Non-exploitative human disturbance provides shelter for prey from predator.

Human activities can influence behaviors of predators and prey, as well as predator-prey interactions. Using camera trap data, we investigated whether or to what extent human activities influenced behaviors of predators (tigers and leopards) and prey (sambar deer, spotted deer, wild boar, and barking deer), and predator-prey interactions in the Barandabhar Corridor Forest (BCF), Chitwan District, Nepal. A multispecies occupancy model revealed that the presence of humans altered the conditional occupancy of both prey and predator species. Specifically, the conditional occupancy probability of prey was substantially higher (ψ = 0.91, CI = 0.89-0.92) when humans were present than when humans were absent (ψ = 0.68, CI = 0.54-0.79). The diel activity pattern of most prey species overlapped strongly with humans, whereas predators were generally more active when humans were absent. Finally, the spatiotemporal overlap analysis revealed that human-prey interactions (i.e., the probability that both humans and prey species being present on the same grid at the same hourly period) was ~3 times higher (10.5%, CI = 10.4%-10.6%) compared to spatiotemporal overlap between humans and predators (3.1%, CI = 3.0%-3.2%). Our findings are consistent with the human shield hypothesis and suggest that ungulate prey species may reduce predation risk by using areas with high human activities.

ATM and the catalytic subunit of DNA-dependent protein kinase activate NF-kappaB through a common MEK/extracellular signal-regulated kinase/p90(rsk) signaling pathway in response to distinct forms of DNA damage.

We have identified a novel pathway of ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK) signaling that results in nuclear factor kappaB (NF-kappaB) activation and chemoresistance in response to DNA damage. We show that the anthracycline doxorubicin (DOX) and its congener N-benzyladriamycin (AD 288) selectively activate ATM and DNA-PK, respectively. Both ATM and DNA-PK promote sequential activation of the mitogen-activated protein kinase (MAPK)/p90(rsk) signaling cascade in a p53-independent fashion. In turn, p90(rsk) interacts with the IkappaB kinase 2 (IKK-2) catalytic subunit of IKK, thereby inducing NF-kappaB activity and cell survival. Collectively, our findings suggest that distinct members of the phosphatidylinositol kinase family activate a common prosurvival MAPK/IKK/NF-kappaB pathway that opposes the apoptotic response following DNA damage.

Transient activation of NF-kappaB through a TAK1/IKK kinase pathway by TGF-beta1 inhibits AP-1/SMAD signaling and apoptosis: implications in liver tumor formation.

NF-kappaB has been implicated in the regulation of apoptosis, a key mechanism of normal and malignant growth control. Previously, we demonstrated that inhibition of NF-kappaB activity by TGF-beta1 leads directly to induction of apoptosis of murine B-cell lymphomas and hepatocytes. Thus, we were surprised to determine that NF-kappaB is transiently activated in response to TGF-beta1 treatment. Here we elucidate the mechanism of TGF-beta1-mediated regulation of NF-kappaB and induction of apoptosis in epithelial cells. We report that TGF-beta1 activates IKK kinase, which mediates IkappaB-alpha phosphorylation. In turn, the activation of IKK following TGF-beta1 treatment is mediated by the TAK1 kinase. As a result of NF-kappaB activation, IkappaB-alpha mRNA and protein levels are increased leading to postrepression of NF-kappaB and induction of cell death. Inhibition of NF-kappaB following TGF-beta1 treatment increased AP-1 complex transcriptional activity through sustained c-Jun phosphorylation, thereby potentiating AP-1/SMADs-mediated cell killing. Furthermore, TGF-beta1-mediated upregulation of Smad7 appeared independent of NF-kappaB. In hepatocellular carcinomas of TGF-beta1 or TGF-alpha/c-myc transgenic mice, we observed constitutive activation of NF-kappaB that led to inhibition of JNK signaling. Overall, our data illustrate an autocrine mechanism based on the ability of IKK/NF-kappaB/IkappaB-alpha signaling to negatively regulate NF-kappaB levels thereby permitting TGF-beta1-induced apoptosis through AP-1 activity.

Direct phosphorylation of proliferative and survival pathway proteins by RET.

BACKGROUND: Gain-of-function mutations in the RET tyrosine kinase receptor cause the multiple endocrine neoplasia syndromes type 2a and 2b, and medullary thyroid cancer. We have previously shown that RET signals through focal adhesion kinase (FAK) in medullary thyroid cancer cells and that extracellular signal-regulated kinase (ERK) activity can be blocked by pp2, an inhibitor of both Src and RET. We hypothesized that RET could directly phosphorylate FAK and ERK. METHODS: RET and ERK kinase activity were measured with the use of an in vitro kinase assay. The relative contribution of RET in phosphorylation of ERK was tested by treating cells with PD98059, an inhibitor of MEK, and the RET inhibitor PP2, then measuring ERK activity. RESULTS: Immunoprecipitated, mutant RET from cells or the recombinant RET kinase domain was able to directly phosphorylate tyrosine residues on FAK. Specifically Y576/577, Y861, and Y925, but not the autophosphorylation site Y397 of FAK, were phosphorylated by RET. Similarly ERK 2 could be phosphorylated at Y187 (Y204 in ERK1). Inhibition of both MEK (upstream of ERK) and RET was more potent than inhibition of either alone in decreasing ERK activity. Furthermore, tyrosine residues in DOK1, the p85 subunit of phosphatidylinositol 3' kinase, JNK 1 and 2, P-38, and phospholipase-gamma were directly phosphorylated by RET. CONCLUSIONS: RET directly phosphorylates tyrosine residues on FAK, ERK 1/2, DOK1, the p85 subunit of of phosphatidylinositol 3' kinase, JNK 1 and 2, P-38, and phospholipase-gamma. These data indicate a direct interaction between RET and a broad range of effector molecules that may contribute to tumor pathogenesis.

