MM-1 facilitates degradation of c-Myc by recruiting proteasome and a novel ubiquitin E3 ligase.

We have reported that a novel c-Myc-binding protein, MM-1, repressed the E-box-dependent transcription activity of c-Myc by recruiting the HDAC1 complex via TIF1beta/KAP1, a transcriptional corepressor. We have also reported that a mutation of A157R in MM-1, which is often observed in patients with leukemia or lymphoma, abrogated all of the repressive activities of MM-1 toward c-Myc, indicating that MM-1 is a novel tumor suppressor. In this study, we found that MM-1 was bound to a component of proteasome and stimulated degradation of c-Myc in human cells. Knockdown of endogenous MM-1 in human HeLa cells by introduction of siRNA against MM-1 stabilized the endogenous c-Myc. To identify proteins that participate in c-Myc degradation by MM-1, in vivo and in vitro binding assays were carried out. The results showed that MM-1 directly bound to Rpt3, a subunit of 26S proteasome, and that c-Myc directly bound to Skp2, which recruited ElonginC, ElonginB and Cullin2, thereby forming a novel ubiquitin E3 ligase. Knockdown of endogenous Cullin2 stabilized the endogenous c-Myc. Thus, MM-1 is a factor that connects c-Myc to the ubiquitin E3 ligase and the proteasome

Bulk Scale Synthesis of Monodisperse PDMS Droplets above 3 μm and Their Encapsulation by Elastic Shells

We report several facile, surfactant-free methods to prepare monodisperse polydimethylsiloxane (PDMS) droplets in the size range 3–8 μm in water. These methods, of which the pros and cons are discussed, are extensions of a procedure described before by our group which focused on smaller droplet sizes. The PDMS oil droplets are formed by ammonia catalyzed hydrolysis and condensation of the monomer dimethyldiethoxysilane (DMDES) in water. One of the methods entails a seeded growth procedure in which other oils, such as lower molecular weight hydrocarbons, were found to be able to swell the PDMS droplets if their solubility in water was higher than that of the seed droplets. This way, larger droplets with mixed composition could be prepared. It also turned out to be possible to load the monodisperse droplets with an oil soluble dye. The droplets could be coated with an elastic, partially permeable, shell formed by cross-linking the PDMS with tetraethoxysilane (TES) in the presence of poly(vinylpyrrolidone) (PVP) that provided colloidal stability. Besides, the liquid interior of these shells could be changed by solvent exchange