Vaccinia H1-related Phosphatase Is a Phosphatase of ErbB Receptors and Is Down-regulated in Non-small Cell Lung Cancer

Abstract

Vaccinia H1-related phosphatase (VHR) is classified as a dual specificity phosphatase. Unlike typical dual specificity phosphatases, VHR lacks the MAPK-binding domain and shows poor activity against MAPKs. We found that EGF receptor (EGFR) was a direct substrate of VHR and that overexpression of VHR down-regulated EGFR phosphorylation, particularly at Tyr-992 residue. Expression of VHR inhibited the activation of phospholipase C␥ and protein kinase C, both downstream effectors of Tyr-992 phosphorylation of EGFR. Decreasing VHR expression by RNA interference caused higher EGFR phosphorylation at Tyr-992. In addition to EGFR, VHR also directly dephosphorylated ErbB2. Consistent with these results, suppression of VHR augmented the foci formation ability of H1299 non-small cell lung cancer (NSCLC) cells, whereas overexpression of VHR suppressed cell growth in both two-and three-dimensional cultures. Expression of VHR also suppressed tumor formation in a mouse xenograft model. Furthermore, VHR expression was significantly lower in NSCLC tissues in comparison to that in normal lung tissues. Collectively, this study shows that down-regulation of VHR expression enhances the signaling of ErbB receptors and may be involved in NSCLC pathogenesis.Among protein modifications, tyrosine phosphorylation is extensively used only in multicellular, eukaryotic organisms. Protein-tyrosine phosphorylation plays an important role in signaling transduction pathways that are involved in embryogenesis, development, and homeostasis. Disorders in proteintyrosine phosphorylation are found in many human diseases from cancer to immune disorders. Although protein phosphorylation is a balanced action of protein kinases and phosphatases, the experimental data of protein phosphatases is proportionally much less than that of protein kinases. Dual specificity phosphatases (DUSPs) 3 are structurally related to protein-tyrosine phosphatases (PTP) and are initially implicated in the down-regulation of MAPKs (1). Distinct from PTPs, which have a deep catalytic cleft; DUSPs have shallow catalytic sites, which permit the less stringent phospho-amino acid specificity of DUSPs (2-4). Several DUSPs including MAPK phosphatases (MKP)-1 to -7, M3/6 (also called VH5), and VHR have been shown to inactivate one or several MAPKs (5-12). The expression of certain DUSPs is increased by mitogenic signaling (5, 13-15). Both ERK and JNK pathways induce the expression of MKPs (15-17). The induction of MKP expression by MAPK signaling may, in turn, lead to the down-regulation of MAPK activities. Recently, many newly identified DUSPs were found to have little or no phosphatase activity against MAPKs, indicating that MAPK inactivation is not the sole function of DUSPs (18 -21). These novel DUSPs are smaller in size compared with MKPs and lack the MAPK-binding domain. These groups of DUSPs have been classified as atypical DUSPs (1). Others' and our recent studies reveal that atypical DUSPs may play a critical role in the regulation of signaling triggered by protein tyrosine...

KDM2A promotes lung tumorigenesis by epigenetically enhancing ERK1/2 signaling

“…We also demonstrated that low DUSP3 levels had a significant correlation with high KDM2A levels and often occurred in NSCLC tumors. In line with our results, it has been shown that DUSP3 is downregulated in NSCLC and that DUSP3 overexpression leads to decreased cell proliferation and reduced tumor growth in a xenograft mouse model (24). Together with this Stably KDM2A-depleted (shKDM2A#1 and shKDM2A#2) cells and control cells (shControl) were subcutaneously implanted into mice.…”

“…DUSP3 has been shown to suppress the activities of ERK1/2 and JNK1/2 in HeLa cells and the activity of EGFR in the lung cancer cell line H1299 by dephosphorylating these kinases (22)(23)(24)(25). ERK1/2 and JNK1/2 are a family of MAPKs that play a critical role in mediating cellular signaling events, including cell proliferation and invasion (26)(27)(28)(29).…”

Emerging Roles of Atypical Dual Specificity Phosphatases in Cancer

“…Increased ErbB tyrosine kinase activity drives several cancer-relevant properties including proliferation, cell motility, and invasion [36]. dusp3 over-expression removed the activating phosphate from Y992 of ErbB, preventing ErbB kinase activity [33]. As the ErbB family of proto-oncogenes is strongly associated with cancers in a kinase dependent manner [37], the ability of DUSP3 to inhibit its activity may have important implications for cancer therapies.…”

“…Nevertheless, as a functional MAPK phosphatase, it is not surprising that DUSP3 is implicated in cancer, where it has been alternatively described as having both oncogenic [30][31][32] and tumor suppressive [33,34] properties.…”

Specificity Profiling of Dual Specificity Phosphatase Vaccinia VH1-related (VHR) Reveals Two Distinct Substrate Binding Modes*

“…This raises the question whether dephosphorylation of the MAPKs by VHR in vivo is aided by any recruiting strategy. Other than the MAPKs, signal transducers and activators of transcription 5 (STAT5) with a single Tyr(P) site, epidermal growth factor receptor, and ErbB2 have also been reported as VHR substrates (18,19). Two recent studies showed that phosphorylation of VHR at Tyr 138 is required for its efficient dephosphorylation of MAPKs and STAT5 in vivo (18,20).…”