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The aim of this review is to present a concrete model of apoptosis, namely the physiological death of mammary epithelial cells, and put emphasis on the role of Bcl-2 related proteins in the regulation of this process. The `paper is based on the literature and our own observations related to the regulatory mechanisms of mammary gland remodelling. Bax and Bcl-2 belong to the key regulators of apoptosis controlling ion (K+, H+, Cl-, Ca2+) and reactive oxygen species fluxes within the cell, releasing apoptogenic factors (AIF,cytochrome c) from mitochondria and activating executors of apoptosis (caspases, DNases). Apoptosis of mammary epithelial cells studied both in vitro (cell cultures i.e. HC11 and MCF-7) and in vivo (i.e. mammary gland of goat during lactation and involuting mammary gland of sow) is associated with the altered expression of bax and bcl-2 and intracellular redistribution of their products. In general, "survival factors" i.e. prolactin, EGF increase expression of bcl-2 and inhibit expression of bax, whereas "death factors" i.e. auto-/paracrine functioning TGF-b1 increase intracellular Bax/Bcl-2 ratio. TGF-b1 in addition to transcriptional activation stimulates redistribution of Bax protein from cytosol to organellar membranes (mitochondrial, endoplasmic reticulum, Golgi apparatus) and to nucleus. The end of lactation is associated with the drop of endocrine secretion of lactogenic hormones (prolactin, growth hormone), which in turn leads to augmented expression of local, intramammary derived growth inhibitors and inductors of apoptosis (TGF-bS, FIL, MDGI, mammastatin). Consequently, increased expression of apoptotic promoters (Bax, Bcl-xs) and activation of executors inevitably leads to massive apoptosis of epithelial cells, responsible for involution of mammary gland.

The Editorial Board
Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

Editorial address:
Katedra i Zakład Histologii i Embriologii Uniwersytetu Medycznego w Poznaniu, ul. Święcickiego 6, 60-781 Poznań, tel. +48 61 8546453, fax. +48 61 8546440, email:

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