Messenger (Los Angeles, Calif. : Print)最新文献

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃1] mobilizes intracellular Ca²⁺ through the Ins(1,4,5)P₃ receptor [InsP₃R]. Although some progress has been made in the design of synthetic InsP₃R partial agonists and antagonists, there are still few examples of useful small molecule competitive antagonists. A "multivalent" approach is explored and new dimeric polyphosphorylated aromatic derivatives were designed, synthesized and biologically evaluated. The established weak InsP₃R ligand benzene 1,2,4-trisphosphate [Bz(1,2,4)P₃2] is dimerized through its 5-position in two different ways, first directly as the biphenyl derivative biphenyl 2,2',4,4',5,5'-hexakisphosphate, [BiPh(2,2',4,4',5,5')P₆8] and with its regioisomeric biphenyl 3,3',4,4',5,5'-hexakisphosphate [BiPh(3,3',4,4',5,5')P₆11]. Secondly, a linker motif is introduced in a flexible ethylene-bridged dimer (9) with its corresponding 1,2-bisphosphate dimer (10), both loosely analogous to the very weak antagonist 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA 7). In permeabilized L15 fibroblasts overexpressing type 1 InsP₃R, BiPh(2,2',4,4',5,5')P₆ (8) inhibits Ins(1,4,5)P₃-induced Ca²⁺ release in a apparently competitive fashion [IC₅₀ 187 nM] and the Bz(1,2,4)P₃ dimer (9) is only slightly weaker [IC₅₀ 380 nM]. Compounds were also evaluated against type I Ins(1,4,5)P₃ 5-phosphatase. All compounds are resistant to dephosphorylation, with BiPh(2,2',4,4',5,5')P₆ (8), being the most effective inhibitor of any biphenyl derivative synthesized to date [IC₅₀ 480 nM] and the Bz(1,2,4)P₃ ethylene dimer (9) weaker [IC₅₀ 3.55 μM]. BiPh(3,3',4,4',5,5')P₆ (11) also inhibits 5-phosphatase [IC₅₀ 730 nM] and exhibits unexpected Ca²⁺ releasing activity [EC₅₀ 800 nM]. Thus, relocation of only a single mirrored phenyl phosphate group in (11) from that of antagonist (8) does not markedly change enzyme inhibitory activity, but elicits a dramatic switch in Ca²⁺-releasing activity. Such new agents demonstrate the power of the multivalent approach and may be useful to investigate the chemical biology of signaling through InsP₃R and as templates for further design.

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a messenger that regulates calcium release from intracellular acidic stores. Although several channels, including two-pore channels (TPC), ryanodine receptor (RYR) and mucolipin (TRP-ML1) have been implicated in NAADP regulation of calcium signaling, the NAADP receptor has not been identified. In this study, the photoaffinity probe, [³²P]-5-azido-NAADP ([³²P]-5-N₃-NAADP), was used to study NAADP binding proteins in extracts from NAADP responsive Jurkat T-lymphocytes. [³²P]-5-N₃-NAADP photolabeling of Jurkat S100 cytosolic fractions resulted in the labeling of at least ten distinct proteins. Several of these S100 proteins, including a doublet at 22/23 kDa and small protein at 15 kDa displayed selectivity for NAADP as the labeling was protected by inclusion of unlabeled NAADP, whereas the structurally similar NADP required much higher concentrations for protection. Interestingly, the labeling of several S100 proteins (60, 45, 33 and 28 kDa) was stimulated by low concentrations of unlabeled NAADP, but not by NADP. The effect of NAADP on the labeling of the 60 kDa protein was biphasic, peaking at 100 nM with a five-fold increase and displaying no change at 1 µM NAADP. Several proteins were also photolabeled when the P100 membrane fraction from Jurkat cells was examined. Similar to the results with S100, a 22/23 kDa doublet and a 15 kDa protein appeared to be selectively labeled. NAADP did not increase the labeling of any P100 proteins as it did in the S100 fraction. The photolabeled S100 and P100 proteins were successfully resolved by two-dimensional gel electrophoresis. [³²P]-5-N₃-NAADP photolabeling and two-dimensional electrophoresis should represent a suitable strategy in which to identify and characterize NAADP binding proteins.

NAADP is a potent Ca²⁺ mobilizing messenger in a variety of cells but its molecular mechanism of action is incompletely understood. Accumulating evidence indicates that the poorly characterized two-pore channels (TPCs) in animals are NAADP sensitive Ca²⁺-permeable channels. TPCs localize to the endo-lysosomal system but are functionally coupled to the better characterized endoplasmic reticulum Ca²⁺ channels to generate physiologically relevant complex Ca²⁺ signals. Whether TPCs directly bind NAADP is not clear. Here we discuss the idea based on recent studies that TPCs are the pore-forming subunits of a protein complex that includes tightly associated, low molecular weight NAADP-binding proteins.