A self-restricted CD38-connexin 43 cross-talk affects NAD+ and cyclic ADP-ribose metabolism and regulates intracellular calcium in 3T3 fibroblasts.
Connexin 43 (Cx43) hexameric hemichannels, recently demonstrated to mediate NAD(+) transport, functionally interact in the plasma membrane of several cells with the ectoenzyme CD38 that converts NAD(+) to the universal calcium mobilizer cyclic ADP-ribose (cADPR). Here we demonstrate that functional uncoupling between CD38 and Cx43 in CD38-transfected 3T3 murine fibroblasts is paralleled by decreased [Ca(2+)](i) levels as a result of reduced intracellular conversion of NAD(+) to cADPR. A sharp inverse correlation emerged between [Ca(2+)](i) levels and NAD(+) transport (measured as influx into cells and as efflux therefrom), both in the CD38(+) cells (high [Ca(2+)](i), low transport) and in the CD38(-) fibroblasts (low [Ca(2+)](i), high transport). These differences were correlated with distinctive extents of Cx43 phosphorylation in the two cell populations, a lower phosphorylation with high NAD(+) transport (CD38(-) cells) and vice versa (CD38(+) cells). Conversion of NAD(+)-permeable Cx43 to the phosphorylated, NAD(+)-impermeable form occurs via Ca(2+)-stimulated protein kinase C (PKC). Thus, a self-regulatory loop emerged in CD38(+) fibroblasts whereby high [Ca(2+)](i) restricts further Ca(2+) mobilization by cADPR via PKC-mediated disruption of the Cx43-CD38 cross-talk. This mechanism may avoid: (i) leakage of NAD(+) from cells; (ii) depletion of intracellular NAD(+) by CD38; (iii) overproduction of intracellular cADPR resulting in potentially cytotoxic [Ca(2+)](i).
Bruzzone
S
S
Department of Experimental Medicine, Section of Biochemistry, University of Genova, Viale Benedetto XV/1, Genova, Italy.
Franco
L
L
Guida
L
L
Zocchi
E
E
Contini
P
P
Bisso
A
A
Usai
C
C
De Flora
A
A
D016475:3T3 Cells; D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives* / Q000378:metabolism*; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000378:metabolism*; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D018031:Connexin 43 / Q000378:metabolism*; D036563:Cyclic ADP-Ribose; D017931:DNA Primers; D004789:Enzyme Activation; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D008562:Membrane Glycoproteins; D051379:Mice; D009243:NAD / Q000378:metabolism*; D009244:NAD+ Nucleosidase / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism
D015703:Antigens, CD; D000943:Antigens, Differentiation; D018031:Connexin 43; D017931:DNA Primers; D008562:Membrane Glycoproteins; D009243:NAD; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D011493:Protein Kinase C; D036541:ADP-ribosyl Cyclase; C498155:Cd38 protein, mouse; D009244:NAD+ Nucleosidase; D051997:ADP-ribosyl Cyclase 1; D002118:Calcium