Thyrotropin and serum regulate thyroid cell proliferation through differential effects on p27 expression and...

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Thyroid cell proliferation is controlled by TSH/cAMP and serum growth factors.
• The precise roles of cAMP-dependent and -independent signaling in cell cycle progression remain unclear.

Purpose of the Study:

• To investigate the molecular mechanisms behind the synergistic effects of TSH and serum on G1/S phase cell cycle progression in rat thyroid cells.
• To elucidate the distinct and combined roles of TSH and serum in regulating key cell cycle proteins and pathways.

Main Methods:

• Analysis of G1/S phase cell cycle progression in rat thyroid cells.
• Assessment of retinoblastoma protein hyperphosphorylation, cyclin-dependent kinase 2 activity, and cyclin A expression.
• Examination of p27 protein localization and turnover.
• Measurement of p70S6K activity.

Main Results:

• TSH alone did not stimulate G1 phase progression but increased cycling cells when combined with serum.
• TSH potentiated serum-induced hyperphosphorylation of retinoblastoma protein, increased CDK2 activity, and elevated cyclin A expression.
• TSH promoted nuclear accumulation of p27, while serum induced its nuclear export; TSH enhanced nuclear p27 depletion in serum-treated cells.
• Combined TSH and serum treatment resulted in rapamycin-sensitive p27 turnover and sustained p70S6K activity through S phase.

Conclusions:

• TSH contributes to thyroid cell cycle progression by increasing the number of cycling cells.
• TSH exerts its effects partly through p70S6K-mediated regulation of p27 localization.
• The interplay between TSH and serum signaling pathways is crucial for precise control of thyroid cell proliferation.