Localization of the stem cell markers LGR5 and Nanog in the normal and the cancerous human ovary and their inter-relationship.

LGR5 and Nanog were recently characterized as stem cell markers in various embryonic, adult and cancer stem cells. However, there are no data on their precise localization in the normal adult ovary, which may be important for the initial steps of development of ovarian cancer, the most lethal gynecological cancer. We analyzed by immunocytochemistry the precise localization of these markers in normal ovary (11 specimens, age range 43-76), in borderline specimens (12 specimens), and in serous ovarian cancer (12 specimens of stage II) which comprises the vast majority (80%) of all ovarian cancer. Surprisingly, we revealed that both Nanog and LGR5 are clearly localized in the epithelial cells of the normal ovary. However, in 5 of 12 ovaries there was no labeling at all, while in 3 ovaries staining of Nanog was more prominent with only weak labeling of LGR5. In addition, we found in 3 of 11 ovaries clear labeling in foci of both LGR5 and Nanog antibodies, with partial overlapping. Occasionally, we also found in the stroma foci labeled by either Nanog or LGR5 antibodies. In general, the stroma area of tissue sections labeled with LGR5 was much greater than that labeled with Nanog. In borderline tumors a significant portion of the specimens (7 of 12) was labeled exclusively with Nanog and not with LGR5. In ovarian carcinomas almost 100% of the cells were exclusively labeled only with Nanog (6 of 12 of the specimens) with no labeling of LGR5. These data may suggest the potential of ovaries from postmenopausal women, which express Nanog, to undergo transformation, since Nanog was shown to be oncogenic. We conclude that Nanog, which probably plays an important role in ovarian embryonic development, may be partially silenced in fertile and post-menopausal women, but is re-expressed in ovarian cancer, probably by epigenetic activation of Nanog gene expression. Expression of Nanog and LGR5 in normal ovaries and in borderline tumors may assist in the early detection and improved prognosis of ovarian cancer. Moreover, targeting of Nanog by inhibitory miRNA or other means may assist in treating this disease.

Differential localization of LGR5 and Nanog in clusters of colon cancer stem cells.

One paradigm of cancer development claims that cancer emerges at the niche of tissue stem cells and these cells continue to proliferate in the tumor as cancer stem cells. LGR5, a membrane receptor, was recently found to be a marker of normal colon stem cells in colon polyps and is also expressed in colon cancer stem cells. Nanog, an embryonic stem cell nuclear factor, is expressed in several embryonic tissues, but Nanog expression is not well documented in cancerous stem cells. Our aim was to examine whether both LGR5 and Nanog are expressed in the same clusters of colon stem cells or cancer stem cells, using immunocytochemistry with specific antibodies to each antigen. We analyzed this aspect using paraffin embedded tumor tissue sections obtained from 18 polyps and 36 colon cancer specimens at stages I-IV. Antibodies to LGR5 revealed membrane and cytoplasm immunostaining of scattered labeled cells in normal crypts, with no labeling of Nanog. However, in close proximity to the tumors, staining to LGR5 was much more intensive in the crypts, including that of the epithelial cells. In cancer tissue, positive LGR5 clusters of stem cells were observed mainly in poorly differentiated tumors and in only a few scattered cells in the highly differentiated tumors. In contrast, antibodies to Nanog mainly stained the growing edges of carcinoma cells, leaving the poorly differentiated tumor cells unlabeled, including the clustered stem cells that could be detected even by direct morphological examination. In polyp tissues, scattered labeled cells were immunostained with antibodies to Nanog and to a much lesser extent with antibodies to LGR5. We conclude that expression of LGR5 is probably specific to stem cells of poorly differentiated tumors, whereas Nanog is mainly expressed at the edges of highly differentiated tumors. However, some of the cell layers adjacent to the carcinoma cell layers that still remained undifferentiated, expressed mainly Nanog with only a few cells labeled with antibodies to LGR5. Considering the different sites and pattern of expression in the tumor, our data imply that targeting the clustered stem cells expressing LGR5 in poorly differentiated colon cancer may require different strategies than targeting the stem cells expressing Nanog in the highly differentiated tumors. Alternatively, combined application of specific inhibitory miRNAs to Nanog and to LGR5 expression may assist therapeutically.

Use of multiple biomarkers for the localization and characterization of colon cancer stem cells by indirect immunocytochemistry.

In this study, we used LGR5, γ-synuclein, p53, KRAS and epiregulin antibodies to localize stem cells by indirect immunocytochemistry in paraffin sections of normal and cancerous colon tissues. In the normal colon tissue, no staining of cells with LGR5, γ-synuclein, p53 and KRAS antibodies was observed, apart from a few scattered cells in between the colon villi that were faintly stained with antibodies to LGR5. Staining of highly differentiated cancer tissue with LGR5 antibodies revealed single cells or clusters of up to 4 cells in the interior space of the carcinoma cell layers. Staining of poorly differentiated cancer tissues (stage I-IV) revealed 9-81 clustered stem cells. The number of clustered stem cells increased significantly with the tumor stage, when comparing stage II to stage IV (p<00048). Occasionally, the clustered stem cells appeared in the interphase between the colon stroma and the tumor tissue. Surprisingly, antibodies to p53 clearly stained the clusters of stem cells both in the nuclei and the cytoplasm. The staining of the nuclei of other cells in the undifferentiated tumors was in general weaker, and no staining was found in the cytoplasm. Antibodies to γ-synuclein heavily stained the endothelial cells of the blood vessels and some other scattered cells in the highly differentiated tumors. Antibodies to γ-synuclein heavily stained the stem cells in both the cytoplasm and the nuclei of poorly differentiated tumors. Antibodies to KRAS stained the cytoplasm and the nuclei of stem cells in poorly differentiated tumors and also stained the cytoplasm of some scattered cells. Antibodies to epiregulin stained the cytoplasm of normal colon tissue cells in the crypt-villus axis. The antibodies weakly stained the highly differentiated tumor cells and moderately stained the moderately differentiated tumor cells. Of note, the antibodies intensively stained the clustered stem cells of the poorly differentiated tumor cells. These antibodies also clearly stained the clustered stem cells of poorly differentiated tumors but were not specific as they clearly stained cells in the crypt-villus axis of the normal colon wall. Our results show that LGR5 antibodies can serve as a reliable marker for colon cancer stem cells. Once the colon stem cells are identified, the targeting of specific drugs to kill these cells should be attempted in the future in order to cure this disease. Moreover, the fact that we did not find any stained cells with antibodies to LGR5 in normal tissues apart from a few scattered cells, suggests that the normal colon stem cells differ from the tumor stem cells at least as regards the expression of this protein. In addition, antibodies to γ-synuclein, p53 and KRAS only stained the tumor stem cells and not the normal tissue. Thus, they can serve as multiple biomarkers for the localization of colon cancer stem cells by indirect immunofluorescence.