ABSTRACT
The preparation of new chiral bicyclic imidazoles 5 and their transformation into imidazolium salts 6 and 7 are reported. The utility of the salts as precursors for chiral N-heterocyclic carbenes was demonstrated by the synthesis of C-N-C pincer Ni-complex 13h, the structure of which was characterized by single-crystal X-ray analysis.
ABSTRACT
BACKGROUND: Parathyroid hormone (PTH) rapidly down-regulates type IIa sodium-dependent phosphate transporter (NaPi-IIa) via an endocytic pathway. Since the relationship between PTH signaling and NaPi-IIa endocytosis has not been explored, we investigated the role of membrane microdomains in this process. METHODS: We examined the submembrane localization of NaPi-IIa in opossum kidney (OK-N2) cells that stably expressed human NaPi-IIa, and searched for a PTH-induced specific phosphorylating substrate on their membrane microdomains by immunoblotting with specific antibody against phospho substrates of protein kinases. RESULTS: We found that NaPi-IIa was primarily localized in low-density membrane (LDM) domains of the plasma membrane; PTH reduced the levels of immunoreactive NaPi-IIa in these domains. Furthermore, PTH activated both protein kinase A (PKA) and protein kinase Calpha (PKCa) and increased the phosphorylation of 250 kD and 80 kD substrates; this latter substrate was identified as ezrin, which a member of the ezrin-radixin-moesin (ERM) protein family. In response to PTH, ezrin was phosphorylated by both PKA and PKC. Dominant negative ezrin blocked the reduction in NaPi-IIa expression in the LDM domains that was induced by PTH. CONCLUSION: These data suggest that NaPi-IIa and PTH-induced phosphorylated proteins that include ezrin are compartmentalized in LDM microdomains. This compartmentalization may play an important role in the down-regulation of NaPi-IIa via endocytosis.
