Induction of transforming growth factor alpha expression in mouse mammary epithelial cells after transformation with a point-mutated c-Ha-ras protooncogene.
NOG-8 ras cells are a normal mouse mammary epithelial cell line transfected with a plasmid containing a glucocorticoid-inducible mouse mammary tumor virus long terminal repeat linked to the activated c-Ha-ras protooncogene. After addition of dexamethasone, there is a rapid induction (within 1-3 h) of p21ras protein that is concomitant with a parallel induction of the c-Ha-ras specific mRNA. After 4-6 days of dexamethasone treatment, NOG-8 ras cells are able to grow as colonies in semisolid medium. Between 9 and 12 days of dexamethasone treatment, there is a 5- to 6-fold increase of transforming growth factor alpha (TGF alpha) activity in the conditioned medium from NOG-8 ras cells. A 60-65% reduction in epidermal growth factor cell surface receptors on NOG-8 ras cells also occurs during this time interval. A 3- to 4-fold increase of the expression of a specific TGF alpha mRNA can be detected within 2 days of dexamethasone treatment, preceding the increase in TGF alpha protein found in the conditioned medium. Exogenous TGF alpha is able to stimulate in a dose-dependent fashion the anchorage-dependent and anchorage-independent growth of NOG-8 ras cells to a level comparable to that observed in dexamethasone treated ras-transformed NOG-8 ras cells. These results suggest that the enhanced expression of TGF alpha after induction of an activated ras protooncogene may be necessary for the anchorage-independent growth and subsequent morphological changes and the enhanced growth rate observed in ras-transformed mammary epithelial cells.
Ciardiello
F
F
Laboratory of Tumor Immunology and Biology, National Cancer Institute, Bethesda, Maryland.
Kim
N
N
Hynes
N
N
Jaggi
R
R
Redmond
S
S
Liscia
D S
DS
Sanfilippo
B
B
Merlo
G
G
Callahan
R
R
Kidwell
W R
WR
D000818:Animals; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004847:Epithelial Cells; D066246:ErbB Receptors / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000494:pharmacology*; D016283:Proto-Oncogene Proteins p21(ras); D014170:Transformation, Genetic / Q000187:drug effects*; D015291:Transforming Growth Factors / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D011518:Proto-Oncogene Proteins; D015291:Transforming Growth Factors; D003907:Dexamethasone; D066246:ErbB Receptors; D016283:Proto-Oncogene Proteins p21(ras)