Nullin Flashcards
Why is bringing proteins to the membrane important for cellular function?
Bringing proteins to the membrane drives downstream signaling, which is essential for regulating cellular processes like proliferation and differentiation.
How do receptors control the localization of proteins?
Receptors, when activated by ligands, interact with proteins and drive their localization to the membrane. This is often achieved through binding to phosphorylated residues or through lipid tethers.
How does RAS control its localization to the membrane?
RAS is lipid-anchored to the plasma membrane via a lipid tether, and its localization to the membrane is a key mechanism controlling its signaling function, particularly in proliferation.
What is the role of PtdIns in membrane localization?
PtdIns signaling changes the lipid composition of the membrane, creating specific binding sites for proteins with lipid-binding domains, thus driving their localization to the membrane after activation by receptors.
How does protein localization affect downstream signaling?
The location of a protein in the cell affects which signaling pathways it activates. For example, RAS can activate different pathways depending on its membrane compartment, such as the ERK pathway in the plasma membrane and the JNK kinase stress response in the endoplasmic reticulum.
What happens when RAS is moved to different membrane compartments?
Moving RAS to different compartments, like the Golgi, activates different downstream pathways, such as the ERK pathway or PI3K pathway, altering cellular responses to signals.
What role does the PI3K pathway play in cancer?
The PI3K pathway is critical for cell growth and survival. Mutations in PI3K or PTEN can lead to constitutive activation of the pathway, driving uncontrolled cell growth and contributing to cancer.
How does PI3K activate downstream signaling?
PI3K phosphorylates PIP2 to create PIP3, which then binds to signaling proteins like PKB kinase. This activates a cascade of phosphorylation events, promoting cell survival and growth
How does the PTEN phosphatase regulate the PI3K pathway?
PTEN dephosphorylates PIP3 back to PIP2, serving as a negative regulator of the PI3K pathway. Mutations in PTEN can lead to uncontrolled signaling through PI3K.
How do mutations in PI3K contribute to cancer?
Specific mutations in PI3K lead to constitutive activation of the pathway, resulting in excessive production of PIP3, which drives PKB kinase activity and tumorigenesis.
How do mutations in PTEN contribute to cancer?
PTEN mutations lead to loss of its phosphatase function, preventing the conversion of PIP3 back to PIP2, which results in continued activation of the PI3K pathway and promotion of cancer cell survival.
How does PKB kinase mutation affect cancer progression?
A mutation in PKB kinase (e.g., E17 glutamate to lysine) causes a charge reversal, enabling PKB to bind PIP2 instead of PIP3, leading to oncogenic signaling and promoting cancer growth.
How does the insulin receptor system regulate signaling?
Insulin binding to its receptor activates PI3K, which generates PIP3. PIP3 activates PKB kinase, initiating a signaling cascade that regulates various cellular processes like glucose uptake.
How do tumor cells alter insulin receptor signaling?
Tumor cells often acquire mutations that constitutively activate PI3K, leading to persistent production of PIP3 and continuous activation of PKB kinase, contributing to uncontrolled cell growth and cancer.
What does PIP signaling provide for cells?
PIP signaling transduces environmental changes into changes in cell behavior, creates novel membrane surfaces for protein interactions, and modulates nuclear surfaces to transduce environmental signals into epigenetic changes.
How do phosphoinositides influence membrane surfaces?
Phosphoinositides provide highly regulated novel surfaces that can flag and identify different membrane types, and they also modulate protein interactions and regulation at the membrane.
What is the role of phosphoinositides in cell signaling?
Phosphoinositides act as receptor- and environment-regulated messengers that modulate location and interaction of proteins on membranes, facilitating changes in cellular functions in response to signals.
How are phosphoinositides structurally related to lipid molecules?
Phosphoinositides are lipids with two fatty acid chains (18-24 carbon atoms) and double bonds, which allow them to play a role in membrane dynamics and protein binding.
What is the basic structure of phosphoinositides?
Phosphoinositides are composed of a glycerol backbone, two fatty acid chains, and an inositol head group that is linked to a phosphate group. The phosphate group is crucial for their role in signaling.
What is the significance of the inositol head group in phosphoinositides?
The inositol head group is attached to a glycerol molecule via a diester bond, and it plays a key role in phosphorylation/dephosphorylation processes that regulate membrane interactions and signaling pathways.
