Abstract 4120: SHP-1 tyrosine phosphatase in early stage lung cancer

Abstract

Abstract SHP-1 tyrosine phosphatase potentiates mitogenic signalling cascades in multiple cellular pathways, by dephosphorylating inhibitory phospho-tyr sites on kinases. The SHP-1 gene is highly expressed from a 3′ promoter (promoter 2) in lymphocytes, but not in lymphomas or leukemic cells. Gene silencing of SHP-1 by aberrant methylation and loss of heterozygosity has been associated with the pathogenesis of leukemias/lymphomas. With its central role in regulation of cell proliferation, SHP-1 is a logical candidate biomarker for malignant transformation, however, its role in solid tissues is unclear. SHP-1 dephosphorylates a number of phospho-targets including PI3 kinase, EFGR, src family kinases, and activated cKit, the stem cell factor receptor. Dephosphorylation of inhibitory phospho-tyr sites in these kinases results in increased signaling and gene expression. In the present study, western blot analyses of protein expression in two of four NSCLC cell lines which reportedly have silenced SHP-1 but had elevated levels of SHP-1 protein revealed inhibitory ser591 phosphorylation suggesting that this phosphatase was not activated in those cells. Altered expression of SHP-1 in leukemias and lymphomas was recently shown to be associated with clinical stage and pathogenesis with decreased levels evident in residual disease. Furthermore, altered expression of SHP-1 in epithelial tumors has been reported in ovarian and breast cancer, due to changes in the 5′ promoter (promoter 1) methylation. Previous observations by ourselves and others are consistent with the involvement of aberrant tumor suppressor gene promoter methylation in non-small cell lung cancer (NSCLC) particularly in recurrent cases. To investigate the role of epigenetic regulation of SHP-1 promoter 2 methylation in NSCLC, we used pyrosequencing to quantify methylation in 22 normal blood leukocytes, 19 normal lung specimens, 112 cases of early stage (Ib, IIa and IIb) NSCLC and 8 cell lines. Average SHP-1 promoter 2 methylation was 5.1% in leukocytes, 52.9% in normal lung 58.6% in NSCLC, and 96.2% in the cell lines. Promoter hypermethylation of SHP-1 (defined as more than 55% methylated) was observed in 68/112 of lung tumors. When compared to those tumors with methylation less than 55%, hypermethylation of SHP-1 at position −449 (+6025) was associated with shorter time to recurrence (51.4 months vs. 112 months; p=0.010) and marginally associated with five year survival (92.0 months vs. 125 months; p=0.073). These results demonstrate tissue-specific epigenetic control of SHP-1 promoter 2 and suggest a role for promoter 2-regulated signalling in early stage NSCLC. Furthermore, considering the relative low levels of SHP1 protein expression detected in the lung cancer cell lines, SHP-1 promoter 1 methylation in NSCLC is currently under investigation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4120.