Oncogenic c-H-ras deregulates survivin expression: An improvement for survival

Survivin Modulates Squamous Cell Carcinoma-Derived Stem-Like Cell Proliferation, Viability and Tumor Formation in Vivo

Squamous Cell Carcinoma-derived Stem-like Cells (SCC-SC) originate from alterations in keratinocyte stem cells (KSC) gene expression and sustain tumor development, invasion and recurrence. Since survivin, a KSC marker, is highly expressed in SCC-SC, we evaluate its role in SCC-SC cell growth and SCC models. Survivin silencing by siRNA decreases clonal growth of SCC keratinocytes and viability of total, rapidly adhering (RAD) and non-RAD (NRAD) cells from primary SCC. Similarly, survivin silencing reduces the expression of stem cell markers (OCT4, NOTCH1, CD133, β₁-integrin), while it increases the level of differentiation markers (K10, involucrin). Moreover, survivin silencing improves the malignant phenotype of SCC 3D-reconstruct, as demonstrated by reduced epidermal thickness, lower Ki-67 positive cell number, and decreased expression of MMP9 and psoriasin. Furthermore, survivin depletion by siRNA in Ras^G12V-IκBα-derived tumors leads to smaller tumor formation characterized by lower mitotic index and reduced expression of the tumor-associated marker HIF1α, VEGF and CD51. Therefore, our results indicate survivin as a key gene in regulating SCC cancer stem cell formation and cSCC development.

Discovery of novel second mitochondria-derived activator of caspase mimetics as selective inhibitor of apoptosis protein inhibitors

Inhibitor of apoptosis (IAP) proteins are widely considered as promising cancer drug targets, especially for drug-resistant tumors. Mimicking the IAP-binding motif of second mitochondria-derived activator of caspases (SMAC) is a rational strategy to design potential IAP inhibitors. In this report, we used the bioactive conformation of AVPI tetrapeptide in the N terminus of SMAC as a template and performed a shape-based virtual screening against a drug-like compound library to identify novel IAP inhibitors. Top hits were subsequently docked to available IAP crystal structures as a secondary screening followed by validation using in vitro biologic assays. Four novel hit compounds were identified to potently inhibit cell growth in two human melanoma (A375 and M14) and two human prostate (PC-3 and DU145) cancer cell lines. The best compound, UC-112 [5-((benzyloxy)methyl)-7-(pyrrolidin-1-ylmethyl)quinolin-8-ol], has IC50 values ranging from 0.7 to 3.4 µM. UC-112 also potently inhibits the growth of P-glycoprotein (P-gp)-overexpressed multidrug-resistant cancer cells, strongly activates caspase-3/7 and caspase-9 activities, and selectively downregulates survivin level at a concentration as low as 1 µM. Coincubation of UC-112 with a known proteasome inhibitor Z-Leu-Leu-Leu-CHO (MG-132) rescued survivin inhibition, consistent with the anticipated mechanism of action for UC-112. As a single agent, UC-112 strongly inhibits tumor growth and reduces both X chromosome-linked IAP and survivin levels in an A375 human melanoma xenograft model in vivo. Overall, our study identified novel scaffolds, especially UC-112, as new platforms on which potent and selective IAP antagonists can be developed.

Targeting survivin in cancer: the cell-signalling perspective

Survivin, a prominent anticancer target, is ubiquitously expressed in a plethora of cancers and the evolving complexity in functional regulation of survivin is yet to be deciphered. However, pertaining to the recent studies, therapeutic modulation of survivin is critically regulated by interaction with prominent cell-signalling pathways [HIF-1α, HSP90, PI3K/AKT, mTOR, ERK, tumour suppressor genes (p53, PTEN), oncogenes (Bcl-2, Ras)] and a wide range of growth factors (EGFR, VEGF, among others). In our article we discuss, in detail, an overview of the recent developments in the pharmacological modulation of survivin via cell-signalling paradigms and antisurvivin therapeutics, along with an outlook on therapeutic management of survivin in drug-resistant cancers.

PAK1 is a novel MEK-independent raf target controlling expression of the IAP survivin in M-CSF-mediated osteoclast survival

As activation of the Ras/Raf/MEK/ERK pathway is a critical component of M-CSF-promoted osteoclast survival, determining specific mechanism by which M-CSF activates this signal transduction pathway is paramount towards advancing treatment of pathological conditions resulting in increased bone turnover. The p21 activated kinase PAK1 modulates activation of the Raf/MEK/ERK pathway by either directly activating Raf or priming MEK for activation by Raf. Therefore a role for PAK1 in M-CSF-mediated activation of the MEK/ERK pathway controlling osteoclast survival was assessed. Here we show that PAK1 is activated by M-CSF in a Ras-dependent mechanism that promotes osteoclast survival. Surprisingly, PAK1 did not modulate Raf activation or Raf-mediated MEK activation. M-CSF mediated activation of Raf was required for PAK1 activation and osteoclast survival promoted by PAK1. This survival response was MEK-independent as expression of constitutively active MEK did not rescue osteoclasts from apoptosis induced by blocking PAK1 function. Functionally, PAK1 promoted osteoclast survival by modulating expression of the IAP family member Survivin. M-CSF therefore functions to promote PAK1 activation as a novel MEK-independent Raf target to control Survivin-mediated osteoclast survival.

Molecular docking and analysis of survivin delta-ex3 isoform protein

This project explores molecular models of Survivin Delta-Ex3, H-Ras, and their binding sites, and generates energy optimized 3D coordinates of docked poses and conformations of the XY2 ligand molecule in the active site of Delta-Ex3. The aim is to propose an effective anti-cancer drug that induces apoptosis and inhibits tumor angiogenesis.

An anti-apoptotic protein human survivin is a direct inhibitor of caspase-3 and -7

Survivin, an apoptosis inhibitor/cell-cycle regulator, is critically required for suppression of apoptosis and ensuring normal cell division in the G2/M phase of the cell cycle. It is highly expressed in a cell cycle-regulated manner and localizes together with caspase-3 on microtubules within centrosomes. Whether survivin is a physiologically relevant caspase inhibitor has been unclear due to the difficulties with obtaining correctly folded survivin and finding the right conditions for inhibition assay. In this study, recombinant, active human survivin was expressed in Escherichia coli and purified to homogeneity. The protein, existing as a homodimer in solution, binds caspase-3 and -7 tightly with dissociation constants of 20.9 and 11.5 nM, respectively, when evaluated by surface plasmon resonance spectroscopy. Consistently, survivin potently inhibits the cleavage of a physiological substrate poly(ADP-ribose) polymerase and an artificial tetrapeptide by caspase-3 and -7 in vitro with apparent inhibition constants of 36.0 and 16.5 nM, respectively. The data suggest that sequestering caspase-3 and -7 in inhibited states on microtubules is at least one mechanism of survivin in the suppression of default apoptosis in the G2/M phase. The localization of survivin on microtubules, which is essential for its function, should increase the protective activity at the action site.