Human placental tissue expresses a novel 22.7 kDa apolipoprotein A-I-like protein.

Academic Article

Abstract

  • Since apolipoprotein A-I (apo A-I) and HDL stimulate the expression of the placental hormone human placental lactogen (hPL), experiments were performed to determine whether the human placenta synthesizes apo A-I. Western blot analysis of a partially purified extract of human term placenta with an antiserum to human apo A-I yielded an immunoreactive band with an apparent mass of approximately 23.5 kDa, which is smaller than human plasma apo A-I (28 kDa). HPLC chromatography of the partially purified placental extract on a preparative reverse-phase C-18 column yielded two fractions that reacted to the apo A-I antiserum. The mass of both fractions by mass spectral analysis was 22 721 daltons, and N-terminal amino acid sequences were identical to the first four amino acids of apo A-I (Asp, Glu, Pro, Pro). The apo A-I-like protein was not a proteolytic product of apo A-I since Northern analysis of placental RNA with a 641 bp apo A-I cDNA fragment encoding most of the 5' region of the apo A-I mRNA detected a single band of 850 nt, which is smaller than the size of apo A-I mRNA (1100 nt). Placental mRNA, however, did not hybridize with a 3' apo A-I riboprobe, indicating that the 3' region of the apo A-I-like mRNA is different from that of apo A-I mRNA. Differences in the mRNAs were confirmed by S1 nuclease analysis of placental RNA with a cDNA probe that included the 3' end of the apo A-I cDNA and by RT-PCR analysis with a series of oligonucleotide primers that span the entire cDNA for apo A-I. Since there is only a single apo A-I gene in the human genome, these findings strongly suggest that human placental tissue expresses a novel 22.7 kDa apo A-I-like protein (ALP) that results from alternative splicing of the apo A-I primary transcript.
  • Published In

  • Biochemistry  Journal
  • Keywords

  • Apolipoprotein A-I, Base Sequence, Blotting, Northern, Carcinoma, Hepatocellular, Cell Line, Chromatography, High Pressure Liquid, DNA Primers, DNA Probes, Exons, Female, Humans, Introns, Liver, Liver Neoplasms, Molecular Sequence Data, Molecular Weight, Placenta, Pregnancy, RNA, Messenger, Tumor Cells, Cultured
  • Digital Object Identifier (doi)

    Authorlist

  • Richardson B; Palgunachari MN; Anantharamaiah GM; Richards RG; Azrolan N; Wiginton D; Handwerger S
  • Start Page

  • 7580
  • End Page

  • 7585
  • Volume

  • 35
  • Issue

  • 23