RET signals through focal adhesion kinase in medullary thyroid cancer cells.

BACKGROUND: The RET proto-oncogene is implicated in medullary thyroid cancer (MTC) and has been shown to signal indirectly to focal adhesion kinase (FAK) in cell types other than MTC. We have previously shown that FAK is phosphorylated in MTC cells. We hypothesized that inhibition of RET with pharmacologic inhibitors or by depletion with siRNA would decrease FAK phosphorylation in MTC cells, thereby implicating a RET-FAK signaling pathway. METHODS: Human MTC cells (TT cells) were treated with pharmacologic inhibitors or transfected with RET siRNA. Total protein was detected by immunoblotting. Phosphorylated FAK was detected by immunoprecipitating total FAK and immunoblotting with antiphosphotyrosine. RESULTS: Treatment of MTC cells with the inhibitor PP2 significantly inhibited RET phosphorylation and, to a lesser extent, FAK phosphorylation. Imatinib mesylate inhibited FAK phosphorylation only at high doses. RET siRNA significantly decreased RET expression and FAK phosphorylation. CONCLUSIONS: RET signals through FAK in MTC cells. Whether this is due to a direct or indirect interaction is not yet clear. PP2 or a similar inhibitor might be a useful treatment for MTC.

Circumvention of nuclear factor kappaB-induced chemoresistance by cytoplasmic-targeted anthracyclines.

Nuclear factor kappaB (NF-kappaB) has been implicated in inducible chemoresistance against anthracyclines. In an effort to improve the cytotoxicity of anthracyclines while reducing their cardiotoxic effects, we have developed a novel class of extranuclear-localizing 14-O-acylanthracyclines that bind to the phorbol ester/diacylglycerol-binding C1b domain of conventional and novel protein kinase C (PKC) isoforms, thereby promoting an apoptotic response. Because PKCs have been shown to be involved in NF-kappaB activation, in this report, we determined the mechanism of NF-kappaB activation by N-benzyladriamycin-14-valerate (AD 198) and N-benzyladriamycin-14-pivalate (AD 445), two novel 14-O-acylanthracylines. We show that the induction of NF-kappaB activity in response to drug treatment relies on the activation of PKC-delta and NF-kappaB-activating kinase (NAK), independent of ataxia telengectasia mutated and p53 activities. In turn, NAK activates the IKK complex through phosphorylation of the IKK-2 subunit. We find that neither NF-kappaB activation nor ectopic expression of Bcl-X(L) confers protection from AD 198-induced cell killing. Overall, our data indicate that activation of novel PKC isoforms by cytoplasmic-targeted 14-O-acylanthracyclines promotes an apoptotic response independent of DNA damage, which is unimpeded by inducible activation of NF-kappaB.

Inhibition of CK2 activity by TGF-beta1 promotes IkappaB-alpha protein stabilization and apoptosis of immortalized hepatocytes.

Nuclear factor kappaB (NF-kappaB) is an antiapoptotic factor involved in development, regeneration, and neoplastic progression of the liver. Previously, we have shown that stabilization of inhibitor kappaB (IkappaB)-alpha protein following treatment of hepatocytes with transforming growth factor (TGF)-beta1 promoted NF-kappaB repression, which then permitted induction of AP-1/SMAD-mediated liver cell death. Because basal IkappaB-alpha protein turnover is regulated by protein kinase CK2, here we have elucidated the regulation of CK2 kinase activity and its role in control of NF-kappaB levels following treatment with TGF-beta1. We show that both messenger RNA (mRNA) and protein levels of the CK2alpha catalytic subunit are down-regulated following TGF-beta1 stimulation in murine hepatocyte cells. The ensuing inhibition of CK2 kinase activity promotes stabilization of IkappaB protein, which is followed by the shutoff of constitutive NF-kappaB activity and induction of apoptosis. Ectopic expression of CK2alpha inhibits TGF-beta1-induced apoptosis through sustained activation of NF-kappaB. Conversely, expression of a kinase-dead mutant of CK2alpha potentiates TGF-beta1 cell killing. Importantly, we show that hepatocellular carcinomas (HCCs) derived from TGF-beta1 transgenic mice and human HCC cell lines display enhanced CK2 IkappaB kinase activity that contributes in part to an elevated NF-kappaB activity in vivo. In conclusion, inhibition of CK2 expression levels by TGF-beta1 is crucial for the induction of apoptosis of hepatocytes. Circumvention of this process by up-regulation of CK2 activity in transformed cells may contribute to the promotion of TGF-beta1-induced liver carcinogenesis.