Adenoviral constructs encoding phosphorylation-competent full-length and truncated forms of the human retinoblastoma protein inhibit myocyte proliferation and neointima formation.
BACKGROUND
The retinoblastoma (Rb) protein is a key cell-cycle regulator that controls entry into the S phase by modulating the activity of the E2F transcription factor. We analyzed the effects of full-length phosphorylation-competent and a mutant truncated form of human Rb for their effects on vascular smooth muscle cell (VSMC) proliferation and neointima formation.


RESULTS
A number of mutant forms, both phosphorylation competent and incompetent, of human Rb protein were evaluated for their ability to inhibit E2F activity. The results of these assays indicated that a phosphorylation competent, amino-terminal-truncated Rb protein (Rb56) was a particularly potent inhibitor of E2F-mediated transcription relative to the full-length Rb construct (Rb110). Adenoviral constructs containing Rb56 or Rb110 expressed their respective Rb forms in VSMCs, as determined by Western immunoblot analysis, and were similar in their abilities to arrest the cell cycle, as determined by assays of 3H-thymidine incorporation and by flow cytometric analyses. When examined for their effect on neointima formation after balloon injury of the rat carotid artery, both full-length and truncated forms of Rb inhibited formation of this VSMC-derived lesion.


CONCLUSIONS
These analyses revealed that the maintenance of high levels of phosphorylation-competent human Rb, either full-length or truncated forms, in VSMCs is an effective method of modulating the extent of intimal hyperplasia that occurs after balloon-induced vascular injury.
Smith
R C
RC
Department of Medicine, Tufts University School of Medicine, St. Elizabeth's Medical Center, Boston, Mass 02135, USA.
Wills
K N
KN
Antelman
D
D
Perlman
H
H
Truong
L N
LN
Krasinski
K
K
Walsh
K
K
D000256:Adenoviridae; D000800:Angioplasty, Balloon / Q000009:adverse effects; D000818:Animals; D015153:Blotting, Western; D016893:Carotid Stenosis / Q000209:etiology / Q000473:pathology; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000235:genetics; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D004195:Disease Models, Animal; D050684:E2F Transcription Factors; D005434:Flow Cytometry; D015967:Gene Expression Regulation, Viral; D005822:Genetic Vectors; D006801:Humans; D006965:Hyperplasia; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000293:injuries; D009154:Mutation / Q000502:physiology; D010766:Phosphorylation; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D012008:Recurrence; D016160:Retinoblastoma Protein / Q000032:analysis / Q000235:genetics*; D056465:Retinoblastoma-Binding Protein 1; D012501:Saphenous Vein / Q000166:cytology; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D017539:Tunica Intima / Q000293:injuries / Q000473:pathology*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors