LOSS OR ALTERED SUBCELLULAR-LOCALIZATION OF P27 IN BARRETTS ASSOCIATED ADENOCARCINOMA

The cyclin-dependent kinase inhibitor p27 is a negative regulator of t he cell division cycle. It is expressed at the highest levels during t he quiescent (G(0)) and prereplicative (G(1)) phases, and its degradat ion is required for entry into the S phase. Because lack of p27 is ass ociated with aggressive behavior in a variety of tumors of epithelial and lymphoid origin, we used immunohistochemistry and in situ hybridiz ation to evaluate the expression of p27 in metaplastic and dysplastic Barrett's epithelium and to assess its prognostic significance in Barr ett's associated adenocarcinoma (BAA) of the esophagus. In metaplastic Barrett's epithelium, p27 protein and mRNA were restricted to the sup erficial third of glands in all cases and extended to the lower third in 4 cases. In contrast, expression of p27 message and protein was bot h increased and full-thickness, in the 23 cases with high-grade dyspla sia adjacent to BAA and in carcinoma in situ. Although all invasive ca rcinomas had elevated levels of p27 mRNA, 45 (83%) of 54 invasive carc inomas had low p27 protein levels (<50% positive tumor cells). Low p27 protein correlated with higher histological grade (P<0.0001), depth o f invasion (P=0.0120), presence of lymph node metastasis (P=0.05), and survival (P=0.0197). In addition to the nuclear staining, cytoplasmic staining of p27 was noted in 11 of 23 (48%) of cases with dysplasia a nd in 14 of 54 (26%) adenocarcinomas and confirmed, in a subset of cas es, by subcellular fractionation of protein lysates obtained from fres h tumor tissues. Cytoplasmic localization of p27 was also associated w ith decreased survival (P=0.0239). Loss of p27 conferred poor prognosi s independently of proliferative index, as assessed by Ki-67 (MIB-1) i mmunostaining, which was not significantly different in survivors vers us nonsurvivors. These results show that: (a) distribution of p27 mess age and protein parallel one another in metaplastic and dysplastic Bar rett's epithelium, suggesting transcriptional regulation of the gene i n the nonneoplastic setting; (b) p27 is inactivated in the majority of BAA as a result of either post-transcriptional modification or altere d subcellular localization; and (c) loss of the cell cycle inhibitor p 27 is associated with parameters of aggressive behavior and unfavorabl e outcome in BAA.