Cellular inhibitor of apoptosis protein 2 promotes the epithelial-mesenchymal transition in triple-negative breast cancer cells through activation of the AKT signaling pathway

Targeting Upregulated cIAP2 in SOX10-Deficient Drug Tolerant Melanoma

Drug tolerance and minimal residual disease (MRD) are likely to prelude acquired resistance to targeted therapy. Mechanisms that allow persister cells to survive in the presence of targeted therapy are being characterized but selective vulnerabilities for these subpopulations remain uncertain. We identified cellular inhibitor of apoptosis protein 2 (cIAP2) as being highly expressed in SOX10-deficient drug tolerant persister (DTP) melanoma cells. Here, we show that cIAP2 is sufficient to induce tolerance to MEK inhibitors, likely by decreasing the levels of cell death. Mechanistically, cIAP2 is upregulated at the transcript level in SOX10-deficient cells and the AP-1 complex protein, JUND, is required for its expression. Using a patient-derived xenograft model, we demonstrate that treatment with the cIAP1/2 inhibitor, birinapant, during the MRD phase delays the onset of resistance to BRAF inhibitor and MEK inhibitor combination therapy. Together, our data suggest that cIAP2 upregulation in SOX10-deficient subpopulations of melanoma cells induces drug tolerance to MAPK targeting agents and provides a rationale to test a novel therapeutical approach to target MRD.

Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Cancer invasion and metastasis accounts for the majority of cancer related mortality. A better understanding of the players that drive the aberrant invasion and migration of tumors cells will provide critical targets to inhibit metastasis. Postnatal pubertal mammary gland morphogenesis is characterized by highly proliferative, invasive, and migratory normal epithelial cells. Identifying the molecular regulators of pubertal gland development is a promising strategy since tumorigenesis and metastasis is postulated to be a consequence of aberrant reactivation of developmental stages. In this review, we summarize the pubertal morphogenesis regulators that are involved in cancer metastasis and revisit pubertal mammary gland transcriptome profiling to uncover both known and unknown metastasis genes. Our updated list of pubertal morphogenesis regulators shows that most are implicated in invasion and metastasis. This review highlights molecular linkages between development and metastasis and provides a guide for exploring novel metastatic drivers.

Induction of Breast Cancer Cell Apoptosis by TRAIL and Smac Mimetics: Involvement of RIP1 and cFLIP

Smac mimetics are a group of compounds able to facilitate cell death in cancer cells. TNF-related apoptosis-inducing ligand (TRAIL) is a death receptor ligand currently explored in combination with Smac mimetics. The molecular mechanisms determining if the combination treatment results in apoptosis are however not fully understood. In this study, we aimed to shed light on these mechanisms in breast cancer cells. Three breast cancer cell lines, MDA-MB-468, CAMA-1 and MCF-7, were used to evaluate the effects of Smac mimetic LCL-161 and TRAIL using cell death assays and Western blot. The combination treatment induces apoptosis and caspase-8 cleavage in MDA-MB-468 and CAMA-1 but not in MCF-7 cells and downregulation of caspase-8 blocked apoptosis. Downregulation, but not kinase inhibition, of receptor-interacting protein 1 (RIP1) suppressed apoptosis in CAMA-1. Apoptosis is preceded by association of RIP1 with caspase-8. Downregulating cellular FLICE-like inhibitory protein (c-FLIP) resulted in increased caspase cleavage and some induction of apoptosis by TRAIL and LCL-161 in MCF-7. In CAMA-1, c-FLIP depletion potentiated TRAIL-induced caspase cleavage and LCL-161 did not increase it further. Our results lend further support to a model where LCL-161 enables the formation of a complex including RIP1 and caspase-8 and circumvents c-FLIP-mediated inhibition of caspase activation.

Sulfated Hyaluronan Modulates the Functional Properties and Matrix Effectors Expression of Breast Cancer Cells with Different Estrogen Receptor Status

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan (GAG) that plays a pivotal role in breast cancer. While HA is the only GAG not normally substituted with sulfate groups, sulfated hyaluronan (sHA) has previously been used in studies with promising antitumor results. The aim of the present study was to evaluate the effects sHA fragments have on breast cancer cells with different estrogen receptor (ER) status. To this end, ERα-positive MCF-7, and ERβ-positive MDA-MB-231 cells were treated with non-sulfated HA or sHA fragments of 50 kDa. The functional properties of the breast cancer cells and the expression of key matrix effectors were investigated. According to the results, sHA attenuates cell proliferation, migration, and invasion, while increasing adhesion on collagen type I. Furthermore, sHA modulates the expression of epithelial-to-mesenchymal transition (EMT) markers, such as e-cadherin and snail2/slug. Additionally, sHA downregulates matrix remodeling enzymes such as the matrix metalloproteinases MT1-MMP, MMP2, and MMP9. Notably, sHA exhibits a stronger effect on the breast cancer cell properties compared to the non-sulfated counterpart, dependent also on the type of cancer cell type. Consequently, a deeper understanding of the mechanism by which sHA facilitate these processes could contribute to the development of novel therapeutic strategies.

