Regulation of osteoclastic acid secretion by cGMP-dependent protein kinase.
Nitric oxide (NO) down-regulates osteoclastic activity. The mechanism is unknown, although, in some cells NO acts by stimulating guanylate cyclase which activates cGMP-dependent proteins. We demonstrated cGMP-dependent protein kinase in osteoclasts by immunofluorescence microscopy. Specificity was confirmed by Western blot analysis showing a single 78 kDa band, the size of the Type I isoform, in isolated avian osteoclasts. Osteoclast function centers on HCl secretion at a specialized membrane organelle. We found that purified cGMP-dependent protein kinase inhibits ATP-dependent acid transport in reconstituted osteoclast membrane vesicles >90%, while cAMP-dependent kinase catalytic subunit, calmodulin kinase II, or cGMP alone were ineffective. This novel, direct modulation of acid transport by cGMP-dependent kinase and the occurrence of the enzyme in osteoclasts suggest that a mechanism of NO-regulation of bone turnover is via cGMP and cGMP-dependent protein kinase inhibition of HCl transport.
Van Epps-Fung
C
C
Department of Pathology, University of Alabama at Birmingham 35294.
Williams
J P
JP
Cornwell
T L
TL
Lincoln
T M
TM
McDonald
J M
JM
Radding
W
W
Blair
H C
HC
D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002645:Chickens; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology*; D006851:Hydrochloric Acid / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010010:Osteoclasts / Q000201:enzymology / Q000378:metabolism*
D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D006851:Hydrochloric Acid