Ha-Ras(G12V) induces senescence in primary and immortalized human esophageal keratinocytes with p53 dysfunction

Area of Science:

• Cellular senescence
• Oncogenesis
• Tumor suppressor pathways

Background:

• Oncogenic Ras proteins initiate a senescence response, acting as a tumor suppressor mechanism.
• Mouse cells utilize the ARF-p53 pathway for Ras-induced senescence, unlike human cells.
• The behavior of Ras in human epithelial cells with altered p53 and telomerase is not well understood.

Purpose of the Study:

• To investigate the effects of oncogenic Ras (Ha-Ras G12V) on human esophageal keratinocytes.
• To determine if p53 mutation or telomerase activation influences Ras-induced senescence in these cells.

Main Methods:

• Ectopic expression of Ha-Ras G12V in primary and hTERT-immortalized human esophageal keratinocytes.
• Utilized keratinocytes with stable dominant-negative p53 mutants.
• Assessed cellular morphology, senescence-associated beta-galactosidase activity, cell proliferation, retinoblastoma protein (pRb) phosphorylation, p16INK4a, and Cdk4 expression.

Main Results:

• Ha-Ras G12V induced senescence in human esophageal keratinocytes independently of p53 status and telomerase activation.
• Senescence was characterized by morphological changes, increased beta-galactosidase activity, and suppressed proliferation.
• Ras activation led to reduced pRb hyperphosphorylation, increased p16INK4a, and decreased Cdk4.

Conclusions:

• Ras-mediated senescence in human cells involves distinct pathways compared to mouse cells, particularly concerning the retinoblastoma protein (pRb) pathway.
• Inactivation of the pRb pathway may be crucial for Ras to overcome senescence and drive malignant transformation in human esophageal epithelial cells.