How do phosphoinositides interact with the membrane?
The diester glycerol sits in the membrane, while the inositol head group projects outside, where it is subject to phosphorylation or dephosphorylation, altering its function in membrane dynamics and protein recruitment.
How does phosphorylation/dephosphorylation of phosphoinositides regulate cellular processes?
The phosphorylation and dephosphorylation of phosphoinositides on the inositol head group create different membrane surfaces that regulate protein recruitment, signal transduction, and location modulation of proteins at the membrane.
How does phosphoinositide signaling affect epigenetic regulation?
Phosphoinositides can create novel nuclear surfaces that directly transduce environmental signals to the nucleus, influencing epigenetic processes like gene expression and chromatin remodeling.
What is the role of phosphoinositides in response to environmental changes?
Phosphoinositides act as environment-regulated messengers, enabling cells to adapt to changing environments by altering membrane properties, protein localization, and nuclear signaling pathways.
What is the parental lipid in phosphoinositides?
The parental lipid in phosphoinositides is phosphatidylinositol, which consists of a glycerol backbone, two fatty acid chains, and an inositol head group without a phosphate group. The phosphate group is added in various positions to create different phosphoinositides.
How does the position of phosphate groups affect phosphoinositide signaling?
The addition of phosphate groups at different positions (such as 3, 4, or 5) on the inositol ring generates distinct phosphoinositides that act as signaling molecules with specific roles in membrane dynamics and protein interaction.
Which positions on phosphoinositides can be phosphorylated?
Phosphoinositides can be phosphorylated at the 3, 4, and 5 positions on the inositol ring.
What are examples of bis-phosphorylated phosphoinositides?
Examples of bis-phosphorylated phosphoinositides include PI(3,4)P2, PI(4,5)P2, and PI(3,5)P2.
What happens when all three positions on phosphoinositides are phosphorylated?
When all three positions are phosphorylated, the result is PI(3,4,5)P3, a key lipid in intracellular signaling.
Why isn’t the 6th position of phosphoinositides phosphorylated?
The 6th position of phosphoinositides isn’t phosphorylated because it is adjacent to the membrane, and its negative charge would cause repulsion due to the membrane’s negative charge.
What is the role of PIP2 in signal transduction?
PIP2 acts in signal transduction by being cleaved by phospholipase C upon receptor activation, generating two second messengers: DiPIP3 and diacylglycerol (DAG). These regulate calcium signaling and PKB (protein kinase B) signaling.
How do lipids act as intracellular messengers?
Lipids like PIP2 act as intracellular messengers by being phosphorylated and interacting with proteins, leading to changes in signaling pathways.
Who first discovered the activation of lipids by receptor signaling?
Mabel and Lowell Hokin discovered lipid activation in 1953, showing that acetylcholine activated lipids in the pancreas, leading to their phosphorylation.
What happens when phosphoinositides are hydrolyzed by phospholipase C?
Phospholipase C cleaves PIP2 at the phosphodiester bond, generating diacylglycerol (DAG) and IP3. DAG stays in the membrane, while IP3 enters the cytoplasm to activate calcium signaling.
How does IP3 activate calcium signaling?
IP3 binds to the IP3 receptor on the endoplasmic reticulum, causing calcium release into the cytoplasm.
What role does DAG play in signaling?
DAG binds to the C1 and C2 domains of protein kinase C (PKC), translocating PKC to the membrane and driving downstream signaling.
How do viral oncogenes transform cells using PIP2?
Viral oncogenes, like the middle T antigen, activate lipid kinases, resulting in PIP2 phosphorylation and PIP3 generation, which transforms the cell and drives cancer development.
What was discovered about PIP3 in the context of cancer research?
It was discovered that PIP3 is not a substrate for phospholipase C but is generated by PIP3 kinase and plays a key role in cellular transformation during cancer development.
What experimental approach helped identify proteins that bind to phosphoinositides?
The fishing experiment involved using phosphoinositide-bound beads to capture and identify proteins that interact with phosphoinositides, revealing that 400 proteins bind to PtdIns species in cells.
How do phosphoinositides regulate signaling pathways?
Phosphoinositides create membrane surfaces that modulate protein interactions with the membrane, leading to signaling events that regulate cellular functions.
