Role of Src family members in breast cancer-dependent on site of phosphorylation.

Abstract

Abstract Abstract #2074 Background: In vitro work implicates c-Src in breast cancer. However there is little evidence to support this in clinical specimens. Activation of Src family members are associated with phosphorylation at two different tyrosine sites Y419: the classical activation site and Y215, known to induce a 50-fold increase in activation.
 We have analysed a cohort of human breast cancers to establish if expression levels of 2 Src family members (c-Src and Lyn) are associated with survival and whether this is dependent on site of activation.
 Methods: Tissue microarrays were constructed from 895 breast cancer tumors. Median follow up was 6 years with 229 breast cancer specific deaths. Immunohistochemistry was performed using antibodies to c-Src, Lyn, pSrc419 and pSrc215 (antibodies to Y419 and Y215 will detect phosphorylation of either c-Src and Lyn). Expression was assessed by two independent scorers. All statistical calculations were performed using SPSS 15.
 Results: Membrane expression of c-Src and Lyn was rarely observed. However, cytoplasmic expression of c-Src and Lyn was frequently observed and further results presented relate to this site. High expression levels of c-Src but not Lyn were associated with HER2 positivity (p=0.001) and ER negativity (p<0.001).
 High c-Src expression was associated with a poor outcome. In direct contrast pSrc215 was associated with improved outcome on univariate and multivariate analysis.
 Antibodies to phosphorylation sites will detect both activated c-Src and Lyn (and other family members). The individual impact of phosphorylation on clinical outcome was determined by categorising expression based on overexpression of c-Src or Lyn in combination with activation at each site.
 
 Discussion: Our findings demonstrate that phosphorylation of c-Src at Y419 is associated with poor prognosis in breast cancer. In contrast phosphorylation at Y215 was independently associated with better outcome.
 Further work is ongoing to explore our hypothesis that:
 1. phosphorylation at 215 'deactivates' c-Src or desensitizes downstream pathways or,
 2. that activation of Lyn or other Src family members at 215 is responsible for good outcome.
 If confirmed, these results strongly suggest that commercial development of highly specific Src inhibitors is necessary and that these will require appropriate patient selection. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2074.