Identification of PTPN23 as a novel regulator of cell invasion in mammary epithelial cells from a loss-of-function screen of the ‘PTP-ome'

Abstract

We used an RNAi-mediated loss-of-function screen to study systematically the role of the protein tyrosine phosphatase (PTP) superfamily of enzymes in mammary epithelial cell motility in the absence or presence of the oncoprotein tyrosine kinase ERBB2. We report that although shRNAs directed against most of the PTP family were without effect, suppression of three PTPs-PRPN23, PTPRG, and PTPRR-enhanced cell motility. Furthermore, we found that suppression of PTPN23, but not PTPRG or PTPRR, induced cell invasion. Suppression of PTPN23 increased E-cadherin internalization, impaired early endosome trafficking of E-cadherin, induced the expression of mesenchymal proteins, and caused cell scattering. The activity of SRC and b-catenin was elevated when PTPN23 was suppressed. Moreover, we identified SRC, E-cadherin, and b-catenin as direct substrates of PTPN23. Inhibition of SRC with the small molecular inhibitor SU6656 blocked the effects of PTPN23 depletion. These findings suggest that loss of PTPN23 may increase the activity of SRC and the phosphorylation status of the E-cadherin/b-catenin signaling complex to promote tumor growth and invasive behavior in breast cancer. In addition, our studies highlight functional specificity among PTPs and reveal new roles for PTPs in mammary epithelial cell biology.

Cullin5 destabilizes Cas to inhibit Src-dependent cell transformation

“…This suggests that Src activation could be sufficient for transformation. Indeed, highly active mutant Src causes similar changes in acinar morphogenesis (Reginato et al, 2005) and Src is a direct substrate for PTPN23, a pY phosphatase that inhibits Src and inhibits invasion by MCF10A cells (Lin et al, 2011). However, the increased migration and dysmorphic colonies of Cul5-deficient cells cannot be explained simply by the modest increase in Src activity.…”

The regulation of cell-cell adhesion during epithelial-mesenchymal transition, motility and tumor progression

“…Rather than acting as pleiotropic suppressors of tyrosine kinases, PTPs recently have been described to act as specific regulators of signaling pathways. 83 In mammary epithelial cells, loss of the PTPs PTPRG, PTPRR and PTPN23 was associated with enhanced cell motility. However only PTPN23 was been shown to directly induce E-cadherin internalization and was associated with increased invasion.…”

“…The suppression of PTPN23 is also associated with caveolin-1 mediated internalization and blocking of early endosome vesicle trafficking. 83 Caveolin-1 plays an important role in EGFR signaling 84,85 as downregulation of caveolin-1 in response to EGF results in the expression of SNAI1, EMT and loss of E-cadherin. 86 In cancer cells, EGF can induce caveolin-1-mediated degradation of Ecadherin and tumor cell dissociation.…”

A Novel Phosphatidic Acid-Protein-tyrosine Phosphatase D2 Axis Is Essential for ERBB2 Signaling in Mammary Epithelial Cells

“…For stable suppression of PTPD2, we expressed pMLP retroviral vector using the targeting sequences GACGGTGTGGCATTTACAA (shRNA#1) and GCCACAAGATATCAGTATT (shRNA#2) as described in Ref. 10 and selected stable cell lines using puromycin (2 g/ml).…”

“…There are several studies that implicate specific PTPs as negative regulators of signaling pathways initiated by ERBB2. For example, loss-of-function analyses of PTPs in mammary epithelial cells have revealed a negative role for PTPRR, PTPRG, PTPN23 (10), and RPTP␣ (11) in ERBB2-dependent cell migration. In contrast, some PTPs have also been shown to act as positive regulators of ERBB2-driven carcinogenesis.…”