Summary
Plasminogen activator inhibitor type 2 (PAI-2) is a urokinase inhibitor that is expressed
primarily in monocytes. THP-1 monocytes, however, contain a unique defect in the production
of PAI-2 in that the PAI-2 transcript is truncated and the expressed protein inactive
(1). Here we describe the basis of this mutation in THP-1 cells. Southern blot analysis
of THP-1-derived genomic DNA indicated that there were no obvious deletions in the
structure of the PAI-2 gene. However, assessment of the THP-1-derived PAI-2 transcript
by RT-PCR indicated that only exons seven and eight of the normal PAI-2 mRNA could
be detected. Cloning of the 5’ region of the PAI-2 mRNA by 5-’RACE indicated that
the PAI-2 cDNA derived from THP-1 cells is approximately 1329 bp long and contains
180 bp of sequence derived from intron 5, followed by sequences corresponding to exons
seven and eight of the normal PAI-2 mRNA. The presence of the intron five fragment
in endogenous THP-1 derived PAI-2 mRNA was confirmed by Northern blotting. The absence
of any wild-type PAI-2 mRNA in these cells suggests that one copy of the PAI-2 allele
has been deleted. The remaining allele producing the truncated mRNA appears to have
undergone a translocation event and contains a mutation that has disrupted the splicing
of the PAI-2 primary transcript.
Key words
PAI-2 - THP-1 monocytes - plasminogen activation
