Phospholipase C-related catalytically inactive protein participates in the autophagic elimination of Staphylococcus aureus infecting mouse embryonic fibroblasts

Phospholipase C-related catalytically inactive protein enhances cisplatin-induced apoptotic cell death

Cisplatin is one of the most widely used chemotherapeutic agents and induces caspase-9-mediated apoptosis. Here, we examined whether phospholipase C-related catalytically inactive protein (PRIP) enhances cisplatin-induced apoptosis of breast cancer cells. PRIP depletion increased expression of X-linked inhibitor of apoptosis protein (XIAP) by inhibiting protein degradation, which is downstream of the phosphatidylinositol 3-kinase/AKT pathway and inhibits apoptotic signaling by blocking caspase-9 activation. Conversely, the viability of MCF-7 cells transfected with Prip1 was significantly lower than that of control cells in the presence of cisplatin. The number of apoptotic nuclei and expression levels of cleaved caspase-9 and downstream cleaved caspase-7 and poly-ADP ribose polymerase were greater in PRIP1-expressing MCF-7 cells treated with cisplatin than in control cells. XIAP was decreased by expression of pleckstrin homology domain of PRIP1 (PRIP1-PH domain) that blocked phosphatidylinositol 4,5 bisphosphate metabolism. In an orthotopic transplantation model, combined administration of PRIP1-PH domain-containing liposomes and cisplatin reduced the size of MCF-7 tumors compared with cisplatin alone. Our findings demonstrate that PRIP promotes XIAP degradation by inhibiting PI(3,4,5)P₃/AKT signaling and enhances cisplatin-induced apoptotic cell death. Therefore, we propose that PRIP1-PH liposomes are a novel agent to avoid cisplatin resistance.

Autophagy in Staphylococcus aureus Infection

Staphylococcus aureus is an invasive, facultative intracellular pathogen that can colonize niches in various host organisms, making it difficult for the host immune system to completely eliminate. Host autophagy is an intracellular clearance pathway involved in degrading S. aureus. Whereas the accessory gene regulatory system of S. aureus that controls virulence factors could resist the host immune defenses by evading and even utilizing autophagy. This article reviews the interaction between autophagy and S. aureus, providing insights on how to use these mechanisms to improve S. aureus infection control.

Suppression of cell migration by phospholipase C-related catalytically inactive protein-dependent modulation of PI3K signalling

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.

Phospholipase C-related catalytically inactive protein can regulate obesity, a state of peripheral inflammation

Obesity is defined as abnormal or excessive fat accumulation. Chronic inflammation in fat influences the development of obesity-related diseases. Many reports state that obesity increases the risk of morbidity in many diseases, including hypertension, dyslipidemia, type 2 diabetes, coronary heart disease, stroke, sleep apnea, and breast, prostate and colon cancers, leading to increased mortality. Obesity is also associated with chronic neuropathologic conditions such as depression and Alzheimer's disease. However, there is strong evidence that weight loss reduces these risks, by limiting blood pressure and improving levels of serum triglycerides, total cholesterol, low-density lipoprotein (LDL)-cholesterol, and high-density lipoprotein (HDL)-cholesterol. Prevention and control of obesity is complex, and requires a multifaceted approach. The elucidation of molecular mechanisms driving fat metabolism (adipogenesis and lipolysis) aims at developing clinical treatments to control obesity. We recently reported a new regulatory mechanism in fat metabolism: a protein phosphatase binding protein, phospholipase C-related catalytically inactive protein (PRIP), regulates lipolysis in white adipocytes and heat production in brown adipocytes via phosphoregulation. Deficiency of PRIP in mice led to reduced fat accumulation and increased energy expenditure, resulting in a lean phenotype. Here, we evaluate PRIP as a new therapeutic target for the control of obesity.

Phospholipase C-related Catalytically Inactive Protein Is a New Modulator of Thermogenesis Promoted by β-Adrenergic Receptors in Brown Adipocytes

Phospholipase C-related catalytically inactive protein (PRIP) was first identified as an inositol 1,4,5-trisphosphate-binding protein, and was later found to be involved in a variety of cellular events, particularly those related to protein phosphatases. We previously reported that Prip knock-out (KO) mice exhibit a lean phenotype with a small amount of white adipose tissue. In the present study, we examined whether PRIP is involved in energy metabolism, which could explain the lean phenotype, using high-fat diet (HFD)-fed mice. Prip-KO mice showed resistance to HFD-induced obesity, resulting in protection from glucose metabolism dysfunction and insulin resistance. Energy expenditure and body temperature at night were significantly higher in Prip-KO mice than in wild-type mice. Gene and protein expression of uncoupling protein 1 (UCP1), a thermogenic protein, was up-regulated in Prip-KO brown adipocytes in thermoneutral or cold environments. These phenotypes were caused by the promotion of lipolysis in Prip-KO brown adipocytes, which is triggered by up-regulation of phosphorylation of the lipolysis-related proteins hormone-sensitive lipase and perilipin, followed by activation of UCP1 and/or up-regulation of thermogenesis-related genes (e.g. peroxisome proliferator-activated receptor-γ coactivator-1α). The results indicate that PRIP negatively regulates UCP1-mediated thermogenesis in brown adipocytes.