Matilde Y. Follo

PLC and PI3K/Akt/mTOR signalling in disease and cancer

Cancer cell metabolism is deregulated, and signalling pathways can be involved. For instance, PI3K/Akt/mTOR is associated with normal proliferation and differentiation, and its alteration is detectable in cancer cells, that exploit the normal mechanisms to overcome apoptosis. On the other hand, also the family of Phospholipase C (PLC) enzymes play a critical role in cell growth, and any change concerning these enzymes or their downstream targets can be associated with neoplastic transformation. Here, we review the role of PLC and PI3K/Akt/mTOR signal transduction pathways in pathophysiology.

Nuclear PI-PLCβ1: an appraisal on targets and pathology.

Lipid signalling molecules are essential components of the processes that allow one extracellular signal to be transferred inside the nucleus, where specific lipid second messengers elicit reactions capable of regulating gene transcription, DNA replication or repair and DNA cleavage, eventually resulting in cell growth, differentiation, apoptosis or many other cell functions. Nuclear inositides are independently regulated, suggesting that the nucleus constitutes a functionally distinct compartment of inositol lipids metabolism. Indeed, nuclear inositol lipids themselves can modulate nuclear processes, such as transcription and pre-mRNA splicing, growth, proliferation, cell cycle regulation and differentiation. Nuclear PI-PLCβ1 is a key molecule for nuclear inositide signalling, where it plays a role in cell cycle progression, proliferation and differentiation. Here we review the targets and possible involvement of nuclear PI-PLCβ1 in human physiology and pathology.

Phosphoinositide-specific phospholipase C in health and disease.

Phospholipases are widely occurring and can be found in several different organisms, including bacteria, yeast, plants, animals, and viruses. Phospholipase C (PLC) is a class of phospholipases that cleaves phospholipids on the diacylglycerol (DAG) side of the phosphodiester bond producing DAGs and phosphomonoesters. Among PLCs, phosphoinositide-specific PLC (PI-PLC) constitutes an important step in the inositide signaling pathways. The structures of PI-PLC isozymes show conserved domains as well as regulatory specific domains. This is important, as most PI-PLCs share a common mechanism, but each of them has a peculiar role and can have a specific cell distribution that is linked to a specific function. More importantly, the regulation of PLC isozymes is fundamental in health and disease, as there are several PLC-dependent molecular mechanisms that are associated with the activation or inhibition of important physiopathological processes. Moreover, PI-PLC alternative splicing variants can play important roles in complex signaling networks, not only in cancer but also in other diseases. That is why PI-PLC isozymes are now considered as important molecules that are essential for better understanding the molecular mechanisms underlying both physiology and pathogenesis, and are also potential molecular targets useful for the development of innovative therapeutic strategies.

Primary phospholipase C and brain disorders

In the brain, the primary phospholipase C (PLC) proteins, PLCβ, and PLCγ, are activated primarily by neurotransmitters, neurotrophic factors, and hormones through G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). Among the primary PLC isozymes, PLCβ1, PLCβ4, and PLCγ1 are highly expressed and differentially distributed, suggesting a specific role for each PLC subtype in different regions of the brain. Primary PLCs control neuronal activity, which is important for synapse function and development. In addition, dysregulation of primary PLC signaling is linked to several brain disorders including epilepsy, schizophrenia, bipolar disorder, Huntingtons disease, depression and Alzheimers disease. In this review, we included current knowledge regarding the roles of primary PLC isozymes in brain disorders.

Molecular Mechanisms Underlying Psychological Stress and Cancer.

Psychological stress is an emotion experienced when people are under mental pressure or encounter unexpected problems. Extreme or repetitive stress increases the risk of developing human disease, including cardiovascular disease (CVD), immune diseases, mental disorders, and cancer. Several studies have shown an association between psychological stress and cancer growth and metastasis in animal models and case studies of cancer patients. Stress induces the secretion of stress-related mediators, such as catecholamine, cortisol, and oxytocin, via the activation of the hypothalamic-pituitary-adrenocortical (HPA) axis or the sympathetic nervous system (SNS). These stress-related hormones and neurotransmitters adversely affect stress-induced tumor progression and cancer therapy. Catecholamine is the primary factor that influences tumor progression. It can regulate diverse cellular signaling pathways through adrenergic receptors (ADRs), which are expressed by several types of cancer cells. Activated ADRs enhance the proliferation and invasion abilities of cancer cells, alter cell activity in the tumor microenvironment, and regulate the interaction between cancer and its microenvironment to promote tumor progression. Additionally, other stress mediators, such as glucocorticoids and oxytocin, and their cognate receptors are involved in stress-induced cancer growth and metastasis. Here, we will review how each receptor-mediated signal cascade contributes to tumor initiation and progression and discuss how we can use these molecular mechanisms for cancer therapy.

