with BRRS/CS overlap (features of both). Thus 3 (11%) of 27 patients with BRRS or BRRS/CS-overlap had PTEN deletions. Analysis of the PTEN promoter revealed nine cases (7.4%) harboring heterozygous germline mutations. All nine had classic CS, representing almost 10% of all subjects with CS. Eight had breast cancers and/or benign breast tumors but, otherwise, oligo-organ involvement. PTEN protein analysis, from one deletion-positive and five PTEN-promoter-mutation-positive samples, revealed a 50% reduction in protein and multiple bands of immunoreactive protein, respectively. In contrast, control samples showed only the expected band. Further, an elevated level of phosphorylated Akt was detected in the five promoter-mutation-positive samples, compared with controls, indicating an absence of or marked reduction in functional PTEN. These data suggest that patients with BRRS and CS without PCR-detected intragenic PTEN mutations be offered clinical deletion analysis and promoter-mutation analysis, respectively.

Base Sequence↗

PubMed2003

BMP2 exposure results in decreased PTEN protein degradation and increased PTEN levels.

The tumour suppressor gene PTEN encodes a dual-specificity phosphatase that recognizes protein and phosphatidylinositiol substrates and modulates cellular functions such as migration and proliferation. Germline mutations of PTEN have been shown to cause Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome and Proteus syndrome. Recently, germline mutations in BMPR1A, the gene encoding the type 1A receptor of bone morphogenetic proteins (BMP) have been found in rare families with Cowden syndrome, suggesting that there may be a link between BMP signaling and PTEN. We thus sought to determine whether BMP2 stimulation alters PTEN protein levels in the breast cancer line, MCF-7. We found that exposure to BMP2 increased PTEN protein levels in a time- and dose-dependent manner. The increase in PTEN protein was rapid and was not due to an increase in new protein synthesis, as cycloheximide treatment did not inhibit BMP2-induced PTEN accumulation, suggesting that BMP2 stimulation inhibited PTEN protein degradation. Indeed, we found that BMP2 treatment of MCF-7 cells decreased the association of PTEN with two proteins in the degradative pathway, UbCH7 and UbC9. These data indicate that BMP2 exposure can regulate PTEN protein levels by decreasing PTEN's association with the degradative pathway. This opens up a new mode of regulating PTEN activity to be investigated further and may explain why BMPR1A can act as a minor susceptibility gene for PTEN mutation negative Cowden syndrome.

Blotting, Western↗

PubMed2003

From developmental disorder to heritable cancer: it's all in the BMP/TGF-beta family.

Transforming growth factor-beta (TGF-beta) regulates many cellular processes through complex signal-transduction pathways that have crucial roles in normal development. Disruption of these pathways can lead to a range of diseases, including cancer. Mutations in the genes that encode members of the TGF-beta pathway are involved in vascular diseases as well as gastrointestinal neoplasia. More recently, they have been implicated in Cowden syndrome, which is normally associated with mutations in the phosphatase and tensin homologue gene PTEN. Molecular studies of TGF-beta signalling are now showing why mutations in genes that encode components of this pathway result in inherited cancer and developmental diseases.

Animals↗

PubMed2002

Protean PTEN: form and function.

Germline mutations distributed across the PTEN tumor-suppressor gene have been found to result in a wide spectrum of phenotypic features. Originally shown to be a major susceptibility gene for both Cowden syndrome (CS), which is characterized by multiple hamartomas and an increased risk of breast, thyroid, and endometrial cancers, and Bannayan-Riley-Ruvalcaba syndrome, which is characterized by lipomatosis, macrocephaly, and speckled penis, the PTEN hamartoma tumor syndrome spectrum has broadened to include Proteus syndrome and Proteus-like syndromes. Exon 5, which encodes the core motif, is a hotspot for mutations likely due to the biology of the protein. PTEN is a major lipid 3-phosphatase, which signals down the PI3 kinase/AKT pro-apoptotic pathway. Furthermore, PTEN is a protein phosphatase, with the ability to dephosphorylate both serine and threonine residues. The protein-phosphatase activity has also been shown to regulate various cell-survival pathways, such as the mitogen-activated kinase (MAPK) pathway. Although it is well established that PTEN's lipid-phosphatase activity, via the PI3K/AKT pathway, mediates growth suppression, there is accumulating evidence that the protein-phosphatase/MAPK pathway is equally important in the mediation of growth arrest and other crucial cellular functions.

Animals↗

PubMed2002

Choline deficiency-induced liver damage is reversible in Pemt(-/-) mice.

Hepatic tissue has two pathways for phosphatidylcholine (PC) synthesis, i.e., the cytidinediphosphocholine (CDP-choline) pathway and the methylation pathway, which utilizes phosphatidylethanolamine-N-methyltransferase (PEMT). Fatal liver damage occurs in Pemt(-/-)mice fed a choline-deficient (CD) diet. We investigated whether liver damage can be reversed by the addition of dietary choline. Mice (8 wk old) were fed the CD purified diet for 4 d, a choline-supplemented (CS) diet (CD diet + 0.4% choline chloride) for 4 d, or the CD diet for 3 d and a CS diet for 1 d (CD/CS). Pemt(-/-)mice fed the CD diet for 3 d exhibited liver damage as assayed by plasma aminotransferase levels. The livers appeared normal after subsequent feeding of the CS diet for 1 d (CD/CS). The activities of plasma aminotransferases of CD/CS fed mice were comparable to Pemt(-/-)mice fed the CS diet. Hepatic PC and triacylglycerol levels as well as plasma PC levels in the CD/CS-fed Pemt(-/-)mice were lower than those of mice fed the CD diet and began to approach normal levels. Although the CD diet induces liver damage in Pemt(-/-)mice, this damage can be rapidly reversed by the addition of dietary choline.

Animals↗