RNAi and ER Stress: Molecular Mechanisms and Biological Implications
(RNAi)highly evolutionally conserved process of post-transcriptional
gene silencing by which double stranded RNA (dsRNA), when introduced into a cell, causes sequence-specific degradation of homogolous mRNA sequences.
causes sequence-specific degradation of homogolous mRNA sequences.
Dicer: RNAse III enzyme
siRNA: 21-23 nt short interfering RNA
RISC: RNA-inducing silencing complex
Argonaute(Ago) protein is one of the main components in RISC. Ago cleaves and discards the passenger (sense) strand of the siRNA duplex leading to activation of the RISC.
ER stress: In order for protein fold properly a balance between ER protein load and folding capacity to precess this load must be establish. But, paththo-physio-logical stimuli can disrupt this ER homeostasis resulting to an accumulation of misfolded and unfolded proteins.
Unfolded Protein response: ER stress activate a complex singnaling network to reduce+restore ER hemeostasis
3 aims of UPR: 1.restore normal function of cell by halting protein translation. 2.degrading misfolded protein. 3.activate signaling pathways lead to increase production of molecular chaperones involved in protein folding.
ATF6:Activating Transcription Factor 6. PERK:PKR-like ER kinase. ERE1: Inositol requiring 1
Trametitinib: clinical use to treat metastatic melanoma with BRAF V600E(Inhibit MEK->extends lifespan)
DAF-2: works in NEURONs/Fat tissues, detect dietary food signal.
FOXO:only work in fat tissue
14-3-3: pretein eluted in the 14th fraction of bovine brain homogenate/were found on position 3.3 of subsequent electrophoresis. Have ability binding multitude of functionally diverse signaling proteins, including kinases, phosphatases,transmembrane receptors. It binding shows variably regulate its partners.Ranging from + to – regulation via different mechanisms (binds specific phosphoserine/threonine motifs on target protein)
14-3-3 functions:can alter ability of target protein to interact with other proteins (binding to IRS-1 attenuates its ability to recruit/activate Pi3 Kinases). Modify target protein localization, cause its target’s exclusion from nucleus and its retention in cytoplasm. Bridge two proteins togethers, thus serving as phosphrylation dependent scaffold protein. Binding can alter instrinsic catalytic activity of target protein, inhibit/augment its function.Binding can protect target protein from other modifications such proteolysis.
Sirtuin:protein deacetylases dependent on nicotine adenine dinucleotide/found in organisms ranging from bacteria to human. (Overexpression of Sirtuin extended lifespan/promotes localization DAF-16 &FOXO transcription factor)
Sirtuin: various enzyme activities such mono-ribosyl and deacylase. Its protein deacylase activity is important for lifespan regulation. Sirtuin deacylase activity depends on NAD level, linked its enzymatic activity directly to energy status of the cell via the cellular NAD:NADH ratio. Sirtuin required for lifespan extension resulted from glucose restriction in yeast cells, by reducing accumulation of rDNA cycles.
SIRT1(Sir2α):homolog of Sir2.Overexpression mimics DR
SIRT2:expressed in the brain
3-4-5:activiate in mitochondria. 6-7:in nucleus of cell. Overexpression Sirt6 decreases level of phosphorylated AKT/also increases longevity of male mice by reducing IGF signaling pathway in white adipose tissues.
Autophagy:a catabolic process involving the degradation of a cell’s own components through lysosomal machinery
3 types auto:1.Chaperone-mediated autophagy: A cytosolic chaperone protein recognize & bind these proteins to form a substrate-chaperone complex that is delivered to lysosome through the lysosome-associated membrane protein. 2.Microautophagy:a direct engulfment of cellular components by invagination of lysosomal membrane. 3.Macroautography:a process which cytosol/organelles are sequestered within double-membrane vesicles that deliver the contents to lysosome/vacuole for degradation and recycling of resulting macromolecules.
Autophagy regulation: mTOR supress Autophagy, AMPK stimulate
Biological functions of autophagy: Survival during starvation, Anti-aging, Protection against neurodegeneration, Differentiation/development, innate immunity.
Telomere: a region of repetitive nucleotide sequences at the end of a chromosome, which protects the end of chromosome from deterioration or from fusion with neighboring chromosomes. Telomeres shorten with each cell division. It’s estimated human telomeres lose 100 base pairs from their telomeric DNA at each mitosis. Cellular senescence is triggered when telomeres are on average 4-6kb.
Telomere hypothesis of aging: Telomeres shorten with age(tissue with high cell turnover).Thus,telomere shortening is a cause of aging.
Telomerase: an enzyme that adds telomere repeat sequences to the 3′ end of DNA strands.Telomerase is reverse transcriptase that carries its own RNA molecule, used as template when it elongates telomeres.
p53:protein repair damage. (guardian of the genome)
Progeria:extremely rare genetic condition wherein symptoms resembling aspects of aging are manifested at an early age. The disorder has low incidences/occurs in 1per8 million. Live only to mid-teens and early 20, genetics condition occurs as new mutation,rarely inherited. Refered to Hutchinson-Gilford Progeria Syndrome (HGPS)
Werner syndrome:autosomal recessive disorder. lies on chromosome 8 in humans.The disease is caused by mutation in WRN gene which codes in DNA helicase that functions 3′ to 5′. Increased telomere attrition/genomic instability been observed in Werner, rapid telomere decay is thought to play a causal role in the clinical and pathological manifestations of disease.