Abstract 2114: PTPN13 regulates ephrinB1 reverse signaling, MAP kinase signaling and tumor growth
Authors: Vermeer Paola D. , Haag Nichole , Lee Kimberly M. , Vermeer Daniel W. , Wieking Bryant G. , Lee John H. 
Published: July 2012

Human papillomaviruses (HPV's) are a causative factor in over 90% of cervical and 25% of head and neck squamous cell carcinomas. The C-terminus of high risk HPV 16 E6 associates and degrades PTPN13, a non-receptor protein tyrosine phosphatase. PTPN13 has recently been dubbed a putative tumor suppressor. Moreover, its decreased expression correlates with decreased overall survival in breast cancer. PTPN13 contains 5 PDZ (protein-protein interaction) domains and associates with several proteins. Thus, decreased PTPN13 expression likely results in many cellular consequences, some of which may impact cellular proliferation, tumor growth and metastasis. EphrinB1 belongs to a family of ligands which bind and activate the Eph family of receptor tyrosine kinases. Following activation of Eph receptors, Ephrin ligands too become activated and initiate intracellular signals. Importantly, the Eph/Ephrin system functions in cancer biology. EphrinB1 associates with PDZ4 of PTPN13 and is also a phosphatase substrate. As predicted, shRNA-mediated knock-down of PTPN13 leads to increased phosphorylated EphrinB1. Surprisingly, it resulted in a concomitant increase in phosphorylated Erk1/2. In addition, shRNA-mediated knock-down of EphrinB1 attenuates phosphorylated Erk1/2. These data suggest that activated EphrinB1 crosstalks with the MAP Kinase pathway. We have found that EphrinB1 associates with two cellular oncoproteins, ErbB1 and ErbB2. EphrinB1 co-immunoprecipitates and co-localizes with both ErbB1 and ErbB2. This association of a signaling ligand with known kinase oncoproteins is novel and may significantly increase the complexity of signals mediated both in the context of normal tissue growth and development as well as in cancer. In addition, expression of a constitutively activated erbB2 mutant (mNeuNT) robustly activates EphrinB1 and Erk1/2 signaling. To determine the in vivo significance of EphrinB1 in tumor growth, mouse tonsillar epithelial cells stably expressing HPV16 E6, E7 and Ras (MEERL) or those stably knocked down for PTPBL (murine homolog of PTPN13) and expressing mNeuNT were knocked down for EphrinB1 by shRNA and antibiotic selection (sh-EphrinB1). Stable cells lines over-expressing wildtype EphrinB1 were also generated. Injection of sh-EphrinB1 cells into the hind limb of mice resulted in faster tumor growth and poor survival as compared to controls, while cells over-expressing wildtype EphrinB1 either never grew tumors or grew them very slowly, greatly enhancing survival. These data suggest that the interaction between EphrinB1 and ErbB receptors activate signaling cascades important in tumor growth. PTPN13 modulation of these signals is critical in regulation of tumor growth and survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2114. doi:10.1158/1538-7445.AM2011-2114