Regulation of C-myc and C-Ha-ras oncogene expression by cell shape

Area of Science:

• Cell Biology
• Molecular Biology
• Oncology

Background:

• Cell shape is a critical factor influencing cellular behavior and function.
• Proto-oncogenes play a vital role in cell growth and proliferation.
• Contact inhibition is a phenomenon where normal cells stop dividing when they come into contact with each other.

Purpose of the Study:

• To investigate the influence of cell shape on proto-oncogene expression in normal and malignant human cells.
• To determine the relationship between cell shape, proliferation, and the expression of specific oncogenes (c-myc, c-ras, c-fos, c-fes).
• To elucidate the regulatory mechanisms underlying shape-dependent gene expression and cell growth control.

Main Methods:

• Cells were cultured on surfaces with varying concentrations of poly(2-hydroxyethyl methacrylate) (poly[HEMA]) to control cell shape (degree of roundness).
• Proliferation capacity was assessed in normal (CUA-1 fibroblasts, HT-IFNr) and malignant (HT-1080) cells.
• mRNA levels of c-myc, c-ras, c-fos, and c-fes were analyzed using Northern blotting.
• Transcription rates were quantified using the nuclear run-off assay.

Main Results:

• Normal cells (CUA-1) exhibited shape-dependent proliferation, ceasing division upon reaching a critical roundness.
• Expression of c-myc and c-ras oncogenes was highly sensitive to cell shape in normal cells, declining with increased roundness.
• Malignant (HT-1080) and variant (HT-IFNr) cells showed proliferation independent of cell shape and lacked shape-dependent regulation of c-myc and c-ras.
• c-fos and c-fes oncogene expression was independent of cell shape in all cell types tested.
• Shape modulation of c-myc and c-ras expression occurred at the transcriptional level.

Conclusions:

• Cell shape is a significant regulator of specific proto-oncogene expression (c-myc, c-ras) and proliferation in normal cells.
• Loss of shape-dependent regulation of c-myc and c-ras is associated with malignant transformation and loss of contact inhibition.
• While altered oncogene regulation contributes to uncontrolled growth, it is not the sole factor releasing cells from contact inhibition.