Hormones and the single cell: a relationship prerequisite for transformation

Area of Science:

• Cell Biology
• Oncology
• Endocrinology

Background:

• Neoplastic transformation can be studied in cell cultures, free from host influences.
• Retinoids inhibit late-stage transformation and promotion, while thyroid hormones impact early initiation events.

Purpose of the Study:

• To investigate the role of thyroid hormones in the initiation of neoplastic transformation.
• To determine the specific timing and conditions under which thyroid hormones influence radiation- and chemical-induced transformation.

Main Methods:

• Utilized cloned hamster embryo cells and mouse 10T 1/2 cells in culture.
• Exposed cells to X-rays or benzo[a]pyrene under varying thyroid hormone (triiodothyronine, T3) concentrations and timing.
• Assessed cell transformation frequency, survival, and growth.

Main Results:

• No transformation occurred in cells cultured under hypothyroid conditions, despite unaffected cell survival and growth.
• T3 supplementation before X-ray exposure dose-dependently increased transformation frequency, peaking at 10-10M.
• T3 addition during or after radiation reduced or abolished transformation, respectively.
• The T3 effect was specific, not mimicked by reverse T3, and inhibited by cyclohexamide, suggesting protein synthesis involvement.

Conclusions:

• Thyroid hormones, specifically triiodothyronine (T3), are essential prerequisites for the initiation of neoplastic transformation induced by X-rays and benzo[a]pyrene.
• The action of T3 appears to involve the synthesis of a cellular 'transforming protein' during early events.
• These findings highlight thyroid hormone-dependent mechanisms in early oncogenesis.