1,25-Dihydroxyvitamin D3 selectively translocates PKCalpha to nuclei in ROS 17/2.8 cells

Activation of rapid signaling pathways does not contribute to 1 alpha,25-dihydroxyvitamin D3-induced growth inhibition of mouse prostate epithelial progenitor cells

The active form of vitamin D, 1 alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D) inhibits the growth of prostate epithelial cells, however the underlying mechanisms have not been clearly delineated. In the current study, the impact of 1,25(OH)(2)D on the rapid activation of extracellular-regulated kinase (ERK) 1/2 and protein kinase C alpha (PKC alpha), and the role of these pathways in growth inhibition was examined in immortalized mouse prostate epithelial cells, MPEC3, that exhibit stem/progenitor cell characteristics. 1,25(OH)(2)D treatment suppressed the growth of MPEC3 in a dose and time dependent manner (e.g., 21% reduction at three days with 100 nM 1,25(OH)(2)D treatment). However, ERK1/2 activity was not altered by 100 nM 1,25(OH)(2)D treatment for time points from 1 min to 1 h in either serum-containing or serum-free medium. Similarly, PKC alpha activation (translocation onto the plasma membrane) was not regulated by short-term treatment of 100 nM 1,25(OH)(2)D. In conclusion, 1,25(OH)(2)D did not mediate rapid activation of ERK1/2 or PKC alpha in MPEC3 and therefore the growth inhibitory effect of 1,25(OH)(2)D is independent of rapid activation of these signaling pathways in this cell type.

Calcitriol modulation of cardiac contractile performance via protein kinase C

Vitamin D(3) deficiency enhances cardiac contraction in experimental studies, yet paradoxically this deficiency is linked to congestive heart failure in humans. Activated vitamin D(3) (1alpha,25-dihydroxyvitamin D(3)) or calcitriol, decreases peak force and activates protein kinase C (PKC) in isolated perfused hearts. However, the direct influence of this hormone on adult cardiac myocyte contractile function is not well understood. Our aim is to investigate whether 1alpha,25-dihydroxyvitamin D(3) acutely modulates contractile function via PKC activation in adult rat cardiac myocytes. Sarcomere shortening and re-lengthening were measured in electrically stimulated myocytes isolated from adult rat hearts, and the vitamin D(3) response (10(-10) to 10(-7) M) was compared to shortening observed under basal conditions. Maximum changes in sarcomere shortening and relaxation were observed with 10(-9) M 1alpha,25-dihydroxyvitamin D(3). This dose decreased peak shortening, and accelerated contraction and relaxation rates within 5 min of administration, and changes in the Ca(2+) transient contributed to the peak shortening and relaxation effects. The PKC inhibitor, bis-indolylmaleimide (500 nM) largely blocked the acute influence of the most potent dose (10(-9) M) on contractile function. While peak shortening and shortening rate returned to baseline within 30 min, there was a sustained acceleration of relaxation that continued over 60 min. Phosphorylation of the Ca(2+) regulatory proteins, phospholamban, and cardiac troponin I correlated with the accelerated relaxation observed in response to acute application of 1alpha,25-dihydroxyvitamin D(3). Accelerated relaxation continued to be observed after chronic addition of 1alpha,25-dihydroxyvitamin D(3) (e.g. 2 days), yet this sustained increase in relaxation was not associated with increased phosphorylation of phospholamban or troponin I. These results provide evidence that 1alpha,25-dihydroxyvitamin D(3) directly modulates adult myocyte contractile function, and protein kinase C plays an important signaling role in the acute response. Phosphorylation of key Ca(2+) regulatory proteins by this kinase contributes to the enhanced relaxation observed in response to acute, but not chronic calcitriol.

Molecular action of 1,25-dihydroxyvitamin D3 and phorbol ester on the activation of the rat cytochrome P450C24 (CYP24) promoter: role of MAP kinase activities and identification of an important transcription factor binding site

Although investigations of the transcriptional regulation of the rat cytochrome P450C24 [CYP24 (25-hydroxyvitamin D3 24-hydroxylase)] gene by 1,25D (1,25-dihydroxyvitamin D3) at either the genomic, or more recently at the non-genomic, level have provided insight into the mechanism of control of 1,25D levels, this regulation is still poorly characterized. Using HEK-293T cells (human embryonic kidney 293T cells), we reported that 1,25D induction of CYP24 requires JNK (c-Jun N-terminal kinase) but not the ERK1/2 (extracellular-signal-regulated kinase 1/2). The phenomenon of synergistic up-regulation of CYP24 expression by PMA and 1,25D is well known and was found to be protein kinase C-dependent. Whereas ERK1/2 was not activated by 1,25D alone, its activation by PMA was potentiated by 1,25D also. The importance of ERK1/2 for transcriptional synergy was demonstrated by transfection of a dominant-negative ERK1(K71R) mutant (where K71R stands for Lys71-->Arg), which resulted in a reduced level of synergy on a CYP24 promoter-luciferase construct. JNK was also shown to be required for synergy. We report, in the present study, the identification of a site located at -171/-163, about 30 bp upstream of the vitamin D response element-1 in the CYP24 proximal promoter. This sequence, 5'-TGTCGGTCA-3', is critical for 1,25D induction of CYP24 and is therefore termed the vitamin D stimulatory element. The vitamin D stimulatory element, a target for the JNK module, and an Ets-1 binding site were shown to be vital for synergy between PMA and 1,25D. This is the first report to identify the DNA binding sequences required for the synergy between PMA and 1,25D and a role for JNK on the CYP24 gene promoter.

