The human transforming growth factor type alpha coding sequence is not a direct-acting oncogene when overexpressed in...

Area of Science:

• Molecular Biology
• Cell Biology
• Oncogenesis

Background:

• Transforming growth factor alpha (TGF-alpha) is a peptide secreted by tumor cells that can induce anchorage-independent growth in normal cells.
• Its role as a direct-acting oncogene was investigated due to its association with tumor cell secretions.

Purpose of the Study:

• To directly assess the transforming potential of the human TGF-alpha gene.
• To investigate the mechanism of TGF-alpha action in NIH 3T3 cells.

Main Methods:

• Transfection of NIH 3T3 cells with TGF-alpha expression vectors under metallothionein or retroviral promoters.
• Comparison with transfection of known oncogenes (v-sis, v-erbB) and their receptors.
• Analysis of secreted TGF-alpha, EGF receptor expression, and growth inhibition by TGF-alpha antibodies.
• Assessment of colony formation on contact-inhibited monolayers and tumorigenicity in nude mice.

Main Results:

• TGF-alpha expression vectors did not induce morphological transformation in NIH 3T3 cells, unlike viral oncogenes.
• Secreted TGF-alpha interacted with its receptor on the cell surface, leading to population growth but not individual cell transformation.
• TGF-alpha-expressing cells showed high saturation density but were not tumorigenic and failed to form colonies on contact-inhibited monolayers.

Conclusions:

• The normal coding sequence for TGF-alpha is not a direct-acting oncogene when overexpressed in NIH 3T3 cells.
• TGF-alpha exerts a growth-promoting effect on the cell population after secretion, rather than directly transforming individual cells.