Retinoic Acid Mediates Regulation of Network Formation by COUP-TFII and VE-Cadherin Expression by TGFβ Receptor Kinase in Breast Cancer Cells

Tumor development, growth, and metastasis depend on the provision of an adequate vascular supply. This can be due to regulated angiogenesis, recruitment of circulating endothelial progenitors, and/or vascular transdifferentiation. Our previous studies showed that retinoic acid (RA) treatment converts a subset of breast cancer cells into cells with significant endothelial genotypic and phenotypic elements including marked induction of VE-cadherin, which was responsible for some but not all morphological changes. The present study demonstrates that of the endothelial-related genes induced by RA treatment, only a few were affected by knockdown of VE-cadherin, ruling it out as a regulator of the RA-induced endothelial genotypic switch. In contrast, knockdown of the RA-induced gene COUP-TFII prevented the formation of networks in Matrigel but had no effect on VE-cadherin induction or cell fusion. Two pan-kinase inhibitors markedly blocked RA-induced VE-cadherin expression and cell fusion. However, RA treatment resulted in a marked and broad reduction in tyrosine kinase activity. Several genes in the TGFβ signaling pathway were induced by RA, and specific inhibition of the TGFβ type I receptor blocked both RA-induced VE-cadherin expression and cell fusion. Together these data indicate a role for the TGFβ pathway and COUP-TFII in mediating the endothelial transdifferentiating properties of RA

Tyrosine Phosphorylation of the Nuclear Receptor Coactivator AIB1/SRC-3 Is Enhanced by Abl Kinase and Is Required for Its Activity in Cancer Cells▿ †

Overexpression and activation of the steroid receptor coactivator amplified in breast cancer 1 (AIB1)/steroid receptor coactivator-3 (SRC-3) have been shown to have a critical role in oncogenesis and are required for both steroid and growth factor signaling in epithelial tumors. Here, we report a new mechanism for activation of SRC coactivators. We demonstrate regulated tyrosine phosphorylation of AIB1/SRC-3 at a C-terminal tyrosine residue (Y1357) that is phosphorylated after insulin-like growth factor 1, epidermal growth factor, or estrogen treatment of breast cancer cells. Phosphorylated Y1357 is increased in HER2/neu (v-erb-b2 erythroblastic leukemia viral oncogene homolog 2) mammary tumor epithelia and is required to modulate AIB1/SRC-3 coactivation of estrogen receptor alpha (ERα), progesterone receptor B, NF-κB, and AP-1-dependent promoters. c-Abl (v-Abl Abelson murine leukemia viral oncogene homolog 1) tyrosine kinase directly phosphorylates AIB1/SRC-3 at Y1357 and modulates the association of AIB1 with c-Abl, ERα, the transcriptional cofactor p300, and the methyltransferase coactivator-associated arginine methyltransferase 1, CARM1. AIB1/SRC-3-dependent transcription and phenotypic changes, such as cell growth and focus formation, can be reversed by an Abl kinase inhibitor, imatinib. Thus, the phosphorylation state of Y1357 can function as a molecular on/off switch and facilitates the cross talk between hormone, growth factor, and intracellular kinase signaling pathways in cancer

GTF2I MUTATIONS ARE FREQUENT IN THYMIC EPITHELIAL TUMORS

Aim: To investigate the molecular aberrations of thymic epithelial tumors (TETs) which, currently, are largely unknown, hampering progress in diagnosis, prognostication and targeted therapy. Methods: Frozen tumor and normal blood were available for 28 TETs with a high proportion of cancer cell content (>80%). Exome capture was performed using Sure Select All Exon (Agilent) and TruSeq Exome Enrichment kit (Illumina) in 21 and 35 samples, respectively. Sequencing was performed using Genome Analyzer-II (Illumina) and HiSeq2000 (Illumina) in 21 and 35 samples, respectively. Reads were aligned using Novoalign (Novocraft) and somatic mutations were detected comparing exome sequencing of tumor and normal DNA of each patients using VarScan2. A single nucleotide missense mutation of GTF2I was the most common in TETs, and was confirmed in an independent cohort of 268 formalin fixed paraffin embedded TETs. Results: Thymic carcinomas had a higher number of mutations than thymomas with a mean of 43.5 and 17.4, respectively (p=0.001). In thymic carcinomas (11), genes with recurrent mutations included TP53 (4), CYLD (3), BAP1 (2), CDKN2A (2) and PBRM1 (2). A single nucleotide mutation of GTF2I (chr7:74146970T/A) was observed in 35% of thymomas (17). The mutation was missense (leucine to histidine), not previously described in cancer or as a polymorphism in dbSNP137 database. The mutation was predicted to alter the structure of the protein or its function according to Poliphen2 and SIFT algorithms. The presence of GTF2I mutation was confirmed in an extended cohort of 268 TETs: 82% of A (56), 74% of AB (54), 32% of B1 (28), 22% of B2 (32), 21% of B3 thymomas (62) and 8% of thymic carcinomas (36). The mutation was more frequent in stages I-II (57%) than in stages III-IV (19%; p<0.001). Patients with GTF2I mutation had a better disease related survival than those without (96% vs 70% 10-year survival, respectively; Log-Rank p<0.001). In a multivariate model only tumor stage but not GTF2I mutation or WHO histotypes were independent prognostic factors (p=0.008, p=0.209 and p=0.242, respectively). GTF2I mutation stimulated cell proliferation in in vitro models. Conclusions: GTF2I mutation is frequent in thymic epithelial tumors, especially in A-AB histotypes and is associated with a better outcom