ERα-LBD, an isoform of estrogen receptor alpha, promotes breast cancer proliferation and endocrine resistance

Estrogen receptor alpha (ER alpha) drives mammary gland development and breast cancer (BC) growth through an evolutionarily conserved linkage of DNA binding and hormone activation functions. Therapeutic targeting of the hormone binding pocket is a widely utilized and successful strategy for breast cancer prevention and treatment. However, resistance to this endocrine therapy is frequently encountered and may occur through bypass or reactivation of ER-regulated transcriptional programs. We now identify the induction of an ER alpha isoform, ER alpha-LBD, that is encoded by an alternative ESR1 transcript and lacks the activation function and DNA binding domains. Despite lacking the transcriptional activity, ER alpha-LBD is found to promote breast cancer growth and resistance to the ER alpha antagonist fulvestrant. ER alpha-LBD is predominantly localized to the cytoplasm and mitochondria of BC cells and leads to enhanced glycolysis, respiration and stem-like features. Intriguingly, ER alpha-LBD expression and function does not appear to be restricted to cancers that express full length ER alpha but also promotes growth of triple-negative breast cancers and ER alpha-LBD transcript (ESR1-LBD) is also present in BC samples from both ER alpha(+) and ER alpha(-) human tumors. These findings point to ER alpha-LBD as a potential mediator of breast cancer progression and therapy resistance

Stat3 Mediates Expression of Autotaxin in Breast Cancer

We determined that signal transducer and activator of transcription 3 (Stat3) is tyrosine phosphorylated in 37% of primary breast tumors and 63% of paired metastatic axillary lymph nodes. Examination of the distribution of tyrosine phosphorylated (pStat3) in primary tumors revealed heterogenous expression within the tumor with the highest levels found in cells on the edge of tumors with relatively lower levels in the central portion of tumors. In order to determine Stat3 target genes that may be involved in migration and metastasis, we identified those genes that were differentially expressed in primary breast cancer samples as a function of pStat3 levels. In addition to known Stat3 transcriptional targets (Twist, Snail, Tenascin-C and IL-8), we identified ENPP2 as a novel Stat3 regulated gene, which encodes autotaxin (ATX), a secreted lysophospholipase which mediates mammary tumorigenesis and cancer cell migration. A positive correlation between nuclear pStat3 and ATX was determined by immunohistochemical analysis of primary breast cancer samples and matched axillary lymph nodes and in several breast cancer derived cell lines. Inhibition of pStat3 or reducing Stat3 expression led to a decrease in ATX levels and cell migration. An association between Stat3 and the ATX promoter, which contains a number of putative Stat3 binding sites, was determined by chromatin immunoprecipitation. These observations suggest that activated Stat3 may regulate the migration of breast cancer cells through the regulation of ATX

NRF2 Activation Confers Resistance to eIF4A Inhibitors in Cancer Therapy

Inhibition of the eIF4A RNA helicase with silvestrol and related compounds is emerging as a powerful anti-cancer strategy. We find that a synthetic silvestrol analogue (CR-1-31 B) has nanomolar activity across many cancer cell lines. It is especially active against aggressive MYC+/BCL2+ B cell lymphomas and this likely reflects the eIF4A-dependent translation of both MYC and BCL2. We performed a genome-wide CRISPR/Cas9 screen and identified mechanisms of resistance to this new class of therapeutics. We identify three negative NRF2 regulators (KEAP1, CUL3, CAND1) whose inactivation is sufficient to cause CR1-31-B resistance. NRF2 is known to alter the oxidation state of translation factors and cause a broad increase in protein production. We find that NRF2 activation particularly increases the translation of some eIF4A-dependent mRNAs and restores MYC and BCL2 production. We know that NRF2 functions depend on removal of sugar adducts by the frutosamine-3-kinase (FN3K). Accordingly, loss of FN3K results in NRF2 hyper-glycation and inactivation and resensitizes cancer cells to eIF4A inhibition. Together, our findings implicate NRF2 in the translation of eIF4A-dependent mRNAs and point to FN3K inhibition as a new strategy to block NRF2 functions in cancer

Stat3 mediates expression of autotaxin in breast cancer.

