Rapamycin inhibition of baculovirus recombinant (BVr) ribosomal protein S6 kinase (S6K1) is mediated by an event other than phosphorylation

<p>Abstract</p> <p>Background</p> <p>Ribosomal protein S6 kinase 1(S6K1) is an evolutionary conserved kinase that is activated in response to growth factors and viral stimuli to influence cellular growth and proliferation. This downstream effector of target of rapamycin (TOR) signaling cascade is known to be directly activated by TOR- kinase mediated hydrophobic motif (HM) phosphorylation at Threonine 412 (T412). Selective loss of this phosphorylation by inactivation of TOR kinase or activation/recruitment of a phosphatase has accordingly been implicated in mediating inhibition by rapamycin.</p> <p>Findings</p> <p>We present evidence that baculovirus driven expression of S6K1 in insect cells (Sf9) fails to activate the enzyme and instead renders it modestly active representing 4-6 folds less activity than its fully active mammalian counterpart. Contrary to the contention that viral infection activates TOR signaling pathway, we report that BVr enzyme fails to exhibit putative TOR dependent phosphorylation at the HM and the resultant phosphorylation at the activation loop (AL) of the enzyme, correlating with the level of activity observed. Surprisingly, the BVr enzyme continued to exhibit sensitivity to rapamycin that remained unaffected by mutations compromised for TOR phosphorylation (T412A) or deletions compromised for TOR binding (ΔNH _2-46/ΔCT₁₀₄).</p> <p>Conclusions</p> <p>These data together with the ability of the BVr enzyme to resist inactivation by phosphatases indicate that inhibition by rapamycin is not mediated by any phosphorylation event in general and TOR dependent phosphorylation in particular.</p

Starch-based nanocomposites for gene delivery

Polysaccharide nanocomposites have drawn attention for their peculiar property of being renewable and green alternatives. Starch is a naturally renewable polymer having great potential owing to properties such as total compostability, biocompatibility, biodegradability, and are without toxic residues, besides few limitations including low mechanical properties, high water sensitivity, and poor processability. However, insertion of nanofillers into starch nanocomposites results in substantial changes and improvements in the stability and applicability of starch-based nanocomposites. This chapter aims to provide the fundamental knowledge on the role of starch nanocomposite polysaccharides, as specific in the field of biomedical applications, especially in gene delivery, as well as recent developments in this area

Enzyme-responsive polymer composites and their applications

Enzymes play a vital role in a broad spectrum of fundamental physiological processes and therefore could be exploited as biological triggers to achieve a controlled release of cargo at the desired site. Enzyme-responsive materials are a class of stimuli-responsive materials with a variety of applications in biological systems. They have been proved to be potential biomaterials, biomedicine, and biosensing candidates. These types of smart materials undergo macroscopic changes when triggered by a selective action of enzymes. This idea has been applied successfully for the development of drug carrier systems where the tissue of interest is targeted by the release of cargo triggered by the catalytic action of an enzyme. This chapter mainly emphasizes on the few key enzyme-responsive nanomaterials such as proteases, lipases, and glucosidases and oxidoreductases for various biomedical applications

Growth Inhibition by Bupivacaine Is Associated with Inactivation of Ribosomal Protein S6 Kinase 1

Bupivacaine is an amide type long acting local anesthetic used for epidural anesthesia and nerve blockade in patients. Use of bupivacaine is associated with severe cytotoxicity and apoptosis along with inhibition of cell growth and proliferation. Although inhibition of Erk, Akt, and AMPK seemingly appears to mediate some of the bupivacaine effects, potential downstream targets that mediate its effect remain unknown. S6 kinase 1 is a common downstream effector of several growth regulatory pathways involved in cell growth and proliferation known to be affected by bupivacaine. We have accordingly attempted to relate the growth inhibitory effects of bupivacaine with the status of S6K1 activity and we present evidence that decrease in cell growth and proliferation by bupivacaine is mediated through inactivation of S6 kinase 1 in a concentration and time dependent manner. We also show that ectopic expression of constitutively active S6 kinase 1 imparts substantial protection from bupivacaine induced cytotoxicity. Inactivation of S6K1 though associated with loss of putative mTOR mediated phosphorylation did not correspond with loss of similar phosphorylations in 4EBP1 indicating that S6K1 inhibition was not mediated through inactivation of mTORC1 signaling pathway or its down regulation