Paul Cao

Yin Yang 1: a multifaceted protein beyond a transcription factor.

As a transcription factor, Yin Yang 1 (YY1) regulates the transcription of a dazzling list of genes and the number of its targets still mounts. Recent studies revealed that YY1 possesses functions independent of its DNA binding activity and its regulatory role in tumorigenesis has started to emerge.

Yin Yang 1 regulates the transcriptional activity of androgen receptor

The multifunctional protein Yin Yang 1 (YY1) has an important role in epigenetic regulation of gene expression. YY1 is highly expressed in various types of cancers, including prostate cancer. Currently, the mechanism underlying the functional role of YY1 in prostate tumorigenesis remains unclear. In this report, we investigated the functional interplay between YY1 and androgen receptor (AR), and the effect of YY1 on AR-mediated transcription. We found that YY1 physically interacts with AR both in a cell-free system and in cultured cells. YY1 is required for the optimal transcriptional activity of AR in promoting the transcription of the prostate-specific antigen (PSA) promoter. However, ectopic YY1 expression in LNCaP cells did not further enhance the reporter driven by the PSA promoter, suggesting that an optimal level of YY1 is already established in prostate tumor cells. Consistently, YY1 depletion in LNCaP cells reduced endogenous PSA levels, but overexpressed YY1 did not significantly increase PSA expression. We also observed that YY1–AR interaction is essential to YY1-mediated transcription activity of AR and YY1 is a necessary component in the complex binding to the androgen response element. Thus, our study demonstrates that YY1 interacts with AR and regulates its transcriptional activity.

Yin Yang 1 contains G-quadruplex structures in its promoter and 5′-UTR and its expression is modulated by G4 resolvase 1

Yin Yang 1 (YY1) is a multifunctional protein with regulatory potential in tumorigenesis. Ample studies demonstrated the activities of YY1 in regulating gene expression and mediating differential protein modifications. However, the mechanisms underlying YY1 gene expression are relatively understudied. G-quadruplexes (G4s) are four-stranded structures or motifs formed by guanine-rich DNA or RNA domains. The presence of G4 structures in a gene promoter or the 5′-UTR of its mRNA can markedly affect its expression. In this report, we provide strong evidence showing the presence of G4 structures in the promoter and the 5′-UTR of YY1. In reporter assays, mutations in these G4 structure forming sequences increased the expression of Gaussia luciferase (Gluc) downstream of either YY1 promoter or 5′-UTR. We also discovered that G4 Resolvase 1 (G4R1) enhanced the Gluc expression mediated by the YY1 promoter, but not the YY1 5′-UTR. Consistently, G4R1 binds the G4 motif of the YY1 promoter in vitro and ectopically expressed G4R1 increased endogenous YY1 levels. In addition, the analysis of a gene array data consisting of the breast cancer samples of 258 patients also indicates a significant, positive correlation between G4R1 and YY1 expression.

Yin yang 1 plays an essential role in breast cancer and negatively regulates p27

Yin Yang 1 (YY1) is highly expressed in various types of cancers and regulates tumorigenesis through multiple pathways. In the present study, we evaluated YY1 expression levels in breast cancer cell lines, a breast cancer TMA, and two gene arrays. We observed that, compared with normal samples, YY1 is generally overexpressed in breast cancer cells and tissues. In functional studies, depletion of YY1 inhibited the clonogenicity, migration, invasion, and tumor formation of breast cancer cells, but did not affect the clonogenicity of nontumorigenic cells. Conversely, ectopically expressed YY1 enhanced the migration and invasion of nontumorigenic MCF-10A breast cells. In both a monolayer culture condition and a three-dimensional Matrigel system, silenced YY1 expression changed the architecture of breast cancer MCF-7 cells to that resembling MCF-10A cells, whereas ectopically expressed YY1 in MCF-10A cells had the opposite effect. Furthermore, we detected an inverse correlation between YY1 and p27 expression in both breast cancer cells and xenograft tumors with manipulated YY1 expression. Counteracting the changes in p27 expression attenuated the effects of YY1 alterations on these cells. In addition, YY1 promoted p27 ubiquitination and physically interacted with p27. In conclusion, our data suggest that YY1 is an oncogene and identify p27 as a new target of YY1.

SOX7: from a developmental regulator to an emerging tumor suppressor.

SOX7 belongs to the SOX (SRY-related HMG-box) family of transcription factors that have been shown to regulate multiple biological processes, such as hematopoiesis, vasculogenesis and cardiogenesis during embryonic development. Recent studies indicate that several SOX family members play important roles in tumorigenesis. In this review, we introduce SOX7 gene and protein structures, and discuss its expression and functional role in cancer development and progression. SOX7 is frequently downregulated in many human cancers and its reduced expression correlates with poor prognoses of several cancers. Functional studies reveal many tumor suppressive properties of SOX7 in prostate, colon, lung, and breast cancers. To date, although a few target genes of SOX7 have been identified, SOX7-mediated gene expression has not been investigated in a cancer-relevant context. Our recent studies not only for the first time demonstrate a tumor suppressive role of SOX7 in a xenograft mouse model, but also unravel that many genes regulating cell death, growth and apoptosis are affected by SOX7, strongly supporting a pivotal role of SOX7 in tumorigenesis. Thus, currently available data clearly indicate a tumor suppressive role of SOX7, but the mechanisms underlying its gene expression and tumor suppressive activity remain undetermined. The research of SOX7 in cancers remains a fertile area to be explored.

