Calbindin Expression in Renal Tubular Epithelial Cells. ALTERED SODIUM PHOSPHATE CO-TRANSPORT IN ASSOCIATION WITH CYTOSKELETAL REARRANGEMENT

Abstract

Sodium-phosphate transport in the opossum kidney (OK) cell line was studied in an OK clonal cell line that was transfected with an episomal vector expressing high levels of rat calbindin (28 kDa). High level expression of calbindin buffered the influx of calcium induced by ionomycin by 53% and raised the basal intracellular calcium from 100 +/- 6 to 150 +/- 8 nM. The decrement in sodium phosphate uptake induced by parathyroid hormone or forskolin was identical in the two cell lines. However, phorbol esters (10(-10)-10(-7) M), which decreased sodium phosphate uptake in the parental OK line, increased it in the calbindin-expressing line. Similarly, the parental clone did not respond to phosphate deprivation, while the calbindin-expressing clone did increase phosphate uptake in response to phosphate deprivation. In the calbindin-expressing cells, phorbol 12-myristate 13-acetate or low phosphate medium, which increased phosphate transport, produced actin filament aggregation, dissociation of the myristoylated alanine-rich C kinase substrate protein from sub-apical actin, and membrane-associated tyrosine phosphate staining. Agonists that reduced sodium phosphate uptake (cAMP, parathyroid hormone) did not affect these cellular features. The cytoskeletal rearrangement, redistribution of the myristoylated alanine-rich C kinase substrate protein, and membrane tyrosine phosphorylation are suggested to be involved in the events by which phosphate transport is increased in this cell line.

Modulation of Phosphate Uptake and Amphotropic Murine Leukemia Virus Entry by Posttranslational Modifications of PIT-2

“…In parental CHO cells as well as in CHO-PIT-2V and TE671 cells, the abundance of actin stress fibers was inversely related to extracellular [P i ]. A similar observation has been reported previously (29). PIT-2V staining was precisely localized with that of actin stress fibers, while coimmunoprecipitation experiments demonstrated a physical association of PIT-2 with actin.…”

Biological actions and mechanism of action of calbindin in the process of apoptosis

“…Caspase 3 activity in vivo was quantified by analyzing the subcellular localization of a caspase 3 sensor (YFP-caspase 3, Clonetech, Palo Alto, CA). Expression plasmids were designated pBSR␣-calbindin-D 28k or pREP-4 calbindin-D 28k as described previously [7]. CaT1 mRNA was measured using real time PCR [8].…”

Apoptosis Mediated by Activation of the G Protein-Coupled Receptor for Parathyroid Hormone (PTH)/ PTH-Related Protein (PTHrP)

“…H. Jü ppner and G. Segre). Complementary DNA encoding human bcl-2 (kindly supplied by Dr. S. Massa) and the Cterminal fragment of GRK2 (CtGRK2, kindly supplied by Dr. R. Lefkowitz) were subcloned into pCEP4; the rat calbindin 28 kDa cDNA was in pREP4 (45). After transfection using the Ca 2 PO 4 precipitation method (44), clones were selected with G418 antibiotic (200 g/ml) and isolated using limiting dilution in 96 well plates.…”