The presynaptic cytomatrix protein Piccolo, encoded by PCLO, is frequently mutated and amplified in esophageal squamous cell carcinoma (ESCC), but its exact roles in ESCC remain unclear. Here we report that Piccolo expression correlates significantly with clinical stage, patient survival and tumor embolus. Functional studies demonstrate that PCLO knockdown remarkably attenuates ESCC malignancy in vitro and in vivo, and ectopic EGFR expression partially compensates for Piccolo loss. PCLO knockdown promotes ubiquitination and degradation of EGFR, which is associated with the negative regulatory effect of Piccolo on E3 ligase Siah1. An anti-Piccolo monoclonal antibody inhibited tumor proliferation in a mouse model of ESCC. These results demonstrate that Piccolo contributes to tumor aggressiveness in ESCC, likely by stabilizing EGFR and promoting EGFR-dependent signaling. Our results further suggest that Piccolo may represent a novel prognostic biomarker and therapeutic target for patients with ESCC.
Soluble Flk-1, a soluble vascular endothelial growth factor (VEGF) receptor, is a potent inhibitor of angiogenesis, which could restrain growth and metastasis of some experimental tumors. However, antiangiogenic agents alone cannot eradicate tumor completely, and should be combined with other therapy to enhance their effects. In this study, we evaluated the antitumor activity of the combination therapy in the immunocompetent BALB/c mice bearing H22 hepatoma and Meth A fibrosarcoma, respectively. Mice were treated with either msFlk-1 i.m. at 100 mg/mouse once every 3 days for four times from day 3 after the tumor cell injection, cisplatin cycled twice (2 mg/kg i.p. on days 4 and 11 after the tumor cell inoculation), or both agents together. Tumor growth and survival time were continually observed. Antiangiogenesis in vivo was determined by CD31 immunohistochemistry. Assessment of apoptotic cells and histological analysis was also conducted in tumor tissues. Our results showed that the combination therapy could evidently improve antitumor efficacy, including tumor growth suppression, mice survival prolongation, tumor cell apoptosis augmentation as well as neovascularization inhibition as compared with controls, without serious adverse effects. Our data suggest that the combination of DDP with msFlk-1 is more effective to suppress tumor growth in mice than either agent alone, and this combination regimen showed its potential for future clinical application.
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