P2X1 receptor-mediated inhibition of the proliferation of human coronary smooth muscle cells involving the transcription factor NR4A1.

Adenine nucleotides acting at P2X1 receptors are potent vasoconstrictors. Recently, we demonstrated that activation of adenosine A2B receptors on human coronary smooth muscle cells inhibits cell proliferation by the induction of the nuclear receptor subfamily 4, group A, member 1 (NR4A1; alternative notation Nur77). In the present study, we searched for long-term effects mediated by P2X1 receptors by analyzing receptor-mediated changes in cell proliferation and in the expression of NR4A1.

A₂B receptors mediate the induction of early genes and inhibition of arterial smooth muscle cell proliferation via Epac.

Aims: Extracellular adenosine and adenine nucleotides play important roles in the regulation of the blood vessel tonus and platelet aggregation. Less is known about the effects of these extracellular signalling molecules on gene expression in vascular smooth muscle cells involved in long-term vascular effects. In the present study, we therefore searched for adenosine-induced changes in the expression of early genes in cultured human coronary artery smooth muscle cells (HCASMCs).

The middle domain of Hsp90 acts as a discriminator between different types of client proteins.

The mechanism of client protein activation by Hsp90 is enigmatic, and it is uncertain whether Hsp90 employs a common route for all proteins. Using a mutational analysis approach, we investigated the activation of two types of client proteins, glucocorticoid receptor (GR) and the kinase v-Src by the middle domain of Hsp90 (Hsp90M) in vivo. Remarkably, the overall cellular activity of v-Src was highly elevated in a W300A mutant yeast strain due to a 10-fold increase in cellular protein levels of the kinase.

Aha1 competes with Hop, p50 and p23 for binding to the molecular chaperone Hsp90 and contributes to kinase and hormone receptor activation.

The ATP-dependent molecular chaperone Hsp90 (heat-shock protein 90) is essential for the maturation of hormone receptors and protein kinases. During the process of client protein activation, Hsp90 co-operates with cofactors/co-chaperones of unique sequence, e.g.

Aha1 binds to the middle domain of Hsp90, contributes to client protein activation, and stimulates the ATPase activity of the molecular chaperone.

The ATP-dependent molecular chaperone Hsp90 is an essential and abundant stress protein in the eukaryotic cytosol that cooperates with a cohort of cofactors/cochaperones to fulfill its cellular tasks. We have identified Aha1 (activator of Hsp90 ATPase) and its relative Hch1 (high copy Hsp90 suppressor) as binding partners of Hsp90 in Saccharomyces cerevisiae. By using genetic and biochemical approaches, the middle domain of Hsp90 (amino acids 272-617) was found to mediate the interaction with Aha1 and Hch1.