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  • Title: PCNA bearing structures are retained in apoptotic phase of childhood ALL cell cycle.
    Author: Ball LM, Lannon CL, Yhap M, Pyesmany AF, Henry M, Laybolt K, Riddell DC, van Velzen D.
    Journal: Adv Exp Med Biol; 1999; 457():289-96. PubMed ID: 10500804.
    Abstract:
    BACKGROUND: Drug resistance to DNA directed therapy may depend on proliferative as well as apoptotic cell fraction. PCNA/Ki67 ratio excess, possibly reflecting DNA excision repair, is of additional interest to drug resistance in MTT testing. The cell cycle phase/antigen expression pattern in childhood acute lymphoblastic leukemia (ALL) is not known. AIMS: To study the relationship between nuclear expression of PCNA, Ki-67 and Frag-EL positivity in childhood ALL. METHODS: 1.3.1. Study Groups. Diagnostic bone marrow trephine biopsies of 32 consecutive unselected cases of childhood ALL were included in the study. 1.3.2. Immunohistochemistry. Commercially available Moab PCNA (PC10, DAKO, USA), Ki-67 (MM1, NovaCastra, UK) were used to label cycling cells in routinely processed 5 microns paraffin sections. 1.3.3. In-Situ Labelling of Apoptotic Cells. The 3'-OH ends of apoptosis specific DNA fragments were labelled in-situ on subsequent 10 microns sections (Frag-EL, CalBiochem, USA). 1.3.4. Quantitation. After blinding and randomisation, 10 systematic random fields of > 20 nuclei and nuclear size bias correction was used to determine positive nuclei fraction. RESULTS: While the sum of apoptotic and proliferative cell fraction (Ki-67 + Frag-EL%) equalled 100% in 5/32 cases, PCNA expression into at least the early phases of apoptosis ([%PCNA-%K-67] > [100-%Frag-EL] was found in 17/32 cases. CONCLUSIONS: PCNA/Ki67 ratio excess may not reflect DNA excision repair activity but rather slow degradation of antigen bearing structures limiting relevance to drug resistance study.
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