Identification and characterization of a new member of the prolactin family, placental lactogen-I variant.
This report describes the identification and characterization of a new member of the placental prolactin (PRL) family, termed placental lactogen-I variant (PL-Iv). PL-Iv was isolated from medium conditioned by late gestation placental explants. Rat PL-Iv was found to be closely related to rat PL-I. Amino-terminal sequence analysis indicated that PL-Iv shared approximately 88% sequence identity with the amino terminus of PL-I. PL-Iv proteins cross-reacted with antiserum to recombinant mouse PL-I and PL-Iv mRNA hybridized with a PL-I cDNA. Multiple PL-I and PL-Iv species were present in placental cytosol. Despite the structural similarities between PL-I and PL-Iv, distinct differences were also evident. Antibodies generated to the amino-terminal 19 amino acids of PL-Iv specifically recognized PL-Iv, while failing to recognize PL-I. Secreted PL-Iv had an affinity for concanavalin A, whereas secreted PL-I lacked affinity for the lectin. PL-I was predominantly secreted as a 36-40-kDa species and PL-Iv was predominantly secreted as a 33-kDa species. Furthermore, PL-I and PL-Iv were synthesized at different times during gestation and by different cell types. PL-I was synthesized by trophoblast giant cells during the first half of gestation, while PL-Iv was predominantly synthesized by spongiotrophoblast cells during the later stages of gestation. PL-Iv was shown to stimulate the proliferation of rat Nb2 lymphoma cells, an in vitro measure of lactogenic activity. In summary, PL-Iv shares structural similarities with PL-I; however, it shows other structural differences in addition to unique cell- and temporal-specific patterns of expression in the rat chorioallantoic placenta.
Deb
S
S
Department of Physiology, University of Kansas Medical Center, Kansas City 66103.
Faria
T N
TN
Roby
K F
KF
Larsen
D
D
Kwok
S C
SC
Talamantes
F
F
Soares
M J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D006023:Glycoproteins / Q000737:chemistry / Q000276:immunology; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010920:Placenta / Q000166:cytology / Q000502:physiology; D010928:Placental Lactogen / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
D006023:Glycoproteins; D012333:RNA, Messenger; C066927:placental lactogen I-variant; D010928:Placental Lactogen