Regulation of phospholipase C activation by the number of H(2) receptors during Ca(2+)-induced differentiation of mouse keratinocytes.
We have reported previously that the histamine H(2) receptor (H(2)R) can stimulate the phospholipase C (PLC) signaling pathway in mouse keratinocytes. In the present work, we examined the physiological mechanisms involved in this activation by studying histamine metabolism and H(2)R expression and coupling during mouse keratinocyte differentiation. Ca(2+)-induced differentiation decreased histidine decarboxylase (HDC) mRNA, the enzyme responsible for histamine synthesis, by 68.9+/-5.0%. Concomitantly, intracellular histamine content and its release into the extracellular medium were reduced significantly by 68.2+/-2.0 and 74.1+/-1.7%, respectively. Binding of [3H]tiotidine to H(2)Rs present on the surface of whole cells was also decreased by cellular differentiation [(18.17+/-2.1)x10(4) vs. (6.27+/-0.87)x10(4) sites/cell, undifferentiated and differentiated cells, respectively], without affecting H(2)R affinity. Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of the H(2)R mRNA showed that the expression was also down-regulated at the transcriptional level. Moreover, the inhibition of H(2)R expression strongly affected the ability of the receptor to induce PLC activation. Our findings suggest that H(2)R signaling through the PLC second messenger system is inhibited during keratinocyte differentiation by an autocrine loop involving down-regulation of H(2)R expression and inhibition of histamine metabolism.
Fitzsimons
Carlos
C
Radioisotopes Laboratory, School of Pharmacy and Biochemistry, University of Buenos Aires, Junín 956, (1113), Buenos Aires, Argentina.
Engel
Nora
N
Policastro
Lucía
L
Durán
Hebe
H
Molinari
Beatriz
B
Rivera
Elena
E
D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D002118:Calcium / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D002927:Cimetidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006632:Histamine / Q000378:metabolism; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D006640:Histidine Decarboxylase / Q000235:genetics / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism; D011970:Receptors, Histamine H2 / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014316:Tritium; D010738:Type C Phospholipases / Q000378:metabolism*
D006635:Histamine H2 Antagonists; D012333:RNA, Messenger; D011970:Receptors, Histamine H2; D014316:Tritium; D002927:Cimetidine; D006632:Histamine; D000242:Cyclic AMP; D010738:Type C Phospholipases; D006640:Histidine Decarboxylase; C023990:tiotidine; D002118:Calcium