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Phosphoinositides are lipid second messengers that are essential for many cellular processes, including signal transduction and cell compartmentalization. Among them, phosphatidylinositol 5-phosphate (PtdIns5P) is the least characterized, although several proteins involved in its regulation are implicated in human diseases. We studied the distribution of 32 PtdIns5P-metabolizing proteins in 39 eukaryotic genomes. Phylogenetic profiles identify four groups of co-evolving proteins, confirming known protein complexes and revealing new ones. The complexes comprise a phosphatase, a kinase and a regulator; this indicates that physical interactions between the three partners are necessary for the acute spatial regulation of PtdIns5P turnover. By examining PtdIns5P metabolism in this new perspective, we propose a role for PtdIns5P in membrane trafficking from late endosomal compartments to the plasma membrane.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. The most common mutation, a deletion of the phenylalanine at position 508 ([DELTA]F508), disrupts processing of the protein. Nearly all human CFTR-[DELTA]F508 is retained in the endoplasmic reticulum and degraded, preventing maturation to the plasma membrane. In addition, the F508 deletion reduces the activity of single CFTR channels. Human CFTR-[DELTA]F508 has been extensively studied to better understand its defects. Here, we adopted a cross-species comparative approach, examining human, pig, and mouse CFTR-[DELTA]F508. As with human CFTR-[DELTA]F508, the [DELTA]F508 mutation reduced the single-channel activity of the pig and mouse channels. However, the mutant pig and mouse proteins were at least partially processed like their wild-type counterparts. Moreover, pig and mouse CFTR-[DELTA]F508 partially restored transepithelial [Cl.sup.-] transport to CF airway epithelia. Our data, combined with earlier work, suggest that there is a gradient in the severity of the CFTR-[DELTA]F508 processing defect, with human more severe than pig or mouse. These findings may explain some previously puzzling observations in CF mice, they have important implications for evaluation of potential therapeutics, and they suggest new strategies for discovering the mechanisms that disrupt processing of human CFTR-[DELTA]F508. airway epithelia | chloride transport | cystic fibrosis | mouse models

Physical cues, such as forces applied to a cell membrane or the stiffness of materials to which cells adhere, are increasingly recognized as essential determinants of biological function, and mechanical stimuli can be as important as chemical stimuli in determining tissue fate or contributing to pathological states. The physical environment of the cell can act in concert with, or sometimes override, the signals given by proteins and other cellular ligands to change cell morphology, growth rates and transcriptional programs. Recent developments in technology and techniques have facilitated studies of how forces trigger cellular events on the molecular level. As the mechanisms of force transduction are identified, methods and concepts from the physical sciences might become as important as those of biochemistry in elucidating how cells function and how these functions might be altered or corrected in therapeutic and biotechnological contexts.

An innovative membrane filter equipped with a positively charged membrane that electrostatically attracts and/or retains the endotoxins is used to demonstrate high levels of endotoxin retention. The endotoxin retention capabilities of filters equipped with a positively charged membrane revealed that the filters could be safely used for periods of up to 4 days.