Abstractp70 S6 kinase (p70S6K) plays an important role in protein translation and cell cycle progression. Increased levels of p70S6K have been associated with drug resistance. In the present study, we have investigated the involvement of p70S6K in DNA damage-induced apoptosis. The DNA damaging agent cisplatin caused a concentration-dependent decrease in full-length p70S6K in small cell lung cancer H69 and non-small cell lung cancer A549 cells with concomitant increase in an approximately 45-kDa fragment. The proteolytic cleavage of p70S6K was inhibited by a broad specificity caspase inhibitor but not by the proteosome or calpain inhibitor. Cell-permeable peptide inhibitor and siRNA against capsase-3 inhibited cisplatin-induced proteolytic cleavage of p70S6K. In vitro-translated p70S6K was cleaved by human recombinant caspase-3. Cisplatin failed to induce cleavage of p70S6K in MCF-7 cells that lack functional caspase-3 but ectopic expression of caspase-3 in MCF-7 cells resulted in the cleavage of p70S6K. p70S6K was primarily cleaved at a noncanonical recognition site Thr-Pro-Val-Asp, after Asp-393. Site-directed mutagenesis of Asp-393 to Ala resulted in protection against cisplatin-mediated apoptosis whereas introduction of the N-terminal cleaved fragment resulted in potentiation of cisplatin-induced apoptosis. These results suggest that p70S6K is a novel substrate for caspase-3 and that the proteolytic cleavage of p70S6K is important for cisplatin-induced apoptosis. Keywords p70S6K; caspase; apoptosis p70 ribosomal S6 kinase (p70S6K) is a serine/threonine protein kinase which phosphorylates ribosomal S6 protein (S6) and promotes translation of a subset of mRNAs necessary for cell cycle progression (1). An elevation/activation of p70S6K has been associated with several cancers and resistance to chemotherapeutic drugs (2-6). Many anticancer drugs kill cancer cells by inducing apoptosis and a failure to induce apoptosis leads to treatment failure. While several reports implicated the involvement of p70S6K in DNA damage-induced apoptosis (3,5), little is known about how p70S6K regulates apoptosis induced by DNA damaging agents.Apoptosis is initiated by the activation of caspases, a family of cysteine proteases that cleave after Asp residues (7-9). Caspases are present in most healthy cells as inactive precursors known as procaspases, which undergo proteolytic processing to generate the active enzyme when an apoptotic signal is received (8). While caspase-8 and −9 participate in the initiation phase of apoptosis, caspase-3, −6 and −7 are involved in the execution phase of apoptosis (7-9). Caspase-2 can function both as an initiator as well as an effector caspase (10)(11)(12) Proteolytic cleavage of critical cellular proteins, such as poly(ADP-ribose) polymerase (PARP), DNA-dependent protein kinase, lamin B and protein kinase C-δ by executioner caspases has been associated with cell death (7,13,14).Since p70S6K acts downstream of mammalian target of rapamycin (mTOR), most of the studies have utilized rapamycin to inve...

Abstract. Cisplatin is widely used for the treatment of solid tumors, including small cell lung cancers, but its success is often compromised due to relapse and resistance to further treatment. p70 ribosomal S6 kinase (p70S6K) has been shown to be upregulated in lung cancer cells. In the present study, we investigated whether the p70S6K pathway contributes to cisplatin resistance in human small cell lung cancer H69 cells. The levels of phosphorylated p70S6K and its downstream target S6 but not total p70S6K or S6 were elevated in the H69 cells that acquired resistance to cisplatin (H69/CP) compared to parental H69 cells. Cisplatin treatment resulted in the activation of p70S6K and downregulation of p70S6K was associated with cisplatin-induced PARP cleavage. While the ability of cisplatin to induce apoptosis was attenuated in H69/CP cells, inhibition of p70S6K by rapamycin enhanced cisplatin-induced apoptosis in these cells as evident by the increase in cisplatin-induced poly(ADP-ribose) polymerase (PARP) cleavage. The phosphoinositide 3-kinase (PI3K) inhibitor Ly294002 alone induced PARP cleavage and further augmented cisplatin-induced PARP cleavage. In contrast, inhibition of extracellular signal-regulated kinase (ERK) by U0126 attenuated cisplatin-induced PARP cleavage. Both rapamycin and Ly294002 enhanced cisplatin-induced activation of ERK1/2. Taken together, these results suggest that activation of p70S6K contributes to cisplatin resistance in small cell lung cancer H69 cells, and inhibition/downregulation of p70S6K as well as activation of ERK1/2 could circumvent cisplatin resistance.

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Background: Pediatric infraumbilical surgeries are often performed under general anaesthesia using different modes of ventilation through Laryngeal Mask Airway .Although controlled ventilation has been successfully used, very less studies have been done to compare them with spontaneous ventilation for short duration surgeries. Aims: We tried to measure quantitave differences in haemodynamic and respiratory parameters and assess the recovery profile between controlled and spontaneous ventilation using Proseal LMA. Settings and Design: This was a prospective, randomized, double-blind study that comprised 90 American Society of Anaesthesiologist (ASA) classes I and II pediatric patients posted for infra umbilical surgery. Materials and Methods: 90 paediatric patients undergoing infraumbilical surgeries were included. Three different ventilation strategies: spontaneous , pressure support and pressure-controlled ventilation were applied depending on attending anaesthesiologist's preference. Haemodynamic and respiratory parameters were recorded during the procedure. Post procedure parameters including need for supplementary oxygen, recovery time, complications were recorded. Statistical Methods: Analysis of variance (ANOVA) was employed for inter group analysis and for multiple comparisons, least significant difference (LSD) test was applied. Chi-square test or Fisher's exact test, whichever appropriate, was used for comparison of categorical variables. Results: The mean time interval between end of surgery and removal of LMA was significantly higher in PCV group in comparison to SV and PSV groups. In SV group lesser number of patients required oxygen supplementation and had shorter stay in recovery than PCV group. Conclusion: We conclude that spontaneous mode of ventilation can be used as safely as controlled /assist ventilation mode in short duration surgeries in high turn over settings.

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