We determined that signal transducer and activator of transcription 3 (Stat3) is tyrosine phosphorylated in 37% of primary breast tumors and 63% of paired metastatic axillary lymph nodes. Examination of the distribution of tyrosine phosphorylated (pStat3) in primary tumors revealed heterogenous expression within the tumor with the highest levels found in cells on the edge of tumors with relatively lower levels in the central portion of tumors. In order to determine Stat3 target genes that may be involved in migration and metastasis, we identified those genes that were differentially expressed in primary breast cancer samples as a function of pStat3 levels. In addition to known Stat3 transcriptional targets (Twist, Snail, Tenascin-C and IL-8), we identified ENPP2 as a novel Stat3 regulated gene, which encodes autotaxin (ATX), a secreted lysophospholipase which mediates mammary tumorigenesis and cancer cell migration. A positive correlation between nuclear pStat3 and ATX was determined by immunohistochemical analysis of primary breast cancer samples and matched axillary lymph nodes and in several breast cancer derived cell lines. Inhibition of pStat3 or reducing Stat3 expression led to a decrease in ATX levels and cell migration. An association between Stat3 and the ATX promoter, which contains a number of putative Stat3 binding sites, was determined by chromatin immunoprecipitation. These observations suggest that activated Stat3 may regulate the migration of breast cancer cells through the regulation of ATX

Signal transducer and activator of transcription 3 (Stat3) phosphorylation is mediated through Janus kinases (Jaks) but not epidermal growth factor receptor (EGFR) or Src kinases

<p><b>Copyright information:</b></p><p>Taken from "Stat3 is tyrosine-phosphorylated through the interleukin-6/glycoprotein 130/Janus kinase pathway in breast cancer"</p><p>http://breast-cancer-research.com/content/9/3/R32</p><p>Breast Cancer Research 2007;9(3):R32-R32.</p><p>Published online 25 May 2007</p><p>PMCID:PMC1929096.</p><p></p> Radioimmunoprecipitation assay (RIPA) extracts (50 μg) isolated from MDA-MB-468 cells treated for 4 hours with dimethyl sulfoxide (DMSO), P6 1 μM, BMS 50 nM, and ZD 2 μM were analyzed for pEGFR, total EGFR, tyrosine-phosphorylated Stat3 (pStat3), Stat3, pSrc, Src, pJak2, and Jak2. Nuclear extracts (20 μg) isolated from MDA-MB-435 cells (upper panels) and RIPA extracts (bottom panels) treated as in and probed with the indicated antibodies. Nuclear extracts (20 μg) isolated from MDA-MB-231 cells (upper panels) and RIPA extracts (bottom panels) treated as in and probed with the indicated antibodies. Ten thousand cells (MCF10A, MCF7, MDA-MB-468, and MDA-MB-435) were plated into a 96-well culture dish and treated with DMSO control or P6 (1 μM) for 48 hours, and proliferation was measured using an MTT (3- [4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay

Signal transducer and activator of transcription 3 (Stat3) phosphorylation in primary breast cancer

<p><b>Copyright information:</b></p><p>Taken from "Stat3 is tyrosine-phosphorylated through the interleukin-6/glycoprotein 130/Janus kinase pathway in breast cancer"</p><p>http://breast-cancer-research.com/content/9/3/R32</p><p>Breast Cancer Research 2007;9(3):R32-R32.</p><p>Published online 25 May 2007</p><p>PMCID:PMC1929096.</p><p></p> Tissue microarrays of primary breast tumors (85) were analyzed for nuclear tyrosine-phosphorylated Stat3 (pStat3) by immunohistochemical analysis. Ten percent expressed high levels (3+), 36% moderate levels (+2), 23% low levels (+1), and 31% no detectable pStat3 (0)