LncRNA IPW inhibits growth of ductal carcinoma in situ by downregulating ID2 through miR-29c.

BACKGROUND: Ductal carcinoma in situ (DCIS) of breast is the noninvasive lesion that has propensity to progress to the malignant form. At present, it is still unknown which lesions can potentially progress to invasive forms. In this study, we aimed to identify key lncRNAs involved in DCIS growth. METHODS: We employ disease-related lncProfiler array to identify IPW in specimens of DCIS and matching control samples and validate the observations in three DCIS-non-tumorigenic cell lines. Further, we examine the mechanism of IPW action and the downstream signaling in in vitro and in vivo assays. Importantly, we screened a library containing 390 natural compounds to identify candidate compound selectively inhibiting IPW low DCIS cells. RESULTS: We identified lncRNA IPW as a novel tumor suppressor critical for inhibiting DCIS growth. Ectopic expression of IPW in DCIS cells strongly inhibited cell proliferation, colony formation and cell cycle progression while silencing IPW in primary breast cells promoted their growth. Additionally, orthotropic implantation of cells with ectopic expression of IPW exhibited decreased tumor growth in vivo. Mechanistically, IPW epigenetically enhanced miR-29c expression by promoting H3K4me3 enrichment in its promoter region. Furthermore, we identified that miR-29c negatively regulated a stemness promoting gene, ID2, and diminished self-renewal ability of DCIS cells. Importantly, we screened a library containing 390 natural compounds and identified toyocamycin as a compound that selectively inhibited the growth of DCIS with low expression of IPW, while it did not affect DCIS with high IPW expression. Toyocamycin also suppressed genes associated with self-renewal ability and inhibited DCIS growth in vivo. CONCLUSION: Our findings revealed a critical role of the IPW-miR-29c-ID2 axis in DCIS formation and suggested potential clinical use of toyocamycin for the treatment of DCIS.

A Fusion Transcription Factor-Driven Cancer Progresses to a Fusion-Independent Relapse via Constitutive Activation of a Downstream Transcriptional Target.

Targeted monotherapies usually fail due to development of resistance by a subgroup of cells that evolve into recurrent tumors. Alveolar rhabdomyosarcoma is an aggressive myogenic soft-tissue cancer that is associated with a characteristic PAX3-FOXO1 gene fusion encoding a novel fusion transcription factor. In our myoblast model of PAX3-FOXO1-induced rhabdomyosarcoma, deinduction of PAX3-FOXO1 simulates a targeted therapy that antagonizes the fusion oncoprotein. This simulated therapy results initially in regression of the primary tumors, but PAX3-FOXO1-independent recurrent tumors eventually form after a delay. We report here that upregulation of FGF8, a direct transcriptional target of PAX3-FOXO1, is a mechanism responsible for PAX3-FOXO1-independent tumor recurrence. As a transcriptional target of PAX3-FOXO1, FGF8 promoted oncogenic activity in PAX3-FOXO1-expressing primary tumors that developed in the myoblast system. In the recurrent tumors forming after PAX3-FOXO1 deinduction, FGF8 expression was necessary and sufficient to induce PAX3-FOXO1-independent tumor growth through an autocrine mechanism. FGF8 was also expressed in human PAX3-FOXO1-expressing rhabdomyosarcoma cell lines and contributed to proliferation and transformation. In a human rhabdomyosarcoma cell line with reduced PAX3-FOXO1 expression, FGF8 upregulation rescued oncogenicity and simulated recurrence after PAX3-FOXO1-targeted therapy. We propose that deregulated expression of a PAX3-FOXO1 transcriptional target can generate resistance to therapy directed against this oncogenic transcription factor and postulate that this resistance mechanism may ultimately be countered by therapeutic approaches that antagonize the corresponding downstream pathways. SIGNIFICANCE: In a model of cancer initiated by a fusion transcription factor, constitutive activation of a downstream transcriptional target leads to fusion oncoprotein-independent recurrences, thereby highlighting a novel progression mechanism and therapeutic target.

Role of myoepithelial cells in breast tumor progression.

Myoepithelial cells form a semi-continuous protective sheet separating the human breast epithelium and the surrounding stroma. They suppress stromal invasion of tumor cells by the secretion of various anti-angiogenic and anti-invasive factors. The disruption of this cell layer results in the release of the growth factors, angiogenic factors, and reactive oxygen species causing an alteration in the microenvironment. This helps in the proliferation of surrounding cells and increases the invasiveness of tumor cells. Two theories are proposed for the mechanism of tumor epithelial cells progression from in situ to invasive stage. According to the first theory, tumor cell invasion is triggered by the overproduction of proteolytic enzymes by myoepithelial cells and surrounding tumor cells. The second theory states that tumor invasion is a multistep process, the interactions between damaged myoepithelial cells and the immunoreactive cells trigger the release of basement membrane degrading enzymes causing tumor progression. Further studies in understanding of molecular mechanism of myoepithelial cell functions in tumor suppression may lead to the identification of novel therapeutic targets for breast cancer.