Apoptosis and autophagy induced by TGF-beta1 in bovine mammary epithelial BME-UV1 cells

Mammary gland growth and involution is based on a dynamic equilibrium between proliferation and apoptosis of mammary gland epithelial cells (MEC). TGF-ß1 is an important antiproliferative and apoptogenic factor for mammary gland epithelial cells, acting in auto/paracrine matter and thus considered an important local regulator of mammary tissue involution. So far the studies on mammary gland involution concerned only apoptosis as a type I of MEC programmed cell death (PCD). Autophagy is known to be type II of PCD and this paper is the first, supporting evidence for the TGF-ß1-induced autophagy in bovine mammary epithelial cell line BME-UV1, as a distinct to apoptosis type of PCD. Laser scanning cytometry and confocal microscopy were used for analysis of MAP1 LC3 and Beclin1 expression - two proteins considered being the most reliable biochemical markers of autophagy. The significant increase of MAP1 LC3 and Beclin1 expression in cells treated with TGF-ß1 (2 ng/ml) was observed. Ultrastructural observation in electron microscopy revealed that autophagy is not only alternative, but also complementary to apoptosis type of cell death in TGF-ß1-treated bovine MEC. It was manifested by typical morphological features of apoptosis (cell shrinkage, margination and condensation of chromatin) and autophagy (autophagosomes, autophagic vacuoles) in the same cell.