The Multiple Roles of the IAP Super-family in cancer

The Inhibitor of Apoptosis proteins (IAPs) are a family of proteins that are mainly known for their anti-apoptotic activity and ability to directly bind and inhibit caspases. Recent research has however revealed that they have extensive roles in governing numerous other cellular processes. IAPs are known to modulate ubiquitin (Ub)-dependent signaling pathways through their E3 ligase activity and influence activation of nuclear factor κB (NF-κB). In this review, we discuss the involvement of IAPs in individual hallmarks of cancer and the current status of therapies targeting these critical proteins.

SAHA and EGCG Promote Apoptosis in Triple-negative Breast Cancer Cells, Possibly Through the Modulation of cIAP2

BACKGROUND/AIM

Inhibition of apoptosis is one of the hallmarks of cancer, and anti-apoptotic genes are often targets of genetic and epigenetic alterations. Cellular inhibitor of apoptosis 2 (cIAP2) has a role in degrading caspases by linking them to ubiquitin molecules, and is upregulated in triple-negative breast cancer (TNBC). Previous studies have demonstrated that cIAP2 may play a role in the epithelial-to-mesenchymal transition (EMT).

MATERIALS AND METHODS

Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, was administered to triple-negative breast cancer (TNBC) cells alone or in combination with epigallocatechin-3-gallate (EGCG), a DNA methyltransferase (DNMT) inhibitor isolated from green tea.

RESULTS

The compounds were able to decrease the expression of cIAP2 while increasing the expression of pro-apoptotic caspase 7. There were also changes in histone modifications, suggesting a role of epigenetic mechanisms in these changes in expression of cIAP2. These changes resulted in an increase in apoptosis. SAHA and EGCG were also capable of limiting TNBC cell migration across a fibronectin (FN) matrix.

CONCLUSION

SAHA and EGCG reduce the metastatic potential of TNBC by inducing the apoptotic pathway.

Molecular size-dependent specificity of hyaluronan on functional properties, morphology and matrix composition of mammary cancer cells

High levels of hyaluronan (ΗΑ), a major extracellular matrix (ECM) glycosaminoglycan, have been correlated with poor clinical outcome in several malignancies, including breast cancer. The high and low molecular weight HΑ forms exert diverse biological functions. Depending on their molecular size, ΗΑ forms either promote or attenuate signaling cascades that regulate cancer progression. In order to evaluate the effects of different ΗΑ forms on breast cancer cells' behavior, ΗΑ fragments of defined molecular size were synthesized. Breast cancer cells of different estrogen receptor (ER) status - the low metastatic, ERα-positive MCF-7 epithelial cells and the highly aggressive, ERβ-positive MDA-MB-231 mesenchymal cells - were evaluated following treatment with HA fragments. Scanning electron microscopy revealed that HA fragments critically affect the morphology of breast cancer cells in a molecular-size dependent mode. Moreover, the ΗΑ fragments affect cell functional properties, the expression of major ECM mediators and epithelial-to-mesenchymal transition (ΕΜΤ) markers. Notably, treatment with 200 kDa ΗΑ increased the expression levels of the epithelial marker Ε-cadherin and reduced the expression levels of HA synthase 2 and mesenchymal markers, like fibronectin and snail2/slug. These novel data suggest that the effects of HA in breast cancer cells depend on the molecular size and the ER status. An in-depth understanding on the mechanistic basis of these effects may contribute on the development of novel therapeutic strategies for the pharmacological targeting of aggressive breast cancer.

