BRCA1, a familial breast and ovarian cancer susceptibility gene encodes nuclear phosphoproteins that function as tumor suppressors in human breast cancer cells. Previously, we have shown that overexpression of a BRCA1 splice variant BRCA1a accelerates apoptosis in human breast cancer cells. In an attempt to determine whether the subcellular localization of BRCA1 is cell cycle regulated, we have studied the subcellular distribution of BRCA1 in asynchronous and growth arrested normal, breast and ovarian cancer cells using dierent BRCA1 antibodies by immuno¯uorescence and immunohistochemical staining. Upon serum starvation of NIH3T3, some breast and ovarian cancer cells, most of the BRCA1 protein redistributed to the nucleus revealing a new type of regulation that may modulate the activity of BRCA1 gene. We have also characterized two new variant BRCA1 proteins (BRCA1a/p110 and BRCA1b/ p100) which are phosphoproteins containing phosphotyrosine. Immuno¯uorescence and Western blotting analysis indicate cytoplasmic and nuclear localization of BRCA1a and BRCA1b proteins. To elucidate the biological function of BRCA1, we created a bacterial fusion protein of glutathione-transferase (GST) and BRCA1 zinc ®nger domain and detected two cellular proteins with molecular weights of approximately 32 and 65 kD, one of which contains phosphotyrosine designated p32 and p65 BRCA1 interacting proteins (BIP) that speci®cally interact with BRCA1. Western blot analysis of BIP with cyclins/CDKs and E2F antisera indicated association with cdc2, cdk2, cdk4, cyclin B, cyclin D, cyclin A and E2F-4 but not with cdk3, cdk5, cdk6, E2F-1, E2F-2, E2F-3, E2F-5 and cyclin E. Furthermore, we have also demonstrated a direct interaction of in vitro translated BRCA1a and BRCA1b proteins with recombinant cyclin A, cyclin B1, cyclin D1, cdc2, cdk2 and E2F fusion proteins in vitro. Taken together these results seem to suggest that BRCA1 could be an important negative regulator of cell cycle that functions through interaction with E2F transcriptional factors and phosphorylation by cyclins/cdk complexes with the zinc ring ®nger functioning as a major protein-protein interaction domain. If the interactions we observe in vitro is also seen in vivo then it may be possible that lack or impaired binding of the disrupted BRCA1 proteins to E2F, cyclins/CDKs in patients with mutations in the zinc ®nger domain could deprive the cell of an important mechanism for braking cell proliferation leading to the development of breast and ovarian cancers.

Background-Peroxisome proliferator-activated receptor-␣ (PPAR-␣) is expressed in the heart and regulates genes involved in myocardial fatty acid oxidation (FAO). The role of PPAR-␣ in acute ischemia/reperfusion myocardial injury remains unclear. Methods and Results-The coronary arteries of male mice were ligated for 30 minutes. After reperfusion for 24 hours, ischemic and infarct sizes were determined. A highly selective and potent PPAR-␣ agonist, GW7647, was administered by mouth for 2 days, and the third dose was given 1 hour before ischemia. GW7647 at 1 and 3 mg · kg Ϫ1 · d Ϫ1 reduced infarct size by 28% and 35%, respectively (PϽ0.01), and myocardial contractile dysfunction was also improved. Cardioprotection by GW7647 was completely abolished in PPAR-␣-null mice. Ischemia/reperfusion downregulated mRNA expression of cardiac PPAR-␣ and FAO enzyme genes, decreased myocardial FAO enzyme activity and in vivo cardiac fat oxidation, and increased serum levels of free fatty acids. All of these changes were reversed by GW7647. Moreover, GW7647 attenuated ischemia/reperfusion-induced release of multiple proinflammatory cytokines and inhibited neutrophil accumulation and myocardial expression of matrix metalloproteinases-9 and -2. Furthermore, GW7647 inhibited nuclear factor-B activation in the heart, accompanied by enhanced levels of inhibitor-B␣. Conclusions-Activation of PPAR-␣ protected the heart from reperfusion injury. This cardioprotection might be mediated through metabolic and antiinflammatory mechanisms. This novel effect of the PPAR-␣ agonist could provide an added benefit to patients treated with PPAR-␣ activators for dyslipidemia.

