[Apoptosis: molecular aspects]

Many signals and external stimuli regulate the apoptosis activity by interaction with the genome. These stimuli include morphogenetic signals, physiological factors, and environmental influence. The signals mediate their effect on cells with suitable receptors, relevant signalling pathways, and competence to execute the apoptosis cascade. Apoptosis is triggered indirectly by deprivation of survival factors, or directly by intercellular cell death signalling factors, and also by unbalanced intracellular messenger molecules, which are, more or less, involved in regulation of both programmed cell death and survival. Several genes are involved in regulation of cell survival and apoptosis: bcl-2/bax, p53, c-myc and transcription factors such as cdk, c-myc, c-fos and c-jun. Apparently, apoptosis could be triggered by increased or inhibited gene expression as well as biochemical reactions without changed gene expression. The morphological changes during apoptosis reflect a cascade of genetic and biochemical reactions in the cell. In the signal transduction pathway both secondary messenger Ca2+, different kinases, and polyamines are involved. Cysteine proteases cleave cytoskeletal proteins, endonucleases divide DNA into fragments, and transglutaminases cross-link macromolecules. Degradative enzymes such as proteases, endonucleases and transglutaminases are activated during apoptosis, leading to cellular collapse and formation of vesicular apoptotic bodies. Both increased and inhibited apoptosis activity may have pathological consequences. New therapeutic strategies aim to counteract dysregulation of apoptosis in specific tissues by pharmacological intervention. Thus there is a need for identification of molecules and gene products involved in regulation of apoptosis activity and clarification of the conditions where this knowledge may be used.