Fatty acid synthase is a primary target of MiR-15a and MiR-16-1 in breast cancer

Fatty acid synthase (FASN) is upregulated in breast cancer and correlates with poor prognosis. FASN contributes to mammary oncogenesis and serves as a bona fide target in cancer therapies. MicroRNAs inhibit gene expression through blocking mRNA translation or promoting mRNA degradation by targeting their 3′-UTRs. We identified four microRNAs in two microRNA clusters miR-15a-16-1 and miR-497-195 that share a common seed sequence to target the 3′-UTR of the FASN mRNA. In reporter assays, both of these microRNA clusters inhibited the expression of a reporter construct containing the FASN 3′-UTR. However, only ectopic miR-15a-16-1, but not miR-497-195, markedly reduced the levels of endogenous FASN in breast cancer cells. Both miR-15a and miR-16-1 contributes to inhibiting FASN expression and breast cancer cell proliferation. Consistently, a sponge construct consisting of eight repeats of the FASN 3′-UTR region targeted by these microRNAs could markedly increase endogenous FASN levels in mammary cells. When FASN expression was restored by ectopic expression in breast cancer cells, retarded cell proliferation caused by miR-15a-16-1 was partially rescued. In conclusion, we demonstrated that FASN expression is primarily downregulated by miR-15a and miR-16-1 in mammary cells and FASN is one of the major targets of these two tumor suppressive microRNAs.

Abstract B025: The role and regulation of SOX7 in breast cancer

Loss of tumor suppressors by both epigenetic silencing and genetic deletion contributes to the development and progression of breast cancer. SOX7 is an important developmental transcription factor and its downregulation has been reported in tumor tissues and cell lines of prostate, colon and lung cancers. Our current study demonstrates that SOX7 mRNA and protein expression are downregulated in breast cancer tissues and cell lines compared to adjacent normal tissues and nontumorigenic cells, respectively. Further, we show that both hypermethylation of the SOX7 promoter and microRNAs contribute to SOX7 downregulation. SOX7 silencing by shRNAs in nontumorigenic immortal breast cells leads to increased proliferation and invasion, and they form structures resembling that of breast cancer cells in a three-dimensional culture system. Conversely, ectopic SOX7 expression inhibits proliferation, and invasion of breast cancer cells in vitro and tumor growth in vivo. Importantly, we discovered that SOX7 transcript levels positively correlated with clinical outcome of 674 breast cancer patients. Collectively, our data suggest that SOX7 acts as a tumor suppressor in breast cancer. SOX7 expression is likely regulated by multiple mechanisms and potentially serves as a prognostic marker for breast cancer patients. Citation Format: Daniel B. Stovall, Meimei Wan, Lance D. Miller, Paul Cao, Qiang Zhang, Martha Stampfer, Wennuan Liu, Jianfeng Xu, Guangchao Sui. The role and regulation of SOX7 in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B025.

Abstract 4001: SOX7 is a potential tumor suppressor in breast cancer

Among U.S. women, breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer-related deaths. Both epigenetic silencing and genetic deletion of tumor suppressors are critical for the development and progression of breast cancer. The SOX (Sex-determining region Y-box) genes encode a family of over 20 transcription factors, including SOX7. The SOX7 gene is located on chromosome arm 8p and is deleted in a number of human cancers, including breast cancer. Previously, SOX7 has been demonstrated to be down-regulated in human tissues of prostate and colon cancers and its ectopic expression inhibits proliferation and increase apoptosis in prostate and colon cancer cell lines. However, the functional role of SOX7 in breast cancer has not yet been reported. Our studies revealed a significant correlation between SOX7 transcript levels and clinical outcome in gene array data from an international meta-cohort of 674 breast cancer patients. Consistently, we observed that SOX7 mRNA levels and protein expression are down-regulated in multiple breast cancer tissues and breast cancer cell lines compared to adjacent normal tissue and non-tumorigenic cells, respectively. Further, we have observed that the SOX7 promoter is hyper-methylated in breast cancer cell lines compared to non-tumorigenic breast cells, and that inhibition of SOX7 methylation results in an increase in SOX7 mRNA. Importantly, shRNA-mediated silencing of SOX7 conferred a growth advantage to non-tumorigenic breast cells, while induced ectopic SOX7 expression inhibited proliferation and migration of breast cancer cells. Overall, our data suggest that SOX7 may act as a novel tumor suppressor in breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4001. doi:1538-7445.AM2012-4001