5420

PODXL

podocalyxin-like;PODXL;podocalyxin-like

GCTM-2 antigen|podocalyxin|podocalyxin-like protein 1

7q32-q33

protein-coding

AIMS: Previous studies have shown that membranous expression of podocalyxin-like protein (PODXL) is associated with poor prognosis in colorectal cancer (CRC). In this study, we compared PODXL expression in primary CRC and synchronous lymph node metastases. We further analyzed whether its expression changed in rectal tumours after neoadjuvant radiation therapy. METHODS AND RESULTS: The studied cohort consists of 73 consecutive patients from the South-Swedish Colorectal cancer Biobank. Immunohistochemical PODXL expression was examined on full-face sections from all primary tumours and all 140 available lymph node metastases from 31 cases. Membranous PODXL expression was denoted in 18/73 (24,7%) primary tumours, with a high concordance between primary and metastatic lesions. While all negative primary tumours had negative metastases, some PODXL positive primaries had a varying proportion of positive and negative metastatic lymph nodes. PODXL expression was also found to be mainly unaltered in pre- and post-irradiation surgically resected tumour specimens in rectal cancer patients (n=16). CONCLUSIONS: The findings in this study suggest that analysis of PODXL expression in the primary tumour is sufficient for its use as a prognostic and treatment predictive biomarker in CRC, also in patients with metastatic disease. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/9014177329634352.

High grade serous ovarian tumors often metastasize transperitoneally, a process that begins when small tumor nodules de-adhere and are released into the fluid of the abdominal cavity where they float freely to reach new sites on the peritoneal wall. Podocalyxin, a small anti-adhesive sialomucin, has been shown to contribute to non-adhesive membrane domain formation in some epithelia and is overexpressed in a variety of cancers. We therefore assessed podocalyxin expression on a previously characterized tissue microarray and found that 87% (169/194) of high grade serous epithelial ovarian carcinomas were positive for podocalyxin. In addition, cell surface localization of podocalyxin was associated with a significant decrease in disease-free survival in these tumors. When podocalyxin was force-expressed in serous ovarian carcinoma-derived OVCAR-3 cells it was targeted to the cell surface and it decreased the adhesion of these cells to mesothelial monolayers, fibronectin and immobilized beta1 integrin-binding antibodies. This decrease in adhesion was associated with a modest decrease in cell surface beta1 integrin. In monolayer culture, podocalyxin was targeted to the free, apical domains of OVCAR-3 cells and it appeared to decrease beta1 integrin levels on the attached basolateral domains of the same cells. Furthermore, in 3-dimensional basement membrane gel culture, the cells formed small, cohesive nodules and podocalyxin localized to membrane domains at the cell-basement membrane interface. Therefore, podocalyxin's ability to facilitate the formation of non-adhesive membrane domains may contribute to the formation of free-floating high grade serous tumor nodules during the initial steps of transperitoneal metastasis.

Selectin-mediated interactions in the vasculature promote metastatic spread by facilitating circulating tumor cell binding to selectin-expressing host cells. Therefore, identifying the selectin ligand(s) on tumor cells is critical to the prevention of blood-borne metastasis. A current challenge is to distinguish between structures expressed by circulating tumor cells that can bind selectins in vitro from the functional ligands whose depletion suppresses selectin-dependent binding under flow in vivo. Interestingly, podocalyxin (PODXL), which can bind E- and L-selectin, is upregulated in a number of cancers, including those of the breast, colon, and pancreas. In this work, we show that metastatic pancreatic cancer cells overexpress PODXL compared with nonmalignant pancreatic epithelial cells. We further demonstrate via tissue microarray that 69% of pancreatic ductal adenocarcinomas stain positive for PODXL. In cases of focal expression, positive staining is restricted to the invasive front of primary tumors. By combining immunoblot, immunodepletion, short-hairpin RNA-mediated gene silencing, and flow-based adhesion assays, we evaluated the functional role of sialofucosylated PODXL in selectin-mediated adhesion under flow. Our data indicate that sialofucosylated PODXL is a functional E- and L-selectin ligand expressed by metastatic pancreatic cancer cells, as specific depletion of this molecule from the cell surface significantly interferes with selectin-dependent interactions. Cumulatively, these data support a correlation between sialofucosylated PODXL expression and enhanced binding to selectins by metastatic pancreatic cancer cells and offer additional perspective on the upregulation of PODXL in aggressive cancers.