Impaired PTPN13 phosphatase activity in spontaneous or HPV-induced squamous cell carcinomas potentiates oncogene signaling via the MAP kinase pathway

Department of Otolaryngology-Head and Neck Surgery, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
Oncogene (Impact Factor: 8.46). 10/2009; 28(45):3960-70. DOI: 10.1038/onc.2009.251
Source: PubMed


Human papillomaviruses (HPVs) are a causative factor in over 90% of cervical and 25% of head and neck squamous cell carcinomas (HNSCCs). The C terminus of the high-risk HPV 16 E6 oncoprotein physically associates with and degrades a non-receptor protein tyrosine phosphatase (PTPN13), and PTPN13 loss synergizes with H-Ras(V12) or ErbB2 for invasive growth in vivo. Oral keratinocytes that have lost PTPN13 and express H-Ras(V12) or ErbB2 show enhanced Ras/RAF/MEK/Erk signaling. In co-transfection studies, wild-type PTPN13 inhibited Ras/RAF/MEK/Erk signaling in HEK 293 cells that overexpress ErbB2, EGFR or H-Ras(V12), whereas an enzymatically inactive PTPN13 did not. Twenty percent of HPV-negative HNSCCs had PTPN13 phosphatase mutations that did not inhibit Ras/RAF/MEK/Erk signaling. Inhibition of Ras/RAF/MEK/Erk signaling using MEK inhibitor U0126 blocked anchorage-independent growth in cells lacking PTPN13. These findings show that PTPN13 phosphatase activity has a physiologically significant role in regulating MAP kinase signaling.

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Available from: Aloysius J Klingelhutz
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    • "Mouse oropharyngeal epithelial cells (MOEs) were previously internally derived from C57Bl/6 mouse oropharyngeal epithelium retrovirally transduced with the indicated vectors and oncogenes [7]. MOEs are routinely internally screened for the presence of cytokeratin and HPV-16 mRNA as means of authentication, and our model HPV+ HNSCC line harboring the E6, E7, and mutated H-Ras V12 oncogenes (E6/E7/Ras MOEs) [32] is routinely grafted into syngeneic mice for animal studies. Human squamous cell carcinoma cell ( "
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    ABSTRACT: Human papillomavirus (HPV)-related head and neck squamous cell carcinoma (HNSCC) incidence is increasing at a near epidemic rate. We investigated whether the mammalian (or mechanistic) target of rapamycin (mTOR) inhibitor, rapamycin, can be used as a concurrent agent to standard-of-care cisplatin/radiation therapy (CRT) to attenuate tumor lactate production, thus enhancing CRT-induced immune-mediated clearance of this antigenic tumor type. A C57Bl/6-derived mouse oropharyngeal epithelial cell line retrovirally transduced with HPV type 16 E6/E7 and human squamous cell carcinoma cell lines were evaluated for their response to rapamycin in vitro with proliferation assays, Western blots, and lactate assays. Clonogenic assays and a preclinical mouse model were used to assess rapamycin as a concurrent agent to CRT. The potential of rapamycin to enhance immune response through lactate attenuation was assessed using quantitative tumor lactate bioluminescence and assessment of cell-mediated immunity using E6/E7-vaccinated mouse splenocytes. Rapamycin alone inhibited mTOR signaling of all cancer cell lines tested in vitro and in vivo. Furthermore, rapamycin administered alone significantly prolonged survival in vivo but did not result in any long-term cures. Given concurrently, CRT/rapamycin significantly enhanced direct cell killing in clonogenic assays and prolonged survival in immunocompromised mice. However, in immunocompetent mice, concurrent CRT/rapamycin increased long-term cures by 21%. Preliminary findings suggest that improved survival involves increased cell killing and enhanced immune-mediated clearance in part due to decreased lactate production. The results may provide rationale for the clinical evaluation of mTOR inhibitors concurrent with standard-of-care CRT for treatment of HPV-positive HNSCC.
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    • "mNeuNT and PTPN13C/S have been previously described [23]. Full length wildtype human EphrinB1 cDNA was obtained from Open Biosystems (IHC1380), sequence verified, cloned by PCR into the p3XFLAG CMV vector (Sigma-Aldrich, St. Louis, MO) by using the KpnI/XbaI sites. "
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    Full-text · Article · Jun 2012 · PLoS ONE
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    • "These phosphatases are also commonly mutated or downregulated in cancer and E6-mediated degradation of the phosphatases appears to be necessary for tumorigenic transformation by E6 (Spanos et al., 2008b). A recent study indicated that downregulation of PTPN13 by E6 is associated with activation of MAP kinase signaling (Hoover et al., 2009). While the PDZ binding motif is conserved among high-risk virus types, the motif is generally not found in low-risk HPV E6's. "
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