Colon cancer cells that are not growth inhibited by TGF-beta lack functional type I and type II TGF-beta receptors.
OBJECTIVE
The authors determined the molecular mechanisms for the failure of transforming growth factor-beta (TGF-beta) to inhibit the growth of SW1116 and SW48 colon cancer cell lines.


BACKGROUND
Transforming growth factor-beta is a bifunctional regulator of cell growth that typically stimulates proliferation of mesenchymal cells, but inhibits proliferation of normal epithelial cells. In the colon, TGF-beta appears to arrest proliferation of enterocytes as they leave the intestinal crypt and move to the villus tip. Transforming growth factor-beta actions are mediated by binding to heteromeric complexes of type I and type II TGF-beta receptors. Loss of TGF-beta responsiveness may contribute to uncontrolled cell growth and cancer.


METHODS
The effects of TGF-beta 1 on DNA synthesis were measured by incorporation of tritiated thymidine into DNA of cultures of moderately differentiated adenocarcinoma (SW48) and poorly differentiated adenocarcinoma (SW1116) colon cell lines and a mink lung epithelial cell line (CCL-64). The effects of TGF-beta on the expression of c-myc, TGF-alpha, and TGF-beta in SW48 cells, SW1116 cells, and CCL-64 cells (c-myc only) were measured by Northern blot analysis. Expression of TGF-beta receptors in the cell lines was measured using competitive binding assays, receptor affinity labelling techniques, and reverse transcriptase-polymerase chain reaction.


RESULTS
Incubation with TGF-beta 1 (50 ng/mL) did not decrease serum-stimulated uptake of [3H]-thymidine into actively growing cultures of SW48 or SW1116 cells, but suppressed DNA synthesis of actively growing CCL-64 cells by 90%. Similarly, incubation with TGF-beta 1 (12 ng/mL) for 4 hours did not substantially alter the mRNA levels of c-myc, TGF-alpha, and TGF-beta 1 in either colon tumor cell line, although levels of c-myc mRNA in CCL-64 cells were reduced by TGF-beta 1 treatment. Competitive displacement of [125I]-TGF-beta 1 binding detected high levels (16,500 TGF-beta receptors per cell) of specific, high-affinity (200 pmol/L half-displacement) TGF-beta receptors on CCL-64 cells. In marked contrast, very low levels of TGF-beta 1 binding to SW1116 cells (250 receptors per cell) and SW48 cells (260 receptors per cell) were detected. Autoradiograms of CCL-64 cells affinity labelled with [125I]TGF-beta 1 revealed the presence of type I, type II, and type III TGF-beta receptors. No TGF-beta receptors were identified on SW1116 cells, and only very low levels of the nonsignaling type III TGF-beta receptors were detected on SW48 cells. Reverse transcriptase-polymerase chain reaction amplification detected mRNAs for type I, type II, and type III TGF-beta receptors in CCL-64 cells. SW48 cells, and SW1116 cells.


CONCLUSIONS
These results suggest that the lack of growth inhibition by TGF-beta in SW48 and SW1116 colon cancer cells may be caused by a lack of expression of functional TGF-beta receptors.
MacKay
S L
SL
Department of Obstetrics/Gynecology, University of Florida College of Medicine, Gainesville, USA.
Yaswen
L R
LR
Tarnuzzer
R W
RW
Moldawer
L L
LL
Bland
K I
KI
Copeland
E M
EM
Schultz
G S
GS
D030201:Activin Receptors, Type I; D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000473:pathology*; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004848:Epithelium / Q000737:chemistry; D016259:Genes, myc / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases; D011509:Proteoglycans / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*; D016211:Transforming Growth Factor alpha / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D011509:Proteoglycans; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D016211:Transforming Growth Factor alpha; D016212:Transforming Growth Factor beta; C071736:betaglycan; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II