Expression of Bovine Mammary Gland SMAD 4 and its Relationship to BRCA1

Abstract

Little is known about the role of TGF-ß in ruminant mammary growth and development. The literature suggests that TGF-ß could play an active role in influencing early mammary development and involution. SMADs are proteins that function as intracellular signaling effectors for the TGF-ß super family of polypeptides. We cloned bovine SMAD 4 and examined its mRNA expression in the mammary gland at various developmental stages. Sequencing analysis showed that bovine SMAD 4 had 96 and 94% homology to human and rat SMAD 4, respectively. Therefore, SMAD 4 appeared to be a very conserved gene in these species. SMAD 4 mRNA expression was highest in early pregnancy and involution, and then decreased in late pregnancy and maintained a low level through lactation. We speculate that SMAD 4 is involved in induction of regulatory genes involved in mammary gland growth and apoptosis. BRCA1 is a breast and ovarian cancer-specific tumor suppressor protein, with properties of a transcription factor involved in cell cycle regulation, DNA repair and apoptosis. BRCA1 gene expression is induced by steroid hormones and its pattern of mRNA expression mimicks that for TGF-ß and SMAD 4. We thought it of interest to determine if various doses of TGF- ß would induce BRCA1 gene expression. TGF- ß1 treated bovine mammary cells showed a dose dependent increase in BRCA1 mRNA expression compared to control treatments. Our results suggest that TGF- ß1, SMAD 4 and BRCA1 may play important roles in regulating ruminant mammary cell proliferation, differentiation, and involution or apoptosis.