Greensporone A, a Fungal Secondary Metabolite Suppressed Constitutively Activated AKT via ROS Generation and Induced Apoptosis in Leukemic Cell Lines

Greensporone A is a fungal secondary metabolite that has exhibited potential in vitro for anti-proliferative activity in vitro. We studied the anticancer activity of greensporone A in a panel of leukemic cell lines. Greensporone A-mediated inhibition of proliferation is found to be associated with the induction of apoptotic cell death. Greensporone A treatment of leukemic cells causes inactivation of constitutively activated AKT and its downstream targets, including members GSK3 and FOXO1, and causes downregulation of antiapoptotic genes such as Inhibitor of Apoptosis (IAPs) and Bcl-2. Furthermore, Bax, a proapoptotic member of the Bcl-2 family, was found to be upregulated in leukemic cell lines treated with greensporone A. Interestingly, gene silencing of AKT using AKT specific siRNA suppressed the expression of Bcl-2 with enhanced expression of Bax. Greensporone A-mediated increase in Bax/Bcl-2 ratio causes permeabilization of the mitochondrial membrane leading to the accumulation of cytochrome c in the cytoplasm. Greensporone A-induced cytochrome c accumulation causes the activation of caspase cascade and cleavage of its effector, poly(ADP-ribose) polymerase (PARP), leading to apoptosis. Greensporone A-mediated apoptosis in leukemic cells occurs through the generation of reactive oxygen species (ROS) due to depletion of glutathione (GSH) levels. Finally, greensporone A potentiated the anticancer activity of imatinib in leukemic cells. In summary, our study showed that greensporone A suppressed the growth of leukemic cells via induction of apoptotic cell death. The apoptotic cell death occurs by inhibition of AKT signaling and activation of the intrinsic apoptotic/caspase pathways. These results raise the possibility that greensporone A could be developed as a therapeutic agent for the treatment of leukemia and other hematological malignancies.

Effects of SAHA and EGCG on Growth Potentiation of Triple-Negative Breast Cancer Cells

Triple-negative breast cancer comprises approximately 15–20% of all breast cancers diagnosed and is nearly twice as common in black women than white women in the United States. We evaluated the effects of two epigenetic-modifying compounds on markers of growth potential in several triple-negative breast cancer cell lines. Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor currently used in the treatment of cutaneous T cell lymphoma, was administered to triple-negative breast cancer cells alone or in combination with epigallocatechin-3-gallate (EGCG), a DNA methyltransferase (DNMT) inhibitor isolated from green tea. The compounds affected the expression of oncogenic miR-221/222 and tumor suppressors, p27 and PTEN, in addition to estrogen receptor alpha (ERα). E-cadherin expression was increased while N-cadherin was decreased, indicating a more epithelial phenotype. In addition, the activity of DNMTs was diminished with the treatments, and there was a significant enrichment of AcH3 within the promoter of p27 and PTEN, suggesting a role of epigenetic mechanisms for the aforementioned changes. These results translated to reduced migration of the triple-negative breast cancer cells with the treatments. Together, these findings support the role of SAHA and EGCG in limiting growth and proliferation of breast cancer cells.

Greensporone C, a Freshwater Fungal Secondary Metabolite Induces Mitochondrial-Mediated Apoptotic Cell Death in Leukemic Cell Lines

Therapeutic agents used in the treatment of cancer are known to develop resistance against cancer cells. Hence, there is a continuing need to investigate novel agents for the treatment and management of cancer. Antitumor activity of greensporone C (GC), a new resorcylic acid lactone isolated from an organic extract of a culture of a Halenospora sp. freshwater fungus, was subjected for screening against a panel of leukemic cell lines (K562, U937, and AR320). In all the three cell lines, cell proliferation was inhibited in dose-dependent fashion. GC further arrested the cells in SubG0 phase in dose-dependent manner. Annexin V/PI dual staining data confirmed apoptotic death of treated K562 and U937 leukemic cells. Treatment with GC suppressed constitutively phosphorylated AKT and downregulated expression of inhibitor of apoptotic proteins XIAP, cIAP-1, and cIAP-2. In summation to this, GC-treated leukemic cells upregulated protein expression of pro-apoptotic proteins, Bax with concomitant decrease in expression of anti-apoptotic proteins including Bcl-2 and Bcl-xL. Upregulation of Bax was associated with cytochrome c release which was confirmed from the collapse of mitochondrial membrane. Released cytochrome c further activated caspase cascade which in turn initiated apoptosis process. Anticancer activity of this isolated fungal compound GC was potentiated via stimulating production of reactive oxygen species (ROS) along with depletion of reduced glutathione (GSH) levels in K562 and U937 leukemic cells. Pretreatment of these cells with N-acetyl cysteine prevented GC-induced depletion of reduced GSH level and mitochondrial-caspase-induced apoptosis. Altogether, our data show that GC modulates the apoptotic response of human leukemic cells and raises the possibility of its use as a novel therapeutic strategy for hematological malignancies.