Antisense inhibition of the PTI-1 oncogene reverses cancer phenotypes

Abstract

The genetic alterations and molecular events mediating human prostate cancer development and progression remain to be defined. Rapid expression cloning and differential RNA display detect a putative oncogene, prostate tumor-inducing gene 1 (PTI-1), that is differentially expressed in human prostate (as well as breast, colon, and small cell lung) cancer cell lines, patient-derived prostate carcinomas, and blood from patients with metastatic prostate cancer. PTI-1 consists of a unique 5 untranslated region (5 UTR) with significant sequence homology to Mycoplasma hyopneumoniae 23S ribosomal RNA juxtaposed to a sequence that encodes a truncated and mutated human elongation factor 1␣ (Trun-EF). Stable expression of a nearly full-length 1.9-kb PTI-1 gene, but not the separate PTI-1 5 UTR or Trun-EF region, in normal rat embryo fibroblast cells, CREF-Trans 6, induces an aggressive tumorigenic phenotype in athymic nude mice. Blocking PTI-1 expression with antisense PTI-1 results in reversion of transformed PTI-1-expressing cells to a more normal cellular morphology with suppression in both anchorage-independent growth and tumorigenic potential in athymic nude mice. These findings document that PTI-1 is indeed an oncogene, and directly blocking PTI-1 expression can nullify cancer phenotypes. In these contexts, PTI-1 not only represents a gene with discriminating diagnostic properties but also may serve as a target for the gene-based therapy of human prostate and other cancers.Prostate cancer is the most frequently diagnosed internal cancer of men in the United States and the second leading reason for cancer-related deaths of men (1-3). These statistics underscore the need for improved molecular staging of and therapeutic approaches for this prevalent neoplastic disease.

Guanine nucleotides regulate sphingosine kinase 1 activation by eukaryotic elongation factor 1A and provide a mechanism for eEF1A-associated oncogenesis

“…As PTI-1 is unable to undergo the GTP-binding-induced conformation change proposed for intact eEF1A, we examined whether it may function as a constitutive activator of SK1. Furthermore, although the origin of PTI-1 has been the subject of some debate (Mansilla et al, 2005), a number of studies have reported its expression specifically in tumour cells and tissues (Gopalkrishnan et al, 1999), and demonstrated its ability to induce neoplastic transformation (Su et al, 1998). The mechanism whereby PTI-1 exerts its oncogenic effects, however, has not been established.…”

“…Ectoptic expression of PTI-1 or overexpression of SK1 have both been shown to induce neoplastic cell transformation (Su et al, 1998;Xia et al, 2000). Thus, we next examined the possible role of SK1 in PTI-1-induced oncogenesis.…”

The role of translation elongation factor eEF1A in intracellular alkalinization-induced tumor cell growth

“…Antisense-mediated blocking of PTI-1 inhibits tumorigenesis and results in the reversion of tumor cells to a normal cellular phenotype. 32 As it bears a strong sequence similarity to eEF1A1, eEF1A2 is also involved in cancer. The amplification of the eEF1A2 gene, which maps to 20q13, occurs in 20-30% of ovarian cancer cases 18 and two-thirds of breast tumors.…”

Anti-K-ras ribozyme induces growth inhibition and increased chemosensitivity in human colon cancer cells

“…Thymidine uptake for DNA synthesis was determined by the measurement of the rate of [ 3 H]dThd incorporation into trichloroacetic acid-precipitable material. 4 Colony formation in soft agar was performed as described previously. 4 For cytotoxicity, a 50% inhibition of cell growth (IC 50 ) of these cells for the drugs was determined by a dye reduction assay using 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) (Sigma, St. Louis, Mo).…”

“…Antisense therapeutics, which exploit the high degree of specificity offered by the base pair recognition of genetic information 1 may have promising therapeutic value in cancers, including colon cancers, because of their specificity in targeting gene products with minimal side effects. This therapy has the ability to suppress neoplastic phenotypes in cancer cells [2][3][4] and bring about an inhibition of chimeric bcr-abl gene expression in Philadelphia chromosome-positive cells in chronic myeloid leukemia, such as a reduction in bcr-abl mRNA at p210bcr-abl levels. 5,6 Successful results in antisense technology, however, have been demonstrated only in in vitro or culture systems.…”