title: The Max b-HLH-LZ can transduce into cells and inhibit c-Myc transcriptional activities.
abstract: The inhibition of the functions of c-Myc (endogenous and oncogenic) was recently shown to provide a spectacular therapeutic index in cancer mouse models, with complete tumor regression and minimal side-effects in normal tissues. This was achieved by the systemic and conditional expression of omomyc, the cDNA of a designed mutant of the b-HLH-LZ of c-Myc named Omomyc. The overall mode of action of Omomyc consists in the sequestration of Max and the concomitant competition of the Omomyc/Max complex with the endogenous c-Myc/Max heterodimer. This leads to the inhibition of the transactivation of Myc target genes involved in proliferation and metabolism. While this body of work has provided extraordinary insights to guide the future development of new cancer therapies that target c-Myc, Omomyc itself is not a therapeutic agent. In this context, we sought to exploit the use of a b-HLH-LZ to inhibit c-Myc in a cancer cell line in a more direct fashion. We demonstrate that the b-HLH-LZ domain of Max (Max*) behaves as a bona fide protein transduction domain (PTD) that can efficiently transduce across cellular membrane via through endocytosis and translocate to the nucleus. In addition, we show that the treatment of HeLa cells with Max* leads to a reduction of metabolism and proliferation rate. Accordingly, we observe a decrease of the population of HeLa cells in S phase, an accumulation in G1/G0 and the induction of apoptosis. In agreement with these phenotypic changes, we show by q-RT-PCR that the treatment of HeLa cells with Max* leads to the activation of the transcription c-Myc repressed genes as well as the repression of the expression of c-Myc activated genes. In addition to the novel discovery that the Max b-HLH-LZ is a PTD, our findings open up new avenues and strategies for the direct inhibition of c-Myc with b-HLH-LZ analogs.
authors.affiliation: Département de Pharmacologie, Faculté de Médicine et des Sciences de la Santé, Université de Sherbrooke, Québec, Canada.
authors.forename: Martin
authors.initials: M
authors.lastname: Montagne
authors.forename: Nicolas
authors.initials: N
authors.lastname: Beaudoin
authors.forename: David
authors.initials: D
authors.lastname: Fortin
authors.forename: Christine L
authors.initials: CL
authors.lastname: Lavoie
authors.forename: Roscoe
authors.initials: R
authors.lastname: Klinck
authors.forename: Pierre
authors.initials: P
authors.lastname: Lavigne
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000737:chemistry*; D050976:Basic-Leucine Zipper Transcription Factors / Q000737:chemistry / Q000502:physiology*; D002453:Cell Cycle; D049109:Cell Proliferation; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D004705:Endocytosis; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal / Q000379:methods; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014168:Transferrin / Q000737:chemistry
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D018076:DNA, Complementary; C067850:Myc associated factor X; D010446:Peptide Fragments; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D014168:Transferrin; C568271:omomyc protein