Lack of induction of tissue transglutaminase but activation of the preexisting enzyme in c-Myc-induced apoptosis of CHO cells.
The intracellular activity and expression of tissue transglutaminase, which crosslinks proteins through epsilon(gamma-glutamyl)lysine isodipeptide bond, was investigated in CHO cells and those stably transfected with either inducible c-Myc (which leads to apoptosis) or with c-myc and the apoptosis inhibitor Bcl-2. Protein-bound cross-link content was significantly higher when apoptosis was induced by c-Myc while the concomitant presence of Bcl-2 markedly reduced both apoptosis and enzymatic protein cross-linking. The expression of tissue transglutaminase did not change following the initiation of apoptosis by c-Myc or when it was blocked by Bcl-2. Studying transiently co-transfected elements of the mouse tissue transglutaminase promoter linked to a reporter enzyme revealed their overall repression in cells expressing c-Myc. This repression was partially suspended in cells also carrying Bcl-2. Our data suggest that tissue transglutaminase is not induced when c-Myc initiates apoptosis but the pre-existing endogenous enzyme is activated.
Balajthy
Z
Z
Department of Biochemistry, University of Medical School of Debrecen, Hungary.
Kedei
N
N
Nagy
L
L
Davies
P J
PJ
Fésüs
L
L
D000818:Animals; D017209:Apoptosis; D016466:CHO Cells; D006224:Cricetinae; D004151:Dipeptides / Q000378:metabolism; D004789:Enzyme Activation; D004790:Enzyme Induction; D015971:Gene Expression Regulation, Enzymologic; D016259:Genes, myc; D006358:Hot Temperature; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D011503:Transglutaminases / Q000378:metabolism*
D004151:Dipeptides; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; C001299:epsilon-(gamma-glutamyl)-lysine; D011503:Transglutaminases