Characterization of pregnancy-specific beta 1-glycoprotein synthesized by human placental fibroblasts.
We have previously demonstrated that human placental fibroblasts produce a pregnancy-specific beta 1-glycoprotein (PS beta G) immunologically indistinguishable from placental PS beta G. This was confirmed by the immunocytochemical localization of PS beta G in these fibroblasts. In addition, placental fibroblasts contain all three PS beta G mRNAs of 2.3, 2.2, and 1.7 kilobases which hybridize with the three PS beta G cDNAs (PSG16, PSG93, and PSG95) identified, although at 1.4-2.5% of the levels in human term placenta. The major PS beta G species synthesized by placental fibroblasts is a 62K glycopolypeptide formed from a 58K intracellular precursor polypeptide. However, the PS beta G species found in human placenta are one major glycoprotein of 72K and two minor ones of 64K and 54K. Poly(A)+ RNA from placental fibroblasts directed the synthesis of two polypeptides of 48K and 46K (major), whereas, poly(A)+ RNA from human placenta directed the synthesis of higher levels of four polypeptides of 50 K, 48 K (major), 46 K, and 36 K. Thus, the major PS beta G species found in fibroblasts and human placenta differ. The carbohydrate side-chains are essential for the stability of fibroblast PS beta G, because PS beta G synthesis in these fibroblasts could not be detected in the presence of tunicamycin, a protein glycosylation inhibitor which did not affect PS beta G mRNA expression. Our finding that a variant PS beta G species is produced in placental fibroblasts raises the possibility that the authentic placental PS beta G species may have different functions.
Chou
J Y
JY
Human Genetics Branch, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Sartwell
A D
AD
Wan
Y J
YJ
Watanabe
S
S
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002474:Cell-Free System; D015342:DNA Probes; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation; D006031:Glycosylation; D006801:Humans; D007150:Immunohistochemistry; D007163:Immunosorbent Techniques; D008970:Molecular Weight; D009693:Nucleic Acid Hybridization; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000096:biosynthesis*; D011268:Pregnancy-Specific beta 1-Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D017026:Swainsonine; D014415:Tunicamycin / Q000494:pharmacology
D000470:Alkaloids; D015342:DNA Probes; D011257:Pregnancy Proteins; D011268:Pregnancy-Specific beta 1-Glycoproteins; D012333:RNA, Messenger; D014415:Tunicamycin; D017026:Swainsonine