Aggrus (T1α/podoplanin, known as a specific marker for type I alveolar cells or lymphatic endothelial cells) is a transmembrane sialoglycoprotein that aggregates platelets. Previously, we showed that upregulated expression of Aggrus occurs in colorectal tumors or testicular tumors and could be associated with platelet-aggregating activity and metastatic ability. In testicular tumors, Aggrus is specifically expressed in seminoma. The present study investigates Aggrus expression in human primary lung cancer tissues of different types. Microarray analysis demonstrated that aggrus was significantly expressed in squamous cell carcinoma (10/15; 66.7%). Immunohistochemical analysis also showed that the incidence of positive staining in sections of squamous cell carcinoma (7/8; 87.5%) was higher than that in adenocarcinoma (2/13; 15.4%). Furthermore, Aggrus expression was detected in a squamous cell carcinoma cell line, NCI-H226, by real-time PCR. These findings indicated that overexpression of Aggrus occurred in squamous cell carcinoma of the lung. Therefore, Aggrus could be a useful diagnostic marker for squamous cell carcinoma of the lung.

A human cDNA encoding an 841-aa guanine nucleotide-exchange protein (GEP) for ADP-ribosylation factors (ARFs), named ARF-GEP 100, which contains a Sec7 domain, a pleckstrin homology (PH)-like domain, and an incomplete IQ-motif, was identified. On Northern blot analysis of human tissues, a Ϸ8-kb mRNA that hybridized with an ARF-GEP 100 cDNA was abundant in peripheral blood leukocytes, brain, and spleen. ARF-GEP100 accelerated [ 35 S]GTP␥S binding to ARF1 (class I) and ARF5 (class II) 2-to 3-fold, and to ARF6 (class III) ca. 12-fold. The ARF-GEP 100 Sec7 domain contains Asp 543 and Met 555 , corresponding to residues associated with sensitivity to the inhibitory effect of the fungal metabolite brefeldin A (BFA) in yeast Sec7, but also Phe 535 and Ala 536 , associated with BFA-insensitivity. The PH-like domain differs greatly from those of other ARF GEPs in regions involved in phospholipid binding. Consistent with its structure, ARF-GEP 100 activity was not affected by BFA or phospholipids. After subcellular fractionation of cultured T98G human glioblastoma cells, ARF6 was almost entirely in the crude membrane fraction, whereas ARF-GEP 100, a 100-kDa protein detected with antipeptide antibodies, was cytosolic. On immunofluorescence microscopy, both proteins had a punctate pattern of distribution throughout the cells, with apparent colocalization only in peripheral areas. The coarse punctate distribution of EEA-1 in regions nearer the nucleus appeared to coincide with that of ARF-GEP 100 in those areas. No similar coincidence of ARF-GEP100 with AP-1, AP-2, catenin, LAMP-1, or 58K was observed. The new human BFA-insensitive GEP may function with ARF6 in specific endocytic processes.

The Saccharomyces cerevisiae Sec7 protein (ySec7p), which is an important component of the yeast secretory pathway, contains a sequence of Ϸ200 amino acids referred to as a Sec7 domain. Similar Sec7 domain sequences have been recognized in several guanine nucleotide-exchange proteins (GEPs) for ADP ribosylation factors (ARFs). ARFs are Ϸ20-kDa