No abstract

Insulin receptor substrate 1 (IRS-1) is the major signaling molecule for the insulin and insulin-like growth factor I receptors, which transduces both metabolic and growth-promoting signals, and has transforming properties when overexpressed in the cells. Here we show that IRS-1 is translocated to the nucleus in the presence of the early viral protein-T-antigen of the human polyomavirus JC. Nuclear IRS-1 was detected in T-antigenpositive cell lines and in T-antigen-positive biopsies from patients diagnosed with medulloblastoma. The IRS-1 domain responsible for a direct JC virus T-antigen binding was localized within the N-terminal portion of IRS-1 molecule, and the binding was independent from IRS-1 tyrosine phosphorylation and was strongly inhibited by IRS-1 serine phosphorylation. In addition, competition for the IRS-1-T-antigen binding by a dominant negative mutant of IRS-1 inhibited growth and survival of JC virus T-antigen-transformed cells in anchorageindependent culture conditions. Based on these findings, we propose a novel role for the IRS-1-T-antigen complex in controlling cellular equilibrium during viral infection. It may involve uncoupling of IRS-1 from its surface receptor and translocation of its function to the nucleus. Insulin receptor substrate 1 (IRS-1)1 is a 160-kDa cytosolic protein implicated in insulin and IGF-I signal transduction. IRS-1 plays an essential role in IGF-I-mediated cell proliferation (1, 2), and has transforming properties when overexpressed in different cell types (3, 4). The structure of IRS-1 reveals two conserved regions within the N-terminal portion of the protein (5, 6). The first one is called PH for its similarity to a pleckstrin homology domain (7), and the second shows similarity to a putative phosphotyrosine-binding (PTB) domain present in Shc and other proteins (6). The PTB domain recognizes phosphorylated tyrosine within NPXY motifs, providing a mechanism to couple IRS-1 with the Tyr 950 in the juxtamembrane region of the IGF-IR (8). PH domains contain a positively charged binding pocket that may mediate interaction with phospholipids (9) and with proteins containing acidic motifs (10). Following activation, over 20 phosphorylation sites on the IRS-1 docking molecule can recruit a variety of proteins equipped with Src homology domains (11). Independent from its tyrosine phosphorylation, IRS-1 interacts with ␣ v ␤ 3 (12) and ␣ 5 ␤ 1 (13, 14) integrins, with typical nuclear proteins such as the SV40 large T-antigen (3) and nucleolin (10) and is constitutively phosphorylated in v-Src transformed cells (15). Transforming properties of IRS-1 were suspected for quite some time even before the first convincing evidence was furnished by utilizing R Ϫ cells (3T3-like fibroblasts derived from mice with targeted disruption of IGF-IR gene) (3, 4). Although R Ϫ cells are remarkably resistant to transformation (15, 16), co-expression of IRS-1 and SV40 T-antigen induced R Ϫ transformation, a phenotype efficiently reversed by antisense IRS-1 mRNA (4). Importantly, overexpressio...

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that lacks expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor (HER2). TNBC constitutes about 15–30 percent of all diagnosed invasive breast cancer cases in the United States. African-American (AA) women have high prevalence of TNBC with worse clinical outcomes than European-American (EA) women. The contributing factors underlying racial disparities have been divided into two major categories based on whether they are related to lifestyle (non-biologic) or unrelated to lifestyle (biologic). Our objective in the present review article was to understand the potential interactions by which these risk factors intersect to drive the initiation and development of the disparities resulting in the aggressive TNBC subtypes in AA women more likely than in EA women. To reach our goal, we conducted literature searches using MEDLINE/PubMed to identify relevant articles published from 2005 to 2019 addressing breast cancer disparities primarily among AA and EA women in the United States. We found that disparities in TNBC may be attributed to racial differences in biological factors, such as tumor heterogeneity, population genetics, somatic genomic mutations, and increased expression of genes in AA breast tumors which have direct link to breast cancer. In addition, a large number of non-biologic factors, including socioeconomic deprivation adversities associated with poverty, social stress, unsafe neighborhoods, lack of healthcare access and pattern of reproductive factors, can promote comorbid diseases such as obesity and diabetes which may adversely contribute to the aggression of TNBC biology in AA women. Further, the biological risk factors directly linked to TNBC in AA women may potentially interact with non-biologic factors to promote a higher prevalence of TNBC, more aggressive biology, and poor survival. The relative contributions of the biologic and non-biologic factors and their potential interactions is essential to our understanding of disproportionately high burden and poor survival rates of AA women with TNBC.

Tumor necrosis factor-a converting enzyme (ADAM17) is a major metalloproteinase involved in the shedding of several membrane-bound cytokines and cytokine receptors. Interplay of cytokines and their soluble receptors might be an important regulatory element in the network of interactions responsible for maintaining homeostasis in the immune system. ADAM17 thus has the potential to participate in a broad range of immune reactions. We studied the mechanisms of ADAM17 activation in endothelial cells and found that pro-inflammatory cytokines (tumor necrosis factor-a, interleukin-1b, interferon-c) and growth factors (epidermal growth factor, vascular endothelial growth factor) are able to upregulate transcription of ADAM17 and expression of ADAM17 protein. This process might constitute an important mechanism of regulation of ADAM17 activity. Stimulation of transcription, rather than increased ADAM17 mRNA stability, was responsible for increased levels of ADAM17 mRNA. Importantly, the increase in ADAM17 was accompanied by increased shedding of TNFReceptor I (p55) in tumor necrosis factor-a-stimulated endothelial cells. Therefore, ADAM17-dependent depletion of membrane-bound tumor necrosis factor receptors from endothelial cells might constitute a mechanism of selfprotection in states of prolonged immunostimulation.

In medulloblastomas, which are highly malignant cerebellar tumors of the childhood genotoxic treatments such as cisplatin or γ-irradiation are frequently associated with DNA damage, which often associates with unfaithful DNA repair, selection of new adaptations and possibly tumor recurrences. Therefore, better understanding of molecular mechanisms which control DNA repair fidelity upon DNA damage is a critical task. Here we demonstrate for the first time that estrogen receptor beta (ERβ) can contribute to the development of genomic instability in medulloblastomas. Specifically, ERβ was found highly expressed and active in mouse and human medulloblastoma cell lines. Nuclear ERβ was also present in human medulloblastoma clinical samples. Expression of ERβ coincided with nuclear translocation of insulin receptor substrate 1 (IRS-1), which was previously reported to interfere with the faithful component of DNA repair when translocated to the nucleus. We demonstrated that ERβ and IRS-1 bind each other, and the interaction involves C-terminal domain of IRS-1 (aa 931–1233). Following cisplatin-induced DNA damage, nuclear IRS-1 localized at the sites of damaged DNA, and interacted with Rad51—an enzymatic component of homologous recombination directed DNA repair (HRR). In medulloblastoma cells, engineered to express HRR-DNA reporter plasmid, ER antagonist, ICI 182,780, or IRS mutant (931–1233) significantly increased DNA repair fidelity. These data strongly suggest that both molecular and pharmacological interventions are capable of preventing ERβ-mediated IRS-1 nuclear translocation, which in turn improves DNA repair fidelity and possibly counteracts accumulation of malignant mutations in actively growing medulloblastomas.