Biomedical subjects
Scott E Kern
Publications and source records attributed to Scott E Kern.
High-throughput measurement of the Tp53 response to anticancer drugs and random compounds using a stably integrated Tp53-responsive luciferase reporter.
Human Tp53 is normally a short-lived protein. Tp53 protein is stabilized and levels are increased in response to a variety of cellular stresses, including those induced by genotoxic anticancer drugs and environmental exposures. To engineer an efficient assay based on this property, we constructed and integrated a Tp53-specific reporter system into human cancer cells, termed p53R cells. We tested a range of conventional chemotherapeutic agents as well as over 16 000 diverse small compounds. Ionizing radiation and two-thirds of conventional chemotherapeutic agents, but only 0.2% of diverse compounds activated Tp53 activity by two-fold or greater, consistent with the presumptive genotoxic activation of Tp53 function. Cytotoxicity was independent of TP53 genetic status when paired, syngeneic wild-type TP53 and TP53-null cells in culture were treated with compounds that activated Tp53. From the unbiased survey of random compounds, Tp53 activation was strongly induced by an analog of AMSA, an investigational anti-cancer agent. Tp53 was also strongly induced by an N-oxide of quinoline and by dabequine, an experimental antimalarial evaluated in humans; dabequine was reported to be negative in other screens of mutagenicity and clastogenicity but carcinogenic in animal studies. Further exploration of antimalarial compounds identified the common medicinals chloroquine, quinacrine, and amodiaquine as Tp53-inducers. Flavonoids are known to have DNA topoisomerase activity, a Tp53-inducing activity that is confirmed in the assay. A reported clinical association of Tp53 immunopositive colorectal cancers with use of the antihypertensive agents was extended by the demonstration of hydralazine and nifedipine as Tp53-inducers. p53R cells represent an efficient Tp53 functional assay to identify chemicals and other agents with interesting biologic properties, including genotoxicity. This assay may have utility in the identification of novel chemotherapeutic agents, as an adjunct in the pharmaceutical optimization of lead compounds, in the exploration of environmental exposures, and in chemical probing of the Tp53 pathway.
Immunohistochemical validation of a novel epithelial and a novel stromal marker of pancreatic ductal adenocarcinoma identified by global expression microarrays: sea urchin fascin homolog and heat shock protein 47.
We extended the results of a previous microarray analysis by immunohistochemical validation of differential protein expression in a series of 57 surgically resected infiltrating ductal pancreatic adenocarcinomas. Two representative genes were examined: sea urchin fascin homolog (overexpressed in both cell lines and primary tumors) and heat shock protein 47 (HSP47; overexpressed in primary tumors only). Protein expression also was evaluated in the precursor lesions of pancreatic cancer pancreatic intraepithelial neoplasia (PanIN), and normal ductal epithelium. Fascin expression was seen in the neoplastic cells of 54 (95%) of 57 ductal adenocarcinomas but not in 49 (94%) of 52 adjacent nonneoplastic epithelium. In the multistep pathogenesis of ductal adenocarcinomas, fascin expression seemed to be a late event, usually present in PanINs 2 and 3. HSP47 expression was almost universal and most intense in the ductal adenocarcinoma-associated stromal desmoplasia (57/57), although 37 cases (65%) also expressed HSP47 in the neoplastic epithelium. HSP47 expression was absent in the majority of nonneoplastic pancreata (46 [88%]). Fascin and HSP47 are novel tumor markers with potential diagnostic and therapeutic implications for pancreatic carcinoma. These results establish the usefulness of global expression platforms to identify novel tumor markers.
Fellowship goals for PhDs and MDs: a primer on the molecular biology postdoctoral experience.
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Whose hypothesis? Ciphering, sectorials, D lesions, freckles and the operation of Stigler's Law.
Common references to the famous two-hit hypothesis of tumorigenesis are pervasively erroneous, and the recited tenets of this model vary enormously. Exploration of the history of this model reveals a rich philosophical progression that profited from perceptive observations, clever musings, and rediscoveries by many investigators over a period of decades. The current work is intended to raise the appreciation for this rich history and to address some of the more common errors.
The essential similarity of TGFbeta and activin receptor transcriptional responses in cancer cells.
