Phosphatase regulation of gene expression during development of the palate.
In mammalian cells, including those of the embryonic palate, the level of phosphorylation of cellular proteins at any given time reflects the activities of protein kinases and protein phosphatases. Both protein phosphatase-1 (PP-1) and PP-2A inhibit cAMP-mediated increases in transcription by dephosphorylating CREB at ser-133. Western blot analysis indicated that protein phosphatase 1 (PP-1) was expressed constitutively in palatal tissue during its development. Expression of PP-2A was regulated developmentally with maximal expression on gestational day (gd) 14. Densitometric scanning revealed a 30% increase in expression from gd 13 to gd 14. Virtually all phosphatase activity in the tissue extracts could be inhibited by 5 microM okadaic acid, demonstrating that PP-1 and PP-2A account for all detectable ser/thr protein phosphatase activity present in the developing palate. Moreover, no significant differences in PP-1 and PP-2A activities were observed during the period of palate development. Treatment of primary cultures of murine embryonic palate mesenchymal (MEPM) cells with forskolin (20 microM) to elevate intracellular cAMP levels, resulted in a time-dependent increase in CREB ser-133 phosphorylation and a corresponding time dependent decrease in PP-1 and PP-2A levels. Moreover, treatment of MEPM cells with okadaic acid resulted in a dramatic increase in basal CREB ser-133 phosphorylation. This suggests that PP-1 activity may contribute to transcriptional regulation of CREB and that PP-1 and PP-2A are regulated differentially by cAMP. Treatment of MEPM cells with TGF beta 1 (1 ng/ml) under conditions of TGF beta-induced CREB phosphorylation resulted in no effect on the expression of either PP-1 or PP-2A proteins and no significant alterations in total basal protein phosphatase activity. These results demonstrate that transcriptional regulation of CREB in embryonic palatal issue is dependent on the coordinate activity of specific kinases and phosphatases.
Weston
Wayde M
WM
Pulmonary/Diabetes Therapeutic Unit, UP4310, SmithKline Beecham Pharmaceuticals, 1250 South Collegeville Road, PO Box 5089, Collegeville, PA 19426, USA.
Freeman
Angela B
AB
Haberecht
Christian
C
Hackmiller
Rita C
RC
Ma
Linh
L
Nugent
Paul
P
Warr
Edward
E
Pisano
M Michele
MM
Greene
Robert M
RM
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000302:isolation & purification; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010159:Palate / Q000254:growth & development*; D010749:Phosphoprotein Phosphatases / Q000096:biosynthesis; D010744:Phosphoric Monoester Hydrolases / Q000502:physiology*; D054645:Protein Phosphatase 1; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000502:physiology
D017362:Cyclic AMP Response Element-Binding Protein; D016212:Transforming Growth Factor beta; D005576:Colforsin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D010744:Phosphoric Monoester Hydrolases