miRNA-128 suppresses prostate cancer by inhibiting BMI-1 to inhibit tumor-initiating cells.

microRNA-128 (miR128) is reduced in prostate cancer relative to normal/benign prostate tissues, but causal roles are obscure. Here we show that exogenously introduced miR128 suppresses tumor regeneration in multiple prostate cancer xenograft models. Cancer stem-like cell (CSC)-associated properties were blocked, including holoclone and sphere formation as well as clonogenic survival. Using a miR128 sensor to distinguish cells on the basis of miR128 expression, we found that miR128-lo cells possessed higher clonal, clonogenic, and tumorigenic activities than miR128-hi cells. miR128 targets the stem cell regulatory factors BMI-1, NANOG, and TGFBR1, the expression of which we found to vary inversely with miR128 expression in prostate cancer stem/progenitor cell populations. In particular, we defined BMI-1 as a direct and functionally relevant target of miR128 in prostate cancer cells, where these genes were reciprocally expressed and exhibited opposing biological functions. Our results define a tumor suppressor function for miR128 in prostate cancer by limiting CSC properties mediated by BMI-1 and other central stem cell regulators, with potential implications for prostate cancer gene therapy.

In vivo functional studies of tumor-specific retrogene NanogP8 in transgenic animals.

The current study was undertaken to investigate potential oncogenic functions of NanogP8, a tumor-specific retrogene homolog of Nanog (expressed in pluripotent cells), in transgenic animal models. To this end, human primary prostate tumor-derived NanogP8 was targeted to the cytokeratin 14 (K14) cellular compartment, and two lines of K14-NanogP8 mice were derived. The line 1 animals, expressing high levels of NanogP8, experienced perinatal lethality and developmental abnormalities in multiple organs, including the skin, tongue, eye, and thymus in surviving animals. On postnatal day 5 transgenic skin, for example, there was increased c-Myc expression and Ki-67(+) cells accompanied by profound abnormalities in skin development such as thickened interfollicular epidermis and dermis and lack of hypodermis and sebaceous glands. The line 3 mice, expressing low levels of NanogP8, were grossly normal except cataract development by 4-6 mo of age. Surprisingly, both lines of mice do not develop spontaneous tumors related to transgene expression. Even more unexpectedly, high levels of NanogP8 expression in L1 mice actually inhibited tumor development in a two-stage chemical carcinogenesis model. Mechanistic studies revealed that constitutive NanogP8 overexpression in adult L1 mice reduced CD34(+)α6(+) and Lrig-1(+) bulge stem cells, impaired keratinocyte migration, and repressed the expression of many stem cell-associated genes, including Bmp5, Fgfr2, Jmjd1a, and Jun. Our study, for the first time, indicates that transgenically expressed human NanogP8 is biologically functional, but suggests that high levels of NanogP8 may disrupt normal developmental programs and inhibit tumor development by depleting stem cells.