Involvement of microRNA214 and transcriptional regulation in reductions in mevalonate pyrophosphate decarboxylase mRNA levels in stroke-prone spontaneously hypertensive rat livers.

Hypocholesterolemia has been epidemiologically identified as one of the causes of stroke (cerebral hemorrhage). We previously reported that lower protein levels of mevalonate pyrophosphate decarboxylase (MPD), which is responsible for reducing serum cholesterol levels in stroke-prone spontaneously hypertensive rats (SHRSP), in the liver were caused by a reduction in mRNA levels. However, the mechanism responsible for reducing MPD expression levels in the SHRSP liver remains unclear. Thus, we compared microRNA (miR)-214 combined with the 3'-untranslated region of MPD mRNA and heterogeneous nuclear RNA (hnRNA) between SHRSP and normotensive Wistar Kyoto rats (WKY). miR-214 levels in the liver were markedly higher in SHRSP than in WKY, whereas hnRNA levels were significantly lower. These results indicate that the upregulation of miR-214 and downregulation of MPD transcription in the liver both play a role in the development of hypocholesterolemia in SHRSP.

Constitutive expression of a COOH-terminal leucine mutant of lysosome-associated membrane protein-1 causes its exclusive localization in low density intracellular vesicles.

Lysosome-associated membrane protein-1 (LAMP-1) is a type I transmembrane protein with a short cytoplasmic tail that possesses a lysosome-targeting signal of GYQTI(382)-COOH. Wild-type (WT)-LAMP-1 was exclusively localized in high density lysosomes, and efficiency of LAMP-1's transport to lysosomes depends on its COOH-terminal amino acid residue. Among many different COOH-terminal amino acid substitution mutants of LAMP-1, a leucine-substituted mutant (I382L) displays the most efficient targeting to late endosomes and lysosomes [Akasaki et al. (2010) J. Biochem. 148: , 669-679]. In this study, we generated two human hepatoma cell lines (HepG2 cell lines) that stably express WT-LAMP-1 and I382L, and compared their intracellular distributions. The subcellular fractionation study using Percoll density gradient centrifugation revealed that WT-LAMP-1 had preferential localization in the high density secondary lysosomes where endogenous human LAMP-1 was enriched. In contrast, a major portion of I382L was located in a low density fraction. The low density fraction also contained approximately 80% of endogenous human LAMP-1 and significant amounts of endogenous ß-glucuronidase and LAMP-2, which probably represents occurrence of low density lysosomes in the I382L-expressing cells. Double immunofluorescence microscopic analyses distinguished I382L-containing intracellular vesicles from endogenous LAMP-1-containing lysosomes and early endosomes. Altogether, constitutive expression of I382L causes its aberrant intracellular localization and generation of low density lysosomes, indicating that the COOH-terminal isoleucine is critical for normal localization of LAMP-1 in the dense lysosomes.