Fis1 and Bap31 Bridge the Mitochondria/ER Interface to Establish a Platform for Apoptosis Induction

Mitochondria and the endoplasmic reticulum (ER) are two organelles that critically contribute to apoptosis induction. It is established that they communicate and several factors for this have been identified. However, how cell death signals are transmitted from mitochondria to ER is unknown. During my PhD, I found that the mitochondrial fission protein Fis1 conveys an apoptosis signal from mitochondria to the ER by physically interacting with Bap31, which facilitates its cleavage into the pro-apoptotic p20Bap31 fragment. Exogenous apoptosis inducers likewise use this signalling route and induce the procession of Bap31. Initiator caspases are the apical apoptosis proteases that comprise protein-protein interaction domains in their N-terminal prodomains, which allow them to aggregate through adaptor proteins. Procaspase-8 is one of the most prominent initiator caspase; yet there are only two known procaspase-8-activating complexes identified to date: DISC and Hip1/Hippi complex. The cleavage of Bap31 is reported to be mediated by procaspase-8. I have found that procaspase-8 is recruited to the Fis1-Bap31 platform early during apoptosis. Apoptosis stimulation induces the dimerization of Bap31 and an in-depth dissection of this tripartite protein complex revealed that the association between procaspase-8 and the Fis1-Bap31 complex is dependent on the vDED domain present in Bap31. This signalling pathway emanating from Fis1 or caused by the application of exogenous apoptosis signals eventually results in calcium release from the ER leading to cytosolic calcium elevation. Additionally, production of the proapoptotic p20Bap31 fragment was found to be necessary for this event. The released calcium ions are subsequently taken up by mitochondria to induce mitochondrial dysfunction via the permeability transition pore thereby establishing a feedback loop from the ER that activates mitochondria for apoptosis execution. Hence, the Fis1-Bap31 complex, which we named ARCosome, bridges two critical organelles for apoptosis signalling and serves as a novel platform to activate the initiator procaspase-8

Erratum: PGC-1α controls mitochondrial biogenesis and dynamics in lead-induced neurotoxicity.

In this article, the additional author Aine Brigette Henley is added to this manuscript: http://www.impactaging.com/papers/v7/n9/pdf/100790.pdf

Potential Activity of Amrubicin as a Salvage Therapy for Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin with an aggressive clinical course. Although anthracycline- and platinum-based regimens are empirically used as first-line treatments for metastatic or unresectable cases, no salvage therapy has been established. A 73-year-old man with platinum-refractory recurrent MCC was treated with amrubicin. The symptoms improved soon, and a partial response was achieved. A total of nine cycles of amrubicin were administered in nine months with manageable adverse events until disease progression was finally observed. The present findings suggest the potential of amrubicin monotherapy as a second-line therapy for patients with advanced/recurrent MCC

Fis1 and Bap31 bridge the mitochondria/ER interface to establish a platform for apoptosis induction

Mitochondria and the endoplasmic reticulum (ER) are two organelles that critically contribute to apoptosis induction. It is established that they communicate and several factors for this have been identified. However, how cell death signals are transmitted from mitochondria to ER is unknown. During my PhD, I found that the mitochondrial fission protein Fis1 conveys an apoptosis signal from mitochondria to the ER by physically interacting with Bap31, which facilitates its cleavage into the pro-apoptotic p20Bap31 fragment. Exogenous apoptosis inducers likewise use this signalling route and induce the procession of Bap31. Initiator caspases are the apical apoptosis proteases that comprise protein-protein interaction domains in their N-terminal prodomains, which allow them to aggregate through adaptor proteins. Procaspase-8 is one of the most prominent initiator caspase; yet there are only two known procaspase-8-activating complexes identified to date: DISC and Hip1/Hippi complex. The cleavage of Bap31 is reported to be mediated by procaspase-8. I have found that procaspase-8 is recruited to the Fis1-Bap31 platform early during apoptosis. Apoptosis stimulation induces the dimerization of Bap31 and an in-depth dissection of this tripartite protein complex revealed that the association between procaspase-8 and the Fis1-Bap31 complex is dependent on the vDED domain present in Bap31. This signalling pathway emanating from Fis1 or caused by the application of exogenous apoptosis signals eventually results in calcium release from the ER leading to cytosolic calcium elevation. Additionally, production of the proapoptotic p20Bap31 fragment was found to be necessary for this event. The released calcium ions are subsequently taken up by mitochondria to induce mitochondrial dysfunction via the permeability transition pore thereby establishing a feedback loop from the ER that activates mitochondria for apoptosis execution. Hence, the Fis1-Bap31 complex, which we named ARCosome, bridges two critical organelles for apoptosis signalling and serves as a novel platform to activate the initiator procaspase-8.EThOS - Electronic Theses Online ServiceDeputy Rector's Award, Imperial College London and the Student Opportunity Fund, Imperial College LondonGBUnited Kingdo

