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A bipartite signal regulates the faithful delivery of apical domain marker podocalyxin/Gp135.

ABSTRACT: Podocalyxin/Gp135 was recently demonstrated to participate in the formation of a preapical complex to set up initial polarity in MDCK cells, a function presumably depending on the apical targeting of Gp135. We show that correct apical sorting of Gp135 depends on a bipartite signal composed of an extracellular O-glycosylation-rich region and the intracellular PDZ domain-binding motif. The function of this PDZ-binding motif could be substituted with a fusion construct of Gp135 with Ezrin-binding phosphoprotein 50 (EBP50). In accordance with this observation, EBP50 binds to newly synthesized Gp135 at the Golgi apparatus and facilitates oligomerization and sorting of Gp135 into a clustering complex. A defective connection between Gp135 and EBP50 or EBP50 knockdown results in a delayed exit from the detergent-resistant microdomain, failure of oligomerization, and basolateral missorting of Gp135. Furthermore, the basolaterally missorted EBP50-binding defective mutant of Gp135 was rapidly retrieved via a PKC-dependent mechanism. According to these findings, we propose a model by which a highly negative charged transmembrane protein could be packed into an apical sorting platform with the aid of its cytoplasmic partner EBP50.

SUBMITTER: Yu CY

PROVIDER: S-EPMC1855014 | biostudies-literature | 2007 May

REPOSITORIES: biostudies-literature

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A bipartite signal regulates the faithful delivery of apical domain marker podocalyxin/Gp135.

Yu Chun-Ying CY Chen Jen-Yau JY Lin Yu-Yu YY Shen Kuo-Fang KF Lin Wei-Ling WL Chien Chung-Liang CL ter Beest Martin B A MB Jou Tzuu-Shuh TS

Molecular biology of the cell 20070301 5

Podocalyxin/Gp135 was recently demonstrated to participate in the formation of a preapical complex to set up initial polarity in MDCK cells, a function presumably depending on the apical targeting of Gp135. We show that correct apical sorting of Gp135 depends on a bipartite signal composed of an extracellular O-glycosylation-rich region and the intracellular PDZ domain-binding motif. The function of this PDZ-binding motif could be substituted with a fusion construct of Gp135 with Ezrin-binding p ...[more]

PMID: 17332505

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Project description:BACKGROUND: Over two decades ago, a proposal was that two different colorectal cancer (CRC) entities existed, based on tumour location either proximal (right) or distal (left) of the splenic flexure. Proximal and distal tumours exhibit different clinical, epidemiological, and biological characteristics. Improvement of the prognostic evaluation of CRC requires new molecular markers. Podocalyxin-like 1 (PODXL), an anti-adhesive transmembrane sialomucin, is associated with an aggressive tumour phenotype and poor prognosis. For colorectal cancer, it has been suggested to be a marker of poor prognosis. The aim of this study was to investigate the role of PODXL in CRC by use of a novel monoclonal antibody. METHODS: In 1983-2001, 840 consecutive colorectal cancer patients were treated at Helsinki University Central Hospital, of whom 767 were successfully scored for PODXL immunohistochemical expression from tumour tissue microarrays by use of a novel monoclonal in-house antibody. Associations of PODXL expression and tumour location with other clinicopathological variables were explored by Fisher's exact-test, linear-by- linear association test, and binary logistic regression. Survival analyses were done by the Kaplan-Meier method and Cox proportional hazards model. RESULTS: PODXL protein expression was high in 44 (5.7%) specimens. High expression associated strongly with poor differentiation (p < 0.0001), advanced stage (p = 0.011), and location of the tumour in the right hemicolon (RHC) (p < 0.001). Tumours of the RHC were more poorly differentiated (p < 0.0001) and showed higher PODXL expression (p < 0.001).High PODXL expression associated significantly with higher risk for disease-specific death from CRC (hazard ratio (HR) = 2.00; 95% confidence interval (CI) 1.31-3.06, p = 0.001) and also in the subgroups of left hemicolon (LHC) cancers (HR = 2.60; 95% CI 1.45-4.66, p = 0.001) and rectal cancers (HR = 3.03; 95% CI 1.54-5.60, p = 0.001). Results remained significant in multivariable analysis (respectively, HR = 1.82; 95% CI 1.15-2.86, p = 0.01; HR = 2.59; 95% CI 1.41-4.88, p = 0.002; and HR = 2.69; 95% CI 1.30-5.54, p = 0.007). CONCLUSION: Podocalyxin was an independent factor for poor prognosis in colorectal cancer and in the subgroups of left hemicolon and rectum. This is, to our knowledge, the first evidence of such difference in PODXL expression, its function possibly being dependent upon tumour location.

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A bipartite signal regulates the faithful delivery of apical domain marker podocalyxin/Gp135.

Publications

A bipartite signal regulates the faithful delivery of apical domain marker podocalyxin/Gp135.

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