The Kdp system is widely distributed among bacteria. In Escherichia coli, the Kdp-ATPase is a high-affinity K ؉ uptake system and its expression is activated by the KdpDE two-component system in response to K ؉ limitation or salt stress. However, information about the role of this system in many bacteria still remains obscure. Here we demonstrate that KdpFABC in Staphylococcus aureus is not a major K ؉ transporter and that the main function of KdpDE is not associated with K ؉ transport but that instead it regulates transcription for a series of virulence factors through sensing external K ؉ concentrations, indicating that this bacterium might modulate its infectious status through sensing specific external K ؉ stimuli in different environments. Our results further reveal that S. aureus KdpDE is upregulated by the Agr/RNAIII system, which suggests that KdpDE may be an important virulence regulator coordinating the external K ؉ sensing and Agr signaling during pathogenesis in this bacterium.

Extracellular signal-regulated kinase signal transduction pathway could regulate cell proliferation, the secretion of type I collagen and transforming growth factor-beta-1 mRNA expression of rat hepatic stellate cells stimulated by acetaldehyde. This is most likely related to its regulative effect on the cell cycle.