EEA1, an early endosome-associated protein. EEA1 is a conserved alpha-helical peripheral membrane protein flanked by cysteine "fingers" and contains a calmodulin-binding IQ motif.

Early endosomes are cellular compartments receiving endocytosed material and sorting them for vesicular transport to late endosomes and lysosomes or for recycling to the plasma membrane. We have cloned a human cDNA encoding an evolutionarily conserved 180-kDa protein on early endosomes named EEA1 (Early Endosome Antigen1). EEA1 is associated with early endosomes since it co-localizes by immunofluorescence with the transferrin receptor and with Rab5 but not with Rab7. Immunoelectron microscopy shows that it is associated with tubulovesicular early endosomes containing internalized bovine serum albumin-gold. EEA1 is a hydrophilic peripheral membrane protein present in cytosol and membrane fractions. It partitions in the aqueous phase after Triton X-114 solubilization and is extracted from membranes by 0.3 M NaCl. It is a predominantly alpha-helical protein sharing 17-20% sequence identity with the myosins and contains a calmodulin-binding IQ motif. It is flanked by metal-binding, cysteine "finger" motifs. The COOH-terminal fingers, Cys-X2-Cys-X12-Cys-X2-Cys and Cys-X2-Cys-X16-Cys-X2-Cys, are present within a region that is strikingly homologous with Saccharomyces cerevisiae FAB1 protein required for endocytosis and with Caenorhabditis elegans ZK632. These fingers also show limited conservation with S. cerevisiae VAC1, Vps11, and Vps18p proteins implicated in vacuolar transport. We propose that EEA1 is required for vesicular transport of proteins through early endosomes and that its finger motifs are required for this activity.

Calcium and phosphorus metabolism in nephrotic syndrome.

Calcium and phosphorus balance studies were performed on 13 nephrotic patients and eight patients during clinical remission of the nephrotic syndrome. Marked impairment of intestinal absorption of calcium was found among nephrotic patients, in eight of whom faecal calcium equalled or exceeded dietary calcium. The mean faecal:dietary calcium ratio of nephrotic patients, 1-06 +/- 0-23 (SD), was significantly higher (p less than 0-005) than that of patients in remission, 0-58 +/- 0-21 (SD). The mean 24-hour urinary excretion of calcium of nephrotic patients, 0-68 +/- 0-68 (SD) mmol, was significantly lower (p less than 0-005) than that of patients in remission, 3-02 +/- 1-91 (SD) mmol. Calciferol administered to three nephrotic patients in the dosage of 1.25 mg per day did not significantly influence intestinal absorption or renal excretion of calcium. There was no difference between the two groups of patients in intestinal absorption or renal excretion of phosphorus; there was net intestinal absorption in all subjects. Quantitative bone histology was studied in seven of the nephrotic patients. None had osteomalacia or osteitis fibrosa, while only one had evidence of mild osteoporosis.