Defect in serine 46 phosphorylation of p53 contributes to acquisition of p53 resistance in oral squamous cell carcinoma cells

Oncogene. 2006 Feb 23;25(8):1216-24. doi: 10.1038/sj.onc.1209158.


To investigate whether dysregulation of p53 phosphorylation confers tumor resistance to p53, we analysed the effects of wild-type p53 on oral squamous cell carcinoma (SCC) cell lines carrying various mutations of p53. Introduction of exogenous p53 neither induced apoptosis nor suppressed colony formation in HSC-3 cells lacking any detectable p53 and HSC-4 cells expressing mutant p53R248Q protein. Consistently, exogenous p53 did not induce proapoptotic p53-target genes in these p53-resistant cells. We found that phosphorylation of exogenous p53 on serine 46 (Ser46) was severely impaired in HSC-3 but not HSC-4 cells. A mutant mimicking Ser46-phosphorylation (p53S46D) enhanced proapoptotic Noxa promoter activity, and overcame the resistance to p53-mediated apoptosis and growth suppression in HSC-3 cells. Conversely, a mutant defective for Ser46-phosphorylation (p53S46A) failed to suppress the growth of p53-sensitive HSC-2 cells. In contrast to HSC-3 cells, p53S46D had no effect on HSC-4 cells, and inhibition of endogenous p53R248Q by siRNA restored p53-mediated apoptosis in HSC-4 cells, indicating a dominant-negative effect of p53R248Q protein on wild-type p53 function. These results demonstrate that the defect in Ser46 phosphorylation accounts for the p53 resistance of HSC-3 cells, and provide evidence for a mechanism underlying the acquisition of p53 resistance in oral SCC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoviridae / genetics
  • Apoptosis
  • Carcinoma, Non-Small-Cell Lung / genetics
  • Carcinoma, Non-Small-Cell Lung / metabolism
  • Carcinoma, Squamous Cell / genetics
  • Carcinoma, Squamous Cell / metabolism*
  • Humans
  • Lung Neoplasms / genetics
  • Lung Neoplasms / metabolism
  • Mouth Neoplasms / genetics
  • Mouth Neoplasms / metabolism*
  • Mutation / genetics*
  • Phosphorylation
  • RNA, Small Interfering / pharmacology
  • Serine / metabolism*
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / metabolism*


  • RNA, Small Interfering
  • Tumor Suppressor Protein p53
  • Serine