Recombinant human retinoblastoma protein inhibits cancer cell growth.
Aberrant expression of the tumor suppressor gene RB1 is associated with a variety of solid tumors and hematopoietic neoplasms. Certain cancer cell lines in which the protein encoded by RB1 (p110RB) is absent have been reported to show decreased growth rate, clonogenicity, or tumorigenicity following insertion of a transcriptionally active RB1 gene. We asked whether these RB-deficient cells could be growth inhibited by direct exposure to purified p110RB. We report a decrease in uptake of tritiated thymidine by 5637 bladder carcinoma cells (RB-negative) when purified recombinant p110RB is added to culture media. Internalization of the protein by cells and translocation to the nucleus are demonstrated by immunohistochemistry, FACS, and detection of radiolabeled protein in subcellular fractions. Next, we chose a well-described leukemia cell culture model to investigate the potential effect of recombinant p110RB in clinical disease. We observed dose-related decreases in cell number of colony formation in vitro in 8 of 20 acute myelogenous leukemia samples, 7 of which did show endogenous p110RB detectable by immunohistochemistry. Histological appearance following exposure to p110RB shows cytoplasmic vacuolization and nuclear lobulation of degenerating cells. We conclude that purified p110RB added to culture media is internalized by cells, translocated to the nucleus, and exerts a growth-inhibitory effect on certain cancer cell types.
Pagliaro
L C
LC
Division of Medicine, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Antelman
D
D
Johnson
D E
DE
Machemer
T
T
McCulloch
E A
EA
Freireich
E J
EJ
Stass
S A
SA
Shepard
H M
HM
Maneval
D
D
Gutterman
J U
JU
D000208:Acute Disease; D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D005260:Female; D006801:Humans; D007951:Leukemia, Myeloid / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D014411:Neoplastic Stem Cells / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D016160:Retinoblastoma Protein / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D001749:Urinary Bladder Neoplasms / Q000473:pathology*
D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein