Necroptosis is mediated by a signaling complex called necrosome, containing receptor-interacting protein (RIP)1, RIP3, and mixed-lineage kinase domain-like (MLKL). It is known that RIP1 and RIP3 form heterodimeric filamentous scaffold in necrosomes through their RIP homotypic interaction motif (RHIM) domain-mediated oligomerization, but the signaling events based on this scaffold has not been fully addressed. By using inducible dimer systems we found that RIP1-RIP1 interaction is dispensable for necroptosis; RIP1-RIP3 interaction is required for necroptosis signaling, but there is no necroptosis if no additional RIP3 protein is recruited to the RIP1-RIP3 heterodimer, and the interaction with RIP1 promotes the RIP3 to recruit other RIP3; RIP3-RIP3 interaction is required for necroptosis and RIP3-RIP3 dimerization is sufficient to induce necroptosis; and RIP3 dimer-induced necroptosis requires MLKL. We further show that RIP3 oligomer is not more potent than RIP3 dimer in triggering necroptosis, suggesting that RIP3 homo-interaction in the complex, rather than whether RIP3 has formed homo polymer, is important for necroptosis. RIP3 dimerization leads to RIP3 intramolecule autophosphorylation, which is required for the recruitment of MLKL. Interestingly, phosphorylation of one of RIP3 in the dimer is sufficient to induce necroptosis. As RIP1-RIP3 heterodimer itself cannot induce necroptosis, the RIP1-RIP3 heterodimeric amyloid fibril is unlikely to directly propagate necroptosis. We propose that the signaling events after the RIP1-RIP3 amyloid complex assembly are the recruitment of free RIP3 by the RIP3 in the amyloid scaffold followed by autophosphorylation of RIP3 and subsequent recruitment of MLKL by RIP3 to execute necroptosis. Cell Death and Differentiation (2014) 21, 1709-1720; doi:10.1038/cdd.2014.77; published online 6 June 2014Necroptosis is a type of programmed necrosis characterized by necrotic morphological changes, including cellular organelle swelling, cell membrane rupture, 1-3 and dependence of receptor-interacting protein (RIP)1 4 and RIP3. [5][6][7] Physiological function of necroptosis has been illustrated in host defense, [8][9][10][11] inflammation, 12-16 tissue injury, 10,17,18 and development. [19][20][21] Necroptosis can be induced by a number of different extracellular stimuli such as tumor necrosis factor (TNF). TNF stimulation leads to formation of TNF receptor 1 (TNFR1) signaling complex (named complex I), and complex II containing RIP1, TRADD, FAS-associated protein with a death domain (FADD), and caspase-8, of which the activation initiates apoptosis. If cells have high level of RIP3, RIP1 recruits RIP3 to form necrosome containing FADD, [22][23][24] caspase-8, RIP1, and RIP3, and the cells undergo necroptosis. 25,26 Caspase-8 and FADD negatively regulates necroptosis, 27-30 because RIP1, RIP3, and CYLD are potential substrates of caspase-8. [31][32][33][34] Necrosome also suppresses apoptosis but the underlying mechanism has not been described yet. Mixed-lineage kinase domain-like (ML...

ABSTRACT. We investigated the expression of S-phase kinaseassociated protein 2 (SKP2) in breast cancer tissues, and the effects of SKP2-specific small interfering RNA (siRNA) interference on breast cancer cell proliferation. Thirty subjects provided breast cancer tissue samples and 18 subjects provided normal breast specimens for this study. The expression of SKP2 in breast cancer patient tissues and normal breast tissues was detected by western blotting analysis and reverse transcription-polymerase chain reaction. SKP2-specific siRNA was used to decrease SKP2 expression in breast cancer cell line MDA-MB-231. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to detect cell proliferation. SKP2 expression in breast cancer tissues was significantly higher than in normal breast tissues (P < 0.05). Two pairs of siRNA specific to SKP2 were required to downregulate SKP2 expression in the breast cancer cell line MDA-MB-231. The MTT assay showed that MDA-MB-231 growth significantly slowed after SKP2 interference. Patients with breast cancer have an increased 9245 SKP2 expression and breast cancer cell proliferation ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 14 (3): 9244-9252 (2015) SKP2 level. Interference in SKP2 gene expression can inhibit breast cancer cell growth, suggesting that SKP2 is potentially a new target for breast cancer therapy.