Modulation of nuclear PI-PLCbeta1 during cell differentiation

PI-PLCbeta1 plays an important role in cell differentiation, and particularly in myogenesis, osteogenesis and hematopoiesis. Indeed, the increase of PI-PLCbeta1, along with Cyclin D3, has been detected in C2C12 mouse myoblasts induced to differentiate, as well as in human cells obtained from myotonic dystrophy. Also in the case of osteogenic differentiation there is a specific induction of PI-PLCbeta1, but in this case the role of PI-PLCbeta1 seems to be independent from Cyclin D3, so that a different mechanism could be involved. As for the hematopoietic system, PI-PLCbeta1 has a peculiar behavior: it increases during myeloid differentiation and decreases during erythroid differentiation, thus confirming the role of PI-PLCbeta1 as a modulator of hematopoiesis.

PLC-β1 and cell differentiation: An insight into myogenesis and osteogenesis

Phosphoinositide-phospholipase C-β1 (PLC-β1) plays a crucial role in the initiation of the genetic program responsible for muscle differentiation and osteogenesis. During myogenic differentiation of murine C2C12 myoblasts, PLC-β1 signaling pathway involves the Inositol Polyphosphate Multikinase (IPMK) and β-catenin as downstream effectors. By means of c-jun binding to cyclin D3 promoter, the activation of PLC-β1 pathway determines cyclin D3 accumulation. However, osteogenesis requires PLC-β1 expression and up-regulation but it does not affect cyclin D3 levels, suggesting that the two processes require the activation of different mediators.

An increased expression of PI-PLCβ1 is associated with myeloid differentiation and a longer response to azacitidine in myelodysplastic syndromes

This study tested the hypothesis that PI‐PLCβ1 is associated with myeloid differentiation and that its expression could be useful for predicting the response of MDS patients to azacitidine, as the clinical effect of epigenetic treatments is often detectable only after several cycles of therapy. To this end, PI‐PLCβ1 was quantified on 70 MDS patients (IPSS risk: 13 Low, 20 Int‐1, 31 Int‐2, 6 High) at baseline and during the first 3 cycles of azacitidine. Results were then compared with the hematologic response, as assessed after the sixth cycle of azacitidine therapy. Overall, 60 patients completed 6 cycles of azacitidine, and for them, a clinical and molecular evaluation was possible: 37 of these patients (62%) showed a specific increase of PI‐PLCβ1 mRNA within the first 3 cycles, which was associated with a longer duration of response and with an increased myeloid differentiation, as evidenced by PI‐PLCγ2 induction and the recruitment of specific myeloid‐associated transcription factors to the PI‐PLCβ1 promoter during azacitidine response. Moreover, the increase of cyclin D3 gene expression throughout all of the therapy showed that PI‐PLCβ1‐dependent signaling is indeed activated in azacitidine responder patients. Taken together, our results show that PI‐PLCβ1 quantification in MDS predicts the response to azacitidine and is associated with an increased myeloid differentiation.

Critical Roles of EGFR Family Members in Breast Cancer and Breast Cancer Stem Cells: Targets for Therapy.

The roles of the epidermal growth factor receptor (EGFR) signaling pathway in various cancers including breast, bladder, brain, colorectal, esophageal, gastric, head and neck, hepatocellular, lung, neuroblastoma, ovarian, pancreatic, prostate, renal and other cancers have been keenly investigated since the 1980s. While the receptors and many downstream signaling molecules have been identified and characterized, there is still much to learn about this pathway and how its deregulation can lead to cancer and how it may be differentially regulated in various cell types. Multiple inhibitors to EGFR family members have been developed and many are in clinical use. Current research often focuses on their roles and other associated pathways in cancer stem cells (CSCs), identifying sites where therapeutic resistance may develop and the mechanisms by which microRNAs (miRs) and other RNAs regulate this pathway. This review will focus on recent advances in these fields with a specific focus on breast cancer and breast CSCs. Relatively novel areas of investigation, such as treatments for other diseases (e.g., diabetes, metabolism, and intestinal parasites), have provided new information about therapeutic resistance and CSCs.

Nuclear Nox4-Derived Reactive Oxygen Species in Myelodysplastic Syndromes

A role for intracellular ROS production has been recently implicated in the pathogenesis and progression of a wide variety of neoplasias. ROS sources, such as NAD(P)H oxidase (Nox) complexes, are frequently activated in AML (acute myeloid leukemia) blasts and strongly contribute to their proliferation, survival, and drug resistance. Myelodysplastic syndromes (MDS) comprise a heterogeneous group of disorders characterized by ineffective hematopoiesis, with an increased propensity to develop AML. The molecular basis for MDS progression is unknown, but a key element in MDS disease progression is the genomic instability. NADPH oxidases are now recognized to have specific subcellular localizations, this targeting to specific compartments for localized ROS production. Local Nox-dependent ROS production in the nucleus may contribute to the regulation of redox-dependent cell growth, differentiation, senescence, DNA damage, and apoptosis. We observed that Nox1, 2, and 4 isoforms and p22phox and Rac1 subunits are expressed in MDS/AML cell lines and MDS samples, also in the nuclear fractions. Interestingly, Nox4 interacts with ERK and Akt1 within nuclear speckle domain, suggesting that Nox4 could be involved in regulating gene expression and splicing factor activity. These data contribute to the elucidation of the molecular mechanisms used by nuclear ROS to drive MDS evolution to AML.