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Open Access Research article

p27Kip1 is expressed in proliferating cells in its form phosphorylated on threonine 187

Giancarlo Troncone1*, Juan C Martinez2, Antonino Iaccarino1, Pio Zeppa1, Alessia Caleo1, Maria Russo1, Ilenia Migliaccio1, Maria L Motti3, Daniela Califano4, Emiliano A Palmieri1 and Lucio Palombini1

Author Affiliations

1 Dipartimento di Scienze Biomorfologiche e Funzionali, Facoltà di Medicina e Chirurgia, Università Federico II, Napoli, Italy

2 Istituto Oftalmico, Hospital Universitario Gregorio Maranon, Madrid, Spain

3 Dipartimento di Biologia e Patologia Cellulare e Molecolare "L Califano", Facoltà di Medicina e Chirurgia, Università Federico II, Napoli, Italy

4 Dipartimento di Oncologia Sperimentale, Fondazione G. Pascale, Napoli, Italy

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BMC Clinical Pathology 2005, 5:3  doi:10.1186/1472-6890-5-3

Published: 23 February 2005

Abstract

Background

G1/S cell cycle progression requires p27Kip1 (p27) proteolysis, which is triggered by its phosphorylation on threonine (Thr) 187. Since its levels are abundant in quiescent and scarce in cycling cells, p27 is an approved marker for quiescent cells, extensively used in histopathology and cancer research.

Methods

However here we showed that by using a specific phosphorylation site (pThr187) antibody, p27 is detectable also in proliferative compartments of normal, dysplastic and neoplastic tissues.

Results

In fact, whereas un-phosphorylated p27 and MIB-1 showed a significant inverse correlation (Spearman R = -0.55; p < 0,001), pThr187-p27 was positively and significantly correlated with MIB-1 expression (Spearman R = 0.88; p < 0,001). Thus proliferating cells only stain for pThr187-p27, whereas they are un-reactive with the regular p27 antibodies. However increasing the sensitivity of the immunocytochemistry (ICH) by the use of an ultra sensitive detection system based on tiramide signal amplification, simultaneous expression and colocalisation of both forms of p27 was shown in proliferating compartments nuclei by double immunofluorescence and laser scanning confocal microscopy studies.

Conclusion

Overall, our data suggest that p27 expression also occurs in proliferating cells compartments and the combined use of both regular and phospho- p27 antibodies is suggested.