Effects of sodium butyrate on the synthesis of human pregnancy-specific beta 1-glycoprotein.
Human pregnancy-specific beta 1-glycoprotein (PS beta G) is a polymorphic placental protein which shows strong sequence similarity with the oncofetal protein, carcinoembryonic antigen. To better understand the role of PS beta G in pregnancy, we examined its synthesis and regulation in placental fibroblasts, which had been shown to express the PS beta G gene. The major placental PS beta G is a 72-kDa glycoprotein, while the major fibroblast PS beta G is a 62-kDa species. Administration of sodium butyrate to these fibroblasts slightly stimulated the synthesis of the 62-kDa species but markedly increased the production of two additional PS beta Gs of 72 and 48 kDa. The similarity between the PS beta Gs synthesized by butyrate-treated fibroblasts and human placenta was confirmed by cell-free protein synthesis. Poly(A)+ RNA from butyrate-treated fibroblasts and placenta directed the synthesis of two polypeptides of 48 and 36 kDa, which form the polypeptide backbone of the 72- and 48-kDa glycoproteins. Moreover, the predicted molecular weights of PS beta Gs encoded by the two types of PS beta G cDNA clones were 48,000 and 36,000. Most PS beta G cDNAs identified to date, including the three cDNAs (PSG16, PSG93, and PSG95) isolated in this laboratory, share strong sequence similarity at the 5' region (designated PSG-5') but differ in sequences at their 3' regions. The PSG-5', PSG93-specific, PSG16/PSG93-3', and PSG95-3' probes, which identify the majority of PS beta G mRNAs, hybridized with three PS beta G mRNAs of 2.3, 2.2, and 1.7 kilobases from placental fibroblasts. Butyrate increased the steady-state levels of all three mRNAs. Ribonuclease protection analysis showed that butyrate increased the PS beta G mRNAs containing the PSG-5' or PSG93-specific sequence to approximately 20% of human placental levels. However, unlike human term placenta, which predominantly expressed PS beta G mRNAs with 3'-sequences similar to PSG16/PSG93, the butyrate-treated fibroblasts expressed roughly equal levels of PS beta G mRNAs with the PSG16/PSG93-3' and PSG95-3' ends. All PS beta G cDNAs identified encode proteins with distinct carboxyl termini, suggesting that the composition of the 72-kDa species in placenta and butyrate-treated fibroblasts is likely to be different. Placental fibroblasts provide a unique model for the study of the mechanisms responsible for the differential expression of the PS beta G gene.
Chou
J Y
JY
Human Genetics Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Sartwell
A D
AD
Lei
K J
KJ
Plouzek
C A
CA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002087:Butyrates / Q000494:pharmacology*; D020148:Butyric Acid; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000235:genetics*; D011268:Pregnancy-Specific beta 1-Glycoproteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
D002087:Butyrates; D011257:Pregnancy Proteins; D011268:Pregnancy-Specific beta 1-Glycoproteins; D012333:RNA, Messenger; D020148:Butyric Acid