Potentiation of genomic actions of estrogen by membrane actions in mcf-7 cells and the involvement of protein kinase C activation

It is now well established that estrogens (E) have at least two kinds of actions: genomic and nongenomic. But the relationship between these actions has hardly been explored. In this study we investigated this relationship in MCF-7 cells, a human breast cancer cell line, and explored the possible involvement of protein kinase C (PKC) signaling pathways. For this purpose a two-pulse paradigm was used: cells were treated with 17beta-estradiol (E), E conjugated with bovine serum albumin (E-BSA or fE'), or other test agents in the first pulse and with E in the second pulse following a 4-h interval. An E-BSA+E paradigm was used to show that replacement of E with the membrane-impermeable E-BSA in the first pulse could potentiate genomic actions of E, in the second pulse. To investigate involvement of signaling pathways, two PKC activators, phorbol 12,13-diacetate (PDAc) or phorbol 12-myristate 13-acetate (PMA), and inhibitors (chelerythrine chloride and H7-dihydrochloride) were used to replace E or E-BSA in the first pulse. PDAc was as effective as E or E-BSA in potentiating the genomic action of E in the second pulse, while PMA was almost without an effect. Conversely, the potentiating effects of E-BSA and PDAc were blocked by chelerythrine chloride but, interestingly, not by H7. The exact reason underlying these differences is not known. In summary, in MCF-7 cells a membrane action of E can potentiate a later genomic action and involves PKC signaling.

1,25-dihydroxyvitamin D3 stimulated protein kinase C phosphorylation of type VI adenylyl cyclase inhibits parathyroid hormone signal transduction in rat osteoblastic UMR 106-01 cells

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) treatment of osteoblastic cells was shown previously to attenuate Parathyroid hormone (PTH) response by inhibiting adenylyl cyclase (AC) activity. In this study, we have investigated the mechanism by which 1,25(OH)(2)D(3) inhibits AC in rat osteoblastic UMR 106-01 cells. 1,25(OH)(2)D(3) treatment inhibited both PTH and forskolin-stimulated AC activity by 25%-50% within 12 min in a concentration-dependent manner suggesting a direct inhibition of the AC enzyme. Treatment with 25(OH)D(3) had no effect on basal or stimulated AC activity. We determined the profile of AC subtypes expressed in UMR cells and found AC VI to be the dominant subtype accounting for 50% of AC mRNA. Since AC VI can be inhibited by protein kinase C (PKC) phosphorylation, we examined 1,25(OH)(2)D(3) activation of various PKC isoforms. 1,25(OH)(2)D(3) increased the membrane translocation of PKC-betaI, -delta, and -zeta with a concomitant increase in PKC activity. The translocation of PKC-betaI and -delta was blocked by the PLC inhibitor U73122 whereas that of PKC-zeta was abolished by the PI-3 kinase inhibitor wortmannin. The attenuation of cAMP production by 1,25(OH)(2)D(3) was antagonized by the PKC inhibitors Go6850, calphostin C, and wortmannin, but not by a calmodulin kinase II (CaMKII) inhibitor. Treatment with 1,25(OH)(2)D(3) for 20 min increased AC VI phosphorylation by 10.8-fold and this was blocked partially by Go6850 and partially by wortmannin but was unaffected by CaMKII inhibitor. These results demonstrate that 1,25(OH)(2)D(3) activation of PKC isoforms leads to phosphorylation of AC VI and inhibition of PTH-activation of this pathway in osteoblasts.

The second galanin receptor GalR2 plays a key role in neurite outgrowth from adult sensory neurons

Expression of the neuropeptide galanin is markedly upregulated within the adult dorsal root ganglion (DRG) after peripheral nerve injury. We demonstrated previously that the rate of peripheral nerve regeneration is reduced in galanin knock-out mice, with similar deficits observed in neurite outgrowth from cultured mutant DRG neurons. Here, we show that the addition of galanin peptide significantly enhanced neurite outgrowth from wild-type sensory neurons and fully rescued the observed deficits in mutant cultures. Furthermore, neurite outgrowth in wild-type cultures was reduced to levels observed in the mutants by the addition of the galanin antagonist M35 [galanin(1-13)bradykinin(2-9)]. Study of the first galanin receptor (GalR1) knock-out animals demonstrated no differences in neurite outgrowth compared with wild-type animals. Similarly, use of a GalR1-specific antagonist had no effect on neuritogenesis. In contrast, use of a GalR2-specific agonist had equipotent effects on neuritogenesis to galanin peptide, and inhibition of PKC reduced neurite outgrowth from wild-type sensory neurons to that observed in galanin knock-out cultures. These results demonstrate that adult sensory neurons are dependent, in part, on galanin for neurite extension and that this crucial physiological process is mediated by activation of the GalR2 receptor in a PKC-dependent manner.