Spontaneous immortalization of clinically normal colon-derived fibroblasts from a familial adenomatous polyposis patient.

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancer-suppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, and E6/E7) can lead to escape from senescence, additional doublings, and entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, and will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

Intestinal metaplasia at the gastroesophageal junction: Barrett's, bacteria, and biomarkers.

For patients found to have intestinal metaplasia at the gastroesophageal junction, technical problems can make it difficult to distinguish short-segment Barrett's esophagus from intestinal metaplasia of the gastric cardia. Whereas the risk of malignancy for the former condition seems to be higher than that for the latter, the distinction between these conditions can have practical clinical implications. Immunostaining for cytokeratins has been proposed as a means to distinguish intestinal metaplasia of esophageal and gastric origins. We review recent data on this issue, and conclude that immunostaining for cytokeratins has no clear advantages over other biomarkers that have been proposed for identifying Barrett's esophagus (e.g., mucin histochemistry, mAb Das-1 immunoreactivity). Presently, the importance of intestinal metaplasia at the gastroesophageal junction remains unclear, and the clinical utility of biomarkers in distinguishing short-segment Barrett's esophagus from intestinal metaplasia of the gastric cardia has not yet been established.

Bypass of telomere-dependent replicative senescence (M1) upon overexpression of Cdk4 in normal human epithelial cells.

Many stimuli causing 'stress' or DNA damage in cells can produce phenotypes that overlap with telomere-based replicative senescence. In epithelial systems, the p16/RB pathway may function as a stress senescence-signaling pathway independent of telomere shortening. Overexpressing cyclin-dependent kinase 4 (Cdk4) in human epidermal keratinocytes and human mammary epithelial cells not only prevents the p16(INK4a)-associated premature growth arrest due to telomere-independent stress (e.g., inadequate culture conditions), but also bypasses the ensuing telomere-dependent senescence (M1). Overexpressed Cdk4 in epithelial cells induces a dramatic upregulation of p16(INK4a) and milder upregulation of p53 and p21(WAF1), which become unresponsive to UV irradiation. Despite the high levels of these checkpoint factors, Cdk4-overexpressing cells divide in an apparently normal regulated fashion, are able to respond to changes in calcium levels, retain the stem cell phenotype, and fully differentiate and stratify. These results suggest that the differentiation pathways in Cdk4-overexpressing cells remain intact.

Hallmarks of cancer progression in Barrett's oesophagus.

CONTEXT: Hanahan and Weinberg proposed in 200 that carcinogenesis involves DNA changes that enable cells to:provide their own growth signals, ignore growth-inhibitory signals, avoid apoptosis, replicate without limit, sustain angiogenesis, and invade and proliferate in unnatural locations. The metaplastic cells of Barrett's oesophagus are predisposed to develop these cancer hallmarks. STARTING POINT: The genetic changes that have been described in Barrett's oesophagus can be categorised according to the predominant cancer hallmark affected. For example, M Auvinen and colleagues recently observed abnormalities in the expression of vascular endothelial growth factors (VEGFs) in Barrett's oesophagus (J Clin Oncol 2002; 20: 2971-79). These abnormalities can be categorised as those that affect angiogenesis, a process that is essential for the development and progression of tumours. WHERE NEXT? The cancer hallmarks of Barrett's oesophagus provide a framework to categorise the genetic abnormalities described and to further understanding of the genetic events that underlie oesophageal carcinogenesis.