The binding of activin and TGFbeta to their respective receptors initiates signals that are carried by common intermediates (Smad proteins) to induce transcriptional activation of downstream genes. Mutations in tumors indicate that both receptor types convey tumorsuppressive signals, among other biologic roles, but their respective sets of transcriptional targets (transcriptomes) and the shared degree of transcriptome similarity are not well explored in these cells. Transcriptome changes were analyzed by gene expression profiling after expression of constitutively active activin type I (ALK4m) and TGFbeta type I (ALK5m) receptors and by variation of Smad4 expression in cancer cells. Eleven of 15 previously reported TGFbeta downstream genes were confirmed to be responsive to TGFb and activin receptors in cancer cells. Expression profiling detected eight of these 11, as well as 13 new Smad4-dependent transcripts. Although Smad4-dependent CDKN1A/p21 induction represents the sole known effector of TGFbeta and activin tumor-suppressor effects, many downstream genes have not yet been evaluated for a suppressive role. A high similarity of TGFbeta and activin responses among the known and new transcriptional target genes indicated an essential redundancy of the two related inputs. This similarity helps relate the mutations seen in both receptor systems and their Smad mediators in human cancers.
Analysis of anaphase figures in routine histologic sections distinguishes chromosomally unstable from chromosomally stable malignancies.
A classification of neoplasms as chromosomally stable vs. unstable is of importance in assessing inherited risks but is primarily defined in cell lines where rates of instability can be directly measured. The confirmation of such a mechanistic theory in primary tissues is desirable. We examined anaphase figures in histologic slides to evaluate such criteria. The process of chromosomal instability (CIN) involves mis-segregation of chromosomes at anaphase in some or most instances, whereas chromosomally stable tumors should lack these particular abnormalities. Anaphase bridges are associated with chromosome mis-segregation and have occasionally been observed in colorectal neoplasia and in sarcomas, but have not been considered for use as a diagnostic tool. We assembled series of sarcomas, colorectal and pancreatic carcinomas belonging to two groups: those associated with or lacking chromosomal instability. Among the chromosomally stable tumors, all lacked anaphase bridges, while anaphase bridges were found in most sarcomas and carcinomas having complex genomic alterations. These results confirm a mechanistic explanation involving chromosome mis-segregation for primary human cancers having aneuploidy/CIN. A basic mechanistic distinction between neoplasms with CIN and those with minimal chromosomal changes is supported. Most importantly, our data suggest a diagnostic utility for the examination of anaphase bridges in the routine practice of pathology with a high potential to impact clinical decision-making processes regarding colorectal cancer treatment.
An introduction to pancreatic adenocarcinoma genetics, pathology and therapy.
Cancer is bad, but pancreatic cancer is especially so. Underlying the aggressive behavior of pancreatic cancer is a highly patterned set of biologic rules for its development. The accumulating discoveries regarding the genetic basis of pancreatic cancer and developments in the clinical management of the disease provide hope for meaningful improvements in the understanding and control of this disease.
Quantitative selection constants.
The study of the genetics of human tumors produces numerical data concerning the frequencies of mutation of individual genes. These frequencies are dependent on a number of processes that act individually and differentially upon genes, and can in turn be conceptualized in quantitative terms to encompass the rates of random mutations within cells, the efficiencies of the evolution of initial mutations to produce the functional inactivation of genes, and selective pressures that act upon cellular populations. Some intuitive mathematical models can be used to organize and formalize our interpretation of the mutation rates of tumor-suppressor genes.
Polymorphisms of SPINK1 N34S and CFTR in patients with sporadic and familial pancreatic cancer.
Long standing chronic pancreatitis is a risk factor for developing pancreatic cancer. Inheritance of polymorphisms in SPINK1 and CFTR are associated with an increased risk of developing pancreatitis. The aim of this study was to determine if patients who carry polymorphisms in SPINK1 and CFTR are at increased risk of developing pancreatic cancer through the development of chronic pancreatitis. DNA from patients with histologically-confirmed surgically-treated chronic pancreatitis, familial and sporadic pancreatic adenocarcinoma and controls were analyzed for the N34S polymorphism of SPINK1 and the two commonest polymorphisms of the CFTR gene, the DF508 mutation and the 5T polymorphism. These polymorphisms were determined using restriction fragment length polymorphism, PCR and cycle sequencing methods. The SPINK1 N34S polymorphism was detected in 5 of 172 (2.9%) patients with chronic pancreatitis, in 4 of 200 (2.0%) patients with sporadic pancreatic adenocarcinoma, in 0 of 36 (0%) of patients with familial pancreatic cancer and in 3 of 177 (1.7%) controls of chronic cholecystitis. The CFTR 5T polymorphism was identified in 31 of 334 (9.3%) patients of sporadic pancreatic cancer, in 5 of 43 (11.6%) patients with familial pancreatic cancer and in 10 of 112 (8.9%) controls with colorectal cancer. The CFTR DF508 mutation was recognized in 6 of the 240 (2.5%) patients with pancreatic adenocarcinoma, a prevalence similar to that of control populations. We conclude that the N34S polymorphism of SPINK1 and the 5T and DF508 CFTR polymorphisms do not predispose to the development of pancreatic adenocarcinoma. Furthermore, the N34S polymorphism is rarely found in patients with severe idiopathic chronic pancreatitis.