The protein p130 was originally isolated from rat brain as an inositol 1,4,5-trisphosphate-binding protein with a domain organization similar to that of phospholipase C-δ1 but which lacks phospholipase C activity. Yeast two-hybrid screening of a human brain cDNA library for clones that encode proteins that interact with p130 has now led to the identification of the catalytic subunit of protein phosphatase 1α (PP1cα) as a p130-binding protein. The association between p130 and PP1cα was also confirmedin vitro by an overlay assay, a “pull-down” assay, and surface plasmon resonance analysis. The interaction of p130 with PP1cα resulted in inhibition of the catalytic activity of the latter in a p130 concentration-dependent manner. Immunoprecipitation and immunoblot analysis of COS-1 cells that stably express p130 and of mouse brain extract with antibodies to p130 and to PP1cα also detected the presence of a complex of p130 and PP1cα. The activity of glycogen phosphorylase, which is negatively regulated by dephosphorylation by PP1cα, was higher in COS-1 cells that stably express p130 than in control COS-1 cells. These results suggest that, in addition to its role in inositol 1,4,5-trisphosphate and Ca²⁺ signaling, p130 might also contribute to regulation of protein dephosphorylation through its interaction with PP1cα.

Phosphorylation of hormone-sensitive lipase (HSL) and perilipin by protein kinase A (PKA) promotes the hydrolysis of lipids in adipocytes. Although activation of lipolysis by PKA has been well studied, inactivation via protein phosphatases is poorly understood. Here, we investigated whether phospholipase C-related catalytically inactive protein (PRIP), a binding partner for protein phosphatase 1 and protein phosphatase 2A (PP2A), is involved in lipolysis by regulating phosphatase activity. PRIP knockout (PRIP-KO) mice displayed reduced body-fat mass as compared with wild-type mice fed with standard chow ad libitum. Most other organs appeared normal, suggesting that mutant mice had aberrant fat metabolism in adipocytes. HSL in PRIP-KO adipose tissue was highly phosphorylated compared to that in wild-type mice. Starvation of wild-type mice or stimulation of adipose tissue explants with the catabolic hormone, adrenaline, translocated both PRIP and PP2A from the cytosol to lipid droplets, but the translocation of PP2A was significantly reduced in PRIP-KO adipocytes. Consistently, the phosphatase activity associated with lipid droplet fraction in PRIP-KO adipocytes was significantly reduced and was independent of adrenaline stimulation. Lipolysis activity, as assessed by measurement of non-esterified fatty acids and glycerol, was higher in PRIP-KO adipocytes. When wild-type adipocytes were treated with a phosphatase inhibitor, they showed a high lipolysis activity at the similar level to PRIP-KO adipocytes. Collectively, these results suggest that PRIP promotes the translocation of phosphatases to lipid droplets to trigger the dephosphorylation of HSL and perilipin A, thus reducing PKA-mediated lipolysis.

The metabolic processes of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] into PI(3,4,5)P₃ and the subsequent PI(3,4,5)P₃ signalling are involved in cell migration. Dysfunctions in the control of this pathway can cause human cancer cell migration and metastatic growth. Here we investigated whether phospholipase C-related catalytically inactive protein (PRIP), a PI(4,5)P₂-binding protein, regulates cancer cell migration. PRIP overexpression in MCF-7 and BT-549 human breast cancer cells inhibited cell migration in vitro and metastasis development in vivo. Overexpression of the PRIP pleckstrin homology domain, a PI(4,5)P₂ binding motif, in MCF-7 cells caused significant suppression of cell migration. Consistent with these results, in comparison with wild-type cells, Prip-deficient mouse embryonic fibroblasts exhibited increased cell migration, and this was significantly attenuated upon transfection with a siRNA targeting p110α, a catalytic subunit of class I phosphoinositide 3-kinases (PI3Ks). PI(3,4,5)P₃ production was decreased in Prip-overexpressing MCF-7 and BT-549 cells. PI3K binding to PI(4,5)P₂ was significantly inhibited by recombinant PRIP in vitro, and thus the activity of PI3K was downregulated. Collectively, PRIP regulates the production of PI(3,4,5)P₃ from PI(4,5)P₂ by PI3K, and the suppressor activity of PRIP in PI(4,5)P₂ metabolism regulates the tumour migration, suggesting PRIP as a promising target for protection against metastatic progression.

Background: The aim of this double-blind randomized cross-over trial was to evaluate the effect of oral intake of glucosylceramide extracted from pineapple on oral moisture and xerostomia symptoms. Methods: Sixteen participants who had xerostomia symptoms were randomly allocated into two groups. One group received, as test samples, tablets containing glucosylceramide extracted from pineapple (GCP) followed by placebo tablets. The other group received the test samples in the reverse order. Participants were instructed to take tablets of the first test sample once a day (after breakfast) for two consecutive weeks. Then, after a washout period of four weeks, participants were instructed to take the other test sample for two consecutive weeks. The oral moisture level of the lingual mucosa, xerostomia symptoms, and the number of fungiform papillae was evaluated. Results: The oral moisture significantly increased, and the visual analog scale (VAS) of “How is the dryness of your mouth?” significantly improved after GCP tablets intake and not after placebo tablets intake. The number of fungiform papillae was not significantly different following the intake of GCP tablets or placebo tablets. Conclusion: Results suggested that oral intake of GCP may improve the moisture level and xerostomia symptoms.