Influence of protein kinase inhibitors on Streptococcus uberis internalization into bovine mammary epithelial cells

Previous reports indicated that bovine mammary epithelial cells internalized Streptococcus uberis, a bovine mastitis pathogen, and that inhibitors of F-actin microfilament polymerization inhibited bacterial internalization into mammary epithelial cells. In the present report, we show that inhibitors of eukaryotic cell tyrosine protein kinase (TPK) and protein kinase C (PKC), staurosporine, genistein and tyrphostin, significantly reduced internalization of S. uberis into mammary epithelial cells. Short-term treatment (15 min) of mammary epithelial cells with 12- O -tetradecanoylphorbol-13-acetate (TPA), shown previously to up-regulate activity of PKC, significantly increased internalization of S. uberis. Conversely, long-term incubation (24 h) of epithelial cells with TPA, which down-regulates PKC activity, significantly reduced the number of internalized S. uberis. These results suggest that protein kinases (TPK and PKC) are involved in internalization of S. uberis into bovine mammary epithelial cells. Identification of host cell surface receptor(s) and ligands that trigger the uptake signal by S. uberis need to be delineated.