[Effects of panax quinquefolius saponin of stem and leaf on glucose-lipid metabolism and insulin signal transduction in insulin resistant model adipocytes].

OBJECTIVE: To observe the effects of panax quinquefolius saponin (PQS) of stem and leaf on glucose-lipid metabolism and insulin signal transduction in the insulin resistant model of adipocytes. METHODS: The insulin resistant model of differentiated 3T3-L1 adipocytes was established in vitro with free fatty acid. After induction of insulin resistance, cells were treated with metformin or PQS for 2 days. The glucose consumption in culture fluid was detected by glucose oxidase method; the effects of PQS on the lipolysis induced by tumor necrosis factor (TNF-alpha) was observed using colorimetry; and the phospholation of signal proteins was detected by Western-blot. RESULTS: The amount of glucose consumption (mmol/L) in the model group (5.250 +/- 2. 671) was significantly lower than that in the normal control group (14.133 +/- 1.305, P < 0.01), it increased in the meformin treated group (11.807 +/- 1.358), and the groups treated with high-, middle- and low-dose PQS dose-dependently (10.784 +/- 2.373, 10.217 +/- 1.237 and 9.984 +/- 2.006, respectively), significantly higher than that in the model group (P < 0.01). Upon TNF-alpha treatment, the concentration of free fatty acid (FFA) (nmol/ microg) in culture medium was 2.479 +/- 0.597, predominantly higher than that in the control group (1.320 +/- 0.538, P < 0.01), while it was 1.210 +/- 0.566 in the metformin group, 1.105 +/- 0.631 in high-dose PQS group, 1.108 +/- 0.260 in the middle-dose PQS group, 1.201 +/- 0.593 in the low-dose PQS group, all were lower than that in the TNF-alpha group (P < 0.05 or P < 0.01), and a dose-dependent tendency of PQS's action was seen. The tyrosine phosphorylation of insulin receptor and IRS-1 as well as Ser473 phosphorylation of PKB were lower in the model group than in the control group; they were insignificantly changed in the low-dose PQS group, but did show significant difference in comparing with those in the high-and middle-dose PQS groups or metformin group. CONCLUSION: PQS can accelerate the glucose utilization and depress the lipolysis in adipocytes induced by TNF-alpha, which may be correlated with its promoting insulin signal transduction and improving insulin resistance in adipocytes.

ERK binds, phosphorylates InsP3 type 1 receptor and regulates intracellular calcium dynamics in DT40 cells.

Modulation on the duration of intracellular Ca(2+) transients is essential for B-cell activation. We have previously shown that extracellular-signal-regulated kinase (ERK) can phosphorylate inositol 1,4,5-trisphosphate receptor type 1 (IP(3)R1) at serine 436 and regulate its calcium channel activity. Here we investigate the potential physiological interaction between ERK and IP(3)R1 using chicken DT40 B-cell line in which different mutants are expressed. The interaction between ERK and IP(3)R1 is confirmed by co-immunoprecipitation and fluorescence resonance energy transfer (FRET) assays. This constitutive interaction is independent of either ERK kinase activation or IP(3)R1 phosphorylation status. Back phosphorylation analysis further shows that type 1 IP(3)R (IP(3)R1) is phosphorylated by ERK in anti-IgM-activated DT40 cells. Finally, our data show that the phosphorylation of Ser 436 in the IP(3)-binding domain of IP(3)R1 leads to less Ca(2+) release from endoplasmic reticulum (ER) microsomes and accelerates the declining of calcium increase in DT40 cells in response to anti-IgM stimulation.

Inositol 1,4,5-trisphosphate receptor type 1 phosphorylation and regulation by extracellular signal-regulated kinase.

Type 1 inositol 1,4,5-trisphosphate receptor (IP(3)R1) is a widely expressed intracellular calcium-release channel found in many cell types. The operation of IP(3)R1 is regulated through phosphorylation by multiple protein kinases. Extracellular signal-regulated kinase (ERK) has been found involved in calcium signaling in distinct cell types, but the underlying mechanisms remain unclear. Here, we present evidence that ERK1/2 and IP(3)R1 bind together through an ERK binding motif in mouse cerebellum in vivo as well as in vitro. ERK-phosphorylating serines (Ser 436) was identified in mouse IP(3)R1 and Ser 436 phosphorylation had a suppressive effect on IP(3) binding to the recombinant N-terminal 604-amino acid residues (N604). Moreover, phosphorylation of Ser 436 in R(224-604) evidently enhance its interaction with the N-terminal "suppressor" region (N223). At last, our data showed that Ser 436 phosphorylation in IP(3)R1 decreased Ca(2+) releasing through IP(3)R1 channels.

Strontium promotes calcium oscillations in mouse meiotic oocytes and early embryos through InsP3 receptors, and requires activation of phospholipase and the synergistic action of InsP3.

BACKGROUND: Sr2+ is the most efficient agent for mouse oocyte activation and functions by inducing Ca2+ oscillations. However, its specific mechanism of action remains unknown. Here we investigated the specificity and possible mechanism of Sr2+-induced Ca2+ oscillations in mouse oocytes and early embryos. METHODS: Ca2+ oscillations in oocytes and embryos were measured by ratiometric fluorescence imaging using fura-2AM. The role of phospholipase C (PLC) and inositol trisphosphate (InsP3) receptors in Sr2+-induced Ca2+ oscillations was examined by selective inhibitors. RESULTS: Sr2+ can induce Ca2+ oscillations in both immature and mature oocytes, and in early embryos. A cell cycle stage-dependent phenomenon to Sr2+ stimulation was observed in 1-cell embryos. By using a low molecular weight heparin to antagonize the function of InsP3 receptors, we were able to show that InsP3 receptors are essential for Sr2+-induced Ca2+ oscillations. Treating metaphase II (MII) oocytes with the PLC inhibitor, U73122, abolished Sr2+-induced increases in Ca2+. This inhibitory effect of U73122 could be rescued by microinjection of InsP3, indicating that Sr2+-induced Ca2+ oscillations require the synergistic action of InsP3. CONCLUSIONS: Sr2+-induced calcium oscillations in mouse oocytes and early embryos are mediated through InsP3 receptors, and require PLC activation and the synergistic action of InsP3.