The mechanism responsible for the enhanced myocardial susceptibility to ischemic insult in patients with type 2 diabetes is not clear. The present study examines the effect of rosiglitazone treatment on cardiac insulin sensitization and its association with cardioprotection from ischemia/reperfusion injury in an animal model of diabetes. Male Zucker diabetic fatty (ZDF) rats were treated with rosiglitazone (3 mg ⅐ kg ؊1 ⅐ day ؊1 orally) or vehicle for 8 days before undergoing 30 min of coronary artery ligation, followed by reperfusion for 4 h (apoptosis) or 24 h (infarction). Rosiglitazone reduced the blood levels of glucose, triglycerides, and free fatty acids; enhanced cardiac glucose oxidation; and increased Akt phosphorylation (Akt-pS473) 2.1-fold and Akt kinase activity 1.8-fold in the ischemic myocardium. The phosphorylation of two downstream targets of Akt, glycogen synthase kinase-3␤ and FKHR (forkhead transcription factor), was also enhanced by 2-and 2.9-fold, respectively. In rosiglitazone-treated rats, the number of apoptotic cardiomyocytes and the myocardial infarct size were decreased by 58 and 46%, respectively, and the myocardial contractile dysfunction was improved. Blockade of the insulin-Akt signaling pathway by wortmannin in the 8-day rosiglitazone-treated ZDF rats resulted in a markedly diminished cardioprotective effect of rosiglitazone. In addition, 8-day rosiglitazone treatment in Zucker lean rats or 2-day rosiglitazone treatment in ZDF rats, both of which showed no change in whole-body insulin sensitivity, resulted in a significant reduction in cardiac infarct size, but to a lesser degree when compared with that observed in 8-day rosiglitazone-treated ZDF rats. These results suggest that chronic treatment with rosiglitazone protects the heart against ischemia/reperfusion injury in ZDF rats, and that the enhanced cardiac protection observed after rosiglitazone treatment might be attributable in part to an improvement in cardiac insulin sensitivity. Diabetes 54:554 -562, 2005

Elk-1, an ets related gene codes for at least two splice variants Elk-1, which regulates c-fos transcription and DElk-1, both of which function as transcriptional activators. To investigate the role of Elk-1 and DElk-1 proteins in apoptosis; we have developed rat ®broblast cell lines and human breast cancer cell lines expressing Elk-1 and DElk-1. The expression of Elk-1 and DElk-1 proteins in the Elk-1/DElk-1 transfectants were analysed by immuno¯uorescence, immunohistochemistry, and Western blot analysis. The Elk-1 unlike DElk-1 transfectants showed a shortened and¯attened morphology compared to the parental cells. We have found that calcium ionophore treatment of Rat-1 Elk-1, MCF-7 Elk-1, Rat-1 DElk-1 and MCF-7 DElk-1 transfectants resulted in programmed cell death. These results indicate that constitutive expression of Elk-1 and DElk-1 proteins triggers apoptosis in Rat-1 ®broblasts and breast cancer cells when treated with calcium ionophore.Keywords: Elk-1; DElk-1; apoptosis; calcium ionophore; breast cancer; MCF-7; Rat-1The Elk-1 gene belongs to the ets family of ternary complex factors (TCFs), i.e. Elk-1, SAP1, and NET/ ERP/SAP2/Elk-3 (Rao et al., 1989;Hipskind et al., 1991;Giovane et al., 1994;Lopez et al., 1994;Dalton and Treisman, 1992;Price et al., 1995;Nozaki et al., 1996). The Elk-1 gene codes for at least two alternately spliced products Elk-1 (Rao et al., 1989) and DElk-1 (Rao and Reddy, 1993) which function as transcriptional activators (Rao and Reddy, 1992;Bhattacharya et al., 1993), are substrates for MAP kinases Marias et al., 1993;Hill et al., 1993) and JNK protein kinases (Gupta et al., 1996;Whitmarsh et al., 1995). As mentioned earlier, the Elk-1 protein is a TCF which in association with serum response factor (SRF) forms a ternary complex on the serum response element (SRE) of the c-fos promoter and regulates cfos transcription (Hipskind et al., 1991). The TCF's which includes Elk-1 have three domains with similar sequences and functions. The ets domain mediates DNA binding, the SRF interaction domain interacts with SRF to form a ternary complex with the c-fos SRE and the C-terminal domain activates transcription upon phosphorylation by MAP kinases (Rao et al., 1989;Rao and Reddy, 1992;Dalton and Treisman, 1992;Janknecht et al., 1993Janknecht et al., , 1994Marias et al., 1993;Giovane et al., 1994;Hipskind et al., 1994;Kortenjann et al., 1994;Lopez et al., 1994;Hill et al., 1995;Price et al., 1995;Whitmarsh et al., 1995) and JNK kinases (Gupta et al., 1996). Thus Elk-1 represents a key link between signal transduction and induction of gene transcription.The Gag-Myb-Ets fusion protein, identi®ed in the avian acute leukemia virus E26 was shown to inhibit apoptosis and induce erythroid di erentiation in hematopoietic cells (Athanasiou et al., 1996). Similarly the Ets-1 proto-oncogene was shown to be required for the normal survival and activation of B and T cells while an Ets-1 splice variant was shown to induce apoptosis in human colon cancer cells indicating a role in apoptosis (Bories et al....

