Background:The function of oxysterol-binding protein-related protein (ORP4) is unknown. Results: Silencing ORP4L or all ORP4 isoforms triggers growth arrest and apoptosis, which is suppressed by H-Ras and involves the C-terminal lipid binding domain. Conclusion: ORP4 is a sterol and PI-4P-binding protein required for survival and proliferation of immortalized and transformed cells. Significance: This is the first study to identify a mammalian ORP with growth regulatory activity.

Cholesterol and its numerous oxygenated derivatives (oxysterols) profoundly affect the biophysical properties of membranes, and positively and negatively regulate sterol homoeostasis through interaction with effector proteins. As the bulk of cellular sterols are segregated from the sensory machinery that controls homoeostatic responses, an important regulatory step involves sterol transport or signalling between membrane compartments. Evidence for rapid, energy-independent transport between organelles has implicated transport proteins, such as the eukaryotic family of OSBP (oxysterol-binding protein)/ORPs (OSBP-related proteins). Since the founding member of this family was identified more than 25 years ago, accumulated evidence has implicated OSBP/ORPs in sterol signalling and/or sterol transport functions. However, recent evidence of sterol transfer activity by OSBP/ORPs suggests that other seemingly disparate functions could be the result of alterations in membrane sterol distribution or ancillary to this primary activity.

The self-assembly properties of fibrous proteins such as collagen are frequently used to form three-dimensional scaffolds. In this study we investigated the effect of nonuniform alternating and static electric-fields on the self-assembly properties of a dilute solution of vimentin. In the presence of both types of fields at the same time, vimentin was observed to accumulate at the positive electrode and to form microscaffolds bridging the two electrodes in 20-30 min. Atomic force microscopy of the surface of dried microscaffolds revealed the presence of dense 8-12 nm diameter vimentin filament meshworks as well as bundles with typical diameters of 100-200 nm. Stretching of the scaffolds revealed that either the bundles or drawn meshworks could be extended to at least 6-fold and the presence fibers with a width of several μm.