Global changes in gene expression accompany the development of cancer. Thus, inherited variants in miRNA-binding sites are likely candidates for conferring inherited susceptibility. Using an in silico approach, we compiled a comprehensive list of SNPs predicted to modulate miRNA binding in genes from several key lung cancer pathways. We then investigated whether these SNPs were associated with lung cancer risk in two independent populations. In general, SNPs in miRNA-binding sites are rare. However, some allelic variation was observed. We found that rs1126579 in CXCR2 was associated with a reduced risk of lung cancer in both European American [ORTT vs. CC 0.56 (0.37–0.88); P = 0.008] and Japanese [ORTT vs. CC 0.62 (0.38–1.00); P = 0.049] populations. Furthermore, we found that the SNP disrupted a novel binding site for miR-516a-3p, led to a moderate increase in CXCR2 mRNA and protein expression, and increased MAPK signaling. Moreover, analysis of rs1126579 with serum levels of IL8, its endogenous ligand, supported an interaction whereby rs1126579-T and high serum IL8 conferred synergistic protection from lung cancer. Our findings demonstrate a function for a 3′UTR SNP in modulating CXCR2 expression, signaling, and susceptibility to lung cancer. Cancer Res; 75(3); 1–10. ©2014 AACR.

Global changes in gene expression accompany the development of cancer. Thus, inherited variants in microRNA binding sites are likely candidates for conferring inherited susceptibility. Using an in-silico approach, we compiled a comprehensive list of SNPs predicted to modulate microRNA binding in genes from several key lung cancer pathways. We then investigated whether these SNPs were associated with lung cancer risk in two independent populations. In general, SNPs in microRNA binding sites are rare. However, some allelic variation was observed. We found that rs1126579 in CXCR2 was associated with a reduced risk of lung cancer in both European American (ORTT vs. CC 0.56 [0.37 – 0.88]; P=0.008) and Japanese (ORTT vs. CC 0.62 [0.38 – 1.00]; P=0.049) populations. Further, we found that the SNP disrupted a novel binding site for miR-516a-3p, led to a moderate increase in CXCR2 mRNA and protein expression and increased MAPK signaling. Moreover, analysis of rs1126579 with serum levels of IL-8, its endogenous ligand, supported an interaction whereby rs1126579-T and high serum IL-8 conferred synergistic protection from lung cancer. Our findings demonstrate a function for a 3’UTR SNP in modulating CXCR2 expression, signaling and susceptibility to lung cancer.

BRCA1 expression is lost frequently in breast cancers where it promotes malignant development. In the present study, we performed a global expression analysis of breast cancer cells where the tumor suppressor candidate gene TUSC4 was silenced to gain insights into its function. TUSC4 silencing affected genes involved in cell cycle and cell death which have broad reaching influence on cancer development. Most importantly, we found a cluster pattern of gene expression profiles in TUSC4-silenced cells that defined a homologous recombination (HR) repair defect signature. Mechanistic investigations indicated that TUSC4 protein couljd physically interact with the E3 ligase Herc2, which prevents BRCA1 degradation through the ubiquitination pathway. TUSC4 silencing enhanced BRCA1 polyubiquitination leading to its degradation and a marked reduction in HR repair efficiency. Notably, ectopic expression of TUSC4 suppressed the proliferation, invasion, and colony formation of breast cancer cells in vitro and tumorigenesis in vivo. Furthermore, TUSC4 silencing was sufficient to transform normal mammary epithelial cells and to enhance sensitivity to poly(ADP-ribose) polymerase inhibitors. Our results provide a set of genetic and biological proofs that TUSC4 functions as a bona fide tumor suppressor by regulating the protein stability and function of BRCA1 in breast cancer.

Estrogen receptor (ER) α–positive breast cancers initially respond to antiestrogens but eventually become estrogen independent and recur. ER+ breast cancer cells resistant to long-term estrogen deprivation (LTED) exhibit hormone-independent ER transcriptional activity and growth. A kinome-wide siRNA screen using a library targeting 720 kinases identified Polo-like kinase 1 (PLK1) as one of the top genes whose downregulation resulted in inhibition of estrogen-independent ER transcriptional activity and growth of LTED cells. High PLK1 mRNA and protein correlated with a high Ki-67 score in primary ER+ breast cancers after treatment with the aromatase inhibitor letrozole. RNAi-mediated knockdown of PLK1 inhibited ER expression, estrogen-independent growth, and ER transcription in MCF7 and HCC1428 LTED cells. Pharmacologic inhibition of PLK1 with volasertib, a small-molecule ATP-competitive PLK1 inhibitor, decreased LTED cell growth, ER transcriptional activity, and ER expression. Volasertib in combination with the ER antagonist, fulvestrant, decreased MCF7 xenograft growth in ovariectomized mice more potently than each drug alone. JUNB, a component of the AP-1 complex, was expressed 16-fold higher in MCF7/LTED compared with parental MCF7 cells. Furthermore, JUNB and BCL2L1 (which encodes antiapoptotic BCL-xL) mRNA levels were markedly reduced upon volasertib treatment in MCF7/LTED cells, while they were increased in parental MCF7 cells. Finally, JUNB knockdown decreased ER expression and transcriptional activity in MCF7/LTED cells, suggesting that PLK1 drives ER expression and estrogen-independent growth via JUNB. These data support a critical role of PLK1 in acquired hormone-independent growth of ER+ human breast cancer and is therefore a promising target in tumors that have escaped estrogen deprivation therapy. Cancer Res; 75(2); 1–10. ©2014 AACR.

Estrogen receptor α (ER)-positive breast cancers initially respond to antiestrogens but eventually become estrogen-independent and recur. ER+ breast cancer cells resistant to long-term estrogen deprivation (LTED) exhibit hormone-independent ER transcriptional activity and growth. A kinome-wide siRNA screen using a library targeting 720 kinases identified Polo-like kinase 1 (PLK1) as one of the top genes whose downregulation resulted in inhibition of estrogen-independent ER transcriptional activity and growth of LTED cells. High PLK1 mRNA and protein correlated with a high Ki67 score in primary ER+ breast cancers after treatment with the aromatase inhibitor letrozole. RNAi-mediated knockdown of PLK1 inhibited ER expression, estrogen-independent growth and ER transcription in MCF7 and HCC1428 LTED cells. Pharmacological inhibition of PLK1 with volasertib, a small molecule ATP-competitive PLK1 inhibitor, decreased LTED cell growth, ER transcriptional activity and ER expression. Volasertib in combination with the ER antagonist, fulvestrant, decreased MCF7 xenograft growth in ovariectomized mice more potently than each drug alone. JUNB, a component of the AP-1 complex, was expressed 16-fold higher in MCF7/LTED compared to parental MCF7 cells. Further, JUNB and BCL2L1 (which encodes anti-apoptotic BCL-xL) mRNA levels were markedly reduced upon volasertib treatment in MCF7/LTED cells while they were increased in parental MCF7 cells. Finally, JUNB knockdown decreased ER expression and transcriptional activity in MCF7/LTED cells, suggesting that PLK1 drives ER expression and estrogen-independent growth via JUNB. These data support a critical role of PLK1 in acquired hormone-independent growth of ER+ human breast cancer and is therefore a promising target in tumors that have escaped estrogen deprivation therapy.