Prominin-1 (CD133) modulates the architecture and dynamics of microvilli.

Prominin-1 is a cell surface biomarker that allows the identification of stem and cancer stem cells from different organs. It is also expressed in several differentiated epithelial and non-epithelial cells. Irrespective of the cell type, prominin-1 is associated with plasma membrane protrusions. Here, we investigate its impact on the architecture of membrane protrusions using microvilli of Madin-Darby canine kidney cells as the main model. Our high-resolution analysis revealed that upon the overexpression of prominin-1 the number of microvilli and clusters of them increased. Microvilli with branched and/or knob-like morphologies were observed and stimulated by mutations in the ganglioside-binding site of prominin-1. The altered phenotypes were caused by the interaction of prominin-1 with phosphoinositide 3-kinase and Arp2/3 complex. Mutation of tyrosine 828 of prominin-1 impaired its phosphorylation and thereby inhibited the aforementioned interactions abolishing altered microvilli. This suggests that the interplay of prominin-1-ganglioside membrane complexes, phosphoinositide 3-kinase and cytoskeleton components regulates microvillar architecture. Lastly, the expression of prominin-1 and its mutants modified the structure of filopodia emerging from fibroblast-like cells and silencing human prominin-1 in primary hematopoietic stem cells resulted in the loss of uropod-associated microvilli. Altogether, these findings strengthen the role of prominin-1 as an organizer of cellular protrusions.

Divalent transition-metal-ion stress induces prodigiosin biosynthesis in Streptomyces coelicolor M145: formation of coeligiosins.

The bacterium Streptomyces coelicolor M145 reacts to transition-metal-ion stress with myriad growth responses, leading to different phenotypes. In particular, in the presence of Co(2+) ions (0.7 mM) S. coelicolor consistently produced a red phenotype. This phenotype, when compared to the wild type, differed strongly in its production of volatile compounds as well as high molecular weight secondary metabolites. LC-MS analysis revealed that in the red phenotype the production of the prodigiosins, undecylprodigiosin and streptorubin B, was strongly induced and, in addition, several intense signals appeared in the LC-MS chromatogram. Using LC-MS/MS and NMR spectroscopy, two new prodigiosin derivatives were identified, that is, coeligiosin A and B, which contained an additional undecylpyrrolyl side chain attached to the central carbon of the tripyrrole ring system of undecylprodigiosin or streptorubin B. This example demonstrates that environmental factors such as heavy metal ion stress can not only induce the production of otherwise not observed metabolites from so called sleeping genes but alter the products from well-studied biosynthetic pathways.