Apoptosis and proliferation: correlation with p53 in astrocytic tumours

Apoptosis and cell proliferation occur simultaneously in tumour tissue with tumour suppressor gene, p53 being one of the key players in the complex relationship between these two key phenomena. We, as well as several other groups, have earlier demonstrated the association of p53 immunopositivity with increased degree of cell proliferation in astrocytic tumours. Here we have studied the extent of apoptosis in 62 primary human astrocytic tumours [25 Diffuse Astrocytoma (DA), 9 Anaplastic Astrocytoma (AA) and 28 Glioblastoma multiforme (GBM)] in relation to tumour grade, proliferative status and p53 protein expression. Apoptosis was measured by the TUNEL assay while, cell proliferation (MIB-1 index) and p53 protein immunoreactivity were evaluated by immunohistochemical staining using MIB-1 and DO-1 monoclonal antibodies respectively. The apoptotic index (AI) was greater in GBM than in AA or DA, and more in tumours with p53 immunopositivity than in those without. The most striking observation was the strong correlation between Apoptotic index (AI) and proliferation index (PI) in p53 negative GBM (r=0.766, P<0.005). However this was not observed in p53+ve GBM or in low grade DA either p53 positive or negative. Taking p53 negativity in IHC as evidence of a functional gene/protein, this extends the link between proliferation and apoptosis, hitherto observed only in cultured cells with functional p53, to a subset of solid tumours.