Neuroblastomas, which have sympathoadrenergic origin, are the most frequent childhood extracranial tumors. Good prognosis tumors (favourable cytogenetics, differentiated) express nerve growth factor (NGF) receptor tyrosine kinase trkA, whereas poor prognosis neuroblastomas (adverse cytogenetics, Myc amplification, poor differentiation) express neurotrophin receptor tyrosine kinase trkB. On NGF stimulation, trkA is activated by tyrosine phosphorylation and outcome is cell/tissue-dependent, and can signal for differentiation.
We have shown that in rat sympathoadrenergic PC12 cells, wild-type (wt)p53 expression induces trkA tyrosine phosphorylation and trkA dependent signalling, promoting their NGF independent differentiation. In breast cancer tumors and neuroblastomas, high trkA levels are associated with good prognosis. In both tumour types the p53 mutation incidence is 20-25%. The tyrosine phosphatase SHP-1 dephosphorylates trkA tyrosines 674/675(Y674/Y675). We have shown that in breast cancer wt-p53 represses SHP-1 expression and induces trkA-Y674/Y675 phosphorylation, leading to NGF-independent trkA activation. This signals to suppress breast cancer proliferation by promoting cell-cycle arrest. Furthermore, in breast cancer, coexpression of phosphorylated trkA-Y674/Y675, wt-p53 and low SHP-1 levels, correlates with prolonged 15 years disease free survival (DFS). Our experiments provide a mechanism for trkA expression correlation with good prognosis in breast cancer and emphasise the importance of this mechanism in cancer.
As neuroblastomas contain different cell populations, it has been difficult to identify prognostic biomarkers that would predict patient outcome. We have shown that wt-p53 repression of SHP-1 leads to trkA-Y674/Y675 phosphorylation and neuroblastoma differentiation. Neuroblastoma differentiation is associated with improved DFS. Thus we asked if, the presence of wt-p53 and SHP-1 downregulation, together with phosphorylated trkA, in neuroblastoma samples, correlates with favourable outcome. Confirmation of this mechanism would validate new molecular targets for neuroblastoma.
Neuroblastoma arrays containing 169 samples were stained for p53, SHP1 and phosphorylated trkA-Y674/Y675 expression. Multivariate analysis showed low p53 levels associated with 65% 5 years DFS (hazard-ratio (HR)=0.35, p=0.09), whereas, high SHP1 expression was associated with a worse DFS (HR=1.37, p=0.028). Phosphorylated trkA-Y674/Y675 expression correlated with 88% 5 years DFS (HR=0.12, (p=0.001)). As differentiation is associated with improved survival, the differentiation markers MAP2 and Vimentin were included. Expression of MAP2 and Vimentin correlated with good DFS (71% (HR=0.29, p=0.027) and 35% (HR=0.65, p=0.014)). Myc amplification correlated with reduced DFS (HR=4.84, p=0.001) as expected. Importantly, multivariate-analysis of patients with tumors harbouring p53 together with high SHP-1 levels and phosphorylated trkA-Y674/Y675 showed 69% 5 years DFS (HR=0.29, p=0.001). Favourable DFS was seen when MAP2 and Vimentin (HR=0.53, p=0.032 and HR=0.51, p=0035) were included. Further statistical analysis which considers tumor cytogenetics will be presented. Our results will allow refinement of the prognostic tools available for neuroblastoma with direct impact on child healthcare.
Citation Format: Gehad Youssef, Cheryl Gillet, Dyanne Rampling, Mirza Chagtay, Alex Virasami, Neil Sebire, John Anderson, Ximena Montano. SHP-1, p53 and Y674/Y675-phosphorylated-trkA: a molecular pathway and prognostic marker for neuroblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-328. doi:10.1158/1538-7445.AM2014-LB-328