Expression and activity of protein kinase C isoenzymes during normal and abnormal murine palate development

Protein kinase C (PKC) plays a critical role in signal transduction, mediat ing various cellular events critical for normal development, including that of the palate. In vivo and in vitro studies suggest the relevance of the i nhibition of PKC by the mycotoxin, secalonic acid D (SAD), to its induction of cleft palate (CP) in mice. In the present study, temporal and spatial e xpression and the activity of various PKC isoenzymes were studied in the co ntrol and SAD-exposed murine embryonic palate during gestational days (GD) 12-14.5 by western blotting, immunohistochemistry, and phosphotransfer assa y. The Ca2+-dependent isoenzymes, PKC alpha and PKC beta II, showed signifi cant expression on GD 12.0, which gradually decreased through GD 14.5, wher eas PKC beta I and PKC gamma were negligible throughout. All Ca2+-independe nt isoenzymes (epsilon, delta, and zeta) were expressed more abundantly and , in contrast to the Ca2+-dependent ones, progressively increased with age. SAD failed to alter this pattern of expression but enhanced the phosphoryl ation of PKC epsilon throughout development. Immunohistochemical analysis r evealed an isoenzyme-specific distribution of PKC between the epithelium an d mesenchyme. As expected, SAD significantly inhibited the total Ca2+-depen dent PKC activity in palatal extracts. Although total Ca2+-independent PKC activity in palatal extracts was unaffected by SAD, individual pure isoenzy mes were either selectively inhibited (PKC zeta), stimulated (PKC delta), o r unaffected (PKC epsilon) by SAD. These results show that PKC isoenzymes e xhibit dynamic temporal and spatial patterns of expression and activity in the developing palate and that the induction of CP by SAD is associated wit h an alteration in their activation and/or activity.