Inhibition of retinoblastoma protein degradation by interaction with the serpin plasminogen activator inhibitor 2 via a novel consensus motif.
Plasminogen activator inhibitor-2 (PAI-2) is well documented as an inhibitor of the extracellular serine proteinase urokinase-type plasminogen activator (uPA) and is expressed in activated monocytes and macrophages, differentiating keratinocytes, and many tumors. Here we show that PAI-2 has a novel intracellular function as a retinoblastoma protein (Rb)-binding protein. PAI-2 colocalized with Rb in the nucleus and inhibited the turnover of Rb, which led to increases in Rb protein levels and Rb-mediated activities. Although PAI-2 contains an LXCXE motif, Rb binding was primarily mediated by the C-D interhelical region of PAI-2, which was found to bind to the C pocket of Rb. The C-D interhelical region of PAI-2 contained a novel Rb-binding motif, termed the PENF homology motif, which is shared by many cellular and viral Rb-binding proteins. PAI-2 expression also protected Rb from the accelerated degradation mediated by human papillomavirus (HPV) E7, leading to recovery of Rb and inhibition of E6/E7 mRNA expression. Protection of Rb by PAI-2 begins to explain many of the diverse, uPA-independent phenotypes conferred by PAI-2 expression. These results indicate that PAI-2 may enhance Rb's tumor suppressor activity and suggest a potential therapeutic role for PAI-2 against HPV-transformed lesions.
Darnell
Grant A
GA
Australian National Centre for International and Tropical Health and Nutrition, Queensland Institute of Medical Research and University of Queensland, 300 Herston Road, Brisbane, Queensland 4029, Australia.
Antalis
Toni M
TM
Johnstone
Ricky W
RW
Stringer
Brett W
BW
Ogbourne
Steven M
SM
Harrich
David
D
Suhrbier
Andreas
A
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016384:Consensus Sequence; D017124:Conserved Sequence; D004268:DNA-Binding Proteins; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism; D017396:Plasminogen Activator Inhibitor 2 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D011233:Precipitin Tests; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D015842:Serine Proteinase Inhibitors / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
D004268:DNA-Binding Proteins; C052633:E7 protein, Human papillomavirus type 18; D009856:Oncogene Proteins, Viral; D017396:Plasminogen Activator Inhibitor 2; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D015842:Serine Proteinase Inhibitors