We found a significant difference in tumorigenicity between CD49fhigh and CD49flow cells. CD49fhigh cells very frequently formed tumors with histological features of parental ones while CD49flow cells Crizotinib NSCLC were not tumorigenic (HGC-1 to -5, Table 1). Moreover, cell surface antigen profiles were maintained in tumors formed by injection of CD49fhigh cells (Figure S2), indicating that CD49fhigh cells retained self-renewal and differentiation potencies. We found that the cell surface antigen profiles of PDTX cells (HGC-1 to -5) were altered when passage number exceeded 12 (data not shown), possibly because highly tumorigenic subpopulations were selected during in vivo passages, as has been reported in pancreatic cancer [28]. We thus examined whether CD49fhigh cells were more tumorigenic than CD49flow cells using newly-dissected gastric tumors (HGC-6 to -15, Table 1).

We found that CD49fhigh cells always formed tumors with histological features of parental ones, while CD49flow cells were not tumorigenic, independent of the tumor type (Table 1 and Figure 1: Figure 1A for a moderately-differentiated adenocarcinoma from patient #8 and Figure 1B for a poorly-differentiated one from patient #9). There was a significant difference between CD49fhigh and CD49flow cells on their tumorigenicity (Table 1). We thus concluded that CD49f is a useful marker for gastric TICs. Figure 1 CD49fhigh cells form tumors while CD49flow cells do not.

CD49f is Localized at the Epithelial-stromal Interface in the Normal Gastric Mucosa, but is Found on Apical, Lateral and Basal Surfaces in Some Tumor Cells We immunohistochemically examined the localization of CD49f in the tumor and non-tumor tissues in the stomach, and found CD49f at the epithelial-stromal interface in the normal gastric mucosa (Figure 2A). The result is consistent with the report that CD49f functions as a subunit of receptors for laminins, major proteins in the basal lamina. Gastric mucosae with chronic gastritis showed expression of CD49f along the basal lamina of the gastric foveolae as in normal ones (Figure 2B), and similar expression pattern was found in the intestinal metaplasia (Figure 2C). In tumor cells, however, expression of CD49f was diversified. It was found at the epithelial-stromal interface in some tumor cells (Figure 2G), but it was detected on apical, lateral and basal surfaces in some cells, and some cells only weakly expressed it (Figure 2E).

It is interesting that in gastric dysplasias adjacent to carcinoma, Drug_discovery CD49f was found on not only basal but also lateral surfaces, as in gastric carcinomas (Figure 2D), indicating that disorganized expression of CD49f might not be a result but a cause of tumorigenesis. A small proportion of tumor cells expressing CD49f all along the cell membrane (Figure 2E) may possibly represent gastric TICs. Figure 2 Localization of CD49f in gastric tissues.