D-Leucyl-leucine

L-leucyl-L-leucine methyl ester (LLOMe) induces apoptosis, which is thought to be mediated by release of lysosomal cysteine cathepsins from permeabilized lysosomes into the cytosol. Here, we demonstrated in HeLa cells that apoptotic as well as sub-apoptotic concentrations of LLOMe caused rapid and complete lysosomal membrane permeabilization (LMP), as evidenced by loss of the proton gradient and release into the cytosol of internalized lysosomal markers below a relative molecular mass of 10,000. However, there was no evidence for the release of cysteine cathepsins B and L into the cytosol; rather they remained within lysosomes, where they were rapidly inactivated and degraded. LLOMe-induced adverse effects, including LMP, loss of cysteine cathepsin activity, caspase activation and cell death could be reduced by inhibition of cathepsin C, but not by inhibiting cathepsins B and L. When incubated with sub-apoptotic LLOMe concentrations, lysosomes transiently lost protons but annealed and re-acidified within hours. Full lysosomal function required new protein synthesis of cysteine cathepsins and other hydrolyses. Our data argue against the release of lysosomal enzymes into the cytosol and their proposed proteolytic signaling during LLOMe-induced apoptosis.

The non-zeolitic behavior of l-leucyl-l-leucine and its self-organization in solid state and from solutions with the formation of different nanostructures are reported. This dipeptide forms porous crystals, but does not exhibit molecular sieve effects typical of classical zeolites and biozeolites. The specific sorption properties of l-leucyl-l-leucine result from a change in its crystal packing from channel-type to layered-type, when binding strong proton acceptors or proton donors of molecular size greater than 18-20 cm3 mol-1. The high sorption capacity of l-leucyl-l-leucine toward dichloromethane results from the self-organization of the dipeptide, by forming nanofibers or web-like structures. The low thermal stability of clathrates of the dipeptide containing large guest molecules and the selectivity of l-leucyl-l-leucine toward alcohols over nitriles can be used to separate organic mixtures such as methanol/n-butanol and methanol/acetonitrile.

The balance between cell proliferation and apoptosis is critical for normal development and for the maintenance of homeostasis in adult organisms. Disruption of this balance has been implicated in a large number of disease processes, ranging from autoimmunity and neurodegenerative disorders to cancer. The ubiquitin-proteasome pathway, responsible for mediating the majority of intracellular proteolysis, plays a crucial role in the regulation of many normal cellular processes, including the cell cycle, differentiation and apoptosis. Apoptosis in cancer cells is closely connected with the activity of ubiquitin-proteasome pathway. The peptide-aldehyde proteasome inhibitor MG132 (carbobenzoxyl-L-leucyl-L-leucyl-L-leucine) induces the apoptosis of cells by a different intermediary pathway. Although the pathway of induction of apoptosis is different, it plays a crucial role in anti-tumor treatment. There are many cancer-related molecules in which the protein levels present in cells are regulated by a proteasomal pathway; for example, tumor inhibitors (P53, E2A, c-Myc, c-Jun, c-Fos), transcription factors (transcription factor nuclear factor-kappa B, IκBα, HIFI, YYI, ICER), cell cycle proteins (cyclin A and B, P27, P21, IAP1/3), MG132 induces cell apoptosis through formation of reactive oxygen species or the upregulation and downregulation of these factors, which is ultimately dependent upon the activation of the caspase family of cysteine proteases. In this article we review the mechanism of the induction of apoptosis in order to provide information required for research.