Homogeneous blue luminescent MoS2 quantum dots are fabricated by using a lithium intercalation method from MoS2 nanoparticles, and the unique blue photoluminescence property is utilized in the Alexa Fluor 430-dsDNA-MoS2 FRET system, demonstrating the dual function of MoS2 quantum dots as a donor and an acceptor.

The intestinal brush border (BB) Na+/H+ exchanger isoform 3 (NHE3) is acutely inhibited by elevation in the concentration of free intracellular Ca2+ ([Ca2+]i) by the cholinergic agonist carbachol and Ca2+ ionophores in a protein kinase C (PKC)-dependent manner. We previously showed that elevating [Ca2+]i with ionomycin rapidly inhibited NHE3 activity and decreased the amount of NHE3 on the plasma membrane in a manner that depended on the presence of the PDZ domain-containing protein E3KARP (NHE3 kinase A regulatory protein, also called NHERF2). The current studies were performed in PS120 fibroblasts (NHE-null cell line) stably transfected with NHE3 and E3KARP to probe the mechanism of PKC involvement in Ca2+ regulation of NHE3. Pretreatment with the general PKC inhibitor, GF109203X prevented ionomycin inhibition of NHE3 without altering basal NHE3 activity. Similarly, the Ca2+-mediated inhibition of NHE3 activity was blocked after pretreatment with the conventional PKC inhibitor Gö-6976 and a specific PKCalpha pseudosubstrate-derived inhibitor peptide. [Ca2+]i elevation caused translocation of PKCalpha from cytosol to membrane. PKCalpha bound to the PDZ1 domain of GST-E3KARP in vitro in a Ca2+-dependent manner. PKCalpha and E3KARP coimmunoprecipitated from cell lysates; this occurred to a lesser extent at basal [Ca2+]i and was increased with ionomycin exposure. Biotinylation studies demonstrated that [Ca2+]i elevation induced oligomerization of NHE3 in total lysates and decreased the amount of plasma membrane NHE3. Treatment with PKC inhibitors did not affect the oligomerization of NHE3 but did prevent the decrease in surface amount of NHE3. These results suggest that PKCalpha is not necessary for the Ca2+-dependent formation of the NHE3 plasma membrane complex, although it is necessary for decreasing the membrane amounts of NHE3, probably by stimulating NHE3 endocytosis.

Lysophosphatidic acid (LPA) activates a family of cognate G protein-coupled receptors and is involved in various pathophysiological processes. However, it is not clearly understood how these LPA receptors are specifically coupled to their downstream signaling molecules. This study found that LPA 2 , but not the other LPA receptor isoforms, specifically interacts with Na ؉ /H ؉ exchanger regulatory factor2 (NHERF2). In addition, the interaction between them requires the C-terminal PDZ domain-binding motif of LPA 2 and the second PDZ domain of NHERF2. Moreover, the stable expression of NHERF2 potentiated LPA-induced phospholipase C-␤ (PLC-␤) activation, which was markedly attenuated by either a mutation in the PDZ-binding motif of LPA 2 or by the gene silencing of NHERF2. Using its second PDZ domain, NHERF2 was found to indirectly link LPA 2 to PLC-␤3 to form a complex, and the other PLC-␤ isozymes were not included in the protein complex. Consistently, LPA 2 -mediated PLC-␤ activation was specifically inhibited by the gene silencing of PLC-␤3. In addition, NHERF2 increases LPA-induced ERK activation, which is followed by cyclooxygenase-2 induction via a PLC-dependent pathway. Overall, the results suggest that a ternary complex composed of LPA 2 , NHERF2, and PLC-␤3 may play a key role in the LPA 2 -mediated PLC-␤ signaling pathway.

Na ؉ /H؉ exchanger 3 (NHE3) kinase A regulatory protein (E3KARP) has been implicated in cAMP-and Ca 2؉ -dependent inhibition of NHE3. In the current study, a new role of E3KARP is demonstrated in the stimulation of NHE3 activity. Lysophosphatidic acid (LPA) is a mediator of the restitution phase of inflammation but has not been studied for effects on sodium absorption. LPA has no effect on NHE3 activity in opossum kidney (OK) proximal tubule cells, which lack expression of endogenous E3KARP. However, in OK cells exogenously expressing E3KARP, LPA stimulated NHE3 activity. Consistent with the stimulatory effect on NHE3 activity, LPA treatment increased the surface NHE3 amount, which occurred by accelerating exocytic trafficking (endocytic recycling) to the apical plasma membrane. These LPA effects only occurred in OK cells transfected with E3KARP. The LPAinduced increases of NHE3 activity, surface NHE3 amounts, and exocytosis were completely inhibited by pretreatment with the PI 3-kinase inhibitor, LY294002. LPA stimulation of the phosphorylation of Akt was used as an assay for PI 3-kinase activity. LY294002 completely prevented the LPA-induced increase in Akt phosphorylation, which is consistent with the inhibitory effect of LY294002 on the LPA stimulation of NHE3 activity. The LPA-induced phosphorylation of Akt was the same in OK cells with and without E3KARP. These results show that LPA stimulates NHE3 in the apical surface of OK cells by a mechanism that is dependent on both E3KARP and PI 3-kinase. This is the first demonstration that rapid stimulation of NHE3 activity is dependent on an apical membrane PDZ domain protein. Naϩ /H ϩ exchanger 3 (NHE3) 1 plays an essential role in NaCl and NaHCO 3 absorption in ileum, colon, gallbladder, and proximal tubule of kidney (1-3). NHE3 cycles between the plasma membrane and recycling endosomal compartment under basal conditions (4 -9). NHE3 is both rapidly stimulated and inhibited by several growth factors, neurotransmitters, and hormones that are released as part of digestion (1). These act by altering the amount of the NHE3 in the plasma membrane, as well as by changes in the NHE3 turnover number (1). For instance, epidermal growth factor and clonidine stimulate ileal sodium absorption by increasing the percentage of total NHE3 in the ileal brush border (BB) (10). In PS120 fibroblasts stably transfected with NHE3, the surface NHE3 amounts are stimulated by treatment with fibroblast growth factor (4). In opossum kidney proximal tubule cells exogenously transfected with the endothelin ␤ receptor, treatment with endothelin-1 increased the surface NHE3 amount and NHE3 activity (11,12) by an increase in exocytosis. Thus modulation of surface NHE3 amounts is a major mechanism in the acute stimulation of NHE3 activity by growth factors and hormones.Phosphatidylinositol (PI) 3-kinase has been implicated in stimulation of several plasma membrane transport processes, including those of GLUT4 and NHE3 (1,[4][5][6][7][8][9][13][14][15]. PI 3-kinase activation is associated with...