Spontaneously immortalised bovine mammary epithelial cells exhibit a distinct gene expression pattern from the breast cancer cells

Abstract

BackgroundSpontaneous immortalisation of cultured mammary epithelial cells (MECs) is an extremely rare event, and the molecular mechanism behind spontaneous immortalisation of MECs is unclear. Here, we report the establishment of a spontaneously immortalised bovine mammary epithelial cell line (BME65Cs) and the changes in gene expression associated with BME65Cs cells.ResultsBME65Cs cells maintain the general characteristics of normal mammary epithelial cells in morphology, karyotype and immunohistochemistry, and are accompanied by the activation of endogenous bTERT (bovine Telomerase Reverse Transcriptase) and stabilisation of the telomere. Currently, BME65Cs cells have been passed for more than 220 generations, and these cells exhibit non-malignant transformation. The expression of multiple genes was investigated in BME65Cs cells, senescent BMECs (bovine MECs) cells, early passage BMECs cells and MCF-7 cells (a human breast cancer cell line). In comparison with early passage BMECs cells, the expression of senescence-relevant apoptosis-related gene were significantly changed in BME65Cs cells. P16INK4a was downregulated, p53 was low expressed and Bax/Bcl-2 ratio was reversed. Moreover, a slight upregulation of the oncogene c-Myc, along with an undetectable level of breast tumor-related gene Bag-1 and TRPS-1, was observed in BME65Cs cells while these genes are all highly expressed in MCF-7. In addition, DNMT1 is upregulated in BME65Cs. These results suggest that the inhibition of both senescence and mitochondrial apoptosis signalling pathways contribute to the immortality of BME65Cs cells. The expression of p53 and p16INK4a in BME65Cs was altered in the pattern of down-regulation but not "loss", suggesting that this spontaneous immortalization is possibly initiated by other mechanism rather than gene mutation of p53 or p16INK4a.ConclusionsSpontaneously immortalised BME65Cs cells maintain many characteristics of normal BMEC cells and exhibit non-malignant transformation. Although this cell line displays altered patterns of gene expression, it is clearly distinct from malignant breast cancer cell line. It showed that co-inhibition of cellular senescence and mitochondrial apoptosis pathways coordinates BME65Cs cells immortalisation. Additionally, mechanisms other than gene mutation are likely to be involved in regulation of cellular functions. This study provides an insight into the relationship between cell senescence and immortalisation. BME65Cs cells will be useful in future studies of cellular senescence and tumorigenesis.

Spontaneous immortalization of mouse liver sinusoidal endothelial cells

“…Furthermore, these immortalized LSECs did not show any chromosomal changes or tumorigenic potential in vitro and in vivo . Similar findings have also been reported in the establishment of a spontaneously immortalized bovine mammary epithelial cell line ( 35 ). Based on these results, we speculated that a ‘non-classical’ immortalization may exist, consistent with previous studies demonstrating that the spontaneous immortalization of mouse myogenic cells can occur without the loss of p53 ( 36 ) or karyotype abnormality ( 35 ).…”

Establishment and Characterization of a Buffalo (Bubalus bubalis) Mammary Epithelial Cell Line

“…Presence of very few senescent cells among a largely populated viable BuMECs suggests that the cells have undergone random transformation events leading to possible immortalization. Spontaneously immortalized bovine MECs have been reported to maintain normal morphology and proliferation characteristics with 10% of the cells being positive for SA- β-gal staining, which constituted non-immortal cells [40] . Classical features of senescence in Human mammary epithelial cells show flat morphology, presence of vacuoles and positive staining for senescence-associated β-galactosidase (SA-β-gal), a marker for senescence [41] .…”

Effects of Hydroxytyrosol against Lipopolysaccharide-Induced Inflammation and Oxidative Stress in Bovine Mammary Epithelial Cells: A Natural Therapeutic Tool for Bovine Mastitis

“…Bovine mammary epithelial cell lines, like mammary alveolar (MAC-T) cells, are one of the most used cell lines to study inflammation, lipid metabolism and apoptosis [ 38 , 39 , 40 , 41 ]. In particular, MAC-T cells represent a convenient validation system for investigating lactation and bioactive substances with the mammary tissue-specific casein promoter [ 42 ].…”