Translational regulatory elements function in cells to rapidly change the protein expression landscape in response to internal or external stimuli. Among these elements are upstream open reading frames (uORFs) located at the 5′-untranslated region of mRNAs. Bioinformatics studies revealed the presence of uORFs in ~40% of human mRNAs. uORFs usually correlate with reduced protein expression levels since they decrease the efficiency of translation initiation of downstream ORF. The family of protein kinase C (PKC) can be divided into three subgroups; Classical (alpha, beta, gamma), Novel (delta, epsilon, eta, theta) and Atypical (zeta, iota). Our studies demonstrate that a uORF upstream of protein kinase C eta (PKCeta) contains a novel Atypical pseudosubstrate motif present in all PKCs, which acts as an internal inhibitor to suppress PKCs kinase activity by binding to their kinase domain. This finding is relevant to the market of PK inhibitors that had overall global sales of over $15.2 billion in 2009 and, it is estimated to increase to over $25 billion by 2019.
We have identified the novel PKCeta which is a stress anti-apoptotic kinase and a predictor for poor prognosis in breast (BC) and lung cancer (LC). Moreover, we have identified a uORF-encoded peptide that in PKCeta transcript is an efficient inhibitor of the kinase activity of an atypical PKCeta and can also inhibit other PKCs of the novel PKC-subfamily while not affecting conventional PKCs subfamilies. Importantly, this peptide (and its mutated forms) suppresses cell proliferation/survival and migration of BC cells and acts in synergy with chemotherapeutic agent to cause cell death. Hence, we unravel a new, unique mechanism of regulation of eukaryotic enzyme function by a uORF-encoded peptide, pertinent to cancer therapy. Our uORF-encoded peptide (inhibitor), reduces cell viability of BC and glioblastoma cells compared to controls. The inhibitor significantly inhibited cell proliferation of MCF-7 and MDA-MB-231 BC and U251 MG glioblastoma tumor lines but not of the non-transformed cells MCF10A. In addition, the uORF-encoded peptide is synergistic with etoposide in the induction of cell death. Under conditions in which death by either etoposide or the inhibitor resulted in only 10-30% cell death, the presence of both agents augmented cell death to about 95-100%, demonstrating synergism.
- Novel PKCs are validated targets in invasive tumors of various tissue origins.
- Selectively inhibits novel PKCs while not affecting conventional PKCs.
- Treatment based on a modified naturally occurring peptide.
- Inhibition has a synergic activity with selected approved chemotherapeutic agents.
International Patent Application No. PCT/IL2018/050182
Prof. Etta Livneh, the Department of Microbiology Immunology & Genetics and Prof. Esti Yeger-Lotem, NIBN and the Department of Clinical Biochemistry & Pharmacology, Ben-Gurion University of the Negev, Beer- Sheva, Israel