Anomalous High p27/KIP1 Expression in a Subset of Aggressive B-Cell Lymphomas Is Associated With Cyclin D3 Overexpression. p27/KIP1—Cyclin D3 Colocalization in Tumor Cells

Abstract

p27 cyclin-dependent kinase inhibitor downregulation is essential for transition to the S phase of the cell cycle. Thus, proliferating cells in reactive lymphoid tissue show no detectable p27 expression. Nevertheless, anomalous high p27 expression has been shown to be present in a group of aggressive B-cell lymphomas with high proliferation index and adverse clinical outcome. This suggests that abnormally accumulated p27 protein has been rendered functionally inactive. We analyzed the causes of this anomalous presence of p27 in a group of aggressive B-cell lymphomas, including 54 cases of diffuse large B-cell lymphomas and 20 Burkitt’s lymphomas. We simultaneously studied them for p27, cyclin D3, cyclin D2, cyclin D1, and cyclin E expression, because it has been stated that high levels of expression of cyclin D1 or E lead to increased p27 levels in some cell types. A statistically significant association between p27 and cyclin D3 expression was found for the group as a whole. Additionally, when dividing the cases according to the level of expression of cyclin D3 by reactive germinal centers, it was observed that cases with stronger cyclin D3 expression also show higher p27 expression. The relationship between both proteins was also shown at a subcellular level by laser confocal studies, showing that in cases with high expression of both proteins there was a marked colocalization. Additional evidence in favor of p27 sequestration by cyclin D3 was provided by coimmunoprecipitation studies in a Burkitt’s cell line (Raji) showing the existence of cyclin D3/p27 complexes and the absence of CDK2/p27 complexes. These results could support the hypothesis that there are cyclin D3/p27 complexes in a subset of aggressive B-cell lymphomas in which p27 lacks the inhibitory activity found when it is bound to cyclin E/CDK2 complexes. This interaction between both proteins could lead to an abnormal nuclear accumulation, detectable by immunohistochemical techniques.

Growth regulation by p27Kip1 is abrogated by multiple mechanisms in aggressive malignant lymphomas

“…This observation was in keeping with our results, which showed that a significant proportion (approximately 40%) of total p27 Kip1 protein was found in the cytoplasmic fraction of 6/11 of lymphoma cell lines. Previous laser confocal microscopy and co‐immunoprecipitation studies (Sanchez‐Beato et al , 1999) have shown the existence of cyclin D3/p27 Kip1 complexes within the nucleus of Burkitt lymphoma cells. Cytoplasmic displacement/sequestration of p27 Kip1 has been reported to be a potential mechanism of its inactivation (Barnouin et al , 1999).…”

“…A positive correlation between p27 Kip1 and cyclin D3 levels was observed in Jurkat and PB697 while a negative correlation was seen in HPB, Nalm‐6 and Raji cells. Sanchez‐Beato et al (1999) have previously demonstrated that cyclin D3/p27 Kip1 complexes within the nucleus are inactive in a subset of aggressive B lymphomas. Immunoprecipitation studies of seven cell lines with variable levels of p27 Kip1 expression, including three with high p27 Kip1 levels (Jurkat, CEM‐ and PB697) and low (NCEB) to minimal levels of p27 Kip1 (Raji, OCI LY‐1 and Nalm‐6), followed by immunoblotting with anticyclin D3 antibody (Fig 5C), demonstrated the presence of cyclin D3/p27 Kip1 complexes within both the nuclear and cytoplasmic fractions.…”

“…Cytoplasmic displacement and sequestration of p27 Kip1 has been reported to be potential mechanisms of p27 Kip1 inactivation in a number of neoplastic cells (Singh et al , 1998; Sgambato et al , 1999). In addition, anomalous high p27 Kip1 expression and its association with overexpressed cyclin D3 in some aggressive B‐cell lymphomas (Barnouin et al , 1999; Sanchez‐Beato et al , 1999) is suggested to be a mechanism contributing to p27 Kip1 inactivation. This, together with our current in vivo and in vitro observation of cytoplasmic expression of p27 Kip1 , led us to analyse its expression in subcellular fractions of lymphoma cells.…”

“…A subset of lymphomas, however, failed to demonstrate an inverse relationship between p27 Kip1 and MIB1 (Quintanilla‐Martinez et al , 1998). More recent studies have reported anomalous high p27 Kip1 expression in subsets of aggressive B lymphomas (Barnouin et al , 1999; Sanchez‐Beato et al , 1999), as well as in malignant gliomas (Nakasu et al , 1999) with altered subcellular localization of p27 Kip1 contributing to the neoplastic process in oesophageal carcinoma (Sgambato et al , 1998; Singh et al , 1998). In this study, we expanded on these observations to determine the prevalence of high p27 Kip1 expression in a diverse group of malignant lymphoma cell lines and tissues and to determine potential mechanisms by which lymphoma cells abrogate the growth inhibitory effect of high p27 Kip1 .…”

Prognostic significance of the F‐box protein Skp2 expression in diffuse large B‐cell lymphoma

“…Dysregulation in expressions of CDK inhibitors, such as p15 and p16, has also been shown to be involved in lymphomagenesis [21]. Tracing these trends, recent studies have focused on the involvement of the universal CDK inhibitor p27 in lymphomagenesis [12,13,22,23], because p27 is known to be an amount-dependent tumor-suppressive protein [6]. Indeed, a reduced intracellular concentration of p27 protein in cancer cells has been shown to correlate with poor prognosis [6,8], and the loss of p27 allele in mice increased the sensitivity of these animals to carcinogenic agents [24].…”