The tumor suppressor p53 is an important cellular protein, which controls cell cycle progression. Phosphorylation is one of the mechanisms by which p53 is regulated. Here we report the interaction of p53 with another key regulator, cdk9, which together with cyclin T1 forms the positive transcription elongation complex, p-TEFb. This complex cooperates with the HIV-1 Tat protein to cause the phosphorylation of the carboxyl terminal domain (CTD) of RNA polymerase II and this facilitates the elongation of HIV-1 transcription. We demonstrate that cdk9 phosphorylates p53 on serine 392 through their direct physical interaction. Results from protein-protein interaction assays revealed that cdk9 interacts with the C-terminal domain (aa 361-393) of p53, while p53 interacts with the N-terminal domain of cdk9. Transfection and protein binding assays (EMSA and ChIP) demonstrated the ability of p53 to bind and activate the cdk9 promoter. Interestingly, cdk9 phosphorylates serine 392 of p53, which could be also phosphorylated by casein kinase II. Kinase assays demonstrated that cdk9 phosphorylates p53 independently of CKII. These studies demonstrate the existence of a feedback-loop between p53 and cdk9, pinpointing a novel mechanism by which p53 regulates the basal transcriptional machinery.

BackgroundLung cancer stem cells have the ability to self-renew and are resistant to conventional chemotherapy. MicroRNAs (miRNAs) regulate and control the expression and function of many target genes; therefore, miRNA disorders are involved in the pathogenesis of human diseases, such as cancer. However, the effects of miRNA dysregulation on tumour stemness and drug resistance have not been fully elucidated. miR-181b has been reported to be a tumour suppressor miRNA and is associated with drug-resistant non-small cell lung cancer.MethodsCancer stem cell (CSC)-like properties were tested by a cell proliferation assay and flow cytometry; miR-181b expression was measured by real-time PCR; and Notch2 and related proteins were detected by Western blotting and immunohistochemistry. A mouse xenograft model was also established.ResultsIn this study, we found that ectopic miR-181b expression suppressed cancer stem cell properties and enhanced sensitivity to cisplatin (DDP) treatment by directly targeting Notch2. miR-181b could inactivate the Notch2/Hes1 signalling pathway. In addition, tumours from nude mice treated with miR-181b were significantly smaller than tumours from mice treated with control agomir. Decreased miR-181b expression and increased Notch2 expression were observed to have a significant relationship with overall survival (OS) and CSC-like properties in non-small cell lung cancer (NSCLC) patients.ConclusionsThis study elucidates an important role of miR-181b in the regulation of CSC-like properties, suggesting a potential therapeutic target for overcoming drug resistance in NSCLC.Electronic supplementary materialThe online version of this article (10.1186/s13287-018-1072-1) contains supplementary material, which is available to authorized users.

BRCA1 is a tumor suppressor gene that is mutated in families with breast and ovarian cancer. Several BRCA1 splice variants are found in different tissues, but their subcellular localization and functions are poorly understood at the moment. We previously described BRCA1 splice variant BRCA1a to induce apoptosis and function as a tumor suppressor of triple negative breast, ovarian and prostate cancers. In this study we have analyzed the function of BRCA1 isoforms (BRCA1a and BRCA1b) and compared them to the wild type BRCA1 protein using several criteria like studying expression in normal and tumor cells by RNase protection assays, sub cellular localization/fractionation by immunofluorescence microscopy and western blot analysis, transcription regulation of biological relevant proteins and growth suppression in breast cancer cells. We are demonstrating for the first time that ectopically expressed GFP-tagged BRCA1, BRCA1a, and BRCA1b proteins are localized to the mitochondria, repress ELK-1 transcriptional activity and possess antiproliferative activity on breast cancer cells. These results suggest that the exon 9,10 and 11 sequences (aa 263 – 1365) which contain two nuclear localization signals, p53, Rb, c-Myc, γ- tubulin, Stat, Rad 51, Rad 50 binding domains, angiopoietin-1 repression domain are not absolutely required for mitochondrial localization and growth suppressor function of these proteins. Since mitochondrial dysfunction is a hallmark of cancer, we can speculate that the mitochondrial localization of BRCA1 proteins may be functionally significant in regulating both the mitochondrial DNA damage as well as apoptotic activity of BRCA1 proteins and mislocalization causes cancer.

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