Crizotinib-Induced Abnormal Signal Processing in the Retina.

Molecular target therapy for cancer is characterized by unique adverse effects that are not usually observed with cytotoxic chemotherapy. For example, the anaplastic lymphoma kinase (ALK)-tyrosine kinase inhibitor crizotinib causes characteristic visual disturbances, whereas such effects are rare when another ALK-tyrosine kinase inhibitor, alectinib, is used. To elucidate the mechanism responsible for these visual disturbances, the responses to light exhibited by retinal ganglion cells treated with these agents were evaluated using a C57BL6 mouse ex vivo model. Both crizotinib and alectinib changed the firing rate of ON and OFF type retinal ganglion cells. However, the ratio of alectinib-affected cells (15.7%) was significantly lower than that of crizotinib-affected cells (38.6%). Furthermore, these drugs changed the response properties to light stimuli of retinal ganglion cells in some of the affected cells, i.e., OFF cells responded to both ON and OFF stimuli, etc. Finally, the expressions of ALK (a target receptor of both crizotinib and alectinib) and of MET and ROS1 (additional target receptors of crizotinib) were observed at the mRNA level in the retina. Our findings suggest that these drugs might target retinal ganglion cells and that the potency of the drug actions on the light responses of retinal ganglion cells might be responsible for the difference in the frequencies of visual disturbances observed between patients treated with crizotinib and those treated with alectinib. The present experimental system might be useful for screening new molecular target agents prior to their use in clinical trials

Effects of crizotinib or alectinib on firing rate.

<p>Effects of crizotinib or alectinib on firing rate.</p

Effect of crizotinib and alectinib on stimulus preference of retinal ganglion cells.

<p>(A and B) Post-stimulus time histogram before (pre), during (crizotinib), and after (wash) the application of 1.0μM of crizotinib in an OFF-cell (A) and in an ON-OFF cell (B). The bin size for the histogram was 50 ms. (C and D) Cumulative distributions of the differences in <i>SPI</i> for crizotinib and alectinib. The difference in <i>SPI</i> was calculated from the <i>SPI</i> values evaluated before and during drug application. The cells were divided into “Decrease” type (C) and “Increase” type (D) according to the change in the <i>SPI</i>. The difference in (D) was an absolute value. (E and F) STA before (pre), during (crizotinib), and after (wash) the application of crizotinib in the cells shown in Figs 2A (E) and B (F). The amplitude “A” was defined as the difference in light intensity between the maximum and the minimum (double-headed arrow). (G and H) Plot of the amplitude “A” before (pre) and during drug application (drug) for the cells shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135521#pone.0135521.t004" target="_blank">Table 4</a>. The cells were divided into “Decrease” type (G) and “Increase” type (H). **<i>P</i> < 0.01; *** <i>P</i> < 0.001; paired <i>t</i>-test.</p

Effect of crizotinib (A-C) or alectinib (D-F) on firing rate of retinal ganglion cells.

<p>The timing of the drug application is indicated by the bar above the traces. The drug concentration was 1.0μM for both crizotinib and alectinib. The results for no change-type (A, D), increase-type (B, E), and decrease-type (C, F) cells are shown. The retina was repeatedly exposed to a set of light stimuli (1-s bright stimulation and 1-s dark stimulation at a frequency of 0.5 Hz). The ordinate shows the average firing rate for 10 cycles of stimuli (20 s).</p

Effects of crizotinib or alectinib on <i>SPI</i>.

<p>Effects of crizotinib or alectinib on <i>SPI</i>.</p

Oligonucleotide primers used for qPCR.

<p>Oligonucleotide primers used for qPCR.</p