Characterization of YY1 OPB Peptide for its Anticancer Activity

Background:The oncoprotein binding (OPB) domain of Yin Yang 1 (YY1) consists of 26 amino acids between G201 and S226, and is involved in YY1 interaction with multiple oncogene products, including MDM2, AKT, EZH2 and E1A. Through the OPB domain, YY1 promotes the oncogenic or proliferative regulation of these oncoproteins in cancer cells. We previously demonstrated that a peptide with the OPB sequence blocked YY1-AKT interaction and inhibited breast cancer cell proliferation.Objective:In the current study, we characterized the OPB domain and determined a minimal region for peptide design to suppress cancer cellMethods:Using alanine-scan method, we identified that the amino acids at OPB C-terminal are essential to YY1 binding to AKT. Further studies suggested that serine and threonine residues, but not lysines, in OPB play a key role in YY1-AKT interaction. We generated GFP fusion expression vectors to express OPB peptides with serially deleted N-terminal and found that OPB1 (i.e. G201-S226) is cytoplasmic, but OPB2 (i.e. E206-S226), OPB3 (i.e. E206-S226) and control peptide were both nuclear and cytoplasmic.Results:Both OPB1 and 2 inhibited breast cancer cell proliferation and migration, but OPB3 exhibited similar effects to control. OPB1 and 2 caused cell cycle arrest at G1 phase, increased p53 and p21 expression, and reduced AKT(S473) phosphorylation in MCF-7 cells, but not in MDA-MB-231 cells.Conclusion:: Overall, the serines and threonines of OPB are essential to YY1 binding to oncoproteins, and OPB peptide can be minimized to E206-S226 that maintain inhibitory activity to YY1- promoted cell proliferation.

Oncogenic Signaling in Tumorigenesis and Applications of siRNA Nanotherapeutics in Breast Cancer

Overexpression of oncogenes and cross-talks of the oncoproteins-regulated signaling cascades with other intracellular pathways in breast cancer could lead to massive abnormal signaling with the consequence of tumorigenesis. The ability to identify the genes having vital roles in cancer development would give a promising therapeutics strategy in combating the disease. Genetic manipulations through siRNAs targeting the complementary sequence of the oncogenic mRNA in breast cancer is one of the promising approaches that can be harnessed to develop more efficient treatments for breast cancer. In this review, we highlighted the effects of major signaling pathways stimulated by oncogene products on breast tumorigenesis and discussed the potential therapeutic strategies for targeted delivery of siRNAs with nanoparticles in suppressing the stimulated signaling pathways.

Cancers

With more than half of all cancer cases occurring in less developed nations of the world, cancer is a source of significant and growing mortality worldwide, with an increase to 19.3 million new cancer cases per year projected for 2025. Standard current treatments for cancer include surgery, radiotherapy, and a host of other systemic treatments comprising cytotoxic chemotherapy, hormonal therapy, immunotherapy, and targeted therapies. Referred to as the “guardian of the genome,” the alteration or inactivation of p53 tumour-suppressor gene by mutation or by its interactions with oncogene products or DNA tumour viruses can lead to cancer. The p53 is mutated in about half of almost all types of cancer arising from a wide spectrum of tissues. This chapter focuses on several types of cancer including breast and ovarian, colorectal, small cell lung carcinoma, malignant melanoma, pancreatic, prostate, neurofibromatosis, multiple endocrine neoplasia, and retinoblastoma.

Cbl Mutants Interact with c-Kit and Lead to Factor Independent Growth and Transformation of a Myeloid Cell Line 32D.

The Cbl proto-oncogene products have emerged as important components of the signal transduction cascades downstream of both non-receptor and receptor tyrosine kinases (RTKs). By regulation of receptor trafficking and degradation, they have been shown to tightly regulate the intensity and amplitude of RTK activation. c-Kit belongs to the family of the class-III RTKs and plays an important role in the pathogenesis of acute myeloid leukemia (AML). So far, very little is known about the role of c-Cbl mutants in the role of c-Kit signaling. We analyzed the interaction of c-Cbl with c-Kit and the functional relevance of this interaction in the IL-3-dependent murine myeloid progenitor cell line 32Dcl3. We analyzed the effect of c-Cbl and two different dominant negative mutants of c-Cbl (Cbl-70Z and Cbl-R420Q) on c-Kit-ligand-activated internalization. The transfection of c-Cbl mutants, but not of wildtype c-Cbl, significantly inhibited receptor internalization, as analyzed by FACS analysis. Expression of Cbl-70Z in 32Dcl3 cells severely inhibited apoptosis induced by growth factor deprivation, as has been described before. However, when coexpressed with wildtype c-Kit, 32Dcl3 cells also rapidly proliferated in the absence of any exogenously added growth factors. We furthermore analyzed SCF induced c-Kit ubiquitination in the presence and absence of c-Cbl mutants. SCF induced rapid ubiquitination of c-Kit that was strongly reduced in the presence of Cbl-70Z and abolished by Cbl-R420Q. Also, the Cbl mutants altered the amplitude and changed the quality of c-Kit dependent signaling events. In colony assays we were able to show ligand independent colony growths in methyl cellulose only in the presence of wildtype c-Kit together with a c-Cbl mutant. Our results indicate that c-Cbl has an important role in c-Kit signal mitigation. Furthermore, they demonstrate that disturbed mechanisms of c-Kit internalization have important implications for its transforming potential, possibly in the development of AML.

Senescence As an Anticancer Mechanism

Senescence was originally described as a terminal nondividing state of normal human cells reached after many cell divisions in culture. The cause was shown to be shortening of telomeres, leading to telomere dysfunction and cell cycle arrest. Subsequently, a more rapid, nontelomere-dependent form of senescence, often termed stress-induced premature senescence, was described. Mostly importantly, it occurs in response to activated oncogene products. Oncogene-induced senescence has been shown to play a role in tumor suppression in vivo; it does not seem to involve changes in telomeres. A second phenomenon that plays a role in tumor suppression, which does involve progressive telomere shortening, is crisis, the state that cells reach when cell cycle checkpoints are impaired and cells can no longer respond to telomere shortening or oncogene activation by entering senescence. These two processes, oncogene-induced senescence and telomere-based crisis, exert powerful anticancer effects.

Autoinhibitory Regulation of p73 by ΔNp73 To Modulate Cell Survival and Death through a p73-Specific Target Element within the ΔNp73 Promoter

ABSTRACT p73 is a p53-related tumor suppressor but is also induced by oncogene products such as E2F-1, raising a question as to whether p73 is a tumor suppressor gene or oncogene. Unlike p53, p73 has several variants, including ΔNp73, which lacks the NH2-terminal transactivation domain. Although, in developing neurons, ΔNp73 is expressed abundantly and seems to inhibit the proapoptotic function of p53, the role of p73 and ΔNp73 and their regulatory mechanism in cell growth and differentiation are poorly understood. Here we report that p73, but not p53, directly activates the transcription of endogenous ΔNp73 by binding to the p73-specific target element located at positions −76 to −57 within the ΔNp73 promoter region. The activation of ΔNp73 promoter by p63 was marginal. ΔNp73 was associated with p73α, p73β, and p53, as demonstrated by immunoprecipitation assays, and inhibited their transactivation activities when we used reporters of Mdm2, Bax, or ΔNp73 itself in SAOS-2 cells. Furthermore, induction or overexpression of ΔNp73 promoted cell survival by competing with p53 and p73 itself. Thus, our results suggest that the negative feedback regulation of p73 by its target ΔNp73 is a novel autoregulatory system for modulating cell survival and death.