ELAS1 induces apoptotic death in adenocarcinoma DU145 and squamous-cell carcinoma SAS cancer cells, but not in normal KD cells

Abstract

We previously reported that an ELAS1 peptide containing 29 amino acids induces apoptotic death in U2OS human osteosarcoma cells following DNA double-strand break insults. Here, we show that ELAS1 also caused apoptosis in prostate adenocarcinoma DU145 cells and tongue squamous-cell carcinoma SAS cells. ELAS1 appears to be safe because it induced apoptosis only in cancer cells, not in normal KD cells. Because the effect of ELAS1 is dependent on increased stability of p53 and enhanced phosphorylation of p53-S46, we exogenously expressed wild-type p53 protein to fully promote ELAS1-mediated induction of apoptosis in SAS cells. Interestingly, simultaneous expression of Myc-ELAS1 and FLAG-p53 mediated by an internal ribosome entry site efficiently induced apoptosis in SAS cells. Moreover, we prepared a recombinant adenovirus that simultaneously expressed Myc-ELAS1 and FLAG-p53. This adenovirus also killed SAS cells, as determined by a cell viability assay, in the presence of camptothecin, an inducer of DNA double-strand breaks. Moreover, nude mice harboring Myc-ELAS1-expressing SAS cells lived longer than mice harboring Myc-vector-expressing SAS cells, suggesting the usefulness of ELAS1 in vivo. Notably, Cy5-tagged ELAS1-t, which contained only ten amino acids, also efficiently induced apoptosis in both DU145 and SAS cells, suggesting the usefulness of ELAS1-t as a peptide. Taken together, our results suggest that ELAS1 is therapeutically useful as a peptide drug.

Cell cycle checkpoint control: The cyclin G1/Mdm2/p53 axis emerges as a strategic target for broad‑spectrum cancer gene therapy - A review of molecular mechanisms for oncologists

“…The development of Mx-dnG1 (Rexin-G), which, by itself, induces apoptosis in cancer cells and tumor-associated vasculature (in the presence or absence of p53), is a powerful clinical tool in terms of applied cell cycle checkpoint control, which merits conscientious clinical development. Indeed, the functional characterization of discrete structural domains that are present within the cytocidal dnG1 have recently identified the ELAS1 peptide, which is based on a conserved sequence motif within the extended C-terminal domain of cyclin G1, as a therapeutically useful peptide drug ( 133 ). Reportedly, the ELAS1 peptide, which competitively blocks the physical association of cyclin G1 with the B’γ subunit of PP2A, sensitizes osteosarcoma cells to camptothecin and irinotecan, and induces apoptotic death in both prostate adenocarcinoma and squamous cell carcinoma, albeit in a wild-type TS53 -dependent manner.…”

“…9 ), presents a rational, stable and competitive intracellular inhibitor of cyclin G1/CKD5 activity (and possibly cyclin G1/CDK2 activity), which blocks the phosphorylation/activation of c-Myc, thwarts proliferative competence and leads to cell death via apoptosis and necrosis in cancer cells derived from all three germ layers, save for artificially-immortalized ‘vector producer’ cell lines (e.g., 293T cells) that have been purposefully transformed by the strategic integration of the SV40 large T antigen, a dominant-acting oncoprotein, which coincidently targets pRb, p53 and PP2A for subversion ( 139 ) and often leads to malignant transformation. Retaining the structural interaction domains that bind Mdm2 and PP2A, the C-terminus of cyclin G1 not only exhibits the PP2A-B’γ association domain, it apparently ‘displays’ this domain at least an order of magnitude more efficiently as a protein than the ELAS1 peptide drug, which was designed to mimic, thus compete with, this interaction ( 133 ). Of note, this ELAS1 peptide (thus dnG1) was found to sensitize U2OS osteosarcoma cells to radiation therapy (RT), as well as camptothecan/irinotecan chemotherapy ( 140 ), thereby providing a new avenue for dnG1 (Rexin-G) to further improve the efficacy of chemoradiotherapy (CRT).…”