How are genetically encoded fluorescent proteins used to study phosphoinositides?
GFP (green fluorescent protein) can be fused to a phosphoinositide-binding domain, allowing researchers to track the localization of specific phosphoinositides like PIP2, PIP3, and PIP4 in live cells.
Where are phosphoinositides located in cells?
PIP2 is enriched at the plasma membrane.
PIP4 is found in the Golgi apparatus.
PIP3 is enriched in early endosomes.
How does colocalization of phosphoinositides with proteins help?
It helps understand protein complexes, such as in early endosomal fusion or identifying proteins that do not localize in particular compartments.
What is PIP3 and how does it function?
PIP3 is a second messenger that does not act as a substrate for phospholipase C. It is important in signaling pathways that involve cellular responses to extracellular signals.
What is the role of phosphoinositides in endosomal systems?
PIP3 is enriched in the endosomal system, which plays a role in vesicular trafficking. The levels of enzymes for making and breaking phosphoinositides change as they traffic through the system.
How are PIP lipids interconverted in cells?
PIP lipids are interconverted through the action of kinases (which add phosphates) and phosphatases (which remove phosphates). This interconversion can lead to chain reactions of lipid alterations, influencing various cellular processes.
What impact do mutations in lipid kinases and phosphatases have?
Mutations in lipid kinases and phosphatases have been found in human diseases, but the exact mechanisms and effects are still not fully understood.
How many lipid and inositol messengers can be generated?
The system can generate 7 lipid messengers and 63 other inositol messengers through the interconversion of phosphoinositides.
What role do lipid-interacting domains play in phosphoinositide signaling?
Lipid-interacting domains transduce phosphoinositide signals into functional outputs by interacting with phosphoinositides and altering downstream cellular pathways.
How do phosphoinositides help define membrane identity in cells?
Phosphoinositides enrich certain lipids in different regions of the cell, helping to define membrane identity and regulate function based on intracellular and extracellular cues.
How do cells use phosphoinositides to regulate signaling?
Cells generate distinct pools of phosphoinositides that interact with proteins, resulting in functionally diverse outputs and regulating different pathways in response to specific signals.
What is the function of PIP5K?
PIP5K (phosphoinositide-5-kinase) converts PI4P to PtdIns(4,5)P2, a crucial lipid involved in cell signaling.
How is PIP5K related to cancer?
In many tumors, PIP5K is upregulated but not mutated. High PIP5K levels correlate with poor prognosis and shorter disease-free survival in cancer patients.
Why is PIP5K considered a potential pharmaceutical target?
PIP5K is important for regulating various cellular processes, and inhibiting it could suppress tumor growth. However, inhibiting PIP5K could also cause significant cellular dysfunction, making it a challenging target for drug development.
How many isoforms of PIP5K exist, and what are their functions?
There are 3 isoforms of PIP5K:
Alpha is located on the membrane and in the nucleus, possibly involved in epigenetic signaling.
Beta is found on endomembranes.
Gamma is localized to focal adhesions, where it regulates cell-extracellular matrix interactions, actin polymerization, cell polarization, and survival signaling.
How does PIP5K regulate signaling in focal adhesions?
In focal adhesions, PIP5K gamma interacts with integrins to control actin dynamics, influencing cell movement, polarization, and survival signaling.
What is the relationship between PIP5K and protein kinases?
PIP5K functions similarly to protein kinases, with specificity determined by its loops, which dictate interactions with specific phosphoinositides and downstream signaling pathways.
How does actin polymerization drive cell migration?
Actin polymerization pushes against the plasma membrane, forming protrusions at the leading edge of the cell, which helps drive cell movement forward.
What role does actin play in morphogenetic processes like neuronal outgrowth?
In processes like neuronal outgrowth, actin polymerization contributes to membrane protrusions and cell elongation, without the need for retraction of the trailing edge.
How does actin polymerization contribute to endocytosis?
During endocytosis, actin polymerization generates membrane invaginations and provides the force needed for scission of the endocytic vesicles from the plasma membrane.
What is the structure of actin filaments?
Actin filaments consist of polar, helical structures formed from actin monomers (G-actin), with two distinct ends:
Barbed end: The fast-growing end.
Pointed end: The slow-growing end.
